I've just bought a BS1566 1500 x 450mm (210L) indirect vented cylinder to connect to the existing central heating system, which uses a pumped 35kw gas boiler. I'm intending to use two 2 port zone valves for independent control of CH and HW.
The cylinder will be positioned 15m from the boiler, and the guy who sold it to me said it will need 28mm pipe to feed the heating coil, otherwise the boiler will 'hunt'. The coil itself is 28mm.
However, reading my plumbing book seems to indicate that 22mm will be more than adequate for a pumped system, and using larger bore pipe would result in an imbalance between HW and CH circuits - there would be very little resistance in the HW circuit so the radiators wouldn't get hot when the cylinder was being heated up.
My book says that 22mm pipe can handle up to 13.5kW over a max length of 36m. So the question seems to be what is the heat load of this cylinder? Assuming a temperature rise of 56C over 1.5 hours, the standard equation gives 4.186 x 210 x 56/5400 = 9kW - fine for 22mm.
But I'm confused as BS1566 cylinders are meant to have a recovery period of 30 minutes. If I feed that into the equation I get 27kW, which is higher than even 28mm pipe is rated at!
So what pipe size should I use?
The cylinder will be positioned 15m from the boiler, and the guy who sold it to me said it will need 28mm pipe to feed the heating coil, otherwise the boiler will 'hunt'. The coil itself is 28mm.
However, reading my plumbing book seems to indicate that 22mm will be more than adequate for a pumped system, and using larger bore pipe would result in an imbalance between HW and CH circuits - there would be very little resistance in the HW circuit so the radiators wouldn't get hot when the cylinder was being heated up.
My book says that 22mm pipe can handle up to 13.5kW over a max length of 36m. So the question seems to be what is the heat load of this cylinder? Assuming a temperature rise of 56C over 1.5 hours, the standard equation gives 4.186 x 210 x 56/5400 = 9kW - fine for 22mm.
But I'm confused as BS1566 cylinders are meant to have a recovery period of 30 minutes. If I feed that into the equation I get 27kW, which is higher than even 28mm pipe is rated at!
So what pipe size should I use?