Discuss Weather comp settings at night? in the Central Heating Forum area at PlumbersForums.net

How does the weather comp. work when you go to bed.
If you have a lower temperature at night surely the next day the boiler then has to work that bit harder to reach the correct temperature for that day. What do you do?
I don't like it hot at night, so want heating off or at least down in temperature with nothing to do with saving money. However the hotter some thing is, the more heat it will loose, so the boiler is replacing heat lost, so the cooler the rooms the less heat lost.

The problem is the reheat, and hysteresis, if I look at the TRV report for my living room
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it shows how my heating has gone up/down all day, the ideal is a smooth pattern so we are kept warm without any hysteresis, but with my oil fired boiler which simply switches on/off I will never get a smooth pattern.

However with gas we have a modulating boiler, so the boiler can adjust its output, so two plus points, one it can gain latent heat from flue gases, and two it can heat just enough, so as the room warms up, the radiator cools down, so it maintains the room spot on the setting of the TRV heads, as long as nothing upsets the system by switching boiler off/on.

So wall thermostats also need to modulate the boilers output with OpenTherm and the like, or the wall thermostat is only there to turn off boiler in warm weather, in other words we want to reduce on/off control to the minimum, or you get same as my oil boiler with a high hysteresis.

This means some careful setting of the controls, in an ideal world we would have each TRV head linked to a central hub which in turn tells boiler if more or less heat is required, but in the real world the return water is used. So the boiler turns up or down depending on the temperature of the return water.

As each TRV closes, the pressure will rise slightly, causing at first more water through radiators still open, then lifting the by-pass valve so it slowly returns warmer and warmer so the boiler turns further and further down with its output. Unless it is told to switch off, if that happens it has to start all over again to regulate output once turned on again.

So unless the TRV heads are linked to the hub/thermostat, one needs to very carefully set the wall on/off thermostat so in winter the TRV works first, so it will never turn off unless we program a change in temperature, in which case also the TRV needs programming for same change. Only as summer comes will the wall thermostat turn off the boiler and stop it cycling.

So in order to turn off the boiler when likely we will have a warm day, the wall thermostat needs to be in a room normally kept cool, on ground floor as heat rises, and with no outside doors, or alternative heating including sun through the windows, I don't know your home, but in mine no such room exists, so we try next best thing which is the hall.

One thing the books don't point out, is the room needs to be the fastest cooling room too, or other rooms get cold before heating switches on, so the boiler manufacturers try to compensate for the problems, including if the sun is shining we feel conformable in cooler rooms.

So in the main we use near enough engineering and the system is way off perfect.


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It'll naturally have to work a bit harder for a time to get up to day temp setting but it'll do so in the most efficient way.
I have considered many times how to speed up the reheat, it would depend on max and min output of the boiler, but in theroy not reason not to have a sequential start up, so on return home say kitchen, then dinning room, then living room, and finally bedrooms.

However my boiler min and max is 19 kW, so my boiler would start to cycle.

We want radiators far bigger to be able to turn off rooms without the boiler cycling.

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