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Geothermal Closed Loop System


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HVAC Gurus,

I did an inspection yesterday where the client had a gas fired split-system with a closed loop Geothermal Water Furnace. It was an odd set-up because the gas furnace was in the attic and the Geothermal unit was in the basement.

Anyways, the water lines (closed loop) from the ground were icing up. To be honest, I'm not that familiar with these units. The owner swore that the tech said that it was normal.

However, it seemed odd to me. Should there be ice on these lines?

Thanks,

Kevin

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If the glycol and water mixture is wrong and the closed loop (in & out feeds) are icing, does that mean that the system is not producing any heat?

Also, would the controls indicate that the supplemental furnace is actually heating the house?

I have seen just one of these systems and had trouble understanding how the system monitored itself. Any information would be appreciated.

Thanks,

Jeff Beck

Foresight Home Inspection

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Originally posted by energy star

Water mixture is wrong or refrigerant charge is incorrect. Did the same contractor do the loop and the unit? Needs to look at the water mixture.

Originally posted by Chad Fabry

Could you explain that please?

Originally posted by energy star

Explain it? Sure. Water will freeze at 32. If they are extracting all the heat from the water so the temp drops below, they need to have Glycol or (like anti freeze) to keep the water from freezing when it gets below 32.

OK, but the ice in the pic is on the outside of the pipe....I don't see the connection between that and the mixture being "wrong".

Originally posted by RichNSpect

HVAC Gurus,

I did an inspection yesterday where the client had a gas fired split-system with a closed loop Geothermal Water Furnace. It was an odd set-up because the gas furnace was in the attic and the Geothermal unit was in the basement.

Anyways, the water lines (closed loop) from the ground were icing up. To be honest, I'm not that familiar with these units. The owner swore that the tech said that it was normal.

However, it seemed odd to me. Should there be ice on these lines?

Thanks,

Kevin

I'm not an expert on geothermal (more accurately, ground-source heat pump) HVAC systems but I know enough to take a stab at your question.

The unit in your pic contains the compressor and water-refrigerant heat exchanger of a split system. The AHU is somewhere off your picture, probably in the attic with the gas furnace. The top two lines coming out of the unit are for a heat assist loop for the hot water system. The bottom two lines are for the ground loop. The lines in the center are the hi/lo pressure refrigerant lines heading to the AHU.

Since this unit is located in the basement and not outdoors, ice on the outside of the lines means that the temperature of the fluid inside the lines has fallen below 32 degrees F. Some ground-source heat pump systems are designed for ground loop low temps above 32 and others for temps below.

If the system is designed to operate with a low temp above 32, then ice on either of the ground loop lines is a symptom of a problem.

If the system is designed to operate with a low temp below 32, the loop will have some antifreeze in it (as noted by energy star), and ice on the ground loop return line is to be expected. You can control it by putting insulation on the outside of the pipe where it is exposed to the humidity in the air.

Both of the ground loop lines in your pic have ice on them. Ice on the ground loop supply line (regardless of the low temp design value for the loop) is a problem. The supply line should be a fairly constant temp around 50-55 degrees, year-round. It shouldn't have ice on it. Ice on both lines means the temp of the entire ground loop has dropped below 32 degrees.

If you are getting ice on lines that should not ice up, it means that the ground loop cannot supply enough heat to keep up with the demand created by the equipment that is extracting the heat from it. The causes of that problem could be many: the ground loop could be too short, the ground loop could be too shallow below grade, there could be air or a blockage in the ground loop line, pump problems, incorrect refrigerant charge or valve problems in the compressor loop of the heat pump, etc. If the problem is not corrected the ground loop can freeze.

Digging up the loop can be an expensive repair....

Brandon

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OK, but the ice in the pic is on the outside of the pipe....I don't see the connection between that and the mixture being "wrong".

I admit my question was loaded. I didn't want the discussion to end at "the water mixture was wrong" and I didn't have time to type a response. Thanks Brandon.

Btw, how's the hand?

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Originally posted by Brandon Chew

Originally posted by energy star

Water mixture is wrong or refrigerant charge is incorrect. Did the same contractor do the loop and the unit? Needs to look at the water mixture.

Originally posted by Chad Fabry

Could you explain that please?

Originally posted by energy star

Explain it? Sure. Water will freeze at 32. If they are extracting all the heat from the water so the temp drops below, they need to have Glycol or (like anti freeze) to keep the water from freezing when it gets below 32.

OK, but the ice in the pic is on the outside of the pipe....I don't see the connection between that and the mixture being "wrong".

Originally posted by RichNSpect

HVAC Gurus,

I did an inspection yesterday where the client had a gas fired split-system with a closed loop Geothermal Water Furnace. It was an odd set-up because the gas furnace was in the attic and the Geothermal unit was in the basement.

Anyways, the water lines (closed loop) from the ground were icing up. To be honest, I'm not that familiar with these units. The owner swore that the tech said that it was normal.

However, it seemed odd to me. Should there be ice on these lines?

Thanks,

Kevin

I'm not an expert on geothermal (more accurately, ground-source heat pump) HVAC systems but I know enough to take a stab at your question.

The unit in your pic contains the compressor and water-refrigerant heat exchanger of a split system. The AHU is somewhere off your picture, probably in the attic with the gas furnace. The top two lines coming out of the unit are for a heat assist loop for the hot water system. The bottom two lines are for the ground loop. The lines in the center are the hi/lo pressure refrigerant lines heading to the AHU.

Since this unit is located in the basement and not outdoors, ice on the outside of the lines means that the temperature of the fluid inside the lines has fallen below 32 degrees F. Some ground-source heat pump systems are designed for ground loop low temps above 32 and others for temps below.

If the system is designed to operate with a low temp above 32, then ice on either of the ground loop lines is a symptom of a problem.

If the system is designed to operate with a low temp below 32, the loop will have some antifreeze in it (as noted by energy star), and ice on the ground loop return line is to be expected. You can control it by putting insulation on the outside of the pipe where it is exposed to the humidity in the air.

Both of the ground loop lines in your pic have ice on them. Ice on the ground loop supply line (regardless of the low temp design value for the loop) is a problem. The supply line should be a fairly constant temp around 50-55 degrees, year-round. It shouldn't have ice on it. Ice on both lines means the temp of the entire ground loop has dropped below 32 degrees.

If you are getting ice on lines that should not ice up, it means that the ground loop cannot supply enough heat to keep up with the demand created by the equipment that is extracting the heat from it. The causes of that problem could be many: the ground loop could be too short, the ground loop could be too shallow below grade, there could be air or a blockage in the ground loop line, pump problems, incorrect refrigerant charge or valve problems in the compressor loop of the heat pump, etc. If the problem is not corrected the ground loop can freeze.

Digging up the loop can be an expensive repair....

Brandon

Brandon,

I think you know more than you think you know :)

Thank you for this response. It was very helpful.

Yes, the furnace for this system was in the attic. The entire house was very drafty, so I was called out to conduct an ITI Energy Survey. While scanning the basement, I noticed that the ground loop lines were iced up. I told my client that I didn't know much about these systems, but ice on both of the lines seemed odd to me.

I'm going to call my client and see if I can explain this to him, so he can have a good grasp of what is going on.

I got some pretty cool images from this particular house. The second floor and attic were extremely warm due to an absurd amount of energy loss (poor insulation, leaking ducts, open chases in attic, etc.).

Again, thanks for the response.

Kevin

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Wow thats a nice pic of the gable end of the house. Look at that loss! Does it have a Gable vent? You can see a perfect outline of the scissor trusses..

You also have a de-super heater on that Geo system, nice. Also you need to check the flow rate at the equipment. It may need to be balanced (water balanced) rate. You can see on the valve or rather the water connection to the unit that the connection body has two access ports where you stick a water pressure meter. All this data will assist in proper set-up.

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