Delta T decreasing in a few hours

Balakay

I have an open loop Bard geothermal unit that is about 16 years old and acting up. I wonder if anyone has seen symptoms like this and has suggestions. With an indoor temperature of 65°, it will blow air at 90° (Delta T of 25°) for about an hour. Then it starts to drop from 90° to 85, 80, 75, 70, then shuts the compressor down. This takes about 2 to 3 hours. Then to reset it, I have to shut the power off for an hour or so. I had a technician come and they didn't find any codes. I have 6gpm water flow, which is recommended. Water flow is still good when it starts losing temp, so no frozen lines. Airflow feels OK. Any thoughts on what might cause these symptoms?

Larry Weingarten

Hi, I'm not a geothermal guy, but am wondering if you have temperature gauges on the fluid going to and from the geo loop. I've heard of poor heat transfer in the field causing the fluid to go colder than it should. That sorta fits with your description.

Yours, Larry

Jamie Hall

You really do need to know what the temperatures going to and from the field are, as well as being sure what the actual flow is (how are you measuring that 6 gpm?) You can calculate the actual BTUh being extracted from the ground that way (same old equation!). I wouldn't be at all surprised, depending on how the field was installed in the first place, to find your heat transfer from the field had degraded.

And by open loop, by the way, do you mean you are extracting ground water and reinjecting it somewhere else, or dumping it? Then I would be even less surprised if performance dropped over time... some very interesting things happen to wells, both in the immediate area of the well and over a surprisingly wide radius, if they are pumped continuously or nearly so for long periods of time.

ratio

The only open-loop geo system I've worked on would plug the inlet screen on a regular basis. How confident of that 6 GPM are you?

hot_rod

The coaxiel HX that the open loop pumps across may be limed up. Very common on open loop systemsBard has a procedure for cleaning the coil

https://techdoc.bardhvac.com:8443/digcat/S3364_TechDoc_CD/TechDoc-PDF/2100-738.pdf