Which pump or pumps?

[Mbear]

We're Pricing heating for a small church hall (rough size - 3/4 of five aside pitch)

Hall is upstairs, boiler being fitted at top of stairway adjacent to hall, 8rads in total...

6 on one level along with boiler and pump (upper level) and 2 at opposite end of building from boiler at ground level. My worry is with the last 2rads and distance away from the boiler/pump, I'm concerned about the heat getting to them and gd circulation back to boiler. If these two rads weren't in the picture then I'd happily go for a 15/60 but as they are then I'm swaying towards either 2 x 15/60's (one flow&one return) or one 25/55. Cost wise the 2 smaller ones would be better but cost isn't really the issue, the correct pump or pumps is needed regardless of cost. Rads are all between 1000 -1600 long and pipe size I've already decided 22mm From boiler all the way to every rad and with 15mm tails at each valve.
Any input is appreciated, this is a slighter bigger job than we'd usually do, ta

 

[Dannypipe]

Its late and I'm off to bed so I won't go into detail, but work out the pipe runs (pipe size and lengths). Then speak with Grundfos and they will advise you.

Obviously the longer the run, the higher the resistance, plus heat losses.

Get some advice, and if they're no good, come back on here with some more details, and I'm sure we can advise you .

 

[Mbear]

Boiler to last rad approx 40/45m

I'll try illustrate will lettering using an R to show where rads are going
Birds eye view top floor
----------------R1----R2
Boiler.---R5
Pump
Here
----------R6
----------------R7----R8
Ground floor

-----------------------------R3
--------------------------------R4

 

[Mbear]

Pipework will carry on in 22mm past R2 to R3 and R4 and return on the same side as will R1 and R5

Pipework for Rads R6, R7 & R8 will return straight to chb

 

[Mbear]

Boiler to rads R2 & R8 Approx 20/25m (pipe run distance)

 

[doitmyself]

If you design the system so the temperature differential across the boiler and the rads is 20C, the flow rate will be halved and the pressure loss round the circuit will be much lower. This means you may be able to use a 15/50 or 15/60 pump.

I would also design the system so it runs with a flow temp of 70C as running at these temps (70C flow, 50C return) means the boiler will be condensing all the time.

However, the rads will have to be increased in size by 40% because outputs are lower when run at these temperatures.

It might also be worth having weather compensation and a controller with optimization so the heating is turned on at the correct time to bring the hall up to temperature.

If you want to size the pump yourself, Copper Tubes in Domestic Heating Systems tells you how to do it. Small Bore Heating Systems is also worth reading.

 

[Mbear]

DO u think 2x 15/60's (one flow&one return) would do the same job as one 25/55?

 

[doitmyself]

DO u think 2x 15/60's (one flow&one return) would do the same job as one 25/55?

Your guess is as good as mine. Work out the index circuit (using the links I gave) and you will know which pump to fit.

 

[Gray0689]

Stick a grundfos 25-80 in then no problem or if money no problem put in a grundfos magna
Also on long runs put in an expansion loop