NIGHT VENTILATION IN MEDIUM RISE OFFICE BUILDINGS. CASE STUDY: LIMA, PERU

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Passive Design Annual Conference PDAC 2014

SUMMER PERIOD EVALUATION OF NIGHT VENTILATION PERFORMANCE IN MID-RISE OFFICE BUILDINGS IN A HOT ARID CLIMATE WITH HIGH RELATIVE HUMIDITY INDEX. CASE STUDY: LIMA, PERU C1469285 1Welsh

School of Architecture, Cardiff University, Cardiff, UK

ABSTRACT: Nocturnal ventilation benefits has been evaluated and demonstrated in different climates; however, given the particular mild temperatures, high humidity index but no appreciable precipitations, and low daily temperature swings, further research in this context was required. This study contributes with nocturnal ventilation evaluation and assessment as a passive cooling technique in a typical summer week, in order to encourage its application and further investigation to maximize its potential. Findings show, due to the typical office related interior incidental gains, indoor temperatures were found higher than the outdoor ones along a summer day. Therefore, mass exposure to external conditions by ventilation was the most effective cooling strategy. Night ventilation, among the other passive strategies by wind air flow, is the least effective for a free running office building, while daytime and full day ventilation take us closer to the comfort band. Furthermore, potential coupling for night ventilation and mechanical cooling is identified, as it can reduce indoor temperatures by 2°C, cut back cooling loads and energy saving, suggestions for further research fall in this area. Keywords: nocturnal ventilation, hot arid desert climate, high relative humidity, low daily temperature swing, midrise office building.

1. INTRODUCTION Nowadays, the mild temperatures that used to characterize Lima’s meteorological condition has been changing over the past 10 years, as temperature increase can be easily perceived as consequence of global warming. Accordingly, passive cooling strategies application have not been significant in architecture practice up until the moment as environmental awareness has arisen in the recent years. The current Peruvian building code does not contemplate an environmental aspect, yet there are some voluntary sustainable related building parameters (National building regulation Annex EM110. Energy efficient thermic and light fitting). In order to neglect the use of mechanical cooling services so as to overcome the climatic change challenges and cut down greenhouse gasses emissions, an environmental approach in architecture is necessary, along with supportive research that encourages its application. This conference paper aims to evaluate nocturnal ventilation potential in mid-rise free running office buildings during the summer cooling period and the factors that affect its performance in Lima context.

2. LITERATURE Ventilation can improve internal comfort by two means, a direct and indirect mode. The first is related to a direct physiological effect due to air flow, hence, convective heat transfer among occupancy can take place. Nocturnal ventilation refers to the indirect mode, ventilating a space and thermal mass during

night and during the following day, the cooling stored in the thermal mass will reduce the internal temperatures experienced indoor (Givoni, p. 37, 1994). Extensive research has been conducted in a variety of climates (hot arid, hot humid and temperate climate) evaluating nocturnal ventilation performance in residential and commercial buildings; accordingly, cooling potential has been acknowledged and put in practice. Three significant factors have been identified in order to maximize its cooling effect. First, climate, best results have been observed in hot arid weather conditions as it presents a high diurnal temperature range (15 °C to 20°C), yet even low daily temperature rages have attained beneficial outcomes. For example, lightweight and heavyweight buildings with an average outdoor temperature amplitude of 8 °C to 10°C can achieve from 1 to 2.5 °C of indoor cooling effect. Second, the technical aspect, which refers to the optimum number of air changes per hour and period of ventilation time required to optimize results, 8 ACH and twelve hours of constant ventilation have been found to be the most appropriate (Blondeau, Spérandio, and Allard, 1997; (Kolokotroni, Webb, and Hayes, 1998). Last but not least, building parameters need to be taken in consideration, fabric density and heat capacity allows a high thermal storage, hence, greater cooling effect. In addition, cooling efficiency is strongly related to space volume, since the bigger is the ratio of volume to wall surface area, the more effective convective heat exchange is (Blondeau, Spérandio, and Allard, 1997).

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NIGHT VENTILATION IN MEDIUM RISE OFFICE BUILDINGS. CASE STUDY: LIMA, PERU by Leslie Berdiales - Issuu