VRC 470 set up

[scoobydo123]

Have I set the VRC up correctly?

Have the outside sensor installed and reporting the outdoor temp. Have set the vrc 470 to room temp control modulation, heat curve 1.6, min flow temp 34c . What is pump blocking time? Any other settings that need a tweak?What is OT constant heating?

Boiler is the new 831 so modulates down 1:6 have set CH at the boiler to 75.

Cheers

 

[ALEC1]

why change the minimum flow temperature?

In reality its only the curve, control strategy and timings that need changing..

 

[bell824]

as your in essex i would suggest a heat curve of minimum 2.0 although about 2.5 would be better, always set maximum ch temp on the boiler as the 470 control's that itself, other than that all else seems ok!

 

[scoobydo123]

To stop the potential of overshoot but I think the 8xx series dont suffer like the 4xx as they seem to start low but only had half an hour round there so didnt have time to observe everything. Numpty installer couldnt get it working and also didnt fully insert the return in the compression coupling for the fernox TF1 so this blew off and there was no slack on the pipe due to it being tight up against the joists. When I went to re-assemble it was 25mm too short! So had a panic on to get a 22mm compression fitting at 19:30 on a Saturday.


.Can you explain what OT constant is? Is every thing else ok such as setting it to modulation?

 

[scoobydo123]

Unless I am very much mistaken surely setting a higher heat curve will increase flow temps and then much advantage will be lost of the advanced controls?

 

[bell824]

your heat curve is dependant on lot's of things, especialy if you have undersized radiator's. 2.0 as a min is just my suggestion, were i live it is recommended at 2.5 as a minimum.

the OT is outside of timing, basically a frost stat if you set OT to ten then when the system is of it will not allow the temperature to fall below that!

 

[scoobydo123]

Thanks for the explanation on OT. Luckily the rads are oversize, with it set to 1.6 last night everything seemed fine.

 

[ALEC1]

where you live has no bearing on heat curve... a highly insulated house will always have a lower curve than a draughty and uninsulated one...even in renfrewshire!

 

[David937]

Pump blocking time on my 430f happens mainly in milder weather, the burner will switch off but the pump continues to run for a short period of time before the burner comes on again. Sometimes in this 'blocking period' the target temperature is reached so the boiler won't come back on again.

It happens when the target flow temperature has been attained for a long time to prevent the house overheating - if it was to stay on right until the room temperature has been reached, the excess heat from the radiators could cause overshoot. I have mine set to Thermostatic though.

Hope this makes sense, it's a little difficult to explain!

Oh and the minimum flow temperature is essential for my boiler as it only modulates down to 12kw, if the 430f requests anything much lower than 45ºc it can't really maintain it comfortably.

 

[ALEC1]

ideally at 20c outside the room temp is 20c and the flow temp 20c...

What vaillant boiler modulates down to 12kws, the exclusive?

of course if you have a high minmum flow temp you need the thermostat setting...

 

[David937]

ideally at 20c outside the room temp is 20c and the flow temp 20c...

What vaillant boiler modulates down to 12kws, the exclusive?

of course if you have a high minmum flow temp you need the thermostat setting...

It's the 2008 Ecotec 937, the new one goes down to about 6kw I think.

On Modulating without any minimum flow temperature set the boiler cannot heat the house in good time because it excessively cycles, this is because the system cannot absorb 12kw at such low flow temperatures. It actually works quite well with a minimum flow temp of 45ºc on Thermostat, it does switch off once the room reaches the required temperature but it's a good compromise and it's been working very well for over a year. It's a lot better than it was when I had a CM927 controlling it.

 

[ALEC1]

thats the virtue of these controls you can run them anyway you want...far more flxible than people imagine..

FWIW weather compensation and the accompanying controls are nothing new, its been mandatory in Germany since 1985, as they design out over heating which is wasteful.

I would just add that rapid heat up times aren't really how the systems are designed to be run...generally you are talking about running the house is a pretty stable temperature with may be a minor set back at night...

I guess though it all depends on usage of the house....

 

[FinnFrog]

Hello, Based on the conversation here, I'm hopping someone might be able to help with a query about "room temp control" setting in the installer level>system configuration>HEATING 1>Room temp control of the VRC 470 ?

the manual ( section 8.4.10) refers to 3 modes: "None", "Thermostatic control" and "thermostat". It provides explanations for these.

The unit has 3 setting on the display: "None", "Modulation" and "Thermost." This is consistent with the Table 7.1 a few pages earlier in the manual

Am i correct to assume the explanation for "Thermostatic control" = "modulation" setting, and that the explanation for "thermostat" = "Thermost" setting ?

In truth, I don't think I really follow the explanations of either. Can anyone shed any light on how they work, which temperature they respond to (inside or outside or both) and how they differ?

To get the most efficiency out the boiler, which mode should I set it to?

Thanks for your time

[/i]

 

[FinnFrog]

I think I may have got to the bottom of this, and for anyone else searching, I hope the explanation below helps.

(from the settings on the unit under room temp control)

None= Flow temp is controlled by the EXTETERNAL temperature and the heat curve set. It ignores the internal room temp altogether

Modulating= Flow temp is controlled by the EXTERNAL temp and the heat curve BUT is or modulated by the internal temperature in the reference room. Its ramped up or down accordingly to reduce heating overshoot, based on a calculation.

Thermost.= Similar to the above (modulating), i.e. flow temp is controlled by external temperature and the heat curve but this time, as the desired internal temperature is hit in the ref. room, the boiler shuts down and turns the heating system off. When, or if, the temperature inside drops below the desired temp, it turns on again.

Which is best? Vaillant say modulating is the most efficient (if the central heating and house is well set up, and there are no hydraulic problems). This is because low and slow burn is better than on/off firing. They said it will depend on the house and system, but generally modulating is the most efficient, especially for well insulated, open plan or combi set ups. The chap went through some scenarios quickly, and said that modulating could save as much as 5% per day, if on all day.

I hope this helps others. If I’ve got something wrong, please let me know. I'm not a heating engineer. Thanks

 

[David937]

This is exactly what I found out based on my own experiments with my VRC430f, at the time Vaillant really didn't give me a satisfactory answer. I found the Thermostat option worked best for me as I have a 937 which can only modulate down to 12kW which meant it would struggle to maintain a low flow temperature. My system can only output 17kW and that is only on the coldest of days.

Since you have the newer 831, try using Modulating and see how you get on.