Geothermal heating/cooling question

[Z-Michigan]

Again, I want to thank people for all the replies and info.

We decided to have a tech come out yesterday. The place that installed it has changed ownership, but is still basically around. Unfortunately they don't have complete records of our install, particularly our ground loop location.

The unit is a Carrier and is rated (I'm told) at 3 tons 350lbs. Not sure if that means 6350lbs capacity or if the two numbers are separate for a reason. Anyway, the owner and the tech of the service company both assured us the unit was more than big enough for our house, and that although the ground would heat up in late summer we should still have adequate cooling.

The tech came out and diagnosed a defective thermistor (temp sensor, I think) on the ground loop. It was apparently indicating a negative temp for the ground loop fluid. He replaced it and the loop is apparently at 77F, which seems a bit warm. However, the system immediately started working well again. It took about 12 hours to cool our house down from an extremely humid 82 to a dry 72, but it's now very pleasant.

The tech also noted that the ground loop is losing pressure and he thinks there may be a leak in the buried portion of it. Uh oh! Can this be fixed with a sealant or will this mean digging up the whole loop at some point? Also, what type of fluid is in that loop - anything harmful?

 

[dooleysm]

Yikes, a leak in the ground loop doesn't sound like fun, especially if they don't know where it's buried.

I've been trying to come up with the liquid in that loop but I just can't remember it. I don't think you'd want to drink it, but I doubt if enough is leaking out to poison your land, especially at 6 feet down or however deep yours is.

 

[techman]

If you have a very small, slow leak, it would indicate a very small hole. There is a product called "loop conditioner" that is normally used on the initial install. This will fill small leaks, as a radiator leak stop would. It basically solidifies at the leak point.

I would not necessarily jump to the conclusion that there is a leak. The loop pressure normally drops during cooling season and rises during heating. Your loop may have been a bit low on the fill pressure and is just lower now. If you have at least 10 PSI or so (static) you should be fine. You can put a bit more pressure in, up to 20-25 PSI, which should get you up to about 50 PSI in the peak heating season.

As for your loop temp, that is not that unusual for this time of year. Depending on the loop depth, type of soil, amount of rain, etc you will see a warming like you have. Normal ground temp rise in the summer for depths under 15 feet is about 15 degrees. This gets you to about 70 degrees. Additional increases are due to the relatively poor heat flow in soil (about 1 deg/BTU/foot of pipe) and the need to have a "delta" in the temperature from the loop to the ground to get the heat to flow into the ground.

paul

 

[KYErik]

I believe that I saw the installers of my system mixing methanol with the water as they filled the loop on my system.

 

[techman]

I believe that I saw the installers of my system mixing methanol with the water as they filled the loop on my system.

Methanol is an antifreeze for winter operation. The loop conditioner compound is a separate liquid that would be added (about 6-8 oz total). You can check it out at: Geo-Loop Conditioner - Fixes Geothermal System Leaks

paul