Climate & Climatic Design Building Science 1 Sujatavani Gunasagaran
Climate & Weather • Climate is the average weather usually taken over a 30-year time period for a particular region and time period. Climate is not the same as weather, but rather, it is the average pattern of weather for a particular region. Weather describes the short-term state of the atmosphere. • Climate is about long-term records, trends and averages; weather is the day to day experience. 2
Climatic Design • We need to know how both the regional (macro) climate and local micro climate affects our levels of comfort. • Through design, reduce the amount of energy used to achieve comfortable levels of temperature and humidity.
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Climate change and the need for bioclimatic design
Roaf (2003) has identified 4 main reasons for bioclimatic design: • The rate of change in the level of climate variability and modification is increasing, requiring human adaptation to a rapidly warming world. • The fundamental means to this adaptation in the b env. is the adoption of more effective, and widely used, methods for passively cooling buildings. • AC systems are increasingly seen as a part of the climate change problem, as well as its solution. Not only is the rising cost of energy a problem, but the energy used to run these systems is a major contributor to greenhouse gas emissions. • It is imperative to create a new ‘cool vernacular’ building approach, which matches human and environmental needs.
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Thermal Comfort • Human thermal comfort is defined by ASHRAE as the state of mind that expresses satisfaction with the surrounding environment (ASHRAE Standard 55). Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC design engineers. 5
Factors Determining Thermal Comfort Environmental Factors
+
• Air Temperature • Relative Humidity • Solar Radiation / Mean radiant Temperature • Air Movement / Air Velocity
Physiological Factors • Clothing Level • Metabolic Rate
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Calculation of Insulation in Clothing 0.5 Clo
1.2 Clo
0,15 Clo
1.0 Clo
• 1 Clo = Insulation value of 0,155 m2 oC/W 7
Clo Values Table Garment description
Iclu Clo
Iclu m2 ď‚°C/W
Underwear
0.02 0.04 0.10 0.01 0.09 0.14 0.06 0.09 0.25 0.06 0.25 0.28 1.03 1.13 0.20 0.28 0.35
0.003 0.006 0.016 0.002 0.014 0.022 0.009 0.029 0.039 0.009 0.039 0.043 0.160 0.175 0.031 0.043 0.054
Underwear, shirts Shirts
Trousers
Insulated coveralls Sweaters
Pantyhose Briefs Pants long legs Bra T-shirt Half-slip, nylon Tube top Short sleeves Normal, long sleeves Shorts Normal trousers Overalls Multi-component filling Fibre-pelt Thin sweater Normal sweater Thick sweater
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Clo Values Table Garment description
Iclu Clo
Iclu m2 ď‚°C/W
Jackets
0.13 0.35 0.60 0.70 0.52 0.02 0.02 0.10 0.05 0.10 0.25 0.40 0.10 0.50 0.72 0.00 0.10 0.20
0.020 0.054 0.093 0.109 0.081 0.003 0.003 0.016 0.008 0.016 0.039 0.062 0.016 0.078 0.112 0.000 0.016 0.032
Coats overtrousers Sundries
Skirt, dresses Sleepwear
Chairs
Vest Jacket Coat Parka Overalls Socks Shoes (thin soled) Boots Gloves Light skirt, 15cm above knee Heavy skirt, knee-length Winter dress, long sleeves Shorts Long pyjamas Body sleep with feet Wooden or metal Fabric-covered, cushioned Armchair
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Calculation of Clo Value (Clo)
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Metabolic Rate 0.8 Met
• Energy released by metabolism depends on muscular activity. • Metabolism is measured in Met (1Met=58.15 W/m2 bodysurface).
8 Met 1 Met
4 Met
• Body surface for normal adult is 1.7 m2. • A sitting person in thermal comfort will have a heat loss of 100 W. • Average activity level for the last hour should be used when evaluating metabolic rate, due to body’s heat capacity. 11
Met Value Table Activity
Metabolic Rates [M]
Reclining
46 W/m2
0.8 Met
Seated relaxed
58 W/m2
1.0 Met
Clock and watch repairer
65 W/m2
1.1 Met
Standing relaxed
70 W/m2
1.2 Met
Car driving
80 W/m2
1.4 Met
Standing, light activity (shopping)
93 W/m2
1.6 Met
Walking on the level, 2 km/h
110 W/m2
1.9 Met
Standing, medium activity (domestic work)
116 W/m2
2.0 Met
Washing dishes standing
145 W/m2
2.5 Met
Walking on the level, 5 km/h
200 W/m2
3.4 Met
Building industry
275 W/m2
4.7 Met
Sports - running at 15 km/h
550 W/m2
9.5 Met
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Met Value Examples
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Optimum room temperature in relation to activity and clothing. The temperatures are valid for middle-European conditions.
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temperature - activity - clothing • Source: ISO 7730 (1984): Moderate environment, Determination of the PMV and PPD indices and specifications for thermal comfort, and element 29, Zurich, 1990 • The white and shaded areas indicate an incidence of less than 10% of persons dissatisfied (PPD). This illustrates that the higher the clo value or the activity level of a person, the greater his tolerance for differences in temperature will be. • Example: For a seated person wearing a suit (clo = 1.0; met = 1.2) the ideal room temperature is 21.5°C with a tolerance of +-2°C. • Other factors Factors other than climatic ones influence also the well being of the inhabitants, for example, psycho-social condition, age and health condition, air quality and acoustical and optical influences. Although these factors cannot be improved by climatically adapted construction, they should not be forgotten, because they may considerably reduce the tolerance. For example, ill people lying in a hospital or people under extreme noise stress are much more sensitive to climate than people enjoying a garden restaurant. 15
Relevant Climatic Data • • • •
Temperature Relative Humidity Solar radiation Mean Wind Speed and Wind Frequency
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Bioclimatic chart - relation of these 4 factors
The chart indicates the zone where comfort is felt in moderate climate zones, wearing indoor clothing and doing light work. It also assumes that not only the air temperature, but also the 17 temperature of surrounding surfaces lie within this range.
Temperature • • •
•
•
Temperature is measured using a thermometer. The basic unit of temperature (symbol: T) in the International System of Units (SI) is the kelvin (Symbol: K). The kelvin and Celsius scales are, by international agreement, defined by two points: absolute zero, and the triple point of Vienna Standard Mean Ocean Water (water specially prepared with a specified blend of hydrogen and oxygen isotopes). Absolute zero is defined as being precisely 0 K and −273.15 °C. – Absolute zero is where all kinetic motion in the particles comprising matter ceases and they are at complete rest in the “classic” (nonquantum mechanical) sense. At absolute zero, matter contains no thermal energy. Also, the triple point of water is defined as being precisely 273.16 K and 0.01 °C. This definition does three things: 1) it fixes the magnitude of the kelvin unit as being precisely 1 part in 273.16 parts the difference between absolute zero and the triple point of water; 2) it establishes that one kelvin has precisely the same magnitude as a one degree increment on the Celsius scale; and 3) it establishes the difference between the two scales’ null points as being precisely 273.15 kelvins (0 K = −273.15 °C and 273.16 K = 0.01 °C).
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Comparison of temperature scales Comment
Kelvin K
Celsius °C
Fahrenheit °F
Absolute zero
0
−273.15
−459.67
Lowest recorded natural temperature on Earth (Vostok, Antarctica - 21 July 1983)
184
−89
−128
Water freezes (at standard pressure)
273.15
0
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Average surface temperature on Earth
288
15
59
Average human body temperature ²
310.0 ±0.7
36.8 ±0.7
98.2 ±1.3
Highest recorded surface temperature on Earth (Al 'Aziziyah, Libya - 13 September 1922)
331
58
136
Water boils (at standard pressure)
373.1339
99.9839
211.97102
Gas Flame
1773 ~
1500 ~
2732 ~
Titanium melts
1941
1668
3034
The surface of the Sun
5800
5526
9980 19
Temperature • • • •
Air temperature (Dry Bulb) Wet bulb temperature Dew Point Temperature Mean Radiant temperature
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Air Temperature (DBT) • Air temperature simply refers to the absolute temperature of the air within a space. It is most often measured using a dry bulb thermometer, hence it is also called the dry-bulb temperature (DBT).
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Wet Bulb Temperature • The thermometer bulb is wrapped in muslin, which is kept wet. Evaporation of water from the thermometer has a cooling effect, so the temperature indicated by the wet bulb thermometer is less than the temperature indicated by a dry-bulb thermometer.
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Dew Point Temperature • This is a measure of the moisture content of the air and is the temperature to which air must be cooled in order for dew to form. The dew-point is generally derived theoretically from dry and wet-bulb temperatures, with a correction for the site's elevation. 23
Mean Radiant Temperature (MRT) • Mean radiant temperature is simply the area weighted mean temperature of all surrounding objects. • Technically, MRT is defined as the uniform temperature of a surrounding surface giving off blackbody radiation (emissivity e = 1) which results in the same radiation energy gain on a human body as the prevailing radiation fluxes which are usually very varied under open space conditions. 24
Relative Humidity (RH) • Humidity determines the rate of evaporation from the wet-bulb thermometer - evaporation is slower when the air is saturated. • For this reason, the difference in the temperatures indicated by the two thermometers gives a measure of atmospheric humidity. • Relative humidity (RH) is the ratio between absolute humidity and saturation, expressed as a percentage. 25
Relative Humidity
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Solar Radiation • Direct solar energy and diffuse solar energy, measured in MJ/m2 (megajoules per square metre). • The values are usually highest in clear sun conditions during the summer, and lowest during rainy or very cloudy days. The watt (symbol: W) is a derived unit of power in the International System of Units (SI). It measures rate of energy conversion. One watt is equivalent to 1 joule (J) of energy per second. 27
Solar Radiation
Major factors influencing the amount of solar energy received are the weather and the pollution content of the atmosphere.
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Wind • Wind is the motion of air relative to the surface of the Earth. It is one of the most highly variable climatic elements, both in speed and direction. • For this reason it is often studied by means of frequency analyses, provided here in the form of wind roses, rather than as averages. 29
Wind • Wind Frequency Analysis Wind roses summarise the occurrence of winds at a location, showing their strength, direction, and frequency.
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Wind Speed
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Climatic averages • Bureau of Meteorology data provides: • maximum and minimum temperatures; • temperatures and humidity (nominally) at 4-5am and 1-2pm; • sunshine and evaporation where available; and • rainfall, for each calendar month.
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The world climate
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Hot & Humid
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LOCATION, CLIMATE AND SOLUTIONS studies of housing design from a range of locations in warm climates. Cold – very high temperature insulated, controlled ventilation
Hot arid – high temperature, ground coupling, light colour and shaded 35
LOCATION, CLIMATE AND SOLUTIONS studies of housing design from a range of locations in warm climates. Temperate – moderate equator-facing windows to collect winter sun, shading of summer sun and thermal mass, well ventilated in summer
Warm humid –lightweight, elevated and well ventilated 36
IslandWood Environmental Center, Bainbridge Island, WA “Operable windows are combined with solar strategies to heat and cool this Washington State building eight months each year.” —Terry Zeimetz, Pella® Windows and Doors. (Images courtesy of Mithun Architects)
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The climate • The weather in Kuala Lumpur is hot and humid all year, with ave.temps of 23–33ºC and average rainfall of 190mm. • Showers occur almost daily, and downpours during the rainy season are not much worse than the rest of the year. • Kuala Lumpur is affected by the south-west monsoon from April to September. • The psychometric chart of Kuala Lumpur shows that all temperatures fell outside the recommended (ASHRAE) Standard 55 summer comfort zone. The cooling period is throughout the year. • The wind direction is mainly from the north-west to the southwest throughout the year, as shown in the wind roses. 1
Kuala Lumpur wind rose.
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Psychometric chart
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BIO CLIMATIC CHART
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BIOCLIMATIC CHART
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CLIMATIC DESIGN A method for the classification of climates is presented based on monthly climatic averages, with a basic set of design guidelines then developed to help deal with the particular characteristics of each zone. • Hot Humid • Hot Arid • Temperate 6
3-tier design approach
Mechanical systems
Passive systems Basic Building Design
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Designing with the Hot Humid climate Design Aims: In this humid climate
you need to maximise cooling through ventilation and minimise building heat gain.
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Shophouse
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Shophouse Shop house interior looking towards the street; interior looking towards the air well; shop houses uses lightweight materials for the internal floors and walls
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Shophouse
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Stack Effect
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Stack Effect
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Overhang
Double-storey detached at Kesuma Lakes
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Vernacular - Malay house
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Vernacular house
Thiel Residence, 1998, Darwin, Troppo Architects
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Wind Turbine
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Awnings
Solar pergola
Eaves overhang
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3 Types of External Shading Devices • horizontal
• vertical
• egg-crate
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• Clay roof tiles
• North-south orientation • Vertical fins as external shading device
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Renzo Piano, Menil Collection, 1982, Houston
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Shading devices - Malaysia
radiotherapy bldg, hospital Kuala Lumpur 23
Shading devices - Malaysia • General hospital Kuala Lumpur
• All windows are well shaded
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Melaka Hospital – shading devices
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Norton’s House, MCKK
Deep overhang
South facing
Recessed wall
Full height window with louvers on top
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• Covered terrace
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Organic architecture
MarchĂŠ des Halles in Avignon
The Siam Paragon Shopping Center in Bangkok
Botanist Patrick Blanc overgrows the vertical surfaces of buildings in the most beautiful way. His Vertical Garden could rather be called eco-art, or greener architecture consisting of a variety of plants trailing gently up any interior or outside wall. 28
Organic architecture
The Underground Art Gallery in Brewster, Mass., illustrates Malcolm Wells’s beliefs about the benefits of underground architecture. He built this gallery for himself and for his wife, Karen North Wells, a landscape painter.
Concept for a house at Raven Rocks, a cooperative Ohio community for which Wells has designed a complex of solar underground buildings. Work on some of these structures has gone on for decades, because residents do the construction 29 themselves.
References Lechner, N. Heating Lighting and Cooling, Sustainable Design Methods for Architects 3rd edition. John Wiley & Sons. Benjamin Stein and john S. Reynolds, 2000, Mechanical and electrical Equipment For Buildings , New York , John Wiley Givoni, B., “Urban Design In Different Climates”, World Meteorological Organization, Geneva, 1989. Ballinger, Kay, Hora and Harris, “Energy-Efficient Site Planning Handbook”, The Housing Commission Of NSW, Sydney, 1982. King, Rudder, Prasad and Ballinger, “Site Planning In Australia”, AGPS, Canberra, 1996 Dr Sabarinah Sh.Ahmad et all,Achieving Thermal Comfort in Malaysian Building: Bioclimatic Housing,Universiti Teknologi MARA
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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HEAT GAIN CALCULATIONS Appendix
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Thermal Comfort Thermal balance & comfort Factors of comfort Adjustment mechanisms Comfort conditions Building Science 1 Sujatavani Gunasagaran
Thermal balance & comfort • The living body constantly produces heat and this must be transferred to the environment. • Heat balance (thermal equilibrium) is the balance between the rate of heat production and the rate of heat loss. 2
Thermal balance & comfort
Heat Produced
Heat Lost
Thermal Comfort can only be maintained when heat produced by metabolism equals the heat lost from body. 3
Heat balance equation Heat production = the rate of heat production = M - W where: M = total rate of energy production which can be found from the rate of oxygen consumption (1 litre O2 = 5 kcal = 20,000 joules)(1cal = 4.184j)(1 kcal = 1000 cal) W = rate at which external work (force x distance) is being performed. M - W = total energy - work energy
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Heat balance equation
Parameters influencing the heat loss from a person
•
The dry heat loss (R+C) represents ~70% at low Clovalues and ~60% at higher Clovalues.
•
The evaporative heat loss (E) represents ~25% at moderate activities
•
Heat Loss by Conduction (K) and Respiration (RES) are normally insignificant compared to the total heat exchange.
•
Man is a poor machine. The efficiency is less than 20% even for well-trained athletes. Normally set to zero in the comfort equation. 5
Heat balance equation Heat loss = the rate of heat loss = R + C + E + L + K + S where: R = radiation (heat loss or gain) between skin or clothing surface and surrounding surfaces e.g. walls, sun etc. At rest, in a thermoneutral environment (21°C), 60% heat loss from nude body is by radiation. Mention radiant asymmetry. C = convection (air close to body absorbs heat ), which is a form of conduction to the surrounding air and is the heat loss (or gain) by the mixing of air close to the body surface. 2 types: natural convection (in still air the body produces an upward flow of warm air) and forced convection (movement of air past the body e.g. wind. At rest as above, convection accounts for 18% of heat loss. E = evaporation. The evaporation of water through the outer layers of skin (insensible perspiration) or from the skin surface when this is wetted by sweat (perspiration) or some other external agency. L = warming and wetting of air which is inhaled and then exhaled (this is sometimes included under E). K = conduction to the surfaces by direct contact with skin or clothing e.g. sitting on a cold surface etc. This is sometimes included under C. At rest as above, this accounts for 3% of heat loss. S = rate of storage of heat in the body. 6
Heat balance equation Heat balance exists when
M-W=R+C+E+L+K+S R + C + K = 72% of heat loss Eskin = 15% (Excretion of feces and urine = 3%) Llungs = 7% exhaled, 3% warming inhaled Ideally S should equal 0 when the body is in heat balance i.e. heat production = heat loss with no storage. In practice the body rarely attains or maintains heat balance and many factors influence the relative importance of the heat exchange processes.
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Thermoregulation • Shell - skin temperature varies over a greater range than core temperature. Skin temperature depends primarily on environmental conditions. • Core - core temperature is controlled within a relatively narrow band by thermoregulatory systems. Core temperature depends primarily on work rate.
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Adjustment mechanism 37 oC
34 oC •
•
The normal body core temperature is 37 oC. We have separate heat and cold sensors. Heat sensors are located in the skin. Signals when temperature o is higher than 37 C. Cold sensors are located in the skin. They send signals when skin temperature is below 34 o C. There are more cold sensors that warm sensors. Heating mechanism:
•
Cooling mechanism:
• • •
•
Hot
Cold
– – – –
Reduced blood flow. Shivering.
Increased blood flow. Sweating (Evaporation).
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3 Heat exchange mechanism •
Vasomotor - all skin needs some blood supply to keep it alive but skin blood flow can be increased many times this basic level. Increasing skin blood flow raises skin temperature and increases heat transfer to the environment, and cools the core. Decreasing skin blood flow cools the skin and reduces heat transfer to the environment and warms the core. Changes in skin blood flow are most marked at the extremities of limbs (hands and feet) and less marked in the trunk and head. This is why hands and feet frequently feel cold first.
•
Sweating - (max. continued total sweat rate = 1 litre/hour; max. short-term = 10-15 litres per 6 hours; always 650 ml/day.). As skin temperature approaches core temperature, transferring heat from the core to the skin becomes increasingly difficult. In hot environments the evaporation of sweat from the skin surface cools this thereby improving heat transfer from the core. 2 types of sweat: appocrine - forehead, back, palms of hands, armpits - protein-containing sweat eccrine - water sweat from all other skin areas (latent heat of water is 600 cal/gm)
•
Shivering - when skin blood flow is minimal there may be excessive heat loss from the core by conduction through the shell tissues. Maintenance of core temperature requires an increase in heat production and shivering is disorganised muscular activity which has this effect, and increases heat production 300-400%. To evaporate max. sweat takes 6000-9000 kcal, which equals heat of a lumberjack in cold weather!. 10
Thermal adjustment systems • Changing from a warm to a cold environment entails the following: -
skin becomes cool blood is routed away from the skin to the core where it is warmed before flowing back to the skin core temperature rises slightly then falls with prolonged exposure shivering and "gooseflesh" may occur if the body stabilizes then large areas of the skin will receive little blood. If cooling continues then eventually core temperature falls producing hypothermia which may result in death. 11
Thermal adjustment systems • Changing from a cold environment to a warm one entails the following: -
more blood is routed from the core to the skin surface thereby raising skin temperature core temperature falls but with continued exposure rises again sweating begins if the body stabilizes then large areas of the skin will receive blood and sweating will occur. If warming of the body continues eventually core temperature rises, producing hyperthermia (heatstroke) which may result in death.
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Acclimatization to heat and cold Acclimatization consists of a series of physiological adjustments that occur in a person who is habitually exposed to either hot or cold conditions. It has been said that acclimatization consists of two processes: "getting used to it" and "not getting used to it"!
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Acclimatization to heat In hot climates physiological adaptations occur which help to cool the body: • water intake increases (note it's better to drink warm fluids because these will elevate core temperature and encourage sweating to increase cooling, whereas cold fluids decrease core temperature, which discourages sweating to decrease cooling, which increases discomfort. • sweating increases. With "training" sweat glands produce more sweat. • blood volume increases and more blood is diverted to the skin (may even get a "red" face) • behavioral changes occur: less clothing is worn, or heat is avoided e.g. resorting to an air-conditioned room (an example of getting used to not getting used to it because such behavior does not produce physiological acclimatization). 14
Acclimatization cold The processes of cold acclimatization are less clear. Unlike sweating, the rate of shivering does not increase with prolonged exposure to cold. However, other changes do take place. • the body core contracts so that much more of the body tissues are in the shell. The contracted core is now better insulated and therefore less heat is needed to maintain core temperature. • there is a tendency to reduce blood flow to the extremities and so the use of hands is more difficult and is normally reduced. However, prolonged use of the hands in cold climates results in more blood being diverted to these e.g. herring filleters on the North Sea Coast used to work in the open with their hands either immersed in near-freezing water or exposed, wet to the wind. For an unacclimatised person this rapidly produces severe pain, yet the filleters worked all day with little discomfort. Such changes may take a long time (months or years) to occur. 15
Factors of comfort
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ASHRAE Comfort Chart WINTER
SUMMER • • • • •
M = 1 – 1.3 met Clo = 0.5 – 1.0 v ≤ 0.2 m/s -0.5 ≤ PMV ≤ +0.5 PPD ≤ 20%
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Predicted Mean Vote Scale - +3 Hot - +2 Warm - +1 Slightly warm - +0 Neutral - - 1 Slightly cool - -2 Cool
The PMV index is used to quantify the degree of discomfort
Percentage people dissatisfied (PPD) index
- -3 Cold
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The adaptive mechanism
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The adaptive mechanism • The adaptive approach to thermal comfort starts, not from a consideration of the heat exchange between man and the environment, but from the observation that there are a range of actions that we can and does take in order to achieve thermal comfort.
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The adaptive mechanism An adaptive principle is at work stating that: • If a change occurs such as to produce discomfort, people react in ways that tend to restore comfort
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The adaptive mechanism • The centre of our temperature regulation is the temperature of the brain. This is used to control the equilibrium between us and the environment using physiological responses or behavioural actions which tend to maintain the brain temperature within close limits. If a change occurs, in the environment or elsewhere, causing the brain temperature to deviate from the close limits, physiological responses occur. If these are not enough to prevent discomfort then an action may be taken which will tend to restore it to these limits. 22
The adaptive mechanism The types of behavioural action which can be taken are: • modification of the internal heat generation • modification of the rate of body heat loss • modification of the thermal environment • selecting a different environment 23
The adaptive mechanism • Modifying the internal heat generation can be achieved unconsciously with raised muscular tension or, in a more extreme situation, the shivering reflex, or consciously, for instance through jumping about in the cold to increase metabolic heat or having a siesta in the warm to reduce it. • The rate of body heat loss can be changed unconsciously through vasoregulation or sweating or consciously by such actions as changing ones clothing, cuddling up or by taking a cooling drink. 24
The adaptive mechanism • Modifying the thermal environment can be achieved through lighting a fire, opening a window, or in the longer term by insulating the loft or moving house. • Selecting a different environment can be achieved within a room by moving closer to the fire or catching the breeze from a window, between rooms in the same house with different temperatures or by moving house or visiting a friend. • These are only examples of the actions which can be taken, and if we are always free to take the necessary actions then thermal discomfort should not be a problem. 25
Constraints • In the dynamic relationship with the environment, constraints are the key to deciding whether a particular temperature is comfortable, and whether comfort can be achieved. • The implication of the adaptive principal is that given sufficient time, people will find ways in which to adapt to any temperature so long as it does not pose a threat of heat stroke or hypothermia. Discomfort will arise where temperatures: – change too fast for adaptation to take place – are outside normally accepted limits – are unexpected – are outside individual control 26
Comfort & Design Strategies Human Body Designing in context to climate Design Stategies for Cooling
Building Science 1 Sujatavani Gunasagaran
Climate-People-Building Strand www.learn.londonmet .ac.uk/packages/clear /thermal/buildings
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Introduction • In the world history of the traditional, classical and vernacular; buildings are often described as the notion of the "fabric" as a modifier of exterior and interior climates. • However, it is important to recognize that buildings serve many purposesfunctional, social, symbolic and aesthetic. 3
Introduction • These functions are interwoven in the design of buildings and in the use and experience of buildings. • In the architecture of the Renaissance, the climatic principles were generally overridden by the requirements of proportion, symmetry and the correct use of the Orders. 4
Introduction • Several theories may explain external environment, internal environment, people’s responses and the building fabric as interconnected and these four categories interacting in a complex way.
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Climatic Controls • The variations in the natural climatic conditions are plotted graphically the form of a sinusoidal curve describing the diurnal pattern of increasing and decreasing temperatures. The diagram shows an abstraction of the levels of climatic controls possible. 6
Climatic Controls • Precisely controlled indoor climate can only be achieved by active or mechanical systems (the straight lines in the diagram above). • However, this should not be the aim of the building designer. • Passive design can well attenuate the extremities of the climate and sometimes cause desired comfort indoors, with little seasonal or diurnal variations. • The passive systems may not provide 100% climatic control, but they substantially reduce the task of the active systems and hence make them more economical. 7
Building Fabric •
•
The building fabric is a critical component of any building, since it both protects the building occupants and plays a major role in regulating the indoor environment. Consisting of the building's roof, floor slabs, walls, windows, and doors, the fabric controls the flow of energy between the interior and exterior of the building.
•
•
•
The building fabric must balance requirements for ventilation and daylight while providing thermal and moisture protection appropriate to the climatic conditions of the site. Fabric design is a major factor in determining the amount of energy a building will use in its operation. Also, the overall environmental life-cycle impacts and energy costs associated with the production and transportation of different envelope materials vary greatly.
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Building Fabric • In keeping with the whole building approach, the entire design team must integrate design of the fabric with other design elements including material selection; daylighting and other passive solar design strategies; heating, ventilating, and air-conditioning (HVAC) and electrical strategies; and project performance goals. • One of the most important factors affecting fabric design is climate. Hot/dry, hot/humid, temperate, or cold climates will suggest different design strategies. Specific designs and materials can take advantage of or provide solutions for the given climate.
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Building Fabric • A second important factor in fabric design is what occurs inside the building. If the activity and equipment inside the building generate a significant amount of heat, the thermal loads may be primarily internal (from people and equipment) rather than external (from the sun). This affects the rate at which a building gains or loses heat. • Building Configuration also has significant impacts upon the efficiency and requirements of the building fabric. Careful study is required to arrive at a building footprint and orientation that work with the building fabric to maximize energy benefit.
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External/Internal Climate
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3-tier design approach
Mechanical systems
•Comfort
Passive systems
•Economy / cost
Basic Building Design
•Energy efficient
•Economy / space •Sustainable building
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Rules for comfort ventilation • • • •
Use fans to supplement the wind Max. air flow across the occupants Lightweight construction Operable window area split about equally between windward and leeward walls • Windows should be open during the day and night 13
Control of Overall Heat Shift Control of Air movement • Ventilation necessary to achieve Air Change Rates (ACH) • Heat gain through Ventilation • Heat differential between levels, stack effect • Night flush cooling to remove daytime heat build-up
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Wind driven ventilation
CROSS VENTILATION
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Cross-Ventilations Plan
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Vegetation near Buildings
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Funneling cool breezes
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Airflow through internal spaces / Natural ventilation Natural cross-flow ventilation depends upon: • Prevailing wind • Location of openings • Design and Size of openings • Relationship of opening to outlet • Presence of internal obstructions
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Natural ventilation If the iguanas become too hot, they stiffen their tails and loft their bodies off the ground to allow the wind to circulate
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Single sided ventilation
Wing wall 21
Eave and Floor Vents • Vents located in joist and beam spaces or between studs under roof overhangs are an economical method of perimeter ventilation. Heated interior air will rise out or cooler outside air will dump down through as pressure and temperature dictate. • Floor vents allow intake of cooler ground air and are a natural complement to eave vents as they provide the inlet to a ventilation cycle. 22
Outlet & Inlet •
•
• • •
•
•
Direction and speed of airflow determine the cooling effect of natural ventilation. Inlets should be placed low on the windward side facing the prevailing wind Outlets should be placed high on the leeward side Narrow plan form to enhance crossflow To encourage ventilation there must be an inlet and outlet on opposite or adjacent sides of a space. Airflow into an opening on the windward side of a space is most effective when the wind direction is within 30o of normal to the opening. On the leeward or downwind side openings should be larger than on the incoming or windward side.
23
Fenestration • Door and windows are the natural means of ventilating houses. • The placement, size and type of openings govern the effectiveness of this fenestration. • UBBL codes that opening at dwellings should be 10% of the floor area. • Window types should be oriented to catch or slow down prevailing breezes. • Awning windows allow air to enter by keeping out rain. • Casement windows can open to catch or buffer wind. • Louvered openings permit uninhibited air flow. • Hopper windows allow free, upward motion.
24
Window design
Double-hung
Casement
Effective open area Double hung Casement Awning Horizontal sliding
Awning
Sliding
Vented skylight
45% 90% 75% 45% 25
Window design Vented Skylight
Awning Clerestory windows
26
Window Design
Casement Window Louvred internal screens 27
Window Design Operable Skylights
• Effective ventilations and also allow natural illumination. • Seal well when closed, keeping moisture out and minimize infiltration. • Use double-glazed types for increased insulation. 28
Inlet Size vs Outlet Size
29
Inlet – Outlet Relationship
30
Opening on the facade
Vents and Louvres Affect Wind Speed & Flow
High vent
Louvre 31
Wind field • Wind patterns around buildings. • Wind acting on a building causes higher pressure on the incident side and a vacuum on the opposite side, drawing air in openings on the windward face and sucking it out downward. • Fluctuations owing to boundary layer turbulence • Periodic sampling of average wind data,10 m above ground • Topography, structures, surface texture
32
Wind and Boundary Layer
Urban
Open
Marine
33
Wind field Turbulence around buildings
Avoiding wind shadows
34
Baffling Ventilation
35
Mashrabiya • Ventilation and Sun controlled facades
36
Brise Soleil
37
Ventilated facades • Uses both airflow and insulative capacity of facades to improve thermal performance 38
Mechanical ventilation Overhead ceiling fans
• Fan assisted ventilation • Generally considered as energy efficient • Enhanced Night ventilation • Air movement over the skin creates thermally comfortable conditions up to two degrees higher than normal 39
Wind driven ventilation • Hot air rises, and cool air falls • Airflow up and down stairwells need to be controlled • Ceiling height and temperature gradient
STACK EFFECT – control of overall heat shift
40
Atriums / courtyards • Allow the stack effect to be effective • wind effect is more powerful than stack effect
41
Stack Ventilation Sections
42
Room Organization Strategies That Facilitate Both Cross and Stack Ventilation
43
Room Organization Strategies That Facilitate Both Cross and Stack Effect
44
Room Organization Strategies That Facilitate Both Cross and Stack Effect
45
Room Organization Strategies That Facilitate Both Cross and Stack Effect
46
Room Organization Strategies That Facilitate Both Cross and Stack Effect
47
Room Organization Strategies That Facilitate Both Cross and Stack Effect
48
Room Organization Strategies That Facilitate Both Cross and Stack Effect
49
Wind towers /shafts / scoops
50
Stair well
51
Nat / Mechanical Roof Vents
• Heated interior air gathers and tries to get out easily through high points of roofs or attics. • When combined with screening and an insulated closure flap on the inside, these roof vent methods are very effective way to ventilate and keep the weather out. • It may need to extend roof vents to a point above adjacent structures to catch the main wind currents. 52
Middle Eastern wind towers
53
Wind Scoops • Wind - strongest at 6 to 12 m above ground. • The ventilating air as it is funneled downward depends on the velocity of prevailing wind and associated pressure to move through the building. • To have even distribution throughout various rooms, properly proportioned and located exhaust vents with ducts are necessary.
54
Tracking Scoops • Multidirectional or tracking wind scoops areas where winds come from varying directions. • Where winds blow from one direction in the morning and opposite direction in the evening, a 2 directional pivot scoop can be used. • A 360o rotating scoops with directional sail will react to subtle changes in wind direction. 55
Wind Scoops
56
Wind Scoops
57
Ventilation towers
Residential buildings, Seville
58
Ventilation towers
Portcullis House, London. 59
Wind driven ventilation
Thermo-siphon – solar chimneys
60
Solar Chimney
• Solar chimneys, plenums or black boxes - air inside heats, expands and rises in turn pulling interior air up and out. Solar chimney can self balance, the hotter the day, the hotter the chimney and the faster the air movement. • West facing glazed chimney surfaces are suitable for venting during the hot afternoon part of the day. By integrating thermalstorage mass behind the glazing, the chimney will actually store daytime heat and continue to exhaust air after the sun has set thus acting as a night ventilator.
61
Solar Induction Vents • A solar air ramp, windows with radiant barrier curtains or a solar mass wall can be used for induction vents. • When sunlight trapped behind east or west glazing, air is heated and rises. If the heated air is vented outside at top, interior air will be sucked up.
62
Building as a Flue
• A building can act as a flue for ventilating by the chimney effect. The building can be shaped to optimize natural convective ventilation. • The challenge with ventilation is to provide sufficient fresh air during extreme climate conditions – effectively and comfortably. 63
Night flush cooling 1. Thermal mass acts as a heat sink for heat gained during the day. 2. At night, cooler air passes over the exposed thermal mass surfaces. 3. Heat exchange occurs between the mass and the air, and the heat is removed. 4. The thermal mass is cool ready to repeat the cycle.
64
1. Thermal mass acts as a heat sink for heat gained during the day. 2. At night, cooler air passes over the exposed thermal mass surfaces. 3. Heat exchange occurs between the mass and the air, and the heat is removed. 4. The thermal mass is cool ready to repeat the cycle. 65
Radiant cooling • Temperature difference of day and night • Direct radiant – Passive – Mechanical
• Indirect radiant – Roof ponds, – Mechanical, ducted
66
Direct radiant Cooling
67
Direct radiant Cooling
68
Indirect radiant cooling
69
Evaporative cooling • Direct evaporation – Passive – Mechanical, domestic, ducted, – Fountains, salsabils – PDEC
• Indirect evaporation – Roof ponds, – Mechanical, ducted
70
Indirect Evaporative cooling
71
Indirect Evaporative cooling No humidity is added to indoors
72
Direct Evaporative Cooling Water features • Water droplets increase evaporation • Decorative pattern enhances evaporation • Air is cooled • Cool air sinks into lower chamber
Salsabil-Water trickles over the decorated surface to increase evaporation
Fountain - A large surface area of water droplets increases 73 evaporation
Direct earth coupling • In hot climates, the earth temperature is usually too high shading the earth surface with a layer of gravel or wood chips or encouraging evaporation by irrigating the surface of the earth.
74
Indirect earth coupling • The refrigerant absorbs heat from the air circulating through your home. • Once the heat is removed, the cold air is circulated via the ductwork to cool your home. • The heat from the refrigerant is transferred to the water in the loops and deposited back into the earth. • The water is cooled as it circulates underground and is ready to absorb more heat from your home.
75
References • Daniels, 1995, The Technology of Ecological Buildings, Birkhauser Verlag, Basel • Environmental Design Guide. • http://www.greenhouse.gov.au/yourhome/home.htm
76
Principle of Solar Angles Building Science 1 Sujatavani Gunasagaran
Position of sun • Earth rotates around sun in elliptical orbit once every year & about own axis every 24 hours • due to tilted axis of rotation, different locations experience different solar intensity & different hours of sunlight
– solstice = where sun stands still – equinox = time when length of day & night equal
Position of sun
Section through sun, elliptical plane & earth
The tilt of the earth creates seasons on earth
Solar radiation measurement • duration of sunshine- expressed either as number of hrs per day or average per month • cloud cover - with 2 observations/ day, expressed as percentage of sky covered by cloud • average daily amounts of solar radiation (MJ/m2 or kW/m2) for each month provide indication of climatic conditions • for detailed calculations, hourly average intensities (W/m2) required for typical day in critical month
Solar radiation & thermal comfort
• Outdoor temperatures vary due to the changing position of the earth relative to the sun • Decide when/where, direct solar gain is to be avoided. • To maximise your control of solar radiation in design, you must know where it will shine, at what intensity and at what time • Best way of minimising solar gain indoors is through external shading devices • VSA and HSA will provide design information regarding size of shading devices required
Introduction - Shading Devices
• To prevent unwanted sun penetration in hot seasons, windows and other openings must be shaded. • Provide protection against glare & direct sunlight into building
• Classified as one or more of the following – Internal or External – Fixed or Adjustable
• External shading devices are most efficient – horizontal – vertical – egg-crate
3 Types of External Shading Devices • horizontal • vertical • egg-crate
Shading devices Awnings
Solar pergola
Eaves overhang
Shading devices
Radio therapy bldg, Hospital Kuala Lumpur
Renzo Piano, Menil Collection, 1982, Houston
Shading devices - Perth
Police HQ, Perth
Arch School, Curtin Uni.
Shading devices - Perth
Wellington St Office, Perth
Shading devices - Malaysia
Hospital Kuala Lumpur
Window orientation
• Shading of north facing windows is easy to control; • Shading of east and west facing windows is difficult; • Therefore, minimise east and west facing windows.
North-facing windows
North-facing windows are easy to shade
East and west-facing
East and west-facing windows need vertical shading devices Manley Hydraulics Laboratory, 1999, Poulet
Sun Radiation & Position • Determination of sun position required before shading devices or indoor solar gain can be established. • Movement of sun is predictable but varies at different times of year depending on latitude and longitude of a place. • We can identify how building will be sunlit and intensity of radiation at different times of day and different months. • Stereographic diagrams are useful way to identify sun position and to understand the implication of solar radiation on surfaces of different orientations
Seasonal variation
Sun Path Diagrams
Altitude & Azimuth • Position of sun described by 2 angles
– angle of altitude - vertical angle between horizontal ground plane & earth-sun line
– angle of azimuth - horizontal angle of earth-sun line relative to north angles determined using sun path diagram
Sun path diagrams • 2D representation of sun path across sky for specified days in a year for specific latitudes. • Stereographic diagrams are like a photograph of sky, taken looking straight up towards zenith, with 180° fish eye lens. • Sun’s path for particular dates projected onto this flattened hemisphere for particular latitude. • Sun Path diagrams provide means to calculate the size and location of shading devices.
Sun Path Diagrams Stereographic Projection
Stereographic diagram for Perth Latitude 32.5°S Phillips R 1996 Sunshine & Shadein Australiasia, AGPS
Latitude
• Kuala Lumpur Latitude 03° 10 N Longitude 101° 42 E • Penang Latitude 05° 25' N Longitude 100° 19' E • Melaka Latitude 02° 11' N Longitude 102° 14' E
Shadow angle protractor Semi-circular protractor showing 2 sets of lines – radial - readings of HSA – arcual - coincide with altitude circles at centre line, deviate & converge at corners- readings of VSA
Use of shadow angle protractor • To find when a wall or window will be in the sun • To design sun shading to prevent sun penetration • To determine when a space will have sun entry • To determine when adjoining structures may shade a building
Sun path diagram
For particular latitude with shadow angle protractor
Shadow angles
• Not all windows face north • Acceptable orientation of ‘north-facing’ windows is between ±15o of north • Shading may be required for a period of the day eg 9am to 4pm. • Designer needs to calculate shadow angles
Shadow Angles
Vertical (VSA)
Horizontal (HSA)
Horizontal Shadow Angle • This is the horizontal angle relative to the normal of the window pane.
Vertical Shadow Angle
• The angle a plane containing the bottom two points of the wall and the sun makes with the ground when measured perpendicular to the wall.
Shadow angles
Horizontal shadow angles
Shadow angles
Vertical shadow angles
Example 1
• Pair of vertical fins in plan • Shading mask
• Shading mask on sun path diagram if bldg oriented 30°E of N
Example 2
• Canopy over window in section - VSA of 60°
• Shading mask of canopy on protractor
• Placed over sun-path diagram, shows when shading device is effective
EXAMPLE 3
Tutorial/Exercise – Next Week A Shadow Angle Protractor is placed over a sun-path diagram. HSA is read directly off the radial lines. VSA is read directly of the semicircular lines.
Designing a shading device
• Design a horizontal shading device for a window 1mx1m, facing 20o west (sill height 1m) • Shading is required from 0900-1600, 17 October – 21 March.
Designing a shading device
References
• Phillips, R. (1996) Sunshine & Shade in Australia. AGPS • Szokolay S. (1982) Climatic Data and its use in Design RAIA Canberra • Szokolay S. (1996) Solar geometry. Univ of Queensland Printery • Paolino, S. 1979, Living with the Climate, Advance Press, Perth. • Baverstock, G. and Paolino, S. 1986.Low Energy Buildings in Australia, Graphic Systems, Perth.
Physics of Heat & Thermal Heat Properties of Materials
Building Science 1 Sujatavani Gunasagaran
Thermal performance of buildings This session provides a much needed analysis of the thermal behaviour of buildings, considering the means by which heat flows into and out of a structure as well as a summary of relevant control mechanisms. .
What does this mean to Architects Improving thermal performance of buildings through energy efficient design is an important program to reduce greenhouse gas emissions and global climate change towards sustainable design. In other words:
• Through design, reduce the amount of energy used to achieve comfortable levels of temperature and humidity, and adequate levels of lighting in buildings. • (Australian Building Codes Board, 2001)
Thermal performance of buildings Under all situations, heat flows either into or out of a building.
Conduction Convection Radiation
What is Conduction? • Heat energy travels through/transfer between bodies in direct contact. • Heated excited molecules bump into and transfer some of their energy into adjacent, cooler ones. • The faster the rate of heat flow, or molecular interaction at a given temperature through a material, the higher the conductivity.
What is Convection? • Heat is transferred by the bodily movement of a carrying medium (gas or liquid). Movement maybe self-generating due to temperature differences or propelled by an applied force. • The rate of heat transfer in convection depends on: • Temperature difference • The rate of movement of carrying medium • Specific heat of the carrying medium.
What is Radiation? • Heat energy transmitted from the source through the space to the bodily contact without a medium. • Radiant energy is transmitted as electromagnetic waves. • Rate of heat flow depends on: • Temperature of emitting and receiving surfaces. • Certain qualities of these surfaces.
• Radiation received by a surface can be partly absorbed and partly reflected (a + r =1).
What is Radiation? • Light coloured, smooth & shiny surfaces tend to have higher reflectance. • A perfect reflective surface : r=1, a=0 • A perfect absorber (black surface : r=0, a=1 • Measurement of radiation = W/m2.
Thermal balance Heat may be lost – outwards flow, or Heat may be gained – inwards flow. The net result may be either too hot, too cold, or just right.
Heat Flow • Heat energy tends to distribute itself evenly until a perfectly diffused uniform thermal field is achieved. • It tends to flow from high temperature to lower temperature zones by conduction, convection and radiation. • The greater the temperature difference the faster the rate of heat flow.
Heat Flow Rate
• It is equivalent to Power – the ability to carry out certain work (energy to carry out the work) in unit time. • J/s = Watt (can be measured in kilowatt (1kW = 1000 W)
Density Of Heat Flow Rate
• In heat calculations – the term is Intensity (which is heat flow in relation to unit area) is used. • I = W/m2
Modifications to adjust thermal comfort If it is likely to be too hot or too cold, then: • •
Design the building to control heat flow, and Add heating or cooling to modify temperature.
Three basic considerations of design to control heat flow • Consider thermal properties of materials (insulation or heat storage) • Consider solar radiation (shading) • Consider airtightness (ventilation)
Thermal properties of materials
• Insulation • Thermal mass heat storage
Insulation • Insulation is the use of a material with a low overall conductance to reduce the energy flow across another material. • The insulation acts to retard and/or reduce the flow of heat, thus it must have a high resistance (resistance being the inverse of conductance).
Thermal Mass Heat Storage • Solid mass elements such as concrete, solid brick, stone, earth, rammed earth, absorb and release heat slowly. • The effect is to stabilize the effects of diurnal temperature changes.
Airtightness and Ventilation • Heat may be lost (exfiltration), or gained (infiltration) • Control of airflow in and out of a building is an essential design consideration. - Window design, - vent and opening location - avoid uncontrollable gaps and cracks
Conductivity, k-value (M&E Book pg 179)
• In order to calculate heat transfer and to compare different materials it is necessary to quantify just how well a material conducts heat. • k = rate of heat flow in watts across a thickness of 1m for a temperature difference of 1 degree C. • Or a measure of the rate at which heat is conducted through a particular material under specified conditions • Unit measurement is W/m deg C. • The lower the k-value, the better the insulation (good insulator = 0.03 W/m deg.C) •
(tables M&E page 1547 and Metric Handbook page 38-3)
Conductivity and resistivity of some materials – (Book: Manual of Tropical Housing and Building page 285)
Resistance (R) and Resistivity where:
R=t/k
m2 C/W
R is the resistance of the material (m²C/W), t is the thickness of the material (m), and k is the conductivity of the material (W/mC).
• Reciprocal of conductivity is resistivity = 1/k • Resistivity is a material property and refers to that material's ability to resist the flow of heat • Better insulators will have higher resistivity values
Conductance, C • C = is the heat flow rate through unit area of body (density of heat flow rate) when the temperature difference between 2 surfaces is 1 degree C. C= 1 R
=
1 m2 deg C W
= W/ m2 deg C
• Conductivity values are more readily available for most building materials than resistivity • Conductance unit is - (W/m²C ). • Conductance is the inverse of resistance,
C = 1 = R
k t
W/m² W/m²C
Rt-value and U-value
• Resistance is usually given as an "R" value which is given as the resistance of one square metre of the structural element subject to a one degree temperature difference. R includes surface air resistances. Rt = Rso + ΣR Rn + Rsi
m2C/W
• The U-Value is the overall heat transfer property of a structural element (W/m² K) and is the reciprocal of its total resistance. U= 1 Rt
W/m² W/m² C
Transmittance, U-value • The reciprocal of the air to air resistance is the air to air transmittance or U-value (use for heat gain/loss calculation) • U = 1/Rt (total thermal resistance) or U = 1/Rsi+1/R1+1/R2+….+1/Ra+Rso • unit is the same as conductance ie. • W/m2 deg C except that the difference is the air temperature difference and not the surface temperature difference.
Overall heat transfer property U = 1/Rsi+1/R1+1/R2+….+1/Ra+Rso
• U = U value • Rsi= standard inside surface resistance • R1, R2= Resistance of that particular material • Ra = Standard resistance of air space • Rso= standard outside surface resistance
Transmittance of some constructions –
(Book: Manual of Tropical Housing and Building page 287)
REFERENCES • Introduction to Architectural Science: Steven V Szokolay • Metric Handbook: David Adler • Manual of Tropical Housing & Building: Koenigsberger • Mechanical & Electrical Equipment for Buildings: Benjamin Stein
Worked example 1 Calculate the U value of a cavity wall with a 105mm thk brick outer leaf, a 75mm unventilated cavity containing 50mm fiberglass quilt then a 100mm light weight concrete block inner leaf with a 15mm layer of light weight plaster. Thermal conductivity, in W/mK, are: brickwork 0.84, light weight concrete block 0.19, fibreglass 0.04 and lightweight plaster 0.16. The standard thermal resistances, in m2K/W are: outside surface 0.055, inside surface 0.123, cavity 0.18
Layers
Thickness
Thermal conductivity Wm/K
outside surface
-
-
light weight plaster 15mm
0.015
cavity 25mm
0.025
fibregalss quilt 50mm lighweight concreteblock inner leaf 100mm Exposed brickwork 105mm inside surface Total Using = =
Resistance (m2K/W) standard
0.16 n/a
0.0105/0.16
0.055 0.09375
standard
0.18
0.05
0.04
0.05/0.04
1.250
0.1
0.19
0.1/0.19
0.526
0.105
0.84
0.105/0.84
0.125
standard
0.123 2.353
U-value = 1 / Rt 1/2.353 0.43
W/m2K
Worked Example 2 •
A certain uninsulated cavity wall has a U-value of 0.91W/m2K. If expanded polyurethane board is included in the construction what minimum thickness of this board is needed to reduce the U-value to 0.45W/m2K? Given that the thermal conductivity of expanded polyurethene = 0.025W/mK.
Target U value
U2 =
Target Total resistance (1/U)
R2 =
1/0.45
Existing U-Value
U1 =
0.91
Existing total resistance v (1/U)
R1 =
1/0.91
Extra Resistance Required
R2 - R1 =
2.222 - 1.099
0.45
=
2.222
1.123
The k-value of the proposed insulating material k= 0.025, so using formula R=d/k Thickness of material d = R x k = 1.123 x 0.025 = 0.028meters So minimum thickness of insulating board needed to give 0.45 U-value is 28mm
Tutorial 1 A cavity wall is constructed as follows brickwork outer leaf 105mm, air gap 25mm, expanded polyurethene board 25mm, lightweight concrete block inner leaf 100mm, plasterboard 10mm. The relevant values of thermal conductivity, in W/mK, are: brickwork 0.88, polystyrene 0.035, concrete block 0.19, plasterboard 0.16. The standard thermal resistances, in m2K/W are: outside surface 0.055, inside surface 0.123, air gap 0.18. a) b)
calculate the U-value of this wall calculate the U-value of the same wall sited in a position of severe exposure for which the outside surface resistance is 0.03m2K/W
Heat Gain in Buildings Calculating OTTV Envelope Heat Flow Heat Flow via air movement Heat flow via transparent/ translucent Elements Internal Heat Gain Calculation
Building Science 1 Sujatavani Gunasagaran
Introduction • Aim of building envelope – control heat transfer • In hot and humid climate aim to keep indoor comfort temperature between 22-26°C all year with minimal space cooling (mean outdoor temperature fluctuates between 3036°C) • consider heat transfer mechanism through wall, roof materials • consider role of insulation and material with low U value 2
Thermal performance of buildings Under all situations, heat flows either into or out of a building.
Conduction Radiation Convection 3
Thermal performance of buildings • • • •
Solar heat gain Internal heat gain Conduction heat gain or loss Ventilation heat gain or loss
4
Thermal performance of buildings • • • •
Solar heat gain Internal heat gain Conduction heat gain or loss Ventilation heat gain or loss
Qs Qi Qc Qv
Thermal balance exists when the sum of all the heat terms are zero:
Qs + Qi + Qc + Qv = 0 5
Thermal performance of buildings • • • •
Solar heat gain Internal heat gain Conduction heat gain or loss Ventilation heat gain or loss
Qs Qi Qc Qv
Thermal balance exists when the sum of all the heat terms are zero: Qs + Qi + Qc + Qv = 0 6
Solar Heat Gain Qs = s . I . A where:
Qs is the resultant heat flow (Watts) A is the surface area through which the heat flows (m²) I is the intensity of solar radiation S is the solar heat gain factor
7
Thermal performance of buildings • • • •
Solar heat gain Internal heat gain Conduction heat gain or loss Ventilation heat gain or loss
Qs Qi Qc Qv
Thermal balance exists when the sum of all the heat terms are zero: Qs + Qi + Qc + Qv = 0 8
Internal Heat Gain Qi = qo + ql + qa • People – activity, numbers, time qo • Lights – rating (watts), heat output, number, time ql • Appliances – electrical, gas, heat gain, time qa 9
Thermal performance of buildings • • • •
Solar heat gain Internal heat gain Conduction heat gain or loss Ventilation heat gain or loss
Qs Qi Qc Qv
Thermal balance exists when the sum of all the heat terms are zero: Qs + Qi + Qc + Qv = 0 10
Conduction Heat Gain or Loss Qc = U A ∆ T where:
Watts
Qc is the resultant heat flow (Watts) A is the surface area through which the heat flows (m²) ⊿T is the temperature difference between the warm and cold sides of the material U is the heat transmission coefficient 11
Conduction Heat Gain or Loss Qs + Qi + Qc + Qv = 0 Qc = U A ∆ T *Qc = U A ∆ Ts
Watts Watts
(*opaque surfaces with severe exposure)
12
Sol-air Temperature, Ts • The heating effect of radiation incident on the building must be added to the temperature of outside air if the surface is not sheltered (exposed to solar radiation) Ts= To + (I x a) fo • • • • •
Ts – Sol-air temperature To – Outside air temperature I – Radiation intensity (W/m2) a – absorbance of surface (cooefficient) fo – surface conductance (outside) (W/m2 degree C)
13
Thermal performance of buildings • • • •
Solar heat gain Internal heat gain Conduction heat gain or loss Ventilation heat gain or loss
Qs Qi Qc Qv
Thermal balance exists when the sum of all the heat terms are zero: Qs + Qi + Qc + Qv = 0 14
Air quality and Air Changes • Air quality standards ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers) • Air changes (ACH) • expressed in litres/person/second eg ventilation requirements for residential living areas 3.5 – 5 l/s (2.5 l/s minimum) 15
Ventilation Heat gain Qv = 1300 . V . (To - Ti)
If number of air change per hour (N ) given
Factors: Specific Heat of Air 1300 J/m3degC V = Ventilation rate (m3/s)
V = N x room volume 3600 ( 1 hour=3600seconds)
To= Outside air temperature Ti = Inside air temperature
16
Thermal performance of buildings Qs + Qi + Qc + Qv = 0 Qs Qi Qc Qv
= = = =
s . I . A qo + ql + qa UA∆T 1300. V . (To - Ti)
Watts Watts Watts Watts
17
References • ASHRAE Standards, 1992 • Introduction to Architectural Science, Steven Szokolay, 2006 • Environmental Design Guide, DES 22, 23 • http://www.dbce.csiro.au/indserv/brochures/nathers/nathers.htm • http://www.seav.vic.gov.au/building/hou sing/firstrate/index.html • http://www.squ1.com/ 18
Tutorial 1 A cavity wall is constructed as follows brickwork outer leaf 105mm, air gap 25mm, expanded polyurethene board 25mm, lightweight concrete block inner leaf 100mm, plasterboard 10mm. The relevant values of thermal conductivity, in W/mK, are: brickwork 0.88, polystyrene 0.035, concrete block 0.19, plasterboard 0.16. The standard thermal resistances, in m2K/W are: outside surface 0.055, inside surface 0.123, air gap 0.18.
a) b)
calculate the U-value of this wall calculate the U-value of the same wall sited in a position of severe exposure for which the outside surface resistance is 0.03m2K/W
Question 1a -Solution
Layers
Thickne ss
outside surface
-
brickwork outer leaf 105mm
Thermal condu ctivity Wm/K
-
0.105
0.84
air gap 25mm
expanded polyurethene board 25mm
lighweight concreteblock inner leaf 100mm
plastewrboard 10mm
inside surface Total
Using U-value = 1 / Rt = 1/1.786 = 0.56W/m2K
0.025
0.035
0.1
0.01
Resistance (m2K/W)
standard
0.055
0.105/0.84
0.125
standard
0.18
0.025/0.035
0.714
0.19
0.1/0.19
0.526
0.16
0.01/0.16
0.063
standard
0.123 1.786
Question 1b -Solution
Layers
severe exposure
brickwork outer leaf 105mm
Thermal cond uctivi ty Wm/ K
Thickn e s s
-
-
0.105
Resistance (m2K/W)
standard
0.84
0.105/0.84
air gap 25mm
expanded polyurethene board 25mm
lighweight concreteblock inner leaf 100mm
plastewrboard 10mm
inside surface Total
• • •
0.03
0.125
0.18
0.025
0.035
0.025/0.035
0.714
0.1
0.19
0.1/0.19
0.526
0.01
0.16
0.01/0.16
0.063
standard
0.123 1.761
Using U-value = 1 / Rt =1/1.761 =0.57W/m2K