Pipe/ pump sizing, one for the forum elders!

[Sharp Point]

Just to say howdee first guys n gals ( i'm a very new member) Right many moons ago.... mid nineties! when i did my level 3, we skirted around the heating design part. Now over the years i've worked to a pretty good 'rule of thumb' picked up from the senior engineers at companies that i've been employed by. Now i've a good understanding of most things, but the last bit of the puzzle i've had missing is pump/pipe sizing. But for the last month or so in between running a business, being daddy to three demanding sproglings, doing up an old vw, going snowboarding....etc i've armed myself with a few books. Fluid dynamics ( woooooah, over my head) domestic heating design guide (cibse) nvq 3 textbook ( recent one) but the easiest one i've been able to work with is a poxy 8 page pdf from the ' copper development association'.

Now the pdf is set for old school 11 degree drop, now can i use the same formulae but for new 20 degree drop systems?

heat emitter size in watts / ( 20 x 4187) kg/s specific heat of water being 4187 joules/kg

The 20 being the new 11 degree design drop.

If so, i'm really pleased. Because that means i've just taught myself( fingers crossed) the dark art of pipe sizing thus matching system to pump design curves.

Please don't shoot me down to quickly chaps, ive had my head in the books for hours and hours....

 

[Nostrum]

Yes you can!

Welcome.

 

[Sharp Point]

Yes you can!

Welcome.

Woohoo!!! i feel real proud.

 

[josh]

The roy treloar book has an easy to follow pipe and pump sizing section, thats how i learnt as same as, college quickly went over it.

 

[doitmyself]

8 page pdf from the ' copper development association'.

I assume you mean Copper Tubes in Domestic Heating Systems.

You should also read Small Bore heating Systems, which explains why there are limits on the amount of heat you can put down a certain sized pipe. It's due to flow velocity.

Now the pdf is set for old school 11 degree drop, now can i use the same formulae but for new 20 degree drop systems?

heat emitter size in watts / ( 20 x 4187) kg/s specific heat of water being 4187 joules/kg

The same formula can be used: it's just working out the water flow rate through the pipe, which will be approximately half at 20C compared to 11C. This means the velocity will be half so, from Table 2 in the second pdf, you will see that the same size pipe can carry approx twice the heat. A max velocity of 1 m/sec is normally used.

If you use 20C as the design differential, don't forget that the radiator output will be reduced, so you need to "oversize" the rads by about 20%.

Also, the head will be considerably reduced, so a smaller pump can be used.

Don't forget that pipe sizing, as advocated in the two pdfs, is theoretical. The typical practical installer will use 22mm for the main backbone and 15mm for the radiator drops.

I do wonder if this is the main cause of sludging up as the velocity through a 15mm pipe with a 1kW rad attached is only 15cm/sec with an 11C drop and half that for a 20C drop. The alternative is to carry multiple pipe sizes and a huge selection of joints and tees etc, if you can get them. Maybe it's a case of practicality wins over theory.

 

[Ermintrude]

Microbore is the answer

 

[Sharp Point]

Microbore is the answer

It may be, but i think it has proved itself to be very poor both copper and plastic! As probably most home owners completely disregard the up keep and maintenance of their heating systems, i.e whipping rads off to decorate and not topping up with inhibitor, constant topping up sealed via filling loop( they know there is problem) or tank topping up automatically with the ole fresh water ( they're not aware) then the problems start.
Then we get the call, to non functioning rads! usually clogged somewhere with broken particles of scale/ sludge and we all know we cant powerflush.......well i wouldn't dare. Then it's 'sorry love, i'll have to rip your house apart to trace the blockage.:disappointed: