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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: ASHP compensation curve, UFH and wood burner

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    Hi,

    I have a 14kw Ecodan ASHP. Had a lot of issues with the original installation, but has worked ok over the years. However, I am wondering if I can run it more efficiently. I currently have 5 zones with individual thermostats and ufh and then the upstairs which has radiators on a separate circuit. These are all fed into a heatmiser control unit and then into the Ecodan unit.

    I have adjusted the compensation curve over the last year or so, but I have read with interest those who manage their house temperature fully from the compensation curve (heat geeks etc). If I understand correctly, they do away with the individual room thermostats and have the whole system open, trying to balance input with heat loss. I suppose my question is - how low a temperature have some of you gone on the compensation curve. Mine currently runs at 37 at zero degrees or below. Wondering if I can go a good bit lower, set all thermostats to a high temp so they are constantly on and see what happens?

    The other thing I wondered is how a wood burner would influence this kind of setup. I have a wood burner in the lounge. Use it during the day and evening if we are in. Some days not at all depending on movements. How do you accommodate this input into the system setup?

    New thoughts appreciated - trying to get electricity bill down to a manageable level!

    Cheers
    • CommentAuthorBeau
    • CommentTimeDec 7th 2022
     
    We have a GSHP and it's entirely run off the weather compensation and heat curve. It's set so the thermostat has no influence. We run the house as one open loop and have no control over the zones to avoid needing a buffer tank. If your heap pump is only heating small zones with no buffer it's likely to be cycling which is inefficient.

    You adjust the curve until it fits with the house heat loss. Set too high and you get too warm when it's cold and set too low you get cold when it is cold. We also use a wood burner. Most years we leave the 'fine tune' set low so the GSHP keeps the chill off the house and let the wood burner do the rest. Mainly using the wood burner this year unless it's sunny enough to run it from the PV. I guess your place is not especially well insulated or you are using rads. We are fortunate to have UFH throughout and have never seen the circulation temps over 30C even on the coldest days when using the GSHP exclusively.

    Hope that makes sense as I am a dyslexic fool when trying to explain things in writing :smile:
  3.  
    Thanks Beau, makes perfect sense.

    I guess what I am struggling to get my head around is the fact the unit is on all the time. When the flow and return temp end up pretty close, does the unit switch off or it stays all the time?

    Other issue is how do you get a slightly cooler temp at night (if at all)?

    It would certainly be a new way of heating for us, but I see the logic. Just now, different zones come on and off at different times according to their thermostat. But maybe not the most efficient way!
    • CommentAuthorBeau
    • CommentTimeDec 7th 2022 edited
     
    Posted By: 1980scotlandThanks Beau, makes perfect sense.

    I guess what I am struggling to get my head around is the fact the unit is on all the time. When the flow and return temp end up pretty close, does the unit switch off or it stays all the time?

    O

    Ours is on all the time in so far as the UFH circulation pump is always running if temps are below the summer disconnection set temp.

    We don't adjust for day and night and not sure our model could easily. It's 12 years old so not state of the art. The snag is if you demand large swings in temps you might need a bigger heat pump which I am led to believe is less efficient than having a small one running almost nonstop on the coldest days. This is as I understand it from what we we were told back then but thinking may have changed so dont take this as gospell
    • CommentAuthorborpin
    • CommentTimeDec 8th 2022
     
    Posted By: 1980scotlandI have a 14kw Ecodan ASHP. Had a lot of issues with the original installation, but has worked ok over the years. However, I am wondering if I can run it more efficiently.
    There is a lot of discussion on the Open Energy Monitor forum on HP efficiency.

    https://community.openenergymonitor.org/latest

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