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heat pump water heater deal

Post in 'The Green Room' started by GaryGary, May 11, 2013.

  1. GaryGary

    GaryGary Feeling the Heat

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  2. semipro

    semipro Minister of Fire

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    Thanks Gary. I'm trying to figure out how to make use of one.
  3. brogsie

    brogsie Feeling the Heat

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    Do you think this would work with a hot water storage tank from an oil boiler? (Superstor) It looks like it hooks up to the draw off.
    I run a dehumidifier in my basement 8 months a year any ways.
  4. maple1

    maple1 Minister of Fire

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    Pretty sure it would.

    Those have been on Ebay for a while - I remember looking at them last year sometime. I think they're wired 220, rather than plugging in to 110? Looks like a pretty decent deal though.
  5. brogsie

    brogsie Feeling the Heat

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    Thanks Maple,
    When you Google Nyletherm it shows a price of $299. when you go to e bay it's $369.
    Interested to see how they look Gary.
  6. dougstove

    dougstove Member

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    Can someone explain the principle a bit more?
    It cools the basement air and transfers the heat to a water tank?
    It has dehumidifier action along with the cooling (capturing the condensation as the air cools)?
  7. GaryGary

    GaryGary Feeling the Heat

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    My understanding is that it extracts heat from whatever space its in, and adds that heat to the water tank its warming. The COP is around 2 to 2.5 meaning that 2 to 2.5 times as much heat is delivered to the hot water tank than if you just used a resistance heating element.

    The heat that it takes out of the airspace its operating in can be good or bad -- if the its located within your conditioned space, then its good in the summer because it reduces the load on your AC and provides some free house cooling, but, bad in the winter because it increases the load on your furnace, which has to reheat the air cooled by the heat pump.

    It also removes moisture from the airspace its operating in, which goes to a condensate drain.

    It is a 220 VAC unit -- I'd guess its 220 because that makes it easy to hook up to an electric water heater.

    I'm hoping to find some clever way of using it so that it does not extract heat from my conditioned airspace in the winter -- maybe some form of simple solar air heating collector to heat the airspace its in, and only run it during the day? Or, maybe something like the scheme shown in this paper http://www.builditsolar.com/Projects/WaterHeating/TC47paperAug05-1-1.pdf.
    Another possibility would be to locate it in an area that you want to be refrigerated, but this would lower the COP some?
    Any other ideas?

    Gary
  8. woodgeek

    woodgeek Minister of Fire

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    Gary gave a great explanation, but I thought I'd expand on the heat stealing...

    There have been several large studies of the heat stealing issue by folks at the national labs, and they have concluded that even in northern climates it is a much smaller issue than one might think. In an unfinished basement install, it pulls down the temp by a couple degrees, most homeowners don't notice or care, and the 'stolen' heat is just BTUs that would have gone into the earth anyway. Mine is in an attached garage, semi-conditioned, and it pulls down the temp about 1 degree on average out there.

    If the COP is 2 (which is more likely in a winter basement), that means half of the heat delivered to the water comes from the grid (work/heat from the compressor motor), and the other half from the space. The math works out that so long as your space heating BTUs are cheaper than electric resistance BTUs, a HPWH will still save money over conventional when 'stealing' from a 100% conditioned space.
  9. mywaynow

    mywaynow Minister of Fire

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    Having my wood stove in my basement, would this be a good choice to reduce the overall cost of heating the domestic water via oil burner vs the added electric cost of running the unit? How far from the holding tank can the exchanger be?
  10. maple1

    maple1 Minister of Fire

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    I think ANYTHING but oil would be a good choice to reduce your overall costs. Even a plain electric water heater should have substantially lower operating costs - for me it was less than half the cost of oil (conservative estimates = 3/4 gallon of oil/day vs $30/mo for electric). So take that COP of 2 or better and you'd cut it in half again (talking rough numbers). If one also uses a dehumidifier, a HPWH could eliminate that usage - factor that in if applicable. You could also do some DIY ducting to draw air into the HPWH from a warmer spot (e.g. behind the fridge or a sun-warmed floor corner), and eject it to where you want it to be cooler (e.g. main living space in hot summer). The unit should be as close as possible to your water tank - plus the lines to & from should be insulated to the point of overkill.
    BoilerMan likes this.
  11. woodgeek

    woodgeek Minister of Fire

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    Myself, with a family of 4, my elec usage went down after I had the HPWH installed...lower dehumidifier and AC costs. Usual estimate is $200/yr electric cost for a family, not including other savings. Compare to your oil expenditures.
  12. Dave A.

    Dave A. Minister of Fire

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    Sorry to sound negative but seems like buying a pig in a poke. Installation manual in pdf not available until after purchase, very few specs given -- don't even see dimensions of the unit, no mfr warranty.

    Agree with Gary's explanation of how they run except

    It's probably more like the cost of running could be 1/2 to 1/2.5 the cost of resistance electric at best. You'll never get 2 to 2.5 times the output. Since you're limited to 6000 btu output with this and a resistance heater is likely putting out over 15,000 btu you can only do a portion of heating the water with it -- likely mostly standby loses. Recovery heating the water up after use is just not going to be fast enough to prevent resistance from kicking in. Just my take on it.
  13. woodgeek

    woodgeek Minister of Fire

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    You're correct.

    Recovery can be slow....to make the most of it, you need a big tank (compared to your max usage in a say 6 hour period), and you need to set the resistance element thermostat (on the tank) low or off to achieve real savings.
  14. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    One of the things I'm thinking about using the HPWH for is really a space heating application.
    I have this system: http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm which provides nearly all our hot water and provides some space heating. Basically the 100 sqft solar collector heats an about 280 gallon non-pressurized storage tank. Domestic water is heated by the tank using a single pass pipe coil heat exchanger, and for space heating, water is pumped from the tank through radiant floor heating loops to the floor above the tank -- the whole thing is in a crawl space under about 500 sf of the house.

    The collector area I had available for this system is smaller than I would have liked, and the space heating the system provides is nice, but not nearly 100% of the demand. I am thinking about using the HPWH for heating the solar storage tank when the temperature falls below something like 90F. The heat loss for this part of the house under typical winter conditions is about 6K BTU/hr, which (I think) is about the same as the HPWH quoted output -- so, it looks to be a bit marginal on heat output for this application.

    On an economic basis, it has to be a winner in that propane in a 90% efficient furnace here is about 12 cents a KWH, and electricity in a COP 2 HP would be about 5 cents a KWH. It looks like for where we are carbon emissions would be just a bit lower for the 90% efficient propane heater.

    Questions/concerns:
    - Will the HPWH operating in the crawl space (about 500 sf and 4 ft high = 2000cf) get cooled off so much that a) the heat pump cop will take a big hit, b) will it get cold enough to freeze pipes. The crawl space ceiling is insulated to R19 and the concrete walls are insulated to R13 -- its a "conditioned crawlspace" with no vents and normally runs about 50F in the winter. The floor is dirt covered with plastic -- I've never kept track of the dirt temperature, but I guess its a potential heat source for replacing the heat the HP takes out?
    I suppose that cooling the crawlspace with the HP will increase the heat loss through the floor above the crawlspace, but maybe not enough to invalidate the scheme if a large fraction of the HP heat can come from the dirt floor?

    - If the HPWH needs to operate a high percentage of the time, will it stand up to this kind of service?

    - Have you seen a COP vs air temperature curve for these HPWHs?

    - Did the studies you mentioned give any analysis on where the HP drew its heat from when operating in an unconditioned basement?

    I realize I need to do my homework and run some numbers on this, but just thought if you (or anyone) knows some of this off the top of the head, or has any other thoughts I'd just ask.

    I bought the heat pump for experimenting, so it would not be the end of the world if I tried this application and it did not work out.

    Gary
  15. woodgeek

    woodgeek Minister of Fire

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    I'm pretty sanguine about using these HPWH for space heating. :(

    In a closed system, the 'stolen' BTUs delivered to the space would just be restolen, and the net heat delivery would be just the compressor work, COP = 1. So, stick it in your conditioned space, and you have a very complicated COP=1 device for space heating BTUs. For DHW, you can still come out ahead IF your space heating BTUs (that you are stealing) are cheap.

    In a semiconditioned space, you are currently losing some fraction of your space heating to the (warm) earth. IF your DHW BTU load is less than this parasitic loss (in the crawl space), you can 'recover' a fraction of that by cooling your crawlspace to something closer to ground temp (reducing the flow into the ground, but increasing your losses from the floor above somewhat). In this case you can recover a fraction of the space heat BTUs you were previously losing (and perhaps didn't care about).

    Note, that in this case if you had superinsulated your floor to eliminate this loss to the earth, then your HP is now outside, and it will shut down at some temp when it gets below 45-55°F. And basically not run in the winter. That is, the units do not have defrost controls (or reverse capability), and are built to not operate under conditions where ice might form on the coils. And the coils get 10-15°F cooler than the airstream.

    The key to this scheme working is based on the idea that 50% of our DHW BTU load is typically much less than the existing parasitic losses through a semi-conditioned basement or garage. If they were instead larger, then then (semi-conditioned) space would get cooled below earth/ground temp, and then presumably shut down the unit.

    IOW, running flat out for space heat it will chill the crawlspace it is in down to its lower operating temp limit and shut down. IF the heat it delivers is sent to the space overhead, then this might not happen, but your COP = 1.

    IDEA: if you want get the max solar BTUs in the winter, you could run down the solar storage temp to below that suitable for DHW, and use the Nyle to make you some DHW (in a new/separate tank). ?? Do you currently run down the storage in the winter, or do you lock out the radiant when the storage gets down to 'tepid shower' temps?
  16. Redbarn

    Redbarn Burning Hunk

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    Something that has been missed is that the Nyletherm HPWH is an earlier model of the Geyser HPWH.
    There are many threads in this Forum about Geysers.
  17. Circus

    Circus Member

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    DHW solar collectors are more efficient at low temperatures, especially in winter.
    A water source heat pump (WSHP) may have merit. You could tap your "solar storage tank", run it through the WSHP drawing heat from the "solar storage tank". The resulting 140 F water would work nominally for heating.
    In effect you'd be cooling the "solar storage tank", not heating it.
    PS. 100 sq. ft of panels and 275 gal. of storage are insufficient. Maybe separate SHAir directly heating the house could supplement.
    Just thinking out loud.
  18. GaryGary

    GaryGary Feeling the Heat

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    Thanks -- I think you are right -- the space heating based on the HP removing heat from the crawl space is too far a reach.

    Will think about the sort of two stage approach with the HP to allow the main heat storage tank to be run at a lower (more efficient) temperature. Seems like there is something there. The efficiency of a typical flat plate solar collector goes from about 42% with a tank temp of 120F up to 52% with a tank temp of 90F (both with 30 F ambient). Would have to look at whether that sort of gain is worth the extra effort or not.

    I currently run this system mostly for the hot water heating, and don't let the tank drop below about 110F -- when its above 120F or so, I use the space heating to use the excess. I realize this is not the way to get the most total heat and best efficiency out of the system, but somehow I have trouble letting go of the 100% solar heated water :)
    I would probably be better off from a fuel saving perspective to just use the system for space heating in the winter and let the tank temp go down as low as 80F, and then use the system to heat domestic water only during summer and fall.

    Gary
  19. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    I have another solar space heating system with 240 sf of collector -- http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm that helps with the heat bills.
    This heats the main part of the house, and the smaller system provides a little space heating to another part of the house.
    I do use a large thermosyphon air heating collector for the shop and it works great.

    The idea of the 100 sf system was to show that its possible to have a pretty simple system design that provides both space and water heating. I tell people that 100sf is the absolute bottom end of whats worth doing and that more collector area is highly advisable. In my case there was only room for a 100 sf collector.

    Gary
  20. brogsie

    brogsie Feeling the Heat

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    Do you know how the Nyletherm knows when the water is at temperature?
    Do you tie into the hot water heater's aqua stat?
    My stand alone storage tank is on it's own zone off the boiler.
  21. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    I don't know really know any details on the unit -- waiting for it to arrive with manual.
    I'll post something when I know more.


    Gary
  22. BoilerMan

    BoilerMan Minister of Fire

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    Gary, I'm curious about it as well. Why is it so cheap? Chinese? How does it compair to the Geyser, whay parts do they share (if any)? Great info, and I've read alot of your projects! Looking to do something different with the 115 gal hot water tank.

    TS
  23. peakbagger

    peakbagger Minister of Fire

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    I think they are US product. It happens all the time when a distributor goes under or a company changes models that they have left over inventory. Nothing wrong with it, they just dont want the old model competing with the new one.
  24. maple1

    maple1 Minister of Fire

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    My understanding was that this unit was a predecessor to the Geyser.

    So it should be rugged.
  25. GaryGary

    GaryGary Feeling the Heat

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    As near as I can tell, this is what happened.
    Gary

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