With a modern HP, the efficiency difference between open- and closed-loop is quite small. For example, with WF's Envision NDV038, open-loop has only a 5% advantage in BTU/kWh (low speed operation, 4 GPM @ 50°F open-loop, versus 8 GPM @ 40°F closed-loop). In my case (Philly 'burbs), open-loop would save about 60 kWh per month, during the coldest 2-3 months. At $0.07/kWh, that's less than $15/year -- not including the difference in maintenance costs. ...you pay for what you get, Looby
Wouldn't open loop in philly run closer to 55? Are you seeing 40 in closed loop? I'd SWAG about a 20 F delta between closed and open loop, which would result in a bit more COP difference
I would love to humor you and go get the numbers off my closed loop this morning, but..... There is a five foot drift against the side of the house, blocking access to my mechanical space. :shock: I am just not that motivated. :roll:
Eric, heck you probably would get 40F if you just laid the pipe on the ground, snow must be a rare treat for you southern folks! Seems like people are always talking about frost on their pipes and temps from 26-30F, closed loop of course, hard to believe it works as well as it does at those temps.
For the penninsula this is the worst winter storm in known recorded history! OMG The Temps in the loops are all relative, 30-25 degrees is a heatwave if your outdoor temp is single digit or worse.
So, if I'm reading the posts correctly here, we should not be afraid of open loop if our contractor and well/water table person tell us it would be a viable option. We'd just want to make sure, as we choose a contractor, that they have plenty of experience installing both. Does that sum it up? And thanks again!
Ultimate Summation Get system designed locally Have design installed by local guy providing garrauntee Local experience and success of various methods of GSHX in your area trumps everything.
Around 52 or 53, but WF quotes HC, kW, COP, etc. at 10° intervals. Anyhoo, the point is that efficiency is only weakly dependent on EWT. Yep, about 40°F all winter. Actually, 38°F to 42°F -- depending on the heating load over the previous day or two. No need to SWAG the open-loop EWT -- it's entirely predictable based only on local long-term average temperature. OTOH, closed-loop EWT is a super-SWAG -- depending on geology, loop length, and heating load. But even assuming a 20°F advantage for open-loop (say, 55°F vs. 35°F), the difference in BTU/kWh interpolates to about 18%. In my case, that would be $50-ish per heating season. ...ymmv, Looby
I've put a call into them... thanks for the tip! I called close to their closing time, but asked the receptionist if they used geothermal. She said 'yes, but it isn't working now because of water quality issues...". Of course, I need to find out more details, and the museum is on the other side of the lake from us... So far, every contractor we've spoken with has advised us against open loop.
On this page: http://www.agiweb.org/geotimes//aug05/f ... ables.html I found this: "Although the system was fully operational when it was installed, it has since experienced some failures. “We are hoping to have additional well-design modifications that will bring the system back to full capacity,” Rigas-Gangi says. “It seems that a major problem is that the wells weren’t designed well for our local bedrock geology; and therefore the system may be fixed with special well-casing adjustments and some equipment replacement.”
In brief I own a open loop geo thermal heat pump. Here are the potential problems. One, water is never perfectly pure. This can cause eventual fouling of heat exchangers. How are you going to clean the heat exchanger and with what? Acid? Alkalies? brushes?, chemicals? I am already coming to the conclusion that it might be better to have a closed loop system which circulates a liquid which is initially pure, neutral, and doesn't change during 20 years of circulation. Think about it.
