Geothermal and FHW

Discussion in 'Homesteading Questions' started by Rodney Phillips, Dec 5, 2005.

  1. Rodney Phillips

    Rodney Phillips New Member

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    I have a 13 year old house (that I built and still have the blue prints to) that uses Forced Hot Water (FHW) baseboard heat off an oil burner.

    I have been looking into Geothermal for a while and am convinced to move in this direction. I currently go through about 600 gallons of oil and 6 cord of wood for a years worth of heat and hot water.

    However, I have seen very little regarding the use of Geothermal and FHW. The one comment I did see indicated that FHW requires the water to be much hotter than that which is normally produced with Geothermal. I am willing to retrofit to Forced Hot Air but am curious if anyone has run across the use of Geothermal with FHW.

    Thanks
     
  2. TnAndy

    TnAndy Well-Known Member Supporter

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    You haven't seen much because they are two entirely different types of systems.

    Geothermal is a heat pump, but instead of using air to exchange heat from, which when the air temp dips below freezing makes the extraction of heat less and less efficient, ground water is a nice 40-50 degrees year around.....perfect temps for a heat pump. A heat pump extracts heat from the medium ( be that air or water ) by boiling freon in a closed system, and condensing it again, releasing that heat into the air handler to be blown thru the ductwork. The temperature of that boiling freon allows for about 80-85 degree air off the condensor coil.

    50 degree water directly in a baseboard heater is useless. Even water cirulated over a condensor coil of freon would only get in the 80 degree range or so....to low for baseboard, which only starts to become effective with 120 water, and most are rated only at 140 and above.
     

  3. Gary in ohio

    Gary in ohio Well-Known Member Supporter

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    Andy is right. Two very different systems. You would have to run duct work and upgrade to a airflow driven heating system to use geothermal.

    You might be able to use some heat transfer device so you only have to heat the boiler water from the 50 ground temp instead of from street temp, but thermal losses might make that impractical.
     
  4. Rodney Phillips

    Rodney Phillips New Member

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    I understand the concepts of both systems but I just wanted confirmation of my assumptions and both of you have given me that.

    As I stated in my original post, I am willing to convert to Forced Hot Air if we make the decision to do this. I have been looking at the costs of the geothermal and feel that the pay back is reasonable enough that long term it is a very wise move for us (I am 43 and want to stay in the house until they have to carry me away). It is also a very good selling point for any future sale.

    Thanks for the feedback! :)
     
  5. WisJim

    WisJim Well-Known Member Supporter

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    Although most geothermal heat pumps are used in forced air systems, they are available for hot water heating systems, too. Of course, not having ductwork would mean not making use of the airconditioning possibilities of a heat pump.
     
  6. TnAndy

    TnAndy Well-Known Member Supporter

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    Rodney,

    I'd look real close and with a sharp pencil before I jumped.

    The cost of a whole new type of system like that retro-fitted into an existing house is likely to be considerable + add the cost of geothermal wells or a ground bed for the lines to suck up earth heat and I'd bet the payback time is a long one.

    And you might consider the cost of electricity is increasing.....dramatically in some areas.....even here in the TVA system, we're getting a 7-8% increase, which is nothing compared to the 50-75% ones I've seen from around the country.

    If I already had a hot water baseboard system in place ( I assume you have an oil fired boiler ? )....I'd consider adding a wood fired boiler in tandem.....especially if you have your own source of wood, which may be like growing your own money ( energywise ) down the road.
     
  7. Rodney Phillips

    Rodney Phillips New Member

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    Thanks Andy.

    I will look at the total cost. I do own 18 acres so the wood source is not really an issue. However, I am looking for a source of heat I can rely on for many years to come. I doubt that when I am 65 I am going to want to fill a wood boiler any more than I want to today (I go through about 6 cord of wood a year now).

    It will be interesting as I look at the whole project and the costs involved.

    Thanks
     
  8. MELOC

    MELOC Master Of My Domain

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    i have considered trying to use geothermal. i too have an old house and require much heat. i have hot water radiators (the big iron type) and a wood/oil combo furnace. we suppliment with two wood stoves. bek\lieve it or not, the furnace can burn up to a chord of wood per week without oil. the other two stove can burn that as well if the temps get into the 20's as a high.

    i figured on sixteen weeks of bad weather at 2 chords per week and was astonished when i realized the total was 32 chords. YES I NEED TO INSULATE ETC. but i digress...

    i was wondering if anyone with the opportunity has ever used the flow of a stream as a geothermal heat source. the water temperature can vary greatly depending on the stream and the flow and the location. i imagine for the purposes of cooling this would be efficient as i belive in the summer water temps only rise a little compared to the amount they decline in the winter. (just speculation).

    can anyone quantify the amount of water that needs to be chilled or heated in a geothermal system? how much piping of what size at what flow rate, etc.? how much exposure to the "heating/cooling field"?

    there may be some of us with an old well that is not used anymore. i have a "hobby" house, a little cottage on 1/3 acre, that has an old well. i thought of trying geothermal on this tiny house via the old well.
     
  9. agmantoo

    agmantoo agmantoo Supporter

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    I have a geothermal force air system. It has been great. The unit is 15 years old and works fine. The discharged hot air is hotter than what I was accustomed from the heat pump I had previously. The unit is small and all is inside the house. Not having anything exposed to the elements is a major benefit for longivity. When the unit I have dies it will be replaced with another geothermal unit. I have found out that there is a tremendous markup by the installer and I will bypass them. The unit I have is a single package and does not require the freon system to be opened during installation. The task of installing just the package is very simple. The duct work is what I was not familiar in installing. My system uses well water and I was considering a loop but I have since changed my mind as the well water system is more efficient and offsets the maintenance of the well. The spent water is dumped back on the ground.
     
  10. JAK

    JAK Well-Known Member

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    You can use the baseboards to distribute hot water from a heat pump. The only real problem with heat pumps is that the smaller ones cost more per kw. I think a lot of this is because a lot of the marketing and engineering and technical sales is built in as a fixed cost per unit. Otherwise it would be nice to buy a small 1 TON unit to replace the 3 tanks of oil, and then use the wood stove to take care of the peaks. If you used it for hot water heating also, the COP would go down, but might still be 2.0 for the water and 3.0 for the baseboards. You could also just preheat the hot water, and provide the extra top up with electricity. If the heat pump heats in from 40F to 100F, that is 60% of the job, for perhaps a 40% savings in you hot water heating cost. You would find your overall annual savings and payback also go by preheating the hot water because the cost of a 2 TON unit is not that much more than a 1 TON unit. A still larger unit would allow you to eliminate perhaps 4 of the 6 cords of wood also. Of course if the electricity is 3 times the cost of wood heat then a COP of 3 would provide no savings in eliminating the wood, only convenience. You might consider changing you woodlot over time to fruits and nuts, or perhaps lumber. Even then you would still 6 cords for some time just from the thinnings.

    What this country needs is a cheap 1 TON heat pump.
     
  11. agmantoo

    agmantoo agmantoo Supporter

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    MELOC,
    I have a flow meter on my geothermal hatpump and the unit is a 3 ton size if memory is correct. I send 8 gallons a minute of 56 degree well water through the tube and shell heat exchanger. This amount could be reduced but the efficiency would drop. This unit is conditioning 3000 sq ft of floor (single level) area with 9 ft ceiling height in western NC. The utility bill is very affordable. If I were to insulate the floor the bill would drop but I like to temper the temperature of the basement with some heat loss for the living area.
     
  12. raymilosh

    raymilosh Well-Known Member

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    Rodney,
    You mentioned that you already burn wood. I would suggest that you look back a few weeks in this forum to a posting by TnAndy about using galvanized pipe to heat water in a woodstove.
    He has a waterjacket in his fireplace that is run to a propane tank full of water in his basement. He uses the hot water that is stored in that tank for the radiator system in his house. the amount of wiring and piping and pumping is pretty minimal and simple and cheap and smart. I'd recommend thinking about it as a possible solution for yourself.
     
  13. WisJim

    WisJim Well-Known Member Supporter

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    It sounds like you could use more insulation and weathertightness in you place--600 gallons of fuel oil plus 6 cords of wood is a lot, in my opinion. We don't use 6 cords in a season in northwestern Wisconsin, in our old early 1900s vintage farmhouse, but we have added insulation, improved windows, etc., and every year we make it a little more comfortable and use a little less wood. Wood is ous only heat besides some passive solar through the sun room that replaced an old porch.
     
  14. Rodney Phillips

    Rodney Phillips New Member

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    I think it is more that it is just a big house. It is a 36 x 50 cape with a full finished/heated walkout basement - about 4000 sq. feet of space.
     
  15. Cindy in PA

    Cindy in PA Well-Known Member

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    My brother is adding on to a real old house for a total of 3200 sq.ft. In the new section they will have radient heat from geothermal, but not sure what they will have in the old part. Their system is estimated at $39,000. I love the thought of geothermal, but what that is going to cost would take me 25-30 years of payback for what I pay to heat with a regular heat pump and that is if it took their heating bills to 0! I cannot see the cost.
     
  16. MELOC

    MELOC Master Of My Domain

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    wow, cha-ching. i think i have found a new career path! $39,000, u sure that was not the whole addition?
     
  17. Alex

    Alex Well-Known Member

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    You can heat water or air to high enough temperature to use for heating. One of the social projects in Vancouver used both in-floor radiant and small fan-coils, both feed with hot water from a ground-coupled heat pump system.

    It works well. The system, unfortunately, only is allowed to supply heating, even though it is capable of cooling and heating. The Provincial government did not want to give cooling to social housing occupants. Cooling is not required, but a nice benefit, and it helps keep the ground temperature stable. Too bad.

    But the system is working well for the last five years -- this is still early in geothermal temperature degradation terms, so we'll see.

    It is always better to use these ground-coupled systems for both heating and cooling.

    Alex

    Go to Mole Hill heat pump project page, then scroll down to the bottom and select Mole Hill and view the slide show for some interesting small Canadian (made in eastern Canada) fan-coil units which can both cool and heat.

    Or for the more technical aspects of all this you can go to this other mole hill web page which shows some interesting calculations.

    Or here for sketches of the mole system.

    P.S. Your local heat pump installer can help you select the correct heat pump and figure out if your soil is OK for this.

    BTW Heat pump condenser coils in a creek, river or ocean can work, if the water temperature is OK and you can get regulatory approval to put big loops of plastic pipe in your waterway (sometimes allowed – depends on your area, etc. – again your local person can help you.)