Heat pump to produce HOT water?

Charlie Richmond · February 2003

I don't understand why, technologically, a heat pump should be able to produce more heat when in the cooling mode than when in the heating mode. This is counterintuitive and perhaps you could explain it....? Besides, our cooling season is very short, we don't have forced air heating/cooling (it's a hydronic heating system and only the upstairs bedrooms need individual air conditioners for cooling) and only want a heat pump that heats (not a reversible one). Our HWT is currently set for 120 degrees F and that is more than adequate for all needs since it is quite large -- so I would think that even a heat pump that can provide an adequate volume of water at that temperature would be fine ;-)

Thanks,
Charlie

Charlie Richmond · February 2003

I am looking at replacing a 40,000 BTU condensing boiler which currently much more than adequately provides all our hot water (and underfloor heating via a heat exchanger inside the HW tank) with a standard (air heated, not geo thermal) heat pump but the suppliers I've talked to so far don't really know how to do this because they say heat pumps won't make the water hot enough. I'm in a climate that only occasionally goes below freezing (although it definitely has to be able to operate at low temps). What is recommended?

Thanks,
Charlie

Steamhead · February 2003

Charlie, A Better Arrangement

would be to have the boiler water heating the domestic hot water in the tank via the heat exchanger, and a reset controller operating a primary-secondary pumping setup or mixing valve that can vary the water temp in your radiant floors. This way you don't have fresh water running thru the boiler all the time, which can shorten its life and add impurities to your faucet water. Variations of this type of system have also resulted in bacterial contamination. I'd change this right away; your family's health is at stake.

I've heard of heat pumps that can route their reject-heat into hot water tanks, but am not that familiar with them. Maybe another Wethead (see our Find a Contractor page) or someone from Trane, Carrier or another heat-pump company could help you there.

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Charlie Richmond · February 2003

Response to steam.head

I understand what you are saying but the boiler we are using is a Delta Temp unit that has a copper tube heat exchanger and is specifically designed to have the potable water circulate through it. It has been working fine since 1995 but the company is now out of business and a heat pump actually would be more efficient in our climate.

Thanks,
Charlie

Glenn Harrison · February 2003

I've never seen an air to air Heat Pump...

that could create hot water. If you come accross one let us know. I believe you would have to go geothermal. I am a WaterFurnace dealer, and they have a combination unit that will heat and cool the air and make hot water for a radiant system and can have a domestic hot water supplement put on it, or you could put a heat exchanger on the hydronic circuit and heat your hot water fully that way too I believe. Plus a geothermal heat pump is far more efficient than an air to air heat pump, especially under extreme condtions. Go to

Water Furnace Synergy3 Unit

and check it out.

Glenn Harrison, Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Services

Crystal Lake, Illinois

Althoff Industries website

Don_2 · February 2003

Air to air

heatpump is not an alternative.For one they are not design for what you are trying to do.And two air to air will decrease in capacity by 30% when temp are 40 degree and lower.
And if you did get lucky and find someone who would even take the chance you will not be happy with the results.
Three-no manufacturer would even stand behind it when it came time for warranty parts.

Geo heatpump is the only option if you are set on going heatpump.Then they too have there limitation.

Steamhead · February 2003

OK, but there's

still the problem of contamination. I'd still rearrange it.

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Charlie Richmond · February 2003

First of all, the manufacturer (Delta Temp) specifically states that the heating loop be open to the potable side of the tank. We went through this quite thoroughly when it was installed and inspected and the water is extremely clean with no contamination.

HOWEVER .... depending on whatever I manage to find as a heat pump setup, I may go through another heat exchanger. But water/water geothermal heat pumps don't require it, either... ;-)

Thanks for the concern but it's not a problem for sure...

Charlie

Glenn Harrison · February 2003

Sorry, my fault

I should have clarified that if you use the radiant side of the Synergy3 unit to heat hot water AND radiant, you should use a HX to separate the hot water from the radiant floor tubing. My appologies

Glenn Harrison, Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Services

Crystal Lake, Illinois

Althoff Industries website

Charlie Richmond · February 2003

No problem, Glenn. If we go that way, I will certainly do it the best way! I have definitely studied the Waterfurnace site and it is very informative.

Thanks,
Charlie

Charlie Richmond · February 2003

Just to clarify all the terminology:

We have a boiler that is specifically intended to heat potable water and the loop that circulates through the boiler comes directly from and returns directly to the 80 Imperial gallon stainless steel HW tank, as specified by Delta Temp, the boiler manufacturer. We keep the tank set to 120 degrees F because that's all that is necessary for the hydronic heating system, all the baths we need and dishwashing using pots'n'pans (heating) cycle.

The hydronic heating system is a completely sealed and closed loop system with 10 zones and programmable thermostats on each. The hydronic system flows through a stainless steel heat exchange coil inside the HW tank. So the hydronic system is indeed completely separate and sealed off from the potable water, as required by the code and according to the manufacturers' instructions.

If you want any further details, I will be pleased to respond ;-)

Thanks for the input,
Charlie

MMC · February 2003

try ECR INTERNATIONAL web site .they have a heatpump/waterheater unit.

Charlie Richmond · February 2003

That looks like a nice unit but I'm not just heating domestic HW, I'm heating an entire house with a hydronic heating loop inside the HW heater.... ;-)

Thanks,
Charlie

Mark A. Custis · February 2003

Why would you do that?

Are they giving away free electricity in your neighborhood? Anything is possible and Water Furnace is at the top of my list.

I own two heat pumps and started installing geothermals while Jimmy Carter was president, but why give up the gas. You heat your home and DHW with fewer BTUs than I throw away in my hot tub this time of year.

Mark

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[Deleted User] · February 2003

The problem...

has to do with "approach temperatures". In order to continue doing things the way you have been doing them, it will require a higher approach temperature in the tank than you can reasonably expect from any heat pump. With heat pumps, you get a copious amount of "free" hot water whenever the system is in the cooling mode. When in the heating mode, the temperature is limited to around 120 degrees F.

You are trying to drive a railroad spike with a tack hammer. Before, you were driving a tack with a sledge hammer.

This happens when you step into the world of the untried and unproven...

Buy a tack hammer (stand alone water heater) before you smash a finger or some other more important appendage. You can always set a de-super heater on this tank to utilize the "free" heat available during cooilng mode.

Personally, I'm not aware of an air to water heat pump, but then again, I'm kinda new to the whole heat pump process.

Let us know what you find.

ME

Glenn Harrison · February 2003

If you want a heating only unit...

look into T.E.T.C.O. Geothermal products. They do make a heating only unit. Didn't see any info availble on the website so you probaly would have to e-mail them an info request.

TETCO Website

As far as the hot water desuperheater goes, what primarily happens is you lower the heating capacity of the unit when making hot water because you take heat out of the refrigerant before it goes thru the air coil. You also could have dimminished hot water capacity if the fluid temp gets extremely low. I just saw a new WaterFurnace unit that we recently put in that the desuperheater pump was off because the water heater tank had gotten to the upper limit of the unit(130º), and the geothermal loop was at 24º.

Glenn Harrison, Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Services

Crystal Lake, Illinois

Althoff Industries website

Charlie Richmond · February 2003

This TETCO unit looks to be perfect. Except that it's geothermal and I was hoping for an air heated unit. Maybe such a thing really doesn't exist.... ?

http://www.geoproducts.com/pdf_files/8-pg18-19.pdf

Charlie

eddie grierson_3 · February 2003

Problems

If you do go with a cast/steel boiler for some reason make sure your radiant piping has an oxygen barrier. The problem I think you will face with an air to water heat pump is the defrost cycle. The colder it gets outside the less BTU the heat pump will produce. You mentioned you have mild winters were you are at, what is the humidity? I see heat pumps iced up around here when it is 50 degrees when it is humid outside. That is why Geo is the way to go in my opinion. Let me know what you end up installing.

Eddie G.

MAhomeowner · December 2013

Integrate air-source heat pump with boiler system?

Who would I talk to about integrating an air-source heat pump, for heat, not A/C, with our current oil boiler system? "HYBRICAL: HEAT PUMP-BOILER INTEGRATION UNIT" at http://ow.ly/28M2sB appears to do this, though I'm sure the flow rate is too low for my system. I'd be willing to manually switch between using the heat pump and oil burner as needed if there's no automatic system available.

We have a 12-year-old Massachusetts house with an oil boiler with four zones including two air handlers, a hot water tank, and one baseboard zone. We currently get about half our heat from a wood-burning fireplace insert, and our electricity usage is offset with wind energy REC's. The central A/C compressors are not at a point where they need to be replaced so replacing them and the air handlers with heat pumps or mini-splits can't be justified.

Thanks in advance.

bld999 · December 2013

Altherma

Here is an air to water system that claims to produce up 130f water:

http://thermalproductsinc.com/wp-content/uploads/2010/06/Daikin-Altherma-Engineering-Data1.pdf

Somebody on here heats their shop with one, wish i could remember who.

Heat pump to produce HOT water?

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