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Author Topic: heat pumps and thermal solar  (Read 3835 times)
mrwhippy99
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« on: August 14, 2006, 08:08:48 PM »

Hi,
  we have recently built a thermal solar panel for our pool. We were wondering if we could use a GSHP to boost the temperature from 20degC to 50degC. we were thinking of getting the 5kw heat pump to almost completely be rid of our oil boiler. would this be enough?
Thanks alot,
                sam
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Ian
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« Reply #1 on: August 14, 2006, 09:24:01 PM »

sam - If I have understood you correctly, ...
1. You have built a solar panel that currently heats your pool to about 20 C and you are impressed with it.
2. You would like to raise the temperature of SOME of the water to 50 C (presumably for showers ?).
3. You currently use your oil boiler to raise the water temperature to 50 C
4. You would like to replace the boiler with a GSHP.

You COULD use a GSHP to do the job. You will need a good supply of low energy heat (like a swimming pool at 20 C or from another panel and a large thermal store).

The GSHP will not run very efficiently with an output of 50 C and so you should not expect a COP greater than, say 1 + 1.5. You could "stack" a couple of GSHPs so that you could increase the COP - maybe to 1 + 2 - 2.5 for the stack. Ideally you would change the gas mixes to give the best characteristics in both of these stacked units.

Currently oil is cheaper than a GSHP operating at a COP <4 operating off standard electricity tarrifs.


If I have misunderstood and you are looking at heating your whole house with a 5 kW GSHP using circulatimg water of 50 C, then the answer is no. Most houses have a boiler rated at about 40 - 60,000 BTU (11 - 17 kW). Most houses that have swimming pools tend to be larger with boilers around 80 - 100,000 BTU (22 - 30 kW). I think you will see that you do not stand a chance to heat your home with a single 5 kW GSHP!

I hope this helps.

Regards,
Ian

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mrwhippy99
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« Reply #2 on: August 15, 2006, 10:38:00 AM »

Thanks, but we were planning on using the panel running at 20 C and then using the heat pump to boost that up a bit (40C-50C).   
The problem we had without a heat pump was that the pool was actually running at about 35C so even when the sun was out, it heated it up a bit but not much in comparison to the pool. We thought that if we could get the solar loop running at about 20C and then use the heat pump to get the pool loop a bit higher.
I understand that the heat pump takes heat from one loop and cools it down and puts heat into the other loop heating it up. Am i right when i say this and if not can you please explain where i am going wrong.

Thankyou

Sam
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Ian
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« Reply #3 on: August 15, 2006, 10:53:00 AM »

Sam - I think I am being extra thick today - I really do not understand what you are trying to do at all (are you trying to heat the pool, use the pool for a heat source, or not use the pool at all?)! What are your objectives ? What do you want to heat up ? Where do you want to extract the heat from ?

You are right apbout the heat pump operation - it takes heat from one area, concenmtrates it, and then releases it to another area.

Regards,
Ian
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mrwhippy99
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« Reply #4 on: August 15, 2006, 10:59:19 AM »

OK, sorry
I have not been explaining very well.

What i would like to do is buy a 5kw heat pump to heat the pool. i would effectivly us it as a GSHP but instead of having the closed loop in the ground i would run it through the solar panel.
would this work?

Sam
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mrwhippy99
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« Reply #5 on: August 15, 2006, 11:03:42 AM »

P.S. i have just read that the 5kw heat pump is water to air. If this is true, is it posibal to convert it into water to water
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Ian
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« Reply #6 on: August 15, 2006, 12:53:03 PM »

Sam - OK I see - sorry for being thick.

The Navitron 5 kW heat pump on the web site is, as you say, ground to air. There is also a 9 kW version on the web site which is ground to liquid. These are just examples and tend to be stock items. It may be that (and I am fairly sure) Navitron can order in a 5 kW liquid to liquid heat pump; it may take some time to get from China. Ask Navitron directly for availability and price.

Whilst it is theoretically possibly to "convert the ground to air device, it is not so practical to do.

Yes, you can take the output from panels and concentrate it for the pool. To get to 50 C will almost certainly require you to stack a couple together for some of the year (winter).

As the temperature coming out of the panel will vary you will get variable performance from the heat pumps. Ideally, you would get the heat pumps re-gassed with the corrct mix for the kind of temperatures you will be dealing with. The Navitron heat pumps will assume intake temperatures of around 5 - 14 C and an output temperature of about 25 - 35 C.

You will need to have either a large panel area or some good antifreeze to stop the panel liquid from freezing when the heat pump is working on a dull winter day.

If we go back to basics (sorry if this is teaching you to suck eggs) - if you currently have a panel that gets your pool to 20 C. If you only take this same panel and add a heat pump - you are not going to significantly increase the energy going into the pool (other than the 1.5 kW or so from the heat pump compressor). Sure, you are going to add less water at a higher temperature but you cannot magic energy from nowhere so the total energy going into the pool can only be what you are getting out of the panel plus the electricity used in the compressor. Hopefully, you can see that in order to get more energy into the pool (hotter) - you are going to have to have a larger panel collection area to get the heat from.

If it was me, and I had enough room for panels, I would just add another panel or two in series and get hotter water that way - without the use of a heat pump.

I hope it helps.

Regards,
Ian
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mrwhippy99
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« Reply #7 on: August 15, 2006, 02:49:20 PM »

ok thanks
 
this is a bit off the pointbut we were also thinking of installing tha 5kw heat pump to heat our new extension, we self built it and it will be undersfloor heating with good insulation, normally i asume that that would be ok. the thing im slightly worried about is that we are on a slight chalk hill making it only possibal to go down 1-1.5 metres. Is chalk ok to do it on any way and will the depth be enough?

Sam
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Ian
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« Reply #8 on: August 15, 2006, 08:50:35 PM »

Sam - If the extension is not too big, then a 5kW heat pump should be fine. The temperatures used in underfloor heating are just right for a heat pump.

1.5m is just about the minimum you should try to use - but it is OK - just. 2m or more is better. Chalk is just about perfect for a ground loop as it tends to retain a lot of moisture. It is the moisture that helps to conduct the heat in and out of the pipe and adjacent groud.

I hope this helps.

Regards,
Ian
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mrwhippy99
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« Reply #9 on: August 16, 2006, 11:10:45 AM »

ok
thanks for just clearing that up for me
 sam
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