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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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  1.  
    Our ASHP runs pretty well, but when it's doing the DHW cycle, it seems to freeze over every 30 minutes, which seems to drastically reduce efficiency. Is this normal for it to freeze so often? If not, does anybody have any thoughts as to what might be causing it?
    • CommentAuthortony
    • CommentTimeOct 27th 2021
     
    Extracting heat too fast, it gets cold, collects condensation and freezes it, costs a lot to melt ice using reverse cycle powered by your electricity 😢
    • CommentAuthortony
    • CommentTimeOct 27th 2021
     
    My advice, run HW 24/7, ie top up as required. Will work out cheaper too 🙂
  2.  
    There's a school of thought that frosting is a good thing, because the latent heat of [condensation+freezing] that you gain from the ice, is a lot more than the latent heat of [melting] that you have to put in to clear it.

    Are you running the HP at a higher temperature or higher power for DHW than for space heating? Extracting more heat from the air means the fins/coil have to run colder.

    Our previous one used to freeze more in mild autumn weather when the air carries lots of moisture, less on cold dry days. The thermostat cycled it on and off every 15mins and it defrosted each time, I think newer ones have smarter control than that.
  3.  
    Posted By: tonyExtracting heat too fast, it gets cold, collects condensation and freezes it, costs a lot to melt ice using reverse cycle powered by your electricity 😢


    Thanks @Tony. I'm not sure that there is an alternative. We can control the temperature of the UFH, but not the DHW. When the ASHP kicks in to heat it, there only seems to be one setting - full power.
  4.  
    Posted By: tonyMy advice, run HW 24/7, ie top up as required. Will work out cheaper too 🙂


    I think you might be right. The only other option was to switch to Octopus's electric car tariff and charge it at a low COP but low cost at night.
  5.  
    Posted By: WillInAberdeenAre you running the HP at a higher temperature or higher power for DHW than for space heating? Extracting more heat from the air means the fins/coil have to run colder.


    Yes - considerably more! UFH can trundle on at 300-500 watts, but DHW takes 2.5 kW!
    • CommentAuthorEd Davies
    • CommentTimeOct 27th 2021
     
    Posted By: tonyMy advice, run HW 24/7, ie top up as required. Will work out cheaper too
    A variation on that theme might be to do HW only for short periods at regular intervals during the day, say for 20 minutes every two hours, in the hope that the ice will defrost by itself during the 100-minute space-heating intervals.
    •  
      CommentAuthordjh
    • CommentTimeOct 27th 2021
     
    Sounds like a design fault, or a system design/sizing fault, if it's icing up so much/regularly?
  6.  
    Posted By: Ed DaviesA variation on that theme might be to do HW only for short periods at regular intervals during the day, say for 20 minutes every two hours, in the hope that the ice will defrost by itself during the 100-minute space-heating intervals.


    That is a good point. I could certainly give it a go.
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