Simplified Method for Calculating Heating and Cooling Energy in Residential Buildings

摘要

A microcomputer-based program, Computerized, Instrumented, Residential Audit (CIRA), for determining economically optimal mixes of energy-saving measures in existing residential buildings was developed which requires extensive calculation of heating and cooling energy consumptions. In this paper, a simplified method of calculation that satisfies the requirements of speed and memory imposed by the type of microcomputer on which CIRA runs is presented. The method is based on monthly calculations of degree days and degree nights for both heating and cooling seasons. The base temperatures used in calculating the degree days and degree nights are derived from thermostat settings, solar and internal gains, sky radiation losses, and the thermal characteristics of the building envelope. Thermostat setbacks are handled by using the concept of effective thermal mass of the house. Performance variations of HVAC equipment with changes of part load and ambient conditions are taken into account using correlation curves based on experimental data. Degree days and nights for different base temperatures are evaluated by using a climate-specific empirical correlation with monthly average daily and nightly temperatures. Predictions obtained by this method and by DOE-2.1 are compared for the so-called Hastings ranch house for seven different climates in the United States. Heating and cooling energy consumptions predicted by CIRA lie generally within +- 10% of DOE-2.1 predictions.