Warm up that ground loop please

Your logic makes sense to me. Seems like a fine time to burn some trees. I would expect avoiding the aux will be the bigger factor than the COP improvement. I thought the loops in groundwater generally had good recovery, cuz the water is almost always flowing, at least a little.

You can't put an IR thermo, or tape a sensor on the ground loop return?

If it makes you feel better...in weather like this I am getting 30-50% of my BTUs from aux, pulling my effective COP down to 1.4-1.5, averaged over the whole day. We'll do better, like 2.0 on a seasonal average.

Any way to increase the water flow around the tubing, like a horizontal bore drain, or shallow well?

without seeing exactly where you are and how your ground water moves, I can't give good advice but ground water usually moves much faster and farther than most people imagine. I know dye tests will show this.
" I have two 250' loops that enter the water table at about 25 feet, so my loop is about 400' submerged in water." I interpret that to mean that your max depth is 100'. That should be plenty to keep it as warm as it will get. I can't see it hurting to turn the system off for a short if your loop is filled with proper anti freeze. Have you had the fluid or system tested? The biggest concern I have is that your system is very undersized if it is on 100% of the time, even without using the resistive heat.

I think you should definitely look into replacing that unit with something more energy efficient. It should pay for itself fairly quickly.

Are you COP figures including the pump and blower energy?

vertical or horizontal loops? The colder weather has had litte effect on my incoming temperature compared to last year (45-50 degrees in winter, 55-60 in summer). I have a vertical loop. They did insulate the horizontal line into the house from the well despite being at 6 ft depth.

The issue I'm having is my ducts for the main floor are in an uninsulated basement and uninsulated garage. The basement part stays warm enough that it's a non issue, but the zone with the garage duct work pushes out some cold air on stage 1 after being cycled off, effectively dropping the temp in the room and engaging the auxilliary when the temps outside are around 0. I plan on dropping soffits and insulating the ductwork further this weekend to combat this.

Jerry_NJ said:

I depend on my 20 year old Waterfurnace HP to handle most of my heating, but I supplement heating with a Quadrafire 4100 I Insert - and mostly hardwood and some White Pine.

The cold, cold January for New Jersey makes me wonder how cold my ground loops are getting. My old system doesn't provide any information on the loop temperature - maybe new ones don't either.

In any case when it is dark and the outside temperatures are single digit my HP is at full load and runs almost 100% of the time (with a periodic hit on the first 4.8 KW resistive aux heat element which drags the COP down to about 2.5 for the time the combined is on). I wonder how much better the HP COP would do if I give it a break so the loop can equalize temperature with the earth. I have two 250' loops that enter the water table at about 25 feet, so my loop is about 400' submerged in water.

Right now I have the insert cranked up so the HP has turned off. I'll keep the insert running for upwards of 12 hours during the colder part of the 24 hours - it cools off when I go to bed, I suppose about 2 hours after I go to bed the HP has to start working again - and I wonder if this results in a higher COP due to the fact the loop and the adjacent water has had a chance to return to earth temperature.

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The duct work is only a year old and it is insulated. The level of insulation works fine in the basement, just not in a freezing cold garage. Nothing building a soffit around and insulating better won't remedy....will also improve the cosmetics. They had to deviate from their install plans when I got the ceiling pulled down...had some obstructions that prevented running the duct in teh floor joists....would have been much easier to insulate and close those up vs soffits.

We, too, are 100% electric now. Spent 2250 last year to heat and cool 3800 sq ft with huge windows and skylights. All in all, it's been a good investment vs what we were spending on oil. I barely burned any wood last year just to get a better assessment on the savings, but even then, we upgraded insulation, air sealing, some doors, LED conversions in lamps and recessed lights. I'm pretty much at the point that I'm going to stop paying attention to it because it's at a level I'm comfortable with spending. I'll keep burning wood in the evenings for ambiance and take the heat gain as a plus.

Jerry_NJ said:

I wonder how much better the HP COP would do if I give it a break so the loop can equalize temperature with the earth

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These seems counterproductive to me. Heat moves faster when the temp difference is greater. It seems to me that shutting down your loops you'll only be slowing down the existing heat flow towards the loops.
I think most ground source recovery occurs very slowly and that what you're using for HP heat now was sunlight last summer.
I'd suggest disabling the HP emergency heat and using wood or whatever to cover the difference between what your HP will produce and what is needed to maintain room temps.

PS: I bought a data logger to monitor the loop temps on my GSHP system. Since ours is open loop and uses our well for supply I was experimenting with where it was best to discharge to (back to the well or nearby sinkhole).

semipro said:

Since ours is open loop and uses our well for supply

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That's interesting. Looking at houses (moving) and have been a little concerned when I come across one with a well (not ruling them out -- just have never had that before). But if having a well makes the cost of GSHP a lot less to install, it puts a different picture on the houses with wells.

Dave A. said:

That's interesting. Looking at houses (moving) and have been a little concerned when I come across one with a well (not ruling them out -- just have never had that before). But if having a well makes the cost of GSHP a lot less to install, it puts a different picture on the houses with wells.

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I think the concern is that a heat exchanger leak could send freon and compressor oil into your well if the water returns to your well. I'm not sure open loop systems are allowed in many areas anymore.
Of course, being open loop, you're using the well pump power to circulate the water and that energy is not recovered when the water is discharged as it would be in an closed loop.

Jerry_NJ said:

My reference to "equalizing the temperature" of the water/earth around my vertical loops is equalizing the water next to my loop with the water in the general area, the earth. That seems a reasonable goal, but, if the water if flowing, nothing gained during a rest period, or very little.

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I would argue that nothing is gained even if water isn't flowing around loop. Heat in the aquifer moves towards absence of heat regardless of water flow. (conduction rather than convection). Obviously, convection could overcome conduction if the flows were opposite and the water velocity high enough.

Thousand and up for well pump replacement? Do you have a below grade well access that requires digging? I had mine replaced at the same time I was having the geo wells dug and it was only 600 bucks and that was to bring my cap up to code as well. The company I used was on the high end of quotes for the geo wells but I liked the honesty and effort they put in pre contract.

Our well is 500 deep with water at 200ft. below ground surface so we're lifting water for the HP 200 ft.
You can only recover a max of 30 ft of head (1 ATM) before a vacuum forms.
I've considered many times converting to a ground loop system along with installing a closed loop in the well to tap some of that thermal capacity.

It sounds like your heat pump is working fine in the weather we've been having this season. I doubt that giving the loop a little rest will do much of anything, unless you had a system that the loop was undersized and you were actually having problems because of that. The limiting factor is how quickly the ground can transmit heat through it. Even if you give the loop a rest, in this weather, with the heat pump running 100%, the heat pump will rapidly pull the temp down back to whatever temp you had in equilibrium before the rest. With your vertical well installation, I would think there would even be less of a reason to try to rest things.

Using firewood to keep the aux off, like you're doing is probably cost effective. The biggest change you could make, that will make your system run more efficiently and make the aux run less, is get rid of your 5 degree setback. It's very hard for a heat pump to get the house back up 1 degree in cold weather, let alone 5.

semipro said:

Our well is 500 deep with water at 200ft. below ground surface so we're lifting water for the HP 200 ft.
You can only recover a max of 30 ft of head (1 ATM) before a vacuum forms.
I've considered many times converting to a ground loop system along with installing a closed loop in the well to tap some of that thermal capacity.

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I thought the ground loop was simply pressurized to avoid cavitation....and meaning there is no gravity work done, only pipe friction.

woodgeek said:

I thought the ground loop was simply pressurized to avoid cavitation....and meaning there is no gravity work done, only pipe friction.

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In our open loop system the same well that supplies potable water supplies water to HP heat exchanger. Then the water is returned back to the aquifer it came from sometimes via the same borehole well that supplied it.
Our return to the well just drops in from the top. You could return the water via a pipe that ran all the way down to the water surface in an attempt to recover the potential energy of the returning water. The return water is not under pressure since the point at which its released is a atmospheric pressure.
My point above is that the laws of physics allow you to recover only 30 ft. of head of that potential energy before a vacuum forms in the return pipe within the well.

Edit: like this except our water table (phreatic surface) is much lower. I believe the red flow arrows in the graphic below are supposed to indicated heat flow rather than water flow.

Thanks SP. I guess I hadn't appreciated previously that open-loop systems must have lower COP than closed loop, because they have a lifting power requirement for the water that the closed loop systems don't.

woodgeek said:

Thanks SP. I guess I hadn't appreciated previously that open-loop systems must have lower COP than closed loop, because they have a lifting power requirement for the water that the closed loop systems don't.

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Yep. That haunts me.a bit

My GSHP is open loop, with the water serving both the heat pump and domestic needs. It's been my understanding that in the unlikely situation where a heat exchanger fails, the chance of ruining the well from toxic contamination isn't there. IIRC, the lubricant is mineral oil (paraffinic, non-toxic). The refrigerant is highly volatile. Both are removed from the well easily by pump & dump.

In my configuration, the heat pump is a two-ton CM Tranquility 27, although the well will support over three tons. Roughly 80 feet of water column is needed per ton of sustained heat load. The well is 330 feet deep, with the 20-ft perforated pipe section starting up 20 feet from the bottom. The HP return line ends in water about 50 ft down. The static water level is about three ft down, and that drops about 10-12 feet when the net water flow (not returned to the well) is around 10 gpm, so the HP return line exit always is under water. The pumping power requirement is thus only for line friction, valves, and the HP. How far down the pump is doesn't matter (other than additional line friction); it's how far the water level is down the bore.

On the other hand, my configuration incurs more pumping power than if it didn't also provide water for the house. The control is constant pressure, and I dropped that from the installed 50 psig down to 40. There is a 6 gpm constant flow device in the return line from the HP. Since the total pressure drop for just the lines and HP is a lot less than 40 psi, that device has to take the rest, and in doing so it made a lot of noise from the turbulence, far more than the HP itself, which is a barely audible hum anywhere else in the house. I resolved the noise issue by partly shutting the two isolation valves for water to/from the HP, thus distributing the pressure drop over the flow controller and the two valves. The noise mostly goes away with that simple adjustment.

Now, as for pumping power for open vs closed loop GSHP configurations, with mine also providing water for house use, yes, there is more power use than otherwise needed for just the HP, and the bulk of that extra power is wasted across the two valves and flow control device. An alternative setup would be to have a booster pump and separate air tank for domestic use, drawing from the line that supplies water to the HP at a lower pressure. Either that or two pressure sensors, for high and low pressure levels. When house usage drops the high pressure portion of the system, electronics would switch the pump control to the high pressure sensor to ramp up the pump speed for higher pressure. I don't even know if such a configuration has been implemented anywhere. I know that a separate booster pump has been used. But my GSHP is approaching its third full year of operation, hasn't needed any servicing, and gives me a heating season cost of $5-600, if I subtract out 6-700 KWH/mo from the total bill (Sept and May bills).

I recently was able to get some crude numbers on HP usage, over a couple of days with day/night temps bracketing the design temp here (-3 F). Reading the hour meter (which I added), the worst 24 hour period gave me 18 hours in use (but only in first stage). The woodstove had been used for about 6 hours, so I figure without burning wood the HP would have been 100%, but in just first stage, which gives about 19 KBTU/hr according to the mfg tables. So perhaps as close as I'll ever get it, I think that is about the heat loss of the house at "steady state" at design outside temperature. I'll never really know for sure, as a house like this (superinsulated, tight) is never really in steady state.