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General: Rafter or Joist Insulation if future ASHP to be housed in loft

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  1.  
    • CommentAuthormoogaloo
    • CommentTimeMay 3rd 2007
     
    I think I have said it all. In the future I may add an Air Source Heat Pump to my Thermal Store to affectively replace the boiler. I think the best location for this would be the loft, but I am also about to insulate and can't work out if if it would be best to insulate the floor or the roof itelf? Maybe both!

    Any advice?
  2.  
    An ASHP will not work in the loft - it needs a lot of air movement over it to extract heat from, plus ASHPs get frosted up - do you really want a lot of "snow" forming inside your loft? The ASHP evaporator coil must be housed where it has good airflow. Where would it get the heat from if it was inside an insulated loft?

    Paul in Montrreal.
    • CommentAuthormoogaloo
    • CommentTimeMay 4th 2007
     
    I got this magazing from WH Smiths Called Home Energy Magazing and it had this article about a guy with an ASHP in his loft? It seemed like a good idea a kind of good idea as the air would allways be warmer in the loft than outside. But maybe the article was wrong?
  4.  
    If you insulated the roof at rafter level, then the ASHP would be within the heated space of your house so it wouldn't be doing you any good as a source of space heating. You would have to insulate at ceiling level to thermally isolate the house from the loft area and site the ASHP above the level of the insulation, then it might work OK (like you say, the air in the loft will be warmer than the air outside).

    Don't know about the air flow required, but my loft (original slates with no felt) always seems pretty windy when I go up there! I think the houses at Hockerton used an ASHP with the air taken from the top of the sun space for heating the water (this is only a vague recollection of something I read so could be wrong). Isn't this the same principle?
  5.  
    The evaporator coil of a heatpump always has a large fan in it to move air over the coil. I guess it could work in a loft, but would require the attic to be leaky enough to allow in enough air to supply the heat. I can't imagine that it is a recommended installation method - it would be noisy too in the bedroom below.

    I guess in the UK heatpumps are not reversible so there's no air conditioning function. If it could be run in airconditioning mode, I doubt you'd want your attic filled with hot air - plus the heat gain through the roof would further reduce the efficiency (of course, in air conditioning mode the coil is now acting as the condensor).

    The only heatpumps that I know of that can be installed inside an occupied building are ground source heat pumps as the heat is supplied from or rejected to the fluid circulating in the ground loop. This is what I have but we're lucky enough to have a full basement so there is no inconvenience in having it inside the building envelope.

    Perhaps time to start a campaign for basements in the UK? Houses used to have them and, with the high price of land, it's a more effective use of a limited resource IMHO.

    Paul in Montreal.
    • CommentAuthormoogaloo
    • CommentTimeMay 4th 2007
     
    I think I will forget the loft then. I don't want to be the one to experiment

    Cheers for the info!
    • CommentAuthormoogaloo
    • CommentTimeMay 9th 2007
     
    BTW here is the air source heat pump in a loft?

    http://www.powertech-solar.com/air-to-water-heat-pump.htm
  8.  
    Interesting photo - doesn't appear to be any condensate collector, though the photo is somewhat small. In a humid climate like that in the UK, the heatpump is bound to get frosted up - the question is what happens to this frost in an attic situation if there's no condensate collection system? Would you want something blowing cold air into your attic? Looking at the technical specs, though, I noticed that the output is pretty small, even for the larger of the two systems so perhaps it's not too bad having it installed in the loft ... so long as there is some way to collect the inevitable condensate and to isolate the ceiling below from the noise of the compressor.

    Paul in Montreal.

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