Development and Evaluation of a Night Ventilation Precooling Algorithm

Abstract

This paper describes the development and evaluation of a simple algorithm for night ventilation precooling that can be integrated at low cost within a controller for packaged air conditioners that employ economizers, such as rooftop units. In addition to reducing operating costs, the algorithm ensures that indoor comfort is maintained. The basic night ventilation precooling algorithm was developed based upon a simple optimization and heuristics derived from simulation results. The cost savings potential of the algorithm was evaluated using simulations for a range of buildings and climates throughout California. The buildings were representative of small commercial buildings that employ packaged air-conditioning equipment with integrated economizers. The annual savings in compressor energy for night ventilation ranged from about 0 to 53% depending on the location and building type. The savings in total air-conditioning electrical energy usage are much smaller than the compressor savings due to an increase in fan energy. The annual electrical energy savings varied between about 0 and 8%. The electrical demand cost savings associated with night ventilation varied between about 0 and 28%, whereas the total annual electrical cost savings ranged from about 0 to 17%. The greatest percent savings occurred in cooler coastal climates having smaller total loads but significant opportunities for night ventilation precooling.