2016 ASHRAE Winter Conference

The single-family residential building stock in California is dominated by gas-fired storage water heaters. This is a result of the building energy efficieny code. For decades the water heater energy consumption calculated in the budget compliance tools has made it very hard to justify using an electric resistance water heater. As a result very few electric water heaters have been installed. The compliance tools were written in a way that poorly calculates the hot water load. Furthermore the calculated time of energy use by water heaters does not account for the buffering effect of a storage tank. An important part of the budget calculation uses a time dependent valuation of electrical generation to capture the societal costs of using electricity for every hour of a typical year. This has meant that the actual effects of the time difference between the hot water use and the energy consumption of electric storage water heaters are not being evaluated properly. The combined effect of these oversights has inadvertently effectively blocked the adoption of heat pump water heaters in new construction in California. This presents a major obstacle for reaching the state's net-zero energy and greenhouse gas emission targets. This paper describes the way the building energy efficiency code currently calculates the water heater energy budget. Problems in the calculation procedure are explained. Our knowledge about residential hot water systems has increased greatly in recent years. These research efforts have significantly improved our ability to characterize these systems. Revisions to the building code calculations are suggested based on this increased knowledge. An enhanced hot water load calculator has recently been adopted by RESNET. Detailed field studies over the past several years of residential hot water draw patterns provide a source for more realistic draw schedules to use in the calculations. An open source water heat simulation model developed for utility incentive programs in the Northwest could be adapted to calculate the amount and timing of energy use. The role of demand response controls to reduce the impact of electric heat pump water heaters on the grid are also discussed.

The purpose of this paper is to study the energy impact of operating a HPWH in the basement of an R-2000 equivalent house, i.e. the Canadian Centre for Housing Technology (CCHT) twin house test facility, located in Ottawa Canada. We included four key parameters in the study: Did the operation of the HPWH have any adverse impacts on the basement air temperature? Was the HPWH operating more efficiently than the baseline water heaters? What if any were the impacts on energy consumption during the heating and cooling seasons and were there energy cost savings during the Heating and Cooling Seasons?

In the effort to achieve net-zero operation of residential buildings, advanced water heating technologies are vitally important.  Solar thermal is the most cost and energy efficient, renewable energy alternative for water heating, but the use of electric resistance as the backup to solar thermal may no longer be the most suitable option. This paper explores the year-long performance of a 189 liter (50 gallon) heat pump water heater (HPWH) serving as an auxiliary unit to an active indirect solar thermal water heater with a 303 liter (80 gallon) storage tank in a net-zero energy test home at the National Institute of Standards and Technology, Gaithersburg campus.

Approximately half of water heaters sold in the U.S. and Canada for residential applications are natural gas fired storage water heaters, and for these products the maximum steady state thermal efficiency of available products is approximately 96%, with transient rated efficiencies much lower.  To move beyond the thermal efficiency limits of standard condensing-efficiency residential gas water heating equipment, this paper describes an effort to develop an economic gas-fired ammonia-water absorption heat pump deployed as a packaged storage water heater.