Pressure loss calculators

[MNW67]

Has anyone used these or recommend one?

I'm trying to get a rough idea of the theoretical pump head needed for my CH pipework.

Currently there is one circuit for upstairs and one for downstairs. Each circuit is about 60m in total (when you add together flow and return). So overall that's 120m.

The calculator I tried shows that it needs 7m of head. But my pump only gives 3.5m head at the current flow rate. So that doesn't make sense. Unless I've made a mistake

 

[Johntheo5]

I get 101.6 (10.16M) using this one (copper pipe) so your pump will "only" flow 21*(3.5/10.16)*0.5, 12.33LPM, but the pump head will rise as the flow decreases so say ~ 4.0M pump head = 21*(4/10.16)^0.5, almost 13LPM (12.96), (12.6LPM per the omnicalculator)

Friction Loss Calculator

Calculate the friction loss in pipes for different materials using the Hazen-Williams equation.

www.omnicalculator.com

 

[MNW67]

I've realised that it is massively more complicated than I had imagined

For instance, it looks like each circuit has to be looked at separately. And lots of other factors to take into account.

For professionals, is software available where you enter the system design and it tells you how much the pressure loss will be?

 

[Dereekoo]

I've realised that it is massively more complicated than I had imagined

For instance, it looks like each circuit has to be looked at separately. And lots of other factors to take into account.

For professionals, is software available where you enter the system design and it tells you how much the pressure loss will be?

Yes as there are 2 circuits does each has its own pump or is it some how split off, if its split off then depending on the frictional resistance of each circuit will depend how much of the flow each circuit takes. The frictional resistance of each circuit depends on length of pipework, number of different fittings along the route and frictional resistance of the pipe (new or clagged up?). I think your expectations in obtaining any realistic results are slim. No doubt central heating installers go on a rule of thumb when sizing the pumps, a bit like when working out heat losses/requirements to size a boiler, get somewhere near, add a safety factor and pick the next size up.

 

[fixitflav]

I get 101.6 (10.16M) using this one (copper pipe) so your pump will "only" flow 21*(3.5/10.16)*0.5, 12.33LPM, but the pump head will rise as the flow decreases so say ~ 4.0M pump head = 21*(4/10.16)^0.5, almost 13LPM (12.96), (12.6LPM per the omnicalculator)

Friction Loss Calculator

Calculate the friction loss in pipes for different materials using the Hazen-Williams equation.

www.omnicalculator.com

I get a similar figure, using pipe roughness 0.05mm. Not clear how the link defines Pipe roughness coefficient.

But 120m pipe is OTT, for a typical house 12m effective length more likely. For one thing, usually the flow splits into parallel paths.

 

[Johntheo5]

Gas boiler manufacturers now seem to be installing up to 7M head circ pumps in their system boilers, they all seem to design their HEXs for a dT of 20C so a 24kw boiler will be designed for a flowrate, of 24*860/60/20, 17.2LPM for ~ a 3.0/3.5M HEX loss, a 7M pump running at 17LPM will run with a head of ~ 5.2M which only leaves a residual head of 1.7/2.2M for the system resistance, not a lot?, a regular gas boiler on the other hand with the same HEX loss with a "6M" UPS3 circ pump which can deliver up to 20.0LPM at a head of 6.3M will leave a residual resistance of 2.8/3.3M, not too bad. Oil boilers which have virtually no HEX loss will have plenty of heating system head available.