Help with new Smart heating system

[dave41]

Hi everyone

I've read so many forum posts here but I can't seem to find an answer to my current conundrum... thanks in advance for any help you can offer!

I'd like to install a Drayton Wiser 3 kit for the house.

Current set up is 2 central heating zones (upstairs/downstairs) and hot water, with a conventional boiler and unvented indirect cylinder.

We have a Horstmann H37XL programmer, 2 x Honeywell DT92E wireless thermostats (upstairs/downstairs) and 2 x BDR91 (upstairs/downstairs). I can see there are mechanical valves on each pipe circuit but I don't know exactly what is controlling them...

Initially I thought we just needed to replace the H37XL programmer with the Wiser HubR, but then I was unsure what we should do about the existing wireless thermostats. I'm guessing they communicate with the BDRs? And do the BDRs in turn communicate with the boiler and/or the mechanical valves?

If so, by just replacing the H37XL programmer, won't the existing thermostats still be in the loop?

Any advice appreciated here.

Many thanks!

 

[CBW]

Ok, so there's a couple of ways you can do this. You can replace the H37XL with the Wiser Kit 3, and it's the BDR's that are wired to the motorised valves which in turn bring the relevant/requested demand. So the switching wires would need to be joined at either the bdr or wiring center.

 

[dave41]

Hi Chris, thanks for your response. I can see this wiring diagram for the BDR91:

so when you say the switching wires need to be joined, do you mean to link terminals B and C together on both BDRs?

 

[CBW]

Hi Chris, thanks for your response. I can see this wiring diagram for the BDR91:
View attachment 315873
so when you say the switching wires need to be joined, do you mean to link terminals B and C together on both BDRs?

No, usually A and B, if yours is the same then you'd need to keep the permanent live there too, so could be more beneficial to do at the wiring center

 

[dave41]

Thanks Chris. Just to check understanding then - are these BDRs connected to the mechanical valves I can see, or to the boiler?

 

[CBW]

The motorised valves (mechanical as you're calling them)

 

[dave41]

Thanks Chris

So:
1) put the HubR in place of the H37XL programmer (with the rewiring of the baseplate required).
2) link the terminals in both BDRs (I think I'd feel more confident doing that then opening up the wiring centre) and then the motorised valves will be permanently open.

With this set up though, won't I lose the separate heating zones, as when the boiler is on it will send hot water to both heating circuits?

Sorry for the beginner questions, really appreciate your responses!

 

[CBW]

Thanks Chris

So:
1) put the HubR in place of the H37XL programmer (with the rewiring of the baseplate required).
2) link the terminals in both BDRs (I think I'd feel more confident doing that then opening up the wiring centre) and then the motorised valves will be permanently open.

No, to bold text above, you've misunderstood, basically linking the 2 wires complete the circuit, so they will work with your wiser control.

With this set up though, won't I lose the separate heating zones, as when the boiler is on it will send hot water to both heating circuits?

No, zones will be kept, as the hub will be the one requesting whether or not to come on, then the wiser thermostats will send signal to hub too

 

[ericmark]

We divide the home into zones, this allows us to select which parts of the home are heated and when, the TRV and the zone valve basic do the same thing, except a zone valve is on/off, and the TRV slowly opens and closes. With oil boilers it hardly matters, the oil boiler does not modulate much if it modulates at all, so motorised valves turning on/off or TRV heads adjusting flow makes very little difference.

Gas however is a different story, most gas boilers have a wide range of output say 8 kW to 28 kW this is so they can keep the return water cool enough to gain the latent heat from the flue gases. Gas boilers can work switching them on/off, and one will not notice much difference in comfort switching on/off or up/down, but you will notice the difference in gas use.

So you want the controls were possible to turn up/down not on/off, however of course this is not always possible, you may want heating off when you go to work and on again when you return no real option, this needs to be on/off, but in the main best control is with the TRV, but the TRV has a problem, it can control the flow, but can't turn boiler off when not required so the boiler would keep switching on/off at lowest output, but would cycle even when not required.

So we need a method to tell the boiler what is required, when to turn up/down and when to turn on/off. To an extent it can turn up/down using the return water temperature, but it can also use electric means, many boilers have some electrical control allowed with their e-bus, some times it has to be the boilers own make, and some can use a system called OpenTherm which is common to many makes of boiler.

So different thermostat/TRV head manufacturers use different methods. EPH use the motorised valves and EvoHome uses the TRV heads and a hub so you can see 6 areas on the hub, they have an add on for opentherm as does Wiser the wiser seems to have both zone valve and TRV control, how well it integrates both I don't know, but the Wiser TRV's are claimed to be about the best on the market, so reading the adverts Wiser seems a very good choice, although expensive, but as to wiring up it depends on if boiler is OpenTherm enabled or not, and if you really want to keep the zone valves.

I have zone valves as there is a flat below the house, which is rarely used in winter, so want to turn whole flat off. In the main house I use programmable TRV heads on most rooms, nine of them, the toilet and bathrooms are only ones without them.

So you have to consider do you want to keep the zone valves? Upstairs we have two bedrooms, a craft room and an office, so to split up/down would not suit me. I did it on the cheap with eQ-3 TRV heads which only have bluetooth for 5 rooms, and the idea was to use Energenie with Nest for 4 rooms down stairs, but Nest removed their support, so the TRV's are not linked to main thermostat, these are being replaced with Kasa (TPLink) TRV heads when they fail as they seem a better stand alone head.

I would love to fit Wiser, but I don't have the wiring I would need, it may be some thing for the future, but you likely need to plan not just for now, but how it can change in the future, design what you want in 10 years time and then decide a plan when each bit will be done, so you don't end up like me with an expensive bit of rubbish on the wall, in my case Nest Gen 3.

Also consider where the electrics are supplied from, all mine are from a single fused connection unit (FCU) in the flat which a month ago to connected to an UPS supply so if there is a power cut my heating still works, splitting the supply for example if my Nest was powered with USB from a socket, means setting up an UPS latter becomes a problem.

So what I am saying wiring to make it work is not the same as wiring to make it work efficiently. Since we don't know what boiler you have, or how much work you are prepared to do, can't give a simple answer. Big question are you connecting to e-bus with analogue control which is likely the best or simple digital i.e. on/off.

 

[dave41]

@chris - I think I understand now, thanks. I think what I'd misunderstood is that the motorised valve is not just opening/closing, but also sending the demand signal to the boiler (I'd assumed this was done by the programmer...)

What I now understand is: By linking the terminals in the BDR/wiring centre the old wireless thermostat is effectively bypassed, and the zone ON signal from the Wiser Hub will now pass through the BDR to the motorised valve, which will then open and also send a demand signal to the boiler. Is that right?

ericmark, thanks for your detailed explanation which helped me get on the right path (assuming what I wrote above is correct!)... we have a gas condensing boiler Greenstar 18i. Planning to fit the Wiser TRVs to most but not all radiators and would like to keep the zoned approach (which was the reason I went for Wiser over Tado - Wiser was more expensive but Tado receiver only had 2 channels.

 

[CBW]

Yes, sounds like you've got it now

 

[dave41]

Thanks a lot for your help!

 

[Mister Banks]

@chris - I think I understand now, thanks. I think what I'd misunderstood is that the motorised valve is not just opening/closing, but also sending the demand signal to the boiler (I'd assumed this was done by the programmer...)

What I now understand is: By linking the terminals in the BDR/wiring centre the old wireless thermostat is effectively bypassed, and the zone ON signal from the Wiser Hub will now pass through the BDR to the motorised valve, which will then open and also send a demand signal to the boiler. Is that right?

ericmark, thanks for your detailed explanation which helped me get on the right path (assuming what I wrote above is correct!)... we have a gas condensing boiler Greenstar 18i. Planning to fit the Wiser TRVs to most but not all radiators and would like to keep the zoned approach (which was the reason I went for Wiser over Tado - Wiser was more expensive but Tado receiver only had 2 channels.

If you are installing Wiser TRV's on nearly all your radiators then i don't think you will need to use the existing zoning of the heating. The TRV's will decide which radiators turn on. Wiser room thermostats will not be required unless you have a requirement to control a room or rooms with multiple TRV's.

 

[dave41]

I did wonder about that - but because the system had already been set up with two zones and because I probably won’t go to all smart TRVs immediately, I thought I’d leave both zones in place.

Are there any downsides to this?

 

[dave41]

Hi all, just wanted to say I got this all wired up with your help and seems to be working exactly as desired. Thanks again for all your help!