I'm trying to work out the losses in my new (1970) bungalow. ATM I
have a spreadsheet that tells me that I need 16 kW with an external
-1C. Strangely, the boiler, a Worcester HeatSlave Oil combi, is a
15-19kW model - perhaps the engineer that spec-ed it back in 1991 could
add up too :-)

Now I can find U-values for most things, but how do I work out the
effect of adding another 150mm to the existing 100mm loft insulation.

Also, my heating pipes run through the loft, and are lagged, but I
think I should allow a loss per meter run, any ideas how to do that?
The house is L-shapped and some of the runs are very long.

Thanks,

R.

Happy Christmas and a Prosperous New year to all.

On Wed, 21 Dec 2005 17:38:44 +0000, Richard A Downing
wrote:

I'm trying to work out the losses in my new (1970) bungalow. ATM I
have a spreadsheet that tells me that I need 16 kW with an external
-1C. Strangely, the boiler, a Worcester HeatSlave Oil combi, is a
15-19kW model - perhaps the engineer that spec-ed it back in 1991 could
add up too :-)

Now I can find U-values for most things, but how do I work out the
effect of adding another 150mm to the existing 100mm loft insulation.

Look up the value for 100mm - call it U1
Look up the value for 150mm - call it U2

Resultant U = 1((1/U1) + (1/U2))

This ignores the surface effects etc. but is good enough for this
exercise


Also, my heating pipes run through the loft, and are lagged, but I
think I should allow a loss per meter run, any ideas how to do that?
The house is L-shapped and some of the runs are very long.

Find the U value of the insulation from the manufacturer.

Calculate the internal surface area by multiplying the circuference of
the end (pi x Dia) by the length. Use pipe diameters and Make sure
you end up with sq. metres.

Treat it as having a temperature drop of 85 degrees and see what you
get.

It should not be more than a few tens of watts and can then be ignored
for boiler size purposes

If it's more, then thicker lagging is needed.. Thickness equivalent
to dia of pipe is typical.



--

..andy

In an earlier contribution to this discussion,
Andy Hall wrote:


Look up the value for 100mm - call it U1
Look up the value for 150mm - call it U2

Resultant U = 1((1/U1) + (1/U2))

I think you must have needed a slash in the middle of typing that last line.
g

Putting it back in gives: U = 1/((1/U1) + (1/U2))

or, in simpler form: U = (U1 x U2)/(U1 + U2)
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

On Wed, 21 Dec 2005 19:36:56 -0000, "Set Square"
wrote:

In an earlier contribution to this discussion,
Andy Hall wrote:


Look up the value for 100mm - call it U1
Look up the value for 150mm - call it U2

Resultant U = 1((1/U1) + (1/U2))

I think you must have needed a slash in the middle of typing that last line.
g

Ho Ho Ho.

Time to dust off my Victor Meldrew starter kit in preparation for the
carol singers showing up.



Putting it back in gives: U = 1/((1/U1) + (1/U2))

or, in simpler form: U = (U1 x U2)/(U1 + U2)

--

..andy

On Wed, 21 Dec 2005 17:38:44 +0000, Richard A Downing
wrote:

Also, my heating pipes run through the loft, and are lagged, but I
think I should allow a loss per meter run, any ideas how to do that?
The house is L-shapped and some of the runs are very long.

What sort of insulation and how thick is it? If it's old sacking I'd
expect it's well worth replacing with thick foam, especially if adding
loft insulation makes freezing temps more likely in the loft.

There's a formula for pipe insulation heat loss in the following
paper:

http://www.anotherurl.com/therm/howmuchenergy.htm

Rcyl = ln(Outer radius / Inner radius)/ (2 * PI * length *
conductivity)

Q = dt / Rcyl

and the thermal conductivity of pipe insulation he

http://www.nmc.be/iso/upload/world_092004.pdf

l = 0.038 W/mK

Using them for 25mm insulation on 15mm pipes with a 60C temp
difference gives a heat loss of ~10W per metre.

Rcyl = ln(32.5/7.5)/(2 * PI * 1 * 0.038) = 6.14 C/W

Q = 60 / 6.14 = ~10W/m

Suprisingly 9mm foam insulation gives ~18W/m, so adding lots more gets
you well into diminishing returns. But 25mm will freeze almost as
twice as slowly...

cheers,
Pete.

Set Square wrote:

Putting it back in gives: U = 1/((1/U1) + (1/U2))

Although, as Andy said, that will underestimate the combined U value
somewhat, since the boundary layer resistances are being included twice.

More accurately: U = 1/((1/U1) + R2) where R2 is the R value of the
added insulation. The R value is found from the thickness of insulation
(in meters) divided by the thermal conductivity of the material (k).

Example: existing U value say 0.5 W/m^2K, add 150 mm of fibreglass or
Rockwool with k value of about 0.034 W/mK. R2 in this case is
0.15/0.034, i.e. about 4.4 m^2K/W and the new U value is 1/(1/0.5 + 4.4)
which is about 0.16 W/m^2K.

--
Andy

On Wed, 21 Dec 2005 17:38:44 +0000
Richard A Downing wrote:

I'm trying to work out the losses in my new (1970) bungalow.

Many thanks to everyone who helped with this or the previous question
about underfloor heating.

My spreadsheet (not guaranteed correct, or even sensible) is on my
website, if anyone is interested:

http://www.langside.org.uk/private.html

There are three scenarios:

1) the original almost uninsulated house (July 2005)
2) what I hope to have by mid January after loft insulation to 250mm
and low-e 28mm double glazing (January 2006)
3) and my plan for the next phase with Cavity Wall insulation and some
other improvements (Next Phase)

Of course, the key thing to realise is that U-values have to be added
up as reciprocals..... Thanks again.

R.

On Thu, 22 Dec 2005 17:46:54 +0000
Andy Hall wrote:

The other thing, Richard, is that you can look at the Approved
Documents (Part L1) for the Building Regulations at www.odpm.gov.uk
for information on combining methods and aspects.

Thanks, that's very useful. The appendixes in particular.

However, when you start to add reciprocals, you realise that if you
add insulation where there has been none, typically the U value for it
dominates the total, almost to the point that the original can be
disregarded. The other is that incremental insulation often does not
make as much difference as one might think to the total story.
For example, for a typical two storey house, adding cavity insulation
will normally make more difference to the total situation than adding
a lot of loft insulation if there already is some. In a bungalow,
this is skewed somewhat because of greater roof vs. wall area.

Yes, I noticed this. At the moment I can't add CWI as some cretin
built a paved path tight to the wall on one side, above the DPC! I
really don't want damp rockwool in the cavity. Moreover, my walls only
have 50mm cavities, the minimum needed to get rockwool in. The other
issue there is that they are not plastered - bare brick - and the
bricks are concrete, not baked clay, the whole rendered with cement on
the outside. I've just guessed at the U-value for that in the
spreadsheets, but it won't be far off 1.

The big problem with this house right now are the air leaks and the
enormous single glazed windows. Unlike most modern or Old houses this
one has big glass walls, so the double glazing 'gain' is going to
be very high. The loft insulation may appear to be 100mm, but in many
places it's been compressed by 'stuff' in the loft - I've teazed this
out a bit but it needs topping up. Finally the pipe runs - over 30
meters to the furthest rad - are wrapped in sacking - so poly-pipe
insulation is also going to make a big difference.

Notice also that the air exchange losses are significant and much less
predictable than surface losses, so the odd 50W here and there in a
room requiring 1kW or more for heating, doesn't matter a great deal.

Two other things.

It is normal these days to work on the basis of an outside temperature
of -3 instead of -1 degrees.

Yes, I realise that. In fact here in Cumbria I want the system to work
well within it's capabilities down to -5, with -10 possible by closing
some rooms. I'm expecting the Gulf Stream to stop, and even this won't
be enough eventually.

If you are going to use a condensing boiler (presumably so because you
have to unless certain exemption conditions are present), then it
makes sense to design for boiler flow and return temperatures of 70
and 50 degrees rather than the conventional 82 and 70 degrees.
Doing this will allow the boiler to run more efficiently for most of
the time.

The current boiler will be OK for a bit I think, it's not pressurised,
and not condensing. But when I replace it, I'll deal with both those
issues, and I may go for Underfloor with a Heatstore, so that I can
keep the mains hot water - even though this will mean finding somewhere
for the damn tank and a lot of extra plumbing! Underfloor will also
mean that I will have to address the issue of insulation of the floor -
currently concrete slabs. This will also address:

However, doing this will reduce the heat output from radiators of a
given size, ergo you have to use a larger output radiator than you
otherwise would. If you look at radiator data sheets, you will see a
correction factor that should be applied. For 82/70, it is normally
0.9 and for 70/50 normally around 0.6
You can obtain increased output by use of double instead of single
panels or with fins rather than necessarily increasing the size.

Thanks very much for all the suggestions. It's really good to have
people to talk these ideas over with.