Need to do system design for 55kw of radiators in office the floor area is 28m x 13m approx with 2.5m ceilings worked all the raditor sizes but am unsure of what the pipesizing will be, also the pipe work will be in the ceiling void is it worth insulating the main runs, looking to install buderus 800 60 kw bioler28mm flow & return tappings, this system only does rads. Also need to fit ex vessel what is the guide lines for this was thinking of 24 litre thanks gazza

The heat carrying capacity of a tube is limited by the maximum velocity that can be accepted for noise reasons. This is generally taken as 1.5 m/s. The other key factor is the temperature drop of the system which is generally taken as 20°K for a condensing boiler, although greater or lesser temperature drops could be specified. For 1.5 m/s and 20°K temp drop, the carrying capacity of each pipe size is as follows - 8mm = 4.5 kW, 10mm = 7.3 kW, 15mm = 18.1 kW, 22mm = 40.2 kW and 28mm = 67.5 kW. However these figures are maxima and may need to be reduced to take account of frictional resistance and available pump head. That can only be calculated for the individual installation, based on the index circuit. With a temperature drop of 20°K or more, care has to be taken with radiator sizing because the average temp of the rad will reduce with temp drop. For example with a max flow temp of 80°C and a 20°K drop the average temp will be 70°C. With a room temp of 20°C the differential temp (delta t) will be 50°K. Many radiator outputs are quoted based on a delta t of 60°K so such output figures would have to be reduced by 17% for delta t of 50°K.

I thought all manufacturers now quoted outputs to BSEN442 i.e Mean Water Temp = 70degC and Room Temp = 20degC The only thing which is different from normal installation practice is the the Standard specifies radiator connections as Top and Bottom, same end.

You could be right. I haven't actually checked that, but I'm sure I've seen some delta 60°K figures recently - ah yes, here.

thanks for that seems surprising & 67kw for 28mm so thats why the buderus 800 has only 28mm f & r i had visions of using 35 & 42mm pipework, how can i work out the ex vessel size is it worth insulating pipes in ceiling void. cheers gazza found out how to work out in the net if anyone is interested http://www.rwc.co.uk/content.aspx?page=ABOUT_EXPVESS#-1_g-ABOUT_EXPVESS_idMainTop(2)

All rads I fit, stelrad and myson have outputs quoted at 50C which was brought in to align us with eec about 2 years ago.

If you use 2 radial lines in stead of one loop, you will only have to deal with 30 kw, that solves half the problem. Secondly, the heating capacity seems enormous. Yes it is a large area, but heatloss will be predominantly from the walls, not the floor space, as I am sure you know. Any chance you made a mistake in the heatloss calculation? I used to live in house with house with about 30 metres of external wall, 3 metres high, times 2 floors is 180 square metres. 20 kw keeps it nice and warn in midst of winter, even with sash windows. Your office is about 200 square metres wall surface, seems a bit odd that it would need 3 times more heat.

And they even mix their units by giving output in BTU (BThU?). I was thinking of manufacturers catalogues, e.g Stelrad, not suppliers. Why the K? I thought system design allowed for a lowest temp of -1°C or -3°C not -273°C. And with global warming this may be too low The OP might like to read: Copper in small bore heating systems

Just showing off really, but I didn't get it quite right! The kelvin (symbol: K) is one of the 7 SI base units, which ideally should be used in preference to non standard units. As it happens a temperature difference of 1K is exactly the same as 1°C, so when referring to temperature intervals it could be considered better (from an academic or anal point of view) to use K than °C, plus it saves having to do that Alt 0176 thing on the keypad to get the ° symbol. When referring to relative temperatures something like 20°C is obviously better understood than 293K. So that is what I attempted to do above, except that I thought it was °K when the correct form is just K.

worked out rads sizes then compared this with total floor space which gave very similar readings used this web site for working total input which comes out at 163254 btu(2 outside walls) then divided this by 3412 to get kw. 47kw times this by 20% for pipeloss then add 10kw for existing rads in system http://www.radcalcs.com/

EH? Size fits with 50 watts per cubic metre, which is nearly always on the high side. 28 x 13 x 2.5 /20 = 45.5kW. Saves hours for a quick guesstimate!

That web site looks like a joke. I really don't think you should base a 50 kW system on such an amateurish calculator. There are much better calculators available. Besides which offices aren't the same as homes. There's all the heat given out by equipment and lighting to take account of, plus the heat from the workers themselves. It would be sensible to get a professional assessment of the heating needs.

thanks need to write all this use full info down the office has some rads and small system bioler, the rest of the office uses warm air in ducts supplied from central commercial gas heater this keeps breaking down even the manufacures cant seem to keep it going longer than two weeks. hence rads need to be fitted a quick ball park figure was needed asap