The Efficient Home Forum

Hi All,

I used Evohome several times before to great success and looking to upgrade my new property. It's a bit different as it has quite a "industrial" heating setup but I was hoping it could be used pretty easily.

The property is split over four flours and each has it's own zone valve and conventional thermostat located in the landing.

The easy answer would be to manually lock open all the zone valves and then use a BDR relay for the boiler linked to an evohome controller and fit HR92's everywhere for zoning.
I'd prefer not to do this as the property is large and pumping all zones for a single HR92 requesting heat is a massive overkill. Also the boiler room is a significant distance away from the property and I suspect the signal would be blocked - so any rewiring in the boiler room is tricky at best.

The next option would be to replace the existing thermostats with 4 x BDR relays and setup up 4 zones with zone's BDR linked to its zone valve. This would "ok" (but not ideal) as it means I can't further subdivide the floors into zones that can demand heat.

One option would be to implement the 4 BDR's and override the rooms that I don't want to use (spare room for example). Then if needed bring them back into sync when occupied. It's ok and works for a couple of floors but the ground floor has rooms with very different heat profiles so it's not ideal.

Now I know I can bind a single BDR relay to multiple controllers so yes it could be solved with additional evohome controllers but this feels like overkill and frustrating if this can't be achieved with a single controller and multiple zones.
If it were possible (but I suspect it is not) to have a single BDR relay bound as an actuator to multiple evohome zones then it could be achieved.

Am I missing something obvious? I'm struggling to find a method to achieve this and I don't see why it should be so difficult!

Its not really difficult... Honeywell designed the evohome system to work as a figure 4 system (as per page 43 of the evohome installation guide).

Why do you think water will 'pump everywhere' if you fit HR92's on to all radiators and latch the valves open? This is a misconception. Water will only pump to the radiator which has the open HR92... A normal heating system is piped in parallel after all.

I think you are trying to overcomplicate what is a simple system. Stick with figure 4 for the best results!

It's the multiple zone valves thats causing the problem.

The house is reasonably large - over 6,000 sq/ft spread over 4 floors (each with their own physical zone valve and thermostat)
The boiler and 4 CH zone valves are located in a plant building approx 100m from the property.
The pipework from the boiler room to the house is all 28mm and the four flow and returns are separated in the plant room.

So if a single radiator in the top floor requests the heat the with open zone valves will mean the (fairly substantial) flow and return pipes for the entire property will be pumped but any connected radiators would be off.

It also means the same when the DHW is activated as the two hot water tanks each have their own zone valve after the individual heating.

Warning: Terrible ASCII Art approaching!

Boiler -->-->-->-->-->-->-->-->-->-->--
| | | | | | |
| V V V V V V
| Z1 Z2 Z3 Z4 HW1 HW2
| | | | | | |
| V V V V V V
---<---<---<---<---<---<---<---<--<--

Z1, Z2, Z3, Z4, HW1 and HW2 are all zone valves.

I'm happy with the DHW setup so will leave that alone.

Now I know I could simply replace each zone's thermostat with a BDR relay mapped as a zone valve actuator which gives 4 zone control.
The boiler has built in cycling protection so I'm not worried there.
Just trying to get a little more control within the physical zone - if you could map the same physical BDR relay on the same Evohome Controller to multiple controller defined zones (as a zone valve actuator) then job done.

So for example in the evo home controller "Zone 1" could be the lounge (physical pipework Zone 1) and then "Zone 2" could be the kitchen and dining room (also physical pipework Zone 1).
Thus if you could map the physical zone valve for that floor to a single BDR but configure both virtual zone 1 and zone 2 to use the same relay then it'll work perfectly. What I'm not sure of is that last step of mapping the relay to two virtual zones on the same evohome controller.

Thanks

I'm researching options for a new property I'm buying, which has two zone valves.

The problem with evohome is that it hasn't got enough 'levels' of control. It assumes a single physical zone, to which you can ad up to 12 virtual zones - in practice, these will probably correspond to rooms.

It really needs a new top level domain, which would correspond to the physical zone valves/pipework, and control them with BDRs. To each physical zone you could then add the virtual zones.

So you'd have physical zone 1 [eg upstairs] with, say, 8 room sub-zones. A BDR would be assigned to the physical zone, and control its motorised valve, and the HR92s in the rooms would call for heat, which would be passed to the relevant and linked BDR.

Similarly for zone 2 downstairs. And indeed for any further physical zones.

This would simplify the concept and both for installing and setting up the system. With many new homes having at least two zones, this should be something Honeywell's programmers should be working on.

Why do you need zone valves on the heating side though? If implemented as per Honeywell's design (HR91 or HR92's on all radiators) there is no need for 'zone valves'.

Zoning is the concept Honeywell bring with evohome... Partial zoning is not what evohome was designed to do.

The EVOHOME Shop wrote:Why do you need zone valves on the heating side though? If implemented as per Honeywell's design (HR91 or HR92's on all radiators) there is no need for 'zone valves'.

Zoning is the concept Honeywell bring with evohome... Partial zoning is not what evohome was designed to do.

You don't [as per your other reply to me - thanks] - but they come with new houses these days. It makes the terminology confusing, as most householders and heating engineers think of "zones" as being controlled by the zone valves, rather than virtual configurations that will generally actually represent rooms. Incorporating both into the control system would align the two. Either would work satisfactorily.

Just pondering the concepts, really, as I'm aware of the 'correct' Honeywell way to set it up, which i hope to install when the house is ready.