Effects of Air Conditioner Sizing on Energy Consumption and Peak Demand in a Hot-Dry Climate

Aaron Townsend and Kohta Ueno, Building Science Corporation

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Abstract

Oversizing of air conditioners is a common practice that reduces comfort and energy efficiency; the practice also results in higher first costs and exacerbates the effects of residential air conditioning on utility peak demand. At a subdivision in a hot dry climate (Redding, CA), a production homebuilder completed several houses at their standard practice equipment sizing of 155 to 185% of the total calculated Manual J load and subsequently built the remainder of the development with equipment resized to 135 to 150% of the total calculated Manual J load. Thirteen of these houses (7 in the standard practice sizing category; 6 in the resized category) were monitored for air conditioner runtime, interior temperature, and electricity consumption of the outdoor condenser unit. Data was collected for three months, covering the end of summer and start of the swing season. This study found that in comparison to the standard practice group, the resized group had longer average and maximum runtimes, consumed the same amount of energy, and if implemented on a large scale would reduce the electric utility's peak demand.