Alton
Veteran Member
Posts:2159
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| 03 Mar 2008 08:55 PM |
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What is the upper limit for entering water temperature for a typical geothermal heat pump. Does it make sense to preheat the entering water with solar thermal?
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Palace Geothermal
Veteran Member
Posts:1609
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| 03 Mar 2008 09:32 PM |
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The literature that I have seen says 90°. The hotter the incoming water temp, the better the COP. |
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Dewayne Dean
<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system |
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Palace Geothermal
Veteran Member
Posts:1609
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| 03 Mar 2008 10:52 PM |
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Posted By Alton on 03/03/2008 8:55 PM
Does it make sense to preheat the entering water with solar thermal?
One heat pump I looked up has a COP of 4.0 with incoming water temp of 32° and COP of 5.3 for incoming water temp of 68°. Your heat pump would be 32% more efficient under those conditions. Makes sense to me!
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Dewayne Dean
<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system |
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tuffluckdriller
Advanced Member
Posts:630
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| 04 Mar 2008 12:42 AM |
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One thing you have to watch out for is that the compressors operate at higher pressures with warmer water temps. It's harder on the compressors. I would definitely not heat it to 90 deg. Maybe 65 tops. |
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| Clark Timothy ([email protected])<br>Geothermal Heat Pumps: Heating and Cooling that's Dirt Cheap!<br>www.pinksgeothermal.com |
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Alton
Veteran Member
Posts:2159
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| 04 Mar 2008 07:47 AM |
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Would it make more sense to add a heat exchanger in the supply main duct after the geothermal. Maybe this way I would not be limited to 90 degrees entering water. I do understand that I should select a heat exchanger with a low static pressure so that the blower fan will not have to work too hard. By doing it this way, I would have too separate systems thermostatically controlled. One system would be the geoghermal and the other system would be the solar loop.
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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tuffluckdriller
Advanced Member
Posts:630
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| 06 Mar 2008 12:54 AM |
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How warm do you expect to get out of the solar? How many btus do you expect to get out of it? |
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| Clark Timothy ([email protected])<br>Geothermal Heat Pumps: Heating and Cooling that's Dirt Cheap!<br>www.pinksgeothermal.com |
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Topgas
New Member
Posts:63
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| 06 Mar 2008 07:15 AM |
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Tuffluckdriller, I'm not sure if I'm butting in here and I'am replying out of context but here's the temps and btu's I get out of my 6 flat panel 240 sf solar hot water system in Maine. When we do have sun in the winter the average water temp coming from the panels varies from around 120-160 degrees. An average solar day would yield aprox. 20K to 80K btu's/day in the tough months, net. Summer can be up into the 160K btu's/day depending on the water temp in the tank starting out. I can average 90-120 degrees in a 400 gal. storage setup winter and 130-170 degrees summer. |
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TechGromit
Advanced Member
Posts:634
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| 06 Mar 2008 08:41 AM |
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I think Alton's Idea of having the solar panel installed right after the water leaves the geothermal unit is a sound. This way when the water is circulated thru the ground and returns to the geothermal unit it would lose enough of it's heat so its not so warm that it could damage the compressor. Also, with warm water circulating thru the ground all day, would warm up the ground and allow the system to work better at night when the sun goes down. The only draw back I can see is when the temperature dropped at night the cold solar panel would proably lose a lot of the heat you build up during the day since the water is curculating thru a cold panel before it re-enters the ground. If you could set up bypass values where once the solar panel is no longer a benifit, water is shut off to it and it routed directly back into the ground.
As for the high temps Topgas reported with his 6 panel solar system, one or two panels should be more than enough to kick the water temp up to the 90's. |
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Alton
Veteran Member
Posts:2159
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| 06 Mar 2008 10:25 AM |
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The approach that I would like to consider for using solar and geothermal consists of the following:
Use the solar collectors as a separate system to heat water to send to an insulated storage tank. Then circulate hot water from the storage tank to an additional heat exchanger in the ductwork. This heat exchanger would be installed in line after the geothermal fan coil thus not increasing the load on the geothermal compressor. Water circulating to this additonal heat exchanger would be controlled according to the temperature in the stored water. The tricky part would be to have the thermostat turn on the circulating pump and blower fan. Ideally, with good solar conditions, the solar loop would heat the home without the compressor being activated. Whether to run the solar loop by itself to heat the home or always run the solar loop (providing the stored water is warm enough) with the heat pump is another question that I have not thought enough about. It may depend upon how complicated the controls become.
In the early 1980's I used solar heated water and an air circulating fireplace to heat a home in the Columbia South Carolina area. Now since fireplaces are not encouraged as much as they used to be, maybe we could use a geothermal heat pump instead of the fireplace. The excess solar heated water could augment the domestic hot water system.
Do you think this system would work? Could one thermostat be used to operate both systems? The valves and circulating pump for the solar loop would have to be controlled based upon the water temperature in the storage tank.
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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tuffluckdriller
Advanced Member
Posts:630
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| 06 Mar 2008 10:59 AM |
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Yes, it could work. The temp of water you need to get enough heat exchange into the air would be about 120-130 deg. If you get this, you need to be sure that water coil is sized right to be able to get the btus you need. |
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| Clark Timothy ([email protected])<br>Geothermal Heat Pumps: Heating and Cooling that's Dirt Cheap!<br>www.pinksgeothermal.com |
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Alton
Veteran Member
Posts:2159
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| 06 Mar 2008 12:20 PM |
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Tuffluckdriller,
Thanks for your comments. Does anyone else have advice or suggestions about my scheme of using geothermal with solar water collectors? |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Topgas
New Member
Posts:63
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| 06 Mar 2008 08:21 PM |
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Using a drainback system with a drainback heat exchanger tank (like AET's 20 gal.) would solve the loss of gained btu's at night thru the panels. I wonder what the net gain would be in energy when you figure in energy lost in pumps and ground etc. I think a large drainback would be in order also for heating after the geo pump. Direct solar to heat exchanger/fan would work also but I'm not sure you would gain much in the end when you have 400 gals. of water at 130 degrees. Say you have 50 degrees useable (80-130 degrees) x400 gals x 8.33= 166,000 btu's. The key here is that the system in Nov.,Dec and Jan rarely is at 130 degrees, 100 to 105 more the norm. Now what's left to heat your DHW? Solar is great, it just needs geothermal to make up for the 2/3 of the month in Maine when it's not working well. From May on, look out. I like the idea of using a heat pump to pull btu's directly from the 400 gals. of stored water in the solar system and then panels work more efficiently with lower temps. |
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caja_ca
New Member
Posts:14
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| 06 Mar 2008 10:16 PM |
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I like the vacuated panels, just not sure what to do with the heat in the summer...they can get HOT |
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TechGromit
Advanced Member
Posts:634
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| 24 Mar 2008 01:57 PM |
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I been thinking alot about pre-heating the water before it enters my open loop geothermal system. My parents have two old solar panels that they no longer use, I think I could set one of them up in the yard, make a bypass in the water line to the Geothemal system and have the water pumped thru the solar panel during the winter months and turn off the bypass during the summer. My only concern is how hot the water would get sitting in the solar panel during the day when the system is off and what effect that how water would have on the compressor, even if the hot water lasts for 30 seconds until cooler water flushed it out. Any thoughts on this?
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