Geothermal from an existing well?
I’ve got a well to my house that will produce 20 gallons per minute or so it said on the original report when the well was drilled. Due to the fact that the well had a very high iron content we eventually stopped using it and instead hooked up to the municipal water supply. We still use the well water for outdoor gardening etc.
With the price of heating oil only going up, how feasible is it to use this well water for a geothermal system. Assuming the water comes out at about 55 degrees F (I’ve never measured it with a thermometer), is 20 gallons/minute enough to heat a 2000 square foot house in coastal Rhode Island?
Also, the cost of electricity is very high here. If I were to actually do this, would I be trading a high oil bill for a high electric bill? How much electricity does it take to run these geothermal systems?
I’m just brainstorming here. Looking for some opinions.
Thanks for your reply.
Edited 5/21/2009 12:48 pm ET by fingers
Replies
The options include pumping water, on demand, through a GSHP (ground source heat pump) and dumping or pump and store to use for non-potable needs.
Dumping the "used" groundwater on the surface (to dayllight) or back in the ground - legal/envirnomental and other issues apply here.
A 5 ton WSHP will use in the range of 14.5 gpm (9.4 to 17.4 is the data Trane publishes). At 55 degree water supply tempearture, it will provide 77.2 MBH (77,200 btu/hr) of cooling (at a EER of 17.0) and just over 66 mbh of heating using 4.86 kW of power. That's just over 20 amps with 240 volt single phase power. (The equivalent heat output from this amount of electricity as resistence heating is 16.5 MBH
You would have to add the energy required to pump ground water through the unit (1 hp = 0.75 kW). IF you can deal with the used water in a responsible fashion, GSHPs can seldom be matched for $/BTU in either heating or cooling. But that's a big IF.
Cost per gallon of oil in your area? Cost per kWh of electricity. Thermal efficiency of your burner? Simple numbers to crunch.
2000 sf well insulated (at 32.5 btuh/sf)? one 5 ton work work, but might be marginal.
BTW, the industry standard term is" water source" or "ground source "heat pump. "Geothermal" technically applies, but used only by laymen.
Time to start reading -
http://www.duanesworld.net/duanesworld.net.geothermal.htm
http://www.consumerenergycenter.org/home/heating_cooling/geothermal.html
The second site states that geothermal is 70% efficient because you are always heating or cooling from 55* rather than 90* and 20*.
Both site refer you to the tax credit and rebate programs available.
Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
The second site states that geothermal is 70% efficient because you are always heating or cooling from 55* rather than 90* and 20*."I did not see where they mentioned that.Maybe this is what you where thinking of."Studies show that approximately 70 percent of the energy used in a geothermal heat pump system is renewable energy from the ground. The earth's constant temperature is what makes geothermal heat pumps one of the most efficient, comfortable, and quiet heating and cooling technologies available today. While they may be more costly to install initially than regular heat pumps, they can produce markedly lower energy bills - 30 percent to 40 percent lower, according to estimates from the U.S. Environmental Protection Agency, who now includes geothermal heat pumps in the types of products rated in the EnergyStar¯ program. Because they are mechanically simple and outside parts of the system are below ground and protected from the weather, maintenance costs are often lower as well."But 70% eff does not make any sense. There can be several different ways to define efficiency, but for heating equipement way that it is usually listed is the ratio of useful energy (heat) out of the system divided by the paid energy put into the systems (gas, electricity, oil, etc).And a heat pump would be several several hundred percent..
William the Geezer, the sequel to Billy the Kid - Shoe
That is to what I was referring. Thank you for correcting me. Poor choice of words as my description.Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
If you have a pond or a stream to dump the water to legally, you are in business.
Designed my own system and built own evaporator, used new copeland scroll compressor and a condensor from a scrapped 7-1/2 ton Carrier.
I use about 10 GPM, inlet is 56F , COP measured is 5.6 not counting air blower and water pumping, which drops cop to around 5.
If you can accomplish the water discharge, e-mail me and I'll send you a bunch of details.
If you have a pond or a stream to dump the water to legally, you are in business.
There's been no processing of the water other than heat removed or added, correct? Could it be put back in the well? I understand that might drop the efficiency some, but by enough to not do it?http://www.quittintime.com/ View Image
"Can it be put back in the well?"
That depends on where you are and who you ask. The answer is usually NO. There is a reason most of these are closed systems. That is all that some states allow. If you can and do return to the well, the well will most likely approach freezing in the winter and will get quite warm in the summer. The degree to which that happens is complex, but has mostly to do with subsurface geology and water table stability.
My folks put one in their house 28 years ago - they drilled 2 wells, one for the return water, far from the source well. No problems with the water in that time (many problems with the heat pumps, but it's been an evolving technology and the new one works fine). Results are in line with the earlier post in terms of efficiency.
No idea if it would be legal today to return this 'processed' water back to the aquifer, but it seems pretty safe (although I guess contamination is possible and would be a disaster).
Ideally, it is safe. Regulations, practical or not, seldom count ideal as usual. In the past, the practical nature of the process would have garnered acceptance. In today's environment, over cautious regulations rule.
Personally, my experience is only with closed loop systems.
A standing column well (SCW) based GSHP that approaches freezing in winter is poorly designed. A properly designed system will have sufficient depth for water temperature recovery that allows sustained heat extraction without depressing the well water temperature severely. Often there is provision for a 10% "bleed" of water (not returned to the well) to promote recovery in extreme conditions.The SCW design does work very well in many areas, but success does depend on the expertise and experience of the designer and installer, water quality, and other things. One cannot generalize. Success is situation-dependent.
I agree. Just raising the concern, given that this is not a "designed"system, poorly or otherwise.
If you are serious about use of the well in a GSHP configuration, ultimately you ought to get an experienced designer involved. It's good that you are exploring the alternative ways it might be done, so that you can eliminate some of them from further consideration or at least understand their limitations.
The first thing you need for any kind of heating system design, particularly for a GSHP system, is the design heat load for the house. For that you need to do a detailed ASHRAE manual J or equivalent calculation. The designer could do this for you, but you ought to at least rough it out yourself both to know what is feasible and what the expected operating costs of the new system would be, and to cross-check the designer's numbers. No "rules of thumb" like "tons per 500 sqft of space" will cut it.
To consider the existing well for SCW use, the first thing you'll need to know to give to the designer are the specifics on the well. What is the depth of the well, what is the depth of the overburden over bedrock, and what is the static level of water in the well? For rough purposes, SCW design needs around 80 feet of water column in rock per ton of heat load, to allow the water returned to the top of the water column time to recover temperature as it drops slowly back down to the pump level.
If you haven't got the water depth needed to support the house heat demand, then the SCW design is eliminated from further consideration unless you want to drill it deeper. For a house of "ordinary" construction (leaky, heat sieve), that could be a lot of drilling ($$). Then you have to consider pump & dump, and if there is no place for dumping some serious water flow then your chances for using that well don't look very good.
Thanks guys for all the information. I guess I'll have to start reading up on this just to learn how to talk intelligently with people who do this for a living.