Eleni Pana Student Number: s1260220 elenapana23@gmail.com
U E MS. A S D MS P
Summertime Temperatures & Overheating Risk Does orientation affect comfort in bedrooms in the UK context? Supervisor: John Brennan
Mentor: Chris Morgan August 2013
I declare that this assignment is all my own work and that I have acknowledged all quotations from published or unpublished work of other people.
Signagure: Date:
Abstract e effects of climate change on the internal environment are of rising interest. e impacts of recent heat waves have caused heat-related deaths which resulted not only from unexpected high temperatures but also from a failure of buildings to amend the external changes. Current research activities indicate that bedrooms of new-build houses are more prone to the risk of overheating. e research presented here investigates the effects of summertime temperatures on modern flats based on the UK context with a particular focus in bedrooms. By selecting four, differently oriented, bedrooms, we try to examine the extent to which orientation affects the internal temperatures and concurrently the thermal comfort of occupants. is is done by monitoring the temperatures of bedrooms for the period between 13th of June until 10th of July 2013 as well as by interviewing the occupants. Having provided all the background needed on issues related to overheating and thermal comfort, the data are then examined under various methods along with methodology used in other, similar studies. Data retrieved from sensors helped for a direct comparison of temperatures recorded in bedrooms. ermal comfort was then assessed by using, recommended from CIBSE, static criteria for overheating along with the BSEN15251 adaptive thermal comfort benchmarks. e information obtained by questionnaires filled by occupants gave a rather different dimension. Overall, the comparison of results obtained by quantitative and qualitative methods show inconsistency between thermal comfort as defined by current standards and the actual thermal sensation of occupants. e study also highlights the complexity of thermal comfort assessment due to the differing levels of personal comfort even for occupants that experience the same conditions. Coming to a conclusion, we see that although slight differences were observed on temperatures of bedrooms, in fact orientation does not form a critical factor affecting thermal comfort of occupants.
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Acknowledgements I would firstly like to express my great thanks to the head of Edinburgh School of Architecture and Landscape Architecture, Senior Lecturer John Brennan for supervising this MSc project. Without his assistance it would be rather difficult to collect and structure the material needed for this project. Especially by providing the technical equipment needed for the measurements, giving the necessary guidance and promoting cooperation with external mentor organizations, he established the baseline for the final result. I am also happy to express my acknowledgements to the principal of Locate Architects, Chris Morgan for accepting to mentor this dissertation. Apart from his insight comments during various phases of the project development life-cycle, he also encouraged contact with the occupants of the houses monitored for the scope of the study. His suggestions where vital for the orientation of the investigation procedure and he assisted in bridging the gap between academic research and practical considerations. Nonetheless, I am indebted to Alistair & Elaine and Ross & Gillian, occupants of the monitored dwellings in Dunblane. Not only did they welcome our sensoring devices in their private space, but also assisted in the precision of our analysis by filling in qualitative forms, at all stages of our experimental study. I sincerely believe, that it is quite hard to meet persons to assist a case study as eagerly and selflessly as they did. Last but not least, I would far and foremost like to thank the most beloved persons of mine. Without the support of my family I would never be able to attend the MSc in Advanced Sustainable Design at the University of Edinburgh and always be free to make my own decisions. I am also grateful to Christos, who is at the core of my heart, for standing next to me and nullifying the distance separating us during this year. is project is dedicated to my parents, Dimitrios and Vasiliki Panas, as a minimum indication of gratitude and respect.
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Contents
1 Introduction
1
2 Literature Review
3
2.1
Summertime temperatures and overheating . . . . . . . . . . . . . . . .
3
2.1.1
Climate change . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.1.2
Heat waves in UK . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.1.2.1
Health impacts . . . . . . . . . . . . . . . . . . . . .
4
2.1.3
Definition of the term “overheating” . . . . . . . . . . . . . . .
5
2.1.4
Factors causing overheating . . . . . . . . . . . . . . . . . . . .
6
2.1.4.1
External factors
. . . . . . . . . . . . . . . . . . . .
6
2.1.4.2
Building design . . . . . . . . . . . . . . . . . . . . .
6
2.1.4.3
Internal factors . . . . . . . . . . . . . . . . . . . . .
7
2.1.4.4
Occupant behaviour . . . . . . . . . . . . . . . . . .
7
2.2
e influence of orientation . . . . . . . . . . . . . . . . . . . . . . . .
7
2.3
ermal comfort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.3.1
Adaptive ermal Comfort . . . . . . . . . . . . . . . . . . . .
8
2.3.2
e range of comfort conditions in homes . . . . . . . . . . . .
9
2.3.2.1
Window operation and comfort . . . . . . . . . . . .
9
2.3.3
Comfort and indoor conditions . . . . . . . . . . . . . . . . . .
10
2.3.4
Comfort and outdoor conditions . . . . . . . . . . . . . . . . .
10
ermal comfort standards . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.4.1
e PMV model . . . . . . . . . . . . . . . . . . . . . . . . .
12
2.4.1.1
Problems with the PMV/PPD . . . . . . . . . . . . .
12
International adaptive thermal comfort standards . . . . . . . . .
12
2.4
2.4.2
v
2.4.3
Overheating criteria . . . . . . . . . . . . . . . . . . . . . . . .
15
2.4.4
Comparison of static and adaptive criteria
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. . . . . . . . . . . .
3 Research Methodology
18
3.1
Current research activities . . . . . . . . . . . . . . . . . . . . . . . . .
18
3.2
Current research methodologies . . . . . . . . . . . . . . . . . . . . . .
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3.2.1
Modeling studies . . . . . . . . . . . . . . . . . . . . . . . . .
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3.2.1.1
Findings from modeling studies . . . . . . . . . . . .
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Monitoring studies . . . . . . . . . . . . . . . . . . . . . . . .
21
3.2.2.1
Findings from monitoring studies . . . . . . . . . . .
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Building Monitoring: Measurement and Recording . . . . . . . . . . . .
23
3.3.1
Overview of approach . . . . . . . . . . . . . . . . . . . . . . .
23
3.3.2
Criteria for selection . . . . . . . . . . . . . . . . . . . . . . . .
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3.3.3
Research Methodology . . . . . . . . . . . . . . . . . . . . . .
24
3.3.3.1
Quantitative method . . . . . . . . . . . . . . . . . .
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3.3.3.2
Qualitative Method . . . . . . . . . . . . . . . . . .
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3.2.2
3.3
4 Findings
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4.1
General observations . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
4.2
Quantitative findings . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
4.2.1
ermal performance of bedrooms . . . . . . . . . . . . . . . .
30
4.2.1.1
Method A: Average Temperatures . . . . . . . . . . .
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4.2.1.2
Method B: Hours over 24 & 26 °C . . . . . . . . . . .
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4.2.1.3
Method C: Combining data . . . . . . . . . . . . . .
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ermal comfort assessment . . . . . . . . . . . . . . . . . . . .
35
4.2.2.1
Assessment using static criteria . . . . . . . . . . . . .
35
4.2.2.2
Assessment using adaptive thermal comfort criteria . . .
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Qualitative findings . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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4.2.2
4.3
5 Discussion
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5.1
Research objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5.2
Summary of findings . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5.2.1
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Interview with occupants . . . . . . . . . . . . . . . . . . . . . vi
5.3
5.2.2
ermal behaviour of bedrooms . . . . . . . . . . . . . . . . . .
41
5.2.3
ermal comfort assessment . . . . . . . . . . . . . . . . . . . .
41
5.2.4
Comparison between qualitative – quantitative results . . . . . .
42
Limitations of the present study and further research . . . . . . . . . . .
42
6 Conclusions
44
A Combining Data
45
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List of Figures 2.1
Projected changes of average daily mean temperature for winter & summer by the 2080s under Medium scenario. Source: [3] . . . . . . . . . . . . .
4
Change in temperature distribution with climate change. Retrieved from: [4]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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e relationship between comfort or neutral temperature (Tn ) and the mean operative temperature (Top ). Source: [13]. . . . . . . . . . . . . . . . . .
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e neutral temperatures for buildings in a free-running mode against the prevailing mean outdoor air temperatures. Source: [13]. . . . . . . . . . .
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2.5
Building categories as defined by BS EN 7730. Source: [33]. . . . . . . .
13
2.6
Acceptable operative temperature ranges for naturally conditioned spaces. Source: [29] retrieved from [13] . . . . . . . . . . . . . . . . . . . . . .
13
2.7
European Standard 15251 category thresholds. Source [30]. . . . . . . . .
14
2.8
Comparison of adaptive thermal comfort standards. Retrieved from [35]. .
15
2.9
General summer indoor comfort temperatures for non air conditioned buildings CIBSE [18]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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2.10 CIBSE Benchmark Summer Indoor comfort temperatures and overheating criteria Source: [18]. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
2.2 2.3 2.4
3.1
Air temperatures measured in a warmer home in the London Government Office Region and the BSEN15251 thresholds. Retrieved from: [55]. . . .
22
3.2
Dunblane & location of homes. . . . . . . . . . . . . . . . . . . . . . .
25
3.3
Plans of House A (left) and House B (right). . . . . . . . . . . . . . . . .
26
3.4
Photos of House A (bottom) and House B (top). . . . . . . . . . . . . .
27
3.5
Photos of monitored bedrooms. . . . . . . . . . . . . . . . . . . . . . .
28
4.1
Percentage of each degree (°C) occurrence. . . . . . . . . . . . . . . . . .
30
4.2
Average temperatures of bedrooms during the monitoring period. . . . . .
31
4.3
Percentage of hours above 24 & 26 °C . . . . . . . . . . . . . . . . . . .
32
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4.4
Charts showing temperatures during a day when all bedrooms has closed windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
4.5
Charts showing temperatures in bedrooms during an overcast day. . . . . .
33
4.6
Charts showing temperatures in bedrooms during an sunny day. . . . . .
34
4.7
Charts showing temperatures in bedrooms during the hottest day. . . . . .
34
4.8
Percentage of occupied hours (22:00 – 06:00) for all four bedrooms for which air temperature exceeded 24 26 °C . . . . . . . . . . . . . . . . .
35
BSEN15251 thresholds and the hourly temperatures measured during occupied hours for the 7th of July. . . . . . . . . . . . . . . . . . . . . . .
36
4.10 BSEN15251 thresholds and the hourly temperatures measured during occupied hours for 8th & 9th of July. . . . . . . . . . . . . . . . . . . . .
36
4.11 BSEN15251 thresholds and the hourly temperatures measured during occupied hours for the coldest and an overcast day. . . . . . . . . . . . . . .
37
4.12 BSEN15251 thresholds and the hourly temperatures measured during occupied hours for a day with closed windows (left) and a sunny day (right).
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4.13 Table summarizing occupant responses on thermal sensation and thermal preference. 0 is for neutral, +1 for slightly warm, +2 for warm, +3 for hot.
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A.1 Graph showing temperature and humidity in bedrooms during a day when all bedrooms had closed windows. . . . . . . . . . . . . . . . . . . . . .
45
4.9
A.2 Graph showing temperature and humidity in bedrooms during a sunny day. 46 A.3 Graph showing temperature and humidity in bedrooms during an overcast day. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
A.4 Graph showing temperature and humidity in bedrooms during the hottest day of the monitoring period. . . . . . . . . . . . . . . . . . . . . . . .
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List of Tables 3.1
T . . . . . . . . . . . . . . . . . .
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C
Introduction
Given the phenomenon of global warming caused by climate change, summertime temperatures at homes and the risk of overheating have become of increasing concern. Heat waves that claimed a huge number of lives, such as in August 2003 in Europe, are predicted to occur more frequently and be more severe over the coming decades. Most victims are vulnerable population groups and the impacts are more intense in bigger cities which suffer from urban heat island effects. Organisations involved in the built environment recognise the need for adaptation of existing dwellings, as most of them will be occupied by the 2050s. However, energy efficiency guidelines, focus more on reducing the heating demands and have led the design of dwellings’ majority towards a more lightweight and airtight construction that maximizes heat gains and reduces heat loses. Although beneficial for winter, occupants risk experiencing discomfort due to elevated internal temperatures during summer. e impact of climate change in indoor temperatures of dwellings has been the focus of many studies. Impacts of location, buildings type, occupancy and wall construction are investigated either by using simulation or real monitoring. A common finding is that, new build houses is the type of dwelling more prone to the risk of overheating with bedrooms being warmer than living rooms. Based on these findings and due to the limited information about thermal comfort in bedrooms, this study focuses particularly on this room type, as it forms a space where human being spends nearly one-third of his/her life [1]. Focusing on bedrooms of all-four orientations, a key issue is to examine the extent to which orientation affects thermal comfort in the bedroom. is is of particular interest, as the aspect of orientation has not be given much attention on its impact in thermal comfort. More specifically, this study looks at how the internal environment of bedrooms operates with regard to their orientation and subsequently identifies the room with warmest temperatures. Having analysed the general trend in room temperatures, we will move to the evaluation of thermal comfort and the investigation of whether a risk of overheating occurs. Four bedrooms of two modern houses located in Scotland are selected for the scope of this study and data are obtained through quantitative(monitoring of temperatures)and qualitative methods (interviews with occupants). Recorded temperatures are then analysed in various ways so that we get a better understanding of the effect of orientation on each bedroom’s thermal environment. Similarly to most monitoring studies, the BSEN15251 thermal comfort standards along with CIBSE overheating criteria will be used for the assessment of thermal comfort and overheating respectively. is study seizes upon the idea of retrieving recent good practice, vital for deeper understanding of issues related to overheating and thermal comfort. It sets a methodology for 1
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the assessment and use of the collected data, in order to answer the research questions. In particular, Chapter 2 reviews literature related to overheating and thermal comfort, before we start with presentation of the research methodology and evaluation criteria employed in Chapter 3. In order to present the practical relevance of the study, Chapter 4 provides contextual information of the monitoring process environment, followed by a detailed analysis of the measured data in Chapter 5 where we present our findings. Chapter 6 has further discussion including limitations and future work before we end this documentation with the conclusions of our study.
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Literature Review
2.1 Summertime temperatures and overheating Overheating in buildings is one of the consequences of climate change, as they cannot provide shelter in a warm external environment [2]. Although changes in external temperatures are instantly affecting internal conditions and discomfort to building occupants, in fact, there are a number of other factors that are significant. In order to better understand the scale of the problem and its causes, this section provides information found on literature concerning the issue of global warming as well as other factors that are proved to result in warmer internal environments.
2.1.1 Climate change e UKCP09 climate projections are the latest in a series of climate change projections for the UK presented by the UK Climate Impacts Programme [3] in conjunction with the Met Office Hadley Centre. is suggests probable suggestions for three climate change scenarios: High, Medium and Low. UKCP09 provides projections for different environmental variables. What we are most interested in this study are the projected summer temperatures rises. As shown in Figure 2.1, under Medium emissions scenario, Southern England is predicted to get warmer than Northern with some parts being over 4 °C and Northern Scotland being about 2.5 °C. is gradient indicates the large difference between locations close to continents where projections show a more rapid warming and those more influenced by oceans [3]. Concerning the projected changes to mean daily maximum temperature in summer , UKCP09 predicts that Southern England can have a change of 5 °C or more and northern Scotland somewhat less than 3 °C. More intense and frequent heat waves are also predicted by UKCP09 projections, along with drier summers and warmer, wetter winters. Figure 2.2 illustrates how a shift in mean temperatures due to climate change leads to a significantly higher frequency of temperatures exceeding the overheating thresholds [4].
2.1.2 Heat waves in UK A heat wave, as defined by the UKCIP, is “a prolonged period of excessively hot weather,which may be accompanied by high humidity”. It is also noted that “there is no universal definition of a heatwave; the term is relative to the climate in the area with a locally identified threshold temperature” [4] [5]. e UK Meteorological office [6] gives heatwave thresholds, which 3
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Figure2.1: Projected changes of average daily mean temperature for winter & summer by the 2080s under Medium scenario. Source: [3] .
vary from region to region. When these thresholds are exceeded for two or more consecutive days, then a heatwave occurs. [4] According to a UK Government report [7], three major heat waves have occurred in the UK during the last 37 years: late June 1976, late July to early August 1995 and early to mid-August 2003. In July 2006 high temperatures that exceeded the Met Office heat wave threshold temperatures were also recorded, and set the ground for the Heat Wave Plan for England [8]; the purpose of the plan was to provide guidance on how to avoid the adverse health effects of excessive heat (as happened in the 2003 heatwave). Even during the development of the present dissertation, UK experienced the first prolonged heatwave since 2006, from 6 to 24 July, when “a maximum of 28 °C was recorded at one or more locations on each of those 19 days” [9]. Specifically, warning by the Met Office raised to “level three” (heatwave action) during mid-July 2013 for South-west England and West Midlands. Although only the first three days of this heatwave were monitored in the present study (monitoring period from 13/6 to 9/7), we can see how internal environment of bedrooms reacted to these elevated temperatures (Chapter 4). 2.1.2.1 Health impacts
e impacts of overheating range from discomfort and poor performance to serious health effects. e severe heatwave that spread over Europe in August 2003 is the most notable 4
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Figure2.2: Change in temperature distribution with climate change. Retrieved from: [4].
because of the high mortality; it caused 35,000 deaths, 2,000 of which were in the UK [10]. Most of the victims were elderly and those living in big cities. Even a moderate heatwave can have impacts on health, especially for vulnerable groups of people such as those of older age, people with chronic or severe illnesses, infants and homeless people [11]. However, even fit and healthy people can be affected during an extreme heatwave such as the one occurred in 2003 in France. e Heatwave plan indicates that the main cause of illness and death during a heatwave are respiratory (which gets worse with air pollution) and cardiovascular diseases.
2.1.3 Definition of the term “overheating” Although the term “overheating” is widely used, at present there is no precise definition. Overheating can be said to occur when the indoor temperature rises beyond the upper limit of the comfort temperature band for that day by enough to make people feel uncomfortably hot [12]. Albeit temperature is the most used factor related to overheating, in fact there are other important environmental factors such as humidity and air movement along with contextual factors such as the type of the building, its design and services, the controls it provides and the occupant habits which are also significant. In order to assess or predict the likelihood of a building to overheat, it is essential that the relationship between the indoor environment and human discomfort is clear [13]. People adapt to their environment [2] and it is not definite that overheating is something to be avoided. For example, people that consider cold as bad do not look for cooler conditions. In some cases, a warm home might be ideal for relaxation so actions to cool the space are not taken [14]. In contrast, keeping cool a working place is desirable in order to be able to concentrate [14]. is leads to the conclusion that, given the variability of thermal perceptions between individuals it is obvious that providing a detailed definition of the term “overheating” is a complex issue.
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2.1.4 Factors causing overheating Overheating is a result of heat trapped in a building causing comfort problems to the occupants. In order to better understand these problems and eliminate them it is important to identify the factors that make a building to overheat and people feel uncomfortably hot within it. is chapter describes these factors by separating them in three categories, from outside to inside: external, building design, internal and behavioural factors. 2.1.4.1 External factors
We have already mentioned the likely of rise in temperatures as a result of climate change. It is then logical to assume that if the external temperature is higher than the internal, then any air that is entering a building (for ventilation purposes or through the fabric) will increase the air inside the building. Cities and large urban locations might experience hotter environments due to the local heating of the air which might be of higher temperature than that in rural areas even in a relatively short distance away. is elevation of temperatures in urban locations has been referred to as Urban Heat Island (UHI) effect and has been extensively studied over that last years (e.g. [15]). Another important source of heat might be the building’s microclimate (or micro-environment). By microclimate we mean the surrounding building area which is up to several tens of meters from the building. UHI, for example is caused by poor microclimate conditions within a dense urban area. e air adjacent to a building is what interests as at this point, as it affects the internal environment when is brought into the building. e temperature of this air depends on the local modification of the external conditions which vary according to the tree planting, the design of ponds, the choice of surface materials etc. Solar gain through building fabric and windows is another important external source of heat. Heat is conducted through the opaque elements of a building fabric as the temperature of the external surface is warmer that the internal [16]. e direct gains through window and glazing areas can be very critical and depend on a number of factors such as the type of glazing unit, orientation, external or internal shading devices, time of day and season. 2.1.4.2 Building design
e design of a building (orientation, materials & services) determines its thermal behaviour. Guidance from energy efficiency and zero carbon agendas have resulted in more insulated and airtight buildings with large glazing areas and lightweight structures with mechanical ventilation and communal heating systems. e Housing Health and Safety Rating System confirms that “e major dwelling factors are solar heat gain, ventilation rates, and thermal capacity and insulation of the structure. Smaller, more compact dwellings, and particularly attic flats, are more prone to overheating than are large dwellings” [17]. Indeed, there is evidence that modern energy efficient flats are warmer than old ones but this will be further analyzed in Chapter 3. e heavyweight construction of older houses, with limited amounts of thermal insulation and high levels of infiltration through gaps have contributed to eliminating overheating. ermal mass is defined as the materials within a building, its fabric and its contents which absorb and store heat from and release heat to, the interior spaces over a period of time. Consequently, thermal mass plays a vital role in the thermal performance of a building. e
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effects of thermal mass have been widely investigated and as explained later in this study, it is suggested that buildings with high thermal mass are in a lower risk for overheating that those that are lightweight. 2.1.4.3 Internal factors
e human body is a source of heat and the rate of heat emission depends on the level of activity of the occupant. CIBSE Guide A [18] offers a range of values for various activity levels. Heat emission increases with the increase of activity levels. Moreover, activities of occupants, such as cooking, bathing or use of domestic appliances that produce heat might also contribute to a rise in the temperature. 2.1.4.4 Occupant behaviour
Occupant behaviour plays a significant role in overheating as it can either cause (or exacerbate) overheating, or respond to elevated temperatures. Actions taken to reduce the risk of overheating might have an adverse effect and actually increase it. For instance, the operation of windows, influence the internal conditions to a great extent. Security and privacy or other reasons such as external noise, air pollution, odours or keeping insects out might lead one to keep the windows closed thus increasing the risk of overheating, particularly in non-air-conditioned buildings. On the other hand, opening windows in air-conditioned buildings might also result in rise of internal temperature either because the air-conditioning is automatically switched off when the window opens or the design of the building make it depended on air-conditioning to keep cool (e.g. lightweight structure with large southfacing windows). Reasons for opening the windows might be to keep cool (even if this has adverse effects), to avoid condensation, to bring fresh air into the building, to prevent odour or simply because of habit and preference [16]. Leaving windows with direct solar radiation exposed (leaving curtains and shutters open), use of heat-producing appliances or high occupancy density are factors that lead a space to overheat. e level of body insulation (clothing) and metabolic rate (activity) could also lead to overheating [16]. Reasons noted above – noise, ventilation, security, etc.- show that overheating is not just an effect of thermal characteristics of a building. It is an effect of the combination of the thermal environment, insulation of the body and metabolic rate. behaviour to mitigate overheating is also based in this combination. Extensive advice is provided by CIBSE in the publication “How to manage overheating in buildings” [12]. It is generally accepted that behaviour is driven by comfort and the consequences will have an effect on energy use. It is critical to understand how a building’s design might affect occupant’s comfort, therefore occupant behaviour and, consequently the energy consumption of the building. behaviour is a consequence of the building design which should allow the occupant to take adaptive measures to mitigate the impact of indoor high temperatures.
2.2 e influence of orientation Orientation in passive design is considered as one of the most important aspects in thermal performance of a house. General principles about orientation indicats that: South-facing rooms have solar gains for most of the day but while this maximizes the desired heat gains 7
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in winter but they might require horizontal shading to prevent overheating in summer, East facing rooms benefit from solar gain in the morning but are cooler in the late afternoon and evening, making them more comfortable for summer sleeping, West-facing rooms provide good afternoon light but require some shading to prevent overheating due to the low-angle afternoon and evening sun and finally North-rooms have little or no heat gains thus been the coolest rooms [19]. With regard to summer overheating, a recent study [20] about summer characteristics of Passive Houses in climates where residential buildings do not require active cooling (such as this of UK) revealed that rooms with large glazed areas with a southern orientation has the maximum frequency of overeating events which can also occur during winter and transitional periods. Additionally, buildings with large glazing units towards West and East have problems with summer comfort. Finally, it was noted that, “the overheating frequencies fall sharply with further orientation towards the North” [20].
2.3 ermal comfort As we saw, overheating is said to occur when people feel uncomfortably hot due to high indoor temperatures. In the previous section we also mentioned that occupant behaviour is driven from comfort. It is then important to understand what are the current approaches to thermal comfort as it is something to be examined later in our study. To make this clearer, we are going to give a short definition of “thermal comfort” and describe the “adaptive” approach of thermal comfort. In addition we will examine the relationship of comfort with the internal and external conditions. As we will see, thermal comfort is closely related to the prevailing external conditions and this relationship has led the creation of international adaptive thermal comfort standards used for thermal comfort evaluation. As our main intention is to assess thermal comfort of occupants, we give a short description of widely used existing standards, so that we can select the most suitable for the case of dwellings to be used later in our analysis. Additionally, we describe the existing static criteria for overheating that will be used in our examination of whether an overheating risk occurs within bedrooms. Finally, we make a comparison between adaptive and static criteria and shortly examine their applicability for assessing measured indoor temperatures.
2.3.1 Adaptive ermal Comfort ermal comfort, based on the generally accepted definition of ASHRAE, is “that state of mind which expresses satisfaction with the thermal environment”. Our thermal interactions with the environment are expressed with our behaviour and with actions that we take in order to regulate our thermal sensation and feel comfortable. As in the example with window operation we described earlier, other behavioural actions can take a number of forms such as clothing changes, changes in posture and activity, use of thermal controls to change the environment or move to another or drink hot or cold drinks. Our tendency to adapt ourselves emerges from the need of our bodies to maintain a stable core body temperature despite the changes we are subject to [2]. is is incorporated into the adaptive approach which is based on the Adaptive Principle: “If a change occurs such as to produce discomfort, people react in ways which tend to restore their comfort”. Adaptive thermal comfort is actually a function of the possibilities of change, as well as the temperatures achieved [21]. Factors such as time, climate, building form, economic and social condition8
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ing as well as the immediate physical environment, make the relationship between people and environment complex. e adaptive model of comfort has been explained by Nicol and Humphreys, by de Dear and Brager and more into depth by Nicol, Humphreys and Roaf [2]. e adaptive model of thermal comfort is basically a chart or graph which relates the prevailing outdoor temperature to the temperature required for comfort. is relationship is of great importance and has been used by building engineers and architects as it suggests temperatures that are likely to be acceptable in a building in a particular climate [2]. In the next section we will explain further the comfort with regard to internal and external conditions.
2.3.2 e range of comfort conditions in homes Definitions of the acceptable range of thermal conditions are mainly based on extensive research undertaken by Ole Fanger. Fanger was the first to create an influential comfort model which was based on physiological issues and takes into account factors such as clothing, activity and environmental parameters [2]. Correspondingly, adaptive approach tells us that indoor temperatures can change either by actions to reduce discomfort or by those not being controlled and thus more likely to result in discomfort [2]. us, the width of comfort “zone” depends on these two factors. In conditions where air movement or possibility for adaptive actions is limited, as in the case of an office, the comfort zone might only range for about ± 2 °C [21]. In contrast, in situations where people have many adaptive opportunities, as in the case of the present study, the comfort zone might be significantly wider. ermal environment of buildings with operable windows, contrary to this of air-conditioned buildings, is more variable and is noted to follow the seasonal shifts of external conditions [22]. Home occupants have full thermal control of their environment and “this sense of control leads to a relaxation of expectations and greater tolerance of temperature excursions” [23]. An explanation is that, as known from environmental scientists, “human reaction to sensory stimulus is modified when a person has control over the stimulus” [23]. Consequently, as in the case of homes, people can find acceptable a variety of thermal conditions that come from a know source. Indeed, many studies have indicated that occupants with more opportunities for personal control are more tolerant for their indoor environment [23],[24]. ermal comfort is an individual issue. Research on the topic suggests that although physiology is the most important mechanism of comfort, psychological and behavioural issues also contribute. However, psychological dimension of comfort, according to Brager and de Dear [25], is individually based and related to “perception of, and reaction to,physical conditions due to past experience and expectations”. It then evident, that people’s thermal sensation might differ, even for the same indoor conditions. 2.3.2.1 Window operation and comfort
Windows are the most important architectural elements of a naturally ventilated building. ey can be used to cool the space or to achieve thermal comfort by bringing air into the building. e effect of air movement on thermal comfort has primarily been investigated in the laboratory so our understanding of its effect in real buildings is limited [23]. However, it has been suggested [23] that people consciously recognize that air movement has direct impact on their thermal comfort so their preference for a change of air movement depends on their need to return to comfort. Preference for air movement has been related to operative temperature; as temperature rises people attempt to control the air velocity to feel cooler. 9
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However, the desire for air movement is not only derived from the need for cooling but also for a feeling of air freshness.
2.3.3 Comfort and indoor conditions Figure 2.3 shows the relationship between comfort or neutral temperature and the mean operative temperature (Top) as resulted from data obtained from field studies conducted in free-running buildings (naturally ventilated buildings or buildings that do not use any form of mechanical cooling). e operative temperature is “a measure that combines the air temperature and the mean radiant temperature into a single value to express their joint effect” and it is used to express the temperature of a space. e method used to calculate the comfort temperature from the comfort data is explained in detail in [2]. e forthcoming edition of CIBSE Guide A [26] will have an adjustment so that the comfort temperature allow for the effect of air movement [13].
Figure2.3: e relationship between comfort or neutral temperature (Tn ) and the mean operative temperature (Top ). Source: [13].
e relationship between comfort and environment is a result of adaptation by the subjects to the environment they normally encounter. e graph shows that indoor temperature found comfortable (neutral temperature on vertical axis) is highly correlated with the mean indoor operative temperature with a range of 3-4 K. More specifically, it indicates that in hotter environments the neutral (comfort) temperature is below indoor suggesting that people would be slightly warmer than they would like to be and in cold conditions they are slightly cooler. is graph applies irrespective of whether the buildings are mechanically or naturally conditioned and the results are for still-air conditions. Air movement would result in higher neutral temperatures [13].
2.3.4 Comfort and outdoor conditions It has been found that indoor comfort temperature is strongly related with the outdoor temperature.Humphreys [27] used data from field surveys from all over the world and produced the graph shown in Figure 2.4. 10
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Figure2.4: e neutral temperatures for buildings in a free-running mode against the prevailing mean outdoor air temperatures. Source: [13].
Compared to the graph for a given indoor mean temperature, the range of mean temperatures people find comfortable in relation to a given outdoor temperature is about 4K, in other words twice as large as the first. Humphreys et al [28], using results from comfort surveys collected since 1978 notes that comfort temperature for any given outdoor temperature has risen by about 2K both for naturally ventilated and heated/cooled buildings. Nicol et al [2] note that a reason for that might be that buildings have become warmer and people have adapted to these higher indoor temperatures as well as that hotter conditions in recent free-running buildings is because they do not provide enough protection against summer heat. e strong relationship between indoor comfort and outdoor temperature forms the basis of adaptive standards (e.g. ANSI/ASHRAE Standard 55-2010 [29] and BS EN 15251 [30] for predicting the comfort temperatures).
2.4 ermal comfort standards With the threat of climate change and global energy insecurity, the control of indoor climate is becoming increasingly problematic, thus making overheating a serious concern. It is, thus, very important to have guidelines or standards that serves as a guide for designers as well as represent the scope and requirements for “comfort” considered appropriate to buildings of specific type and usage. Comfort is described on the basis of an individual’s physiological and psychological comfort. Before giving an overview of the International comfort standards, we describe the PMV/PPD model and it’ s limitations, as it has been used by the comfort standards as an indicator of indoor comfort.
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2.4.1 e PMV model During the last few decades, researchers have been exploring the thermal, psychological and physiological response of people in their thermal environment in order to develop thermal comfort models to predict these responses. e Predicted Mean Vote (PMV) comfort model by Fanger, was the first one developed and is the most well known as it forms the basis for the most national and international comfort standards [2]. e PMV approach predicts the mean comfort vote on the ASHRAE scale of a group of people on the basis of six variables: the air temperature, the radiant temperature, the air speed, the humidity, the insulation of their clothing and their metabolic rate. e model was based on data obtained entirely from climate chamber experiments and optimal conditions (in terms of air temperature, mean radiant temperature and humidity, at different values of air speed) can be read given knowledge of metabolic rate and clothing insulation of the design population. PMV has been extended to predict the proportion of a group of people who would be dissatisfied with the environment. PPD expresses this as a percentage (of people dissatisfied) and its value is calculated from the value of PMV. 2.4.1.1 Problems with the PMV/PPD
Fanger’s method for assessing comfort could be considered advantageous as it takes into account and segregates the effects of the different aspects of thermal environment such as air movement, humidity, as well as clothing and activity. Standards for indoor temperatures (e.g. ANSI/ASHRAE Standard 55-2010 [29] and BS EN 15251 [30]), were based in the PMV model. However, later work of researchers ([31],[32] and others) show that the PMV model is not appropriate for use in the variable conditions of free-running buildings. e thermal standards derived from laboratory-based models might not be applicable to the variability of naturally ventilated buildings (i.e. dwellings) as they do not take into account the behavioural element of occupants who are free to take actions to make themselves comfortable (open or close windows or blinds, change clothing or activity). Moreover, while temperature and humidity can be measured accurately enough, both clothing insulation and metabolic rate might not be assessed precisely. is approach led to creation of new standards which include “adaptive” temperature limits for free-running buildings.
2.4.2 International adaptive thermal comfort standards ere are three accepted and widely used standards related to thermal comfort: ISO Standard 7730 [33], ASHRAE Standard 55 [34] and CEN Standard EN15251 [30]. In more detail: ISO Standard BS EN 7730: e International Standards Organisation (ISO) is the primary source of standards. BS EN 7730 [33] essentially determines the calculation and use of PMV/PPD index, along with some criteria for local thermal comfort. e standard determines “categories” of buildings according to the range of PMV that occurs within them. e requirements of indoor environment that have to be maintained for each category of building (Class A, Class B, Class C) are indicated in Figure 2.5. ANSI/ASHRAE Standard 55 [29]: e American Society of Heating Refrigeration and Air Conditioning Engineers administrate and promote ASHRAE Standard 55 [29]. Due 12
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Figure2.5: Building categories as defined by BS EN 7730. Source: [33].
Figure2.6: Acceptable operative temperature ranges for naturally conditioned spaces. Source: [29] retrieved from [13] .
to the society’s activity outside USA and the dominance of US air conditioning industry in the international market for mechanical cooling, the ASHRAE standard is actually an international standard [2]. e standard follows the form of BS EN 7730 as it is also based on PMV. It includes a phychrometric chart which suggests a comfort zone for the majority of occupants including upper limits of temperature and relative humidity. e ASHRAE was the first standard to incorporate an adaptive component. Since 2004, it has also included a chart using the relationship between the indoor comfort temperature and the monthly mean of the outdoor temperature to represent a range of acceptable operative temperatures in naturally conditioned buildings. As shown in the Figure 2.6, the standard defines two zones – one within which 80 per cent of building occupant are expected to find the conditions acceptable and a second of 90 per cent. e adaptive comfort equation in the basis of the ASHRAE standard is: Tcomf = 0.31 · Trm + 17.8 where Tcomf is the comfort temperature and Trm is the monthly mean outdoor temperature. CEN Standard EN15251 [30]: European standard EN15251 was designed in order to support the Energy Performance of Buildings Directive (EPBD) which is directed towards reduction of energy use in European building stock. BS EN 15251: “Indoor environmental input parameters for design and assessment of energy performance of buildings addressing 13
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indoor air quality, thermal environment, lighting and acoustics”, follows the general lines of ASHRAE standard having separate standards for mechanically cooled buildings based on the PMV index. e standard to be used for evaluating naturally ventilated buildings is following the adaptive approach similarly to ASHRAE as well as the equation relating comfort temperature to outdoor temperature but instead of the monthly mean outdoor temperature, BS EN 15251 uses Trm, the exponentially weighted running mean of the daily mean outdoor air temperature as the measure of outdoor temperature. Tcomf = 0.33 · Trm + 18.8
Figure2.7: European Standard 15251 category thresholds. Source [30].
Similar to that of ASHRAE, the adaptive standard in EN15251 uses categories for buildings but instead of referring to the quality of the indoor conditions, these standards are defined by the type of the building and its use. e acceptable ranges of PMV in Categories I, II and III are shown in Figure 2.7. e category I thresholds represent a high level of thermal expectations (addressed to very sensitive or fragile persons), Cat II are for normal level of expectation and Cat III thresholds are for acceptable moderate expectation and can be used in existing buildings. Cat IV values lie outside the above criteria and should be used only for limited periods. EN 15251 offers different methods of defining the level of thermal discomfort. e easiest is to calculate the percentage of occupied hours for which the temperature exceeds the threshold of interest. It is recommended that the acceptable limit is 5% of hours in any day, week, month or year. BSEN 15251 is the most relevant standard for UK dwellings as “specifies methods for long term evaluation of the indoor environment obtained as a result of calculations or measurements”. e indoor temperatures presented in 2.7 are valid for offices and building types where occupants have with easy access to windows, are free to adapt their clothing and thei r main activity is sedentary [30]. Obviously, this standard is the most appropriate to evaluate thermal comfort in our case study. e use of category thresholds shown in 2.7 will be further explained in next chapter. 14
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CIBSE Guide A [18] provides thermal comfort envelopes similar to BSEN15251 Category I envelopes, but applicable for monthly mean temperatures down to 8 °C (as shown in Figure 2.8).
Figure2.8: Comparison of adaptive thermal comfort standards. Retrieved from [35].
2.4.3 Overheating criteria Universally agreed standards for overheating in buildings in the UK have not yet been defined and little research has been conducted on thermal comfort in dwellings. However, the use of design criteria and standards is crucial in order to enable an objective assessment of the performance of naturally or mechanically ventilated spaces and help designers form successful strategies in terms of building, the controls it provides, and its services. Likewise, they can be used to define whether a building is overheated. ere are number of overheating criteria some of which are based on comfort prediction while other on the number of hours for which a particular temperature is exceeded (static criteria). Static criteria use fixed threshold temperatures that neither take into account external conditions nor temperature influenced by building occupant behaviour. Such standards are demonstrated by the Chartered Institution of Building Services Engineers’ (CIBSE) Guide A [18] are frequently used across UK to lead the thermal design and performance evaluation of buildings. e guide suggests that “summer thermal performance should be measured against a benchmark temperature that should not be exceeded for a designated numbers of hours or a percentage of the annual occupied hours”. During warm weather it recommends target temperatures of 23 – 25 °C for the living areas and bedrooms of dwellings and it gives an overheating criterion for use in assessment of thermal model predictions. e overheating criterion for living rooms suggests that there should be no more than “1% annual occupied hours over an operative temperature of 28 °C”. Concerning bedrooms, the guide indicates that “thermal comfort and quality of sleep begin to decrease if bedroom temperatures rise much above 24 °C” and that “bedroom temperatures at night should not exceed 26 °C unless ceiling fans are available”. Accordingly, many studies use the criterion of 5% over 24 °C and the overheating criterion which suggests that there should be no more than “1% annual occupied hours over an operative temperature of 26 °C”. 15
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Figure2.9: General summer indoor comfort temperatures for non air conditioned buildings CIBSE [18].
Figure2.10: CIBSE Benchmark Summer Indoor comfort temperatures and overheating criteria Source: [18].
2.4.4 Comparison of static and adaptive criteria Generally, all comfort standards or overheating criteria have problems for the simple reason that they try to give precise definitions for something that is innately imprecise. Especially when compliance to standard is tested by monitoring, it may be found that building occupants are, in reality, more comfortable than the limit of the temperature range suggested by the standard [13]. However, it is obvious that the adaptive method has more to offer than the static criteria which are intended mainly for evaluating model predictions. Some of the drawbacks of the static criteria are that they are designed to assess whole years of data; they are able to criticize only high and not low temperatures and they are insensitive to different person’s comfort perceptions. Although useful for ranking the occurrence of increased rooms temperatures, they don’t take into account individuals thermal comfort adaptations (daily, seasonal or climate change) and as a result they cannot reliably indicate whether or not measured temperatures in homes are acceptable (or dangerous) [35]. On the other hand, adaptive thermal comfort methods, such BSEN 15251, are particularly 16
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intended for assessing existing buildings as well as predicted values. Opposite to static, adaptive criteria have thresholds which indicate the possibility of indoor conditions to be perceived either as too warm or too cold. e four category bands that BSEN 15251 suggests can be used for persons or households with different temperature tolerances [35]. Most of the monitoring studies have used this method as it allows the plotting of temperatures which clearly distinguish one day’s values from another’s and together with the overlaid category boundaries helps give a clear understanding of room’s temperatures. e fact that such methods have been developed in great extend using data collected in offices, raises the question whether the method is valid for assessing internal conditions in homes. In offices there is a mix of people with different thermal comfort perceptions and the environment is designed so that most of the people can be comfortable at the same time [35]. Unlike office workers, home occupants have more opportunities to adapt their own environment as they have a wider range of acceptable clothing options, much wider range of activity, ability to open or close windows or blinds, even move from one room to another. Internal gains are much lower in homes as they tend to be less densely occupied. It is also easier to access outdoor spaces in order to create a flow between indoors and outdoors. It is worth to note that home occupants have a much wider range of ages than in typical offices, from the very young to the very old, thus comfort is seen more as an issue for health than for sedentary work. J. Lomas and T. Kane [35] note that in UK homes tend to be poorly insulated and leaky and thus it can be assumed that occupants are adapted to cooler living conditions. It has not been clear yet, how the BSEN 15251 category boundaries could be associated with homes neither is it clear whether 5% of exceedences of any chosen category could be relevant. Comfort measures such as clothing and activity might help one to attain comfort in temperatures below Category III envelope. J. Lomas and T. Kane [35] used standard thermal comfort calculations and deduced that, at a temperature of 15 °C 93% of normal healthy individuals would feel uncomfortable if seated and wearing normal clothing, 28% if doing light domestic work and 5% dissatisfied if these persons wore extra sweaters. is means that a home occupant may be comfortable in temperatures of just 15 °C simply by doing tasks and proper clothing [35]. In the measuring conducted here, the lowest internal temperature was around 15 °C. Although some studies of comfort in homes have been undertaken, they might not reflect the conditions experienced by the occupants at any given time and adaptation actions such as clothing or activity are not always recorded.
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Research Methodology
In this chapter we present a review of the current research activities and we focus in the published studies which investigate summertime thermal performance of dwellings. Along with the review of studies, we report their findings and explain in further detail the methodology used particularly in monitoring studies which will be later employed in our investigation. Much of the information provided in this chapter is based on report titled “Investigation into Overheating in Homes: Literature Review” [14] published by the Department for Communities and Local Government, which summarises the relevant published literature and outlines current ongoing research.
3.1 Current research activities ere are a number of studies and lot of research has been undertaken concerning the impacts of climate change. e Engineering and Physical Sciences Research Council (EPSRC) has funded a number of ARCC projects [36] which explore how the infrastructure of the UK can best adapt to a changing climate, some which are studying overheating by modelled building performance[[37],[31]] and others with a particular focus on urban overheating. A seminar conducted in London on 1st December 2010 [38] aims to inform current and future policy decisions on climate change adaptation with a specific focus on overheating. e seminar concluded that: “there is evidence to show that overheating of the built environment is a serious problem now and it will further intensify in the future, impacting on both health and productivity”. A meeting was held between key policy central makers and relevant ACN projects [36] to draw out the outcomes of the research undertaken in order to inform decision makers with respect to overheating particularly at the neighborhood and city level. e key outcomes from each project have been summarized by ACN and are provided by the ARCC CN website. CIBSE (the Chartered Institution of Building Services Engineers) has published a new guide which aims to provide a greater understanding and better prediction of overheating in commercial buildings. TM52 [13]: “e limits of thermal comfort: avoiding overheating in European building”was published on 9th of July 2013 and is about predicting overheating in buildings. It is intended to inform designers, developers and others responsible for defining the indoor environment in buildings. e CIBSE Overheating Task Force realised that one problem for designers has been the absence of an adequate definition of overheating in naturally ventilated buildings. In the past overheating has been defined as a number of 18
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hours over a particular temperature, irrespective of conditions outside the building. Recent work embodied in European standards suggests that the temperature that occupants will find uncomfortable changes with the outdoor conditions in a predictable way. is research informs the CIBSE guidance presented in this Technical Memorandum (TM). e meaning of the research and the link with overheating are explained and a series of criteria by which the risk of overheating can be assessed or identified are suggested. is publication supports the existing publication KS16:“How to manage overheating in building, which gives guidance for building managers and owners about the causes of overheating and how to mitigate it” [12]. More detailed information about using simulation to predict the danger of overheating is available in CIBSE Guide A [18].
3.2 Current research methodologies As we saw previously, the phenomenon of climate change has triggered the research activities concerning summertime temperatures and adaptation measures of dwellings. In this section we provide an overview of relevant projects and we examine the methodology used along with their most important findings. is will, actually, inform our methodology and the criteria for selection of our case study.
3.2.1 Modeling studies A large number of thermal modeling studies have been published the last few years exploring the impact of climate change on indoor overheating levels. By using dynamic thermal simulation packages, these studies are able to define the effects related to indoor overheating with some precision. Most studies examine dwelling archetypes that correspond to the biggest part of UK housing stock or represent parts of the region they examine. Given the effects of climate change, these modeling studies use probabilistic predictions for future climate in order to investigate the impact of changing weather on particular designs or examine the risk that a building is exposed to. Most of the studies reviewed here used a methodology created by Belcher et al. [39] for transforming historic weather files into future weather years in accordance with various climate change scenarios produced by the UK Climate Impacts Programme (UKCIP). Before we move to their findings and due to their large number, modeling studies found in literature are presented in Table 3.1 summarizing their subject of investigation and case studies used. As we see, these studies cover a number of issues related to summertime indoor temperatures and their findings will provide useful information not only for the extent of the problem but also for identifying the cases that are more in risk. 3.2.1.1 Findings from modeling studies
According to conclusions of modeling studies, the South of UK is likely to face the largest risk of indoor overheating. CIBSE (2005) suggests that comfort targets will not be met in naturally ventilated buildings in London by the middle of the century without some form of mechanical cooling unless some additional adaptation actions take place. Peacock et al. [50] showed that overheating in well insulated houses in Edinburgh is less likely to occur than it would for London where the levels of solar gains are higher and might be retained
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Table3.1: T
Study-ies
Subject Investigated
Case study used
CIBSE TM 36 [40]
effectiveness & energy use implications of different passive cooling techniques
13 case studies: 3 dwelling archetypes and & 7 non domestic buildings
impact of the thermal mass in the internal tempratures
four bedroom detached house
overheating risk
4 types of super insulated houses
effectiveness of a series of adaption
typical mid-terrace & end terraced houses
assessment of indoor overheating
dwelling archetypes of suburban areas 3 domestic building variants of UK dwellings: climate, construction & internal heat gains 15 dwelling archetypes broadly representative of the London housing stock
Arup R&D et al. [41] Hacker et al. [42] Orme and Palmer [43] Orme et Irving [44] Porritt et al. [45, 46, 47, 48] Cupta et al. [49] Peacock et al. [50] Oikonomou et al. [15] Young et al. [51, 52] Zero Carbon Hub [53]
investigation of internal tempratures assessment of variation in indoor tempratures during periods of hot weather air-conditioning usage & energy efficiency of air-conditioning systems climate change impact assessment
13 dwellings in Southern England dwelling archetypes for locations and time periods similar to CIBSE TM 36
in the interior. In addition, a study by Oikonomou et al. [15] as a part of [31] compared the importance of the urban heat island vs. building thermal quality and concluded that the effects of building form and other dwelling characteristics appear to be more important determinants of variations in high indoor temperatures than the location of a dwelling. Regarding the room type, modeled bedrooms in newly built flats have frequently been reported to perform relatively poorly based on CIBSE overheating criteria [40, 41, 54] Passive cooling strategies have a different effect according to the occupancy pattern, the type of the rooms and the time of the day. Porritt et al. [45, 46, 47, 48] suggested that solar protection strategies such as external shading and shutters are likely to offer more immediate benefits for rooms that are occupied during the daytime. A common finding in the studies reviewed here concerning dwelling construction age and overheating risk is that dwellings built around 1960s and small top-floor purpose-built flats tend to be more prone to overheating [40, 42, 43, 44]. is is due to the low thermal protection offered by the top floor of poorly insulated flats. Studies also found out that the detached archetypes are characterized by the highest risk for overheating followed by semi20
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detached and mid-terrace types. However, there is not a standard way under which house types are characterized, so comparing the studies we might get different results [14]. Newly constructed and retrofitted houses in the UK are intended to provide thermal efficiency during winter by increasing insulation levels and air tightness so as to minimize heat losses. However, an unintended consequence of such strategies may be overheating (16). Indeed, modern highly insulated houses were found to be more in the risk of overheating than older, less well insulated houses [51, 52]. Many studies suggest that different position of insulation might result in better summer thermal performance [50] and that careful consideration of insulation options should be made in the future in the context of energy efficiency retrofit strategies as part of the national carbon reduction targets [15]. Regarding natural ventilation, TM 36 study notes that it may become a “double-edged sword” in the future [40]. As external temperatures are projected to increase, natural ventilation during daytime might not be sufficient for cooling the internal spaces as the incoming air will be at a high temperature. Moreover, night purge ventilation is only effective where there is a relatively high temperature range from day to night to remove warm air and cool the building. However, this is likely to change as window opening does not seem to be a solution to overheating by the 2030s even for the climate of Edinburgh [50]. Another important finding from the comparison of lightweight vs. heavyweight structures was that thermal mass in combination with night-time ventilation forms an effective measure to eliminate overheating [17, 52]. It is noted that building with low thermal mass might not be able to respond to a rise in external temperature because the interior will be rapidly overheated. Whilst thermal mass is an effective measure, it could not fully help reduce overheating without adequate levels of night ventilation [43].
3.2.2 Monitoring studies Apart from modeling studies there is also a smaller number of projects that used data from temperature measurements as in the case of the present study. For this reason, it seems useful to examine the methodology used, as it will serve as a guideline for our investigation. Large scale studies,(e.g. Beizaee et al. [55]) used questionnaires intended to capture a wide range of information such as energy of the household, heating systems and operation, building characteristics and socio-demographics. Weather data were obtained by local weather stations that were closest to the monitored dwellings. Preparation of measured data involved the matching of the data obtained by the sensors along with the data from the surveys. Concerning the assessment of temperatures, all studies used both static (CIBSE Guide A) and adaptive criteria (BSEN 15251) focusing on temperatures recorded during occupied hours of each room. To evaluate the internal temperatures using static criteria, the surveys calculated the percentage of occupied hours with air temperatures above a certain value (according to the criterion for each room type). For assessing the temperatures using the BSEN 15251 adaptive standard, the hourly internal temperatures were plotted against the exponentially weighted running mean of the daily mean external temperature as shown in Figure 3.1 and they were then inspected by eye so that possible errors or anomalies are identified. Given the particular interest in heating systems which are considered more important in the UK climate, there are not many published monitoring studies concerning overheating in houses. Two large scale projects were recently published by Beizaee et al. [55] and K. Lomas 21
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Figure3.1: Air temperatures measured in a warmer home in the London Government Office Region and the BSEN15251 thresholds. Retrieved from: [55].
and Kane [35]. e first is believed to be one of the first national studies of summertime temperatures and thermal comfort in English homes, where temperatures were measured for 207 homes across England with a particular interest in living rooms and bedrooms. e measurements took place in the summer of 2007 and apart from the temperature database, data were also collected by face-to-face household interviews. In their work, Lomas and Kane [35], reported the internal summertime temperatures in 268 homes in Leicester, UK. e housed selected were statistically representative of the socio-technical characteristics of the city’s housing stock and “the data provide insight into the influence of house construction, energy system usage, and occupant characteristics on the incidence of elevated temperatures and thermal discomfort”. According to the report “Investigation into overheating in homes” [14], there are six recent monitoring studies: the analysis of temperature measurements from five houses in London and four houses in Manchester during the 2003 heat wave [56]; 15 low energy houses in Milton Keynes [57]; four houses in Stamford Brook in 2006 [58]; 62 houses in Leicester during the 2006 heat wave [54]; 36 houses (from a total of 110 dwellings in the overall study) in London in 2009 [59]; and a large monitoring campaign involving 224 nationally representative houses across the UK during July and August 2007 [60]. 3.2.2.1 Findings from monitoring studies
ere are some common findings between these monitoring studies and the aforementioned modeling studies. For example, in their study, Firth and Wright [60] found that monitored bedrooms are more prone to overheating than living rooms. Sleeping spaces were recorded to have higher indoor temperatures in all types of houses except from purpose-built flat and temporary dwellings. Compared to living rooms, bedrooms had higher range of temperatures as well as higher percentage of hours above 25 °C. Despite the cool weather during the study of K. J. Lomas & T. Kane [35], it was observed that some free naturally ventilated homes were extremely warm. In particular, more than 15% of bedrooms were found to 22
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have temperatures under 26 °C, temperature that is supposed to inhibit the quality of sleep, for more than 30% of summer night hours. Similarly, bedrooms found to be the warmest room in other studies [54, 56] As noted in the paper of Beizaee et al. [55], the incidence of warm bedrooms in modern homes, even during a cool summer is becoming a serious issue, especially now that “there is a strong trend towards even better insulation standards in new homes and the energy-efficient retrofitting of existing homes”. With reference to building morphology and building age, end terraces, purpose-built flats and houses built after 1990 were found to be at a higher risk of overheating. In post 1990 dwellings, for 7.1% of the monitored period the temperature was above 25 °C while overheating was more common in bedrooms of purpose-built flats and temporary accommodation [60]. Similarly, it was reported that flats tended to be significantly warmer than other types of houses and that solid wall homes and detached houses tended to be significantly cooler [35, 60]. Indoor temperatures above the external during both the heating and cooling season were also found in a monitoring study by Summerfield et al. [57]. is work measured the temperatures of 15 houses in Milton Keynes that were built under good performance standards. e results indicate a probability of overheating risk albeit the sample is too small and not representative of UK dwellings to generalise the outcomes. High internal temperatures (above 30 °C) were also found in high fabric efficient and airtight houses monitored by Wingfield et al. [58]. ese results led the authors to suggest that new housing developments, regardless of whether they have lightweight or heavyweight structures, are likely to overheat in the future. A recent pilot monitoring study is this of Mavrogianni et al. [59], in which data obtained for 36 dwellings across London in summer of 2009. e results revealed that during the hot period, 15 of the monitored bedrooms did not meet the CIBSE overheating criteria during the night time (indoor temperature rose above 26 °C). Although the sample was too small to generalise, this was some form of indication that top floor or purpose-built flats are more likely to overheat. From the studies reviewed here, it is obvious that modeling studies outnumber monitoring ones. Although modelling studies have been conducted by using sophisticated tools, the value of the results is much depended on the quality of input data. Especially in big scale modelling studies, there is much uncertainty concerning these inputs relating to a detailed knowledge of thermal characteristics of the studied houses and the occupant behavior. Although monitored studies might provide more accurate results, they are relatively scarce and only for small samples of houses.
3.3 Building Monitoring: Measurement and Recording 3.3.1 Overview of approach As noted in previous sections, most monitoring studies focus on comparisons between living rooms and bedrooms with regard to characteristics such as building age, building morphology, occupancy patterns, time of the day and location. Bedrooms have been proved to be at higher risk of overheating as the temperatures recorded within them were higher than those of living rooms, especially in new constructions (built after 1990) which tend to be 23
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lightweight, more insulated and airtight. A reason for this might be that bedrooms, unlike living rooms, are usually small so heat can’t dissipate and face only one way so ventilation cannot efficiently remove the heat. To the best of our knowledge, studies focusing particularly on bedrooms (where the problem is more frequent) and examining whether orientation does play a role in internal temperatures, were not identified. However correct orientation, as noted in Chapter 3, and internal room layout is critical in order to achieve energy efficiency as well as provide a comfortable environment to the occupants. us, it is of great importance to understand the effect (if any) of different orientation in room’s temperature. It should be noted, that with the term “orientation” of room, we mean the orientation of the window of the room. e observations noted above along with the fact that monitoring studies are limited formed the basis for this study, which focus particularly on data obtained from monitoring real temperatures of bedrooms and tries to analyze their internal thermal conditions and investigate the extent to which orientation affects the thermal comfort within them. To do so, data retrieved from sensors will be used for direct comparison of temperatures in bedrooms and thermal comfort will be assessed by using both static (CIBSE) and adaptive criteria (BSEN15251). Additionally, questionnaires filled by occupants will be useful in terms of providing important information on occupancy patterns as well as on their actual thermal comfort perception.
3.3.2 Criteria for selection is dissertation presents an analysis of the internal temperatures recorded in four bedrooms of two modern houses; modern houses were selected for the reason that, as seen previously, they have been proved to be more prone to higher internal temperatures. e monitoring takes place in Dunblane, Scotland. Dunblane is a small town north west of Edinburgh and north of Stirling, with a population of 7,911 at the 2001 census. Due to the suburban character of the area, external temperatures might be lower than being in a more dense urban location(this was explained in section 2.1.4.1). is is critical because, as we mentioned in Section 3.2.3, thermal environment of houses with operable windows follow the external variations in temperature. Consequently, we assume that temperatures recorded in this case are going to be lower than they would be if the houses were located in a dense urban environment. In order to be clear, we will name “House A” the one with main direction towards East – West and “House B” the one facing South – North. A working couple lives in House A. eir sleeping area is the bedroom on the East side while the West bedroom is used as an office. House B is occupied by a working couple with their young daughter. In this house, only the two South bedrooms are occupied. Both houses selected are detached, have the same construction – timber frame with insulation in roof– , same location (same street) but whilst one (House A) has bedrooms facing East –West, the other (House B) face East – West. is allows for a direct comparison of orientation, occupancy and potential window/door habits. It worth to note that, neither of the houses has any external shading device for the windows, however, all of them have internal curtains or blinds. Quantitative and qualitative methods were used in this survey in order to form a better understanding of the information obtained. e temperature and humidity database along with the completed questionnaires forms the backbone of this study and therefore analysed in order to answer our research questions. 24
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Figure3.2: Dunblane & location of homes.
3.3.3 Research Methodology 3.3.3.1 Quantitative method
Six “Tinytag” sensors were provided by the university, to measure temperature and humidity and store the data until downloaded. e sensors recorded temperatures and humidity at 5 min intervals from 13th of June to 10th of July 2013. As we want to monitor the temperature experienced by the occupants, particular consideration was given in the placement of the sensors within the bedrooms. Sensors were placed at a height of around 1m from the floor within the bedrooms as, due to stack effect, temperatures near ceiling tend to be warmer than temperature experienced by people sitting or lying on the bed. In order to record the window opening, a small sheet was designed and given to occupants in order to indicate when they open the window and the reason for doing so. e sheet was designed in a form of a table in which each day was separated into four sections-columns (morning, afternoon, evening, night) and one column for the reason of opening the window, so that it would be easier for occupants to fill as well as for later comparison with the downloaded data. To understand the internal temperature in relation to the external temperature, two of the sensors were put on the external North side of each house, so that solar radiation does not fall directly on them. e data logs could be downloaded as graphs showing temperature and humidity as well as excel documents, with the range of temperatures and humidity recorded in two columns accordingly, for each sensor. As we mentioned in previous chapter, one of the most important factors for overheating are the heat gains from lighting. In order to source the times of sunrise and sunset for Dunblane, the closest matching figures available were for Edinburgh whose latitude corresponds with Dunblane. 3.3.3.2 Qualitative Method
e study also aims to understand the occupants’ thermal sensation and relate it to the measured data. To do this, two questionnaires were given to the occupants. e first ques25
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Figure3.3: Plans of House A (left) and House B (right).
tionnaire was filled before the monitoring period and it was filled be both occupants of each house. is contained general questions concerning information about the building, occupancy patterns, opening window habits as well as their general perception about overheating. e second questionnaire was more extensive and it was filled by the occupants after the end of the monitoring period. is questionnaire was formed based on the methodologies for subjective evaluations of the indoor environment suggested by BSEN 15251 [30] as well as on the reported literature containing relevant information. Among the questions, which were focused particularly on bedrooms, the occupants were asked about how they rate their thermal sensation during the day, how they would prefer the temperature in their room and whether they felt thermally uncomfortable inside their rooms. e questions were provided in a way that there would be answers both for daytime and night time. ASHRAE’s [29] seven-point scale with “hot, warm, slightly warm, neutral, slightly cool, cool, cold” numbered from 3 to –3 was used to measure thermal sensation. ASHRAE’s thermal acceptance scale with “clearly acceptable, just acceptable, just unacceptable, clearly unacceptable” was 26
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Figure3.4: Photos of House A (bottom) and House B (top).
also used. Finally, for assessing the thermal preference we used a three-point scale with: “higher, no change, lower”. Specifically, the questions are: 1. How many hours are you in the room? 2. Have you ever felt hot in this room? 3. Have you ever experienced problems in sleeping because of high temperature? 4. Do you sleep with the door open or closed? 5. Please indicate if any problem occurs when opening the windows (e.g noise, smell, security, privacy). 6. How do you rate your thermal sensation (in the bedroom)? 7. How do you want the room temperature? 8. How do you perceive the air quality? 9. Have you noticed different thermal perceptions between you and your husband/wife? 10. Is there a heat source in the bedroom? 11. In the period of the test did you feel any time thermally uncomfortable in your bedroom? 12. Have you ever noticed that the air in your room was too dry or too humid?
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Figure3.5: Photos of monitored bedrooms.
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Findings
is section presents the analysis of the data obtained through monitoring of bedrooms and questionnaires. Data are examined under several methods so that we gradually obtain the information needed for our later discussion. We first describe some general observations concerning external conditions of the monitoring period and we analyse the thermal behaviour of bedrooms in terms of their orientation. After that, similar to monitoring studies reviewed previously, we use static and adaptive criteria for thermal comfort evaluation. Finally we present the findings from interviews with occupants in order to compare them with the findings from quantitative method in our discussion.
4.1 General observations e temperatures from 13 June to 10 of July are the focus of this study. During this period, the external temperature varied from 6.5 °C to a peak of 31.7 °C and the humidity from 36.3 % to 100% respectively. Apart from two days, the 15th of June and the 2nd of July that were unusually cold (peak temperatures of the day 12.4 °C and 14.9 °C respectively), most of the days had daily temperatures ranging from about 11 °C to approximately 20 °C to 22 °C. e warmest day was the 8th of July, when the average daily temperature ranged from 14.7 °C to a peak of 31.7 °C.
4.2 Quantitative findings In this section we are going to give a general description of the external conditions of the monitoring period and then we will try to analyze the gathered data of rooms’ temperatures. Our analysis is divided into two stages: the first is to understand the thermal behaviour of bedrooms with different orientation and the second is to assess thermal comfort given the recorded temperatures. In order to have a grounded analysis for the first stage, we use three different methods of comparison between the four bedrooms and try to identify which of them appears to be the warmest. e three methods are:
1. Method A:Comparison of average temperatures of all rooms for the whole monitoring period. 2. Method B:Percentage of hours over 24 °C & 26 °C for the whole monitoring period. 29
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3. Method C: Comparison of temperatures recorded during individual days selected under criteria such as: hottest day, sunny day, overcast day, day with windows closed In the second stage, we are going to focus more on occupied hours in order to assess thermal comfort under European Standard BSEN 15251 [30] and finally use CIBSE [40] overheating criteria to identify whether an overheating risk occurs.
4.2.1 ermal performance of bedrooms 4.2.1.1 Method A: Average Temperatures
In a first attempt to understand the temperatures of the rooms we created charts showing the percentage of each temperature degree occurrence for all four bedrooms. ese charts show that both in South and North, the temperatures occur mostly range from 19 °C to 21 °C while in East and West the range is greater, with temperatures being mainly from 18 °C to 21 °C. In South and North the temperature with highest percentage was 20 °C (32% and 31,6% respectively), whereas the most frequent temperature in East was 18 °C (20,5%) and in West 19 °C (17,5%). e charts (Figure 4.1)show that South and North have similar variations in temperatures and the same applies for East and West, which also have similar percentages.
Figure4.1: Percentage of each degree (°C) occurrence.
In order to examine the differences among bedrooms and identify which one tends to get warmer in general terms, we need to compare the average temperatures of the whole monitoring period for each bedroom. Looking at the charts (Figure 4.1), we observe a number of outliers, especially for the North and South bedrooms. For this reason, it seems appropriate, apart from the mean average, to calculate the standard deviation ¹ and recount the ¹e standard deviation is a measure that helps us specify a threshold that reduces the impact of values with low frequency in the mean average. e standard deviation number could be easily counted using the
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Figure4.2: Average temperatures of bedrooms during the monitoring period.
new calculated internal. As shown in the table (Figure 4.2), the difference between mean average and average calculated with standard deviation is actually too small. In both cases South appears to have higher temperatures and East has the lowest. However, the order for the second place changes between North and West. Although the second method might present a more precise result, the differences are so slight that other methods of assessment should also be used. 4.2.1.2 Method B: Hours over 24 & 26 °C
Another method for identifying which bedroom recorded highest temperatures is to compare the percentage of hours over 24 °C and 26 °C for the whole monitoring period. e choice of these thresholds is based on the literature that suggests a limit of 24 °C for thermal comfort and 26 °C for overheating. Despite the fact that these thresholds are generally used for the sleeping hours, having in mind that a bedroom might be also used during daytime (e.g. by students who spent more time in their bedrooms), the percentages reported here attempt to draw a general picture of the whole monitoring period. A focus in the sleeping hours will be in section 4.2.2.1. As illustrated in the chart (Figure 4.3), bedrooms facing South and West have the highest percentage of temperatures over 24 °C with 9.9% and 9.4% respectively, followed by North with 9.1%. Surprisingly, the highest percentage of temperatures over 26 °C were reported in North bedroom with a percentage of 5% followed by South with 3.3%. Similarly to the previous method, the results show that South, North and West bedroom can be equally warm. Finally, this chart indicates that South and North might be more prone to the risk of overheating. 4.2.1.3 Method C: Combining data
In order to examine into more detail the behaviour of temperature in each bedroom, a number of combining data were produced based on the original graphs downloaded by the gauges. e diagrams of all the bedrooms during a particular day have been put together in a graph so that it is easier to compare. e thicker coloured line shows the temperatures and the thinner line the humidity. As these graphs need more space in order to be readable, they have been placed in the Appendix and here we present charts showing the temperature recorded for particular times of the occupied hours (22:00 – 06:00).
STDEV function in Excel, this figure is then added in and subtracted from the mean average and a new average is calculated among these two figures.
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Figure4.3: Percentage of hours above 24 & 26 °C .
Closed windows Figure A.1 in Appendix illustrates the recorded temperatures during the 26th of June when windows in all bedrooms were closed for all day long. is allows for a direct comparison of internal temperatures without any influence caused by opening the windows. e external temperature in that day ranged from 11.5 °C to a peak of 20.8 °C. As shown in the graph, the South bedroom appears to be the warmest for most of hours, except from the time between 07:30 and 11:00 in the morning where East-room has higher temperatures. It is clear that the line related to East-room temperatures rises dramatically from 4:00 am until 11:00 am and after that time remains relatively stable until it starts to drop after 9pm. is rise in internal temperature is a result of the morning direct sunlight falling into the East window due to sunrise which takes place at 4:29 am. Consequently, the main heat gains for that bedroom occur during the morning.
Figure4.4: Charts showing temperatures during a day when all bedrooms has closed windows.
All bedrooms’ temperatures, in contrast to East-room, start to rise steadily from 08:00am to 08:00pm when starts to decrease again. Focusing particularly on occupied hours (22:0006:00) which interest us more, we observe that, regardless the fluctuations occurring during the day, South is reported as the warmest followed by North, West and finally East bedroom. e difference in temperatures of South and East room ranges up to 2.4 °C. Overcast day With this graph we try to obtain information about room temperatures in an overcast day in order to see the thermal performance of rooms when there are not heat gains from the sun. Data for overcast and sunny days were obtained based on the weather of Edinburgh 32
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which is the closest city to Dunblane.²
Figure4.5: Charts showing temperatures in bedrooms during an overcast day.
It is easily noticed from the graph that the temperature in South bedroom drops significantly after 8:30 in the morning and rises again after 10:30. is is a result of window opening during the morning which is also proved by the window opening sheet filled by occupants. In contrast to graphs analyzed previously, we observe that the cooling effect of window opening remains until late evening hours resulting in South having the lowest temperatures among the rooms during the daytime. Although North window was also open during the morning, we only see a slight drop in temperature. In North we also observe a sudden increase in temperature which occurs for only 15 minutes. is is most probably because of the hair dryer used in this room, which emits hot air and increases the room air temperature temporarily. If we isolate the occupied hours (grey backgroung color) it is seen that South bedroom is the warmest followed by the West-room. Sunny day Our final way to compare the bedrooms is to examine their temperatures during a sunny day and see their response to solar heat gains. From weather data we found out that the 6th of July was the day with the least percentage of cloud cover. e graph shows (Figure A.2) that West bedroom’s temperature is rising steadily from 07:00 and on, remaining the highest among all bedrooms for most of the daytime. Although someone would expect higher temperatures in South room during the day, we see that from early in the morning until the end of the day the temperature appears to be the lowest of all. is is a consequence of the window operation which, as noted by occupants, remained open during all day as well as the window in the North bedroom. In contrast, there was no exchange between external and internal air of East and West bedrooms resulting in higher temperatures during the daytime. e highest temperatures during the sleeping hours were between South and West bedrooms. In particular, South room temperatures were highest between 00:00 and 06:00 but for the time between 10:00pm to 00:00 West room’s temperatures exceed this of South by up to 2 degrees as a result of South window being open during the night.
²www.weatherspark.com
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Figure4.6: Charts showing temperatures in bedrooms during an sunny day.
Hottest day Before examining the bedrooms’ temperatures during the hottest day, it is important to note that due to the high external temperatures, windows were left open for most of the day as a means to cool the space. For this reason, we will demonstrate the combinatorial diagram of room temperatures along with the diagram of the external temperature (yellow color). Although the 9th of July was the hottest day of the monitoring period, the previous days were also warm and the windows remained open not only during the day but also during the night. e temperature during that day ranged from 14.7 °C to 30.5 °C.
Figure4.7: Charts showing temperatures in bedrooms during the hottest day.
Looking at the graph (Figure A.4)we observe that temperatures are similar in all bedrooms for the whole duration of the day except from the time between 19:30 and 00:00 where East room’s temperature drops from 27 °C. In this case, it seems that South and West appear to be the warmest rooms but there are periods during the day where, due to temperature fluctuations, this order changes. Following the external temperature, all internal temperatures had a steady rise from 07:00 to 19:00 but the biggest variation is noticed in the South bedroom with temperature rising from 23.5 °C to 27.5 °C. Concerning sleeping hours, the graph shows that West-room has higher temperatures for most of the time, followed by South and North whose temperatures are identical. e chart (Figure 4.7) indicates a rather big difference in temperatures of West and East bedrooms which could be critical for the thermal comfort of occupants.
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4.2.2 ermal comfort assessment 4.2.2.1 Assessment using static criteria
Pooling all the results for the daily average temperatures of occupied hours for all four bedrooms (Figure ??) provides an impression on the variability of internal conditions across the whole monitoring period. Temperatures above 24 °C were only recorded during the last three days of the monitoring period due to the high external temperatures. Obviously, the percentage of hours over 24 and 26 °C was only counted for these days.
Figure4.8: Percentage of occupied hours (22:00 – 06:00) for all four bedrooms for which air temperature exceeded 24 26 °C .
e CIBSE thresholds are used in this study to identify the bedrooms that are more prone to elevated temperatures. As these are applied to a small measurement period and not a whole year, values exceeding 1% and 5% do not indicate overheating as defined by CIBSE. As measured from the occupied hours for which bedrooms exceeded 24 °C, the warmest bedrooms were the South, the North and the West, whereas East bedroom exceeds 24 °C only for one day (61% of occupied hours). ere is a clear tendency for the bedrooms to exceed the 5% over 24 °C criterion for comfort during warm days. In particular, South and North show an immediate response to external elevated temperatures with internal temperatures being over 24 °C for 10.3% and 21.6% respectively on 7th of July and up to 100% for the following days. West bedroom’s temperatures were constantly above 24 °C during occupied hours on 8th and up to 82.5% over 24 °C on 9th of July. Concerning the overheating criterion of “1% of occupied hours above 26 °C”, it was only exceeded on 9th of July in South, North and East bedrooms (Figure 4.8). As indicated in Figure 4.8, South was the warmest bedroom with 39% over 26 °C, followed by North and West with 27.8% and 20.6% respectively. 4.2.2.2 Assessment using adaptive thermal comfort criteria
To assess the internal temperatures during occupied hours using the BSEN15251 adaptive standard, the hourly temperatures were plotted against the running mean of the daily average external temperature (Trm), for all bedrooms. e plots illustrate the various temperatures found in all four rooms for particular days. Whilst the warmest bedrooms (South, North 35
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and West) exceeded the Category I upper threshold only for the warmest bedroom, there is a general tendency of temperatures being below Cat II and Cat III thresholds which indicates that, according to the BSEN15251 standard, it is uncomfortably cool.
Figure4.9: BSEN15251 thresholds and the hourly temperatures measured during occupied hours for the 7th of July.
Figure4.10: BSEN15251 thresholds and the hourly temperatures measured during occupied hours for 8th & 9th of July.
Figure 4.9 and Figure 4.10 show the internal temperatures during the three warmest nights of the measuring period. e majority of temperatures are within the Cat I boundaries. Only the East bedroom had temperatures below Cat II which is suggested as normal level of expectation. Contrary to the analysis using static criteria, in these results there is no indication of temperatures being warm. Consequently there is not consistency between results obtained using static criteria and those using adaptive criteria. e plotted temperatures for individual days (Figure 4.11 & Figure 4.12) show that bedrooms tend to be rather cool even when the external temperatures are not very low. e acceptable limit of 5% of hours 36
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below Cat III threshold, as defined by BSEB15251, is exceeded for all bedrooms during the coldest and overcast day as well as for a day that all windows were closed. However, even for a sunny day, the internal temperatures tend to be towards the lower thresholds especially for East, West and North bedrooms. Within the general trend towards cool temperatures, it is obvious that the South and the North bedrooms show higher temperatures than West and particularly East bedroom.
Figure4.11: BSEN15251 thresholds and the hourly temperatures measured during occupied hours for the coldest and an overcast day.
Figure4.12: BSEN15251 thresholds and the hourly temperatures measured during occupied hours for a day with closed windows (left) and a sunny day (right).
4.3 Qualitative findings e findings are divided into two sections: a) one analysis of the first questionnaire which provides mostly generic information about occupation, door/window opening habits and a first approach on the occupants’ opinion in overheating, b) the analysis of the second questionnaire, and the description of the complexity of assessing thermal comfort responses. 37
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e first questionnaire provided a first overview of the occupancy and the perceptions of occupants. As we explained in a previous section, what we are interested in is the conditions during the occupied hours. It was noted that the occupied hours for each bedroom, except from the North which is not occupied, are for South from 22:00 to 06:00, for East from 22:30 to 07:30 and for West from 08:30 to 18:00. In order to make a more accurate analysis of the comparison between the temperatures of the bedrooms, we will assume that all the bedrooms have same occupied hours, from 22:00 to 06:00. Obviously, this might change during the weekends when occupants are not working. Due to the fact that temperatures are, usually lower early in the morning that those occurring later (i.e. 09:00-11:00), it is likely that the occupants might experience a hotter indoor environment. Indeed, this was confirmed by the female occupant of the South bedroom: “ere are some mornings during the weekends that the room is getting warmer, so I close the curtains”. All occupants leave the doors open while sleeping, which means that there could be an exchange of air and temperature between the rooms of the house. As for the windows, they indicated that problems such as noise or security might occur when having them open. However, there are occasions of leaving them open during the whole night, especially during warm summer nights. Although all occupants answered that they have occasionally felt hot in the bedrooms, only the couple of the East bedroom reported problems while sleeping but only for extreme summer temperatures. Moving to the analysis of the second questionnaire which was filled by all the occupants, we aim to understand better the thermal sensation during the day. e questions focus particularly in bedrooms where the occupants sleep; the South and the East bedroom. As we explained in the previous chapter, thermal comfort is a complex issue and differs from one person to another. Indeed, both couples of this study agreed that women feel the cold more than men. at was also reflected in the answers on how they rate their thermal sensation during the morning, afternoon and night, in which male responses were one or two points above the female. e only exception was this of the South bedroom, where, during the morning the female vote was “warm” while her husband’s was “neutral”. Looking at the thermal responses in general, we see that all occupants indicated that they felt warm in their bedrooms with most votes being “slightly warm” (+1) and “warm” (+2) with no recorded votes under “neutral” (0) level. All the occupants tend to feel warmer at night than in the morning (except from the lady in South - bedroom who feels warmer in the morning). In particular, both gentlemen stated that they feel “hot” (+3) at night and both ladies responded that they feel “slightly warm” (+1). e complexity here applies to the fact that, although we received the same answers in terms of thermal sensation among men and women, their thermal preference was not the same. For instance, while both gentlemen say that they feel “hot” at night, the East-room habitant would prefer the indoor temperature lower while the one in the South-room desires no change. However, the latter stated that: “Many times it gets warm at night so we leave the window open for all night long” e same observations were made from women’s responses, who both feel “slightly warm” at night but the one in East-room wants no change, in contrast to the one in South-room who would prefer a “lower” temperature. We should note that the later was the only one who reported that have felt uncomfortably hot during the monitoring period, when the external temperatures were significantly high. With regard to air quality and humidity, all 38
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responses show that it is within an acceptable range with some occasions of East bedroom being too dry.
Figure4.13: Table summarizing occupant responses on thermal sensation and thermal preference. 0 is for neutral, +1 for slightly warm, +2 for warm, +3 for hot.
Taking everything into account, there were clear indications of people feeling warm in their bedrooms, however, there were not significant complaints. Problems such as feeling hot or poor quality of sleep might occur only in cases of unusual hot summer days. e variation in the thermal perception between the occupants of the same room along with the fact that the responses between the two couples did not vary significantly (Figure 4.13), did not allow us to make clear conclusions about which room is considered as the warmest by the occupants. e sheets showing window opening habits indicated that occupants in South open the windows more frequently than in East bedroom. is might be an indication of occupants of South being warmer than those in East bedroom, but since we didn’t finally get the information for the reasons of opening the windows, we cannot confidently support it. In addition, as we mentioned previously, there are many reasons for opening a window; bringing fresh air to the room or simply because of habit or preference.
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Discussion
5.1 Research objectives ere is substantial evidence that the UK climate has been warming and this trend is expected to continue with increases in annual mean temperatures and more frequent heat waves. e impacts of high summertime temperatures in UK dwellings during hot weather events have been investigated through a number of studies. In response to the current interest on the effects of climate change in internal environment of dwellings, this dissertation aimed to investigate the effects of orientation in the thermal performance and thermal comfort of bedrooms during summertime temperatures. To do so, two modern houses with bedrooms in all four orientations were selected for an in-depth analysis, in order to provide useful information in a field that has not yet been thoroughly explored. Literature review and examination of related studies gave useful information that directed the methodology used and helped the analysis of the results. is Chapter discusses the findings and limitations of our investigation before we end with our conclusions.
5.2 Summary of findings 5.2.1 Interview with occupants Occupants’ perception of thermal comfort is the most important factor when investigating thermal comfort. In the present study, the responses of occupants proved very valuable as they gave useful information about their occupancy habits that might affect the internal temperatures, as well as about their actual thermal sensation. Looking at their responses generally, it is obvious that they experience warm temperatures affecting the quality of sleep during warm summer days. In fact, there was no answer indicating cool temperatures. is is particularly important because, as we mentioned, UK is expected to experience more frequent and intense heatwaves. Consequently, occupants might experience more incidents of discomfort in their bedrooms. At this point it should be noted that occupants’ responses took place the last day of the monitoring period which was one of the warmest days and this might have affected their answers. Two are the most interesting findings from the qualitative survey. e first is that, both men indicated that feel hot at nights, but while one is occupant of the warmest bedroom (South) 40
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as classified by quantitative analysis, the other occupies the coldest one (East). is proves what was described in Literature review about thermal comfort; that differs from person to person and depends on numerous parameters such clothing, and metabolic rate. Eventually, it was not noticeable in which bedroom it is more likely to experience discomfort. e second important finding is that even in the case of warm temperatures, it is not certain that all occupants would prefer them to be lower. Consequently, thermal comfort is also a matter of preference; some might find warm conditions ideal for sleeping while others might prefer a slightly cooler environment. It is generally admitted that thermal comfort is rather complex to predict and the present study confirms that as well.
5.2.2 ermal behaviour of bedrooms e analysis concerning the thermal behaviour revealed that temperatures do not differ to a great extent among the bedrooms. As expected, South and West tend to be warmer during the night time; however, North bedroom had often similar temperatures to South. is might be due to the fact that occupants leave the doors open so air can move between these two rooms. Another reason might be the sunlight falling into North windows due to the low angle of the sun during sunrise and sunset in latitude of 56 ° N. Daytime temperatures show bigger fluctuations depending on orientation of bedroom (solar heat gains), on external conditions (external air temperature) as well as on occupant behaviour (occupancy, operations of windows). Similarly to night time, South and West appeared to be the warmest rooms during the day, followed by North and finally East bedroom. According to these findings, orientations seems determinant in the behaviour of temperatures within the bedrooms but this can change by occupants’ actions.
5.2.3 ermal comfort assessment e thermal comfort was assessed by using both static and adaptive thermal comfort criteria. Analysis using the CIBSE criteria, which was only contacted for the three warmest days of the monitoring period, showed that during warm external conditions bedrooms tend to have elevated temperatures that for most of the time exceed 24 °C; according to CIBSE, 24 °C is a threshold for comfort during sleeping hours. e overheating criterion of “1% over 26 °C” was only exceeded in South, North and West bedrooms for one day, showing that it is likely for bedrooms to overheat if they are exposed in a longer period of warm temperatures. Although South seems to be the warmest, the criteria gave the impression that all monitored rooms are likely to have temperatures, that could be deemed as “uncomfortably warm” in the case of high external temperatures. e findings of thermal comfort assessment using the BSEN 15251 adaptive thermal comfort criteria paint a different picture for these three warm days. In contrast to CIBSE recommendations, analysis using the BSEN15251 criteria, show that internal conditions were mainly among the comfort thresholds with no indication of temperatures being warm. is presents an inconsistency between static and adaptive criteria. Concerning the rest of monitoring period, assessment using the BSEN15251 Standard clearly shows a general tendency for cool, rather than warm, temperatures; temperatures that in some cases, according to the Standard are uncomfortable. Within the general trend towards cool temperatures, South bedroom tends to have the highest temperatures while East has the lowest.
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5.2.4 Comparison between qualitative – quantitative results e interesting point here is to compare these observations with the information obtained from the qualitative analysis. Although the South bedroom is defined as the warmest and the East bedroom as the coldest among the monitored rooms, occupants’ responses do not reflect such a difference. Instead, it was noted that occupants experience “warm” and “hot” temperatures in both South and East bedrooms and thus, it was not clear which of these two bedrooms is considered as the warmest. is show, that quantitative analysis itself cannot provide realistic information about occupants’ thermal comfort within the bedrooms. Comparing thermal comfort evaluation with information obtained by the qualitative method, it is apparent that occupants’ perception of thermal comfort does not fully conform to the results obtained by the analysis using adaptive criteria. Instead, occupants’ responses clearly show that their thermal sensation ranges from “neutral”, which means comfortable, to “hot”. It is then evident, that occupants feel satisfied with low internal temperatures as the BSEN15251thermal comfort standard predicts. e reason for this is that, as mentioned in previous chapter, the BSEN15251 method has been derived using data from, and to assess thermal comfort in offices. However, people operate quite differently at home which is an environment that offers plentiful adaptive opportunities. ese opportunities enable temperatures being under Cat III threshold to be considered as comfortable. is raises the question of whether the adaptive criteria suggested by the European Standard are reliable for evaluating thermal comfort in homes and particularly in bedrooms which are mainly used for resting and sleeping.
5.3 Limitations of the present study and further research Despite the aim for investigating all aspects concerning thermal comfort of occupants and thermal behaviour of bedrooms, there were a number of limitations, particularly in regard to information obtained by occupants. For instance, we were not aware of their potential behavioural actions taken to maintain their comfort and have no information about the level of body insulation when being within the rooms or while sleeping. Moreover, it was not noted whether heating was turned on any of the cold days of the monitoring period. Apart from that, the fact that the questionnaires were filled after three consecutive days of elevated external and internal temperatures means that, the results might not fully represent occupants’ thermal sensation during the whole period of measurement. us, it is possible that different results would have been obtained if we had the chance to interview the occupants more frequently in the duration of the measurements. With regard to results obtained through the quantitative method, the small size of samples do not allow for general conclusions. Although some expectations came true, for example South bedrooms had highest temperatures and East the lowest, the reasons why North bedroom’s temperatures were, in many occasions, similar to those in the South cannot be adequately explained. Moreover, windows remained open during some of the nights (mostly in South bedroom), thus set a limitation in terms of comparing the bedrooms under the same conditions. is signifies the need for a more extended analysis based on a larger scale study that will compare a bigger number of bedrooms based on the same context. Similar to existing studies, the present survey brings into question the reliability of the BSEN15251 ermal Comfort Standard and shows that there is a need for new thresh42
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olds that reflect the variation in occupants’ perception. Bearing in mind that homes are, in fact, assessed by standards mainly used for offices, raises the question of whether the BSEN15251 lower threshold of Category III should for homes continue downwards to Trm=8 °C, as the CIBSE thresholds do, instead of running horizontally after Trm=15 °C. In that case, the lower category boundary would be about 18 °C, which could be quite comfortable for someone doing light house work wearing a sweater. Arguably, more work needs to be done towards a better understanding of which temperatures are perceived as acceptable or unacceptable in the UK homes.
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Conclusions
is study investigated the thermal behaviour and thermal comfort in bedrooms of different orientation. e analysis show that, orientation does play a role in determining the internal temperature of bedrooms, however, this is subject to change due to actions taken by occupants (e.g. open windows). Even though temperature differences observed between bedrooms with regard to their orientation (especially between South and East), the study revealed that, regardless of their orientation, all of the tested bedrooms are likely to experience temperatures considered as “uncomfortably warm”. Eventually, we could conclude that although orientation affects internal temperatures, it does not form a critical factor for the thermal comfort of occupants. e present study highlighted the complexity in assessing thermal comfort as occupants have different levels of personal comfort even when experience same conditions. Inconsistency found between thermal comfort as defined by current standards and the actual thermal sensation of occupants adds to this complexity and indicates the need for new thresholds that consider the variation in occupants’ perception and are more suitable in assessing thermal comfort in dwellings. Finally, the fact that occupants have experienced warm conditions during extreme hot summer days indicates that the scale of the problem might become larger in the future, when this phenomenon is predicted to be more usual and actions towards adaptation should be taken.
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Combining Data
In order to examine the behaviour of temperature in each bedroom, a number of combining data were produced based on the original graphs downloaded by the gauges. e graphs showing temperatures and humidity of all the bedrooms during a particular day and have been put together so that the comparison among bedrooms is easier. e thicker coloured line shows the temperatures and the thinner line the humidity.
FigureA.1: Graph showing temperature and humidity in bedrooms during a day when all bedrooms had closed windows.
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FigureA.2: Graph showing temperature and humidity in bedrooms during a sunny day.
FigureA.3: Graph showing temperature and humidity in bedrooms during an overcast day.
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FigureA.4: Graph showing temperature and humidity in bedrooms during the hottest day of the monitoring period.
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