Numerical Analysis of the Building Air Conditioning Induced Antropogenic Heat in Urban Areas

Abstract

A model for the evaluation of building air conditioning energy and exausted heat from air conditioning system during sumer is developed. The purpose of the model is to study a dynamic interaction between buildings in the urban areas and outside air. Three-dimensional ensemble-space averaged Reynolds equations, continuity equation, equations for the transport of turbulent energy, turbulent energy dissipation rate and heat and moisture transfer equations in the atmosphere were numerically integrated. Forest and building canopies were also incorporated in the model by the computation of momentum, heat and moisture exchange between the canopy and the air. Especially, a volume averaging technique, which allows an accounting for the volume of urban structures in the governing equations was applied.For the computation of the building cooling energy, the conduction heat to the building is evaluated by computing the heat exchange between building walls and roof with air in the rooms using an assumption of constant room air temperature. The total heat load in the room is evaluated by the summation of this conduction heat and other heat sources in the room, such as heat release due to machines and anthropogenic heat. The needed air conditioning electricity is evaluated by this total heat load and a coefficient of performance (COP) of the heat pump, defined as the ratio between the heat load, needed to be pumped out of the room and the used electricity. The outside anthropogenic heat release due to air conditioning was evaluated as a summation of used electricity and the in-the-room heat load.The model was also used for an analysis of the heating processes and cooling energy use for a model city.