Weather compensation - pump runs all the time?

[Rory]

Just had a WB combi installed and went for their Wave controller, a feature of which is weather compensation.

Enabled weather compensation during the day yesterday when the temp setting was 14C. Actual inside temp was 19C, and outside was 11C.

I understand (well, perhaps that's over-stating it a bit) that it works by monitoring the water flow temp vs outside temp, but was a bit bemused that the combi's pump runs all the time, with the boiler firing so infrequently that it's basically circulating cold water.

Is that how it's supposed to work - will the pump run 24/7 with weather comp enabled? Seems a bit of a waste of 'leccy.

 

[Rory]

Is the burner actually lit during the pumps running? It could be that its actually still circulating water through the system as long as it is still warmer than the room temperature.

In the time I tested it - a few hours on Saturday afternoon - it fires the boiler very occasionally. Whether that's as a result of some clever calculation it's doing, or it's merely to maintain the minumum flow temp (which I think is 20C) I have no idea.

 

[Rory]

Weather compensation with constant circulation is standard practice in Europe, particularly Germany. It is also becoming popular in the USA.

That's my understanding too. After some heavty duty Googling. I've found that the WB Wave controller, while new in the UK, has been sold in Europe for some time.

As I mentioned earlier, the way it works (constant circulation) makes sense with underfloor heating - maybe that's more common elsewhere. It does have a setting to choose your type of heating though - have that set as radiators.

 

[Ermintrude]

There is a mode where the pump will turn off overnight, but oddly, not at other times when it would seem not to be required.

You've hit on the key question though: Would the gas saving by using weather comp be wiped out by the extra electricity cost (and maybe replacing pump if it wears out ).

I have no idea of the answer to that. Viessmann, who seem to be regarded as something of a reference point in these matters, talk about a 20% saving.

Really based on what?

 

[Gray0689]

Weather comp in domestic is no saving when you factor in cost of installing and cost to run

 

[Silent Dancer]

Sounds like it's working how it should do. With an outside temp of 11℃ and indoor set of point of 19℃ it has calculated that you only need a low flow temp to maintain the house temperature so the pump will run and the burner will fire only occasionally to top up the heat but the pump continues to circulate. Note that if you switch off the weather comp the control is load compensated so it continue to perform similar calculations using the indoor temperature.

 

[chris watkins]

Weather comp in domestic is no saving when you factor in cost of installing and cost to run

Not so! keep it simple, it cost me £20 + 1/2 a reel of 1.5mm 3 core flex.

 

[chris watkins]

Are they installing the new lower ratio burners to the new boilers yet ??

This situation could be made a lot better if the boiler could fire for longer periods at a lower burn.

PS pumps don't fail because they run but normally because they turn on & off.

 

[Gray0689]

Not so! keep it simple, it cost me £20 + 1/2 a reel of 1.5mm 3 core flex.

In general yes

 

[Rory]

Sounds like it's working how it should do. With an outside temp of 11℃ and indoor set of point of 19℃ it has calculated that you only need a low flow temp to maintain the house temperature so the pump will run and the burner will fire only occasionally to top up the heat but the pump continues to circulate.

The indoor set point was 14C (effectively an "off" period), actual indoor temp 19C.

I did wonder if setting the "off" temp lower would make any difference, but based on WB's comments, it doesn't matter what I do, the pump will run all the time (can be made to go off overnight though).

Note that if you switch off the weather comp the control is load compensated so it continue to perform similar calculations using the indoor temperature.

I'm not aware that WB's Wave does that unless weather comp in enabled. They told me it disables the boiler flow temp knob setting.

 

[Rory]

Not so! keep it simple, it cost me £20 + 1/2 a reel of 1.5mm 3 core flex.

OK, the WB Wave is dear, but we got it because I like that kind of techy thing and the ability to turn on and off remotely is pretty neat. The installer had a wobbly when I suggested Nest and I looked at Wave and it seemed OK (and it is, apart from me not understanding weather comp).

Once you've got Wave there's no other capital or install cost for weather comp - you just enable it in the app. The cost you do have is in running the pump (and the boiler PCB at times when it should be on standby) so perhaps an extra 8 hrs a day (it can be shut down overnight). Maybe a Kwh extra per day? Plus a bit of gas for the apparently random firing it's doing.

 

[chris watkins]

If WB have fitted one of the newer multi speed pumps it is likely to be around 5 Watts/h.

The main consideration with this is the level of insulation (i.e. heat loss), a modern well insulated & that small amount of topping up is all that is required to keep the internal temp up & the heat input is not wasted.
Whereas & old style poorly insulated place & you are better off letting the internal temp drop right down if you are not there or if you are working, as the rate of loss will slow as the temp difference gets closer. IMHO

P.S. Mr WB why do you have to be a heating engineer to under this stuff ?? I am a just poor lonely Plumber but think I have a handle on it.
What we need is better educated & qualified engineered covering all relevant fields not a dumbing down into plumber or heating or ???? or ?????
(except bathroom fitters, we can exclude them as it is such a low skill set anyone can join)

 

[Rory]

If WB have fitted one of the newer multi speed pumps it is likely to be around 5 Watts/h.

Sadly the boiler fitted doesn't have a modulating pump - my fault, really, I thought about it too late. Some better guidance from the fitters would have been welcome though.

The main consideration with this is the level of insulation (i.e. heat loss), a modern well insulated & that small amount of topping up is all that is required to keep the internal temp up & the heat input is not wasted.
Whereas & old style poorly insulated place & you are better off letting the internal temp drop right down if you are not there or if you are working, as the rate of loss will slow as the temp difference gets closer. IMHO

I'm not a fan of (almost) sealed boxes and it seems to me that once you start cracking open windows then all bets are off. Having the system trying to maintain background warmth while people are in and out of the house, doors open etc, during the daytime seems futiile.

P.S. Mr WB why do you have to be a heating engineer to under this stuff ?? I am a just poor lonely Plumber but think I have a handle on it.
What we need is better educated & qualified engineered covering all relevant fields not a dumbing down into plumber or heating or ???? or ?????

Certainly, as I mentioned in my other thread, it's a bit disconcerting when the (WB accredited) fitters think the sign of a successful install is when the return quickly gets to the same temp as the flow.

 

[chris watkins]

Sadly the boiler fitted doesn't have a modulating pump - my fault, really, I thought about it too late. Some better guidance from the fitters would have been welcome though.

Certainly, as I mentioned in my other thread, it's a bit disconcerting when the (WB accredited) fitters think the sign of a successful install is when the return quickly gets to the same temp as the flow.

Sad but true I am afraid the quality of plumbers (or heating engineers) is not what it should or could be but then you only have yourself (the general public) to blame !!!!

No one is interested in have a proper licensing system for us coupled with proper training.

Everybody seems to think they can do it, its easy, all push fit fittings & flexible cons, the physical installation may have got easier but the knowledge & technical understanding required has most certainly not.

 

[Rory]

Everybody seems to think they can do it, its easy, all push fit fittings & flexible cons, the physical installation may have got easier but the knowledge & technical understanding required has most certainly not.

To be fair, the plumbing they've done is neat (I visited while the floors were up). They worked quickly and cleanly. System works and the house is lovely and warm. I'm sure 95% of customers would be delighted. Indeed, I'm not unhapppy, I just think they missed an opportunity to make the most of the installation.