Geothermal heating/cooling question

[Bill Barrett]

the systems i have seen have had a way to monitor the loop water temp: ones system i still say was installed wrong, it was a 6 ton unit, with wells, plumbed in parallel: the water temp would go up a lot on hot days and the system never would keep up: i thought the wells should have been in series: the other way, there was no way to tell if all the water flow was going thru just one well? if you can monitor the water temp, it will tell you a lot about the system and how much change there is with seasons.
heehaw

Parallel is right, that's why piping design, flushing, and charging the system with proper antifreeze is so critical. If the system was piped in series the pressure drop through 1000's feet of pipe would make pumping cost prohibitive. All systems monitor the water temp. by freeze stats, temp sensors,low pressure cut out, etc. but not all systems let the homeowner see it, ie. digital read out.

 

[techman]

I also install geo systems. It could be that the system is just undersized, or you could have ducts in an uninsulated space (attic) and no or insufficient duct insulation, or duct leaks.

If you have a 2 stage system, you may not be hitting the second stage, or there could be a problem with a solenoid. This could be wiring or perhaps a thermostat problem.

The subsurface temp in your area is about 50 deg. This will warm to about 75 deg by summers end if the loop was designed correctly. It is a combo of the ground heating (poor heat transfer in dirt) and an overall ground temp increase seasonally of about 15 deg. Likewise in the winter it will cool below freezing. As stated earlier, try to get a temperature reading on the incoming water line. If it gets too hot, the heatpump should fault. Normally the water temp is not the issue. If the water is 75, it is still quite a bit cooler than the outdoor air which is used on a standard heatpump. Next check the air temp coming out of the unit, close to the unit. It should be about 15 deg cooler than the incoming (room) air. If it is not, have a service tech take a look and check for low charge or other problems.

paul

 

[heehaw]

Parallel is right, that's why piping design, flushing, and charging the system with proper antifreeze is so critical. If the system was piped in series the pressure drop through 1000's feet of pipe would make pumping cost prohibitive. All systems monitor the water temp. by freeze stats, temp sensors,low pressure cut out, etc. but not all systems let the homeowner see it, ie. digital read out.

"if" they had run each set of lines back to the building, so each set could be checked an monitored: but with a parallel system, and the lines all connected underground at the wells: there is no way to know that water is going down each and every well: all the water could be going down one well, an that be why it was heating up to a point it didn't work. they dug them up twice trying to see why the system didn't work, but all they did was double check to make sure they weren't kinked above ground and were connected in parallel: they didn't check to see that water was down an back up each well.
heehaw

 

[Bill Barrett]

"if" they had run each set of lines back to the building, so each set could be checked an monitored: but with a parallel system, and the lines all connected underground at the wells: there is no way to know that water is going down each and every well: all the water could be going down one well, an that be why it was heating up to a point it didn't work. they dug them up twice trying to see why the system didn't work, but all they did was double check to make sure they weren't kinked above ground and were connected in parallel: they didn't check to see that water was down an back up each well.
heehaw

Do they know the flow is low, or are they just low on loop capacity?

You can tell by GPM at the P/T's , if you are only flowing through couple of the wells then GPM will be low. Each pump model can only over come so much head pressure. If they know their pump curve, and the delta P at the P/T ports you know your GPM.
6 ton = 16 GPM or close if your were pumping 16 GPM at your P/T's I doubt you are only using a couple of wells because of head pressure would be to high.
So if it is doing that, the pump must be over sized to over come the head, and your loop design is is not equal length on each circuit.

Do they have 6x150' deep wells? They might not be getting proper transfer.

Parallel circuits connected underground is standard of the residential industry.

 

[heehaw]

6 wells, not 100% sure of the depth but over 100ft each i know. they later added on to the building: doubled the size: and had two 3 ton units installed for the new section: and you can hang meat in there in August: while the other side is almost to hot to work in. different installation companies, and i think a different brand unit: the 6 ton unit had to be replaced when it was 7 years old, the replacement doesn't do any better, and is a lot louder: the problem has got to be in the loops, but no one around here has been able to figure it out: system has been in for about 10 years now, and after seeing what kind of problems can come up, anyone that works there that would have considered a geothermal system has changed their minds.
heehaw

 

[Z-Michigan]

I appreciate all the replies - you've been a wealth of knowledge.

Cooling seems to be working somewhat today, but not as strongly as it was working through Friday. It doesn't help that my wife was using the stove for several hours today. The comment about humidity from cooking may well be a factor.

Knowing that the house wasn't built with geothermal in mind, and that both the builder (first owner) and the second owner who we bought it from were a bit shy on cash relative to their horse habits, I wouldn't be surprised if the geothermal system is sized on the small side for the house. I don't know what the wall insulation values are but I think they are very average for 1999. In the winter the geo system supplies all heat until outside temps are below 20F or so and then the propane kicks in more and more frequently (coldest days this past winter had highs around zero with overnight lows in the -teens). The difference is very noticeable - heat from the geo system is only about 5-10F warmer than the indoor temp and has the same humidity, while if the propane furnace is on the heat is 15-20F above indoor temp and painfully dry (there is an air outlet right where my feet go under the desk that I'm typing from).

The statements about standard-book values for my area are very interesting. I think our average soil temp is a bit warmer than 50, at least at a shallow 8' depth, and our average summer high is more like 80 than 88 (Detroit is warmer than where I am). Definitely not too far off though. If the system was designed assuming a summer indoor temp of 75 then we're probably overtaxing it with our preference for 70. I am wondering if between the heat and drought this summer we may have just overloaded the ground surrounding the loop and will have mediocre performance until things cool off in mid September. Oh well, maybe next summer we'll set it at 72 and hope not to have any of these problems. Would it be worth soaking the ground above where the loop is? How many days/weeks does it take for water to penetrate 8' of clay loam?

Can anyone tell me how to detect the ground loop location? The prior owner described where it is, but it's a very vague description. We have called the company that installed the system and asked them (while they were on a service inspection visit) and it sounds like they didn't keep good records of that. Is the piping likely metal or plastic? If plastic, how would you detect it?

 

[Z-Michigan]

More info - we closed the windows last night around dinner time, set the cooling to 70 and waited to see what happened. It *seemed* like it was cooling down and mildly cool air was blowing. But this morning it was warm and stuffy and the temp was still 78, same as it was for most of yesterday. Outside overnight was in the low 70's with nearly 100% humidity.

Our hot water is as hot as it has ever been, so at least that side of the unit is working right (again, as far as I understand we do not have any propane backup for the hot water).

I didn't want to mention earlier for fear of skewing views - when the tech was out a few months ago, he found the system pressure to be low - I think in the ground loop but I'm not sure - but he apparently fixed that (not sure if he had to add fluid or what) and it had been working fine since. He didn't recommend any repairs beyond what he did on the visit. He also mentioned that a circuit board in the unit was melting, but said there was nothing to fix at that time, just to call him back if it fully melted. He didn't say how we would know if that happened, but I'm wondering if we now have the sign?

I appreciate the suggestions on testing it myself but due to lack of expertise and time that's not likely a good option for me. So, here's my question: should we call the repair tech now, or give it another day or two?

 

[heehaw]

what "brand" geothermal system do you have?
heehaw

 

[techman]

Two items come to mind. You stated that it was cool but by morning it was warm and stuffy. Sounds like your evap coil could be freezing up. This can be caused by a low refrigerant charge in the unit, or restricted airflow, such as, but not limited to a dirty filter. Next time it could be worth while to open a cover and see if the coil is iced up when it is not working as expected.

Concerning the loop, the most important thing you can do is to try to get incoming and outgoing water temps at the unit. This will tell you how the outside loops are doing, and how the inside unit is behaving.

The loops should be made from PP plastic pipe, with fusion welded joints on the fittings. If you do not know where it is, it can be difficult to locate. There is some equipment designed to find underground pipes by "listening" to the flow noise, but this is somewhat specialized equipment, not for the average contractor.

paul

 

[homeinwestIL]

I'm not technician, but we did have geothermal installed in our home when we had it built in 1999. My guess is either that you system is undersized or inadequate insulation. You talk about your propane system kicking on in the winter below about 20 degrees, but our back up (ours is electric) rarely kicks on even with temps below zero, and then only briefly. Our house has 2x6 framing and is pretty heavily insulated. I do think that the efficiency of the system falls off somewhat as the season progresses but, again, rarely have the backup kick on in the winter. Our cooling system always keeps thinks cool, and we keep it pretty low. We have separate units for the first and second floor, and have the upstairs turned on only at night.