Geothermal A/C and Heat

[clea]

clea,


thanks a lot for putting up that information.
Is your system capable to put excess heat from solar thermal (or any other heat source) back into the ground? If not, was that a consideration and you decided against it?

I never asked about using the ground loops for anything other than the heating/ac of the house.
I guess they could be used for storing excess heat but i wonder if that would have required me to have more holes dug in the yard as the system was sized for only storing/retrieving the heat from the ground for the house's thermal needs.

But now you've got my curiosity peeked to know what other heat sources would generate enough that i could make use of the ground loops to put it there and what purpose that would serve.

 

[VolkerP]

trying to feed your curiosity a little bit.

ground loops can be used as heat storage. There must be no aquifer with moving water, or the water will move the heat away.
Most bored ground loop installations deliver water at 10°C/50F all around year (=no storage required) but which must be heat pumped.
Solar thermal installations deliver up to 120°C/250F but only at times of little heat demand, so storage is a must.

Some people came up with the idea to combine the two heat sources, using your underground rock+water as a storage. Excessive heat from summer could be stored for the winter, or shorter periods of bad weather in spring/autumn could be leveled out. The water from the ground loops would be >25°C/77F all the time and electricity usage for heat pumping would be greatly reduced.

The problem in storage is always upfront cost versus payback from each cycle. A seasonal storage does 1 cycle/year so you need a fairly large+cheap storage to go anywhere near ROI.

 

[clea]

interesting, thx

but wouldn't that require separate ground loops for the storage as opposed to the heat pump functionality? I can't imagine that storing excess heat from the solar thermal installation in the same loops as the ones used for managing the AC in the house would be efficient ...

 

[VolkerP]

sorry clea - living in a climate where residential AC is unknown, I missed the AC thing completely. You are right, you cannot dump excess heat from AC in the same ground loops while "charging up" with heat from thermal solar collectors. The thermal underground storage is employed e.g. in Canada, and Germany. See http://www.dlsc.ca/.

 

[clea]

sorry clea - living in a climate where residential AC is unknown, I missed the AC thing completely. You are right, you cannot dump excess heat from AC in the same ground loops while "charging up" with heat from thermal solar collectors. The thermal underground storage is employed e.g. in Canada, and Germany. See http://www.dlsc.ca/.

In my area of Canada where the summer weather can get up to (and occasionally over) 30C for stretches with high humidity, AC is almost a must if for nothing else but to be able to sleep at night. Couple that with -30C and below winters and i think i will get full use of my ground loops just for managing the indoor climate of the house.

What i could use solar thermal for would be to heat the swimming pool and for that i don't need to store the heat for later use in the winter (unless i want to try and turn it into a hot tub ;~).

 

[clea]

btw, thanks for the link the project looks very interesting. I grew up in Alberta (in the prairies and much further west of where i am) and i remember the air being much drier and so the summer heat (or winter cold) was never as much of a problem as i currently experience here in Montreal.

 

[W.Petefish]

I'll update my photos in the morning. They installed the heat exchanger on monday and are going to be back soon with the trencher to link the whole thing up.

I know that we discussed with our AC techs to have "Desuperheater" (hot water heater that uses heat from the loop) installed along side our CNG fired one.

Desuperheater (from Bosch):

A desuperheater or HRP (Hot Water Heat Recovery Package) is a feature that takes advantage of waste heat of the compressor and uses it to heat domestic water. Heating your water with FREE waste heat will reduce the use of your inefficient water storage tank heating elements. Hot water is produced by using a double wall coaxial heat exchanger coil. The hot refrigerant gas flows in the outer tubing while the domestic water flows in the inner pipe being heated by the hot refrigerant. The HRP heats water with superheated gas that is being produced by the compressor as you heat or cool your space, thus saving you money in your hot water production.

 

[jkirkebo]

I have a 200m deep hole and a 9kW heat pump. I use the bore hole to cool the house in the summer, heat it in the winter and make all our hot water. The hot water tank is integrated in the heat pump. This is a very common solution here, though it doesn't seem to be so elsewhere ? It is not just pre-heating, the heat pump makes all the hot water with no resistive element doing anything. The tank is 44 gallons and cannot be emptied by showering as the heat pump makes new hot water faster than we can use it in the shower.

Savings are about $3-3.5k/year compared to the old heating oil furnace. Heating is mostly in-floor, but some radiators too.

 

[clea]

Mine is a bosch as well and the tech said that the output for the hot water is not really hot enough for direct use (for showers etc ...).

Jkirkebo, what temperature is the water produced by your system?

Maybe i just need to change my expectations of what hot water means for use in a house.

Is there a minimum temperature that the hot water needs to be at to be useful? I can imagine that i rarely if ever use the water direct without mixing it with some cold water. Maybe i could have gone with just a single tank and just used the output of the unit to provide the hot water need in the house. If true I could maybe also just turn off the breaker on the second tank as well and see if it is hot enough for our needs.

 

[jkirkebo]

My hot water temperature is set at 52 degrees celsius (126 F), plus/minus 3 degrees. It is used mainly for showers, where you definately do not want water that hot. It is also hot enough to do dishes, though we don't do much dishes by hand.

The heat pump can supply water up to 60 degrees C, newer versions can do 65C.

 

[clea]

all very good info thanks.

from what i can find out the water temperature of the output of the desuperheater of the bosch units is between 50 and 60 C and it shuts off when the returning water it is cycling through the system is at 50 C so i probably don't need to heat up the water in the second tank. I will leave the breaker off in the first (feeder) tank and leave it on in the second to manage losses but i need to find out how to manage the temperature of the second tank so that it is at most 60C and then the system will almost never have to heat up the incoming water.

I changed the tanks when i got the system installed (they old furnace and tanks were over 11 years old so it was time anyways) and so the newer insulation properties of them should mean that the cost of maintaining them at the desired temperatures should be minimal ...

 

[W.Petefish]

Uploaded photos to my facebook. They were mainly working in the attic this time.

 

[W.Petefish]

The AC guys are just about finished. Look at my facebook album to see Desuperheater. The water going into the holding tank is upwards of 90+F (32.22C)

 

[woof]

Reviving a long dormant thread--I'm looking to replace two 15 year old HVAC units, and am considering installing geothermal.

We've a large 4000 sq. ft. house, with 2 HVAC units, 3 zones, and I'm not allowed to raise the thermostat above 72 degrees F :scared: This combined with 2 EVs uses a large amount of electrical power, so much so that even 12 kW of solar panels will only provide half the power needed to keep the house cool and the cars running during the summer months.

I'm wondering if switching to geothermal will significantly reduce the electrical power load due to cooling the house.

 

[RichardC]

Has anyone had a geothermal system put in to their house to cool or heat it? If so, How big? How much energy do you save over what you had?

We are using an air source system in Canada and are averaging about 2.5 to 3 times as much energy out as the energy in. I would expect a geothermal unit to produce approximately 3 to 3.5 times as much energy out as the energy in (the difference is most directly measurable when going from electric resistance heat to heat pump technology).

 

[clea]

Reviving a long dormant thread--I'm looking to replace two 15 year old HVAC units, and am considering installing geothermal.

We've a large 4000 sq. ft. house, with 2 HVAC units, 3 zones, and I'm not allowed to raise the thermostat above 72 degrees F :scared: This combined with 2 EVs uses a large amount of electrical power, so much so that even 12 kW of solar panels will only provide half the power needed to keep the house cool and the cars running during the summer months.

I'm wondering if switching to geothermal will significantly reduce the electrical power load due to cooling the house.

I have a similarly sized house and was heating/cooling using an HVAC system until I switched our house to geotherm in Nov 2011 and it has reduced my electrical bill by more than the Model S gobbles up with my daily driving.
My average daily kWh usage in 2010 was 143 but last year it was at 101. In the summer specifically for the period of June to Aug in 2010 my average daily usage was 124 but for the same period in 2012 it was 91 and last year was a bit of a scorcher.

Hope this helps.