Modulation - Should I Expect Efficiency

[Old UKPF 128318]

Hi. Looking for some advice on thermostats.

I've got a Vaillant 835 Ecotec Plus set up but have not yet installed a thermostat.

The house is approx 100sqm, a victorian terrace but fairly well insulated under the ground floor and in the loft. It has two zones: 25sqm of liquid underfloor on a grundfos recirculating pump and the rest of the house is serviced by column radiators.

The radiators have been over-specified in terms of total surface area with the aim of being able to run them at a cooler temperature for longer periods of time whilst still having a good overall output.

Is there an advantage in terms of efficiency regarding going the way of a modulating thermostat like the VRC720F if I don't ever intend for the radiator flow temp to go above 55c? Or will I achieve the same level of efficiency with a standard learning thermostat that doesn't support modulation? I'm struggling to see the benefits of modulation as opposed to just sticking the boiler on a low temperature and letting a non modulating thermostat (like google nest) figure out when to turn it on and off.

My intention is to have the underfloor on a simple on/off timer to maintain a constant surface temperature of the floor and to have the rest of the house gently boosted by the rads.

Thanks!

 

[Last Plumber]

My advice would be to go for the Sensocomfort that suits your system. Your installer will set the right curve for you (unless you do it yourself).

 

[Old UKPF 128318]

My advice would be to go for the Sensocomfort that suits your system. Your installer will set the right curve for you (unless you do it yourself).

Thanks for the advice, what's your reasoning here? Just curious to know exactly why the modulation helps when the boiler itself can just be set to a good temperature for it to condense effectively.

 

[Last Plumber]

If you use Vaillant controls there will be more control over zone water temperatures. So each zone can have its own heat curve set to the correct level for that circuit. This adds to efficiency by only heating water to a necessary temperature. It is more accurate in my opinion.
.

A lot is personal preference to be honest and before the sensocomfort was introduced, I would have steered you away from Vaillant controls. They did do the same job but were not as intuitive as they are now.

 

[DJKent]

Hi BEASTLORD666 - you're question about efficiency, is good.

Regards modulation and efficiency - you're asking (it seems to me) - why would a controller be better than the boiler on it;s own devices?
IE
* the boiler will itself modulate the flame down - as Return temps rise -when controlled by ON/OFF from simple controller
The question then: would it use less gas - with addition of a eBus/Opentherm controller (like VRC720F) - because that can 'tell' the boiler exactly how to modulate (with the extra data, that it has - of room temperature.

Although in your well insulated house -it quickly gets to temperature: so most of the time - the Flow temp would be close to Set Temp - so boiler mostly modulating down anyway: So extra data from the Room temp is of little value.

So does any one know ?

• Is there a possible gas saving if the controller can tell the boiler to Hunt ON/OFF in a better way (ie less short-cycling better than the boiler would do on it's own?