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.
Heat pump type water heaters fail miserably in real life use; it might be a function of the number of duty cycles but I think they’re just too complex for something that needs to be 100% reliable ,It shouldn’t matter if it’s a heat pump pulling heat from air like your A/C or it’s a water to water system as this guy wants to build.
I’ve had 2 tankless electric heaters fail over a 5 year period BIG 3*60 AMP ones ,, with 3 chambers theres a lot of possible failure points and don’t try to reason with the wife when she has to take a cold shower...
What works in any climate is/are GAS tankless water heaters ... my Aunts home in Brooklyn still has their original tankless water heater from 1926 ,, just updated to eliminate the pilot light... amazingly simple , just a copper coil about 6” in diameter and 2 feet in length(THICK COPPER) inside a tube that narrows to become the chimney/exhaust.
The 1970’s/1980’s solution was to capture waste heat from the A/C pressure/liquid side with a sealed heat exchanger box... WORKED GREAT and improved A/C efficiency also... don’t know why it has fallen out of favor.
Best solution now in warm climates is passive solar heat with electric backup.
I would think that the parts of the world which have 70 degree ground water would also have plenty of sunlight and ambient air temps.
A solar hot water heater, or even just heating the pipes to ambient air temp would probably be a far better primary solution in these places.
Perhaps the groundwater heat pump could be used in the “cold” season in those areas to some effect...
Question! What kind of heat pumps are being used, air to air, or ground to air? Also do you have any data/idea on relative temperatures? We have an air to air heat pump for a home at 3600 ft. in northern CA and it holds house ,1500 sq. ft, temp at 69-70F down to about 32-35 degrees.
Don’t ask ME! I live in Alaska! But when I lived in St. George, all the homes had heat pumps on the roofs. Very common. Look them up online and you should be able to find out everything you are interested in.
The way the one I referred to was described was that there was a central pipe (copper) 3” or 4” in diameter, through which the waste water flowed - spliced in to the existing drain line from the bathtub.
It, then, had another copper pipe - normal supply pipe, 1/2” or so, wound tightly on a mandrel so it was slightly deformed to increase the surface-area contact. The cold water flowed through that one on its way to the heater, and warmed significantly.
Worked well for showers, when the supply came in as the same time as the outflow; not so good for baths.
There ya go.
Effectively 7kw in free power while the shower is running.
“No big deal.”
energy loss in both conversions, the guy is BS!
Improving hot water heating efficiency ... with cold water
Why is he heating hot water?
I’m still waiting on that E-cat water heater.
First thing I thought of. I was scrolling down looking to see if anyone brought it up. They might get some gains by capturing some of that ambient heat in the pipe water, but I highly doubt their efficacy numbers. A good amount of that ambient heat will be lost by warming the now too cold tap water. The dish washing machine is about the only thing that uses the fully heated hot water.
I’m in Florida. I heat my house with a heat pump, as do 90% of Floridians. However, the efficiency of a heat pump is quite poor once the outside temps dip below about 25F.
I do like using the outside coils of the AC to heat water. But I think you would get a surplus of hot water.
To preheat water, solar energy is the cheapest.
Best for non-freezing climbs, the pipes can be laid right below the roof. You’ll get 150F water.
just not around anyone’s necks, right. No mandela necklaces?
Damn near any proposal containing the word "green" can get funding these days.
Ummm... did you say your name was Ben Bernanke>
Works the same way as a home heat pump, air conditioner or even the refrigerator. Compress a working fluid, radiate the created heat then take a pressure drop. It creates a cold point below ambient.
>> “Best solution now in warm climates is passive solar heat with electric backup.” <<
Warm climates, with soft water only!
Put it in a cold climate with hard water and the freeze valves will fail within a year. Warm climate with hard water, about two years.
For relatively low delta T, pumping heat requires relatively little energy. Going pumping from 70 degrees to 110 degrees wouldn’t require a huge amount of energy.
I haven’t done the math but going from 70 to 140 degrees might take twice as much energy. The lower the temperature delta, the closer you come to zero energy cost to pump heat. Now that I am rambling, the math is actually pretty cool as you approach 0 delta the amount of heat pumped per unit of energy expended approaches infinity. Ground source heat pumps are very efficient because they make delta T much smaller, both in the summer and the winter.
It was great while it worked, if the maintenance costs were ignored. I also just dumped the cold water. There was a convenient lake nearby. The deer liked the open water. BTW, the well water was a consistent 50 degree year round. Ground water is always at the average annual temperature (or warmer).