Geothermal cooling 'broken', HVAC pro tells us 'nothing can be done'


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Old 07-30-12, 06:41 AM
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Geothermal cooling 'broken', HVAC pro tells us 'nothing can be done'

Hi - this is my first post, I just found these forums, and I'm very hopeful someone here can help.

We have a Bard furnace + geothermal system here. Last week, it stopped providing 55 degree (F) air - only 70-80 degree. I was traveling, my wife brought in an HVAC pro, who said he bled a bit of air out of the system, and that nothing else can be done.

He explained that it's "probably" because of the incredibly dry season we're having, that the ground is just 'hot'. As I recall, the ground loop is 6-12 feet down; for that and other reasons I'm skeptical about this!

I've been experimenting all weekend, and here's what I observed:

turn on A/C 8am - getting good flow of cold (55 degrees F) air. At 10:20am, temp of air flow jumps from 55 to 70 degrees. Shut off A/C (at thermostat, just turned off the system). Wait an hour, turn it back on, and the temp is 55 - until 2pm, when it rose to 70 again. Turn off system, wait 30 minutes tihs time, and turning it back on gave immediate 55 temps. I have not tried 15 minutes yet, but I'll do that this morning. I am curious as to whether I can turn it off, wait a minute, then turn it on and once again get 55 degree air....

So it's ***working*** but it stops. I can also report a non-quantitative impression: I /know/ the moment it stops cooling - it's not a switch sound, nothing so obvious as a click or a thump, but the quality of the air flow sound ....... changes. Three times now it's happened, and each time, I go to the thermometer stuck in a register, and the temp is already rising.

But I don't know exactly what that means. I've never heard the 'pump' for the ground loop make a noise when it turns on or off.

I don't doubt that I need to find another HVAC "pro" but I thought I would post here before I made that phone call.

Does this give anyone a clue as to what is happening? Please, at least tell me it's not a no-win situation as HVAC Pro #1 told my wife

Many thanks -

/Bill
 
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Old 07-30-12, 07:24 AM
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Welcome to the forum.
Although I am not an expert in geothermal, based on what I do know it sounds like you are exhausting the cooling ability of your system.

What is the average ambiant tempurature?
When your system is running, is it running constantly (non-stop)?
Do you have your t-stat set to a constant temperature or have it set to rise and fall according to a schedule?
Have you done any of your testing during the night?

Not knowing your local weather patterns, it sounds like the "pro" could be partly correct. Dry ground would transmit heat from your loop less efficently then it would wet.
Unless the weather you having is really out of the ordinary for your area, I would say that the system should have been designed to compensate for this.

Based on your information, I think you might be supporting the facts that the ground isn't cooling enough.

Again, I'm not an expert.
 
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Old 07-30-12, 07:44 AM
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Hi, Mike - thanks for responding. Let me try to answer your questions...

> What is the average ambiant tempurature?

Here in NW Ohio, we've had 100 degree days, but the last week or so, it's been mid-80's. 65-72-ish at night.

> When your system is running, is it running constantly (non-stop)?

Well, right now, when I've waited that hour or so, the temp in the house on the thermostat is 75 degrees or so. I have the target temp set low, so that it /will/ keep running constantly. It's never gone below 72 though (in my testing) since warm air starts issuing from the registers before then.

> Do you have your t-stat set to a constant temperature or have it set to rise and fall according to a schedule?

Constant - to keep the thing running, so I can detect when it stops cooling.

> Have you done any of your testing during the night?

Hmmm. No.

> Not knowing your local weather patterns, it sounds like the "pro" could be partly correct. Dry ground would transmit heat from your loop less efficently then it would wet.

I get your point about dry ground vs wet.

What I have trouble understanding is that the solid ground could be a store of coolness (55 degrees is fantastic!)... Then, 'poof', it's out of energy, cannot supply any more cooling. Then, an hour or even 30 minutes later, it's wonderfully cool again - just like that? And it lasts another couple of hours? Maybe a cup of water in a microwave could see its temps rise and fall that quickly, but hundreds of feet of ground loop outside my house?

The system is running now, and the moment it runs warm/hot, I'll turn it off, and turn it on 5 minutes later. If it's immediately 55 degrees again, then I hope that would completely prove that it can't be the ground loop. That it must be something inside the furnace/AC unit.

It may not be right to expect it, but I can only use common sense....

> Unless the weather you having is really out of the ordinary for your area, I would say that the system should have been designed to compensate for this.

I agree. I don't think it's the weather, or 'how dry the ground is'.


/Bill
 
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Old 07-30-12, 08:25 AM
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Not sure how much ground source heat pumps knowledge is on here, but it sounds like something much more simple than dry ground. Simple as in the system itself is doing something at the 2 hr mark. Like a reversing valve (?) is switching.

Basically....all you have is a heat pump that uses liquid in tubes in the ground instead of the surrounding air to remove the heat. If it were warm dry ground causing the issue...I would think the temps would slowly rise....not just immediately start after a certain time. Like boiling a pot of water.....it doesn't just sit their absorbing heat and then suddenly shoot up to 212.
 
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Old 07-30-12, 08:27 AM
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Update. It started blowing warm air again. I turned off at tstat, waited FIVE minutes, turned on, and it's 55 degrees again. It must be something in the control of the flow through the ground loop. I can't see how it can be anything else. It can't go from hot to cold (in the ground) in 5 minutes, can it?

Was hoping for affirmation here, but I think now I need to find a local 'geothermal pro'. I wonder if there are certifications or licenses that I could check......

Thanks for the responses so far. Any other thoughts or ideas would be most welcome.

/Bill
 
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Old 07-30-12, 08:51 AM
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I'd call the manufacturer of the equipment and see what they can provide in the way of certified installers/techs in your area.
 
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Old 07-30-12, 09:22 AM
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The systems that I have seen, including my daughter's, have the thermal loop buried more like 100' feet deep, not 6' - 12'. If that's true, it would be my first concern.

What you describe sounds more like the recirculating pump starting - running - stopping - and then restarting. Either the motor is overheating or something is teling the pump to stop.

You do need to get a pro for this.
 
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Old 07-30-12, 09:28 AM
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Not an expert but it's my understanding that there are 2 types of geo thermo units, one uses deep "wells" and the other uses a grid system of loops that are a little lower than the frost line. The latter can be installed with a backhoe and is likely cheaper to install - but it does take up more ground.
 
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Old 07-30-12, 09:41 AM
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Yep - our loop runs 100 feet our or maybe thrice that along the perimeter of the yard. "Horizontal" I think is the term. It's definitely not pump & dump (neat term, that!).

I'm calling someone. I'll follow up here - thanks for all your thoughts!

/Bill
 
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Old 07-30-12, 03:17 PM
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Ok, I am a GEO expert. When it stops producing cold air you need to check that the fan is running, the pump(s) is/are running, that the compressor is operating. If you call a PRO, then let it act up and then DO NOT TOUCH ANYTHING and when the tech gets there explain to him that if you cycle the system it will start operating again so that he/she does not cycle the system and call it fixed. The Tech will need to verify the refrigerant pressures along with the loop pressure and pump and fan operation.
 
 

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