Virginia Geothermal Cooling struggling to maintain when temperature is over 90 and humid.

Hello. I’m bought a home with Geothermal Unit . It was a Waterfurnace Premier 2 that was heating and cooling 1700 square feet. The unit was 21 years old and was tripping the high pressure light when temperatures were over 90F outside and humid.

My set point was 72F and when things would heat up Temp would go to around 75F in house and it would trip the high pressure error light and shut down. I was constantly having to reset the circuit breaker just to get unit to kick in again. I was having to reset the breaker three to four times per day.

I decided that it was a good time to replace the unit. I put in another Waterfurnace Series 3 , 3 ton unit. It seems to work ok but it is not able to maintain a 72F degrees set point. It can climb as high as 78F before cooling down at night. Then around 1:00am it eventually cools back down to the set point of 72F

My question is . Is this normal with Geothermal cooling? Should I expect that in very hot and humid weather that the house temperature will raise to 78F or higher with a 72F set point. Should I raise the set point to 78F and consider this how the system works? Or is there a problem with the system. Any advise is appreciated.

 

No. A properly sized and functioning Geothermal system can easily cool to 72F.

Yes, if your system is slightly undersized for your specific conditions or is not functioning to specification.

That should be determined by calculating HR in cooling (Heat of Rejection in BTUH)=(LWT-EWT)xGPMx485 and compared to the Unit Capacity Chart under given conditions. Within 10% difference is acceptable, mostly due to measurement errors and rounding.

 

Thanks for the info.

The High Pressure indicator (two flashing red lights) on the new unit is triggered and I have to reset the breaker to get the cooling functioning again. The lines were purged prior to unit being installed. The loop pumps seem to get quite hot during operation . I’ll be calling the installer tomorrow. Any questions that I should ask them about?

The new unit is operating no better than the older unit. I’m hoping this isn’t a major ground loop issue. Any ideas?

 

High Pressure faults in cooling are most commonly indicative of inadequate water flow. This causes refrigerant pressures and temperatures to rise above operating limits as the HP system can not reject enough heat to the loop field.
Most common causes-
-Air bound or obstructed or leaking loop
-Failed or under sized pump(s)

Installer should be able to confirm quickly-
-If pump(s) are powered and running or if there is any obvious air gurgling sounds.
-If the loop pressure is "flat" on a pressurized system.

The pressure drop across the water coax coil should be measured and compared to unit charts. This will tell how many GPMs are flowing and should be compared to recommended flow rates for your unit.
If that all checks OK. The EWT and LWT should be checked while running at full capacity to make sure the loop temperatures are within operating limits.

 

Tech checked and found one of the loop pumps was defective. The system was purged and pump replaced. After that the system appears to work better. Setting at 72F on a 95F and humid day the system runs pretty much until the temp goes down at night. It maintains a temp of about 74F through the day then cools back down to 72F at night. I’m guessing the loops are probably not quite up to par.

Outside temps have cooled down and system has no problems. When it gets really hot and humid again I will try a higher set point like 75F to 78F and see if it will maintain that temperature. Thanks for the advise.