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.)
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 :-)
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.
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?
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? :-))
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
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