Boiler sizing calculations
 

What measurements would one need to calculate radiator output HW output
and henceforth boiler output for a domestic premises.

Room volumes, u values?
--
Z
Remove all Zeds in e-mail address to reply.

Boiler sizing calculations
 

Z wrote:

What measurements would one need to calculate radiator output HW output
and henceforth boiler output for a domestic premises.

Room volumes, u values?

Create yourself a spreadsheet with a set of entries for each room. You
need three bits of information to workout the heatloss:

The surface area
The temperature differential
The u value of the surface.

Multiply the lot together to get a figure of watts/hour transferred
through the surface.

(if a wall has a window then subtract the area of the window from that
of the wall, and count the window as a separate surface).

One you know the loss (or gain) through each of the surfaces add them up
to get a nett loss/gain for each room

Lots more info here-

http://www.diydata.com/planning/ch_design/sizing.htm

--
Cheers,

John.

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Boiler sizing calculations
 

"Z" wrote in message
...
:
: What measurements would one need to calculate radiator output HW
output
: and henceforth boiler output for a domestic premises.
:
: Room volumes, u values?
: --

Try 'heatloss manager' from http://www.myson.co.uk/
--
©J.Milton.Hayes©


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Boiler sizing calculations
 

On Sun, 16 May 2004 03:08:55 +0100, "J.Milton.Hayes"
wrote:


"Z" wrote in message
...
:
: What measurements would one need to calculate radiator output HW
output
: and henceforth boiler output for a domestic premises.
:
: Room volumes, u values?
: --

Try 'heatloss manager' from http://www.myson.co.uk/

This is useful, but unfortunately not up on their site at the moment.
It is free softeare, though, and I have a copy that I can email to
anybody wanting it.



..andy

To email, substitute .nospam with .gl

Boiler sizing calculations
 

John Rumm wrote

Z wrote:

What measurements would one need to calculate radiator output HW output
and henceforth boiler output for a domestic premises.

Room volumes, u values?

Create yourself a spreadsheet with a set of entries for each room. You
need three bits of information to workout the heatloss:

The surface area
The temperature differential
The u value of the surface.

Multiply the lot together to get a figure of watts/hour transferred
through the surface.

(if a wall has a window then subtract the area of the window from that
of the wall, and count the window as a separate surface).

One you know the loss (or gain) through each of the surfaces add them up
to get a nett loss/gain for each room


Don't forget the air change factor!

Peter

Boiler sizing calculations
 

On Sun, 16 May 2004 00:57:55 +0100, Z wrote:


What measurements would one need to calculate radiator output HW output
and henceforth boiler output for a domestic premises.

Room volumes, u values?

Both of the other other replies get you to knowing the heat losses for
the rooms - essentially the Myson program has a set of U values and
does the sums for you.

Once you know the heat loss for a room you can size the radiator.

What you go with depends on the boiler type and operating temperature,
because the actual radiator heat output depends on the mean
temperature difference between the radiator and room.

If you look at radiator manufacturer data sheets, you will find that
there is a main table of ratings. However these come from a test
which is done at a higher temperature than is normal for domestic
installations and has to be scaled with another table.

The two typical designs for UK installations are based around a
non-condensing boiler and a condensing boiler.

For a non-condensing boiler, the flow temperature is taken to be 82
degrees and return is 70, making a mean water temperature of 76
degrees. With an air temperature of 21 degrees, it means a Mean
Water to Air Temperature of 55 degrees. So you can refer to the
table and you will find that the derating factor is 0.89. This means
that the radiator gives only 89% of the test value as an output.
So, if you are starting from your heat loss number, you have to divide
it by 0.89 to determine which radiator to choose because it will need
to be a higher number than the main table suggests. Then you go to
the main table on the data sheet with your number and pick from there.
In other words, if your heat loss is 890W then you would need a
nominal 1000W radiator.

For a condensing boiler, the ideal design temperatures are 70 and 50
degrees. For that, the derating factor is generally about 0.6 which
implies a rather larger radiator.
However, you have a choice here. Condensing boilers will run up to
the traditional 80 degrees if needed and still be somewhat more
efficient than a non-condensing one. So if you already have the
radiators then it doesn't mean you have to change them.
Also, the heat loss calculations assume -3 degrees outside which is
not for much of the time - in effect you are designing for a worst
case. For large parts of the year, less heat is needed and the
boiler will modulate its temperature down into a more efficient lower
temperature range. At this point, the radiators are plenty adequate
anyway. So the sensible thing, is that if you are putting in new
radiators, size them for 70/50 operation, but it isn't mandatory if
not.

For the hot water, if you are using a cylinder and are able to change
it, use a fast recovery one. This is able to accept a lot of heat
from the boiler - perhaps 20kW or more.

Therefore it is not unusual to have a boiler sized at 25-30kW to do
that, when the CH requirement might only be 10-15kW. If the boiler
is a modulating type, this will work properly because it may be able
to drop its output to 4-7kW.






..andy

To email, substitute .nospam with .gl

Boiler sizing calculations
 

"Andy Hall" wrote in message
...
: On Sun, 16 May 2004 03:08:55 +0100, "J.Milton.Hayes"
: wrote:
:
:
: "Z" wrote in message
: ...
: :
: : What measurements would one need to calculate radiator output HW
: output
: : and henceforth boiler output for a domestic premises.
: :
: : Room volumes, u values?
: : --
:
: Try 'heatloss manager' from http://www.myson.co.uk/
:
: This is useful, but unfortunately not up on their site at the
moment.
: It is free softeare, though, and I have a copy that I can email to
: anybody wanting it.
:
:

That's odd, I've just been to their homepage and entered via the
'homeowners' link & it is at the top of the page ;-)


--
©J.Milton.Hayes©

--
**I thought I had Schizophrenia, now I'm in two minds**





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Boiler sizing calculations
 

On Sun, 16 May 2004 13:05:51 +0100, "J.Milton.Hayes"
wrote:


"Andy Hall" wrote in message
.. .

:
: Try 'heatloss manager' from http://www.myson.co.uk/
:
: This is useful, but unfortunately not up on their site at the
moment.
: It is free softeare, though, and I have a copy that I can email to
: anybody wanting it.
:
:

That's odd, I've just been to their homepage and entered via the
'homeowners' link & it is at the top of the page ;-)

Are you sure you don't have it cached?

I tried via installer and homeowner options, the page appears but the
HeatLoss Manager link (button in the middle on the right) appears as
Under Construction.....


..andy

To email, substitute .nospam with .gl

Boiler sizing calculations
 

"Andy Hall" wrote in message
...
: On Sun, 16 May 2004 13:05:51 +0100, "J.Milton.Hayes"
: wrote:
:
:
: "Andy Hall" wrote in message
: .. .
:
: :
: : Try 'heatloss manager' from http://www.myson.co.uk/
: :
: : This is useful, but unfortunately not up on their site at the
: moment.
: : It is free softeare, though, and I have a copy that I can email
to
: : anybody wanting it.
: :
: :
:
: That's odd, I've just been to their homepage and entered via the
: 'homeowners' link & it is at the top of the page ;-)
:
: Are you sure you don't have it cached?
:
: I tried via installer and homeowner options, the page appears but
the
: HeatLoss Manager link (button in the middle on the right) appears as
: Under Construction.....
:

My apologies, I didn't realise that the page was offline temporarily.

--
©J.Milton.Hayes©

**The 'mind' is like a parachute......works better open**


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Boiler sizing calculations
 

On Sun, 16 May 2004 14:32:51 +0100, "J.Milton.Hayes"
wrote:



:
: That's odd, I've just been to their homepage and entered via the
: 'homeowners' link & it is at the top of the page ;-)
:
: Are you sure you don't have it cached?
:
: I tried via installer and homeowner options, the page appears but
the
: HeatLoss Manager link (button in the middle on the right) appears as
: Under Construction.....
:

My apologies, I didn't realise that the page was offline temporarily.

No problem at all. I thought that maybe they had put it back up
again. Before the site was reconstructed, they did have a beta of a
new version written IIRC in Java, but it was pretty slow and ropey.

I grabbed a copy of the earlier one some time ago which is reasonably
good.
..andy

To email, substitute .nospam with .gl

Boiler sizing calculations
 

The Barlo calculator is still available Andy. Although not an inspiring program
and written for Win 3.1, it does work.

http://www.barlo.co.uk/pages/download.cfm

Peter

Boiler sizing calculations
 

On Sun, 16 May 2004 18:10:24 +0100, "Peter Taylor"
wrote:

The Barlo calculator is still available Andy. Although not an inspiring program
and written for Win 3.1, it does work.

http://www.barlo.co.uk/pages/download.cfm

Peter

That's probably the no. 2 after Myson, but IIRC it has some errors in
the U value tables, although you can correct them. It's a while since
I used the Barlo one, though




..andy

To email, substitute .nospam with .gl

Boiler sizing calculations
 

What measurements would one need to calculate radiator output HW output
and henceforth boiler output for a domestic premises.

TBH, there is little point calculating the boiler requirement nowadays.
Almost all modern domestic system boilers are modulating (variable) types of
around 24kW. These will do a fairly large and poorly insulated house. Even
if the requirement exceeded 24kW, you would still fit the 24kW boiler, but
would just improve the insulation to bring down the requirement. Obviously,
hotels or other large or commerical buildings may genuinely require more.
Also, if installing a combi boiler, you'd probably want more than 24kW.

Of course, if you need to calculate individual radiator sizes, then you
would need to do the calculations. There are programs available to do the
calculations. You need to know the various dimensions of the rooms and
openings. It isn't done on volumes, but on wall/floor/ceiling areas, the
construction of those areas and the temperatures on the other side. You need
to know the materials used (or the appropriate u-Values) and details of
insulation. You also need to decide on the outside temperature you expect it
to work in. People generally design to -3C now, although -1C used to be
common.

When choosing radiator sizes, don't forget to derate to the average of
flow/return temperatures. Preferably design to 60C (or under) to allow even
greater efficiency for a condensing boiler installation. Even if you don't
install one this time (you should) then you'll be forced to next time, so
you might as well optimise radiator sizes for them. However, even if you
don't optimise radiators for condensing boilers, you'll still get much
better efficiency than with a non-condensing type.

Christian.