In article ,
David J writes:
On Fri, 27 Nov 2009 18:57:03 +0000 (UTC),
(Andrew Gabriel) wrote:

It should be more like this...

T0. - ambient indoor temperature
T1. - surface temp of inside inner wall (plaster)
T2. - surface temp of outside inner wall (thermal block)
T3. - surface temp of inner outer wall (brick)
T4. - surface temp on outer outer wall (brick)
T5. - ambient outdoor temperature

Assuming T0 and T5 remain the same...
There will be an increase in T2 and a decrease in T3 as you say.
However, there will also be a (smaller) increase in T1 and decrease
in T4, because less energy is being drawn though the wall.

Measuring the difference between T0 and T1 (or T0 and T2, or T1 and
T2, as none of these thermal elements change) will give you a figure
which is proportional to the temperature loss through the wall.


Andrew - thanks, I find your correction above is very convincing.

Now to figure out a good way to measure T2 & T3, before the CWI is
installed!

Quite apart from being difficult to measure, I don't think that
measurement will tell you anything useful quantitatively.

Take several temperature reading sets of T0, T1, and T5 (I'd
include T4 too, but it's less useful). Each temperature set is
all of them at the same time.

Do this again after the CWI. If you get a reading set with the
same value for (T0 - T5), you will hopefully find (T0 - T1) is lower.
To a first approximation, if old (T0 - T1) is 3 times the value
of new (T0 - T1), then your heat loss was 3 times higher before.

If you don't get a reading set with the same value for (T0 - T5)
before and afterwards, then you can still work it out, but you'll
have to include a correction factor for the difference.

An infrared thermometer is excellent for measuring wall
temperatures. Ideally, you want to use the same thermometer
for measuring the air temperature, which an IR thermometer can't
do. What you can do is to measure the temperature of something
such as a small sheet of paper hanging in the air, at least a
metre from the wall (but same place every time), and make sure
it doesn't have the sun on it, or it won't be at air temperature.

--
Andrew Gabriel
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