AT-78-08-2 -- Saving Energy by Night Setback of a Residential Heat Pump System

Lowering space temperature at night is recognized as an effective method of reducing buildingheat loss and fuel consumption of both fossil fuel-fired and electrical resistance heatingsystems. With the rapid growth in the number of heat pump installations in recent years,there is increasing interest in methods o~ reducing energy consumption and operating costsof heat pump systems.In this study, a hybrid computer simulation was used to determine whether or not setbackof a heat pump system would reduce energy consumption and operating costs. The simulationconsidered the effects of indoor and outdoor temperatures on both heat pump capacity andheat pump energy consumption, and considered several methods for cont~ol of the auxiliaryheat elements.No attempt was made to determine the effect of relative size of heat pump and auxiliaryheat on night setback economics, nor was any attempt made to analyze the effects of variationsin building construction, level of insulation or structure thermal storage.Also, this study has made no attempt to assess the cost of providing capacity for themorning pick ~p load which may be imposed on the electric utility. In addition, changesin utility rate structures, i.e., time of day metering, peak load pricing, possible futuredemand rates, etc. would influence operational costs and must be considered in assessing theoverall impact of heat pump setback programming.All of these variables can effect heat pump setback economics in varying degrees. Thus,additional studies are necessary before final conclusions can be reached.