I have a HC60NG thermostat on a Potterton 28 NON-condensing boiler. The thermostst operates on TPI control method. It works as it should but boiler fires up 45-50 times a day (short, frequent bursts) to maintain a very steady temp. Will this wear out the boiler? (I know these thermostats were designed to make CONDENSING boilers run efficiently).
Honeywell wireless thermostst TPI on a non-condensing boiler
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Actually it is the other way round.
50 times a day?
What intervals? Driving at the moment, so can't give chapter and verse on tpi... Oh hang on....
What intervals? Driving at the moment, so can't give chapter and verse on tpi... Oh hang on....
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TPI (Time Proportional & Integral) control is an industry standard term for an On/Off control using an advanced energy saving control method that can be used by most heating systems in the UK. The controls simply switch current supplied to the boiler on or off at different times. Unlike a traditional thermostat, these rely on digital technology that matches the boiler firing to the load on the system.
How does TPI Control work?
A thermostat operates using a fixed number of firing periods per hour (normally selected to suit the appliance and system). It then calculates how many minutes are required within each firing period to satisfy the demand of the rooms. This allows the flow temperature from the boiler to fall as demand reduces, which helps the return temperature to stay below the Dew Point (55oC) so that the boiler can operate in condensing mode more frequently.
A TPI room thermostat will have 100% demand when the system first calls for heat. When the room temperature approaches the set point, it enters the proportional bandwhere the demand varies. The TPI thermostat will then reduce the firing time in that cycle period in proportion with the demand (i.e. if the proportional bandis 2oC and the room temperature 1oC from set point, it will fire the boiler for 50% of the cycle period). This means that as the room temperature approaches set point, the boiler is fired progressively less. Further smoothing of this demand is achieved with the Integral part of the calculation, which, when combined, prevent the thermostat ‘hunting’ at all. The control will be at a steady even temperature with little variation, as can be seen in Figure 1.
Building Regulations require that every system has a room thermostat, whether old or new. This will form an essential part of the Boiler Interlock, providing the means to switch the boiler off when it is no longer required. This performance can be enhanced using a TPI thermostat.
How can a system be improved from Building Regulation requirements?
By fitting a TPI, the boiler efficiency is improved, TACMA tests indicate that under steady state conditions this can be as much as 10%. This would be reduced by seasonal and operational losses. But in addition, because the control is so much more accurate, the set point can be reduced, without loss of comfort, introducing extra savings.
The thermostat can then also have an intelligent or self learning facility, so that when it first operates, it can recognise how the system responds to its demand signals and can adjust them to adapt to the fabric of the building and the system as it is installed to give better control.
How does TPI Control work?
A thermostat operates using a fixed number of firing periods per hour (normally selected to suit the appliance and system). It then calculates how many minutes are required within each firing period to satisfy the demand of the rooms. This allows the flow temperature from the boiler to fall as demand reduces, which helps the return temperature to stay below the Dew Point (55oC) so that the boiler can operate in condensing mode more frequently.
A TPI room thermostat will have 100% demand when the system first calls for heat. When the room temperature approaches the set point, it enters the proportional bandwhere the demand varies. The TPI thermostat will then reduce the firing time in that cycle period in proportion with the demand (i.e. if the proportional bandis 2oC and the room temperature 1oC from set point, it will fire the boiler for 50% of the cycle period). This means that as the room temperature approaches set point, the boiler is fired progressively less. Further smoothing of this demand is achieved with the Integral part of the calculation, which, when combined, prevent the thermostat ‘hunting’ at all. The control will be at a steady even temperature with little variation, as can be seen in Figure 1.
Building Regulations require that every system has a room thermostat, whether old or new. This will form an essential part of the Boiler Interlock, providing the means to switch the boiler off when it is no longer required. This performance can be enhanced using a TPI thermostat.
How can a system be improved from Building Regulation requirements?
By fitting a TPI, the boiler efficiency is improved, TACMA tests indicate that under steady state conditions this can be as much as 10%. This would be reduced by seasonal and operational losses. But in addition, because the control is so much more accurate, the set point can be reduced, without loss of comfort, introducing extra savings.
The thermostat can then also have an intelligent or self learning facility, so that when it first operates, it can recognise how the system responds to its demand signals and can adjust them to adapt to the fabric of the building and the system as it is installed to give better control.
It comes on and then fires 6 times an hour. If the heat is on for 8 hours, that is 48 firings. My concern was that this may wear out the non condensing boiler, as this is about 10 times more ons and offs than before the new thermostat was fitted..... I just want to know if this is likely to happen. Thanks for posting the explanation of what TPI is.
I doubt it will have a significant effect on your boiler.
You can change the number of times it cycles if you wish though.
You can change the number of times it cycles if you wish though.
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