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Old 01-19-2021, 02:37 PM
 
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I searched but could not find a thread on this. You use the heat exhaust from your A/C to get hot water. I do own a condo that provides hot water through a ground source heat pump and the result is that we get free A/C in our trash room. This is the reverse and for a single unit.

https://www.hotspotenergy.com/air-co...water-heaters/


https://www.hotspotenergy.com/air-co...water-heaters/

I have a 2 bedroom condo that I pay for hot water and wonder if this would be a green choice that makes sense. Usually 3-5 people taking showers and dishwasher and clothes washer. Electric is expensive. Does anyone have any experience with these units?

Last edited by GoldKona; 01-19-2021 at 03:14 PM..
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Old 01-20-2021, 07:55 PM
 
Location: Puna, Hawaii
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All I know is that they aren't new. HVAC units have been converting A/C to hot water for at least 30 years that I'm aware of.

Also, the reverse is available, they make heat pump hot water heaters (sometimes they are called hybrid hot water heaters) where the byproduct of heating the water is cold air. They are cheaper to operate than heating water with resistance electric heaters and if, for example, they dump cold air into your garage in the process it can lead to cheaper cooling, especially if there is living space above the garage.

I've been on some internet threads where in some climates its most cost effective to heat a room in the winter by turning a window AC unit around so the cold air blows outside and the hot air in... it's just a heat pump afterall. There is a pretty narrow temp margin where it works effectively because it will ice up if its too cold outside.
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Old 01-20-2021, 10:56 PM
 
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Originally Posted by terracore View Post
Also, the reverse is available, they make heat pump hot water heaters (sometimes they are called hybrid hot water heaters) where the byproduct of heating the water is cold air. They are cheaper to operate than heating water with resistance electric heaters
Yeah, that is exactly what I am trying to figure out. Heating the hot water is required. AC is not but nice to have. If it cost $100 a month to heat water and use $150 for AC then if I spend $150 for AC that gets me free hot water then I am $100 ahead so my $2000ish investment is paid off in less than 2 years! Or I spend $200 a month on AC then I have more AC and my payoff is just over 3 years.

This has been around for decades so I'm surprised that it is not more common in Hawaii. The hotels use lots of hot water and lots of AC. Is anyone aware of commercial applications in Hawaii?
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Old 01-20-2021, 11:09 PM
 
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Originally Posted by GoldKona View Post
Yeah, that is exactly what I am trying to figure out. Heating the hot water is required. AC is not but nice to have. If it cost $100 a month to heat water and use $150 for AC then if I spend $150 for AC that gets me free hot water then I am $100 ahead so my $2000ish investment is paid off in less than 2 years! Or I spend $200 a month on AC then I have more AC and my payoff is just over 3 years.

This has been around for decades so I'm surprised that it is not more common in Hawaii. The hotels use lots of hot water and lots of AC. Is anyone aware of commercial applications in Hawaii?
$100/month to heat hot water? What, you got 20 teenagers taking long showers?
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Old 01-20-2021, 11:19 PM
 
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Originally Posted by chairmanoftheboard View Post
$100/month to heat hot water? What, you got 20 teenagers taking long showers?
Well a 2/2 with 4-5 tenants. This is Honolulu with $.35 per kwh! And it is all electric. There is a clothes dryer and dishwasher but everything else is LED, etc. Are you in Hawaii? My other condos have hot water provided by the HOA through solar and ground source heat pumps. What should electric hot water in this instance cost per your experience?

OK, looks like you are in CA. I heat water using gas for about $10 a month. And my electric bill is under $50 in CA. Hawaii is not the same.

Last edited by GoldKona; 01-20-2021 at 11:27 PM..
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Old 01-22-2021, 12:37 AM
 
Location: Moku Nui, Hawaii
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I worked for an engineering company on Oahu that did commercial water systems. They took the heat from the rooftop A/C and used it to heat the water at a big spa facility. We got a federal award for energy savings. That was back in the early eighties.

Is there any way you can use solar to heat the water? Or on demand gas?
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Old 01-22-2021, 08:45 AM
 
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Originally Posted by hotzcatz View Post
I worked for an engineering company on Oahu that did commercial water systems. They took the heat from the rooftop A/C and used it to heat the water at a big spa facility. We got a federal award for energy savings. That was back in the early eighties.

Is there any way you can use solar to heat the water? Or on demand gas?
This is a high rise so solar is not an option. They are claiming the payback is also much quicker than a solar system. No gas to the building and I would still be paying gas and not getting free hot water! There has been an owner occupied unit that has gone to an electric on demand unit but I think mainly to save space. If tenants had continuous hot water I would imagine the use would go up. Now they are limited to how much the storage tank provides. The tenants run the AC enough that I would like to utilize the free waste energy to heat the water.

The company that I linked no longer sells the unit that would be perfect for me. They do have larger 3-5 ton
units for houses. Seems these units are still around but not so much in America. Seems this would be a good business in Hawaii but not sure how many units have their own water tank and a space (lanai) for the compressor.
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Old 01-22-2021, 09:37 AM
 
Location: East of Seattle since 1992, originally from SF Bay Area
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Of course, the ad calls it free hot water, but nothing is free. You still have to pay for the water, and for the electricity to circulate it.
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Old 01-22-2021, 09:46 AM
 
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Originally Posted by Hemlock140 View Post
Of course, the ad calls it free hot water, but nothing is free. You still have to pay for the water, and for the electricity to circulate it.
The hot is the free part.
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Old 01-22-2021, 02:26 PM
 
Location: Moku Nui, Hawaii
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Does the condo have a single water heater for the entire building like hotels do or is it individual water heaters in each unit? If it's a system for the whole building, then you'll probably want to chat with an engineering firm.
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