Improving hot water heating efficiency ... with cold water
By Darren Quick
April 4, 2013
A prototype water heater system that uses cold water to make hot water pictured with Slater's assistant, David Dawson
Apart from heating and cooling the house, water heating is one of the biggest energy drains in the average home. But what if you could literally use cold water to create hot water? That’s just what San Diego inventor Hal Slater claims to have done with the creation of a water heater system that promises to improve water heating efficiency by as much as 50 to 100 percent.
The system works on the basis that cold water supplied to households in temperate climates averages around 70° F (21° C), which the researchers say is 15° to 20° F (8° to 11° C) warmer than it needs to be. By using a small water-to-water heat pump, the system extracts this excess heat from water in a 20-gallon (76 liter) cold water tank and delivers it to a typical 50-gallon (189-liter) water heater.
With funding from a grant from the California Energy Commission, Slater teamed up with a research team from the University of California, San Diego (UCSD), led by Dr. Jan Kleissl of the Mechanical and Aerospace Engineering Department, to test the system. To test real-world performance and determine the effects of different incoming cold water temperatures, they installed three prototype systems in homes in coastal, mountain and desert climates. They also monitored each system for a year to compare performance over different seasons.
Slater told us that all the systems performed better during the summer months when the cold water comes in at over 80° F (26° C), providing more heat that can be extracted. In the winter months in the mountain test home, the incoming water temperature dropped to 55° F (13° C), which is the temperature the cold water tanks are set to. The system basically reverts to an electric water heater at those times.
According to Slater, test results showed an improvement in water heating efficiency by as much as 50 percent over current efficiency leading air-source heat pump water heaters, such as the GE Geospring. However, he believes that with additional refinements the efficiency can be increased to 100 percent, putting it on a par with the best solar water heaters, but without the need for a rooftop solar panel.
Slater has patented the system and is now seeking funds and a manufacturer to commercialize it for single- and multi-family applications.
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