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    • CommentAuthorskyewright
    • CommentTimeSep 10th 2012
     
    What's happening in more extremes climates (e.g. P_i_H, Gotanewlife, Finland) is interesting and perfectly valid, but if I have it right ST is invetigating how thermal mass relates to the situation of the UK, where the climate is in general more moderate (especially so in his part of it)?
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012 edited
     
    Right, just looked at the hourly numbers and worked out the rate of change during the day. This is known as the Slope, and it is only the y axis values divided by the x axis values, so nothing special.

    0 equals no change and 1 equals infinite change.

    Ambient,0.07 °C/hour
    No Mass,0.06 °C/hour
    Granite,0.07 °C/hour
    Water,0.06 °C/hour

    So all pretty close to 0 (and below the accuracy of the measuring equipment).

    And yes, I am just looking at the UK climate, and I am not suggesting that we all live in tents with 2 metre thick polystyrene walls, though I will claim that as far as temperature stability and energy use, you would not notice the difference.

    Chart below shows that the masses track the ambient pretty closely.
    • CommentAuthorGotanewlife
    • CommentTimeSep 10th 2012 edited
     
    ST said:

    "I have been claiming that in the UKs climate regime"

    So Skyewright you are correct but ST also said

    "and I was unsure if it made any difference to the comfort levels"

    and I and others have been commenting on this aspect, and actually my temps in the winter are very similar to Wales for example, albeit I get vast amounts more sun. I can't see how mass per se can significantly reduce fuel requirements as this aspect relates to U values and air changes etc but the characteristics of high mass houses in my experience unquestionably do help comfort levels during the heating season; would cost more fuel than necessary in a infrequently occupied houses (DINK households), churches, guide huts etc; and invariably, at least since OPC began to be used, are intrinsically much more airtight - I just wish I could afford to change my huge numbers of ill fitting, warped, wooden SG windows and my 8 pairs of wooden double doors, 6 pairs of which are fully glassed!

    ST said “I have been claiming that..., thermal mass within the insulated envelope makes no difference to the overall thermal performance of the building” but has anyone claimed the opposite…..or does it depend on your definition of thermal performance, which thus far in this thread seems to be defined as fuel usage but perhaps the buffering effect (and consequent increase in comfort levels) is an aspect of thermal performance.

    Ooops ST added a comment whilst mine was in draft...
  1.  
    Hmmm just looked at your last post ST and something is definitely wrong with your experiment. Adding heat or 'coolth' from the ambient should affect the internal temp the same (just the direction of change waries) but I can tell you that if my house

    Posted By: SteamyTeamasses track the ambient pretty closely


    I would die (metaphorically speaking). Your graph just does not reflect how high mass houses perform, though sadly I am not informed enough to even speculate why your experiment isn't working.
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012 edited
     
    Posted By: GotanewlifeYour graph just does not reflect how high mass houses perform, though sadly I am not informed enough to even speculate why your experiment isn't working.

    What I would like to know too, hence doing this.
    Both myself and JSH have low mass houses and when we looked into the temperature swings we found them to be very thermally stable, I am not claiming that high mass takes anything away, just that in the UK with a relatively stable climate (we are most affected by sea surface temperatures on the west and wind direction on the east) it is unnecessary and adds nothing. By isolating the experiment from solar gain as much as I can and making it airtight, by all having the same initial thermal properties, i.e. U-values, mass, location, shape and size etc, those factors can be discounted.
    Then introducing different amounts of mass, which can be anything but choose the two simplest ones that come up in conversation a lot on here and recorded the differences (or lack of them), it seems to show that having a thermal masses with different properties (SHC between 1 and 4.2 J/(g.K) is just not changing anything.
    I have moved the kit into the sun and shall see what those readings do in a few days time, but suspect that the swings will just be greater because of the solar gain, while the ambient will be pretty similar because the sensor is out of the sun.
    I can see the argument that as my mass is on the base the 'walls' cannot absorb solar gain, but as I am not (just yet) looking at solar gain, just temperature rise and falls, that is not valid at this point in time. My feeling is that the U-Value of a wall will counter any storage (have I mentioned Thermal Inertia :wink:).
    If anyone wants to suggest a different way of testing this, feel free to and I shall see if it is possible to construct (think making things on Blue Peter rather than Tomorrows World).
    • CommentAuthorbillt
    • CommentTimeSep 10th 2012 edited
     
    Posted By: SteamyTeaBy isolating the experiment from solar gain as much as I can and making it airtight, by all having the same initial thermal properties, i.e. U-values, mass, location, shape and size etc, those factors can be discounted.


    If you remove solar gain you're removing one of the main factors that thermal mass takes advantage of. A low mass room with significant solar gains (i.e. a S to W facing window) is very likely to get uncomfortably hot in sunny weather. The excess heat can be absorbed by the thermal mass and will significantly reduce maximum temperature.

    If there's no heat input and the level of insulation and draught proofing is equally high, I doubt that there will be a significant difference between high and low mass construction.

    Our house has elements of both high and low thermal mass. The bottom two floors are solid stone up to 30" thick and mostly with no insulation. The top floor is solid single brick with about 80mm of insulation, which was installed 20 odd years ago. The bottom two floors have very stable temperatures; the top floor suffers from overheating in sunny weather and excessive heat loss in cold weather.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 10th 2012
     
    Maybe I have it - this experiment isn't scaleable. It only works at full size.

    Because lag and decrement are both related to true thickness of material relative to volumetric specific heat capacity. The active part of a real-building sized thermal mass is approx the outer 100mm of a mass that may be say 500kg. Scale that down to the outer 10mm of a 1kg mass, and the lag and decrement that you see will be diminished in that ratio. - i.e. will become negligible.
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012 edited
     
    Have you got data for upstairs?
    You seem to have a delay of about 3 hours between lowest ambient and lowest kitchen/dining room temperature, but your variation is not that different between days, about 1°C difference (internal), though the ambient temp swings greatly between 8°C between the 29/8 and 30/8 and 19°C between the 2/9 and 3/9, so not so different from my temperature swings between experiments days, big differences in ambient but not so different inside the 'houses'.
    Can you send me the raw data as a text file and I shall see if I can do the same tests on it as I have done on mine as there may be an error in the choice of tests.
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012 edited
     
    I am not fully sure how scalable it is, though the masses scale in a linear fashion, the areas do not.
    One thing that would make a difference in a real house is that hot air rises, so where we measure makes a difference, small scale it is much more homogeneous.
    Windows that face the sun will probably make a large difference than ones that do not face the sun, north facing ones just become part of the overall wall U-Value.
    Thermal Inertia affects the time lags, as Billt's chart shows, but his 30"s of stone wall still has a U-Value, and that may account for as much of the temperature stability as the mass it contains, opening and closing windows will affect stability too.
    Has anyone ever built a house with 30" SIPs/Rockwool batts to see what happens?
    (purely as an aside there is a bit on You and Yours about Nibe exhaust air heap pumps in houses, they say it is the lack of insulation: http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9552&page=1#Item_3)
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012 edited
     
    Just plotted the same time slot as BillT's to see what happens (well to the 7th when I stopped it).
    I get a lot of variation in internal temperature and I think this is to do with insulation levels (1 mm of PE has a poor U-Value).
    But the main thing, and the point I am making is that adding mass to the 'houses' does not change the internal variation hardly at all. This has made me think about adding insulation to each of the 'houses' and seeing what happens, so I shall go and get some tape and I have some expanded PE and shall wrap the 'houses' up and put then back and see what happens.
    Question is, should I insulate the base, sides and top or just the sides and how long should I run the test for, last time was 26 days?
    • CommentAuthormw116
    • CommentTimeSep 10th 2012
     
    ST,
    Is part of the problem the relative positions of the thermal mass? In a building the thermal mass is generally in the walls/floor surrounding the air, whereas in your experiment the thermal mass is in the center of the air.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 10th 2012 edited
     
    ST, lag, and indirectly decrement, depend on speed of travel of a temp wavefront thro the thickness a thermal mass material. That speed is dependent on the ratio of thermal resistivity to volumetric specific thermal capacity (not dependent at all, BTW, on initial delta-t - in other words greater delta-t doesn't drive the wavefront any faster).

    So if you scale the sample down, the wavefront's propagation speed stays the same so the wavefront simply gets thro the sample faster, and the decrement is less, in other words the effect of the thermal mass on the space becomes maybe negligible. Not just scaled down pro rata, so that you'd have to speed time up pro rata - but pretty well extinguished to meaninglessness.
    • CommentAuthormike7
    • CommentTimeSep 10th 2012
     
    Posted By: fostertomST, lag, and indirectly decrement, depend on speed of travel of a temp wavefront thro the thickness a thermal mass material. That speed is dependent on the ratio of thermal resistivity to volumetric specific thermal capacity (not dependent at all, BTW, on initial delta-t - in other words greater delta-t doesn't drive the wavefront any faster).

    So if you scale the sample down, the wavefront's propagation speed stays the same so the wavefront simply gets thro the sample faster, and the decrement is less, in other words the effect of the thermal mass on the space becomes maybe negligible. Not just scaled down pro rata, so that you'd have to speed time up pro rata - but pretty well extinguished to meaninglessness.


    What he said.

    You need either a bigger set of houses or a faster spinning planet.
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012 edited
     
    Response to mw116, got ot work out why the initial temperature difference makes no difference to the wave fron tin Toms suggestion before I respond to that.
    Not in the centre, it is on the base (call it floor).
    I can see that walls could get more solar gain from a window opening, but this is about measuring the affects of just thermal mass in identical containers to take way the other variables.
    Using variables to your advantage is a design issue (maybe low mass highly insulated wall to the north and solid walls to the south, solid internal walls that catch the sun, different floor construction between ground floor and successive levels etc.
    What I am trying to show is that thermal mass on its own is not what stabilises temperature, it is a combination of lots of things. As a thought experiment (think I have done this one before), imagine a large block of solid rock shaped like a house, pop a thermometer in the middle and measure the temperature, it will probably be around the annual mean ambient air temperature. Create a small void in the middle and measure that air temperature, be somewhere around the same temp, you have decreased the thermal mass, and the U-value slightly, but it makes no difference. Keep doing this and somewhere along the way you will get to a point where the variation in temperature starts to show but only slightly, well within comfort levels, assuming you are comfortable with the mean annual ambient air temperature (so maybe you have to live in Corpus Christi where it is about 22°C). Now from that point on, as you remove mass, you add insulation so that it matches the U-value you are removing, will the temperature stay the same, will it vary wildly, does anyone know, has anyone tried this out?
    My initial results show that, within the accuracy of my measuring equipment, adding mass to identical 'houses' makes no difference, so I think it may well be work adding insulation and seeing if that dampens out the variation.
    • CommentAuthorskyewright
    • CommentTimeSep 10th 2012
     
    Posted By: SteamyTea
    Question is, should I insulate the base, sides and top or just the sides

    If you are measuring at the base, then I'd guess that insulation below would be very important, else the mass of the ground that the houses are sat could be having a big influence?

    Or maybe I missed something and you've already covered that angle?
    • CommentAuthorskyewright
    • CommentTimeSep 10th 2012
     
    Posted By: SteamyTeaResponse to mw116, got ot work out why the initial temperature difference makes no difference to the wave fron tin Toms suggestion before I respond to that.

    Maybe it's a bit like the speed of sound in a medium not varying with the loudness of the sound. :smile:
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012
     
    Posted By: skyewrightOr maybe I missed something and you've already covered that angle?

    The sensor is in the mid point, just the mas is lower down.
    Having thought about it a while (takes my mind of what I am really meant to be writing), All I need to do is to have one without any insulation, one with one layer and one with 2 layers, maybe a third with 3 and see what happens. No mass in any of them and insulated all over.
    Can always add mass as a third iteration.

    For Tom
    The energy you put into a system makes the molecules move/vibrate faster, this accounts for pressure and expansion, so one can apply the classic formula C=(PV)/T
    P and V are constants, leaving C and 1/T, so as T goes down, C must go up and visa versa, not sure how that fits in, if at all, but shall ponder it more.
    • CommentAuthormike7
    • CommentTimeSep 10th 2012
     
    Not sure if you have taken on board the comments about time scale, but if you have you could try using a shorter diurnal cycle (if your houses are small enough and your fridge/freezer is large enough) by alternately cooling and rewarming them every hour or so, and see what happens then.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 10th 2012
     
    Posted By: SteamyTeagot ot work out why the initial temperature difference makes no difference to the wave fron tin Toms suggestion
    The extra oomph of higher delta-t goes into greater amplitude, not frequency, of the temp wavefront. In other words, if the hot end is hotter to start with, its greater energy immediately makes the first lamina of the sample hotter exactly pro rata, and so on to further laminae; the higher energy content of the wave is fully soaked up into higher temps and none is left over to increase the speed of travel of propagation.
    • CommentAuthorskyewright
    • CommentTimeSep 10th 2012
     
    Posted By: SteamyTeaHaving thought about it a while (takes my mind of what I am really meant to be writing), All I need to do is to have one without any insulation, one with one layer and one with 2 layers, maybe a third with 3 and see what happens. No mass in any of them and insulated all over.
    Can always add mass as a third iteration.

    That sounds good (or at least interesting) to me. :smile:
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 10th 2012
     
    Posted By: skyewrightThat sounds good (or at least interesting) to me.

    I am going to do it, been out and got the sticky take and shall set it up tonight.

    Posted By: fostertomThe extra oomph of higher delta-t goes into greater amplitude, not frequency

    Right, I see what you mean now, though I cant really see what shortening the time between warming and cooling will show, except that it as it warms up in a room it warms up and as it cools in a fridge it cools, I can do that with just a thermometer or two. But if I understand what is being said here, as the 'houses' are small, I need to cycle the temperatures at a higher rate (increase frequency) but keep the amplitude the same, so something like the chart below:
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 13th 2012 edited
     
    Right had a few minutes to look at what was happening when I left it in the sun.
    The temperatures where higher, but again, within the accuracy of the the measuring equipment there was no significant difference (or statistical).
    This was a small, short test so I would not read too much into it.

    Results and pictures.
    At the Student T-Test results (treatment being varying mass) were >0.05, so no difference there.

    Class,Ambient,No Mass,1 kg Granite,1 kg Water
    Mean,16.1,16.6,16.9,17.2
    Median,15.8,15.0,15.5,16.0
    Mode ,15.5,15.0,14.5,15.0
    Min,11.0,9.5,10.0,11.0
    Max,22.5,36.5,36.0,36.0
    Range,11.5,27.0,26.0,25.0
    St Dev,2.4,4.8,4.9,4.6
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 20th 2012 edited
     
    Have given the insulated 'houses' a bit of time to log some data and had a bit of a disaster. One of the temperature loggers has failed (they are getting old now), but luckily it was on one of the insulted 'houses'.
    I don't think it will make much difference as the results were pretty inconclusive. Not sure if it was the weather, the design of the experiment (not enough insulation) or the location (in the shade).
    The basic data is as follows:

    Class,Ambient,Uninsulated,Insulated
    Mean,12.7,12.4,12.5
    Median,12.6,12.0,12.5
    Mode,11.6,12.0,12.0
    Min,7.6,8.0,8.0
    Max,20.1,18.0,17.5
    Range,12.5,10.0,9.5
    St Dev,2.0,1.8,1.7

    There seems to be less dispersion in the range the more insulation there is, but the 3 averages are all the same within the accuracy of the sensors.

    The charts below may show this better.
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