ASHP outdoor unit heating pump Q

[SimonD]

18 hours ago, BotusBuild said:

@SimonD, does the calculations appear to be correct?

 

14 hours ago, BotusBuild said:

crazily LOW.

 

Yes they're crazily low. 

 

By my calculation the pressure drop in your longest ufh loop, 95m and flow rate of 2l/m is something like 12.8kPa. And then we have 10m on the 28mm pipework, assuming up to 7kW is just under 3.5kPa. So you are fine.

 

[JohnMo]

Simple diagram to use, join the dots as demonstrated with the red line

 

[SimonD]

22 minutes ago, JohnMo said:

Simple diagram to use, join the dots as demonstrated with the red line

 

Yes indeed, but for the really geeky ones of us, you've got to use Reynolds and relative roughness depending on material and even better the fluid temperature, and then using the Reynolds number you can even geek out over whether the flow is laminar, transient or turbulent 😊

 

This free calculator is pretty good: https://www.h2xengineering.com/pressure-drop-calculator/ 

[JohnMo]

4 hours ago, SimonD said:

Yes indeed, but for the really geeky ones of us, you've got to use Reynolds and relative roughness depending on material and even better the fluid temperature, and then using the Reynolds number you can even geek out over whether the flow is laminar, transient or turbulent 

But if you need to go that level detail, that's ok, but do you really need too? If your that marginal and you need in depth calculations, good chance you are putting an additional pump in anyway. Or someone will add glycol and screw up the theory anyway.  Or existing piping has some scale or biofilm which changes roughness and dia and turbulence factors, from poor chemical treatment in the past, and then all bets are off anyway.

[BotusBuild]

6 hours ago, SimonD said:

Yes indeed, but for the really geeky ones of us, you've got to use Reynolds and relative roughness depending on material and even better the fluid temperature, and then using the Reynolds number

This is what I was trying to do, but obviously slipped up on a decimal point or seven 😀

[JohnMo]

Loop length 95 x 90Pa, which s 8550Pa or 0.87m head. Have UFH flow meters open and pressure drop through manifold is small. Plus your pipe, filters and strainer etc.

[BotusBuild]

9 hours ago, SimonD said:

This free calculator is pretty good: https://www.h2xengineering.com/pressure-drop-calculator/ 

For anyone who comes back this way to ready this thread, I strongly recommend taking a look at and using the above calculator.

[JohnMo]

Just did a comparison, the chart above reads slightly lower than a full calculation (500Pa less) 0.9m head, instead of 0.87m.

[BotusBuild]

So, unless you're close to a limit on your water pumps capability, the chart is accurate enough would be the conclusion?

[JohnMo]

49 minutes ago, BotusBuild said:

So, unless you're close to a limit on your water pumps capability, the chart is accurate enough would be the conclusion?

I came to same conclusion. Good enough for nearly all cases. If the pump can't cope or is close to not coping you will be installing an additional pump anyway, so keep.it easy.

[BotusBuild]

Time to plan the change 😀