Considering Geothermal Install (retrofit)

Discussion in 'General Discussions' started by Esquire1001, Aug 24, 2016.

  1. Esquire1001

    Esquire1001 New Member

    I have been researching geothermal HVAC systems and I am consider this option on a property I recently purchased and am renovating and plan to stay in for a long time. The home currently has 4 systems and is around 7,000 square feet and 3 of those systems are due for replacement so it is good time to consider geothermal. The property includes a well on the site (I don't know the capacity), not far from the house, and it borders a 3 acre freshwater pond that is spring fed but is shallow. Our summers are very hot, last month averaged over 90 degrees and was the hottest on record. Our winters are cold because of humidity even if the temps don't drop below 20 very often.

    I have found a couple of local vendors that claim to install geothermal, but from the threads on here, it appears that proper system design and install is the key for this to work well out of the gate. Do any installers travel from nearby states, or is this exclusively locally sourced system? If anyone on here knows of an experienced and reputable installer in this area, feel free to share. I also understand that the federal credits for geothermal expire at the end of December, and I guess another question is, is there enough time to design and install a system between now and year end? (I have to think so). The one thing I don't want to do is take this on, have it not work well and regret it. I am in the process of getting proposals now and any feedback could be helpful. Thanks.
     
  2. weedy64

    weedy64 New Member

    Did you indicate where you are?
     
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Charleston, SC
     
  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    If you are deeply renovating a complex 4 system 7000 SF house your first order of business is to consider alternatives that reduce both the heating and cooling loads of the home and the number of systems needed. A target range of 800 - 1200 SF per ton should be doable. Specifics:

    1) Get all ductwork and air handlers into at least indirectly conditioned space
    2) Proactively plan to reduce outdoor air infiltration (air sealing, blower door testing)
    3) Insist on a careful room-by-room heating and cooling load calculation ("Manual J")
    4) Insist that HVAC systems be selected based on the results of Manual J
    5) Insist that ductwork be designed and installed per Manuals J and D
    6) Insist that replacement systems be capable of active dehumidification (and NOT just by separate central dehumidification, a last resort)
    7) Insist that bidders have proven capability to deploy zoned systems - done right only 2 or 3 systems should be needed, but those could easily support anywhere from 4 to 8 or more separate temperature control zones. Contractors who reject zoning should be asked if they don't mind if every light in their own house comes on when they flip the switch nearest to their front door.

    Only after all of the above are taken into account should a discussion of geo vs other HVAC systems ensue.
     
  6. Zoning any HVAC system rather it be Geothermal or air to air is very inefficient with supply plenum boxes. If the zoning is thought out correctly and is designed with radius throat and back fittings per manual D instead of the infamous supply plenum with 4 zones tapped out of it. Then I will agree zoning can be very effective.
    The only problem is that I have traveled this country from one coast to the next to find that very few mechanical contractors truly understand proper design with zoning. Hence forth the proven test results of poor zoning systems. If contractors actually tested the static pressure in their duct systems upon commissioning then they would understand the poor performance they are delivering with their design.
    Proper zoning with the correct fittings takes up a lot of space for the duct system and is best designed under new construction. It is usually very difficult to retrofit existing homes with multiple systems and multiple floors with fewer hvac systems without using the standard supply plenum box that 90% of these guys do which in turn is very restrictive and inefficient.
    We run into guys everyday trying to sell a half*** designed System that are replacing 2-3 systems in a home and using one geothermal system with a butchered zoning system design. just because the cost of doing 2-3 separate geothermal systems is going to drive the budget way overboard hence they will lose the job if bidding using 2-3.
    The main focus should be on the envelope first, ductwork design, ductwork sealing, and proper execution of the installation and equipment selection and sizing. Everything should fall into place after that.
    One of our customers here in Virginia has a 16,000+ sq ft home on a golf course. Under new construction in 2007 we foam insulated the home and installed a 5 ton hydro-delta megatek with a dual zone hvac system, one zone for the finished basement and one zone for the first floor. The entire second floor is on a 3 ton hydro delta split system matched to a Trane variable speed air handler on one ducted zone for the second floor, east, west wings. His average electric bill is $180-240 per month. So yes zoning can be very efficient but it has to be designed and executed that way.
    We recommend zone with equipment if budget allocates you to do so. If not look you might want to look at air to air inverter heat pumps and put the $$$$$ in your pocket and enjoy similar savings to geothermal.
     
  7. Esquire1001

    Esquire1001 New Member

    It sounds like if experts can disagree on whether to retroactively zone a system, then figuring out this GT application may be really difficult. I have figured out the that the pond is 3.5 feet deep (too shallow as is) and that well water here is typically has too many impurities to run open loops very well and is mainly used for irrigation only.
     
  8. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Zoning is not a problem with geo if the zoning system is correctly designed (as with everything) and it talks to the heat pump. If you water is not good, and your pond to shallow, why don't you just dig trenches?
    You can also between the lines here who gives you competent advise and who tells stories.

    Curt above gives you a good list to start with.
     
  9. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    A few zoning dos / do nots:

    1) Do not zone a single stage system except under very very limited circumstances
    2) Do not install return bypass dampers in zoned systems. If your zoning plan calls for a return bypass, redesign it so that it does not. If your contractor insists on a return bypass find another contractor.
    3) Do not exceed 3 zones on two stage systems.
    4) Do pay particular attention to controlling 2nd stage
    5) A duct system capable of distributing system air flow at reasonable velocities, friction rates, and static pressures is required for all systems regardless of zoning or any other technology.

    Note also that the Hydro Delta Mega-Tek brand set forth several posts north has in some cases failed to deliver complete customer satisfaction relative to other more mainstream brands.

    While we often push the envelope as to square feet per ton, the 2000 SF per ton Virginia home(8 tons in a 16,000+ SF home) cited above deserves scrutiny. Its zoning system consists of 3 or 4 total temperature control zones. That seems light. We typically deploy 800 - 1200 SF per zone in well-designed systems.
     
  10. Esquire1001

    Esquire1001 New Member

    Well, it is not looking good for GT. My quote to replace the units that are there with conventional high SEER air to air units is around $40k, and I really only need to replace 3 of them at this time, which would be less obviously. The bid to install Geothermal is $120k. That is with vertical loops as no one is willing to build trenches in the pond or dig it deeper, etc., at least no one I have found or this installer can find. As much as I would like to do the cleaner technology, it doesn't seem to make sense to pay triple to install it. Even if it saves 50% going forward, that is roughly $3k a year and not really economic. I was hoping it was going to come in like 30% more than conventional, and the savings could justify the extra up front cost. Any thoughts on how I could get these numbers more in line would be appreciated though. Supposedly this is based on a load calc and Manual J with the ability cool to 70 in the summer here.
     
  11. ChrisJ

    ChrisJ Active Member Forum Leader

    Trenches not in the pond. How much land is there to dig trenches not in the pond?
     
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    do not know the specifics of the house, but if you can zone the heat pumps usually (2) 5 ton 7-series should be able to take care of it.
     
  13. Esquire1001

    Esquire1001 New Member

    ChrisJ, the pond is a little over 3 acres and very close to the house, maybe 20 feet from the end wall. The current bid assumes vertical closed loops dug in the yard and not using the pond. I can dig trenches in the pond but having trouble getting a quote, but expanding that search now. Not sure how much it would save to dig the pond deeper vs. doing vertical system.

    Docjenser, His calcs he said show that I need a little more tonnage than that, 7 tons on the first level and 5 on the second floor based on a Manual J calc from the plans and desired temp of 70 in the summer. That required 2 systems upstairs and 2 systems down to tie into existing duct work as much as possible. There are currently 4 conventional systems with less tonnage, but hard to say if they are adequate since one is inop. The vendor is quoting 5 series though and not 7 series. I guess my thought is, if I can't make it work here then I have to think it is very hard to make GT work anywhere. I have enough space to get some economies of scale, I have a pond (though these numbers are not taking advantage of that) and I have existing duct work and 3 of 4 systems that are at replacement age. I may run the math to see, economically with some assumptions, where it starts to make economic sense if it can save 50% off of heating and cooling bills over the long haul.
     
  14. arkie6

    arkie6 Active Member Forum Leader

    Do you really need to maintain 70 deg F inside temperature during summer design temps? Typically, 75 deg F is a target used for summer inside temperature under design maximum conditions. This is in part because the unit(s) will be running near continuously (if sized correctly) at design maximum conditions, which will significantly reduce indoor humidity and make 75 deg F comfortable.
     
  15. Esquire1001

    Esquire1001 New Member

    arkie6, it is a fair question, but I based that on where we set our thermostats now on our existing house. Because of differences between the room where we sleep and where the thermostat is located, we set the thermostat on 71 at night, otherwise it is too hot in the bedroom. I didn't want to take a chance on investing in this and have the system not capable of sufficiently cooling the house or having rooms that can't get cool enough to sleep. In fact I would like to think it could get the house to 68 if I wanted it to, even though I wouldn't use it, i.e. I would rather have a system that can outperform the parameter than barely meet it. It is very hot here in the summer, and July was the hottest month on record, in terms of days over 90 degrees, so with no back up, I don't want to undersize it. I don't know, though how much that impacts the design and cost, i.e. is it 10% more to get a system to go from 75 degrees to 70 degrees, 50% more, double? Probably is more a step function than linear.
     
  16. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    To dig the pond much deeper usually does not make much sense from an economic standpoint. The cheapest way, usually, are horizontal loops, thus digging 10-12 trenches should do the work.
    I would not give up and surrender here, the cooling loads seem to have been done with a lot of safety margins. The reason why I mentioned the 7 series is that you would have the potential to go manually in higher cooling capacity. You can temporarily increase cooling capacity by 30% for 24 hours, although you would loose some efficiency for a short period. After 24 hours you would need to engage the higher stages again on the thermostat.
    Thus (2) 7 series units would be able to act temporarily as 13 ton cooling capacity units. You need to watch the loop capacity a bit. They work great for zoning, I would not understand why you would need more, even with your safety margins. I would take (2) 7 series over (4) 5 series any day. Should decrease your price significantly.
    Could you share the manual J calcs?
     
  17. Esquire1001

    Esquire1001 New Member

    Could it have to do with the fact that the four units now do not terminate in the same place, so it easier to replace units where they are now to connect to existing duct work? I can ask if they will share the calculations.
     
  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Sure, but you could find some kind of central location and add some ductwork. Usually much more reasonable than an extra heat pump.
    You should insist to get the manual J, so you can ensure that this was correctly done. You can post it here anonymously
     

Share This Page