I can offer a perspective on the geothermal set up.
Firstly: an air to air system is the cheapest to buy, but it is not the most cost-effective system over time, because the latent heat of the atmospheric air is lower than the latent heat of the earth-warmed water. It takes more electrical energy to get heat for the house out of the atmosphere than out of the earth, so it costs more for the heat captured.
Secondly: Geothermal energy from the earth is a constant, because the mean temperature of water from the ground is 44 degrees F One pound of water carries 1 Btu of heat per degree F. iI the intake water temp difference is 10 degrees warmer than the discharged water temp. The amount of captured heat you get is 100 BTU for every imperial gallon of water passing through the heat pump i. For a normally insulated (R20) home of 1500 sq ft you probably need 60,000 Btu's per hour, or 6000 gallons of water per hour. 10 imperial gallons of water per minute are required to get 6,000 btu per hour
All that the heat pump does is chill the intake water by ten degrees F and then it transfers the captured heat from that water into the house, usually from a radiator in the forced air circuit. 60,000 Btu/hr is the capacity rating of a 4 ton heat pump, give or take. To do this the heat pump uses a refrigeration compressor pump, usually electrically driven by 220 vac power running about 10 to 20 amps draw. That power requirement includes the energy for the forced air fan and the water pump needed to supply ground-temp water to the refrigeration coil from the well.
Thirdly, in hot weather the system reverses its function and passes 44 degree F cool ground temp water through the heat exchange radiator, where it cools the forced air that cools the house. This cooled air passes off air moisture as condensate to waste. This is a so called passive air-cconditioning system that requires only energy for pumping water and forcing air...virtually free AC..and it works very well.; I have just such a system in my home in chilly Canada. In 2002, heating oil was about $4.00 per imperial gallon and I used about a thousand gallons per winter
My total cost for my system all in was $14000, in 2003 CDN doillars, that cost included drilling and plumbing a 120 ft deep 6" dia. 14 GPH water well, a disposal well for the waste chilled water, and a 1 HP Jacuzzi three- stage submerged pump and all water lines made up of 200 feet of 1 1/2" 300 lb test irrigation hose and doubled SS clamps at every joint. It cost me $4000 (discount net)per year for fuel oil heat then, before the Geothermal system was installed, plus about 100 per month for electricity for all purposes. After the pump was set up, the total cost for energy per year was 2500 all in. At an est'd annual savings of about 4500 per year The payback period was 2.5 years
Fourthly, there are other savings from free hot water gained by the super heat removed from the refrigertion compressor heads by water circulation. This amount of heat would probable be worth about 400 per winter..there is no free hot water in the summer, since the refrigeration unit does not run then.
Fifthly, the air duct system is highly filtered air
benefits of geothermal, so no dust in the house, but I need to clean (wash) the air filter twice a year or more That filter is a 40x 40 " electrostatic type adjacent to the big radiator heat exchanger, about the size of a big truck radiator. My system has been in service for 12 years without any maintenance expense, so far, and has saved me about $45,000 - 11,000 or about 34,000 dollars. Quite a bargain, quite a convenience and free AC every hot sweltering summer day. The "passive" AC is very effective and will keep my house below 70 Deg F when the outside air temp is over 95 Deg F.
A couple of notes:
The system must be designed to avoid energy bottlenecks, IE..use BIG air ducts.. at least 20" x40" for the main duct, that means for both the supply air return and the warm air, plus 12 each of x 8" circular lateral ducts to the floor vents and floor vents of at least 40 " sq per duct outlet, at least one duct per room. I used a common return air duct (a big floor register) in the central hallway rather than place a full set of return air ducts in every room.
A water well of at least 12 Gal imperial measure per minute flow capacity and water supply piping of at least 1.5 inch ID..ditto for the discharge water piping to waste, a one hp well pump, and a lift of less than 35 feet to the refrigeration pump. My cold air return ducts are the same theorectical size as the warm air ducts. Since the lower end of the water discharge hose is lower than the intake end, it is a syphon and requires olny a small amount of pumping power to operate ( for friction losses) saving wear and tear and energy losses on the submersion water pump.
There is a lot of ductwork and it takes up a lot of space under the floor, but the capacity of the ducts is a critical system requirement..too little air throughput will overheat the refrigeration pump and fry the system. There is also the capacity of the waste water disposal system to consider. there is a lot of water used in the space of 24 hours in winter...14000 gallons per day. I used a 25 foot deep by 3 foot dia concrete casing down to bedrock with a lid for my spill return, and my ground is hard sand..no clay. It works very well. My supply well is drilled into an artesian spring that flows 30 gal per minute and raises to 4 feet from grade. That well also suppies my house water system. I am favored by having plentiful good water and very good drainage, all of which was proven before I designed my system. The well never goes dry nor becomes turbid.
That is just plain lucky. Artesian wells like that are not a dime a dozen. That well has aswved me $50,000 so far and counting
My heat pump is manufactured in New Brunswick, Canada by Maritime Geothermal to my sepcs It is a three ton refrigeration compressor with a four ton heat exchanger, occupying about a ten sq foot footprint and being about 6 feet high. It runs pretty quietly too. This particular system has a very high co-efficient of performance..about 3.9. There are none better to my knowledge. The owner of Maritime Geothermal is Glenn Kaye, P.Eng out of Pettitcodiac He is a world reknowned expert. and the only recognized CSA authority on heat pumps in Canada. (In plain English the system is 3.9 times as efficient as a unit that saves nothing benefit over cost to operate (Air to air heat pumps work at about 2.0 COP in warm to cool air and at less than 1 in very cold air (32 degree F) at best) These type sometimes do not require ducts, just conduit and refrigerant pipes. They can be had cheap, but do not last as long as a good geothermal system will because the compressors run too hot.
The proof of the pudding is in the system, its efficiency and longievity without failure. The market name for my heat pump is " NORDIC" so far, in service for 12 years no maintenance. I would say that is proof.
I can recommend it unreservedly, in Canada. It is probably available in the USA, but I do not know that.
All costs that I have stated are true, but I did a lot of the labor myself: supply and install all plumbing, wiring and ductwork. Supply and install the heatpump base, Supply and install the well and drain sump.. Those saved me about 5,000. There was no retail mark-up because my friend and I owned a Refigeration company and we bought the stuff wholesale saving perhaps 7,000. We have since retired and no longer operate the company
The retail cost of the system, if contractor built, in 2002 would have been about $25,000 plus 15% sales taxes. The payback period at that cost would have been about seven years, but still a viable and worthwhile idea.
The only downside: It cannot operate on standby power My genny is too small, so I still have a standby oil furnace for when the power is out.
its good here, but it ain't Shangri-La
It must be said that there are a number of different types of "geothermal" heat pump systems. My system is called an "open loop" system because the water comes directly from a well and goes directly back into the earth. There are "closed loop" systems which circulate glycol in pipes in the earth. Closed loop systems require a great deal of pipe and area in the ground so that the earth is not frozen by the chilled glycol in the return loop, or alternatively, a large number of drilled holes that carry glycol in pipes in a vertical grid. Closed loop systems are much more expensive to install and not as efficient. Not everyone has a good well, or a good drain, so that is the reason for closed loop systems. In such cases an examination of the various "air to air" systems (with backup electrical heat) should be examined and analyzed for cost savings. Many of those on the market are of dubious value. IMO
