Is my Honeywell CM927 wasting gas?
- Thread starter staz1000
- Start date
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An alorithmic combination of the current temperature, set point temperature, and the previously observed response curve of the system.
Given that heat loss is constant, and not insignificant in this current weather, I am not surprised by this.
Mathew
Okay I will just have to wait and see. When on my next day off I'll ensure I keep the programmer in the same room, with the temperature set the same, and keep external door opening to a minimum and I'll see if it does indeed fire every single 20 minutes. I would expect that getting into the afternoon when the outside temperature has reached it's highest point that would be the most likely time for the cycles to be skipped.
If not it's going on eBay! lol
I have the same problem, and it drives me nuts!
Below is honeywell's reply to the problem!
The CM927 operates a CYCLIC boiler on/off mode when near (within 1.5C) setpoint ; this is to inject just the right amount of extra heat into the radiator system such that the radiators emit heat to EQUAL that being lost. If the boiler just went OFF the room would COOL. – see attached
The CM927 is a time/temp controller NOT ann ON/OFF type.
SO if you need the boiler OFF at a particular time; you need to set the TEMPERATURE to 5C at the off time - see also attached.
(if the temp is left at same as on time or any other temp eg 18C it will maintain the room to that new temp.)
-------------------------------------------------------------------------------------
What is TPI Control?
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 theload on the system.
How does TPI Control work?
A thermostat operates using a fixed number of firing periods perhour (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. This is called Load Compensation and currently accrues a 3% boiler efficiency increase under the SAP (Standard Assessment Procedure) calculations.
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.
Can TPI controls be used on all boilers?
Yes. What is required of heating controls in the Building Regulations?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 testsindicate 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.
This FAQ sheet is for guidance only and at the time of production represented the latest information available to Honeywell fromvarious sources.
Honeywell reserves the right at any time and without notice to change any product, specification or any other information contained in this publication and cannot accept any responsibility for loss or damage arising out of any errors that may inadvertently be contained herein.
Technical support: Ring 08457 678999 (local rate charge from within the UK) or e-mail [email protected]
Sales enquiries: Ring 01344 656591 or e-mail [email protected]
Sales support literature: Visit the Downloads section of honeywelluk.com, ring 0800 521121 (UK only) or e-mail [email protected]
EN1H-2472 UK01 R0209
Figure 1 Temperature variation with a TPI room thermostat
Temperature
TimeSet pointProportional band
Below is honeywell's reply to the problem!
The CM927 operates a CYCLIC boiler on/off mode when near (within 1.5C) setpoint ; this is to inject just the right amount of extra heat into the radiator system such that the radiators emit heat to EQUAL that being lost. If the boiler just went OFF the room would COOL. – see attached
The CM927 is a time/temp controller NOT ann ON/OFF type.
SO if you need the boiler OFF at a particular time; you need to set the TEMPERATURE to 5C at the off time - see also attached.
(if the temp is left at same as on time or any other temp eg 18C it will maintain the room to that new temp.)
-------------------------------------------------------------------------------------
What is TPI Control?
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 theload on the system.
How does TPI Control work?
A thermostat operates using a fixed number of firing periods perhour (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. This is called Load Compensation and currently accrues a 3% boiler efficiency increase under the SAP (Standard Assessment Procedure) calculations.
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.
Can TPI controls be used on all boilers?
Yes. What is required of heating controls in the Building Regulations?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 testsindicate 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.
This FAQ sheet is for guidance only and at the time of production represented the latest information available to Honeywell fromvarious sources.
Honeywell reserves the right at any time and without notice to change any product, specification or any other information contained in this publication and cannot accept any responsibility for loss or damage arising out of any errors that may inadvertently be contained herein.
Technical support: Ring 08457 678999 (local rate charge from within the UK) or e-mail [email protected]
Sales enquiries: Ring 01344 656591 or e-mail [email protected]
Sales support literature: Visit the Downloads section of honeywelluk.com, ring 0800 521121 (UK only) or e-mail [email protected]
EN1H-2472 UK01 R0209
Figure 1 Temperature variation with a TPI room thermostat
Temperature
TimeSet pointProportional band
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i fit loads of these to both gas and oil boiler installs.
to solve this on/off cycling on the older boilers where they don't have a run on time of 2 to 20 mins you will need to alter the min on time to 4mins and cycle rate to 3
This is the setting that we use for oil boilers where they also do not have a run on capability.
If this still doesn't solve the problem then you have other problems with your system or the location of your stat.
Make sure the stat is about 1.4m high and not on outside wall and not located near to a heat source.
to solve this on/off cycling on the older boilers where they don't have a run on time of 2 to 20 mins you will need to alter the min on time to 4mins and cycle rate to 3
This is the setting that we use for oil boilers where they also do not have a run on capability.
If this still doesn't solve the problem then you have other problems with your system or the location of your stat.
Make sure the stat is about 1.4m high and not on outside wall and not located near to a heat source.
I spent two winters trying various settings to get rid of the cycling, even using a data logger monitoring room temperature and rad inlet pipe temperature to see what was going on.
The settings didn't give me a satisfactory solution but I ended up fitting a Broyce M1EDK variable timer relay between the HC60 relay and the boiler.
This is set to intercept any calls for heat that are less than three minutes long which effectively cuts out all but the longest of cycles.
It's been working great for over 18 months now.
See this thread http://www.automatedhome.co.uk/vbulletin/showthread.php?t=2277&highlight=broyce
The settings didn't give me a satisfactory solution but I ended up fitting a Broyce M1EDK variable timer relay between the HC60 relay and the boiler.
This is set to intercept any calls for heat that are less than three minutes long which effectively cuts out all but the longest of cycles.
It's been working great for over 18 months now.
See this thread http://www.automatedhome.co.uk/vbulletin/showthread.php?t=2277&highlight=broyce
NGBod, I take it you don't have a CM9x7? (Given that the minimum on time can be set as snb described for exactly this purpose)
You'd probably be better off with a different control system that avoids the root cause of your perceived problem(s) rather than fudging a workaround to the symptoms.
Mathew
You'd probably be better off with a different control system that avoids the root cause of your perceived problem(s) rather than fudging a workaround to the symptoms.
Mathew
Yes I have the CM927 controlling in the nursery and several CM67ng's controlling the other zones on a 8 zone CM zone system.
The minimum cycle rate is 3/ hr which the CM927 will always use when close to the set-point (+ or-). Setting the minimum on time to 5 minutes was not the answer in my case as the temperature would then overshoot too much.
The Broyce fudge works and works well.
The CM927 is the best thermostat around IMHO but the fudge makes it even better for some users.
Dave
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