Warm up that ground loop please

[Jerry_NJ]

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.

 

[woodgeek]

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.

 

[Ehouse]

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

 

[Jerry_NJ]

Thanks, I kind of like burning wood for heat/atmosphere, even to some extent recovering, cutting rounds and splitting down wood on my 5 acre property. Then the wood fuel is mostly sweat. Of course I have a few hundred in tools (only an electric light duty splitter).

I spoke of increased COP in the context of both higher when in HP-only mode due to warmer loop water, plus less use of resistive Aux when recovering from a setback of the thermostat. Right now I have a morning fire going as I bring the heat up from 64 to 68. When it is close to zero outside just calling for an increase of 1 degree will result in some Aux run time, but not if my Insert is up to a couple hundred degrees or higher....that's where the White Pine come in, a fast start-up then in goes some hardwood.

I limit the HP Aux to only one stage, 4.8 KW (16KBTU) and with the HP putting out about 32KBTU (maybe 36KBTU if loop is above 40 degrees) I still get a combined COP well over 2.5. That is still lower cost than oil heat. In fact when running in Stage I and Stage II I get closer to 3.8 COP average, assuming about 50/50 on the run time.

I want to have enough wood for emergency heat, spell that power outage, so I am now cutting back and running on just HP during the day even at temps 20 or so, especially if it is sunny, like right now. One more load of 30 pounds of hardwood and I'll let the Insert burn out.

As said, the HP is 20 years old and I am planning to replace, most likely with Water furnace as I have found a local dealer/repari that I like and trust. The guy who installed the current unit was such a guy too, but he has retired, as have I. I figure the compressor will go "any day" and a replacement isn't even available, forget about the cost. Looks like with the 30% tax credit I can install a new HP with higher COP/EER for about $10K. If a compressor were available I'd bet it would cost about 4K just to replace that. I may stay with the two speed compressor, the one I have is a great machine. The new would be a Scroll design, that's were some of the increased efficiency comes from I think. I believe the new offering includes some more informative thermostat control/features. I'd like that.

 

[DougA]

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.

 

[woodgeek]

Are you COP figures including the pump and blower energy?

 

[Jerry_NJ]

I never expected to stay in this house for 20 years when I had the Geoghermal (ground source) HP installed. The total system cost approximately $12,000 and my power company gve me about $3,000 in rebate, there were no government rebates back then. I'd say the system, which has cost me about $4,000 in repairs in the last 5 years, has paid for itself in energy cost. I'd say I save at least $1,000 a year in heating costs and maybe $200 plus in cooling cost. I don't need any encouragement to buy based on pay back, I resolved that 20 years ago before it was so easy to do. I think Oil was well under $1.50 a gallon and electricity was about 10 cents per KWH where I live. Now with Oil up by more than 100% and electricity up 50% the pay back is even quicker. If I had access to natural gas that is what I would have taken. Natural gas is still not available here, and our current government is pushing prices up, which will also affect electricity with coal on the hit-list, but every body, 100%, depend on electricity so it is politically unattractive to run up the cost of that, though the effort goes on.

Yes, I use the full energy input, in Volt-Amps not Watts (assumes PF of zero) and calculate my BTU by measuring the temperature drop across the heat exchanger. The unit also meets specks in that regard and is rated at 4.0 in Stage I and 3.6 in Stage II, both for a loop temperature of 32 degrees. Thus the interest in loop temperature, if the loop is 40 or 45 degrees the COP is even higher. My calculation takes the delta Temp of the 4.8 KWatt resistive element and a fixed air flow to computer the BTU of the HP exchanger. As said this comes in close to factory specs.

While noting the approximate $4,000 in maintenance cost which did not count filter replacement, that comes to $200 per year. I think it must cost at least that much each year to have an oil furnace tuned up. So I consider my maintenance cost to also be low, not add up against the economic analysis of cost.comparison with Oil heat.

 

[jdp1152]

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.

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.

 

[Jerry_NJ]

Thanks, I'd guess you're temperatures are usually a few degrees below mine. As said I don't have access to the ground loop flow, but I have put a stick on thermometer on the PVC pipes under the insulation and I haven't ever read anything near the spec test temperature of 32 degrees.

I hadn't the water table as flowing like a river, I figured was more stationary like a lake. If flowing then my "rest" time makes no difference other than the electricity used when the Insert is in operation is only the circulation fan which would running at one or two stops higher if the HP was on. I'll try to find out more about water table.

No doubt, get that exposed duct insulated. Some of my basement duct work is insulated, indeed some is double walled and looks to not be insulated, could that be the case on you garage run? But I let the HP pull air down into the basement as the drag on the returns is high enough to lower the air pressure in the basement, and given the poor quality window (window wells) I don't want air drawn in from outside or up from the floating slab --- RADON ouch.

Just looked at my electric bill for this last cold period I used a little over 2,100KWH. Of that at least 700 KWH is other than HP, we are ALL electric. We have a 2,000 sq ft two story about 25 years old, but built to be all electric and well insulated... seems it might be time to replace some of the older design Anderson thermopane (sp?) windows. My JCP&L with Dominion for Energy (at 10 Cents a KWH) comes in a little under 14 cents per KWH delivered. So I estimate about $200 for heating one month during the coldest weather in years. I have to add the cost of firewood for the month, a bit under 1/2 cord, I'd valuate at $100 if I had paid for it which brings the total to $300. I have neighbors with larger homes, at least 3,000 square feet and two oil furnaces each coming in closer to $1,000 for Oil for the same period. So even if heating their homes were proportional to mine, add 50% to my heating cost they'd still be spending about $450 for heat (and firewood if any used in a high efficient air tight wood stove/insert) or they'd save over $500 just for one cold month. Sold, yep I'm sold until our President promised to make "the electric will necessarily skyrocket" makes good on that promise and he's working on it. In the meantime I save big money over the cost of oil heat.

 

[jdp1152]

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.

 

[semipro]

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

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).

 

[Jerry_NJ]

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. Of course during the rest period my electric usage goes down by the amount drawn by the compressor and the loop pumps (I have two pumps). I am yet to determine if it is know what the aquifer is doing under my property - flowing or stagnant.

I have operated with the Aux resistive heat disconnected as it is my practice to turn the heat down about 5 degrees at night. Getting that heat back always resulted in the Aux coming on, even if I tried to supervise the thermostat to go up 1 degree at a time - how boring can that be? I finally decided to allow only one of the two 4.8 KW resistive strips come on. I see it comes on intermittently in any case, the controller algorithm is clearly "tilted" toward economy - bring in Aux for 5 minutes and then off, then watch for x-minutes to see if the room temperature is coming up. My unit is old, but the microprocessor/program is rather sophisticated. I suspect some of the program triggers are programmable - I'd like to see more control in the thermostat. I'd also like to see more real-time data, like loop temperature in/out.

 

[Dave A.]

Since ours is open loop and uses our well for supply

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.

 

[semipro]

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.

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.

 

[semipro]

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.

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.

 

[Jerry_NJ]

Sounds right, energy move, not the void or low point of energy, heat is a form of energy... and a relative one even if it can be measured and quantified with a number. Another important point in thinking about moving heat into my loop for heating. Doesn't sound so good when it comes to cooling - there may really be no difference. My EER is around 20 in low for a loop temperature of 70 degrees as I recall.

Good points on the well approach. It was not allowed in NJ 20 years ago, but then there is a lot not allowed in NJ. Also, my well is at about 100 feet, lifting water 100 feet takes some energy as is witnessed by the fact my electric service to my well pump is 230 vac and I believe 20 amp. While pumping water here cost a lot less in electric cost than purchasing from water companies (some are nearby) there is the cost of the pump and its replacement...talk about a thousand and up. I do not know if pumping water up and returning it to the same location reduces the load by "sucking " with the water going down... seem possible. But if the water is dumped in a shallow dry well it is clear the lifting cost is added to the power input sid of the COP computation.

 

[jdp1152]

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.

 

[Jerry_NJ]

Yes, approximately $1,000, in any case way over $600 and that was at least 15 years go. On the good side, the pump still works and I use it some to water shrubs, even some of the lawn near the house. Full story there is only my wife and I in the house, so the pump load is less than that typical for a family with children at home as far as house use goes..

They just pulled up the PVC, installed the new pump and put it back down. I wasn't hone to watch, someone has to work to pay these bills. There may have been some PVC replacement I don't know, but the well head (a 10" or so pipe with a cap) was unchanged. I think they put a new pump control in the basement but nothing was done to the old tank. I replace that a few years later myself for a couple hundred...this time with a more modern one, with a bladder. It too has worked well, so far.

 

[semipro]

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.

 

[sesmith]

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.

 

[woodgeek]

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.

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

 

[semipro]

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

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.
(broken image removed)

 

[woodgeek]

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.

 

[semipro]

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.

Yep. That haunts me.a bit

 

[DickRussell]

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.