EvoHome zoning with S-Plan

[Ben565]

Hi, My central heating is an S-Plan system with 2 port valves. And I'm looking at fitting the Evohome setup with hot water kit and zoning using HR92 on the radiators.

The installation guide for S-Plan system & 2 port valves, uses 1 BDR91 for the hot water port valve and the other for the heating port valve. However it doesn't show the HR92 and uses the controller as sensor for the whole home. That's not what I want.

The diagram showing HR92 and zoning (which I do want) is a different setup using only 1 port valve with a BDR91 connected (hot water) and the other BDR91 connected directly to the boiler.


Can I keep the existing S-Plan setup, with 2 port valves. Use 1 BDR91 on the hot water port valve, and the other BDR91 on the heating port valve. With HR92 on the radiators and have zoning. Will that work ?? Surely it just means the Heating BDR91 controls a port valve, which then controls the boiler. Rather than the BDR91 controlling the boiler directly.

 

[lloyda]

Can I keep the existing S-Plan setup, with 2 port valves. Use 1 BDR91 on the hot water port valve, and the other BDR91 on the heating port valve. With HR92 on the radiators and have zoning. Will that work ?? Surely it just means the Heating BDR91 controls a port valve, which then controls the boiler. Rather than the BDR91 controlling the boiler directly.

Yes you can. Though there are those that say you should convert to x-plan, which has a NO heating valve that closes when the hot water one opens.

 

[Ben565]

Since posting I've found that Evohome regards one BDR91 as Hot Water zone valve, and the other as boiler control. So an S-Plan system with a BDR91 on each zone valve. The heating valve would be opened every time hot water was called for. Might as well connect the heating BDR91 directly to the boiler, and manual fix the heating zone valve open. Which in fact is what the installation manual shows on page 45

It does make sense to me though that there should be a heating zone valve. When hot water is called for the boiler would be running full power to quickly heat the hot water tank. Why would I want that circulating the Heating loop. Heating loop should be off if only hot water is required.

Maybe I just can't get my head around the fact that the radiators now control the heating flow, not the zone valve.

 

[lloyda]

Since posting I've found that Evohome regards one BDR91 as Hot Water zone valve, and the other as boiler control. So an S-Plan system with a BDR91 on each zone valve. The heating valve would be opened every time hot water was called for. Might as well connect the heating BDR91 directly to the boiler, and manual fix the heating zone valve open. Which in fact is what the installation manual shows on page 45

It does make sense to me though that there should be a heating zone valve. When hot water is called for the boiler would be running full power to quickly heat the hot water tank. Why would I want that circulating the Heating loop. Heating loop should be off if only hot water is required.

Maybe I just can't get my head around the fact that the radiators now control the heating flow, not the zone valve.

If you have 1xBDR91 controlling the hw valve, and 1xBDR91 controlling the heating valve, you can keep your S-plan. In this situation you do not bind the 2nd BDR91 as boiler controller, but as a heating valve. You use the existing wiring through the valve microswitches to turn on/off the boiler/pump. Take a look a x-plan for what is regarded as the ideal configuration.

Good source of info on this can be found here

 

[Ben565]

I found this, direct from Honeywell, which seem to say that Hot water priority will only work if there's two zone valves. Yet there own installation manual says to use just one with stored hot water and zoning.

What you are suggesting, binding BDR1 as a heating valve not boiler control, makes sense and ties in with what honeywell are saying below.

The info from Honeywell regards install is so confusing.

The Hot Water Priority will only work if two requirements are met :

1. Hot Water priority is ENABLED
2. You are in a schedule period
3. Application software version is : 02.00.19.33

E.g. If both hot water and central heating are supposed to come ON at 8:00 AM only the Hot Water valve will open until the hot water temperature is satisfied.
If you are not in a schedule period and override both Hot Water and Central Heating both will work at the same time.

NOTE !
Hot Water Priority is only available if there are valves bound to the Hot Water and Central Heating circuits.

 

[Ben565]

Unless that's just for when you're using the controller as single thermostat not the multi zoned setup

 

[lloyda]

And if my ancient memory serves me correctly, priority hot water only works if you have opentherm.

 

[Ben565]

That would also make sense, as I understand for hot water you'd want to run the boiler at high power / higher flow temp. Higher than you'd normally have for the heating loop in order to quickly heat the water tank. Which is what OpenTherm allows you to do.

Makes sense you'd want shut the heating loop off with a zone valve while it was doing that.

The basic S-Plan system I have now uses the same flow temp for hot water as for heating. So that's why it takes an hour or so to heat enough water for a bath. With OpenTherm and HW priority I can heat my HW up much faster, then drop back to a much lower flow temp for the heating. Of course means my heating shuts off while the HW is heating up.


Ok so
-I keep my S-Plan setup
- Bind one BDR91 to HW (connected to HW zone valve)
- Bind the other BDR91 to heating valve (connected to heating zone valve)
- Bind the HR92 radiator valves

If I want to I can then connect an OpenTherm bridge to the boiler and use HW Priority, but I don't have to.


None of this is in the installation manual, the only setup it shows you with 2 port valves is for use with a single thermostat. Presumably the guided configuration will be no good for me ?

 

[Ben565]

Reading from another forum.

"The 1 promising match (p 22 wireless relay box to control a zone valve) only allows a single evohome zone to control the relay."

So wouldn't work with multiple HR92 radiator thermostats.


Power up and bind a Wireless Relay Box (BDR91) to control a Zone Valve
Make sure the Wireless Relay Box (BDR91) is wired to the Zone Valve and powered up. If you want to control the zone temperature with the evohome Controller (the evohome Controller needs to be located in that zone) press YES, otherwise press NO and bind a sensor – either Digital Room Thermostat (DTS92), Single Zone Thermostat (Y87RF), or Room Temperature Sensor (HCW82/HCF82).

All single zone thermostats.


So to use hot water priority mode you need opentherm and two zone valves, one for HW and one for heating, but that won't work with multizone because you can only tie one thermostat to the heating zone valve controller. So you can hot water priority, or multizone, but not both.. I'm confused

 

[lloyda]

The thermostat(s) are bound to the controller, and the controller is bound to the relay. The controller combines the demands from each zone. So you can have upto the maximum 12 zones that Evohome can manage.

 

[Mister Banks]

This seems very convoluted. Have you seen the Drayton Wiser system? Allows up to 16 zones using iTRV’s and if required multiple iTRV’s controlled by a room thermostat. Much simpler to setup than Evohome.

 

[Ben565]

Yeah i realised last night while I was thinking about it in bed. The thermostats (HR92) are bound to the controller not the BDR91

I think I'm getting there and the penny is dropping (slowly)

OpenTherm wireless bridge replaces BDR91 as boiler control. So... in my S Plan system

- R8810A OpenTherm bridge connected to boiler and bound to the Controller as boiler control (orange wire from zone valves not connected)
- BDR91 connected to HW zone valve and bound to the controller as HW valve
- BDR91 connected to the heating zone valve and bound to the controller as Heating Valve
- HR92 (s) bound to the controller.

That satisfies the requirement for two zone valves for Hot Water Priority (which only really works properly with opentherm apparently). And it also satisfies the requirements for multizone because R8810A has direct control of the boiler.


In Hot Water priority mode it shuts off the heating zone valve, opens the HW zone valve, and ramps the boiler up to high power to heat the hot water. Thats why you need the Heating zone valve to prevent the high power/high flow temp overheating the radiators.

In normal heating mode, without any hot water demand. HR92 calls for heat, controller tells heating BDR91 to open the zone valve, and also fires the boiler up via OpenTherm.


Have I got it ?

 

[Ben565]

This seems very convoluted. Have you seen the Drayton Wiser system? Allows up to 16 zones using iTRV’s and if required multiple iTRV’s controlled by a room thermostat. Much simpler to setup than Evohome.

Agreed, but I've already invested in Evohome now.

 

[Mister Banks]

Agreed, but I've already invested in Evohome now.

I incorrectly thought from your first post you were in investigation mode before committing to a purchase.

 

[Ben565]

I incorrectly thought from your first post you were in investigation mode before committing to a purchase.

Sorry, should have said.

Evohome does everything I need it too on paper, so I bought the setup, but install and configuration is proving to be a right PITA