Minimise cycling

[paulh]

We have an evohome system with 11 zones (3 ufh and the rest rads with HR92s). 5 of the zones (all HR92s) we only heat when we are using the rooms which is very occasionally so they are set at a constant 14 degrees.
As the weather gets colder, the zones demand heat on and off throughout the day as they 'bounce' around the target temp but, of course, they rarely demand heat at the same time so the boiler fires up 3 times an hour (the cycle rate I set on the evohome).
I wanted to minimise this so I used Home Assistant via Ramses to lower the target temp of the first zone that demands heat (park it) until there are other zones demanding heat and then raised then the target temp so at least I have 2 zones working together. It does work and is tunable so I could change it so only works when 3 zones need heat.
Now I'm wondering if a better solution would be to raise the target temp in all the zones for a short period (20 mins) twice a day so the boiler works harder but at set times - maybe in line with the other zones that are being used. I know it goes against the thinking of only heating a room when required but that is usually for rooms that are being used.
Thoughts?

[bruce_miranda]

This sounds like the ideal use case for the Load Scaling option that Resideo implemented in the last firmware.

[haggis888]

My Evohome controller has the latest application software and WiFi software versions for the UK but I see no Load Scaling options on the System Parameters page. Is this because I have a hot water storage cylinder (a common feature in the UK)?

[bruce_miranda]

A lot of us are in the UK too and Load Scaling is definitely available, unless you have OT. Load Scaling isnt available when using OT, because Resideo, in their wisdom, felt it wasn't needed for OT systems. Maybe your system isnt configured with Appliance Control?

[paulh]

I did try turning the Load Scaling on but it meant that other zones which are in daily use were adversely affected i.e. took ages to heat up as the demand is throttled back across all zones and totally messed up the UFH. It's a shame you can't apply Load Scaling at the zone level.

[haggis888]

I'm not familiar with the term OT. A Google search suggests that it might refer to the OpenTherm Communication Protocol but I've no idea if that is used by my EvoHome controller. Appliance Control is also an unfamiliar reference. Another Google search suggests you might mean the R9H911RF3000 Appliance control module. I don't have one of these in my system.

My open vented system has two BDR91A Wireless Relay Boxes, one for hot water and another for the central heating, with HR92's on every radiator. Would I need to make changes if I wanted to get access to Load Scaling?

[bruce_miranda]

If you just have 2 x BDR91 each controlling a Zone Valve, you dont have a Appliance Controller configured and that is why Load Scaling isnt visible.

If you have HR92 on every radiator, then you dont need the CH zone valve and you can lock that open and repurpose the CH BDR91 as your Appliance Control. Use that to fire the bouler instead of the zone valves doing it via their Orange wires. You'll have more options to Control the boiler that way.

Yes, Load Scaling isnt perfect. I have an OT OpenTherm system, I don’t miss it.

[haggis888]

If you have HR92 on every radiator, then you dont need the CH zone valve and you can lock that open and repurpose the CH BDR91 as your Appliance Control. Use that to fire the boiler instead of the zone valves doing it via their Orange wires. You'll have more options to Control the boiler that way.

That's interesting. When I installed my Evohome system in 2022 with two BDR91A Wireless Relays I was under the impression that I was following the official guidance from Honeywell (I also received guidance via this forum). Was I misinformed at that time or is locking the zone valve open a more recent alternative approach? How do you lock that valve open?

Load Scaling isnt perfect. I have an OT OpenTherm system, I don’t miss it.

What would I need to do to convert my system to use OpenTherm?

[Somebody]

I'm not familiar with the term OT. A Google search suggests that it might refer to the OpenTherm Communication Protocol but I've no idea if that is used by my EvoHome controller. Appliance Control is also an unfamiliar reference. Another Google search suggests you might mean the R9H911RF3000 Appliance control module. I don't have one of these in my system.

My open vented system has two BDR91A Wireless Relay Boxes, one for hot water and another for the central heating, with HR92's on every radiator. Would I need to make changes if I wanted to get access to Load Scaling?

Appliance control means direct boiler control. I asked Resideo support why I didn't have Load Scaling in my controller and was informed that it only applied to systems with direct boiler control and also would not operate in stored hot water demands. I took that to mean a combination boiler which I don't have.

[bruce_miranda]

Evohome instructions haven't changed in over 20 years. But things aren't as clear as it could be.

If you have HR92s on every radiator then a CH zone valve is unnecessary. You only need a HW zone valve, and that too if you have a HW cylinder.
In this configuration you need something to fire the boiler....that is where the Appliance control comes in. So the zone valves no longer fires the boiler via their Orange wires but its the Appliance Control BDR91 relay.

[haggis888]

If you just have 2 x BDR91 each controlling a Zone Valve, you dont have a Appliance Controller configured and that is why Load Scaling isnt visible.

If you have HR92 on every radiator, then you dont need the CH zone valve and you can lock that open and repurpose the CH BDR91 as your Appliance Control. Use that to fire the boiler instead of the zone valves doing it via their Orange wires. You'll have more options to Control the boiler that way.

Family celebrations over Christmas and New Year have prevented me from pursuing this discussion until today.

I have three questions:

1. How would I "lock open" my 3-position motorised valve?
2. What wiring changes would be needed in my junction box (ref attached diagram)?
3. What actions are required to "repurpose the CH BDR91" as my Appliance Controller?

Central heating & hot water junction box, etc.jpg