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Heating and cooling: Cooling the house in summer

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    • CommentAuthorcjard
    • CommentTimeApr 1st 2017
     
    I'm reasonably pleased with the house performance so far; energy has been about 20 quid a week in the cold season and it's an electricity only house.. We've had a couple of days of sunny weather so far and, despite being a bit chilly outside, rom temps have been getting into the territory that makes the Mrs very happy (24) whereas I (and with a bit of acclimatisation she) preferred the nice 17 it was when it was wintry outside..

    I don't doubt that having 30% of the roof be glass (heritage reasons, perhaps not ideal) is a significant source of somewhat unwanted heat so I'm thinki of cooling options for when proper summer is here (because if it's 24 inside in March..)

    Call me daft, but I've always had this idea that I'd put an air source heat pump inside the house for two reasons: one that they produce cold air as a byproduct of their operation and two, that I'm still going to need hot water that I need to pay for, so pointless running the outside heat pump and cooling the world when what I really want is a cooler house

    At the moment it feels like it would be more sensible to make the system independent of the MVHR rather than try to integrate it: the base of the house is generally cooler; it's just the top floor and knock on effect it has on the Middle floor that causes warm bedrooms.

    Before I get too involved with questions like what size of machine, does anyone think this is a bad idea? I Plan to activate it only when out the house/not trying to sleep.
    • CommentAuthortony
    • CommentTimeApr 1st 2017
     
    1. Best to stop the heat getting in in the first place = external shading of glass
    2. If outdoor air is cooler than indoor air, use that as it is free, i.e. Use a fan
    3. You won't want an ashp cooling the house when it is cold already.

    4. You are right to be worried about overheating, a thermal model would tell you that, my house does not get to 24C no matter what temperature is outside, I do shade my windows in summer.
    • CommentAuthorcjard
    • CommentTimeApr 1st 2017
     
    Considering I'll always need hot water, and I'll always want a cool house..

    1) yes, though why not let the house collect heat -> is it a better collector than the world in general?
    2) remember that cooling the house isn't the only goal; plus using a fan uses electricity like an ASHP does but doesn't orovide the same amount of cold air..
    3) I'd look to implement a thermostat as well as a timer, such that the house wouldn't cool beyond some amount, and include a reasonable hysteresis to prevent cycling..
    4) consequence of having 250mm of kingspan all round to offset the 100sqm of glass I giess. There were some factors that were beyond control (planning restrictions)
    • CommentAuthorEd Davies
    • CommentTimeApr 1st 2017
     
    What sort of ASHP do you have in mind for the cooling? One of those ones which sits on the top of the hot water cylinder?
    • CommentAuthorgyrogear
    • CommentTimeApr 1st 2017 edited
     
    Sounds like you get a bit of stack effect here - could you install the ASHP in the basement, and duct the air exhaust (delivery) to somewhere discrete upstairs or even into the roofspace...

    gg
    oops, I think I meant, "discreet"...
    • CommentAuthorCX23882
    • CommentTimeApr 1st 2017 edited
     
    Posted By: tony1. Best to stop the heat getting in in the first place = external shading of glass


    Absolutely spot on. I fitted solar screens externally, and they make such a noticeable difference to room temperature I don't know why they aren't more common in the UK.

    I can stand behind an externally screened window in full sun, and feel nothing. Stand behind a similar window with interior cellular shades and there is noticeable heat being emitted into the room. As an added bonus, the weave of the screen material means that it blocks more mid-day summer sun, than winter sun.

    This is the material that I used:
    http://www.phifer.com/suncontrol/exterior/product/33/suntex-80-90/26/suntex-80
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 1st 2017
     
    Posted By: gyrogearcould you install the ASHP in the basement, and duct
    Can you just put the ASHP outside in a 'shed' and duct the overheated air from the house to it while haveing a controllable vent to allow cooler air into the house?
    • CommentAuthorgyrogear
    • CommentTimeApr 1st 2017
     
    Posted By: SteamyTeaCan you just put the ASHP outside in a 'shed' and duct the overheated air from the house to it while haveing a controllable vent to allow cooler air into the house?


    Not A Bad Idea ! (better than mine, I have to admit...) :shocked:

    gg
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 2nd 2017
     
    It would need a bit of engineering to make sure that enough air can flow though it, ASHPs shift a few tonnes of air when at full chat.
    • CommentAuthorcjard
    • CommentTimeApr 2nd 2017
     
    You mean, so I only have one ASHP, and can pick and choose where it gets its warm air from?

    Partner asked the same thing, only thing is, the existing ASHP is already mounted on the wall, and the position makes it awkward to duct back into the house; this isn't really a standard house either.. i think the relative costs involved, it'd be much simpler to just buy another ASHP

    What sort was I thinking of? Not sure, that was for discussion after reasoning whether it was a sensible idea. Some non inverter cheapo probably.. there's one on flea bay right now, a 3.5kw ecocent designed to sit atop a DHW tank.. thing is there's also another that includes the entire tank for less, might be simpler to have the extra HW capacity. It may be that these units are undersized for the insolation but as per response to Tony's points it doesn't have to be the only method of controlling the house air temp; it could heat water til there is no more capacity for the water to store it, then shading/summer bypass on the MVHR could be employed..
    • CommentAuthordelprado
    • CommentTimeApr 2nd 2017
     
    Is the shading on the windows visible from the inside or the outside?
    • CommentAuthorgyrogear
    • CommentTimeApr 2nd 2017
     
    The "shed" could be the garage...

    gg
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2017
     
    Posted By: CX23882the weave of the screen material means that it blocks more mid-day summer sun, than winter sun
    How does that work - geometry based presumably? Can't find that info on their website.
    • CommentAuthorCX23882
    • CommentTimeApr 3rd 2017
     
    Yes, it's a combination of the ratio of mesh strand diameter to opening size, and the fact that it is in a basket-weave type arrangement. I haven't measured angles exactly, but looking across a window at approx 15 degree angles blocks vision completely, becoming reasonably unrestricted visually at around 30%. When looking perpendicular it's simply the ratio of mesh to opening, so around 75%.

    In response to an earlier question - yes, you are aware that the screens are there. You can see out easily enough, but there is a slight "greyness", similar to poorly calibrated brightness/contrast on a TV. I wouldn't recommend it if you have a nice view; in my case, 70s suburbia is hardly picturesque. From outside, they stand out more in certain light conditions.

    The mesh is PVC coated and slightly reflective, so even when the sun is high and direct light is being blocked, there is reflected light off the mesh. It is a bit darker indoors, but actually not as dark as I thought it might be. I haven't found the need to turn lights on any earlier; the only exception was on very overcast days over winter.

    Today at around 11:30am, I compared the temperature of the internal face of closed blinds on both a screened and un-screened south-east facing window. The screened windows' blind measured 29degC, compared to 47degC for the unscreened. For comparison, the walls were at 21degC, so although the screens make a difference, there is still more that could be done.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2017
     
    Posted By: CX23882looking across a window at approx 15 degree angles blocks vision completely, becoming reasonably unrestricted visually at around 30%
    That (I think?) means that at sun elevation 75o (i.e. mid day in the tropics) it's blocked but at 60o elevation (UK mid summer mid day and all times/seasons 'below') it's reasonably unrestricted. I hope they don't make much of that claim!
    • CommentAuthorCX23882
    • CommentTimeApr 3rd 2017 edited
     
    By "reasonably unrestricted visually", I mean that you can discern objects on the other side. Even in the worst case with the sun on the horizon, 75% is blocked due to the open-ness factor of the mesh.

    As you move further away from perpendicular, the "square" 25% openings become increasingly trapezoidal, then triangular, then pin-pricks, then full blocking.

    I don't think the manufacturer does make any claims about the mesh shape being a factor, it's just an inherent property of the way the stuff is manufactured. I have seen another mesh material which is orientation-specific, and with that, I believe that there is a more pronounced effect.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2017
     
    So you still mean "at sun elevation 75o ("15o angle"?) it's blocked but at 60o elevation it's 'reasonably unrestricted'" -
    but that's OK because even at near-horizontal elevation it's 75% blocked?
    Can you clarify?
    • CommentAuthorCX23882
    • CommentTimeApr 3rd 2017 edited
     
    Yes, if you assumed it was a 2D plane with no thickness, then 25% of the overall area is open, and 75% blocked by "mesh".

    But, because it's a 3 dimensional material, both due to the thickness of the mesh and the weaving of strands making up that mesh, there is more blocking for smaller angles.

    On reflection I'm not sure that the weaving actually has much (if any) effect at all, at least compared to the property where the mesh has a thickness roughly equal to the diameter of the openings (creating an eggcrate type effect), because if you consider a group of 3 parallel strands (1, 2, 3) running in the same direction - although there could be additional shading between 1 and 2 at a particular cross-section, there is equally less shading between 2 and 3, assuming the material is uniform.

    When I have some free time I'll set up a rig with a lightbulb and measure the effective lux at various angles. There is a difference, since I can see the level of shading varying as I turn a sheet of the material when held between a bright bulb and a wall; in addition to the blocking of sight when installed on a window.
    • CommentAuthorjohnuready
    • CommentTimeApr 16th 2017
     
    Cjard

    You started by saying you use about £20 per week for heating only in the winter weeks. What do you use for heat generation in your all electricity house?

    How do you distribute the heat in the property?
    • CommentAuthorcjard
    • CommentTimeApr 20th 2017 edited
     
    Got a Vaillant 12kw ASHP on the outside wall, mated to UFH at 150 centres in liquid screed downstairs, and approx the same centres in alu spreader plates under chipboard+carpet upstairs. Actually the heating bill probably isn't 20 a week, as the entire house energy bill was 25 and not ever appliance is as efficient as it could be (bedrooms have halogen rather than LED, plasma TV is 500 watts) but then again pretty much all electricity use in a house ultimately ends up contributing to heating the house.. :). DHW is probably £1, maybe £1.50 a day. Not bad for a house with over 100sqm of glass, though that is the cause of the insolation problem too..

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