Domestic hot water consumption estimates for solar thermal system sizing

Accurate domestic-hot water (DHW) consumption information is useful for solar-thermal-hot-water-system designers and policy makers supporting solar-thermal-incentive programs. Conducting field studies of DHW-consumption patterns is difficult and costly, and as a result, there are few studies available in the body of literature. Several DHW models exist, however these aggregate models are often dated and most fail to identify the influence of the number of occupants in the dwelling, instead relying on a standard-per-capita consumption. The standard of 60 liters/capita/day (lcd) is found to be accurate for households of 4 or more occupants, but significantly under estimates per-capita-hot-water consumption for households with 3 or fewer occupants, consequently, under estimating the energy and GHG-emissions savings of solar-DHW programs [1]. The new estimate presented here addresses these issues. This study was conducted using utility-billing data, and occupant responses from a survey of 1594 residences. The data includes annual total-water use, energy consumption, costs, and basic information about the residence and occupants. The method isolates average-oil used in water heaters and then estimates system performance to calculate the volume of hot water heated. The findings include total-water use, oil consumption for water heating, and DHW use based on occupancy for households of 1 through 6 occupants.

► An estimate for per-capita-residential-total-water use according to the number of occupants in the household.
► A method for estimating DHW use through determining oil consumption used for DHW and converting the energy input into DHW volume.
► An estimate of residential-per-capita-DHW use according to the number of people in the household.