CH + DWH circuits controlled separately

[tierrapl]

Hi,

I have following equipment:
* ATC928G3026 (evotouch) central unit
* BDR91 relay for CH
* ATF500DHW set for DWH (incl. CS92 temperature sensor and BDR91 relay for DWH)

I noticed that the way how my boiler is controlled is different than the common patterns people are discussing on forums (S-Plan, Y-Plan, etc.).
And it caused a problem for me to understand if and how could I configure evohome to control both CH (heating) and DWH (hot water) circuits.

The boiler I am using is Termet Unico Elegance Turbo 24.
The exact model does not matter, the important one is how the boiler is being controlled.

There are basically two dedicated switches directly in the boiler. Switch one is enabling CH heating. Switch two is enabling DWH heating.

The boiler is controlling the priority (DWH over CH).
Boiler also controls 3-port valve which is redirecting hot water either to DWH or to CH circuits.
If both switches are ON (DWH+CH) then it will heat DWH and after that CH.

Please notice that setting ON a selected switch on the boiler is automatically turning the boiler ON (start heating the water) and redirecting the hot water to the appropriate circuit.
So I do not "request hot water" separately from controling DWH/CH valves. It's one switch doing both actions in my case.

Initially I connected one BDR91 relay to CH switch in the boiler.
And the CS92+BDR91 relay to DWH switch in the boiler.

Then I started playing with evotouch configuration software...
And then I learned that some of its assumptions do not really fit to my configuration.

Since I want to control both CH and DWH than I needed to configure both options "Boiler Control" (set to Wireless Relay Box) and "Stored hot water" (set to Enabled).

The effect was that:
1. CH request were OK - turning on my CH's BDR91 relay and enabling CH heating on my boiler
2. DWH request didn't work as expected - it was turning ON not only DWH's BDR91 but also forcing CH's BDR91 Boiler Control ON (requesting the heat water).

This is not what I need since the described behaviour for DWH requests enabled both switched on my boiler (CH and DWH).
And I need DWH only.

Is there a way to achieve the configuration where these two DWH and CH circuits are treated seaprately not influencing each other ?
I found some topics on different forums people having the similar observations and the general recommendation like "turn off Boiler Control completely in evohome configuration".
But this is not what I want - I still want to have a Boiler Control enabled for my CH - setting max. number of cycles per hour for CH etc.

Would it be possible with evohome software ?
If there is some other equipment I need to achieve it I would be happy to consider.

Best regards,
Sebastian

[wisniol]

If I understood what you wrote correctly, I would use an additional electromagnetic relay (ordinary, unprogrammed Honewell) and connect it electrically so that when there is a demand for hot water, BDR91 for hot water would simultaneously turn off the power supply of BDR91 for central heating. After the DHW heating is finished, the BDR91 for DHW would turn off, while restoring the power supply to the BDR91 for CH.
IMHO, all the work you need will be done by one small relay.

[Richard]

Is there a way to achieve the configuration where these two DWH and CH circuits are treated separately not influencing each other ?
I found some topics on different forums people having the similar observations and the general recommendation like "turn off Boiler Control completely in evohome configuration".
But this is not what I want - I still want to have a Boiler Control enabled for my CH - setting max. number of cycles per hour for CH etc.

Would it be possible with evohome software ?

Yes this is possible.

When you setup via 'GUIDED CONFIGURATION > ZONE CONTROL CONFIGURATION' you need to press the RED X when it asks you if you want to control the system wirelessly. Then it asks you what control type you want. Select 'ZONE VALVE' and use the evotouch controllers sensor as your heating sensor and then setup the heating BDR91 as your actuator.

When complete go through 'STORED HOT WATER CONFIGURATION' and bind the hot water sensor and then select 'HOT WATER ONLY VALVE' and bind the hot water BDR91.

You will now have independent hot water and heating BDR91's and the ability to change cycle rate and min on times.