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  1. #1
    Join Date
    Dec 2009
    Posts
    4

    Trying to choose between geothermal, other options

    I just joined this forum and have read quite a number of threads dealing with various geothermal issues. Have found quite a bit of useful info, and am wondering if I can get any opinions about options for my specific situation:

    We have a 2-acre property in rural PA, and plan to build a log cabin on in next year. Although we'll only use it several weeks a year as a vacation home, we plan to also rent it to other vacationers and possibly to students at a nearby college during the off-season. Since renters who don't pay for utilities are not known for energy conservation practices, we're interested to invest in an HVAC system with a low cost of operation.

    The property is between the confluence of two streams and has a high water table. We're also thinking of creating a small (maybe 7500 sq ft) pond for fishing and swimming. There is already a well to supply the cabin's plumbing, and a water softener -- left from a cabin we're planning to demolish.

    I've already had a couple geothermal installers out to look at the property, and both are recommending horizontal closed-loop systems.

    My question is this: Should I be looking at other options? What about a pond loop? How big and deep a pond is needed for that? Or a "pump and dump" open-loop system that would feed the pond?

    We need to keep installation costs as low as possible. Ultimately, it might still make the most sense to install an air-source heat pump and deal with the higher utility bills, but first I'd like to explore options for a reasonably well-priced geothermal system that would be efficient, reliable and long-lived.

    Thanks for any advice you can give me ...

    Chris

  2. #2
    Join Date
    Mar 2008
    Location
    northern Indiana
    Posts
    114
    My question is this: Should I be looking at other options? What about a pond loop? How big and deep a pond is needed for that? Or a "pump and dump" open-loop system that would feed the pond?

    Pond loop depends on the size if the unit and depth of pond.
    Open loop depends on water quality. You don't want to pay for softened water.
    The other thing is who keeps an eye on maintenance (filter replacement and misc) as renters surely will not.

  3. #3
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    567
    You possibly have only gotten bids from GSHP folks who have only ever done ground loop and never installed a pump and dump. With a pond and 2 streams it is almost a no-brainer to go pump and dump - the almost is that it is 45 years since I lived in N. IN, and have no idea what present local laws regarding wells are.



    Hard water - if you can find an installer who is not afraid of fabricating their own straight tube in tube evaporator for HP operation (which is the condensor for AC operation), hard water actually improves the performance as it builds a higher turbulent layer on the inner Cu refrigerant tube. Straight tube because then every 15-20 years or so it can be opened and cleaned if the water is so hard it would tend to obstruct the passages.

    My own system is dump to a pond, HP operation get a COP of 5.6 regardless of outdoor temp.

  4. #4
    Join Date
    Dec 2009
    Posts
    4
    Quote Originally Posted by junkhound View Post
    My own system is dump to a pond, HP operation get a COP of 5.6 regardless of outdoor temp.
    Thanks for the advice! I have some ignorant questions about "pump and dump":

    1. Would I need to drill an additional well or can the existing well that supplies the cabin potentially do double duty? (I'm assuming local ordinances would prohibit taking water from the stream, even if it weren't an undesirable option for other reasons like water temperature and water quality.)

    2. How much flow is usually required and am I correct in assuming that the pump is only on when the system is heating/cooling?

    3. Is the electricity used to power the well pump a significant off-set to the energy savings provided by the heat pump?

    4. Since there seems to be a filter required, as indicated by teeball57, how often does that need to be cleaned and how big a job is that (a possible issue since we'll be absentee landlords most of the time)?

    5. Who makes "pump and dump" systems? Or are they always at least partially retrofits (as I'm sensing from junkhound's advice) of another type of water-source system?

    6. Any general idea of potential savings vs. horizontal loop or pond-source closed loop in terms of capital investment or operating cost?

    7. Does "pump and dump" qualify for the federal tax credits?

    Sorry for the barrage of dumb questions -- I'm on a steep learning curve here! Hopefully the answers might also benefit other newbies coming here for information.

    Chris

  5. #5
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    567
    1. existing well OK if it can deliver say 4 GPM continuously - guessing at a 2T unit for a cabin.

    2. yes, correct in assuming that the pump is only on when the system is heating/cooling, own system delivers 59,000 BTU Hr using 4T scroll compressor, I pump 9.7 GPM of unfiltered/untreated water.

    3. Is the electricity used to power the well pump a significant off-set to the energy savings provided by the heat pump?
    Yes, if you pump directly from your normal water supply pressure. A separate pump to avoid the pumping losses avoids many of those losses. If I use the regular house pressure, my effective COP drops from 6 to 5.6. About 8% less efficient operation, just have not gotten around to putting in a separate low pressure system on own system.

    4. Unless you have really 'nasty' water, you do not need a filter.

    5. Who makes "pump and dump" systems? Or are they always at least partially retrofits (as I'm sensing from junkhound's advice) of another type of water-source system?
    Will let others answer that. See your # 7 also. Designed own system as HP only operation, as could not find any commercial units that met my criteria; (dont need AC where I'm at, PNW) and used various components - scroll compressor, 7.5T carrier condensor, parker txv/valves, shop built tube in tube evaporator , etc.
    The best specs for a commercial unit I saw when searching 2 years ago was for the CM Tranquilty 27 system.

    6. Any general idea of potential savings vs. horizontal loop or pond-source closed loop in terms of capital investment or operating cost?
    This varies all over the place. Capital investment of water source should be slightly less that a ground loop system using an existing well - dont have to dig all those trenches.
    Compare COP for your ground water temp for various commercial systems vs. air-air systems to estimate savings.

    7. Does "pump and dump" qualify for the federal tax credits?
    ONLY if it is listed in the ARI test data document, anything a tech could build out of different manugfacuters components would not qualify, even though a good tech could put a system together from different vendors that would likely outperform rated systems with components all from one supplier.

  6. #6
    Join Date
    Mar 2009
    Location
    Russell ON Canada
    Posts
    24

    Pump and Dump

    I am using a 6T CM Tranquility in Ottawa Canada for a 2500 aq ft bungalow. It's a little oversized but I woanted to leave the option of a future closed loop open because I am on a pump and dump to my pond. I had a 5T WF before that and it lasted 15 years - probably would have lasted longer if I had been smart enough to have it descaled. The CM is a great unit.

    Check the local laws first to see if open is allowed then have your water tested. A lot of iron means you may be better off with a cupro-nickel coil ($$$). Bad water quality means a closed loop so you might consider a big pond.

    The most important factor is to get a great installer.

  7. #7
    Join Date
    Dec 2009
    Posts
    4
    Thanks for all the good advice, guys!

    I'm in contact with a couple local installers (there aren't many to choose from in this region of NW Pa.) who install pump-and-dump systems. I'll see what they recommend (and the costs) after they look at the cabin plans, well, property, etc.

    Since this would be a small pond (7500 sq ft, maybe 10'-12' deep), I'm wondering also what the effect of the discharge would be. On the positive side, I'm supposing it would help fill the pond, if the storm drainage and groundwater weren't sufficient. But what impact on water quality and water temperatures (both summer and winter) would it have? I'm also interested in the pond for fishing (and swimming). Would it make the water too hard and low in oxygen for fish?

    Chris

  8. #8
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    238
    With stream water you also have to be carefull of sediment runoff, ie muddy water when it rains.

    I would recomend a horizontal CLOSED loop since you have a hign water table. My loop was burried in a 5 foot deep trench with two feet of water.. I also have a decent creek running through the back yard so I have underground moving water. My contractor tells me my water temps are better than some vertical loops.

    Closed loops negate the need to keep the hx clean which as it scales becomes less effecient. So while it may cost more initially your operating cost will be less because you will have no pump head loss and less maintenance costs keeping it clean.

    I have a WF Envision NDV038 (~3ton) I change the air filter once a year whether it need it or not. It never has needed to be changed. even after a year the manometer still reads the same pressure drop, well maybe 0.05" higher.

  9. #9
    Join Date
    Dec 2009
    Posts
    4

    Inverter-Driven Heat Pump a Better Option?

    A reputable contractor (they just installed a huge geothermal system for a local college) has come back, after doing heat loss and heat gain calculations for my cabin design, with an alternative recommendation. He thinks a geothermal system is overkill for my small, well-insulated cabin, and that installing the ductwork amidst the traditional log construction is going to be very difficult.

    He recommends, instead, something called an "inverter driven heat pump system." There would be an outside unit and several inside units in various rooms (although he's proposing only baseboard heat for the two bathrooms). He says this would have a much lower installed cost than the pump-and-dump and would be almost as efficient.

    I have questions about durability, winter heating cost (this is a very cold area and I'd assume most of the winter would have to be on back-up convection heat), cooling the bathrooms in summer, etc.

    Anyone have any reactions to the contractor's claims on cost and energy efficiency, as well as any general opinions about inverter-driven heat pump systems? I did appreciate the fact that he was making some effort to find a better solution for me than the one I proposed, even though he stood to make less money on it.

    Chris

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