Hello all - I've been dealing with issues with this system for many years. Mainly FP1 and E5 which I believe both are related to freeze protection when the EWTs get too low (i.e. below 15 deg f). During a recent checkup, the loop pressure was in the single digits around 7 PSI and do the tech pumped up. I know another tech increased the pressure from 27 to 38 PSI on a prior visit in January 2018. The average temperature is approximately 60-70 def f higher currently. Can this pressure loss be explained? Isn't this a closed system? I could see some variation dur to temperature differences, but this seems extreme and I'm wondering if this system might have a leak? Additionally, the EWT was in the mid-70s when the outside temperature is only in the upper 70s. These seems abnormal to me. I'd expect the EWTs to be closer to the 50s right now.
According to WF, the loop should be pressurized to 50-75 PSI in winter or 40-50 PSI in summer. When the piping gets cold in winter it contracts and the pressure rises. When the piping gets warm in summer the pressure drops. I don't think the pressure should have dropped from 38 to 7 PSI though. Your water temperature shouldn't be getting to 15 degrees. A properly sized loop would be designed large enough so that it never goes below 30 degrees. I read your old thread about the loop temperatures. I'm going to say I think your loop is likely undersized. Given your story, it sounds like the drillers had a plan and deviated from it once onsite, so it sounds unlikely the proper design work was done to properly size the loop. I punched some quick numbers into LoopLink, assuming Pittsburgh, PA, clay soil, heating load of 60,000, cooling load of 40,000, and 4T WF 7 Series. My assumptions may not match your house, but assuming those parameters, with four loops, each having three bores, LoopLink says you need about 100' depth for each bore to maintain EWT between 30F and 90F. That's 1,200' of loop in the ground versus your 760'. Note that the 100' depth recommendation is based on an "adjusted bore depth" needed in heating mode, to compensate for unbalanced heating and cooling loads.
Thanks for running that calc! The data the designer used was: DESIGN DATA Design Heating Load: 90,000 Btu/hr Design htg Temp Difference:68 deg f Design Cooling Load: 45,000 Btu/hr Design Clg Temp Difference: 17 deg f Hot Water Temp Setting: 120 deg f Hot Water Users: 4 Continuous Fan: No Internal Gains: 15,487 Btu/hr COMFORT CONDITIONS Heating Set Point: 70 deg f Cooling Set Point: 75 deg f Start Cooling Temperature: 75 deg f Weather Location: Harrisburg, PA ANNUAL LOAD Annual Heating Load: 117.7 Million Btu % of heating load: 98% Annual Cooling Load: 30.3 Million Btu Ann. Hot Water Load: 17.7 Million Btu GEO THERMAL LOOP SYSTEM Loop Type: Vertical 1 U-Bend 1.00” PE Soil Type: Average Rock Average Depth: 75.0 ft Trench/Bore: 595 ft Freeze Protection Min: 13.0 deg f Max Geo Extreme Temp: 90.2 deg f Average Clg Loop Temp: 71.7 deg f Average Htg Loop Temp: 39.4 deg f Min Geo Extreme Temp: 28.0 deg f Geo Temp Min-Max: 28.0-95.0 deg f Deep Earth Temp: 53.4 deg f Surface Swing: 22.4 deg f Ground Lag Time: 34 days Soil Conductivity: 1.4 Soil Diffusivity: 0.96
I assume this is the looplink you referred to? LoopLink (looplinkrlc.com) Looks like there is no cost to use the tool - maybe I'll run my numbers through it.
