pipe flow rates

[Gyn_Paul]

I'm about to embark on upgrading my CH system and am eyeing up the l-o-n-g runs of 22mm CU from the boiler to the house (circa 20 m) with a view to either adding a parallell run of 22mm, or replacing them with 32mm, now that I have added heating to additonal rooms.

The question is which size of piping carries the greatest volume (with the least resistance) , 2 x 22mm or 1 x 32mm ?

Coming out of the new boiler it is 32mm anyway (I think) and after the pumps, vannes, mixers and other giggery-pokery I have clear access, so fitting either represents little problem.

paul

[g8vkv]

Try here?

It doesn't give 32mm but you could try extrapolating [+o(]

[jondeau]

Unless you have an exceptionally large boiler in mind, I would imagine that the flow and return pipes would be 28mm at the most.

Two 22mm pipes may theoretically give a marginally greater flow than 28mm but the greater pressure loss on these pipes and their fittings probably means that you would be better off with the 28mm.

 

[Pierre ZFP]

[quote user="Gyn_Paul"]The question is which size of piping carries the greatest volume (with the least resistance) , 2 x 22mm or 1 x 32mm ? [/quote]

The 32mm pipe has a cross section of 804 sq mm for a circumfirence of 50mm  whereas the other has a cross section of 2 * 380 (760mm) for a total circumfirence of 75mm.

So, the bigger pipe has 20% ish more volume for much less drag on the fluid from the pipe itself - go for it!!

[AnOther]

By simple mathematics, PI (3.14) x dia, 2x 22mm will potentially flow more than 1x 32mm but have you checked what the pump in your boiler is capable of. Not much point in having downstream capacity which the pump cannot fully provide. If the boiler typically expects to be connected to 32mm then personally I think I'd stick with that.

I think with an overly large bore, either by individual pipe or aggregate, you could run the risk of cavitation with resultant noise and other air problems.

[Pierre ZFP]

No!  Area is PI*r*r , circumference is 2*Pi*r so my calculations are correct.  A 32 mm pipe will have a lot more flow than 2 * 22mm

[AnOther]

You're right of course Pierre [:$][:$]

I do know all this sh*t but I seriously worry about my rapidly diminishing ability to actually use my brain sometimes which I put down partly to age but more to do with spending far too many years stuck in a boring unchallenging job which unfortunately is far too well paid for me to quit, a problem I'm sure many would realish [:'(]

[Anton Redman]

For the record I get 5.8% more areas if the figures are internal and 12.5 % if external. Broadly resistance will depend on the area of the pipe so 32 mm wins on those grounds as well.