Hello,

I downloaded the Barlo heat loss program as recommended here. As part
of its calculations, it asks for the outside temperature. When I was
using it, I never imagined it could get this cold. I think I used -2C
as the worst case temperature. The car said -13C this morning!
Luckily, the radiators are coping so far. What worse case temperatures
did you use and what will you use next time?

Thanks,
Stephen.

On 06/12/10 16:12, Stephen wrote:
Hello,

I downloaded the Barlo heat loss program as recommended here. As part
of its calculations, it asks for the outside temperature. When I was
using it, I never imagined it could get this cold. I think I used -2C
as the worst case temperature. The car said -13C this morning!
Luckily, the radiators are coping so far. What worse case temperatures
did you use and what will you use next time?

Thanks,
Stephen.

I can keep the ground floor of a dormer bungalow OK (19-20C) with about
7kW peak and about 4-5kW sustained average from 4 oil filled rads. That
house has most of the insulation missing pending roofing work at -3C
day-night average - but I do have to keep that 4-5kW on day and night.

I'd expect to halve that easily once the roof is sorted - noting how
warm my bay window ceilings are with only 50mm celotex between the rafters.

Also the roofing work will remove most of the draughts blowing over the
ceilings elsewhere.

So I would expect average radiator kW sizing to be smaller than one
might expect in a well insulated and draught free house - but of course
you need to oversize otherwise it can take a *long* time to recover a
warm house from a cold one.


--
Tim Watts

On Mon, 06 Dec 2010 16:12:54 +0000
Stephen wrote:

Hello,

I downloaded the Barlo heat loss program as recommended here. As part
of its calculations, it asks for the outside temperature. When I was
using it, I never imagined it could get this cold. I think I used -2C
as the worst case temperature. The car said -13C this morning!
Luckily, the radiators are coping so far. What worse case temperatures
did you use and what will you use next time?

Thanks,
Stephen.

I used -10C, then thought "that's ridiculously low", however looking
at the full model of the current and planned losses before/after
renovations I decided to stick with -10C on both rads and boiler.
Capital costs were not that much more.

As it happened we got this bit of Global Warming just after I
disconnected (drastically) two key rads for some major alterations,
then got sick. Great timing, but I'm mighty glad I went for overkill on
the rad sizing as leaving a few doors open has compensated.

I expect I pay for some loss of efficiency because the condensing oil
boiler will probably cycle more in a normal winter. But, hey, I'm warm.

R.

Stephen wrote:
Hello,

I downloaded the Barlo heat loss program as recommended here. As part
of its calculations, it asks for the outside temperature. When I was
using it, I never imagined it could get this cold. I think I used -2C
as the worst case temperature. The car said -13C this morning!
Luckily, the radiators are coping so far. What worse case temperatures
did you use and what will you use next time?

Thanks,
Stephen.
I used -5c but really should have used -10C. Its rare for outside to
AVERAGE worse than that. That was whole house though.
For individual rooms you can go to -20C if you like.

In article ,
Stephen writes:
Hello,

I downloaded the Barlo heat loss program as recommended here. As part
of its calculations, it asks for the outside temperature. When I was
using it, I never imagined it could get this cold. I think I used -2C
as the worst case temperature. The car said -13C this morning!
Luckily, the radiators are coping so far. What worse case temperatures
did you use and what will you use next time?

Not familiar with that program, but this isn't normally the worse case,
but is the worse case with the boiler operating in condensing mode. You
have plenty more power output by increasing the boiler flow temperature,
albeit the boiler won't be as efficient, but this is supposed to be rare.

I used a beta java version of the Myson heat loss calculator nearly
10 years ago. I used -3C, as is normal for a condensing system (which
is what it is, even though that was not required at the time). The
program significantly over-estimated the heat losses (I didn't investigate
why, but Andy Hall used it too, and said the U values they had for various
building materials were a bit pessimistic). This means I significantly
over-sized the radiators. (Maybe Myson thought that would be to their
advantage, but most if not all of the radiators I bought in the end
were not Myson;-)

In retrospect, I'm really pleased about this. I can heat the house
at 0C outside with the boiler running at 45/40 (flow/return), which means
the condensing boiler is running extraordinarily efficiently. I can boost
the heat output by nearly 3 times by cranking boiler up to maximum, which
means I can heat the house up from stone cold in about 15 minutes if I
need to. (Actually, boiler can't get above about 75C flow, because at
this temperature the radiators dissipate all 23kW of the boiler output.)

When running at 45/40, the boiler output is above minimum burner
modulation of 7kW, because it can do this without cycling on and off, but
probably not by much - let's guess about 8kW. So 8kW is enough to
maintain a 20C difference between inside and outside. This means the
heating system should be able to maintain the house at 20C at 23kW with
outside temperature down to -37C. It might do even better, as I added
another 4" of loft and bay roof insulation since I took these
measurements. This is a 1900 semi with 9" brick walls, so a more modern
house should be able to do better still.

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