Field Validation of the ASHRAI Transfer Function Method for Calculating Cooling Load

Abstract

The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Transfer Function Method (TFM) was validated using two identical wood frame residential-type structures, each containing an east and west-facing room. Each room had a calibrated, thermostatically controlled window air conditioning unit and two south-facing windows. The study included a parametric analysis of the thermostat setpoint and fenestration load effect on space heat extraction rate and cooling energy consumption. Some discrepancies withstanding, the transfer function method predicted the hourly heat extraction rates quite well. The principal discrepancies appeared to be the difference in daily curve amplitude and a phase-like shift of one to two hours. The heat storage capacity of the unoccupied test buildings was less than predicted by the TFM model. Accuracy of the transfer function coefficients to model the roof-ceiling combination was questionable due to the small attic air space which was not accurately described in the ASHRAE table of coefficients.