Weather/load compensating controls 7 March 2021 at 12:30PM in Green & ethical MoneySaving 10 replies 582 views

AntonyTewks

Hi folks

Looking to reduce my gas consumption and not read for a heat pump yet (boiler only 3 years old). We have a Vaillant ecotec, just for the heating now as our hot water switched to electric. We currently control with our Nest which is helpful for operating remotely and keeping heating off when we are out. We've turned heating temp down to 50/55 to condense better (though return is still less than 10deg lower than the glow). Wondering whether to switch to weather/load compensating controls though? Hypothetically should decrease consumption further as it alters flow according to the weather/load required. I can't see that it would stay off whilst we are out though like the Nest so I wonder if there would be no great benefit there as it would lose the benefits the Nest has. Anyone with experience of these? Any good?

Reed_Richards

AntonyTewks said:

... We've turned heating temp down to 50/55 to condense better ...

So you are doing the weather/load compensation yourself!  Doubtless if it got really cold you would turn the heating temperature up again.    

Cardew

I have weather compensation; installed when a new Viessmann boiler was fitted. This varies the temperature of the water to the radiator by sensing the ambient temperature.

It certainly works in varying the water temperature, however it is impossible for the homeowner to quantify the savings over the same boiler without weather compensation.

Viessmann claim 15% savings see - http://viessmanndirect.co.uk/files/8e57dbc7-8a10-4065-bcc6-a27700ee752a/weather_comp.pdf

AntonyTewks

Reed_Richards said:

AntonyTewks said:

... We've turned heating temp down to 50/55 to condense better ...

So you are doing the weather/load compensation yourself!  Doubtless if it got really cold you would turn the heating temperature up again.    

I was mindful of that. I'm replacing some radiators this year and planning to be oversize to make it easier to run the boiler at low temps and be ready for heat pumps much later down the line. So had crossed my mind that simpler thing maybe to just always run at lower temps. In Jan we started at 65 and when dropped to 60 it was still fine even on the really cold days. We had a few days using 60kwh+ in early Jan at 65deg, once down to 55/60deg we only had one 60kwh+ day in the next month despite temps outside being similarly cold. So that 5deg nudge probably pushed the boiler into better condensing. 

AntonyTewks

Cardew said:

I have weather compensation; installed when a new Viessmann boiler was fitted. This varies the temperature of the water to the radiator by sensing the ambient temperature.

It certainly works in varying the water temperature, however it is impossible for the homeowner to quantify the savings over the same boiler without weather compensation.

Viessmann claim 15% savings see - http://viessmanndirect.co.uk/files/8e57dbc7-8a10-4065-bcc6-a27700ee752a/weather_comp.pdf

Yes agree without really scientifically measuring and comparing outside/inside temps etc it's quite hard to be confident of savings of only around 10%. I guess the comparison is to high initial flow temps too 

michaels

WE have it, just makes sense to me rather than on/off rubbish and fluctuating temps and boiler warm up / cool down.  To what extent does your boiler modulate?  We have had a viessman that does this for 10 years, no idea if it saves much energy but it gives an extremely comfortable constant temp environment.

Reed_Richards

But if its a trade-off between weather compensation and out-of-the-house compensation (as indicated) then in normal circumstances I would have thought that the latter would save more energy.   

Cardew

michaels said:

WE have it, just makes sense to me rather than on/off rubbish and fluctuating temps and boiler warm up / cool down.  To what extent does your boiler modulate?  We have had a viessman that does this for 10 years, no idea if it saves much energy but it gives an extremely comfortable constant temp environment.

My Viessmann boiler is in a boiler room that can only be accessed from outside, so I don't know how much the boiler modulates. Again no way to quantify the savings, although subjectively I doubt it is the 15% Viessmann claim.

Cardew

Reed_Richards said:

But if its a trade-off between weather compensation and out-of-the-house compensation (as indicated) then in normal circumstances I would have thought that the latter would save more energy.   

I wonder why(as the OP stated) wearther compensation would be incompatible with Nest. Without Nest - as in my house - weather compensation only operates when the room thermostat calls for heat and the boiler is firing. For instance overnight the thermostat programme is set to 17C which means that, effectively, the boiler is switched off under most circumstances.

So how is that different to Nest?  When Nest activates the boiler, the weather compensation will operate. Weather compensation has no function other than to alter the CH water temperature as the ambient temperature varies.

AntonyTewks

I asked Vaillant and they said it wasn't compatible with 3rd party devices. I think Nest uses opentherm but Vaillant uses ebus

matelodave

I suppose a lot depend on how it operates - if weather compensation just works on the boiler flow temps and adjusts it according to the external temperatures then an internal stat whether Nest or just a crud bimetallic one would just turn the boiler on and off when the house needs heat and the boiler would deliver hot water at the optimum temperature as determined by the outside temp.. So it should be reasonable effective in keeping the boiler temperature as low as possible assuming that you set the heat curve to match your house.

My heatpump has weather compensation and I can set the slope to match the requirements of the house.

If the flow temp goes to low the place doesn't warm up and if its higher than it need to be then the place doesn't actually get any warmer, because the room stats shut it down. Although it gets warmer quicker, the energy consumption increases quite dramatically because the unit's energy efficiency suffers so it's better to run it longer at lower temperatures that to keep giving it short blasts at higher temps

(its a lot easier to monitor how it performs with leccy than it is with gas because the effect of running the unit can be seen almost instantly and I've got an energy monitor which displays it graphically

It's difficult to actually quantify though because you need to be able to both measure and integrate a lot of parameters (outside temp, flow temp, room temp, energy consumption, running times etc both with weather compensation and without

I've tried mine with fixed flow temps and with weather compensation and IMO the energy consumption seems to be less as the unit is running at the lowest temperature commensurate with maintaining the internal temperatures. More often than not the w/c flows are less than I would actually set (I've tried 30, 35 and 40) but w/c generally runs it at about 33-37 with excursions to 40 when its below freezing and down to 30 when it's above around 12 degrees. (we have underfloor heating so can get away with lower flow temps, likewise we are at home all day so dont need or want to run it in short sessions - in fact it just cooks away for 24/7 if it need to). Heatpumps are very sensitive to temperature and a couple of degrees higher or lower can make a big difference to their consumption (a rule of thumb is around 2-2.5% per degree, so 5 degrees is about 10-12%)

However we run ours just by setting back the temperatures rather than on for a couple of hours and then off all day until the evening, so lower flow temps will slow down the reheat times. However if you can adjust the slope to optimise it then I've no doubt that weather compensation should save some energy.