Environment

Improving hot water heating efficiency ... with cold water

Improving hot water heating ef...
A prototype water heater system that uses cold water to make hot water pictured with Slater's assistant, David Dawson
A prototype water heater system that uses cold water to make hot water pictured with Slater's assistant, David Dawson
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The UCSD students who tested the prototype water heater system
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The UCSD students who tested the prototype water heater system
A prototype system installed at one of the test sites
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A prototype system installed at one of the test sites
A prototype water heater system that uses cold water to make hot water pictured with Slater's assistant, David Dawson
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A prototype water heater system that uses cold water to make hot water pictured with Slater's assistant, David Dawson
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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.

A prototype system installed at one of the test sites
A prototype system installed at one of the test sites

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.

Source: Hal Slater

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37 comments
Arahant
Interesting, but i dont see how the water is coming in so warm, if its getting pumped in through pipes that are in the ground, wouldnt they be alot cooler even in temperate regions. I mean that would be horrible to have such hot/warm water to shower with or drink when your already trying to escape the heat.
I feel like im missing something, for one thing why would you even need to heat the water if its coming in so warm. It almost seems like this is a method for creating cold water rather then warm water(well it makes both), I dont know i honestly dont understand this, i know i must missing something.
Mrk White
Interesting idea, I do not doubt there can be an efficiency improvement for certain cases... but I think that overall energy consumption tests should be done before claiming a percentage of improvement. This is why: The cold water in the system will be colder. So when I have a shower and I mix hot and cold water, I will have to use a higher proportion of hot water for the same result, and this would require more energy than without the invention.
Anyway, thumbs up to Hal Slater. Salut!
Samuel Holden Bramah
Mrk White I agree, but a way to circumvent that problem would be to take the "cold" water from the mains system to your shower mixer tap, so you would be using the "really cold" water in the tank for drinking or other cold uses but "street cold" water for showering and maybe the washing machine or dishwasher etc.
Graham Aikman
i'm jus' sayin' but this guy dint invent this, this kind of thing has been known about for years, of course it works its the laws of thermodynamics. you'd be better fitting a ground source heat pump in your garden, and then linking it with an air source and this water based system in order to produce maximum heat output. jus' sayin'
Ian Madden
He should have a model that integrates hot water recirculation. also how much cold water has to be brought into the house and used to keep up with usage of hot water i wonder
RedBaron
This is not a new idea at all. Geothermal system work like this. But water is pumped into pipes running underground a couple of meters where the ambient temperature is constant and warmish through out the year. It then gets pumped through a heat pump etc etc.
Slowburn
How does the efficiency compare to a passive solar water heater?
If for what ever reason I wasn't using solar heat, I would heat the water with the waste heat from the refrigerator, air conditioning, or generator.
Ed Campbell
I love folks suggesting geothermal as an equal or better alternative. Got a spare $20-30,000?
David Clarke
Has anyone heard of thermodynamic panels? It is claimed that they can provide water up to 50°C from one panel about the size of a solar panel. They are basically a refrigerator in reverse.
Bernd
How is this better than an air to water heatpump? In order to extract a reasonnable amount of heat you would have to use lots of water. Not exactly eco-friendly.