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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2017
     
    It was a gorgeous day today, which was part of the reason I switched the heating off yesterday* and the E7 immersion for DHW the day before. Hopefully they can stay off until autumn now.

    * Well, I left the ventilation at trickle setting overnight, which has the side effect of causing the post heater not to switch on because its sensor detects that the flow rate is not sufficient.

    It was up to 24°C in the living room late this afternoon, so I must get on with my pergola! The situation is not that desperate, because if the rest of the house warms up to that sort of temperature then the MVHR summer bypass will operate to stabilise things. As it was, the rest of the house was around 21°C - 22°C. Well, except for the conservatory (really a sun room), which got to be too hot for me to spend any time in, as designed.
    • CommentAuthorJohn Walsh
    • CommentTimeMar 10th 2017
     
    And the point of this thread is ... ?
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 10th 2017
     
    :bigsmile:
    • CommentAuthorgravelld
    • CommentTimeMar 10th 2017
     
    What's the heat output of your system?
    • CommentAuthordickster
    • CommentTimeMar 10th 2017
     
    The point is...showing off your well insulated house and its benefits.

    Whilst we're at it, we had no heating on yesterday, 22.7 C after a bit of solar warming, but of course, that was on top of the heat stored in the house on the day before.
    • CommentAuthorEd Davies
    • CommentTimeMar 10th 2017
     
    DJH, when did you put the heating on? Beginning of November?
    • CommentAuthorgravelld
    • CommentTimeMar 10th 2017
     
    Yeah... I was going to say that our house is crap and the heating didn't come on after 9am. I'm kind of surprised it's taken this long to turn yours off djh? Hence my question... don't want to over fixate on having heating on/off, it's more about the power and energy requirement.
    • CommentAuthortony
    • CommentTimeMar 10th 2017
     
    Is that total energy or heating energy you are talking about?
    • CommentAuthorgravelld
    • CommentTimeMar 10th 2017
     
    Heating only. But actually it's power I'm interested in, as I would've thought the heat loss was low. Just trying to understand living in a high performance house.
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2017
     
    I turned it on 2016-10-22. I don't have any power logging to tell me how much power the heater is actually pulling. It's maximum output is 1.8 kW and it's only switched on 1230-0730 by a timeswitch. We also used some additional 400 W bar heaters overnight sometimes in Dec and Jan as well, because we're trying to use as much power on E7 as possible rather than spread the heating throughout the day.

    Another way to estimate the usage is to look at the total energy drawn from my supplier. The overnight usage each day this winter is: Nov 13 kWh, Dec 17 kWh, Jan 18 kWh, Feb 14 kWh. Those figures also include whatever the immersion heater for DHW took. That's limited to 6 kWh per night, but again I don't know how much it actually took. This year's figures are about 3 kWh per day more than last year, which was a very mild year.

    It's partly because I don't have complete logging that I bother with things like turning the heating off. In theory it isn't necessary of course. I always keep the temperature above 20 °C so the usage figures are comparable to that extent.

    Yes, the point is hopefully to motivate people to insulate, insulate, insulate!
    • CommentAuthorgravelld
    • CommentTimeMar 10th 2017 edited
     
    Thanks Dave, I thought they must be pretty low power. Is the 1.8kW heater modulated (and is it the MVHR post heater or something else)?
    • CommentAuthorJohn Walsh
    • CommentTimeMar 10th 2017
     
    "Yes, the point is hopefully to motivate people to insulate, insulate, insulate!"

    ... well, then, that is a very worthwhile point.

    From what you say, one thing I'm particularly interested in is the role of your mvhr when solar gain kicks in, that "the MVHR summer bypass will operate to stabilise things" when that happens. Presumably, this is your experience of the effect of summer bypass mode, i.e. the mvhr helps with heat distribution around the house.

    I'm interested as the theory would say that a domestic mvhr unit isn't capable of doing that, mostly based on the straightforward physics regarding the heat capacity of air (i.e. the lack of). In contrast to that, people on here do similar things, mostly with distributing pre-warmed air, who report positive effects (as I do). As such, it's useful to hear of your experience of mvhr heat distribution - am I understanding what you are saying correctly?
    • CommentAuthorsnyggapa
    • CommentTimeMar 10th 2017
     
    I think he means that the bypass will operate, and the excess heat in the house put there by solar gain will be taken outside by the MVHR unit. When the bypass operates, it bypasses the heat exchanger, so is in effect a ventilation fan (or an open window, but controlled flow and extracting from every room)
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2017 edited
     
    Yes, the 1.8 kW is the MVHR post heater. The power is limited by a flow rate sensor that makes it cut out if the flow rate is too low and by an in-duct temperature sensor that limits the power to keep the air temperature below the set point. And by the room temperature sensor; I think the unit has a controller that soft senses that (PID?) rather than a simple thermostat. It's a VEAB MQEM.

    The MVHR does help to equalize temperatures throughout the building but it doesn't do a perfect job. As synggapa says, I meant that it takes excess heat out of the house via the extract vents in wetrooms and replaces it with fresh cooler air via the supply vents when the summer bypass is open.

    Temperatures everywhere within the house are fairly close to the average. Those with southerly-facing windows get two or three degrees hotter whilst the sun is shining. I think the generally small variance is mainly due to the much better insulation in the outside envelope than in the inside walls and floor. I do expect the MVHR helps though.
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