Residential water heaters: Energy and cost analysis

Abstract

A detailed computer model is developed to calculate energy flows for residential electric and gas water heaters. Model equations are derived from applications of the first law of thermodynamics, analysis of manufacturers' literature, and related studies. Several energy-saving changes are examined using the model. Changes for both electric and gas water heaters are: increase jacket insulation thickness, reduce jacket insulation thermal conductivity, reduce thermostat setting, and add insulation to the distribution line. Application of all these changes to an electric water heater would reduce electricity use 17% and increase initial cost 27%. Additional changes examined for gas water heaters are: reduce pilot rate, eliminate and add electric ignitor and flue closure, and reduce excess air for combustion by increasing flue baffling. Implementing all these changes to a gas water heater (except addition of electric ignitor) would reduce gas use 27% and increase initial cost 26%. These results show that there are large opportunities for reducing water heater energy use with only small initial cost increases.