ASHRAE - American Society of Heating@ Refrigerating and Air-Conditioning Engineers@ Inc.
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.