I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

It is clearly not good enough to simply measure the surface
temperatures of the inside and outside of the exterior walls, as one
is the source and the other is the sink of the heat transfer through
different materials. And the exterior wall temperature will always be
that of the ambient climate temperature.

I have read about R and U factors, but that does not help. I have also
read that thermal transfer (in buildings) is analagous to electrical
flow through conductors, so what really is required is to obtain the
thermal drops across the wall sections.

So, taking a typical modern exterior wall construction, 4 temperatures
are needed as follows.

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)

With the CWI installed and thermal transfer reduced, under steady
state there will be no change to T1 and T4, but an increase in T2 and
a decrease in T3 with the majority of the thermal drop now occuring
across the cavity insulation.

Does the above reasoning make sense?

David

David J
wibbled on Friday 27 November 2009 15:42

I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

It is clearly not good enough to simply measure the surface
temperatures of the inside and outside of the exterior walls, as one
is the source and the other is the sink of the heat transfer through
different materials. And the exterior wall temperature will always be
that of the ambient climate temperature.

I have read about R and U factors, but that does not help. I have also
read that thermal transfer (in buildings) is analagous to electrical
flow through conductors, so what really is required is to obtain the
thermal drops across the wall sections.

So, taking a typical modern exterior wall construction, 4 temperatures
are needed as follows.

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)

With the CWI installed and thermal transfer reduced, under steady
state there will be no change to T1 and T4, but an increase in T2 and
a decrease in T3 with the majority of the thermal drop now occuring
across the cavity insulation.

Does the above reasoning make sense?

David

That's about it (ignoring the thickness of the plaster and assuming T1 is
the temperature of the inner face of the thermal block).

Do it like a resistors in series calculation:

Current is analagous to power transmission
Potential difference is analagous to temperature difference.

I can never remember which is U/R/K/whatever is analagous to resistance (in
this case more like resistance per unit area), but a look on Wikipedia:

http://en.wikipedia.org/wiki/R-value_(insulation)

Suggests is the R value. U values are the inverse.

--
Tim Watts

This space intentionally left blank...

In article ,
David J writes:
I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

It is clearly not good enough to simply measure the surface
temperatures of the inside and outside of the exterior walls, as one
is the source and the other is the sink of the heat transfer through
different materials. And the exterior wall temperature will always be
that of the ambient climate temperature.

That's not the case. The outside wall must be warmer than the
ambient temperature in order to lose heat to it. Similarly,
the internal side must be cooler than the air temperature in
order for the room to lose heat to the wall. The difference
in temperature between the air and the wall is (roughly)
proportional to the energy loss at the inside. This is also
true at the outside but factors such as wind-chill and dampness
will affect the figures and make comparison readings impossible,
so you'll need to measure this on the inside where wind-chill
and evaporation are hopefully a constant (zero).

I have read about R and U factors, but that does not help. I have also
read that thermal transfer (in buildings) is analagous to electrical
flow through conductors, so what really is required is to obtain the
thermal drops across the wall sections.

So, taking a typical modern exterior wall construction, 4 temperatures
are needed as follows.

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)

With the CWI installed and thermal transfer reduced, under steady
state there will be no change to T1 and T4, but an increase in T2 and
a decrease in T3 with the majority of the thermal drop now occuring
across the cavity insulation.

Does the above reasoning make sense?

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 Gabriel
[email address is not usable -- followup in the newsgroup]

Tim W wrote:
David J
wibbled on Friday 27 November 2009 15:42

I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

It is clearly not good enough to simply measure the surface
temperatures of the inside and outside of the exterior walls, as one
is the source and the other is the sink of the heat transfer through
different materials. And the exterior wall temperature will always be
that of the ambient climate temperature.

I have read about R and U factors, but that does not help. I have also
read that thermal transfer (in buildings) is analagous to electrical
flow through conductors, so what really is required is to obtain the
thermal drops across the wall sections.

So, taking a typical modern exterior wall construction, 4 temperatures
are needed as follows.

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)

With the CWI installed and thermal transfer reduced, under steady
state there will be no change to T1 and T4, but an increase in T2 and
a decrease in T3 with the majority of the thermal drop now occuring
across the cavity insulation.

Does the above reasoning make sense?

David

That's about it (ignoring the thickness of the plaster and assuming T1 is
the temperature of the inner face of the thermal block).

Do it like a resistors in series calculation:

Current is analagous to power transmission
Potential difference is analagous to temperature difference.

I can never remember which is U/R/K/whatever is analagous to resistance (in
this case more like resistance per unit area), but a look on Wikipedia:

http://en.wikipedia.org/wiki/R-value_(insulation)

Suggests is the R value. U values are the inverse.

I just look it up in a manual that tells me that the heatloss with CWI
is about a third as without...

Since mots people have dine lofts and double glazed, that means about a
60% saving in fuel bills, as the walls are the dominant loss now.

In article ,
(Andrew Gabriel) writes:

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.
^^^^^^^^^^^
Sorry, should say _energy_ loss.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Fri, 27 Nov 2009 18:57:03 +0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
David J writes:
I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

It is clearly not good enough to simply measure the surface
temperatures of the inside and outside of the exterior walls, as one
is the source and the other is the sink of the heat transfer through
different materials. And the exterior wall temperature will always be
that of the ambient climate temperature.

That's not the case. The outside wall must be warmer than the
ambient temperature in order to lose heat to it. Similarly,
the internal side must be cooler than the air temperature in
order for the room to lose heat to the wall. The difference
in temperature between the air and the wall is (roughly)
proportional to the energy loss at the inside. This is also
true at the outside but factors such as wind-chill and dampness
will affect the figures and make comparison readings impossible,
so you'll need to measure this on the inside where wind-chill
and evaporation are hopefully a constant (zero).

I have read about R and U factors, but that does not help. I have also
read that thermal transfer (in buildings) is analagous to electrical
flow through conductors, so what really is required is to obtain the
thermal drops across the wall sections.

So, taking a typical modern exterior wall construction, 4 temperatures
are needed as follows.

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)

With the CWI installed and thermal transfer reduced, under steady
state there will be no change to T1 and T4, but an increase in T2 and
a decrease in T3 with the majority of the thermal drop now occuring
across the cavity insulation.

Does the above reasoning make sense?

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!

David

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
[email address is not usable -- followup in the newsgroup]

On Fri, 27 Nov 2009 15:42:39 +0000, David J wrote:

I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

You could get a reasonable estimate using the whole house boiler sizing
method to estimate the total heatloss of your house and do the calculation
with and without CWI.

There are links at
http://wiki.diyfaq.org.uk/index.php?...Heating_Design to some
online calculators, and a spreadsheet with which you can easily do what-if
calculations.

--
John Stumbles -- http://yaph.co.uk

Little Johnny's gone away, his like we'll see no more
For what he thought was H20 was H2SO4

On Nov 27, 3:42*pm, David J wrote:
I have been wondering how to measure the 'effectiveness' of adding CWI
to a domestic house, apart from seeing the resultant change in energy
costs at a much later date.

It is clearly not good enough to simply measure the surface
temperatures of *the inside and outside of the exterior walls, as one
is the source and the other is the sink of the heat transfer through
different materials. And the exterior wall temperature will always be
that of the ambient climate temperature.

I have read about R and U factors, but that does not help. I have also
read that thermal transfer (in buildings) is analagous to electrical
flow through conductors, so what really is required is to obtain the
thermal drops across the wall sections.

So, taking a typical modern exterior wall construction, 4 temperatures
are needed as follows.

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)

With the CWI installed and thermal transfer reduced, under steady
state there will be no change to T1 and T4, but an increase in T2 and
a decrease in T3 with the majority of the thermal drop now occuring
across the cavity insulation.

Does the above reasoning make sense?

David

A simple option is to plug a heater of known power in, let temp
stabilise, and measure temp diff between indoors and out. This takes
account of the whole picture.


NT

"NT" wrote in message
...

A simple option is to plug a heater of known power in, let temp
stabilise, and measure temp diff between indoors and out. This takes
account of the whole picture.

You van make the maths easier by using an angle grinder to cut a 1 m square
section out of the wall.
Mount this ay one end of a well insulated box containing the heater.
Let it run until it stabilises and then measure the temps.