New Central Heating Installation - Timer Questions

[Shanz]

Hi All,

I'm a newbie to this forum so please bare with me.

I have just had a central heating system installed which consists of Baxi Duo-Tec 33, 6 radiators and pipes installed to a new extension ready to supply water-underfloor heating at a later date. My question is more related to the boiler and timer/programmer as follows:

1) The boiler itself didn't come with a timer installed (i was expecting a manual
clock) but it did come with a Honeywell CM927 - 7 Day Wireless Programmable Room
Thermostat and a BDR91 Relay Box which is yet to be installed. My quesion here is
- will this perform the same role as a boiler timer i.e. automatically switch the boiler on/off at programmed times throughout the day/night.

2) When I eventually install the water-underfloor heating can the CM927 and BDR91
control both the main house radiators AND the underfloor heating system in the extension.

3) I was thinking of using a underfloor heating system from the underfloorheatingstore.com to cover an area of 25m2 controlled by a Heatmiser PRT
Digital Thermostat which is a programmable room stat and programmer in one. I've attached a link to the install pdf to explain better. Can this system be controlled by the CM927 and BDR91?

http://www.theunderfloorheatingstor...heat/resources/Other/tufhs-single-circuit.pdf

Sorry for a lengthy info request but I am tearing my hair out tryin to work this out.

Cheers,

Shanz

 

[doitmyself]

I'm a newbie to this forum so please bare with me.

I would want a super-injunction first!

1) The boiler ... did come with a Honeywell CM927 - 7 Day Wireless Programmable Room
Thermostat and a BDR91 Relay Box which is yet to be installed. My quesion here is
- will this perform the same role as a boiler timer i.e. automatically switch the boiler on/off at programmed times throughout the day/night.

Yes

2) When I eventually install the water-underfloor heating can the CM927 and BDR91 control both the main house radiators AND the underfloor heating system in the extension.

NOT a good idea! The underfloor should have its own controller. A second CM927/BDR91 to control the U/F zone valve and an additional BDR91 to control the boiler.

I suggest you get in touch with Honeywell Tech Dept and ask their advice.

 

[Shanz]

Thanks for the reply doitmyself - I wasn't asking you to flash...honest. lol.

So you say I need A second CM927/BDR91 to control the U/F zone valve and an additional BDR91 to control the boiler.

Do you mean that I need a quantity of the following:
1xCM927 (For Radiators)
1xBDR91 (For Radiators)
1xCM927 (For Underfloor Heating)
1xBDR91 (For Underfloor Heating)

Cheers

 

[diamondgas]

You can get away with the Heatmiser PRT and 1xCM927, 1xBDR91

The wiring needs a bit of jiggling around though from what is shown in the pdf ......

 

[doitmyself]

So you say I need A second CM927/BDR91 to control the U/F zone valve and an additional BDR91 to control the boiler.

Yes.

Do you mean that I need a quantity of the following:
1xCM927 (For Radiators)
1xBDR91 (For Radiators)
1xCM927 (For Underfloor Heating)
1xBDR91 (For Underfloor Heating)

Yes, but in addition you need a third BDR91 to control the boiler.

One CM927+BDR91 pair controls the zone valve for the radiators; the second pair controls the zone valve for the UFH. The auxiliary switch on the zone valve is not used; all the CM927 does is control when the zone valve opens.

One of the CM927s has to be configured as a "Synchroniser". When everything has been set up the Synchroniser will control all three BDR91s while the second CM927 controls only the BDR91 connected to the second zone and the one connected to the boiler. Doing it this way means you do not have multiple BDR91s trying to control the boiler.

Unfortunately Honeywell have decided not to make the info available online as to how you use the CM927 for a multizone installation. Which is why I suggest you or your installer contact them.

 

[diamondgas]

Yes, but in addition you need a third BDR91 to control the boiler.

doitmyself .... check out this picture and let me know if I've missed something out OOOPS! this picture is a bit wee

I think this'll do the job with the two controls metioned Shanz ... The Duotec has a 240v suply for the external switching.

 

[diamondgas]

Try again

 

[doitmyself]

doitmyself .... check out this picture and let me know if I've missed something out

It will "work" but not correctly.

You will have two thermostats controlling one boiler, via the auxiliary switches in the rad and UFH zone valves. So one valve may be trying to turn the boiler on while the other is trying to turn it off; which isn't too bad. But the CM927 has TPI and the Heatmiser does not. This means that when both circuits are operating the heatmiser will keep the boiler on continually even though the CM927 is trying to cycle the boiler to maintain close control of the room temperatures.

 

[diamondgas]

Cheers doitmyself ... I thought by switching the boiler heat demand via the zone valves, however, would have surficed the indipendant temp/time controls request for heat? They indipendantly control the zone valves only and then switch on the boiler when there's a demand for heat yeh? I have no experience of UFH apart from basic...

 

[doitmyself]

I have no experience of UFH apart from basic

It's nothing to do with underfloor heating. You would have the same problem if you used a CM927 to control one zone and a Heatmiser PRT to control the other zone of a two zone radiator system.

When both zones are being heated the PRT will keep the boiler running continuously until the set temperature is reached and then turn the boiler off until the temperature has dropped, say 2 degrees, at which point it turns the boiler on. The problem with this is that the room temperature will rise above the set temperature because the rads are pumping out max heat right up to the time the boiler is switched off and will continue to give off heat even when the boiler is off.

The CM927 senses when the temperature is about 1.5 degrees from the set point and then starts to cycle the boiler on and off at varying rates as the set temperature is reached. The effect is that there is virtually no overshoot.

Put these two together and you have one controller wanting to keep the boiler going all the time and a second boiler trying to cycle the boiler. Unfortunately the first one wins.

 

[Shanz]

Re: New Central Heating Installation - Timer Questions

Thanks for your advice guys - really appreciate it. Wow - I wasn't expecting this to be so complicated and it seems that it is becoming very expensive (I have been seriously under quoted by my installer and am a bit worried).
The thing is when you delve in to the many types of underfloor heating systems out there none of the suppliers tell you that you need to buy additional controllers - it is quite frustrating. I'm starting to wish that I had a simple radiator installed in my extension.

1) Would it make more sense to change the CM927 + BDR91 that has been supplied with a different controller/thermostat system that will handle multiple zones? Do you know of any inexpensive ones out there? What is my cheapest option?

2) This is most probably a really silly question but If I were to install a mechanical timer into the boiler and use this for controlling on/off operation to the UFH in conjunction with the Heatmiser. And use the CM927 + BDR91 for controlling the radiators only (obviously also influenced by the mechanical timer)?

Thanks again,

Shanz
​

 

[diamondgas]

Hi shanz,
Regards changing the controller, you could get one without TPI or use the CM927, it should still cycle the boiler circulation via the diverter valve I believe...

Regards the integral timer, well that'd be a step backward in my opinion! What does your plumber/electrician say?

 

[Shanz]

Hi shanz,
Regards changing the controller, you could get one without TPI or use the CM927, it should still cycle the boiler circulation via the diverter valve I believe...

1) Hi diamondgas, im not sure I understand what you mean by the above. If I were to use to CM927 as a boiler circulation I would not be able to control 2 zones independantly - is that correct?

2) I was thinking of using the Honeywell HC60NG(R6660D) as a replacement to the BDR91 as I "think" this can receive multiple RF signals e.g. from 2 x CM927s to control the 2 zones. Is this correct - See attached link to the tech note for this device:

http://www.cm-zone.com/resource/en/documents/hc60ng_td.pdf

3) If I did use the the HC60NG(R6660D) instead can I leave out the 2 x 2 port valves (1 for each zone)? Do you know if this is correct?

As far as my plumber/electrician - he is not being very helpful in this and i'm struggling to get him to complete the work which is why i'm taking this on myself. I'm very frustrated.

Again - Thanks for help

 

[diamondgas]

Now then Shanz,

There are many ways to achieve what you are after but you will need to zone them if you want the desired control and adhere to current building regs. Either of the set-ups will work. You really need to get your plumber and electrician on board to help you though they're the ones installing this for you at the end of the day, it's there co-operation you require! Talk it through with them. If you need a design drawn up try and get a honywell rep on board. There also plenty of reputable engineers here crying out for work. You may strike lucky and find someone willing to alleviate your frustrations.

Remember that this is your own heating system your talking about here. Do you feel confident enough to complete the work? It sounds to me like you're struggling.

If you let folk here know where in the country you are general terms, I'm sure they'd pm you if they can help!

 

[doitmyself]

I was thinking of using the Honeywell HC60NG(R6660D) as a replacement to the BDR91 as I "think" this can receive multiple RF signals e.g. from 2 x CM927s to control the 2 zones. Is this correct - See attached link to the tech note for this device:

http://www.cm-zone.com/resource/en/documents/hc60ng_td.pdf

The BDR91 is just a newer version of the HC60NG. You would still need two CM927 controllers and three Relay boxes (BDR91 or HC60NG).

To clarify:

The HC60NG/BDR91 zone controllers operate zone valves or pumps.

The CM927 room units located in every zone provide heat demand signal for each zone controller.

The HC60NG/BDR91 boiler controller operates the boiler. It is collecting the demand signals from all room units to make sure that the boiler delivers enough heat to satisfy every zone.

To set up a multi zone system you will need:

- one CM927 system pack per zone in the installation.

(The system pack contains one room unit (transmitter) and one zone controller (receiver))

- one HC60NG/BDR91 boiler controller

If I did use the the HC60NG(R6660D) instead can I leave out the 2 x 2 port valves (1 for each zone)?

If there is no valve, how do you prevent the water circulating round the complete system all the time?

A cheaper way of having independent control would be to use simple controls which do not have TPI

 

[Shanz]

Thanks diamondgas & doitmyself, I've now got a clear picture in my head of what I need and what I have to spend.

I spoke to my installer and he is going to put in the 2 x 2 port valves and i'm going to do the electrical/control install. I may need some advice on the wiring but I think if I base it around diamondgas' diagram in the previous replies I should be ok.

Thanks again for your help, time and patience.

Shanz