Appraising a relationship between morphology and energy index of office buildings in tropics:

Abstract

In the last few years, together with the surge in new construction, the energy demand from buildings has also been influenced by current practice on energy demanding mechanically controlled buildings with artificially lit interiors. Present urban development strategy of implementing Mega polis development plan for city of Colombo expands its boundaries of the urban building stock. Thus, it’s vital to explore the end use energy demand of national building stock and comprehend a relationship between building morphology and energy consumption. A walkthrough field investigation was performed in 46 Wards in Colombo Municipal Council region. The structure of the survey was organized in relation to geographical information system (GIS) data and land use maps of the CMC region. Data was collated to formulate a comprehensive database on morphology of office building stock comprising major physical parameters and energy indices. Results revealed the office building stock is primarily composed of Air-conditioned office spaces and of which 78% contains naturally ventilated common spaces. In this stock 53% and 13% of the office buildings have an annual average building energy index above 200KWhm¯² and 300KWhm¯² respectively. Linear shape dominates the plan form representing 70.2% of the stock. Other basic shapes such as square, circular and composites corresponds to 19.5%, 2.3% and 8% respectively. . 54.55% of the office buildings have an average BEI of 150-250 kWhm-². Out of which 37.03% of the office buildings are EW oriented. Nexus between building façade configuration and building energy index were further analyzed using multiple and simple linear regression analysis. The analysis was conducted for buildings in the identified energy index categories by considering all four orientations. EW and NS oriented buildings were considered for further investigation to evaluate the effect of aspect ratio on energy index. It is evident that aspect ratio of 0.70 (1:1.43) in 100-150 kWh-² energy index range was within the optimal range. The optimal aspect ratio for buildings along east west axis is within the range of 1.27:1 to 1.5:1. Further increase of aspect ratio beyond this range result in increase of energy consumption in buildings. The average aspect ratio for NS oriented buildings in 100-150 kWh-² energy index range was 1.49 (1.49:1), which was within the optimal range. Nonetheless, the average aspect ratio for NS oriented buildings in Average Range is 3.22 (3.22:1), which is beyond the optimal range. Further onsite thermal investigations in the selected representative buildings with deep and shallow plan forms revealed a clear indoor temperature difference during air conditioned and non-air-conditioned period. It is evident that deep plan form has a greater potential to control external heat gain and reduce end use energy demand. In contrary, shallow plan forms are more susceptible for external heat gain and higher temperature variation is evident periphery and core. Moreover, overheating building periphery in both shallow and deep plan forms are susceptible for overheating condition. Thus the findings of this study represent the criticality of building morphology based on plan shape, orientation and interior planning which demonstrate a significant impact on end use energy demand due to external heat loads.