Room Thermostats

[Dan Robinson]

I'm too good for this place sometimes. ?...

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.

 

[Alfie25]

I can find this post, which sums up my sentiments exactly!

//www.diynot.com/forums/plumbi...on-on-honeywell-cm927-rf-stat.379697/#2906515

I hope you didn't mean this one as it links to a 117 page document.

//www.diynot.com/forums/plumbing/tpi-thermostats.387835/#2980014

 

[Dan Robinson]

First link just highlights a misunderstanding of how it works and what it aims to achieve, but I admit (and have said here in various places) it is not a perfect system.

However I have fitted thousands of cm and dt based thermostats and the vast majority either love or have never noticed tpi in operation.


Optimisation on the other hand has had a much more varied response.

 

[Alfie25]

Ok well enlighten me on what there is to misunderstand. I can believe it doesn't 'waste gas' and that any impact on boiler internals is only minimal, but I still don't want the boiler firing on and off like a man posessed every few minutes.

I've had a look at the installer instructions for the DT90e and you can set a min off time of 5 mins, and a min of 3 cycles per hour, but there is no other way to adjust the proportional bandwidth. We agree it's not a perfect systemm perhaps for different reasons.

As said before, I'm not a penny pincher and don't care about small savings or minor inefficiencies in energy consumption. I'm happy to have a TPI free system, and if it overshoots a little, so be it. Now if only I could find some decent controls that will allow that...

 

[Dan Robinson]

Then a simple timer and t6360 is fine. Ultimately you have to be Happy with how it work, otherwise you'll be forever picking hopes in the setup.

Have to admit that I rarely bother to play with the default setup apart from turning on optimisation, window open functions, pump exercise and raise the minimum allowable temperature.

 

[Alfie25]

Right, then my next step is to see if the combi boiler I'll be getting fitted requires a mains voltage stat or a volt free one. I'm looking at either a baxi duotec mk1 or a viessman (don't yet know the model number).

Oh, and how do anticipator heaters in the old mechanical (and it seems, Danfoss electronic) thermostats compare to TPI? Reading this link, they also turn the heating on and off, in order to maintain the set temp - see page 3:

http://heating.danfoss.co.uk/PCMPDF/Introducing Room Thermostats.pdf

 

[Dan Robinson]

Oh christ - a whoile new chapter


Right....



Don't bother looking at Viessmann unless you are prepared to pay for the 200 series. I was there for 3 days last week on a training course (albeit on their big stuff). Nice bit of kit but....


Intergas are much better if you are at the Baxi end of the market... followed by the Atag A325ec (if appearances aren't important) and then the Vaillant 8xx series.


All of which mean the last fook knows how many posts are irrelevant as you are dealing with boilers that need much cleverer controls to get the best out of them.


In the case of the Intergas (I've been fitting them since 2004) a weather sensor and CM907 are a perfect match..... if not then the iSense controller is very popular here amongst those in the know.

For Atag.... well... pretty much the same..... their in house controls are good but, like Viessmann, necessarily complicated.

For these two also consider the Honeywell Evo system.... a little pricey but very effective. Even with weather compensation when correctly configured.

For the Vaillant use their own in house controls and get an Advanced installer to supply and fit and get the full 7 year warranty on the boiler and controls. Again good pieces of kit.

All 4 boilers pish over the Baxi.

 

[Alfie25]

Think we need a new thread!

I'm waiting to hear back on the exact viessman model but I know it's a 30kW one. Are you saying the lesser models are no good? Please take no offence, but everyone i ask tells me different. Generally I find an RGI is an accredited installer for a particular brand, and so predominantly sells that brand.

I presume any new combi will still work with the old stye controls? You say 'getting the best out of them' but I'm not concerned about going to the n'th degree of efficiency. Out of interest, what do you prefer when it comes to Baxi vs Viessman (for the sake of argument, probably not the 200 series if thats the top end model)

 

[Dan Robinson]

Oh, and how do anticipator heaters in the old mechanical (and it seems, Danfoss electronic) thermostats compare to TPI?

Having just helped with a controls trial similar to the 117 document you mentioned earlier.... I can concur the end results are not as clear cut as people like me would like, but thems the breaks, and as with my trial there are other agendas/missions and a startling level of "inexperience" amongst those involved... not least people like me.

The actual gains between TPi and a correctly installed mechanical stat are not as much as we would like, but the vast majority of the mechanical T6360 style stats are not installed anywhere near correctly.

Especially in rentals.

I have spoken to Honeywell Tech on many occasion and the number of calls they get from PROFESSIONALS struggling with the concept of anticipators is bewildering.

 

[Alfie25]

The actual gains between TPi and a correctly installed mechanical stat are not as much as we would like, but the vast majority of the mechanical T6360 style stats are not installed anywhere near correctly.

Especially in rentals.

I have spoken to Honeywell Tech on many occasion and the number of calls they get from PROFESSIONALS struggling with the concept of anticipators is bewildering.

How can they not be installed correctly? Once it's wired in, there's nothing to adjust is there? As for anticipators, no wonder I get confused if so called professionals do. Am I right in thinking they still cycle the boiler on and off, perhaps less so than a digital with TPi? The Danfoss link above does say that they shut on and off quite a bit.

 

[Dan Robinson]

Anticipators need a neutral to work.... no neutral= not correctly installed.

They will cycle on and off quicker than a prozzy's libido.



The location of the stat is even more important. try banging the fooker in above a Plasma TV and see how long your heating runs for.


Trust me... I/We have seen it all.

 

[Alfie25]

Haha nice turns of phrase there! Well I definitely have 3 wires as thats how my old Sunvic is wired so I should be ok there, as long as the RGI can suss out installing whatever replacement I get. Are you saying if they aren't wired with an anticipator then they'll cycle on and off like crazy? I'd have thought wiring them without the anticipator would reduce cycling, but I'm no electrician.

Here's one for you. Danfoss themselves say that electronic thermostats don't need an anticipator as they react very quickly to temperature change. They spell this out in the document I linked to above. So in that case, why does this range of electronic thermostats (not mechanical) say they have an anticipator fitted:

http://heating.danfoss.co.uk/xxTypex/296337_MNU17415392_SIT313.html

 

[Dan Robinson]

Anticipators are just little resistors that heat up and even out the temperature fluctuations. The very reason being to eliminate rapid cycling.

Electronic stats don't need anticipators as the on board components compensate accordingly..... or the stat is just pants.

The range in the link directly above all have neutrals in order to provide a non switching circuit to feed the anticipator. Without which, the thermostat will operate poorly.

Just like a car where the driver doesn't really know when to change gear - but still gets to HER destination.

 

[Dan Robinson]

Think we need a new thread!

I'm waiting to hear back on the exact viessman model but I know it's a 30kW one. Are you saying the lesser models are no good? Please take no offence, but everyone i ask tells me different. Generally I find an RGI is an accredited installer for a particular brand, and so predominantly sells that brand.

I presume any new combi will still work with the old stye controls? You say 'getting the best out of them' but I'm not concerned about going to the n'th degree of efficiency. Out of interest, what do you prefer when it comes to Baxi vs Viessman (for the sake of argument, probably not the 200 series if thats the top end model)

I am accredited with the Viessmann 100 series, Intergas, Atag, Vaillant and Worcester (although they booted me off their listings as I didn't fit enough).

I firmly believe in the right tool for the job. Any boiler will work with your old style controls. But for most modern boilers there are better admittedly more expensive controls. You HAVE to relinquish some of the control to the boiler and controller though. The manufacturers spend millions getting things "just so". The type of controller you are talking about was developed 40 years or more ago and whilst very good at what it does, doesn't get the best out of the boiler it is connected to. ESPECIALLY a combi.

The 100 series Viessmann is an OK product, but the ones I have listed (including their own 200 series) are much more worthy of the expenditure.

Yes every installer has his preference. However, if the best reasoning they can give you is paraphrased from the sales brochure, or they only offer one brand (with any knowledge) then you are not getting a considered approach which you deserve as the bill payer (assuming you appreciate paying for a tradesman's expertise and knowledge).

 

[Alfie25]

Crikey Dan, do you never go to bed?!

I sure do appreciate paying for a tradesmans's knowledge. Trouble is all the good ones are super busy (as you'd expect) and their time is at a premium, hence why I try and get my head round the simpler queries (you'd think!) via sites like this.