Room thermostat: Myson MPRT differential

[magicjez]

I cant find any information about this room thermostat, I'm wondering if it can be changed because it seems to come back on when the temperature hasn't changed, example if I set it to 22c it will turn off off at 22.1c but then say 15 minutes later it will come back on when it's still saying 22.1c. It has oil or gas mode I'm not sure what that's supposed to be on because I'm on district heating.

Thanks.

 

[Chuck]

I cant find any information about this room thermostat, I'm wondering if it can be changed because it seems to come back on when the temperature hasn't changed, example if I set it to 22c it will turn off off at 22.1c but then say 15 minutes later it will come back on when it's still saying 22.1c. It has oil or gas mode I'm not sure what that's supposed to be on because I'm on district heating.

Thanks.

Plumbnation has the data sheets available:

Room Thermostats

The UK Room Thermostats Shop. Huge Range of Room Thermostats in stock. Lowest Online Prices - Checked Every Day. Free Next Day Delivery.

www.plumbnation.co.uk

These are a bit short on technical details but I suspect what you are seeing is normal. If I'm right, it's the operation of what's known as 'integral control' and the use of pulse width modulation to keep the temperature accurately at the set point without the offset required by simple proportional control or the hysteresis exhibited by a traditional thermostat with on-off control.

A 0.1°C difference between set point and room temperature is not significant. In fact, anything less than about 0.5°C is not worth worrying about.

 

[snowhead]

As per Chuck.
In the past radiators would heat up and cool down, due to heat lost to the room, under the control of a basic and or stat Thermostatic valve.
In an ideal world the radiator output should exactly match the heat loss for the room, then you wouldn't get the constant heat up / cool down cycle.
It appears your Mysons are getting very close to doing this.
If the radiator can match the heat loss then the set point can be lower as the room temperature won't drift up and down.

 

[John.g]

I cant find any information about this room thermostat, I'm wondering if it can be changed because it seems to come back on when the temperature hasn't changed, example if I set it to 22c it will turn off off at 22.1c but then say 15 minutes later it will come back on when it's still saying 22.1c. It has oil or gas mode I'm not sure what that's supposed to be on because I'm on district heating.

Thanks.

I don't think it should if it works like the Honeywell one (DT90E), the temperature can overshoot but the boiler should not IMO re fire while in this condition, however small.
The stat cycles the boiler (or heat exchanger in your case) on and off as the room temp approaches the set point, if the room temp is lower than the SP- hyseresis (maybe 1.5C) then the boiler is on constantly, if its just at or within the hysteresis (proportional band) it will cycle the boiler on/off but not more frequently than (in a Honeywell stat) something like 6 cycles/hour, as the room temp approaches its SP then the cycle time will increase and the boiler should be switched off permanently if the room temp is > the SP. There is also a learning curve/time for these stats.

 

[magicjez]

Thank you everyone, so there was me thinking it was faulty or set wrong, I have managed to download the manual but it doesn't seem to give you much information about the gas or oil setting accept they advise setting to oil if you have underfloor heating but still have a gas boiler. It seems when I have been playing about with it gas mode will come on more times when it's reached its setpoint so every 5 minutes but stays on for two minutes where oil mode comes on every 15 minutes and stays on for 5 minutes.

 

[John.g]

A oil boiler, because its Hx contains 20/25 litres vs 2 or 3 litres for a gas boiler has a longer natural cycle time as it will take longer to reach its cut in point so maybe that is more suitable for district heating?, 5 mins on and 15 mins off is a cycle time of 20 mins or 3 per hour but one would think that this (or gas mode) should change and increase or decrease as the temperature differential changes for example if the cycle time is 20 mins at 1.5C difference, one might expect it to be 40 mins at 0.75C and so on, might be interesting to watch it.

 

[magicjez]

Cheers I had been playing around before I asked here and did notice I used more when it was set to gas. The one thing I hate about this system (District Heating) when it's reached its set point the HIU takes 2 minutes to come on, so the radiators hardly get hot before it gets switched off again, instead of being on for 5 minutes it's really only on for 3 minutes.

 

[magicjez]

I have been looking at youtube videos I found a demo of the thermostat, the man said it uses pull squid modulation that's what it sounded like to me lol but couldn't find anything so doing a search it's more likely he said pulse width modulation.

 

[John.g]

I don't think anyone will have any complaints when it controls to within 0.1C, but I do wonder why its stlll calling for heat when the room temp is greater than the SP even though its still maintaining that 0.1C differential.

 

[magicjez]

I'm wondering if the digital temp is displaying wrong

 

[Chuck]

I don't think anyone will have any complaints when it controls to within 0.1C, but I do wonder why its stlll calling for heat when the room temp is greater than the SP even though its still maintaining that 0.1C differential.

It's normal (and by some measures optimal) for control systems to overshoot to some extent and 0.1°C is negligible in the context of domestic heating. The behaviour depends on the controller parameters (ratio of proportional, integral and derivative actions) and the time lags between call and response for the rest of the system.

We haven't been told enough about the OPs system, in particular the HIU type, to have any hope of understanding the behaviour in detail. Some HIU's have their own smart control systems and some are pretty dumb.

If the OP doesn't like the 5 minute 'gas' timing cycle using the longer 'oil' setting is not going to cause any problems other than the undershoot may increase a bit.

 

[magicjez]

It's normal (and by some measures optimal) for control systems to overshoot to some extent and 0.1°C is negligible in the context of domestic heating. The behaviour depends on the controller parameters (ratio of proportional, integral and derivative actions) and the time lags between call and response for the rest of the system.

We haven't been told enough about the OPs system, in particular the HIU type, to have any hope of understanding the behaviour in detail. Some HIU's have their own smart control systems and some are pretty dumb.

If the OP doesn't like the 5 minute 'gas' timing cycle using the longer 'oil' setting is not going to cause any problems other than the undershoot may increase a bit.

I have absolutely no idea what type the HIU is, I'm not sure if it has any smart control functions, Something I can ask eon thanks.

 

[John.g]

Are you on oil or gas mode now?
Maybe for interest, change the SP to 21.9c and see does it control to 22C or does it still call for heat with a 0.2C differential.

 

[magicjez]

Are you on oil or gas mode now?
Maybe for interest, change the SP to 21.9c and see does it control to 22C or does it still call for heat with a 0.2C differential.

I'm on oil mode as I found it was just coming on off to quickly on gas mode.

It goes 21c- 21.5c to 22c nothing in between.

 

[John.g]

Well, maybe leave well enough alone as these controllers take days/weeks to adapt, is it still cycling every 20 minutes or so "now"?.

 

[magicjez]

Yes it's still every 15-20 minutes.