What is weather compensation?

[Odds]

That's right, he did only ask what weather compensation is.

A question already answered - then a page or two of boiler discussion.

It's all relative.

 

[ericmark]

Thank you all, it does seem size matters, it seems a great uncle of mine. Stamped his foot, which went through the floor in the billiards room, so he had the whole house ripped down and replaced it with this Looking at the chimneys there seem to be a few rooms, it says 21 bedrooms, but it's a hotel now, so likely changed a bit over the years. OK that is a silly size for a house, as is this in the other direction, not sure can be called the smallest house, when now they are not allowed to live in it?

My first house, was rather small, and having a furnace to heat it, (can't really call it a boiler when it used hot air) with a single thermostat was fine. The second house, open plan, again one thermostat between living room and dinning room in the archway, was ample. With TRV heads to stop bedrooms over heating. Zoopla says my house is 149 m² (last house it says 111 m²) it also says 4 bedrooms and there are 5, so not sure if they counted the flat? But the main change is the things called internal doors.

With an open plan, heat moves around the house, the staircase, was basic a chimney taking the heat upstairs, with no way to stop it.

Even my mothers house, with a hall, we ended up with a curtain around the stairs to stop the heat just going upstairs.

You are still suggesting the best way to control heating is by a single sensor, exactly as we did in the 60s. Slightly different sensor, but the same principle of trying to control heating across a property, with varying per-room requirements, by a single sensor which is almost certainly not in the best place.

This I think was the problem with this house, the wiring was there, and after having problems when a thermostat failed to work due to discharged batteries, I wanted a hard wired thermostat, although when one has multiple thermostats, one failing is no longer an issue.

Out side, the South-West side, stays reasonable cool, the North-West even cooler, the North-East gets the morning sun, but never gets too hot, and the South-East gets sun most of the day, so be it summer or winter, as we walk around the house, the weather changes, so to monitor outside one would need at least 2 sensors and take an average of the two.

But the same goes for inside, wife's bedroom and dinning room are on the coldest corner, my bedroom and living room are on warmest corner, and the flat is half buried into the hillside, so warmer in winter and was until solar panels fitted cooler in summer. The solar panel inverter means the flat now is much warmer in the summer, just slightly too high to brew my beer.

The dinning room, flat, and office, have become store rooms, and hardly used, so heating them over a back-ground heat seems daft. The craft room, is used, and if it is, it will be during the day, this to me is where the splitting of a home upstairs and downstairs does not make sense, be it a baby put to sleep, a child doing homework, using a room as an office, or craft room, thought-out a houses' life, the use rooms are put to will change many times, so the control system needs to be flexible enough to cater for the changes.

We have raising butt hinges on the living room door, and a soft toy to stop the door fully closing, so the cats can open door to come and go as they please. Summer until the AC is used, often prop the door open with another soft toy, and window left cracked open, again for cats, they are quite good at jumping on and off the balcony, I would not like to try it.

But I can't see the point, whatever boiler is fitted, to control the rooms from outside temperatures rather than the room temperature. It seems such a hit-and-miss method.

However, I have noted the TRVs on radiators under the windows, seem a bit poor, as the colder it is outside the warmer it gets inside, as the TRV senses the wall temperature.

And each make of TRV head, seems to have different features, with a fast drop in heat as being taken that the door/window has been opened, and heating auto delayed for a time set by the user, great idea in the kitchen when unloading the shopping. Another has both water and air temperature sensors, so it compensates for heat direct from radiator, another works out how long it takes to reheat the room, and turns on heating earlier in cold weather (without the need for outside sensors) but setting the time in each room, means the dinning room is not heated in the dead of the night.

Also arranging a sequence, with short delay, so kitchen, then dinning room, then living room heated, means the kitchen radiator get hot faster. The idea of at a set time trying to heat all rooms together, seems daft, we never use them all together.

 

[denso13]

But I can't see the point, whatever boiler is fitted, to control the rooms from outside temperatures rather than the room temperature.

It is using the room temperature where the stat is. But it is taking the outdoor temperature to work out the most efficient/best way to get to that room temperature. The colder it is outside the higher the flow temperature will be, as a general rule of thumb.

 

[ericmark]

It is using the room temperature where the stat is. But it is taking the outdoor temperature to work out the most efficient/best way to get to that room temperature. The colder it is outside the higher the flow temperature will be, as a general rule of thumb.

So it is like turning the temperature dial on the boiler?

 

[denso13]

So it is like turning the temperature dial on the boiler?

Not quite. The temperature dial sets the limit and the boiler fires at full rate till it gets there. Weather compensation modulates the boiler, as in it alters the gas rate and subsequently the flow temperature, automatically. But a similar outcome, in a way.

 

[ericmark]

The less heat the boiler generates, the more latent heat can be gained, so the lower the boiler temperature the more economical it runs and less hysteresis one gets. I see that, it makes sense.

This is why we don't want to turn the boiler off/on but rather down/up. So a TRV controlling water flow, is far better to any wall on/off thermostat, OK not for my set-up, with non modulating boiler, but it is for most people.

So this house Autumn and Spring, to maintain rooms in use, likely looking at 2–4 kW, where in the Winter more like 10 kW to maintain temperatures. But to raise the temperature from say 16°C to 21°C that needs more energy, and it depends on time to change as to what size boiler in required, but if there is only one room in use, and the radiators are 1.5 kW each at 70°C and 2 kW each at 90°C then to run boiler hotter until room at new temperature is a balance to running it longer and gaining the latent heat instead.

But clearly the boiler will need to modulate to 3 kW if it can't run that low, then it will use mark/space ratio anyway, and then looking at the delay between boiler running and return water getting too hot.

So it is all down to the algorithms, and how they can get the boiler to run more efficiently. So if the boiler using mark/space restarts at lowest output, then it will run more efficiently to if it restarts at full output.

And this is where the on/off wall thermostat fails, it restarts the boiler at max output, where using OpenTherm and the like, it restarts at a low output. So if I am reading it correct, the weather compensation is doing the same as OpenTherm and restarting boiler at a low output.

So if I am reading this correct, if you have OpenTherm then no real need for weather compensation, as they are doing the same thing.

Have I got it right, or am I still not understanding?

 

[denso13]

So if I am reading this correct, if you have OpenTherm then no real need for weather compensation, as they are doing the same thing.

Similar, but the WC sets the upper flow temperature limit based on the outdoor temperature while the OT modulates things below that limit. Both aren't needed together but they seem to work well. Adds very little to a boiler installation.

 

[Razor900]

Not quite. The temperature dial sets the limit and the boiler fires at full rate till it gets there. Weather compensation modulates the boiler, as in it alters the gas rate and subsequently the flow temperature, automatically. But a similar outcome, in a way.

Are you sure about that? Do the WC charts shows boiler power or temp? The boiler will modify itself as it gets near the setpoint but it does that with any temperature...

 

[Razor900]

To answer the actual question:

If the temperature is different between indoors and outside then heat will move from the higher to the lower.

The difference in temperature is called the delta so if you house is 20 degrees in the heated parts and outside is 5 degrees you have a delta T of 15

Different materials let heat through at different rates so we take all the different materials, their sizes and the amount each one lets through and that gives us a heat loss figure based on a delta of 1 degree C, (ie 19 outdoors and 20 inside).

The current heatloss is found by multiplying the heat loss figure by the delta T

So if your house heatloss is 1kW and the delta T is 1 as above you lose 1kW

But if it's 10 degrees externally making your Delta T 10 then your heatloss is now 10kW

And when you get down to zero the heatloss is now 20kW and you must live in a castle somewhere

So as it gets colder outside you need to get more energy into the building. This is done by making the flow temperature higher so every litre of water that flows through the property has more energy contained in it.

All of that is to explain why we need to modulate flow temp

Weather comp looks at the outside temperature and chooses a flow temp that should balance the heatloss of the house to keep the heat source running at its most efficient output.

I'm not a fan of pure weather compensation in domestic because if you come into a house that's 10 degrees with WC it can set the flow temp too low and it takes forever to warm up. I usually set it with a 10% uplift over what's needed for maintenance to get around this.

It's great for commercial settings where temps are maintained around the clock though.

Modern intelligent WC is a different beast altogether and can give fantastic results if set up properly.

Opentherm is something very different and works extremely well on most UK style houses

 

[denso13]

Are you sure about that?

It wasn't meant to be a technical explanation, only that WC and OT are different.

 

[ericmark]

Thank you both @Razor900 and @denso13 I do realise there are two very different things, one energy to retain the homes temperature and two the energy to increase the homes' temperature within a set time.

The latter is why geo-fencing does not work for my house, well to be frank at least how Nest Gen 3 worked, can't see it working with any house.

So I would leave the house and on the app we could see the heating had auto turned down the temperature, now to work it has to see your returning, and if dropped 20°C to 17°C, and it takes 30 minutes to raise 3°C at 30 miles per hour (½ mile per minute) then at 60 miles away it needs to start raising the temperature, so at 40 miles from home 18°C and 20 miles from home 19°C, so one arrives home and it is at 20°C.

But it waited until ½ mile from home then set to 20°C, may as well have turned the dial down when leaving and back again when I got home, all geo-fencing did was make sure I turned it down on leaving.

So when the local cell site was taken down by high winds, the home drops 3°C, however the Nest thermostat also has a PIR built in which would even without the info from the phone, turn up the heating when it detected someone was home, so each time we went to the thermostat it showed set at 20°C but area (hall) was still at 18°C, so we thought the boiler or radiators were too small, we could hear the boiler switch off, so it had we thought got the water to temperature, so it must be the radiators too small.

Until I looked at the thermostat on the PC, then I clicked it was the thermostat turning down the heating, so that was the end of geo-fencing. Then we found still too cold in the living room, and then we found the second fault, having the thermostat in the hall, as the hall cooled slower than the living room, so fitting a Wiser thermostat in parallel leaving the Nest to do DHW if required, and having a Wiser wall thermostat in living room, cured our problems, well in the main, a slight problem with wife's room, the wiser TRV head turns on the heating too early, as it senses the wall temperature rather than room, as she has so much rubbish in front of the radiator, but I have just turned the temperature down to 15°C her room currently at 20°C where living room even with window open is at 22.5°C on wall thermostat, 22°C on the TRV under open window, and 20.5°C at window 90° to open window. Heat is of course not on.

The two TRVs in living room are set higher than the wall thermostat in the main, but if we use voice commands to change temperature that changes all three together.

So before finding out the thermostats were why we had cool rooms, I raised the flow temperature on the boiler, after all your help, I think I should turn it to around ¼ for Autumn and Spring, and back to ¾ in Winter, but since oil, I have no gas meter to read to see how much energy (oil) is being used, I have to stand on an old caravan step and look in the tank.

I suppose turning down the temperature would save oil, but as to if that is because the immersion heater would then heat DHW instead of the oil, or because using less on heating would be hard to work out, will an immersion heater inhibit thermo-syphon working? The immersion uses either off-peak or solar, so cheaper to heat DHW with electric.

But the way I was led astray with Nest Gen 3, I look at OpenTherm and Weather compensation, and think, will they do the same? With so many controls, how do you know when one has failed?

 

[Razor900]

Been ages since I worked on a Nest now they've withdrawn support. Better stats allow you to set the distance away for geofencing but I would agree unless it turn on when you are 20 miles away its not great and that doesnt suit most of the population.

I did mention earlier but you do need to be careful turning the flow temp down too much on your oil boiler or you could very quickly rot out the heat exchanger depending on which boiler it is

 

[drives]

I'm not a fan of pure weather compensation in domestic because if you come into a house that's 10 degrees with WC it can set the flow temp too low and it takes forever to warm up.

Why would the house be 10 degrees C?

Just keep it running 24/7. That said it’s simple enough just to temporarily take it off weather comp and run a set [higher] outlet flow temp, if for whatever reason we need to heat the house back up from cold.

 

[Razor900]

Why would the house be 10 degrees C?

Just keep it running 24/7. That said it’s simple enough just to temporarily take it off weather comp and run a set [higher] outlet flow temp, if for whatever reason we need to heat the house back up from cold.

As confident as only a DIYer could be

Lots of people with older draughty and poorly insulated properties don't want the cost of running a system 24/7

Tell me how on most heat sources you can simply override the WC. Is there an on off switch for it?

And if you can then what's the point of fitting it then turning it off?

 

[drives]

As confident as only a DIYer could be

Lots of people with older draughty and poorly insulated properties don't want the cost of running a system 24/7

Tell me how on most heat sources you can simply override the WC. Is there an on off switch for it?

And if you can then what's the point of fitting it then turning it off?

Our property is quite poorly insulated and we just keep it running. I trialed setbacks versus just leaving it running all day at a steady indoor temp with our old gas boiler and even with that, the savings were minimal. I recall on cold days it was something like 20p saving at most to have a 16 degree set back during the day when out at work.

With regard to controls that is a fair point as our native midea heat pump controls are not user friendly and switching between weather comp and set flow temp does require a bit of a deep dive into the settings. I’ve customised our controls using a home assistant dashboard which makes it much easier.

That said once the fabric of the house warms up with the low and slow approach, the indoor temp drops much slower as well if for any reason it is turned off for a few hours. I had to do this a few times in winter to change a couple of radiators. I don’t even think I bothered taking it off weather comp mode.