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Old 11-01-12, 06:32 AM   #11
dhaslam
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There is no point in applying heat to an underground loop. One good days rain will take all the stored heat away. I have a clay filled seasonal store that starts about one metre below ground level and goes up to about three metres above ground and insulated with straw bales. There are one wire sensors at five levels. The bottom sensor which is below ground level showed increasing temperatures during the summer but in the autumn with the first heavy rain the temperature dropped down to 13C which is approximately the normal ground temperature.

If you are going to store solar heat from the summer a water store is a good option but large water tanks can be expensive and they could eventually leak. A large clay store above ground is very easy to insulate with straw and to protect from rain but it takes a lot of space and needs to be disguised as a garden feature. Ground source heat pumps generally don't want heat input above 20C to prevent the compressor overheating so some kind of mixing valve arrangement is needed, specially from a hot water store. The store could also be used to boost the temperature from a ground loop. If heat can be fed in at 20C instead of the usual 10C or less from ground loops the COP should be a lot better.

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Old 11-01-12, 09:32 AM   #12
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Quote:
Originally Posted by dhaslam View Post
...I have a clay filled seasonal store that starts about one metre below ground level and goes up to about three metres above ground and insulated with straw bales. There are one wire sensors at five levels. The bottom sensor which is below ground level showed increasing temperatures during the summer but in the autumn with the first heavy rain the temperature dropped down to 13C which is approximately the normal ground temperature...
dhaslam,

Thanks very much for posting to our forum!

Your post was quite good, and more detailed than many posts, but I want to know even more about your thermal store.
  • Do you have any photos?
  • What is the total volume?
  • Do you have any idea how much heat you are able to store and reclaim?
  • Is your thermal store an original idea, or is it common practice in your area?
  • How are you storing & reclaiming energy?
Your above-ground earthen thermal store is the first I have heard of...

Best,

-AC
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I'm not an HVAC technician. In fact, I'm barely even a hacker...
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Old 11-01-12, 11:48 AM   #13
dhaslam
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Originally Posted by AC_Hacker View Post
dhaslam,

Thanks very much for posting to our forum!

Your post was quite good, and more detailed than many posts, but I want to know even more about your thermal store.
  • Do you have any photos?
    Photo below (I think, but can't see it in the preview) of the store in construction. There were pipes for air used initially for heating as well as two separate 1.5" water pipes.
  • What is the total volume?
    Total volume is about 180,000 litres
  • Do you have any idea how much heat you are able to store and reclaim?
    The initial heating idea using hot air didn't work properly. Too much heat was lost on transfer, fans melted etc. The panels were changed to heat through a heat exchanger this summer but the heat has just been used directly to the house initially when testing. The plan is to use the heat pump to cool the mound so that heat can be transferred into it at much lower temperatures in winter. This would be in addition to summer heating. The store holds about 100 kWh per degree of temperature change and that should heat the house for about five days but it may take longer than five days to heat it.
  • Is your thermal store an original idea, or is it common practice in your area?
    It is an original idea, I don't know of any others
  • How are you storing & reclaiming energy?

    The solar panels total about 30 sq metres but need direct sun to produce any useful heat. The surface of the collectors is Correx painted black. The fans now blow the return air into the bottom of the panels so that the fans stay cool. The heat exchanger is a large truck radiator. Maximum temperature reached in the heat exchanger so far is about 50C but it should reach 60C in the summer.
Your above-ground earthen thermal store is the first I have heard of...

Best,

-AC
Very impressed with your efforts with home made heat pump etc.

I am hoping to have an old air to water heat pump modified professionally to boost the temperature of the water coming from the store. The ASHP worked quite well but only lasted two years, possibly the cold wet conditions were too much for it. The big advantage of using the warm water source is that the machine can be indoors and should have a fairly constant input temperature.
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Old 11-01-12, 06:09 PM   #14
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The Master Plan wrote:

This last year just running the loop with nothing hooked to it the high was 58F the low was 38F. I am going to monitor it again this year.

Just from practical experience I would see this loop temp (38 F) after 3 months of cold weather and I would start to notice the GSHP running extra long to keep a comfortable room temp. The heating season would start out with a loop temp of 58 Deg F and seem to stablize at about 45 Deg F. for most of the season.

During the summer I will start "charging" the ground with heat from whatever source I can....solar, ambient air,bon fires etc. lol Even if I installed a reversing valve and used it as a A/C during the summer I could add heat to the loop. How much I wonder and how long would it take? I read somewhere they are doing this in Canada.

IMHO Try the GSHP out without thinking of charging the ground. The lost efficiencies in heating the ground and then try to recover that same heat would in all likelyhood result in a net loss. If you come up short during the heating season, install the extra tubing you had mentioned you have room for. That place in Canada you maybe referring to is Drakes Landing it is a housing community that stores solar heat in a deep and large underground area with wells and inturn during the winter recover the same heat. They don`t use GSHP as the temps are stored and recovered high enough (145 Deg F) to use directly for space heating. You can see their site on the web. They have a nice active display on the current conditions of the system. Temp of the bore hole, outside temp, and if they are collecting any solar heat to be stored, real time.

Why wouldn't the high rise use the heat pump during the summer and thaw out the ground or at least add heat to it?

I believed this was the case, they could pump in some heat during the airconditioning season. However, not enough air-conditioning as the amount of heat ejected into the loop thawed the ground around the tubing and the rest remained frozen. As the air-conditioning season ended and the heating season began that heat immediately next to the tube was used up quickly and refroze.

I think this is going to be a big learning experience and a fun project to tackle. Yes it can be fun. It is very satifying to make your own system from junk and gathered pieces that can perform well. There is a wealth of information here from people who have had success. AC_hacker has un-earthed and tested the black magic and math that make these vapour compression machines work and the low-temp heating methods that work so well. Not to mention Vlad who has done the same with heated floors and drilling vertical loops for the ultimate performance. Fun to be had.

Randen
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Last edited by randen; 11-01-12 at 06:10 PM.. Reason: grammar
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Old 11-02-12, 11:24 AM   #15
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Drakes Landing, how can I find the active display real time monitoring?

Do they use insulation around the heat storage?

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Old 11-02-12, 01:12 PM   #16
randen
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Google Drakes Landing solar community or Drake Landing Solar Community

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Old 11-03-12, 10:50 AM   #17
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The Canadian site seems to be quite dry. There is about one half metre of precipitation in the year and about one third of that is snow. The boreholes are in a circle about 35 metres across and similar depth with just the top covered and insulated. The hotter boreholes are in the centre so the clay and rock acts as a horizontal insulator. Clay is a good insulator when dry and useless when wet. They lose about half of the heat stores and I would suspect that much of this is when the snow melts in the spring when the stored heat is at the lowest level. Obviously in areas that don't have -30c surface temperatures in winter the situation is much different because the rain constantly penetrates in the winter. I am not very familiar with western Canada but my grand uncle Joeseph Keele surveyed large areas of north west Canada and has a river and mountain named after him.

What it boils down to is that the underground situation determines whether it is worth trying to store heat underground but in any case it needs to be concentrated and not spread out like a normla ground source loop.

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