I have a 4T Water Furnace with 3 200' loops. Almost immediately after starting the system the EWT was well over 90 degrees. I have seent it as high as 111. There is generally only 5-6 degrees difference between EWT and LWT. The installer says that this is due to higher temps in KY. He also thought that maybe the fill in the loops hadn't settled yet. That seems likely to be true, but it seems unlikely that if it got blocked near the top it will ever settle. Would it be worth getting water down to the rock around the bore holes to try to help, or improve heat transfer? Other suggestions would be appreciated. Ken
hi and welcome, There are a couple of possibilities. Is it new construction? We often see eleveted ewt during the closing of the construction process if the geo was turned on. Have you verified flow rates at machine? A six degree differance sounds good in relation to machine. Now the settling issue in borehole. If the bore was predominantly in rock and care was not taken during backfill or grouting(prefered) your loops could have very little contact with the ground. Imagine a straw in an empty test tube, little or no contact. In rock bores I would say that grout is more critical to the operation of your system performance than anything else. Without it you have no thermal link unless your bores filled with water from the ground naturally.
knelson4, Our units are rated for entering water temperatures between 20 and 120 degrees. We do not disagree with what your contractor has said. Unfortunately, additional information would be needed to determine if there is an issue with your loop temperatures. We will be more than happy to contact your contractor to discuss this issue if you would like.
While WFs can take EWT of 120, efficiency is greatly degraded and the resulting very high refrigerant pressures and compressor currents are hard on system internals. Capacity takes a substantial hit as well. IMO a properly designed vertical loop field should deliver EWT of about 20 above deep ground temp in summer and about 20 below deep ground temp in winter. Assuming for arguments sake 60* deep ground temp in KY I'd like to see EWT no higher than 80-85 in summer nor lower than 35-40 in winter. If these bores are piped in parallel it may be that one or two are airlocked and not participating in heat exchange. Was the system properly flushed? A contraption (aka "flush cart") consisting of a big pump (1-2 HP) and a barrel or piece of big pipe (8-16") on a hand truck is needed for this. Do you remember such a thing being used? If just one or two bores are operating that could explain both high EWT and moderate delta-T If the loops are piped in series, then it may well be a pipe to ground contact problem - that could be a real bear to resolve. Water might help (It does often help reconsolidate horizontal trenches) but I wouldn't bet on it helping much with vertical bores. Keep us advised...
Thanks for the suggestions. The installer suspects a loop might not be flowing correctly. Since the connections are all buried (instead of coming into a manifold) he will need to uncover them to check temps. He claims that the University of KY tested heat transfer with bore holes filled with the limestone shavings and it was actually better than grout. I turned the system off for about 6 hours, and then started both zones. After about 5 minutes, EWT was 78. After 2 hours, it was 103.
Cudos to the installer going straight to checking temps to determine loop performance. I also would like to see the data for dumping limestone cuttings down the hole being better than pressure grout from the bottom up?
Update on new geo system First comment.... the installer didn't do the temp measurements, and said I was the only customer of his to do it. An inexpensive infra red thermometer is easy and accurate. During the summer the temp went up from the average deep soil temp that should have been 56 degrees to over 100. The installer agreed to drill another well for a 4th loop. I did notice what I'm fairly sure is a problem, but the tech didn't seem concerned. I'll need to discuss it more. The 3rd loop had two elbows at the top which would allow the water to simply return to the house without going through the pipe. There was no temp difference in the two lines. The 4th loop was connected between the 1st and 2nd, and instead of having the two elbows simply went down the hole then back out and back to the house. I checked temps and saw a difference of about 7 degrees in the supply / return lines. We're into heating season now, and there was very little heat accumulated. After being gone for two weeks with the thermostat set at 55, the unit ran for more than 3 hours to warm the house. Input temp started at 56, and got down to 45. In the last 2 weeks we have had two nights of 10 degrees and highs in mid-20's. Coldest input temp I've seen is 46. In addition to the extra loop, I ran a water line to each of 3 of the holes. I trickle water regularly in an attempt to soak the holes, and maybe settle / compact the shavings. (If they do settle, there will be a void that also won't transfer heat -- I still believe grout would have been the right choice) Whether from the 4th (or 3rd functional) loop or water to help heat transfer, the system does seem to be holding appropriate temps now.
Wow! The installer didn't check loop water temperatures!?! If true he / she is completely derelict! Maybe he / she did check, found them marginal and hoped you wouldn't notice... I'm with Dewayne - show us the shavings study! 46 EWT is quite good for winter operation, but I wouldn't expect that to hold until March.
Does any installer actually monitor temps for the first few days or weeks of operation? Just checking the temp at startup wouldn't have shown anything useful, and even a couple of hours probably wouldn't have helped. My installer did agree that mid to upper 80's was about as much as expected, and that there was a problem. I'll ask if he knows how to get a copy of the study.
Few days On startup, we generally take an informal set of readings to make sure all looks well. After running for a few days, we return and take our "initial" readings. That will likely change as we're planning on using the WEL on all our new systems.
Temp readings during start-up are how we discovered poorly flushed vertical loops recently. It would be nice to see a sketch of loops as described. I'm suprised you didn't cycle on high temp limit if only 400' of loops were in play. I think it is folly to rely on an "inexpensive infrared thermometer". You need a probe type thermometer in good contact with piping or brine. joe
No way I'd fail to return to check temps after system has had a chance to stretch its legs. Ideally check it under conditions of high load. IR thermo might be OK for assessing temperature difference between in and out lines, but a needle probe thermometer is the right way to do business. Use the same thermometer for both readings. I sure hope OP didn't have to pay for the bypassed loop!
