Central heating pump sizing

[John.g]

The reason the rad is not circulating is probably that CP1 is limited to a 1.8M head which realistically is a bit low, CP2 at 3M should be a good compromise to get circulation, theoretically, at least, the flow rate should increase from 0.4 m3.hr to 0.52 M3/hr and you may be able to nurse another few kw from the boiler without cut out. CP3 at 4.5M is probably the best choice, hydraulically, you may loose a few % in boiler efficiency but maybe a small price to pay for comfortable heating until Vaillant respond.

 

[Reddwarf4ever]

The reason the rad is not circulating is probably that CP1 is limited to a 1.8M head which realistically is a bit low, CP2 at 3M should be a good compromise to get circulation, theoretically, at least, the flow rate should increase from 0.4 m3.hr to 0.52 M3/hr and you may be able to nurse another few kw from the boiler without cut out. CP3 at 4.5M is probably the best choice, hydraulically, you may loose a few % in boiler efficiency but maybe a small price to pay for comfortable heating until Vaillant respond.

Thank you CP2 did work reasonably well, the ‘ problem rad ‘ began to warm up. I then switched to CP3 and the ‘ problem rad ‘ is now very hot, can still keep my hand on it just....the other rads are really hot, the one next to my Wife’s chair is too hot too touch, with the Boiler flow set at 64oC however the return temperature has now increased to 56oC Might leave it at CP2, where the return was 51-53oC the ‘ problem Rad ‘ is not so important, as it’s in the ‘ ‘game room’ not used very much. Probably need a CP 2 1/2 , since increasing the flow from CP1 to CP2 and more recently CP3 the boiler is modulating a lot better, hasn’t cut out at all yet. Also the Hot water heated from 7am-11am & 8pm to 10pm is working very well, with CP1 & 2, Will be a different story in the Summer months when it will be Hot Water only.....

 

[ShaunCorbs]

Have you tried balancing the rads more with more pressure you will need to close the lockshields more

 

[Reddwarf4ever]

Have you tried balancing the rads more with more pressure you will need to close the lockshields more

only three can be adjusted, the other 9 all have TRVs....will have a look, thanks

 

[ShaunCorbs]

only three can be adjusted, the other 9 all have TRVs....will have a look, thanks

the other side should be a lockshield valve you can adjust that

 

[Reddwarf4ever]

the other side should be a lockshield valve you can adjust that

cant see the point in restricting the lock shield when the TRV is designed to control the room temperature, or am I missing something ?

 

[ShaunCorbs]

cant see the point in restricting the lock shield when the TRV is designed to control the room temperature, or am I missing something ?

the lockshield controls the return temp

you should be getting around 10dc drop through the rad

 

[John.g]

Thank you CP2 did work reasonably well, the ‘ problem rad ‘ began to warm up. I then switched to CP3 and the ‘ problem rad ‘ is now very hot, can still keep my hand on it just....the other rads are really hot, the one next to my Wife’s chair is too hot too touch, with the Boiler flow set at 64oC however the return temperature has now increased to 56oC Might leave it at CP2, where the return was 51-53oC the ‘ problem Rad ‘ is not so important, as it’s in the ‘ ‘game room’ not used very much. Probably need a CP 2 1/2 , since increasing the flow from CP1 to CP2 and more recently CP3 the boiler is modulating a lot better, hasn’t cut out at all yet. Also the Hot water heated from 7am-11am & 8pm to 10pm is working very well, with CP1 & 2, Will be a different story in the Summer months when it will be Hot Water only.***.

What was/is the pump head and flow on CP2 & CP3? , theoretically PP3 should give somewhere in the middle, by my calculations, but your numbers will tell us more.

 

[Reddwarf4ever]

CP1 10W 1.8m 0.4m3/hr
CP2 17W 3.0m 0.7m3/hr
CP3 30W 4.5m 0.9m3/hr
PP3 26W 4.1m 0.8/m3/hr - 0.9m3/hr

CP3 gives a good flow, all rads very hot, but inlet temperature >55oC
CP2 All rads hot except one, which is warm, inlet temperature 52-53oC
CP1 all rads hot except one barely warm, inlet temperature 52-53oC

trying PP3

believe the flow is a ‘ calculated’ one, can’t see how they could fit a flow meter inside the pump....with pump head and watts it’s an easy calculation.

DAB going to send me a ‘ spare’ heat shroud they found. They say the manual and website is for the European model not the UK one....how I am supposed to know that is beyond me.....think for the few pence it costs, all their pumps should have this....

thanks

 

[John.g]

CP2, CP3 & PP3 are doing as I would have expected.
The pump actually only uses the power and pump+motor efficiency to calculate the head and flowrate, it knows which mode/head is selected and can then derive the actual head/flowrate, the clever part IMO is how it derives the pump+motor efficiency for every single point on all the curves. Some hold that it is only a approximation especially on some of the UPS models and it may well be but before I installed my Wilo Yonos Pico, I just connected it up to a a gravity feed with a gate valve on the discharge and measured the flowrates for a number of different operating modes and it seemed to be within 5 to 10% of what the pump curves showed for the displayed power consumptions, (I don't have head & flowrate displayed.), so all in all a good aid to navigation IMO. You can also estimate it (the flowrate) from the (clamped) boiler output and deltaT.