radiator output formula and finless rad specs

After a bit of firkling around with Myson & Kudox radiator output specs I
found a formula which gives a reasonable approximation so one can
calculate output from dimensions (and v.v.)
Heat Output = (Height + 12) * Length * FACTOR
(Watts) (cm) (cm)
where FACTOR is (for Delta-T 50°C)
* 0.13 for SC
*
0.19 for DP
* 0.24 for DC
See
formatting link
might be useful[1] to be able to calculate the output of old-fashioned
radiators without convection fins. Anyone have any data sheets on these?
[1] or at least, marginally interesting :-)
Reply to
John Stumbles
The message from John Stumbles contains these words:
As I mentioned in another thread recently I have some documentation from Ravensbourne Heating. The older catalogue (which I think dates to the mid 70s) has data on radiators from Stelrad, Potterton, International, Harcal and even Finrad. The later catalogue (circa 1988) is a much thinner affair with Barlo as the only standard radiator offering. Heat output in both cases is in btus/hour.
To go off on something of a tangent while flicking through some of the rubbish I have accumulated over the years I came across a leaflet for the Trisave condensing boiler which, unlike all the other stuff I have retained, was actually dated - February 1989.
IIRC Trisave was the first condensing boiler on the British market and was (in retrospect) notoriously unreliable. It was (perhaps thankfully) no longer available when I came to replace my gas boiler a couple of years later so I ended up fitting a conventional fanned flue model which is still working well.
Reply to
Roger
In an earlier contribution to this discussion,
It is certainly useful to be able to estimate the output of existing (obsolescent) radiators - and the question is often asked here by those who are re-jigging their central heating systems, or just doing a sanity check on what they've got.
I don't still have the catalogues which I used back in the late 60's - but I have still got my calculations, from which I developed my own formula - having converted from imperial to metric units. The figues which I use - at a Delta-T of 60 degC are: Single Panel: 1280 watts/M^2 Double Panel: 2170 watts/M^2
This would equate to 1020 and 1730 respecively at a Delta-T of 50 degC.
This would be 0.102 and 0.173 watts/cm^2 to compare with your 'factors' - except that my calculations just take the projected area without adding anything to the height. What is the rationale of your +12 bit?
What sort of radiator is your 'DC'?
Reply to
Roger Mills
Looking at the Myson & Kudox specs it was apparent that their outputs were not linearly related to heights, so that a 600mm high rad was less than twice the output of a 300. I didn't plot the values but I'd guess it's a curve of some sort. Approximating it to an offset as I've done gives a pretty good agreement with the published values.
Intuitively it makes sense that doubling the height wouldn't double the output: since 'radiators' are actually convectors then a greater quantity of warm air has to come off a taller rad, so I'd expect greater resistance from the surrounding air.
What sort of heights were the rads you arrived at your figures for?
Double Convector - like 2 single convectors sandwiched together. Explained in the wiki article (tsk!, you haven't read it? :-))
Reply to
John Stumbles
I recalled such a discussion but couldn't remember anything else about the thread!
Any chance of a scan of some of the specs?
Reply to
John Stumbles
In an earlier contribution to this discussion,
They were all either 24" or 30" high.
Looking at some modern catalogues, it looks as if *very* low radiators (e.g. 300 high) punch above their weight in heat output terms but - although I haven't done the sums in detail - my impression is that, once you get above a certain height, the output is linear. So my formula probably gives pessimistic results for low rads.
Mea Culpa! On reading the Wiki item and looking again at your previous post, it seems that I misunderstood what you initially said. When you said it might be useful to calculate the output of old unfinned rads, I initially thought that you were offering that as the reason for the figures you had quoted - which I had assumed to apply to unfinned rads. I now realise that you were suggesting looking at unfinned rads *in_addition* to what you had quoted. The figures I gave *were* for unfinned.
Having cleared that up, my complete list - with outputs in Watts/M^2 is:
TYPE Output at Delta-T=60 Output at Delta-T=50 Single unfinned 1280 1021 Single finned 2020 1612 Double unfinned 2170 1732 Double with single fins 2790 2226 Double with double fins 3575 2853
Reply to
Roger Mills
The message from John Stumbles contains these words:
I will see what I can do. Is you address genuine?
Reply to
Roger
The message from John Stumbles contains these words:
You have mail.
This just in case it doesn't get through.
Reply to
Roger
On Thu, 17 Jan 2008 00:32:55 GMT, John Stumbles wrote:
Sent you an email with a url of some zipped scans on Stelrad units circa 1979 including a couple of graphs.
Geo
Reply to
Geo

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