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Connecting the output of solar hot water panels and a GSHP desuperheater to preheat domestic hot water?

I am installing both Enerworks solar thermal (hot water panels) and a Bosch GSHP (water to air) with desuperheater and am looking for advice on the best way to connect the two systems together to pre-heat/heat my domestic hot water.

Vendors of GSHP systems know how to plumb their de-superheater output to pre-heat DHW, as do the solar hot water panel vendors, but it seems to be an opinion rich environment when it comes to integrating both systems.

The house is in Northern New Brunswick, Canada. My reasoning for installing both systems is that the de-superheater will produce more preheat potential during the winter, and the solar system will be more productive in the summer.

Can anyone recommend the best way to connect these systems?

Asked by Lee Reed
Posted Tue, 01/22/2013 - 14:04
Edited Tue, 01/22/2013 - 14:24

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4 Answers

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Lee,
You are wrong about the desuperheater, I think.

As far as I understand it, depsuperheaters use waste heat from the heat pump when the heat pump is in air conditioning mode to preheat domestic hot water. So you get more output from the desuperheater during the summer than the winter.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 01/22/2013 - 14:36

2.
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Martin,
I live in the North where the heating load is much greater than the cooling load, so the GSHP will be more active in winter, when the solar will be less effective. In the summer there is really only a 3-4 week period when air conditioning is important. Still wondering how to connect the 2 systems.

Answered by Lee Reed
Posted Tue, 01/22/2013 - 20:28

3.
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Lee,
Whenever you are using a heat source to pre-heat domestic hot water -- whether you are using solar collectors or some other heat source -- the easiest way to design the system is to have a separate pre-heating tank. The least expensive tank to buy is an ordinary electric water heater; just remember that you don't want to hook up the electric elements. You are just using it as an insulated storage tank.

The pre-heat tank is warmed by the solar collectors, either directly or indirectly. Then the pre-heat tank becomes the source of water to feed the main water heater.

If you want, you could have two pre-heat tanks in series -- one heated by the GSPH, and one by the solar collectors. If this seems to complicated, you could try to heat one pre-heat tank with two heat sources. That might work, as long as you figured out how to handle the temperature controls.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 01/23/2013 - 14:01
Edited Wed, 01/23/2013 - 14:02.

4.
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I have a 5 tonne open loop ground source heat pump combination system in northern Nova Scotia. I have 90 evacuated tubes on roof. I run solar to a 80 g tank with twin heat exchangers in it. One exchanger is hooked to solar and the other is hooked to desuperheater. I feel that they compliment one another as I do get heat from desuperheater in both summer/winter which helps during cloudy days. January usually has some bright blue bird days when I also get descent solar. The 80g tank is a pre-feed tank to my 60g electric hot water tank. The solar computer by RESOL prevents me from burning electricity unless certain conditions are met. Good luck my email is marksutherland@eastlink.ca for more info. The only other control I may add is a function to only run desuperheater if 80g tank is below a certain temp. Otherwise the desuperheater can rob heat from solar tank if it is already hot and you are wasting electricity running desuperheater pump

Answered by Mark Sutherland
Posted Sun, 09/29/2013 - 08:34
Edited Sun, 09/29/2013 - 08:36.

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