Vaillant EcoTec Plus 630 dT

[John Carroll]

The boiler flow/return dT can be set in the above by changing  a few parameters to set the dT to between 10C and 20C, see attachment.

However this does not seem to work for someone I know, it worked to a fashion on CH only but not in HW mode (this isn't a big deal though)

The dT was set to its max, 20C in all the examples, below.

The best result (briefly) was a dT of 17C with flow/return temps of 64C/47C, pump speed 58%, next best gave 64C/50C, dT 14C, pump speed 64%, and on HW (cylinder), 64C/60C, dT 4C, pump speed 80%.

Can someone throw any light on this or if they have a EcoTec Plus try these parametrs to see wht results they get, this boiler is just 1 year old.

D.170 is set to 3, which is temperature spread control or dT.

Vaillant EcoTec Plus 630 dT.docx

[JohnMo]

dT is a combination of how much heat can be taken away compared to how much is being generated by the boiler. If your radiators can only transfer 4kW (dT between them and the room for example) and you are generating 16kW something has to give and it's dT. Reducing flow may cause the boiler to short cycle, increased flow will reduce dT.

 

The lower the flow, more heat is extracted from the water flow for a given heat input.

 

On the cylinder with a small coil and high flow rate your dT is always going to be small.

 

Bottom line is what are you trying to achieve?

[John Carroll]

Its not my boiler I have a oil fired boiler.

 

It was running (CH only for first 2 tests) at a modulation level of 4, I think it goes to 5 max?, 16 rads, all fully open so even with flow/return of 64C/44C, dT 20C will still give a rad(s) output of 60% so no way is this boiler output down to minimum, a dT of 20C with a target temp of 64C gives a return of 44C and a nice bit of condensing. if the boiler can achieve this dT of 20C then far easier than spending hours balancing rads to achieve it?, I would say its a excellent feature if it works.

 

[JohnMo]

6 minutes ago, John Carroll said:

If the boiler can achieve this dT of 20C then far easier than spending hours balancing rads to achieve it

Doesn't mean you don't need to balance, that is still needed. Balancing is required to ensure each radiator works as it should, without that the water could just circulate through a single radiator, boiler gives you dT 20, but house is cold because you have bypassed most the radiators.

 

Still not sure what you are trying to do?

[John Carroll]

This is what someone is trying to do (if Vaillant can sort out this dT control problem).

There is a rad(s) demand of 4kw and a UFH demand of 7.5kw, a boiler flow temp of 60C is required to give the required rad output, this means the boiler return is 52.2C, 7.8dT, not too bad, but just about condensing, this is with a boiler circ pump flowrate of 21LPM, if the boiler dT was increased to 16.5C, then the boiler return temp should be ~ 43.5C with quite considerable condensing, this is with a boiler circ pump flowrate of 11.5LPM, if my calcs, attached, are correct.

LLH + Rads and UFH Rev0.xlsx

Edited November 26 by John Carroll

[JohnMo]

2 hours ago, John Carroll said:

boiler return is 52.2C, 7.8dT

So that gives a mean flow temp through the radiators of 48.3 degs.

 

If you flow at 52.2 and have a return of 43.5, you heat output will drop by a big chunk, as the mean flow temp drops to 43.7. So not sure that will work

 

Big gains for not condensing to condensing with the return below 54 degs. Small margins after that.

 

You only have 4kW of water flow going to the radiator and 7kW to the UFH, so the return from the UFH will dominate the return temp.

 

Think I would be more interested in getting rid the LLH

[John Carroll]

The rads flow/return are 60C/50C, mean of 55C, so a, (55-20), T35 Rad, which will emit (35/50)^1.3, 63% of a T50 rating, irrespective of what is going on elsewhere, you then have ( UFH), 3.84LPM@32C mixing with (rads), 5.73LPM@50C to give 9.57LPM@42.8C goint to LLH secondary but because the boiler circ pump is circulating 21LPM then the primary side recirculation of 11.43LPM@60C is mixing with that returning 9.57LPM@42.8C, you end up with a boiler return of 21LPM@52.2C.

As you allude to,  a LLH can becomes a DLH, (Dead Loss Header?) unless the primary and secondary flows are equal., hence the desire to get that dT control working, I have read of other conventional installations (no LLH) where that boiler doesn't  achieve this either.

[JohnMo]

Just had a read of the manual and notice it states with LLH you have to run at fixed speed, but there are plenty of speeds to choose from. So flow rates could be lower. Have you adjusted?

 

 

[John Carroll]

Yes John,

The fixed speed is settable, 50% to 100%, and a few tests showed a (vaillant) flowrate of (converted from LPH) 24.3LPM at 100%,and 11.53LPM at 50% which makes good sense,  since flow is directly proportional to speed. The  dT tests did nothing, there is also a constant pressure option, settable between 100mbar and 400mbar but the tests were inconclusive as 400mbar gave ~ 23LPM but 150mbar didn't produce a much lower flowrate whereas it should theoretically, have been, 23*sqroot (150/400), 14.1LPM.

Edited November 26 by John Carroll