I have a Waterfurnace Envision NDV049 (4-ton) system on two (2) 350' vertical wells. System never goes beyond Stage 1 cooling, which has a heat of extraction of about 20,000 btuh. Delta T across the exchanger is steady at 3.3F, so flow back-calculates to 12 gpm, which is reasonable. So the system works great is sized correctly for the load, etc. My concern is with the health of the loop. The loop temp was entering at 45F on 12/17 (5 weeks ago), but the season has been long and the system has been running quite a lot. Loop temp was 40F last week and 37F today - with 6 weeks or so more of cold weather on the season. My feeling is that if the EWT must go below 30F, then the ground loop is not transferring heat to the loop fast enough. The system will continue to function down to 20F with sufficient flow (>11gpm), but the "normal" operating range is published as 30-70 for heating. Please give me your thoughts.
It looks like MD is in the midst of a cold snap, and most of January has been colder than average. Winter weather tends to ease in Feb as days begin lengthening No promises, but I'll bet you end the season with EWT at or above 30
Remember that systems are designed on a 20 year weather average so EWT's may occasionally dip below design points, but you will notice a real leveling off once we get EWT around freezing. J
Fair enough. This is my first full heating season (and a pretty cold on at that) so I am just getting a feel for how the loop responds to the load. You think the temps will stabilize once the ground has to freeze with LWTs below 32F? Also, is it fair to assume that the field will restore to nominal over the summer without needing to add heat through AC?
Yes if unit is not running ground will slowly recover. Running A/C artificially elevates ground temp. and gives you higher early season heating EWT's. Joe
FWIW, the loop temp has recovered and is now providing 40-41F EWT. Temp are now more normal for the area 35 day and 25 night. I also installed RTDs attached to a data logger, so will be able to track run hours and loop temp short term and seasonally. This should allow a much better understanding of the loop dynamics, but as things stand now, I feel very positive about the ability of the installed loop to deal with long, cold winters. Looks like a great system - properly sized and performing well. the heat is great, BTW and the unit is quiet. I have this connected to a Dri-Steam steam generator-type humidifier that is also awesome.
You may even notice EWT differences throughout the day. For example, late afternoon EWT's (when the geothermal system may not run very much) may be different from mid morning EWT's (immediately after a long period of geothermal system run time.)
My experience with first winter loops is about the same (I'm in central Washington with horizontal closed loops (about 5500ft) feeding a 5 ton Climatemaster 27 and a 4800sq ft house) My loops dropped fairly quickly with an unseasonable cold snap we had down to 34dF LWT and I assumed were going to KEEP dropping through the rest of the heating season which also made me nervous. However, now, 4 weeks later the LWT is back up to 38dF on a typical sunny day with good house heating via passive solar. I'm MORE interested to see what next winter will bring once I have continued ground compaction and some heat storage from the summer (if that in fact happens)
