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  1. #1
    Join Date
    Jan 2010
    Posts
    55

    Ground or air source decision, and just any tips appreciated

    I have around 6 or 7 bids including a mixture of conventional air to air and ground source heat pump systems. It is for a 3100 sqft 1-1/2 story house in NE Oklahoma. I am pretty confident in the load calcs because just about all of them came up with about 4 ton downstairs and 3 ton upstairs. And surprisingly they are all about the same price for similar equipment, etc.

    Considering the tax credits and rebates from the utility the ground source system will cost about 21% more than the conventional. this is for vertical closed loop system. My questions are concerning approximate payback and just general issues. Some geo equipement sites I've used that account for electric rates, etc give me a payback of about 3 years and the contractor claims no more than 5 years payback. the units I would use probably are climate master packaged units and claim around a 27 SEER. The conventinoal units I'm comparing to are about 15 SEER Lennox or Trane equipment. If I go up to 19 Seer the cost difference is almost nothing after credits and rebates.

    So aside from the payback is the quality of the equipment comparable to the a high end trane or lennox, or any other higher end unit?

    One technical question I had involves using antifreeze in the loop. One contractor says he won't use it because it decreased efficiency & isn't necessary. The other disagrees and says he never installs w/o it and that methanol doesn't decrease efficiency. Finally, one said he would drill 4 holes using about 183'/ton and the other said 7 200' wells, so 200' per ton.

    Any general adivice or tips are appreciated. I think w/ the few thousand extra expense and rising energy costs the ground source may make sense. I just am not too familiar with it and wanted some advice.

    Oh, another thing mentioned by a contractor is that he installs very small strip heaters because they are expensive to operate and the heat pump capacity will always catch up, it just might not catch up quite as fast w/o the expensive strip heaters. In fact he says he turns his off in his own home and just deals w/ the occaisional couple degree temp drop. Any thoughts on electric backup heaters? (we don't have gas or any other source)

    thanks.

  2. #2
    Join Date
    Jan 2010
    Posts
    55
    Please excuse this post, I think I should have put it in residential, moderators please delete if so inclined..

  3. #3
    Join Date
    Dec 2003
    Location
    Salisbury, MD.
    Posts
    1,480
    I no nothing about where you live so this may be a little off base, but 7 tons seems like a lot to me. Do you have really cold winters? I believe that unless you are going to move in the next couple of years then the geothermal is the way to go. Climatemaster is excellent equipment as well as the Trane and Lennox. 5 year payback also seems a little wishful thinking, but even if you cost it on 10 year payback it will save you money. The systems should last over 20 years, so after the payback period you will be making money on your systems. If the costs were within 20% it really is a no brainer- go geo. As far as your loops you need to talk to the pros in your area because there are regional differences that I just cant answer for you. Make sure you talk to a contractor that has experience with the geothermal systems. You will be glad you went geo.

  4. #4
    Join Date
    Jan 2010
    Posts
    55
    Thanks for the input. The wells are actually my main concern as it seems like a bigger unknown and many variables can change the "rules of thumb" depending on soil type, water tables, etc. But in this area there is a single company that does all of the geothermal drilling for all hvac contractors and that is all they do, so that makes me a little more comfortable.

    Sizing seems a little large to me as well. I've been told that we live in a cooling dominated area and that I have many west facing windows, large cathedral ceilings, etc.. Also, we have a very nice EPA wood fireplace that we plan to use extensively w/ 40 acres of free firewood..

    One contractor actually claimed it was a tad undersized for cooling but would work.

    That brings up another question. With my plans to use wood as a heat source, is just the cooling portion of a geo heat pump enough to justify the extra 20%. One of the contractors told me that these heat pumps are actually even more advantageous on the cooling cycle as compared to conventional air to air.

  5. #5
    Join Date
    Dec 2004
    Location
    Lynchburg, VA
    Posts
    32
    You would be fortunate to pay back in just 5 years on the geo installation, most likely you are looking at 7+ years. As far as the size of the equipment, I would agree with the existing proposals due to the fact that the 27 seer systems have 2 stage compressors and will operate in the stage 1 mode most of the time. Stage 1 mode decreases the capacity of the system by 30 to 35% and the fan speed will slow thus using less energy. When there is extreme weather or severe load on the system the thermostat will switch to stage 2 causing the sytem to run at full capacity, this helps to minimize the use of the strip heaters which can cancel out any energy savings in a hurry.

    ClimateMaster is a very good line of Geo equipment and would compare in quality with the 16 seer and 20 seer Trane, I personally would not recommend Lennox to any one that I thought very much of.

    Never install a geo system without some form of anti-freeze, methanol is great and has a minimal impact on thermal transfer. Glycol is not a good idea because at 40*f glycol will begin to thicken and by the time the temps reach 30* you will be trying to pump a slurpee through the loops. A freeze-up can split the coaxial heat exchanger and cause great expense and discontent. The increased cost of adding the methanol is only pocket change when pricing systems such as these.

    Typically we average 250' per ton on the loop field design, you can go out to 250' u-bend loops without having to increase the sizing on the circulating pumps. So for a little more digging or boring you can have an additional buffer for little additional cost. Increased capacity on a loop field can give great comfort and confidence, it is very costly to have to come back and add additional loop capacity.

    I agree with the small strip heater kits due to the fact that the systems are already sized a little on the large size for the load which is great for the 2 stage systems and they won't rely on the strip heaters to maintain temps in severe weather and will save you money.

    Did any one explain how you can get free hot water from your geo system?

    FYI: We operate in Central Virginia utilizing pond loops, vertical bores and horizontal ditches.

  6. #6
    Join Date
    Oct 2009
    Posts
    8
    Yeah, they all said the climate master would come with the hot water recovery and that was included in their bids.

    What do they typically do when you have two heat pumps and just a single hot water heater? Would it be wasting heat if they only connected one of the units to the water heater? I considered using the second smaller unit to recirculate hot water through the house sort of like one of those hot water circulation devices.

  7. #7
    Join Date
    Jun 2004
    Location
    Kathleen GA
    Posts
    236
    Can't do payback calculations without data. Three years sounds like snake oil. Five years - maybe but I agree with the 7 years being more likely.

    I am not a fan of oversizing. The reason is that the load is sized for the hottest/coldest days of the year (not "the coldest" but almost). You lose efficiency the remainder of the year. Can you stand to be 4-5 degrees colder than you like for a few hours 1 - 3 times per year? If yes then don;t oversize your unit. Also, you can increase the size of the ground coil and almost never have to use the aux heat.


    Well depth depends greatly upon what is underground. If you hit a aquifer then your heat transfer rate is better. If sand then deeper wells are required. The 183 is from a program, the 200 is the rule of thumb guy (my opinion). I would add well not short change it - cost is minimal to go extra 10 feet in most cases.

    Absolutely use antifreeze. Both lose some efficiency. I could get away without it here in FL but you cannot (unless you live atop a hotspring).

  8. #8
    Join Date
    Jan 2010
    Posts
    55
    When I say payback I am talking the difference between conventional and geothermal, and after the tax credits & rebates. Without getting too much into cost, I can say that the difference between a conventional system and the geo bids I have is about3500. That is compared to standard 15 seer units and the climate master tranquility 27 systems. If I assume I will save about 40% in heating and cooling the payback would be about 3.5 years. Even at 25% savings it would be less than 6 years.

    Now if I compare with 2 stage 16 seer there is no difference in price after the rebates.

    As far as sizing, he sized a 3.5 ton and a 2.5 ton unit for conventional but the climate master doens't come in half tons I guess so he upsized to a 4 and 3 ton. But he also explained that it would tend to operate on the first stage more often if it were a little upsize. It also comes w/ variable speed fans.

  9. #9
    Join Date
    Jan 2010
    Posts
    55
    As far as loop sizing, he claims the drilling company specializes in geothermal loops and thats all they do. He said they told him they were going to drill 183' per ton for my units and that would be 1281' of well, or I guess 2562' of loop for about 366' of loop per ton. He said this is what's required for this area and soil type. He didn't know exactly which pipe size they would use but said 1" to 1-1/2".

    They install honeywell thermostats. Be kind of a techy, I was hoping to get the climate master thermostats with the sensors to tell me efficiencies and water temps. He said they believe firmly in the honeywell controls and don't usually install the climate master controls. Any thoughts on that?

  10. #10
    Join Date
    Jun 2004
    Location
    Kathleen GA
    Posts
    236
    If you really want to "watch" your sytem, buy a WEL instrumentation package. You can monitor everything - and then more.

    Do you think energy costs are going up or down? If down then go with ASHP. If up then go with the GSHP. Here in FL, the power company just asked to increase rates by 30 percent (they got far, far less and more than their proposal actually deserved).

    Seven tons for 3,100 SF would be grossly oversized here in FL. Most use one ton per 500 SF but multiple studies show that one ton per 700 SF is closer to the M J calculations. But rules of thumb are just wags and if you are buying an expensive system you should get the calcs.

    One thing that might push you more toward the GSHP is that its easy to get hot water at a discount from the GSHP unit. But you will need a second water tank to get maximum benefit.

    Good luck either way you choose to go.

    Alex

  11. #11
    Join Date
    Jan 2010
    Posts
    55
    Well, we signed a contract for the geothermal unit. We chose the best guy for the job I believe. They've been doing it for 10 years they claim & have tons of references and been using the same driller and they have zero complaints in the BBB, if that matters much..

    I would have questioned sizing more but they all came up with about the same 7 ton sizing, maybe because of the large cathedral, they say it's about like adding 500sqft of living area because it is over a 500sqft room. They also all claimed you want to operate in the first stage most of the time which would reduce the capacity quite a bit and runs more efficiently in that range. For conventinoal they actualy came up with 6 tons but don't have half ton increments on climate master equipment.

  12. #12
    Join Date
    Apr 2008
    Location
    Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior
    Posts
    1,411
    Quote Originally Posted by dforster2 View Post
    ... It is for a 3100 sqft 1-1/2 story house in NE Oklahoma. I am pretty confident in the load calcs because just about all of them came up with about 4 ton downstairs and 3 ton upstairs. And surprisingly they are all about the same price for similar equipment, etc.

    Considering the tax credits and rebates from the utility the ground source system will cost about 21% more than the conventional. this is for vertical closed loop system. My questions are concerning approximate payback and just general issues. Some geo equipement sites I've used that account for electric rates, etc give me a payback of about 3 years and the contractor claims no more than 5 years payback. the units I would use probably are climate master packaged units and claim around a 27 SEER. The conventinoal units I'm comparing to are about 15 SEER Lennox or Trane equipment. If I go up to 19 Seer the cost difference is almost nothing after credits and rebates.

    ...
    Wow, would I love to see your cost comparison, but alas this is forbotten on this site. Live in extreme NW Arkansas which has got to be close to NE Oklahoma. Considering your 7 tons of capacity, I am amazed! Maybe I should say flabbergasted! Did they throw in the wells for free?

    I got several 4 ton geo proposals, one was for Climate Master as I recall. Compared to a 17 SEER 4 ton DFHP after all credits and rebates for both approaches, the geo costs would have been 2-3 times the DFHP. I'm amazed!

    In addition, our electric rates are quite reasonable, so a 3 or 5 or 10 year payback would have been a pipe dream for me given our energy lifestyle.

  13. #13
    Join Date
    Jan 2010
    Posts
    55
    I was surprised also. The federal 30% credit as well as a $300/ton rebate from my electric utility paid for most of the difference between geo and conventional. Otherwise it wouldn't have made sense to do it. If you want to see a comparison I guess you could Pm me, I don't know if that's allowed either. I could also give you the name of the installers, you're not that far away really.

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