[Strawbale] Forced air

[Mark BP / Low Energy Design Ltd]

dfugler at cmhc-schl.gc.ca wrote:

>Mark,
>
>You are probably having to keep the temperature higher in Saskatchewan 
>than in England because the walls and windows are colder, not because of 
>the change from radiant to forced air heating. The difference between an 
>outside temperature of 5°C and - 35°C is substantial. You will have 
>increased radiant loss to an outside wall or window when the termperature 
>outside is far lower (we could discuss relative wall insulation levels but 
>we won't).
>  
>
Hi Don.

I'm sure you're right that there is a radiant component to my comfort 
disparity.  Not least because I'm wanting higher indoor air temperatures 
in the winter than I was in the autumn.

But your outside temperature comparison needs to be refined a bit.  It 
seems to me that the key temperature parameter for our purposes is mean 
daytime temperature (not design temperature, or even overall mean 
temperature).  I haven't gone to the met data tables to get the hourly 
figures then average them down for waking hours, so what I'm about to 
say is approximate only.  The difference in this parameter between 
Bristol, England and Borden, SK will indeed be large in January (about 
+6 and about -15 respectively, I expect), but the same isn't true for 
September / early October, or for late May / early June, when daytime 
temps are typically about the same in the 2 places.
And my need for a higher indoor air temperature in Borden applies year 
round (though higher still in the winter).  So I don't think radiant 
losses explain more than a fraction of the differences.

Air movement / poor temperature distribution isn't the only candidate to 
explain the rest (the radiator system I had in Bristol probably resulted 
in higher mean wall surface temperatures, for example), but it still 
makes a lot of sense to me.


>As far as the assertion that radiant heated houses have lower thermostat 
>settings, I had heard that frequently as well. So I hired a student in 
>Nova Scotia to check a sample of each type of house: radiant flooring and 
>forced air. Here is the link to the results: 
>http://www.cmhc-schl.gc.ca/odpub/pdf/62675.pdf
>
>Thermostat settings were the same for the forced air and radiant flooring 
>houses. The radiant heating industry didn't like the study. They said it 
>was not big enough, and that we did not measure comfort created in those 
>houses. I challenged them to do their own study, or help us create a 
>bigger survey. So far they have not come up with the money to verify their 
>assertions.
>  
>
Thanks for this Don.  Interesting, and not what I would have expected - 
but to my mind not conclusive because it's a small sample and there are 
a lot of other relevant factors.  I think they should have taken up your 
challenge - it would be interesting to see what came out of a larger 
survey, especially if other factors which might affect thermostat 
setting (resident age + health, occupancy patterns, indoor activity 
levels, income level, thermostat location, etc) were also recorded.
If you become aware of any such larger survey actually happening, could 
you let me know?

atb
Mark

>Don Fugler
>CMHC Policy and Research
>  
>
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