Geothermal heating system and extreme temperatures.

[doxford jim]

Just been down to the basement and took a few readings using a hand held infrared thermometer. These are probably not too accurate as I haven't used this much to date.
Here are the measurements:

Basement wall (in the cooler part) 60F
Heat transfer fluid to/from coils 52F out 94F back
Air temps in/out 67F in 74F out

Unit is WaterFurnace Premier AT 2 Speed

I don't know if the above makes sense to you guys, but as I read and understand what is happening:-
heat transfer fluid leaves the house at 52F and goes underground in coils and is returned at 94F, which is put through the heat exchanger.
Air is recirculated back to the unit at 67F and leaves the unit at 74F to heat the house.
Basement wall temperature in cooler part of the basement is 60F
I don't see any secondary heating coils so can only assume that the refrigeration unit cycle is reversed and the heat goes into the heat exchanger to warm the air more.

Please correct me if I am wrong regarding the above - the return of 94F is very real and is warm to the touch and tallies with the reading I am getting with the hand held IR thermometer.

Power used for last 23 hours extrapolated for 24 = 130 kWh current outside temp. at -19C/-1F

Thanks

 

[irvingj]

bcjmmac: My heat pump, as mentioned, is a 30K BTU unit. It has a three-speed fan, but a single-speed scroll compressor. (Guess mine was too small to have all the bells & whistles, i.e., variable speeds on both.) I do run the fan, which drops to low speed, pretty much all the time. It jumps up in speed when the t-stat energizes the compressor, then drops back afterward. On low speed/"fan on," it draws only 1-1/2 amps; I couldn't do that with my old one!

I was advised not to get the optional hot water generator, but I think I may have missed the boat there; these things can make "free" hot water during AC if they're set up right, like my old one did. I have to admit I really miss that. It just makes so much sense.

At any rate, I'm still pretty happy with the system; I spent 12 years in HVAC, and to quote a very sharp co-worker I had the pleasure to work with, "It costs a lot less to MOVE heat than it does to CREATE it."

Words to live by, IMHO. Not sure what the environmental impact would be on a massive scale, but at present, a water-source --excuse me-- a GEOTHERMAL heat pump is what everyone should be using. ijk

 

[techman]

I was advised not to get the optional hot water generator, but I think I may have missed the boat there; these things can make "free" hot water during AC if they're set up right, like my old one did. I have to admit I really miss that. It just makes so much sense.

I am not sure why you would not want the HW option. It uses waste heat and does not detract from the space heating. Just an FYI, all of the commercial units generate this heat with what is known as a "desuperheater". They actually generate most heat when heating, not cooling.

paul

 

[dodge man]

My understanding of how geo works is as follows. An AC unit compresses freon which makes it hot, it runs thru coils outside which gets rid of heat, it uncompresses inside, gives out cold, then cycles again. A heat pump has the ability to flip flop and put the heat inside.

The problem is in extremes, say really cold in winter or hot in summer, the efficiency drops off.

So some guy says underground temps stay pretty constant. If it 10 below out the ground is say 50 degrees, same thing in the summer, so he invents geo thermal. It doesn't use freon through the ground but fluids instead, usually some kind of water and antifreeze. Just think of geo as an ac unit where the unit is cooled by water from the ground in the summer and gets heat from it in the winter.

So to answer your question, I don't think the water from your system goes out and comes back in at 97 degrees. More like goes out at 40 degrees and comes back in at sat 55 degrees. I don't know the actual numbers so I made them up.

 

[Country Geek]

I just turned on my new geo heat pump about two weeks ago. It's a 5 ton ClimateMaster with propane backup heat. Because I'm **** about controlling it, the propane backup heat is manual-only, i.e., it only runs if I turn it on. We've had a few mornings of 16F and the geo system has kept the house at 70 degrees with no problem and I haven't turned on the backup heat. The house is 2400 SF, a prow-front design with a 26 foot cathedral ceiling in the great room and an open loft with a south-facing wall of windows so it can be a handful to heat. The air-source heat pump it replaced couldn't keep the house at 68 without the backup heat during cold times.

How much electricity am I using? I'll look forward to the first post-geo electric bill to see how it's doing.

 

[irvingj]

"I am not sure why you would not want the HW option. It uses waste heat and does not detract from the space heating. Just an FYI, all of the commercial units generate this heat with what is known as a "desuperheater". They actually generate most heat when heating, not cooling. paul"

Paul, I do have a desuperheater coil, but I'm talking about an additional refrigerant-to-water condensing coil feeding exclusively into the DHW system. My old one had that.

I was advised that the expense of Water Furnace's version of that wasn't worth the payback, that the added condensing coil for hot water was very expensive. (It was very expensive, but I still wish I had it.)

And, to add insult to injury: as mentioned above, during AC my well loop is apparently cool enough that head pressure doesn't rise sufficiently for the desuperheater to activate (this new heat pump apparently has a control on the desuperheater that my old one lacked). Net result, I get no DHW help during AC. Now, that's a waste.

ijk

 

[Pixguy]

"I am not sure why you would not want the HW option. It uses waste heat and does not detract from the space heating. Just an FYI, all of the commercial units generate this heat with what is known as a "desuperheater". They actually generate most heat when heating, not cooling. paul"

Paul, I do have a desuperheater coil, but I'm talking about an additional refrigerant-to-water condensing coil feeding exclusively into the DHW system. My old one had that.

I was advised that the expense of Water Furnace's version of that wasn't worth the payback, that the added condensing coil for hot water was very expensive. (It was very expensive, but I still wish I had it.)

And, to add insult to injury: as mentioned above, during AC my well loop is apparently cool enough that head pressure doesn't rise sufficiently for the desuperheater to activate (this new heat pump apparently has a control on the desuperheater that my old one lacked). Net result, I get no DHW help during AC. Now, that's a waste.

ijk

Can't you still add it now, years later?

 

[dodge man]

I cranked my thermostat up last night to force the electric heat to turn on. It was pulling about 7200 watts at that time, a big jump for the 2100 it normally uses.

A lot of people talked about windows. I can vouch for that also. We had thermo pane windows plus storm windows when we bought the house. We also had the house resided and they used the house wrap at that time. After the new windows were put in I was amazed at how much quieter the house was. The new windows were thermo pane and low E but as far as the sound goes, I just assumed the seals and around the edges of the old windows wasn't that good.

 

[techman]

but I'm talking about an additional refrigerant-to-water condensing coil feeding exclusively into the DHW system. My old one had that.

I was advised that the expense of Water Furnace's version of that wasn't worth the payback, that the added condensing coil for hot water was very expensive. (It was very expensive, but I still wish I had it.)

And, to add insult to injury: as mentioned above, during AC my well loop is apparently cool enough that head pressure doesn't rise sufficiently for the desuperheater to activate (this new heat pump apparently has a control on the desuperheater that my old one lacked). Net result, I get no DHW help during AC. Now, that's a waste.

ijk

I have not seen a water condenser on a residential system. Nice to have, but as mentioned it would be expensive. You would need to have some sort of bypass (on the water side) during heating season. The desuperheater option is usually not that expensive to add (about $ 125 w/o dealer mark-up). During heating there is enough head pressure to get 1-2 KBTU/hr. In the coldest weather I get around 120 deg F in my preheat tank. I am sure that it has paid for itself many times over.

You are correct that in AC, since the loop water is 50-60 deg, there is little head pressure and superheat, so not much to gain. In cold climates like NH the desuperheat option should be worth it.

paul

 

[dodge man]

When my system was installed, they just added cost for another water tank, I don't think any price was added to the furnace itself. The water tank and the electric water heater they installed look indentical, the water storage tank just doesn't have and electric coils in it. I've grabbed the pipe coming from the furnace into the water storage tank and its not to hot to touch but almost. I wish it had a thermometer in it.