SUMMARY

Absorption heat pump water heaters offer improved performance compared to conventional direct-fired water heaters, with the potential for coefficients of performance well in excess of 1. A primary energy usage comparison with electric heat pumps shows that absorption systems can be competitive with current technology. However, the implementation of these systems in the residential and light commercial market has not been practical for several reasons, including a limited knowledgebase on absorption systems for this application and the lack of compact and economically viable heat and mass exchangers. An improved understanding of the coupled heat and mass transfer processes in thermally driven absorption systems to be used as heat pump water heaters will be obtained in the proposed study. In addition, microchannel heat and mass exchangers that enable such compact gas-fired heat pump water heaters will be developed and tested. Performance at design and off-design conditions over a range of water and ambient temperatures will be simulated in detail with a system-level model developed for this purpose. The heat and mass exchangers will be designed using component-level heat and mass transfer models. The heat and mass exchangers will first be installed and evaluated on a breadboard test facility. Insights from these experiments will then be used to design and fabricate a monolithic unit integrating several of the microchannel heat and mass exchangers, coupled with a gas-fired desorber heat exchanger to yield a stand-alone water heater prototype. The performance of the prototype will be investigated over a range of water temperatures. This investigation will provide an improved understanding of the use of thermally driven heat pumps for small-capacity applications that typically operate over a range of conditions. In addition, the investigation will provide insights into the use of monolithic heat and mass exchange processes and components for small-capacity systems. The resulting systems will lead to significant energy savings in water heating applications.