Skip to comments.Improving hot water heating efficiency ... with cold water
Posted on 04/05/2013 10:30:55 AM PDT by Freeport
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? Thats 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.
(Excerpt) Read more at gizmag.com ...
Just a guy, his idea, some parts & cash and a few students.
In St. George, Utah, they don’t use furnaces to heat their homes, they use heat pumps. They work very well, even when the temps drop down into “zero” territory.
So the guy refrigerates his incoming water and sets the exhaust heat into the feed side of his hot water heater. No big deal.
He’d get better results if he tried to do the same thing with the waste water from shower, dishwasher and clothes washer drains instead of the incoming water.
However, I have my doubts that the efficiency numbers work out, or enough to justify the cost of the equipment.
If the cold water is already at 70 F, what colder water source would you transfer the heat to and why? Just fill the water heater with the 70 degree water. o.0 I must be missing something.
I know a guy who installed a drain-water heat-exchanger; from the temperature deltas and flow rates he said he was seeing, I figured he was getting an effective 7kw from it using the warm drain water to preheat the replacement water flowing into the water heater.
I insulate my pipes the the pelts of baby seals.
You got him with that one! :-)
Thanks for the laugh!
Extracting latent heat from one tank of water and transferring it to another is going to have a cost above and beyond the reduced heating expense in the hot water tank benefitting from the transfer. If you want colder tap water you might get it for “free,” cost of the system notwithstanding, imho.
That's a good idea. I wonder if cat skins would work?
I’ve worked that idea in head many mornings standing in the shower watching the warm water go down the drain. My idea centers around a manifold to smaller drain pipes in parallel to increase the surface area. But I keep getting hung up on what a god-awful clog it would create in time. Next thought was to come up with a finned drain pipe similar to old school baseboard hot water heat. Then again if I switch to cold showers I won’t be thinking about it.
I know that I have to use warm water for washing because cold water (as defined for washing clothes) is around 85°F while the cold water from my pipes is below 50°F in the winter and may be up to 60°F in the summer. That's not washing or rinsing anything well. If I get a new washing machine that only has a cold rinse, I'll have to premix hot and cold water before it goes into the cold washer intake.
Tankless water heaters work pretty well and save money. In three years, mine has just about paid for itself and the upgrade in electrical wiring. The wiring cost more than the heater.
I light my house with an arc welder.
Most residential users mix hot and cold to about 90-100 degrees. That is still 30-50 degrees of overall heating. I suppose it can be offset by toilets but those only use 1-1.5 gallons today.
Only the warmest places get 70 degree water out of the ground. That is far from typical in the USA. I did a project at the equator and it was 74 degrees from the ground.
There ARE already heat-pump water heaters that take heat from the air. I think those are far better. Especially if it sits inside a hot mechanical room.
I could heat my water with a few students (in shifts):
Ground source heat pumps have been around for over 100 years. They are hands over more efficient than burning fossil fuels or air to air heat pumps. Their drawback.....huge first costs.....
After a couple of test projects in the Reno area, the State of Nevada determined that they reached payback for the high initial (construction) costs in 3-5 years. Nevada now mandates usage of these type systems in many School and public buildings....
Radiant in floor heating systems are often designed with water to water ground source heat pumps to good effect......
nothing really new here as far as I can see......
I’ve found I can make money with just a cheap computer and an old color printer.