ENERGY ANALYSIS AND MODELLING OF BUILDINGS

Abstract

This project on Energy Analysis and Modelling of Buildings comprises the following major components : (i) the formulation of an improved methodology for calculating the OTTV of building envelope and roof, (ii) the development of a simplified equation for estimating the cooling energy use of large office buildings, and (iii) a study on the energy-efficient performance of commercial buildings through audits, computer simulations, energy target setting, and review of the existing energy standards. The existing Singapore building energy standard incorporates a calculation of the overall thermal transfer value (OTTV) of a building envelope. In this project, an improved methodology has been developed to calculate the envelope OTTV and roof OTTV of air-conditioned buildings. This simple and yet accurate methodology is applicable to rectangular buildings which are oriented in any direction and buildings with non-identical walls or sloping roofs. For a building envelope, the methodology involves first applying the revised envelope OTTV equation to each facade of the building by including the appropriate solar correction factors and then taking the weighted average of all the OTTVs. Similarly, a revised equation has been formulated to calculate the OTTV for a roof This revised roof OTTV equation yields an improved correlation between the roof OTTV and the heat gain through the roof. Solar correction factors have been determined, through parametric DOE-2 simulations, for walls and roofs of various orientations and pitch angles. It has been found that values of the envelope OTTV and roof OTTV calculated using the improved methodology are within 3 % of the corresponding OTTV's obtained from results of DOE-2 simulations. The improved accuracy offered by the revised OTTV methodology lends itself to the further development of a simplified cooling energy estimating equation. The equation, developed from the OTTV and degree-days method for cooling, is based on the correlation of the annual building cooling load with the cooling load attributed to the building envelope. From a database of results generated from parametric DOE-2 simulations, expressions have been obtained to relate the annual cooling load, peak cooling load and sensible heat removal rate to the envelope heat load. Furthermore, the methodology includes the effects of part load performance of the cooling equipment. To validate the accuracy of the simplified energy estimating equation, computed results were compared with those predicted by full-scale DOE-2 simulations. In the energy performance study of commercial buildings in Singapore, several office buildings were selected and subjected to detailed audits of their energy use. Based on the audit results and the incorporation of computer simulations and parametric analyses, applicable energy conservation opportunities are recommended for commercial buildings operating in the tropics. The energy consumption indices of some 60 office buildings distributed into three classes were also analysed. This analysis has led to the recommendation of two levels of energy targets for achieving the near- and long-term energy-efficient operation of such buildings. The current Singapore and ASHRAE standards pertaining to energy conservation in buildings have been reviewed. It is shown that in. order to provide greater flexibility in building design while achieving further energy savings, there is a need for a performance-based building energy standard. Thus, as a first step towards achieving this, the concept of the annual energy budget (AEB) has been proposed. The ABB is the highest allowable limit of annual calculated energy use of a proposed building design. In this project, a simple hand calculation procedure has been developed for calculating the AEB. A proposed building design is deemed to be in compliance with the energy conservation standards if its AEB is higher than the estimate of its actual energy use. Finally, the ABB of four audited buildings have been calculated and it has been found that in each case, the AEB is higher than the estimate of actual energy use.