scope:

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. This new class of gas-fired heat pump water heaters are driven by a direct-fired 2.9 kW (10 kBtu/hr) air source absorption heat pump, which like vapor compression (electric) heat pump water heaters (EHPWH) utilize ambient air to heat stored potable water. With a small 2 kW (6.3 kBtu/hr) gas burner, the packaged unit can exceed this efficiency limitation with Coefficients of Performance (COPs) in excess of 1.5. Unlike EHPWHs however, the prototype gas-fired heat pump water heater (GHPWH) heats potable water with a combination of output from the condenser, absorber, and heat recovery from the products of combustion, hence the evaporator load (space cooling effect) is 30-40% that of an equivalent vapor compression system. Concerning system cost, with a thermal input of 16% of storage GWHs and 3% of tankless GWHs, the cost of GHPWH installation is minimized, requiring only small diameter gas and plastic vent piping, and standard electrical service. This GHPWH represents a step-change in energy efficiency at a projected competitive cost, a critical goal of both government agencies and utility energy efficiency programs. In this paper the authors report on data and findings from a preliminary field evaluation of this prototype GHPWH.