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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.

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    • CommentAuthormarktime
    • CommentTimeApr 30th 2014
    "Yes, that is the idea, but my thinking is that the thermal mass rarely gets hot enough and is often acting as a heat sink, meaning you need extra heating energy (this is for the UK climate, not a mile high at 40°N)"

    What I am noticing here in Tenerife in an end flat with East, South and West elevations is how the building temperature affects our comfort zones. We go down to around 15º C during the winter which starts around December but we only need heat from late January on. This is only an impression at the moment as I haven't monitored temperatures but it appears as if the building was slowly releasing the heat it gained during the Summer and what is more pertinent to this discussion, it still feels cool inside today although internal air temps are around 22º C. Wall temps are obviously affecting our physiological comfort level and I must obviously get down to collecting some data for you!
    • CommentTimeApr 30th 2014
    Sea surface temperatures are at about their lowest around the UK at the moment (no idea about Tenerife), this will depress the air temperature compared to the solar power you are receiving. You probably find that in October you generally feel warmer.
    • CommentAuthorEd Davies
    • CommentTimeApr 30th 2014 edited
    Marktime, yes, it's a lot more complicated than just what the outside air temperature is.

    Does it get cloudier as you go into January, perhaps?

    As you say, the temperature of the building will lag the outside temperature a bit though I'd be surprised if is was by more than a week or so for a conventional build.

    Also as you say, the wall temperatures will have an effect on the perceived comfort level. Within reasonable ranges, the walls being 1 °C warmer will compensate for the air being 1 °C cooler and vice-versa. I use a Lidl IR thermometer to measure temperatures here (caravan in NE Scotland) pointing it at internal walls, windows, floor and ceiling to get an idea of the radiant temperatures and at a bit of paper hanging over the edge of my table to for an air temperature proxy. (Current air temp just under 19 °C but feeling a lot chillier with bit singe glazed windows a 11 °C, floor away from the oil-filled heater about 14 °C and walls just under 18 °C).

    There's also the physiological adaptation effect - you adjust to the general temperatures around you over the last few days or longer though this would tend to have the opposite effect to what you describe.
    • CommentAuthorEbeneezer
    • CommentTimeMay 1st 2014
    The differences may not be large when averaged over the whole time period, but it seems that timing of the differences is perhaps more important than the average. The model suggests that thermal mass suits the way most house are used. Specifically the "house" with thermal mass retains heat into the evening (18:00-00:00) when people are back from work and want to use it.

    I don't know how to calculate the effect of scaling up from the model size to real house size, but suspect it would amplify the above. Can anybody confirm?

    Since I intended to post this (I had to register) there have been some comments discussing whether heat will be maintained over days/weeks/seasons but if it can reduce heating requirements for a few hours in the evening that seems like a clear win, whatever the average (which includes times when the home is unoccupied).
    • CommentAuthorEd Davies
    • CommentTimeMay 1st 2014
    Hi Ebeneezer, welcome to the forum.

    Posted By: EbeneezerSpecifically the "house" with thermal mass retains heat into the evening (18:00-00:00) when people are back from work and want to use it.
    I wonder what proportion of homes are actually used that way, though, with people working at home, retired, with very young children, sick, unemployed and so on. Also, with a lot of non-9-5 type work many homes will have at least one person in during what's a working day for others (e.g, one person working M-F and another working weekends with days off in the week).

    Even in houses occupied solely by people who spend most working days outside there are still weekends and holidays.

    Overall, I'd guess that on average more home·days are occupied than not.
    • CommentAuthorGotanewlife
    • CommentTimeMay 1st 2014 edited
    Quite! We're over 95% occupied here and I love that our house is high mass - for one it means I can be 'sloppy' with my heating and it doesn't really make much difference. 'Sloppy' means for example I can burn when it is convenient, deplete the tank of heat because I forgot to turn the pump down and a whole plethora of other sub-optimal practises. Still it'll be cold after 24hrs of no heat input once it is down below 10 deg and cloudy (I also love my big glass area!).
    The more you insulate a house the less benefit Thermal Mass is because the temperature rarely fluctuates. In our timber frame Solar Enhanced Passive Houses the thermal mass of the floor slab heated to 24 degrees is sufficient to heat the house for 4 days.
    • CommentTimeMay 2nd 2014 edited
    How many tonnes does it weigh Seamus, and what is the insulation under the slab?
    The ground floor slab in a 160m2 two storey house is about 10m2 so about 25 tonnes! When you add in the solar gain the heat-loss for the Solar Passive House is about 2kWh/day in December.
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