Anybody using ground-source HVAC ?

[mkepke]

Does anyone have a ground-source heatpump ? I'm looking for more information to determine if a closed-source (what's allowed in Wake Co.) HP will fit my situation.

I've talked to four local contractors for Florida Heat Pump and been underwhelmed by the contractors themselves.

Ground-source looks promising with the residential water-heater option.

-Mark

 

[Chipper]

Are you looking at vertical well (water loop) or buried loop (ground loop)? I've gotten some quotes recently.
It only heats water in the cooling mode.

 

[scsmith42]

Mark, are you referring to a geothermal system? If so, check out Water Furnace - they have a good reputation.

Scott

 

[junquecol]

Check with Billy Evangelist at Evangelist Heating. He wrote an article for Fine Homebuilding a few years back on ground source heat pumps. The installation used the "slinky coil", which requires a lot less trench.

 

[jeff...]

Someone please explain how a geothermal system works - I hear it's like 75% savings over my gas-pack and uses a 300 ~ 400 foot coil loop of plastic pipe filled with antifreeze buried in the ground like 5 or 6' deep. the earth remains at a constant temp below the frost line like around 50 degrees. there is a heat exchanger involved ok so how do you get enough heat from 50 degree liquid to heat your house? without some other heat source?.?.? I'm lost...

Maybe this is the wrong site to ask such a question

Thanks

 

[mkepke]

Steve (Chipper) - would love to see where you've gotten too on your quotes.

For vertical vs. horizontal, I ASSUME horizontal given the typically lower cost, but haven't found any design guidelines to back up that assertion. Just how much space does one need per ton, etc. I have a 1.7AC lot, but well, septic, outbuildings,...

Jeff - a geothermal heatpump works by exchanging thermal energy with the earth. It uses exactly the same physics as an (air to air) heatpump, which itself uses exactly the same principle as the AC in your house:

the AC compresses a refrigerant causing it to become a hot liquid. This hot liquid is hotter than the ambient outside temperature (even when its 100 degrees out) and run through a heat exchanger, thus giving up some heat to the outside, thus causing thee liquid to cool some. The liquid is then allowed to evaporate to a gas, expanding, which causes its temperature to drop precipitously (Gas Law). This is run through a heat exchanger so that it absorbs heat from the inside of your house, thus cooling your house. Then the AC compresses this warm gas into a hot liquid and the cycle repeats.

In winter, this cycle runs in reverse, so that hot compressed liquid gives its heat up to your house, and the cold gas absorbs heat from the cold-but-warmer-than-the-gas outdoors.

Since the hot liquid and the cold gas states of the refrigerant are usually hotter and colder than the ambient temperature respectively, the process works.

-Mark

 

[Chipper]

I've looked at the "Water source" (open loop) "water loop" (vertical wells).
The open loop where the water is pumped through once from a well is the most efficient but requires a lot of water. COP (coefficient of performance) is about 4.5 for a 3 ton unit. COP is just a ratio of energy out for energy in. So for every kilowatt I buy I get 4.5 back. Water flow rate is about 2 gpm per ton (12,000 btu) so 7gpm. That could be 8000 gal per day so disposal is a problem. I don't have a quote yet on a Fla Heat Pump but a McQuay 3 Ton unit is $3200.00, I expect FHP to be about the same.
The same equipment (for the most part) is used whether open or closed loop.
The closed loop vertical well is the next efecient system with plastic U-tube the entie length of the well. The well is filled with grout to help with heat transfer. Earth is pretty slow to give up heat so you need one well for every Ton of heating/cooling.
The quote I got was $1300 per well 4 wells and about $7000 for the equipment and manifolds, pumps installed.
Here is a one page spec sheet on FHP and you can see how the same unit is rated (COP) vs. the 3 types of heat source.

 

[welldigger]

We have an open loop groundwater heat pump at our office. It works very good in our mountain climate. You need several gallons per minute per "ton"(
not really sure how much,but we have 2 heat pumps serving 2 40x40 offices on a 30 GPM well).It takes a pretty large pump to deliver the required flow, so you have to figure the cost of operating the well pump. If I was going to use open loop at my house, I would use a Variable Frequency Drive pump because it speeds the pump up to meet the flow demand which is more energy efficient. We have done several jobs for commercial buildings where we drilled geo-holes (vertical bore holes 300' deep) @ 1hole per "ton". We have done a few jobs for single family dwellings where we drilled 3 holes 300' deep.The upfront cost for vertical closed loop systems is higher than open loop,but if you get a "dry hole" it makes no difference because you don't need water for the closed loop system. Some counties require an additional well to discharge the water from an open loop system into.

 

[RayH]

A few year ago (like in 1980) I discussed the idea of ground-source heat pumps with the engineering staff at U of VA. We were renovating a place out in the hills and looking for a reasonable heat/cool source. Yes. there was an oil crunch back then also.

Their recommendation at that time was a closed-loop system buried with the septic drain field to almost eliminate the cost of putting in the coil. Don't know where this concept ever went. We already had the septic system in. Day late and dollar short.

Ray

 

[junquecol]

A few year ago (like in 1980) I discussed the idea of ground-source heat pumps with the engineering staff at U of VA. We were renovating a place out in the hills and looking for a reasonable heat/cool source. Yes. there was an oil crunch back then also.

Their recommendation at that time was a closed-loop system buried with the septic drain field to almost eliminate the cost of putting in the coil. Don't know where this concept ever went. We already had the septic system in. Day late and dollar short.

Ray

Unfortunately the health dept doesn't allow this design, even though it is the cheapest. The "Solar House" over at NC State uses this design. One of my neighbors has a vertical loop, three of them to be exact. An open loop (pump and dump) wastes a lot of water. You can also do a loop in a pond. The slinky coil is the cheapest way to go, if you have at least six feet of soil over the rock. In the eastern part of the state, the two well system is competitive. Remember that your recharge well has to have the capacity to receive the flow out of the heat exchanger. With horizontal boring more common, it could also be used to install heat exchanger loop. On campus at NC State, one of the buildings uses the water main as a heat transfer device.

 

[Chipper]

Got some more info today as my neighbor pulled the trigger on a water loop HP. 200ft well per Ton well. 1Ton per well, $1500 per well. He is getting 3 wells and Water Furnace equipment.

 

[jeff...]

* a geothermal heatpump works by exchanging thermal energy with the earth.

* It uses exactly the same physics as an (air to air) heatpump

* the same principle as the AC in your house:

* AC compresses a refrigerant causing it to become a hot liquid

* This hot liquid is hotter than the ambient outside temperature

* Hot refrigerant is run through a heat exchanger giving up some heat to the outside,

* causing the refrigerant to cool some

* The refrigerant is then allowed to evaporate to a gas, expanding, which causes its temperature to drop precipitously (Gas Law)

* The refrigerant is run through a heat exchanger so that it absorbs heat from the inside of your house, thus cooling your house.

* Then the AC compresses this warm gas into a hot liquid and the cycle repeats.

* In winter, this cycle runs in reverse, so that hot compressed refrigerant gives its heat up to your house

* The cold refrigerant absorbs heat from the cold-but-warmer-than-the-gas outdoors.

* Since the hot liquid and the cold gas states of the refrigerant are usually hotter and colder than the ambient temperature respectively, the process works.

Did I get this right?

So basically it's that fact that earth temperature is fairly constant (around 50 degrees) that makes geothermal more efficient than air / air heat pumps?

I was thinking what about a coil of copper pipe routed through a solar collector type attic in your house. a roof of polycarbonate and large tanks to store the warm / hot water? What would be the difference instead of using ground water or water circulated through a snake of plastic pipe to bring it to ground temperature?

If the water were warmer wouldn't the water furnace be even more efficient?

Thanks

 

[mkepke]

Hey Steve - is your neighbor willing to share more info - which model is he putting in, what's it costing for materials and labor, etc ?

I talked to my local WaterFurnace guy and he said his driller is wanting $15/ft :rotflm:

Still no clear 'best' solution: open loop injection *might* be allowed after all, but my well might be marginal for capacity @ 12 gal/min, etc. I'll have the dealers out for a site visit.

Mark

 

[Chipper]

I'll talk to him get the numbers. My main gripe with Water Furnas is their dealer mark-up. It's about 1.7 on the equipment. Of course you get a lot with the install. The dealer had a guy there on Sat all day and all he did was observe to verify the depth of the well and tube install. The drillers were contracted. Dealer will power rake and seed the yard area they disturb.

 

[mkepke]

Did I get this right?

So basically it's that fact that earth temperature is fairly constant (around 50 degrees) that makes geothermal more efficient than air / air heat pumps?
Right. Might also be a few efficiency points gained by using a fluid (water) for the thermal exchange rather than air.

I was thinking what about a coil of copper pipe routed through a solar collector type attic in your house. a roof of polycarbonate and large tanks to store the warm / hot water? What would be the difference instead of using ground water or water circulated through a snake of plastic pipe to bring it to ground temperature?

If the water were warmer wouldn't the water furnace be even more efficient?
Yes this would improve heating efficiency. At that point, you basically have a solar hot water heater:
http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=12850

The big question in my mind is would the added cost and complexity offset the cost of what is already a pretty cheap system to operate ? :icon_scra

-Mark

Thanks[/quote]

 

[Howard Acheson]

Does anyone have a ground-source heatpump ? I'm looking for more information to determine if a closed-source (what's allowed in Wake Co.) HP will fit my situation.

I've talked to four local contractors for Florida Heat Pump and been underwhelmed by the contractors themselves.

Ground-source looks promising with the residential water-heater option.

-Mark

I had a Florida Heat Pump installed four years ago when I built my house. The contractor was Fulford Heating & Cooling from Holden Beach. They were, as still are, excellent. I have a maintenance agreement with them and they are always right there if I need them.

My building contractor first used Fulford with my house and he liked their service so well he uses them for all his new home construction now whether air to air or water systems. The home builder put a FHP unit in his own home and has installed a number in other new construction.

 

[mkepke]

Thanks Howard. What did you install (configuration and model) ?

-Mark

 

[Howard Acheson]

I'm not home now so I can't give you specifics. I have two units. One handles the majority of my 2800 sq ft house and a small unit handles my guest rooms. The main unit has a hot water recovery feature. Free hot water during the summer.

Other than the different sizes for tonnage, I'm not aware of different models.