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1800 SF shop, pex in slab, heat source?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Highbeam, May 31, 2013.

  1. Highbeam

    Highbeam Minister of Fire

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    So I have all 6 -300 foot loops installed and am still researching the heat source. I am impressed with the COP of the minisplit heat pumps when they heat air. I would love to utilize this technology to heat water. Has that happened yet? Daikin altherma but for real?

    I will be using electricity to heat the water. 1" conduit is installed between panel and boiler location. Wood burning is prohibited in my shop by the insurance company so electric for this project at 10 cents per kwh.

    Heat pump boilers going to happen anytime soon?

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  2. Floydian

    Floydian Feeling the Heat

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    Tom in Maine made mention of a heat pump boiler coming out soon. Nyle Systems, I believe. I am guessing any new air to water heat pump is going to be pretty pricey though hopefully a bit less than the Altherma, which looks nice but not THAT nice!

    I guess that leaves an electric boiler..... which kind of makes a mini split seem like a nice option even if it means not hooking up the infloor. Especially if the shop will see intermitent use although heating air in a shop with a large mass of cold concrete is not that appealing either. You probably don't need the AC/dehumidification?

    What temp are you looking to keep the shop?

    Have you run the heat load calculation? It would be nice to calculate your approximate annual heating needs to help make this decision. Electric resistance heating is kind of scary to me but it may be the best option.

    Good luck,
    Noah
  3. Bob Rohr

    Bob Rohr Minister of Fire

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    There are quite a few water to water heat pumps on the market. Is that what you mean by a heat pumps boiler? With water to water HP you can heat, cool and provide DHW The key to high COP is keeping the distribution sized to cover the load with temperatures 100- 120F would be a great operating temperature and doable with radiant and panel rads.

    This same HP could cool then space with hydronic cooling emitters and a small air system to handle humidity.

    The Dakin you mentioned is an air to water HP, I have heard of some excellent results with these in Oregon. It is fairly new to this market and $$, but it takes the cost of the wells out. Performance is not so impressive in sub zero heating climates. I think the GEO with wells or pond loops would be as efficient.

    If you have access to low priced natural gas, or LP,a gas fueled heat pump could see 130% efficiencies. Robur has gas or LP fired HPs on the market currently.
  4. Ehouse

    Ehouse Minister of Fire

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    +1 on water to water if you have a pond close by.
  5. Highbeam

    Highbeam Minister of Fire

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    Heat pump water heater. Air to water just like a space heating minisplit heat pump unit but instead of heating air, heat water. These things have been well refined into highly efficient air heaters but not water heaters.

    No pond nearby. I guess we'll have to go resistance for water heating for awhile. Good thing is that the equipment is cheap.

    Thanks.
  6. BoilerMan

    BoilerMan Minister of Fire

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    I have wondered what kind of COP you'd get out of an air to water heat pump. Basically a 20,000 btu HPWH connected directly to a slab and ducted outside. I wonder how this type of setup would work out?

    TS
  7. Highbeam

    Highbeam Minister of Fire

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    20k btu wouldn't be enough but the concept is right. Heat is heat and if the heatpump technology is able to deliver 40,000 btu to heat air when outside temps are in the teens then it should be able to deliver those same 40,000 btu to heat water with the same high COP. It has been done but is apparently not yet available for the residential market.

    I don't understand why not. If not for radiant space heating application then at least split systems should be available for DHW heating instead of these current noisy heat pump water heaters that foolishly use space heat for DHW heating. There is plenty of heat available from the outside air.
  8. BoilerMan

    BoilerMan Minister of Fire

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    I don't think it's a foolish idea at all. Personally I think resistance DHW heating is foolish, accept in some cases of little use, seasonal etc. I'm in the process of putting in a HPWH and ducting it to my master bedroom for some A/C and dehumidification. I'll valve it off and drain the unit and just use the indirect with the wood boiler in the winter, seems like a win win to me.

    I think the water side, even with radiant return temps, is hotter than and ait to air HP so the COP would be lower. In a DHW situation the return to the HP is in the 50-90 range keeping the COP higher. Just a guess, but I, like you, still wonder why we don't have higher BTU air to water HP available for this purpose. I'm sure if it were as easy as we think it'd have been done by now.

    TS
  9. Highbeam

    Highbeam Minister of Fire

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    Sorry, not foolish, but not as good as a split system. That is, resistance heating DHW is the least efficient, then the current HPWH technology integrated with the tank, and ideally would be a split system utilizing the vastly superior inverter technology and absorbing heat from the unconditioned outside air without dumping noise inside the home.
  10. Bob Rohr

    Bob Rohr Minister of Fire

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    This link below will take you to Idronics 9 with some good examples how to calculate HP performance. If anyone would like a hard copy, let me know. You may also sign up to get future issues copies mailed to you for free at www.caleffi.us click on Idronics on the right side. These are tech journals, not sales materials. Plenty of good, understandable info in these.

    http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_9_us.pdf

    We presented a webinar a week ago on hydronic cooling and discussed air to water equipment. The thing to remember is in extreme cold conditions they kick on some resistance heat to boost. Install them in a climate where they can operate in a high efficiency mode, they are not well suited for all climates. Like any heating or cooling appliance, crunch some numbers, we give you the tools to do the number crunching in the Idronic journals. .

    This graph from the webinar, shows what a Dakin air to water HP is capable of, The webinar on Hydronic Cooling is also archives at the Caleffi site.

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