A Comprehensive, High Efficiency Solution for Water Heating in Multifamily Buildings

Residential dwellings in California use 4,119 million therms of fossil gas of which 19 percent is used by multifamily homes. Fossil gas energy used in domestic hot water production accounts for 33 percent of the total multifamily fossil gas use. It is estimated that about 50 percent of the multifamily apartment buildings use central gas water heaters.

Recent emerging technologies such as the gas-engine heat pump can have a significant impact in reducing fossil gas consumption in central water heating applications because their coeffi-cient of performance can be as high as 2.0, versus the conventional gas water heater thermal efficiency of 82 to 85 percent. Another emerging technology is the evacuated tube solar collector, a new type of solar thermal water heating collector with higher efficiency than the conventional flat plate collector.

This research and demonstration project used an integrated solution for water heating in a multifamily central water heating setting with a gas-engine heat pump and a scalable evacu-ated tube collector solar thermal array. They were used to assess the performance of the integrated solution and validate the research hypothesis that such as solution can cost effec-tively reduce domestic hot water energy consumption in multifamily buildings by 75 percent. Research demonstrates that optimal performance of the gas-engine heat pump is critical for achieving these goals. Successful application (50 percent adoption) of these technologies in California by multifamily buildings could save 99.18 million therms annually and reduce emissions of greenhouse gases by 580,200 tons and nitrogen oxides by 55 tons.