About to install evohome.. Vaillant weather compensation?

[jdp80]

I am about to embark on installing evohome and will gradually replace the existing controls on our system.

I've got a Vaillant ecotec 637 boiler and unistor cylinder. I believe that by installing a VRC470 and corresponding wiring centre with NTC thermistor on the cylinder, the boiler will operate different flow temperatures depending on weather, DHW demand, anti legionella cycles etc.

Currently it's installed with 230v switching because we have three heating zones + HW and Vaillant kit doesn't support that. So we have quite a dumb system which only operates at one flow temp and rarely seems to condense.

Is there be any way to control CH with evohome but also benefit from the Vaillant weather compensation? Obviously this would mean I had to program the DHW from the boiler instead of evohome, but seems worth it to reduce the high flow temps I'm seeing.

Thanks!

[bruce_miranda]

I have a Vaillant boiler myself and rather than go down the weather compensation route, I'm doing the OpenTherm.

I would say that evohome can do what you need.

[jdp80]

Thanks, what boiler do you have? How are you connecting OpenTherm?

Since my original post I've installed the evohome controller as well as an eBus interface to monitor the boiler on a Raspberry pi.

According to posts elsewhere, it's possible to connect the evohome kit alongside the VRC470 etc by connecting evohome's BDR91 to the 240v room stat connection on the boiler.
That way the DHW/CH systems can have varying flow temperatures, weather compensation, and DHW timing controlled via the boiler.

I'm not sure I'm going to bother with weather compensation either, I can't see the benefit given that we have UFH and need so have a relatively small range of flow temps. Especially given the boiler modulates anyway.

I like the idea of separate CH/DHW flow temperatures though. I need to work out whether I can integrate evohome with the VR65/66 wiring centre (via the 240v HW thermostat link, perhaps) or maybe buy a simple, non-WC vaillant controller to run the DHW timings.

tbh the fiddling is quite fun.