Optimumtemperature settings for Gas boiler

Reed_Richards

BUFF said:

& of course controls are very important. From what I understand (certainly Viessmann push it) weather compensation has far more effect than load compensation.

When it is warmer out your house loses heat less quickly, you don't need so much output from your radiators so the flow temperature can be cooler

When your room is at the desired temperature you don't need as much output from your radiators as when the room is being warmed up so the flow temperature can be cooler and controlled to maintain a set temperature precisely and without cycling.

In both cases the main benefit with a gas boiler must be to increase the amount of time that the return temperature is cool enough to achieve good condensation and improve efficiency.  From a comfort point of view, the even room temperature you get from Load Compensation is very nice.    

BUFF

Viessmann seem to reckon that the benefits from weather compensation are potentially 3-4x that of load compensation.

Cardew

BUFF said:

Viessmann seem to reckon that the benefits from weather compensation are potentially 3-4x that of load compensation.

I have a Viesmann boiler with weather compensation. The information is here:

https://viessmanndirect.co.uk/AdditionalDepartments/Header-Content/Weather-Compensation

'But there is a way to save even more - up to 15% in fact, with just a simple outdoor sensor and some very clever Weather Compensation controls, available with the Vitodens range of condensing boilers.
For a relatively small investment you'll not only save up to 15% more fuel each year but you'll also enjoy an incredibly comfortable home - with a pleasant indoor temperature - whatever the weather.'

How much it saves me is impossible to quantify; and I am always suspicious of savings stating UP TO xx% as a claim of saving of 'up to 15%' covers a saving of 0.0001%!!!

All I know is the the temperature of water flow is considerably higher when the ambient temperature is low - which of course is the design aim.

BUFF

I am aware of that & the estimates for load compensation at bus level (e.g. Opentherm etc.) are generally as far as I can see ~3-4% hence why I said that Viesmann reckon weather compensation is more effective & of the order of 3-4X (I too take everything from manufacturers with a grain of salt hence my caveats).

If you have the time this is an interesting article (you can cut to the chase by starting at page 95, interestingly the weather compensated test never actually achieved the set temp.)
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/648337/heating-controls-compensation-tpi-bre.pdf

Cardew

BUFF said:

I am aware of that & the estimates for load compensation at bus level (e.g. Opentherm etc.) are generally as far as I can see ~3-4% hence why I said that Viesmann reckon weather compensation is more effective & of the order of 3-4X (I too take everything from manufacturers with a grain of salt hence my caveats).

If you have the time this is an interesting article (you can cut to the chase by starting at page 95, interestingly the weather compensated test never actually achieved the set temp.)
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/648337/heating-controls-compensation-tpi-bre.pdf

Thanks - the extract at page 95 is interesting.

Initially I had exactly the same experience in that the room would not reach the temperature set on the thermostat. My installer - a Viessman specialist and a proper heating engineer, couldn't understand why, so he called out an engineer from Viessmann.

It transpired that although 'my' installer had set the water temperature as recommended, the weather compensation could not raise the water temperature high enough to achieve the set room temperature. The Viessmann engineer seemed well aware of the issue and the solution was simply to raise the set water temperature and let the weather compensation 'do its thing'.

It now works well and indeed a family member - who I will not name but I married her - messing about with the thermostat in some very cold weather managed to get the room up to 25C while attempting to heat a normally unused bathroom(the TRV was turned to '2'!*

Still no idea how much the weather compensation saves however.

* That 'finger trouble' reminds me of a major conclusion of the EST trials on Heat Pumps which was that the controls are simply too complicated for the non-technical minded user; and the various discussions on this forum to get maximum efficiency give credence to that point. The lady in question above 'ain't thick' as her Masters degree might demonstrate, but she would not have had the inclination to 'play' with controls.  

Reed_Richards

Cardew said:

Still no idea how much the weather compensation saves however.

* That 'finger trouble' reminds me of a major conclusion of the EST trials on Heat Pumps which was that the controls are simply too complicated for the non-technical minded user; and the various discussions on this forum to get maximum efficiency give credence to that point. The lady in question above 'ain't thick' as her Masters degree might demonstrate, but she would not have had the inclination to 'play' with controls.  

@Cardew is a heatpumposceptic.  My heat pump offers very few control options.  As with the Viessmann gas boiler you can either have a fixed (target) water temperature of you can use Weather Compensation.  In the latter case you can raise or lower the target temperature determined by weather compensation by up to 5 degrees (in 1 degree increments).  If that's more than Viessmann lets you do with their gas boiler its not a lot more.   In Installer Mode you can vary the weather compensation parameters; again that seems to be the same as the Viessmann gas boiler.  Maybe they have dumbed-down heat pump controls since that EST trial?    

coffeehound

An interesting thing I've noticed from four years of running gas CH at low flow temperature is that since radiator temperatures are so much closer to the intended room temperature, you get some degree of passive load compensation.  

When the room temps are low, the boiler fires up more frequently until room temperature gets into the comfort zone.  Then the time taken for radiators to coast back down to minimum temperature takes progressively longer until the boiler is cycling maybe once an hour or less.  With flow at 45º peak, I could leave the CH running 24/7 with the wall stat at say 20º and let it look after itself.

On TRVs, the chap I first heard about low flow temp running from - the Telegraph's buildings agony aunt - said to turn all TRVs up to maximum.  I don't see the point in that as there is still value in having rads switched off if e.g. there's solar gain in some rooms and none in others.

ETA, the point I forgot to make is that running with low flow temperature requires only a simple cheap wall stat since it is just functioning as an upper limit switch rather than having to control the process.  Also, no programmer needed at all if controlled on the wall stat and flow temperature.  A moot point since all new installations must be fitted with clever controls.