Development of the Residential Load Factor Method for Heating and Cooling Load Calculations

The recent ASHRAE project, “Updating the ASHRAE/ ACCA Residential Heating and Cooling Load Calculation Procedures and Data” (RP-1199), developed two new residential loads calculation procedures: residential heat balance (RHB), a detailed heat balance method that requires computer implementation, and residential load factor (RLF), a simplified procedure that is hand tractable and suitable for spreadsheet implementation. This paper describes RLF and its development. The form of RLF resembles prior methods. However, the sensible cooling load procedure was derived using linear regression to find relationships between design conditions, building characteristics, and peak cooling load predicted by RHB. This eliminated the need for semi-empirical adjustments, such as averaging, that have been used in the development of other methods. Results comparing RLF to RHB are presented. The RLF heating load calculation is also described; it uses the traditional UA∆T formulation except for improvements to procedures for infiltration leakage rate and ground (slab and basement) losses.