Geothermal Hvac

Discussion in 'Home Construction and Remodeling' started by HippoTwilight, Dec 13, 2017.

  1. Dec 13, 2017 #1

    HippoTwilight

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    Anybody have experience?

    I'm planning my next house, and am seriously considering going this route for temperature control. I'm thinking radiant floor heating on the ground floor, and normal forced air HVAC for the rest. I briefly considered hydronic for everything, but I don't think I want to screw around with that. The major brands (Trane, Carrier, etc...) seem to offer hybrid systems, where there's a normal gas or electric backup just in case it gets too cold for the geotherm to keep up. I would choose gas to minimize my electrical requirements (and the size of my backup generator).

    I'm also looking at having 2 other spaces on the property. A 30x40 shop/garage for projects and toy storage. And another 30x40 "studio apartment" type thing that will serve double duty as guest quarters and photography studio. I'd like these spaces to run off of the same heat well.
     
  2. Dec 13, 2017 #2

    TMT Tactical

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    I have to admit I am not a big fan of in-floor heating. It could last 2o years but eventually it is going to break and then cost a fortune to repair / replace. All system - All systems fail but the cost of repair or replacement differs greatly. Dual duct systems are very efficient but the ducting and diverting actuators have a higher initial installation cost over normal single duct systems. Split systems with individual zone controls are very efficient but again more costly on the install. There are many options, spend the time to evaluate what is best for you now and in the future.
     
  3. Dec 14, 2017 #3

    SheepDog

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    Geothermal heat pumps can produce a lot of heat. It takes time to heat a large area but a well insulated space should not be a problem. I have a mini-split system heating and cooling the garage and shop and it keeps the temp pretty constant all the time. I was a little concerned about heat in the winter because it get below freezing here most of the middle of winter but the system is doing the job.

    I walked past the compressor last night as I was coming in and was surprised the amount of cold being transferred to the outside. So I am adding to the cold temps in the winter and the hot temps in the summer.
     
  4. Dec 14, 2017 #4

    joel

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    I have looked into "Zero net homes", it is a 12 step plan, not just solar panels on the roof.
    In doing this I found geothermal - HVAC.
    I know one person on S.C coast that has had it for 12 years & loves it.
    He said that he has an open loop & wish he had a closed loop instead.
     
  5. Dec 14, 2017 #5

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  6. Dec 15, 2017 #6

    HippoTwilight

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    Good info!
    @TMT Tactical, I agree about the repair costs of embedded hydronics. The only way I'll go through with that is if I can be convinced the piping will outlast me. Even then I'm leaning toward only in "non-living" areas like the garage or shop. If it the plumbing fails, I'll just quit using it with only a minor inconvenience.
    I didn't know dual ducting was a thing. After a quick glance, I don't understand how it could be more efficient, but I'm probably not fully understanding it. If I'm trying to heat a room, why would I use the energy to heat up the air, only to cool it back off at the vent (or vice versa). I'll have to read into that a bit more.
    I'm already set on multi-zone HVAC. My parents had that in most of their house, and it was awesome. My 2 story house could really benefit from it. I've been casually researching how to implement a remote Tstat in each living space for ultimate control. This is probably where the dual ducting thing comes into play.
    The first house I lived in had return vents in all the rooms, I very much like that b/c you still got good airflow in a room with a closed door.

    That's encouraging to hear @SheepDog. Temps in my area can get over 100F in the summer (with near 100% humidity), and below 0F in the winter. If a GHP can keep up with 90% of the requirements, I think I'll be happy. I'm not oppose to adding a gas furnace for auxiliary heat on the coldest January nights. Heating requirements seem to be the primary concern when calculating system sizes. I've never read anything about backup A/C units for the hottest summer days.

    Thanks for the link @joel. I'll have to spend some time there, it looks like there's quite a bit I'd be interested in. My main focus for this new home is to minimize daily resource consumption. I'm not interested in inflating the construction cost just to use eco-freindly materials.
     
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  7. Dec 15, 2017 #7

    TMT Tactical

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    Dual ducting was originally intended to provide individual zones with the option to either heat or cool at the same time with the same system (boilers and chillers operating simultaneously) . The original concept was not efficient but did solve the zone temp control problems. Current dual duct is just a method to direct the air discharge more efficiently. Cold air register (ducting) at ceiling level and hot air registers (ducting) at floor level. The main system would be in either heating mode or cooling mode but not both. Actuators would be required to direct the air flow to the correct ducting system. Multiple zone HVAC is also my preferred choice. Most economical and helps end temp wars or at least minimize them. Individual zone stats with occupancy sensors and reset programming. Don't heat or cool space not being used but don't allow the zone to drop below an economical recovery temp either. In my personal opinion this is the best of all worlds.
     
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  8. Dec 15, 2017 #8

    SheepDog

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    The only problem I have with the mini-split is that there is no "auto" setting. The heads, both of them, have to be set to heat or cool. I can't have one cool and the other heat. I can't just set a minimum and maximum temp and have it stay within that range. It's not a big deal but I would have liked it to be automatic. I have the garage set at 50F and the shop is at 65F for the winter. In the summer I just set the temp at 80F in the garage and the shop.
     
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  9. Dec 15, 2017 #9

    HippoTwilight

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    Ok that makes complete sense. I've actually wanted to do that very thing (separate hot and cold registers). Never came up with the right keywords for a proper search. I was starting to think I'd have to run redundant ducting and with a diverter at the handler.
     
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  10. Dec 15, 2017 #10

    joel

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    Hippo, I agree. But I am a cheap skake & want to lower heating & cooling cost over the next twenty years.
    Also my son will end up with the house, so the 12 step thing will pay off for him too.
    I would not pay 20 to 40% more on some fairy tale that may or may not save the planet.
    But a 75% saving on electric,heating & cooling over a 40 years in a home will make a home pay for it's self.
    Everyone will pay the cost, I just doing it up front, not monthly.
    And I have three years, til I have to nail down what I will do.
     
  11. Dec 15, 2017 #11

    TMT Tactical

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    There is a multi zone system that allow each zone to select it's own mode (heating or cooling) and the main units diverts the refrigerant flow to the correct unit. Example: Zone (A) may want cooling and the base unit would divert the refrigerant from the condensing unit to the zone (A) coil and fan assembly. If zone (B) wanted heating , then the refrigerant would be diverted from the evaporator unit to the zone (B) coil. I am making this a bit simpler that it is but the system and technology already exists and is available. I researched this system a year or two ago for my project. I if I can find my notes I will post the links. This type of system requires minimal ducting (air flow to base unit) but does require more refrigerant lines and more potential for future leaks. How and where you run the refrigerant lines will determine future maintenance costs. This is the most efficient system I cold find for the installation dollar. An you all know just how cheap I am.
     
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  12. Jan 22, 2018 #12

    GaryS

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    Sorry for being late to the party.

    In the past twenty years, we built and lived in three homes heated and cooled by geothermal systems.

    Generally, I love the systems...quiet and efficient. The first house had a Trane unit custom made in Texas from USA-made components. We lived in that house ten years with never a service call, and no maintenance except air filters. It paid for itself in four years.

    Later units have many Chinese manufactured parts, and my current one has been troublesome. However, any other system is also at the mercy of poor quality parts.

    Number two was made by Water Furnace, and quality was so-so, but it was efficient. My latest three-year-old house was built with all the 'best' energy efficient features, and it has a Bosch unit that is less efficient than either of the first two.

    My experience and satisfaction have been a mixed bag, but I would be willing to answer any questions you still have. If building another house, I would again install a geothermal unit, but I would do a few things differently.
     
  13. Jan 22, 2018 #13

    Caribou

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    A friend of mine has an air to air heat pump that he is pleased with. Another friend drew his heat from the ocean with a heat pump and was very pleased.

    I like in floor heat. The tubing I use is Pex. The brands that I recommend and use are Rehau and Wirsbo. The only real threat to Pex is sunlight so keep it in the box till you are ready to use it. I plan to add a staple up system to my current home. I prefer the in slab system but retro fitting with a concrete floor is too expensive. A customer of mine has a concrete floor on both floors of his home and loves it. When the boiler goes out he is unaware of it till he runs out of hot water. The floor will heat his home for about three days so he has time to fix the boiler or, in the case of a power outage, for the power to be restored.
     
  14. Jan 22, 2018 #14

    Tirediron

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    If you decide to got giant fridge "so called geothermal" make sure the local soil transfers heat, sand and certain Clay mixes are better insulators than conductors and sometime heat or cold soak right when you need them.
     
  15. Jan 22, 2018 #15

    joel

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    Carabou, I always wondered if the heated floor was worth the enormous cost here in the south. But liked the geothermal ideal of cooling the floor in summer.
    55 to 60 degree floors year around sounds great.
     
  16. Feb 9, 2018 #16

    buckhuntr

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    Geothermal doesn't have to be in the floor, it usually works with existing hvac ductwork. Here in Oklahoma, in-floor heating/cooling doesn't work so well, since it doesn't react nearly fast enough to keep up with changes in temps outside. By the time it starts heating the floor enough to feel, you need the cooling again!
     
  17. Feb 9, 2018 #17

    hiwall

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    I tried the in-floor heat here in my "new" house this winter. I will not be using it again after this winter is over. Not the right thing for Arizona, even way up in the mountains where I am.
     
  18. Feb 9, 2018 #18

    buckhuntr

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    In-floor heat would be great where it gets cold and stays cold for months on end. In other words, not someplace I'm likely to ever live!
     
  19. Feb 12, 2018 at 4:54 PM #19

    captain belly

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    We built 3 years ago and have a Bosch Geo-T unit. I love it so far. We were lucky enough to catch the big "money back" government deal for ours...... otherwise.... it would have been too expensive to justify. We also built with 6" exterior walls, blow-in wall insulation, and stud-n-insulate basement concrete walls. heating and cooling 4200 square feet on level pay in Missouri for $150 per month. Realize, that we only have electric, and no gas. I'm please with this average......especially when you figure that I have 2 big teenage boys that use as much (actually more....because they don't pay the bills!). So basically, 4 adult usage.
     
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  20. Feb 12, 2018 at 10:14 PM #20

    HippoTwilight

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    I've pretty much decided on doing a vertical closed-loop geo-therm system outside. The inside system has been a struggle though. My climate has a habit of producing 100F with 90% humidity for a week straight in the summer, and then 6 months later have a week straight of sub-zero lows in the winter. Regardless of what inside system I use, I will most likely need a supplemental forced-air system to keep up with those demands.

    Since my original post I have decided to put the apartment above the shop/garage, creating a 2-story 30x40' building. My plan is to live in the apartment short-term while we build the main house. Most of my attention has been on this building rather than the actual house. The shop will be typical garage style construction, insulated walls but not even remotely air-tight like a living space. I'd like to have heat in the shop, A/C would be a waste of time.

    Regardless of the primary system design, I will end up with vents in the apartment for one reason or another. Radiant floor cooling needs dehumidification, which means vents and an air handler. Radiant cooling of the second floor will likely cause chronic condensation on the shop ceiling (since it's an unconditioned space). All things considered, it seems like a no-brainer to just go with forced-air cooling in the apartment.

    The heating aspect is not nearly as simple. I want shop heat. Since I am looking at having roughly 17,000 cubic feet of shop space, I'm not even going to try to use forced air of any kind. Using the concrete slab as a giant radiator seems like the next best thing. I'm just looking for something to take the chill off, and keep things above freezing. The biggest problem I see with in-floor hydronics in the shop is that I'm limited on what I can bolt to the floor down the road. I have plans for a 2-post lift, and an overheat crane. Those can be designed around, but unknown future items may be a problem. I won't be able to start drilling holes in the floor willy-nilly.

    Once the main house is built, the apartment will transition into a home studio/office, and guest space. It won't be practical to winterize the space b/c it will still be used on a limited basis. That limited use is precisely why I'm hesitant to use forced air of any kind. I'm thinking the minimum operating costs of the forced air heating will be prohibitively expensive for just preventing frozen pipes. Since I'm already leaning toward radiant heating in the shop, why not just create another zone for the apartment. I figure size the system to keep things above freezing in 0 degree weather. We can use electric heaters as needed when the space is occupied.
     
  21. Feb 13, 2018 at 8:08 AM #21

    SheepDog

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    Hippo,
    Take the time to make the shop tight. I heat and cool my shop and garage (two buildings 22x28 with 9 foot ceilings) with a single twin head heat pump for peanuts. I used 2x6 studs with half inch OSB on both sides then concrete panels on the outside and drywall over the sheathing on the inside. The shop and garage doors are insulated to R15, the walls at R19 and the ceiling at R60. There are no windows because people don't need to peek in to see if there is something worth stealing and the shop door has double bolts into the overhead P-lam and into the concrete slab with a bolt system tying the doors together in the middle. Everything is sealed with weatherstripping and the structures are tighter than my house (I didn't build the house).
    The new home I am drawing up will use 2x8 studs and 3/4" sheathing with two layers of concrete siding on the exterior and 5/8 sheathing and drywall inside. R30 insulation in the floor and walls with R60 in the ceiling. The windows will be triple glazed glass and lexan and the exterior doors will be 4x8 insulated fire doors with air locks between the exterior and interior. The entire structure will be glued and screwed together with no nails used at all. Heating and cooling will be done using a geo-grid air supply and geo-thermal heat pumps. It is being built to exceed D-2 public shelter specs.
     
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  22. Feb 13, 2018 at 7:36 PM #22

    GaryS

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    A vertical loop in-ground system isn't affected much by the ambient temperatures if the extreme cold doesn't last very long.

    For additional heat, I have backup built into the unit. It is only used when you put a demand on the heat for fast warm-ups, or if needed to maintain demand in extremely cold weather. If the heat exchanger is not operating, the backup will operate along with fan in emergencies.

    A zoned system should accommodate the changing needs when you move, but the system needs to be balanced when it supplies both the apartment and the new construction, so it would need a very talented engineer to design what you need. Geothermal systems rely on moving lots of air, so duct design is critical. I think I'd consider temporary heating and cooling for the apartment, and install the Geothermal system throughout when the new construction takes place.
     
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  23. Feb 16, 2018 at 9:58 PM #23

    HippoTwilight

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    The long-term plan is to turn the apartment into a home-business open to the public, so I'm going to err on the side of caution and have licensed professionals handle some of the work (design, plumbing, electrical, etc). From the first design meeting, I'm going to emphasize tight construction and energy efficiency. I like the idea of a passive home, I want to use similar techniques for this building too.

    When you say concrete panels...are you talking about fiber-cement siding or flat panels? I'd like to do my house in the fiber-cement siding, I'm not sure about that investment for the shop though. I'm already planning on R21 insulation with 1/2" wood panels inside and out. I'm not sure if the added R-value of cement board would offset the cost compared to metal siding panels.
     
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  24. Feb 16, 2018 at 10:10 PM #24

    HippoTwilight

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    How long is "doesn't last very long"? We just had 2 weeks straight weeks of single digit highs around Xmas/New Years. Since then, it's been blow freezing more often than not.

    I've been researching details of GHP's a little bit. Haven't gotten into the details enough to know what's really available. I'd like to have a gas backup (preferably integrated) to keep electrical loads to a minimum.

    From what I've read, part of the appeal of a vertical loop is that it's easier to add capacity since the wells don't take up much land area. I've kind of assumed I could just size the first well for the shop, and then add more when the house gets built. By a zoned system...do you mean each building would be it's own zone? I haven't read up enough to know how it would work having a single well system feeding multiple structures.
     
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  25. Feb 17, 2018 at 11:57 AM #25

    GaryS

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    Here in North Texas, the temps seldom remain in single digits for more than three or four days at a time, and I’ve never seen the ground freeze down more than a couple of inches. When I lived in North Dakota, the frost line was usually around six feet, so totally different needs for different areas.

    My installer told me the optimum, stable ground temperature in our area is at 75 feet. My current 3-ton unit has four wells about 250 feet deep. He said only three are needed, and one is a backup in case there is a problem with one of the other wells. A friend has a horizontal loop in his dam, but wishes he had installed wells since the lake temperature changes too much. What he gained in installation cost, he lost in efficiency.

    Since the wells make up about half the price of the total project, I think it would be difficult to install them as needed. The geothermal system requires more engineering than the more common systems, as everything is balanced for performance and efficiency. Accurate control of the air flow in all zones is critical, as the conditioned air operates at much lower/higher temperature than standard heat and AC systems. In my opinion, the cost would be far less installing to support the end configuration, than making changes in mid-stream.

    I doubt that integrated gas-heat backup could be used because they are so different. I have a propane gas fireplace for short term backup, and a 20-kw whole-house generator that also operates on propane if needed.
     
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  26. Feb 17, 2018 at 3:30 PM #26

    SheepDog

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    Hippo,
    I used Hardie board and it is a (the first ever) fibrous cement product. You might compare the prices because compared to T111 it is cheaper and compared to vinyl or metal siding it will last a lot longer and can be had in different colors or primed and ready for paint. It looks a lot better than the plastic or metal siding and it isn't affected by the UV. (it is also more fire resistant) You can get it in panels, both with and without texture and grooves like T111, or in planks for horizontal or vertical use. While it can be used directly over the studs I would recommend the use of plywood or OSB on the studs and then glue and screw the Hardie board to the sheathing. (you can glue through the house wrap materials without a problem)
     
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  27. Feb 17, 2018 at 7:58 PM #27

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    The wife keeps bringing up the idea of having a heated driveway. The worst is when the drive starts to thaw and then it turns around and freezes before the water can run off it as some of the land drains down the road in certain situations.

    My thought is to drill down 150' to 200' and drop a Pex loop to the bottom of the well. I'd start in the middle of the drive and run and run loops up and down the hill so the runs are shorter. All I need to do is to bring the drive to 33*F/1*c so I'm not thinking about using a heat pump per se but directly using the ground heat to thaw the road.

    The loops would be filled with a glycol mix so freezing would not be a problem. A circulator does not take a lot of electricity and that would be the only energy use. Any ideas would be appreciated.
     
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  28. Feb 18, 2018 at 6:32 AM #28

    GaryS

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    Opinion only...If operated continually, and unless your weather is mild and the sun keeps the driveway clean most of the time, I think the driveway will probably chill the water faster than the earth can warm it.
     
  29. Feb 18, 2018 at 9:53 AM #29

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    Heating your driveway will take more than one geo well. Each well will warm your fluid to about 55F. The transfer of heat is very slow and you need to heat the concrete and the ice to above 33F.
    You might consider using pipe tape buried in the concrete and using it to keep it from freezing, or a combination of the two.
     

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