Can you tell when a modulating boiler is fully modulated?

[EricMark]

The problem with using TRV's to control heating to every room, is as the weather warms up, the boiler starts to cycle as it can't turn down any lower, to some extent anti-cycle software can increase cycle time if on switch on water returns hot, or decrease if it returns cold, but it can never turn the boiler fully off.

So we have a very cleaver boiler that reads return water temperature and modulates so reducing the hysteresis, then we spoil it all by adding an on/off wall thermostat. OK some boilers do allow connection to eBus so an analogue thermostat can be used, but with a on/off thermostat we don't really want it to switch off until boiler fully modulated or each time it does, all heat in boiler is lost out of the flue.

The modern electronic head on the TRV can control each rooms temperature with a programmed change in the target temperature so only thing the wall thermostat does is stop cycling. So the boiler only wants turning off once it has started to cycle, as until that point some room some where in the home is demanding heat. But how does one detect it has started to cycle?

 

[James]

The problem with using TRV's to control heating to every room, is as the weather warms up, the boiler starts to cycle as it can't turn down any lower, to some extent anti-cycle software can increase cycle time if on switch on water returns hot, or decrease if it returns cold, but it can never turn the boiler fully off.

So we have a very cleaver boiler that reads return water temperature and modulates so reducing the hysteresis, then we spoil it all by adding an on/off wall thermostat. OK some boilers do allow connection to eBus so an analogue thermostat can be used, but with a on/off thermostat we don't really want it to switch off until boiler fully modulated or each time it does, all heat in boiler is lost out of the flue.

The modern electronic head on the TRV can control each rooms temperature with a programmed change in the target temperature so only thing the wall thermostat does is stop cycling. So the boiler only wants turning off once it has started to cycle, as until that point some room some where in the home is demanding heat. But how does one detect it has started to cycle?

Flow meter on gas inlet pipe
Use the blower fan supply to sense if it is permanently running or turning on and off
Both of these options could be used with a simple plc that decides if it is running constantly or turning on and off.

 

[EricMark]

Although I have written many PLC programs, I would not like to use a PLC in the home, as it is unlikely that a domestic spark will have his laptop and Medoc installed to read what the PLC is doing, so looking for a more standard method to switch off a central heating system as summer approaches, and of course back on in winter, with maybe some over ride.

In other words what the school caretaker would do years ago, but automated.

Today pure interest, as using oil fired boiler, so does not modulate. But from the time when the TRV first came out, I have considered methods to switch the boiler off/on. The TRV head can control each room rather cheaply, an electronic head starts at £10 so a schedule can be set for each room, and with 13 areas (14 radiators) likely one or more will be on at all times as to if these would use 6 kW which seems to be minimum for most boilers not so sure, but to get to next stage where the TRV heads tell the boiler when to run is a huge jump in price, with a Hive thermostat for example the TRV heads are £80 each.

So looking at some thing between the two extremes. Most gas boilers today modulate using return water temperature, OK some have Ebus but even with Ebus there seems to be either very expensive or lack of control. Having a modulating thermostat in one room seems daft, most homes have at least 4 rooms. One has to ask is a central heating boiler that only monitors one room fit for the job?

Yes Tado and EvoHome have OpenTherm and can control the whole home, but Nest only has a follow command although it is OpenTherm and Hive does not have opentherm, also many boilers do not have Opentherm, and I have failed to work out how to use OpenTherm wall thermostats with a pair of motorised valves splitting the home into living and dormitory areas.

As to why motorised valves are used, instead of programmable TRV heads I have not worked out? Even with 10 rooms, the cost of two zones must be more than fitting 10 programmable TRV heads at £10 each, if you include pipe work.

Well maybe I can, the problem is how to turn whole boiler off and on, well off can be done by monitoring when it starts to cycle, on a bit more of a problem, but cheap on/off thermostats should work.

I tried in old home, thermostat in the hall, not a good location, as open the front door and hall was cooled, but also a TRV on radiator, so careful adjustment and hall door opened and TRV turned on, but before hall heated to wall thermostat temperature the TRV turned down again giving rest of house chance to heat, there was a stop set on wall thermostat so could still be used as a switch, and turning up to stop it matched the TRV. It worked, but not best as could not alter hall temperature night/day as too hard to adjust TRV and wall thermostat to match.

This house using Nest with 4 Energenie TRV heads using follow command, so alter Nest and automatic hall, dinning room and living room TRV's change to same temperature. But only did this because already had 4 TRV's and only two wires hall to where boiler is installed so very few options. And rest of rooms have cheap £15 TRV heads, not cheapest, as got bluetooth so I can alter without needing to view the LCD display on the TRV heads. Still looking at £450 worth of control stuff, OK I can afford it, but there must be a cheaper way?

 

[jackhammerJIM]

Although I have written many PLC programs, I would not like to use a PLC in the home, as it is unlikely that a domestic spark will have his laptop and Medoc installed to read what the PLC is doing, so looking for a more standard method to switch off a central heating system as summer approaches, and of course back on in winter, with maybe some over ride.

In other words what the school caretaker would do years ago, but automated.

Today pure interest, as using oil fired boiler, so does not modulate. But from the time when the TRV first came out, I have considered methods to switch the boiler off/on. The TRV head can control each room rather cheaply, an electronic head starts at £10 so a schedule can be set for each room, and with 13 areas (14 radiators) likely one or more will be on at all times as to if these would use 6 kW which seems to be minimum for most boilers not so sure, but to get to next stage where the TRV heads tell the boiler when to run is a huge jump in price, with a Hive thermostat for example the TRV heads are £80 each.

So looking at some thing between the two extremes. Most gas boilers today modulate using return water temperature, OK some have Ebus but even with Ebus there seems to be either very expensive or lack of control. Having a modulating thermostat in one room seems daft, most homes have at least 4 rooms. One has to ask is a central heating boiler that only monitors one room fit for the job?

Yes Tado and EvoHome have OpenTherm and can control the whole home, but Nest only has a follow command although it is OpenTherm and Hive does not have opentherm, also many boilers do not have Opentherm, and I have failed to work out how to use OpenTherm wall thermostats with a pair of motorised valves splitting the home into living and dormitory areas.

As to why motorised valves are used, instead of programmable TRV heads I have not worked out? Even with 10 rooms, the cost of two zones must be more than fitting 10 programmable TRV heads at £10 each, if you include pipe work.

Well maybe I can, the problem is how to turn whole boiler off and on, well off can be done by monitoring when it starts to cycle, on a bit more of a problem, but cheap on/off thermostats should work.

I tried in old home, thermostat in the hall, not a good location, as open the front door and hall was cooled, but also a TRV on radiator, so careful adjustment and hall door opened and TRV turned on, but before hall heated to wall thermostat temperature the TRV turned down again giving rest of house chance to heat, there was a stop set on wall thermostat so could still be used as a switch, and turning up to stop it matched the TRV. It worked, but not best as could not alter hall temperature night/day as too hard to adjust TRV and wall thermostat to match.

This house using Nest with 4 Energenie TRV heads using follow command, so alter Nest and automatic hall, dinning room and living room TRV's change to same temperature. But only did this because already had 4 TRV's and only two wires hall to where boiler is installed so very few options. And rest of rooms have cheap £15 TRV heads, not cheapest, as got bluetooth so I can alter without needing to view the LCD display on the TRV heads. Still looking at £450 worth of control stuff, OK I can afford it, but there must be a cheaper way?

What are you waffling on about . Fit a room stat and have done with it .

 

[tlangdon12]

My solution, which I haven't implemented yet, is to replace the TRVs with wired thermostats in every room, wired Actuators on every rad and a UFH Controller. Wavin's UFH controller is my current favorite. Unfortunately the thermostats only come in wireless battery or 24v wired format. I hate changing batteries, so will have to have a 24v PSU on each

The UFH controller aggregates the heating demand from all the thermostats and switches the boiler on if there is any demand, and off if there is none. The boiler modulates to meet the heating demand that it sees on the return flow. When the boiler is modulated to it's lowest output, the UFH controller keeps the boiler on until the last room is up to temp, then shuts the boiler down.

 

[EricMark]

What are you waffling on about . Fit a room stat and have done with it .

In this house there are 16 thermostats, mother's house there were 8 thermostats, and in our old house 5 thermostats.

How and where the thermostats are fitted however is the important bit with a modulating boiler, the thermostat at the end of the radiator modulates the flow, not really sure about the inbuilt thermostats on the Myson fan assisted radiator as it does not stop the water flowing, it just turns the fan on/off.

But other than my first house with hot air central heating every house has had more that one thermostat.

I did consider the idea of a wall thermostat in every room, all in parallel and set to same temperature as the radiator mounted room thermostat, although the wall thermostat is digital (off/on) they would only all turn off when the home was warm enough to not require the boiler, it would not matter what the wind direction was or the sun being shinning or not.

So yes it would work, however it seems wrong to fit two thermostats in a room when one would do, and with a modulating boiler it would seem to make sense to use a modulating thermostat, it should reduce hysteresis.

However the normal gas boiler will not modulate to under around 8 kW so at that point it starts to cycle, and will never fully switch off, there is clearly a point where it is no longer required, in fact where your trying to cool the house rather than heat it, what would seem to make sense would be for when the space of the mark/space ratio hits a pre-set valve for the boiler to turn off, and then for a thermostat to turn it back on once the house has dropped to a pre-set valve.

In that way the boiler does not turn off until fully modulated, so assuming boiler is correctly designed, the boiler will already be running cool so very little heat is lost out of the flue.

I am sure a single wall thermostat in a lower floor room, which is normally kept cool, has no outside door, or alternative form of heating, with no build in anti-hysteresis software could switch the boiler off when no longer required and on when required again. However that room needs to exist in the first place.

So the house where I was trying to make it all work, downstairs there were 6 areas.
1) Under stairs, it was not heated so that reduces it to 4.
2) Kitchen has alternative heating, so that reduces it to 3.
3) Living room has a bay window which catches the sun, in the morning the temperature can get high from just the sun, so now down to 2.
4) Best room also has a bay window which catches evening sun, so again not suitable, so just one left.
5) The hall has an outside door, as a result it has a large radiator to reheat the hall after the front door is opened, and the stairs have a chimney effect, it also leads on to all rooms, so leave a connecting door open and it's temperature will alter, so yet again not suitable.
6) The wetroom had underfloor heating and is a wet environment so the last room also not suitable.

So there is no single lower floor room suitable for a wall thermostat, now my own house was open plan, only down stairs door was to kitchen and that house worked A1 with a single wall thermostat between living and dinning room in the archway between the two rooms worked well. But that is maybe the point, no two houses are the same.

In some ways the question is now academic, house now sold, but new house also has doors, so like the mother's old house there is no single room that could house a single thermostat to control whole house. I have however a hall where the so called front door is not used, so likely the hall will work with a single thermostat linked to the other two rooms leading off the hall, but as with mothers house no room is really suitable.

Hall, Kitchen, and living room all have outside doors, the utility room and under stairs have no radiators, and toilet/shower room not really suitable as has an extractor fan.

 

[EricMark]

My solution, which I haven't implemented yet, is to replace the TRVs with wired thermostats in every room, wired Actuators on every rad and a UFH Controller. Wavin's UFH controller is my current favorite. Unfortunately the thermostats only come in wireless battery or 24v wired format. I hate changing batteries, so will have to have a 24v PSU on each

The UFH controller aggregates the heating demand from all the thermostats and switches the boiler on if there is any demand, and off if there is none. The boiler modulates to meet the heating demand that it sees on the return flow. When the boiler is modulated to it's lowest output, the UFH controller keeps the boiler on until the last room is up to temp, then shuts the boiler down.

That sounds like a very good system. I will need to wait and do a winter, I don't want to rip up flooring to wire up any additions until tested.