FBBP
Veteran Member
Posts:1215
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| 18 Feb 2011 01:26 PM |
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Does anyone know of a heat pump that can handle 120ºF input temps? I would like to use one to retrieve heat from my solar storage to boost to 140º from 40 to 120 for dhw and fancoil use. Any recommendations would be appreciated. Bob |
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engineer
Veteran Member
Posts:2749
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| 18 Feb 2011 11:08 PM |
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That's a tough nut to crack especially given the universal use of R410a and its attendant very high pressures at those saturation temperatures.
You may be better served by re-evaluating or redesigning the system components needing 140*F. Fancoils and domestic hot water can be well served by 120*F water. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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docjenser
Veteran Member
Posts:1400
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| 19 Feb 2011 01:45 AM |
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Climatemaster THW model comes to mind. COP goes down dramatically at those high temps. I second Curt here, look into designing around it. |
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| www.buffalogeothermalheating.com |
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FBBP
Veteran Member
Posts:1215
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| 19 Feb 2011 11:56 AM |
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Curt, Doc - thanks for the input. I was starting to come to that myself although I had read an article of a house in Edmonton using one (maybe it wasn't running efficiently).
My set up is 4 30 tube ev. arrays (to be increased to 8) pumping into a large well insulated storage (wet clay). 2000 ft. of 1" pex for input, 2000 ft.. of 3/4" pex for retrieval. Systems runs 365. I had the storage to 120ºf prior to having some problems with the solar collectors malfunctioning. They are being replace.
I suspect based no your comments that if I only want a 20 to 30 degree rise, I will be better served with a resistance hot water heater.
We have calculated that we will have the storage up to 140 by the being of the heating season.
My thinking was to have a heat pump to use the energy out of the storage down to 40ºf if needed. Even though it is slow, the storage can directly heat my radiant floor slab (1.5' concrete with 1/4" stamped concrete overlay) down to 80º after which it becomes a bit iffy.
Based on that, what would the maximum efficient input temperature to a heat pump be? Will a heat pump work satisfactory from 100º down or would it be lower?
Thanks so much for your time. Always interesting to watch the Geo forum, the repairs by remote are incredible! |
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docjenser
Veteran Member
Posts:1400
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| 19 Feb 2011 01:38 PM |
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Posted By FBBP on 19 Feb 2011 11:56 AM
Curt, Doc - thanks for the input. I was starting to come to that myself although I had read an article of a house in Edmonton using one (maybe it wasn't running efficiently).
My set up is 4 30 tube ev. arrays (to be increased to 8) pumping into a large well insulated storage (wet clay). 2000 ft. of 1" pex for input, 2000 ft.. of 3/4" pex for retrieval. Systems runs 365. I had the storage to 120ºf prior to having some problems with the solar collectors malfunctioning. They are being replace.
I suspect based no your comments that if I only want a 20 to 30 degree rise, I will be better served with a resistance hot water heater.
We have calculated that we will have the storage up to 140 by the being of the heating season.
My thinking was to have a heat pump to use the energy out of the storage down to 40ºf if needed. Even though it is slow, the storage can directly heat my radiant floor slab (1.5' concrete with 1/4" stamped concrete overlay) down to 80º after which it becomes a bit iffy.
Based on that, what would the maximum efficient input temperature to a heat pump be? Will a heat pump work satisfactory from 100º down or would it be lower?
Thanks so much for your time. Always interesting to watch the Geo forum, the repairs by remote are incredible!
I am getting confused, what do you mean by "from 100 down" or "down to 40". You need to describe your layout design a bit better, The CM THW would appear to be a nice booster, you might have to play with the delta T and the flow, to make sure you do not heat your underground storage with the heatpump. |
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| www.buffalogeothermalheating.com |
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FBBP
Veteran Member
Posts:1215
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| 19 Feb 2011 02:35 PM |
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If a heat pump does not work efficiently at 120º incoming water, how much lower should the incoming water be? Can I expect a reasonable COP @ 100º or is that still to high? If it works well at 80º it will slowly drop my storage down to 40º as it removes the heat. With a week of bright sunny cold weather the collectors will again boost the storage temperature as well the lower the storage temps the more the collectors will add. As I am running just water (no glycol) I would prevent the HP from coming on if the storage temp dropped much below 40ºf. Hope this makes sense. |
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docjenser
Veteran Member
Posts:1400
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| 19 Feb 2011 04:08 PM |
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Ok, you want to use your storage tank as the heat source, not as a buffer for your load. Well, the THW has tables showing an operating parameters of 20-70F for the source side in heating mode, no reason why it should not go higher even, and the same for a source 20-110 for the DHW side. COPs are really good when working with warmer source fluid. How big is your solar storage tank? Be careful that you do not freeze it quickly. You probably do not want to have the source temp too high above 120F. Most of the time you would not need it all the way up to 145 F supply temp, it has an outdoor reset built in.
http://www.climatemaster.com/share/Res_All_Products_CLM/Section_7_THW.pdf |
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| www.buffalogeothermalheating.com |
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engineer
Veteran Member
Posts:2749
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| 19 Feb 2011 09:01 PM |
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Be careful with source temps above 70 - can load refrigerant with so much heat that high side pressure and current gets out of hand...too much of a good thing. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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docjenser
Veteran Member
Posts:1400
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| 20 Feb 2011 12:06 AM |
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The THW is a Viessmann Clone and should be designed to handle much higher pressures. Although I have never installed one, and I am still looking for feedback from someone who did, it should be able to deal with higher source temps. To be sure, call Climatemaster and inquire about it. Or limit your storage (source) temperature via an aquastat to 70 degrees F. |
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| www.buffalogeothermalheating.com |
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joe.ami
Veteran Member
Posts:4377
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| 20 Feb 2011 09:35 AM |
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I think something could be designed employing the solar storage tank via plate exchanger as source of heat first then entering water for geo backed up by a ground loop.
Cost effectiveness is another question.....
j |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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FBBP
Veteran Member
Posts:1215
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| 26 Feb 2011 10:49 PM |
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Thanks for the input everyone! I think I'll have to limit the hp to under 80º max. I'll use a preheat from the solar storage to a standard electric water heater for domestic. My earth tube is working better than expected so I may not need to temper the incoming fresh air with hot water. That was my biggest load.
Since the main issue with the heat pump is running the fluid and compressor to hot (if I'm understanding this right) would a dsh make a difference? |
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jokin
Basic Member
Posts:105
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| 24 Mar 2011 09:49 PM |
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Just stumbled across this old thread (trying to play get current on past postings) and the warm entering source water just reminded me of something I came across for an airsource cooling only commercial split system 40 tons. Another guy in our office was trying to match an oversized coil to the outdoor unit. Result is high saturated suction temps/pressures - scroll compressors are hermetic (refrigerant cooled) if your saturated suction temp is too high over 50 F for some commercial outdoor air cooled units I've run across... you risk nuisance trips or burning out the compressor. I assume it would be similar scenario with geo unit once you go outside the particular temperature range specified for the unit- nuisance trips or compressor failure.
Not sure if I understand how DSH would affect it. |
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