Weather compensation & Wireless TRV control

[ALEC1]

boilers have minimum flow rates, which need to be respected so that the heat is dissipated.... say the minimum load is 6kws then you need a zone of 6 kws heat loss on the rads to respect that.

Thats easily one floor in most UK houses, and on a mild day the whole house...

(boiler sizing is calculated at -3c, and at higher temperatures the boiler does not need to be so big)

 

[ALEC1]

he hang on a minute Dan, my house has the heating on 16 hours a day at 20c, and costs according to BG just a bit more than the average UK house of the same size.

If I ran the heating at 20c for the same as the average UK house then I have no doubt that it would be lower.

Bearing in mind yours is a well insulated barrett home and mine is a 120 year old victorian end of terrace ground floor flat with no insulation on the walls or floor and a lot of outside wall.

Any way Dan as you designed the system and you are Dan of course it is a whole lot better than anyone else's..

 

[DukeGB]

Appreciate the need to disappate heat, the pump continues to circulate to prevent damage to the heat exchanger. There's a towel rail upstairs to prevent the pump working against a closed valve, this also disappates any excess heat.

 

[Dan Robinson]

Of course it is . But our heatloss at -3 is roughly the same, and as I mentioned in the CC, my hot water use is huge compared to yours, yet still my bill was a tad smaller

The fact is you would have me heating 200 ish metres of House when I am sitting in only 12 metres for most of the day.


To quote Honeywell, you wouldn't have 1 light switch for the whole house?

Thought not.

 

[DukeGB]

Dan, how long does it take for Evohome to adjust its startup time based on a change in flow temp? I'm assuming there's some sort of weighted average based on previous startup performance so it may take a week or so to adjust...

 

[Dan Robinson]

Evo won't have a clue what the boiler will be doing, but it will be monitoring cool down temps and past heat up times and adjusting itself.

UK temps don't change that quickly. If you're caught out by much more than a day I would be surprised.

Like I said before. It works beautifully, although, at the moment I have dezoned it to operate like Alec likes, and got an earful from the missus yesterday about the house being cold.

 

[DukeGB]

I'll look into the WC - so long as it doesn't prevent me from wiring it up to the Evohome system I'll consider it.

I disagree with the principle of keeping the whole building at the same temperature, so long as your zones can be well segmented and the rads aren't in a daft place, Evohome should work well.
It was a while since I did heat loss calcs - will dig out the spreadsheets & check the maths! It's an existing system btw so I don't want to change the rads if I can avoid it.

 

[ALEC1]

To quote Honeywell, you wouldn't have 1 light switch for the whole house?

Yes I would because of two concepts that this approach overlooks

thermal mass, the ability of the fabric of the building to store heat and thermal inertia, the rate at which it takes to absorb heat into the building.

A house is just like a screened floor it takes time to heat up. Micro management of heating systems doesn't work with those two concepts. No particular downside to that other than the minimum zone heat output should match the boiler. In addition doors have to be kept shut..


Of course the best way to reduce gas consumption is to insulate the property...thats what I am doing to reduce my slightly above average heating bill on a property that is kept warmer twice as long as average...

really if you want to zone you might as well have electric fires and turn them on every time you enter a room, just like victorians did!.. frankly I like a nice even heat with a boiler doing as the design engineers intended, working efficiently reliably and economically...

 

[ALEC1]

UK temps don't change that quickly. If you're caught out by much more than a day I would be surprised.

this is absolutely wrong temperatures do change a great deal in the UK, you can have a temperature difference of 6-8c in a day, due to our proximity to the atlantic. Yesterday in London it was 12c, and at night 1c....

 

[ALEC1]

I disagree with the principle of keeping the whole building at the same temperature, so long as your zones can be well segmented and the rads aren't in a daft place, Evohome should work well.

This should be reflected in radiator sizing, and managed with TRVs..

 

[DukeGB]

To quote Honeywell, you wouldn't have 1 light switch for the whole house?

Yes I would because of two concepts that this approach overlooks

thermal mass, the ability of the fabric of the building to store heat and thermal inertia, the rate at which it takes to absorb heat into the building.

A house is just like a screened floor it takes time to heat up. Micro management of heating systems doesn't work with those two concepts. No particular downside to that other than the minimum zone heat output should match the boiler. In addition doors have to be kept shut..

Of course the best way to reduce gas consumption is to insulate the property...thats what I am doing to reduce my slightly above average heating bill on a property that is kept warmer twice as long as average...

really if you want to zone you might as well have electric fires and turn them on every time you enter a room, just like victorians did!.. frankly I like a nice even heat with a boiler doing as the design engineers intended, working efficiently reliably and economically...

Thermal mass - worth considering. I live in a granite house but it's heated by radiators with no UFH so it still reacts faster than a screeded floor or a building with a significant amount of concrete where the time to get up to temperature is measured in days and the building must be seasonally controlled. I have specified and witnessed the commissioning of systems in buildings that are considered thermally massive and use BMS systems such as JCS or Trend that learn the response of the building. This saved the client a significant amount of money compared to the previous approach of always on / manual control.

For me while I'm doing my best to insulate the place and stop draughts the air change rate is still the dominating factor and the house heats up in an hour even with the flow temperature set ~60. The micro management does work if the system learns how long each zone takes to heat up. However you are right in that the zones must be isolated for this to work well, i.e. door shut which takes some discipline. I've already had a campaign to move towels from radiators...

Everyone clearly has different viewpoints and I appreciate the input - even if it doesn't answer my query about Evohome's reaction to weather compensation

Looking at weather compensation it's v cheap to implement <£40 as the boiler's already setup for it and it just needs wiring so pending a query about ability to select an operating curve with Vokera I'll probably run with it.

 

[ALEC1]

reall eve home needs an open therm bridge that can tell the boiler what temperature to run at relative to the demand of a particular room

in other words if on room drops say 4c, and the weather comp is determining a lowish flow temperature, the evohome should tell the boiler to work a bit harder than the curve dictates. the vokera open thermo controller will do it from one point only ideally it should come from every radiator, the evohome telling the boiler to rise the flow temp.

This bridge does exist, but is not supported in the UK

Dan lives in a modern house, so his temperatures may not fall off that much...mine and yours do as they are not modern houses.

 

[DukeGB]

reall eve home needs an open therm bridge that can tell the boiler what temperature to run at relative to the demand of a particular room

in other words if on room drops say 4c, and the weather comp is determining a lowish flow temperature, the evohome should tell the boiler to work a bit harder than the curve dictates. the vokera open thermo controller will do it from one point only ideally it should come from every radiator, the evohome telling the boiler to rise the flow temp.

This bridge does exist, but is not supported in the UK

Dan lives in a modern house, so his temperatures may not fall off that much...mine and yours do as they are not modern houses.

Completely agree - Vokera offer an opentherm controller which isn't very expensive and does just this. However, it only works on one remote thermostat which isn't what I want - I'd combine the two and pick a 'dominant room' a bit like an index run with the greatest heatloss and an area which I always want heated but I think the cost and complexity would outweigh any benefit + my sanity would be at risk!

 

[ALEC1]

of course one of the things that is frequently overlooked is frequency of use of a room...most rooms in most houses are used for at least 8-10 hours a day, some all in one long run, others you want at temperatures over time windows of the day.

Its certainly not worth letting things cool right down, so a reasonable set back has its benefit, but thats going to depend on the rate of heat loss and the speed with which a heating system can put heat in the rooms..both big variables.

Those are actually probably quite unknown, meaning any zonal control is all a stab in the dark..

much better a few trvs set correctly, an OT controller sited as you suggest and an outdoor sensor.... which acts in a predictive manner to the boiler...the thermal inertia being topped up before the house looses its heat...

 

[ALEC1]

oh and the money you save on evohome you put in insulation....