Valiant ecotec plus 832 flow & return temp & balancing rads

[numpty69]

Hello all,
Trying to get the above running efficiently. Boiler fitted to existing system. Installation docs state
flow temp=75
Return temp=65
Everything I read says the dt should be 20?
So if I try to balance the rads what DT am I working to?
I've managed to work out the rad order using digital thermometers & have managed to get them all roughly the same temp (within 3 degrees) but can't get the rad flow & return pipes to differ much.
All advice greatly appreciated

 

[Johntheo5]

Assuming a required rootemp of 20C then flow/return temps of 75C/65C, dT 10C will give 100% rad output, if you reduce the pump speed to reduce the flowrate to 43% of its original speed then the flow/return temps will be 75C/55C dT 20C with a rad output of 87% and a increase in boiler efficiency of ~ 0.45%.
If you leave the pump speed as it was and reduce the boiler flowtemp to 50C then the flow/returt temps will be 50C/45.4C dT of only 4.6C but a increase in boiler efficiency of 5% (due to condensing effect) but rad output will be reduced to 46.4% which may still be quite adequate to maintain your room temperatures.
If your rads are balanced then suggest reducing your boiler flowtemp setpoint gradually but bear in mind that there are no big increases in boiler efficiencies until your return temp is < 55C.

 

[numpty69]

Johntheo5 thank you for your prompt reply. I now realise the condensing boiler has not actually been working efficiently since fitting for 3.5yrs! Lesson learned,,, don't trust tradesmen that owe you a favour.

 

[ScottishGasMan]

You don't balance to a set DT by adjusting valves. You get your primary DT by sizing the radiators correctly and altering pump speed.

If you slow the flow through the rads to get a wider DT, all you do is increase the flow through the bypass, which in turn heats the return to the heat exchanger more, and lowers efficiency.

as john says, reduce flow temperature. Keep it as low as you can get away with but still heat the house, this may be higher at this time of year but a lot lower when the weather picks up a bit. Good controls will do this automatically

 

[numpty69]

ScottishGasMan thank you. My initial point was I've been advised to have a rad flow/return differance of 11C. But if the primary is 10C should I be aiming for 5C?
Got into the D codes & found the following info.
D005= 60C
D015 pump speed = 15%
D040= 54C
D041= 51C
Seems the wife changed the temp to 60C after watching a government add.

 

[Johntheo5]

A pump speed of 15% seems very very low, pump head is proportional to speed squared, assuming a pump head of 7M at 100% then the present head is 7X0.15X0.15, 0.16M which wouldn't circulate any water, check that d.014 is set to 0 (Auto), one might think a setting of 3, 70% or ~ 3.4M would be more appropriate. Do you have a LLH (low loss header) or CCTs (close coupled Ts) ??.

 

[ScottishGasMan]

Leave it on auto. That will give you the best chance of a lower return temperature. It will go much faster if needed.

15% is the signal power it gets, which won't equate to 15% rotational speed.

If you've been advised 11 degree difference then you want an 11 degree differential. If its narrower then so be it as the boiler pump is sized to the boiler and not the system.

In 90%+ cases the system has not been designed so the figures are arbitrary, open the flow up to the rads, set room stat to 21, wait till the room is pretty close to that and check what the primary difference is, then you're checking its the same at individual radiators, if some are much narrower then restrict the flow to them a bit till there all approx the same, which will then match the primary differential.

Could be any where between 5 and 15 depending on how big the radiators are vs size of the pump and boiler.

 

[numpty69]

Johntheo5
'Do you have a LLH (low loss header) or CCTs (close coupled Ts) ??.'
Don't know. I can't see anything looking like a llh.
ScottishGasMan
Thanks for the advice. I'll give it a go this weekend