Analysis of historical residential air-conditioning equipment sizing using monitored data

摘要

Monitored data were analyzed to determine whether residential air conditioners in the Pacific Northwest historically have been sized properly to meet or slightly exceed actual cooling requirements. Oversizing air-conditioning equipment results in a loss of efficiency because of increased cycling and also lowers humidity control. On the other hand, the penalty of undersizing air-conditioning equipment may be some loss of comfort during extremely hot weather. The monitored data consist of hourly space-conditioning electrical energy use and internal air temperature data collected during the past 7 years from 75 residences in the Pacific Northwest. These residences are equipped with central air conditioners or heat pumps. The periods with the highest cooling energy use were analyzed for each site. A standard industry sizing methodology was used for each site to determine a sizing estimate. Both the sizing recommendation based on Manual J and peak monitored loads are compared to the capacity of the installed equipment for each site to study how the actual capacity differed from both the estimate of proper sizing and from actual demands. Characteristics of the maximum cooling loads are analyzed here to determine which conditions put the highest demand on the air conditioner. Specifically, internal air temperature data are used to determine when the highest cooling loads occur, at constant thermostat settings or when the thermostat was set down. This analysis of monitored data also provides insight into the extent that occupant comfort may be affected by undersizing air conditioners. The findings of this research indicate that cooling equipment historically has often but not always been oversized beyond industry-recommended levels. However, some occupants in homes with undersized, properly sized, and, in rare occasions, even oversized cooling equipment appear to suffer because the cooling equipment cannot always provide adequate cooling. Key findings are summarized.