Optimumtemperature settings for Gas boiler

BUFF

skycatcher said:

https://www.ephcontrols.com/section/cp4/

This is the one...i tried a photo but an error kept coming up.

This ought to be pretty good although I don't think that it can communicate with the Worcester EMS bus (very similar to Opentherm but proprietary) for ultimate efficiency but difference should be minimal (<3%). Do you have an outdoor sensor to allow for weather compensation ?

Having said that the system setting itself to a 61C CH flow temp seems  a pretty good starting point.

skycatcher

Yeah, no other inputs to the system. I guess seeing to 61 was based Upton the unit input temperature which was 11. When it turns cooler tomorrow I'll check what it thinking it's the best temp.

Reed_Richards

lohr500 said:

It is important that you try to get a 20 deg C differential between the flow and return temperatures out of and back into the boiler, with the return no higher than around 50 deg C. A lower return temperature whist maintaining the differential is even better. 

I'm not sure this is true; I think the differential is more a matter of convention than necessity.  What is important is that all the radiators are balanced and have the same differential.

I have Heat Pump and that typically aims for a temperature differential of 5 C.  The only significant difference the differential makes is to the average temperature of the radiator.  I also get some flow noise in parts of the system because the pump speed will be about 4 times greater than for a 20 C differential.  

lohr500

@Reed-Richards, it may not be true and could be convention, but it seems to be the advice given for gas/oil boilers on many heating installation websites. Also, most of the radiator and boiler websites suggest achieving a 12 to 15 deg C differential between the flow and return on each radiator.

Won't a heat pump work slightly differently in that you are trying to maintain a core temperature in the heat store which has a high volume of water and which will buffer the flow and return temperatures of the CH circuit? 

Ebe_Scrooge

For the stored hot water (not necessarily the central heating) the recommendation is to keep it at a minimum of 60 degrees to kill legionella bacteria: https://www.hse.gov.uk/legionnaires/hot-and-cold.htm

That's probably more of a concern in hospitals, nursing homes, etc. than in a domestic situation, and I'm not sure how great a risk it is in reality.  But that's the "official" guidance

Reed_Richards

lohr500 said:

@Reed-Richards, it may not be true and could be convention, but it seems to be the advice given for gas/oil boilers on many heating installation websites. Also, most of the radiator and boiler websites suggest achieving a 12 to 15 deg C differential between the flow and return on each radiator.

Won't a heat pump work slightly differently in that you are trying to maintain a core temperature in the heat store which has a high volume of water and which will buffer the flow and return temperatures of the CH circuit? 

So if the radiators have a 12 to 15 C differential but you say the boiler differential has to be 20 C, what is happening to the other 5 to 8 C?  If that is getting lost in the pips between the boiler and the radiators that's potentially very wasteful (depending on where those pipes are situated).  And a lot, if a radiator with its large surface area, loses just 12 to 15 C, you would need a large area of pipe to lose many more degrees.  The last gas boiler I owned had both Weather Compensation and Load Compensation so very much took care of its own water temperature. 

Heat pumps seem to want a minimum volume of water to work with so I think that is why they tend to have a buffer tank.  I haven't yet got my head around how that affects the overall radiator water temperature.,    

skycatcher

Found this interesting website https://www.theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature

FreeBear

Ebe_Scrooge said: For the stored hot water (not necessarily the central heating) the recommendation is to keep it at a minimum of 60 degrees to kill legionella bacteria: https://www.hse.gov.uk/legionnaires/hot-and-cold.htm

That's probably more of a concern in hospitals, nursing homes, etc. than in a domestic situation, and I'm not sure how great a risk it is in reality.  But that's the "official" guidance

Whilst temperatures over 60°C will kill the legionella bacteria within minutes, it is not necessary to store your hot water at that temperature long term. Dropping to 52-55°C will also kill the bacteria within a few hours. In a domestic environment, the risk is minimal - Some 250 cases reported in England & Wales in 2020.

Reed_Richards

skycatcher said:

https://www.ephcontrols.com/section/cp4/

This is the one...i tried a photo but an error kept coming up.

That controller has Opentherm capability which allows for some very sophisticated energy saving measures if suitably wired to a suitable boiler.  Unfortunately it does not look as it your boiler is suitable.

BUFF

skycatcher said:

Found this interesting website https://www.theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature

Just to play devil's advocate :P https://www.hamworthy-heating.com/Knowledge/Articles/Changing-heating-system-design-with-wide-temperature-differentials

In a domestic environment it's usually a balancing act between higher flow temp for speed of space response (for comfort/convenience) & lower temp for efficiency & everybody will have their own idea of what suits them best.

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