The Efficient Home Forum

Hi Guys,

I have this idea of running a fan to cool a room running off the Evohome, The Evohome does not have the cooling feature listed as I am running old firmware, I have emailed there support to put me on the list to get this part done, do I then just need a bdr91t and another single zone stat to be able to do this, or have I missed anything off.

Cheers

Gary

The manual isn't clear and I was told unofficially that the cooling feature doesn't quite work like this. I would keep on to Resideo tech support to obtain reference material how to do this, as I don't think its possible.

You wont be able to automatically switch between heating and cooling but there is absolutely no reason why the system cannot control a fan in its own zone.

Created a new zone for the fan.
Name - PIV (Positive Input Ventilation)
Heating Type - Electric Heat (Small electric load controlled by a BDR91 only)
Tempurature Sensor - Evotouch Sensor (I don't have a Y87RF to test with but it might be a neater alternative)
Changeover Device - None (this is where you would use a BDR91T if you needed it, you don't for cooling only)
Parameters, Heat, Cool - Cooling Only

In summer temperatures the heating will never come on anyway so put the system in cooling mode permanently. This turns off all the zones with HR92 and activates the normally off zone controlled by the BDR91A. A separate schedule for cooling is activated with different set points. Once the temperature exceeds the set point for the PIV zone it signals to activate the BDR91A. This triggers the boost mode of my PIV to pump the maximum volume of air into the house from outside where it is several degrees cooler. This works exactly how you would expect except for a few issues I am working with Resideo to resolve;
The app and website are completely unaware of the cooling mode, it cannot be controlled from there and the view becomes confusing - only solution will be when they update them with that capability.
When in system cooling mode, even though the opentherm boiler is not triggered, the HR92 all get set to 35 C rather than off like it shows on the Evotouch display. They are looking at this issue but its cosmetic really. It just makes amess of my graphs in Home Assistant, for which the Evohome integration also doesn't yet understand cooling mode.

If you don't yet have the latest firmware I would recommend you get it first, otherwise you would have to try and bodge it with a zone and connect the fan to the normally closed contacts of the relay so when the "electric heating" device comes on in the zone it trips the relay and turns off the fan. If you don't know how are aren't prepared to reprogram your Evohome system I wouldn't touch it because the schedules messed themselves up a couple of times doing this. I cannot see how I could have done it and Resideo said it was probably just a bug like the ghost zone issue.

Not one installer I spoke to fully understood the cooling features when they came out and the sellers were mislabelling products they were selling such as the BDR91 relays confusing the A and T functionality. This wasn't helped by the fact that Honeywell / Resideo technical documentation contained incorrect technical information about the relays and lacked detailed setup instructions. I figured out how to do this myself and confirmed with Resideo that it was correct. They apologised for the documentation issues and mistakes of the seller and sent me a BDR91T for free so I have tested all functionality and know it can be done with just the BDR91A relay depending on firmware / manufacture date.

mrlm wrote:You wont be able to automatically switch between heating and cooling but there is absolutely no reason why the system cannot control a fan in its own zone.

Created a new zone for the fan.
Name - PIV (Positive Input Ventilation)
Heating Type - Electric Heat (Small electric load controlled by a BDR91 only)
Tempurature Sensor - Evotouch Sensor (I don't have a Y87RF to test with but it might be a neater alternative)
Changeover Device - None (this is where you would use a BDR91T if you needed it, you don't for cooling only)
Parameters, Heat, Cool - Cooling Only

In summer temperatures the heating will never come on anyway so put the system in cooling mode permanently. This turns off all the zones with HR92 and activates the normally off zone controlled by the BDR91A. A separate schedule for cooling is activated with different set points. Once the temperature exceeds the set point for the PIV zone it signals to activate the BDR91A. This triggers the boost mode of my PIV to pump the maximum volume of air into the house from outside where it is several degrees cooler. This works exactly how you would expect except for a few issues I am working with Resideo to resolve;
The app and website are completely unaware of the cooling mode, it cannot be controlled from there and the view becomes confusing - only solution will be when they update them with that capability.
When in system cooling mode, even though the opentherm boiler is not triggered, the HR92 all get set to 35 C rather than off like it shows on the Evotouch display. They are looking at this issue but its cosmetic really. It just makes amess of my graphs in Home Assistant, for which the Evohome integration also doesn't yet understand cooling mode.

If you don't yet have the latest firmware I would recommend you get it first, otherwise you would have to try and bodge it with a zone and connect the fan to the normally closed contacts of the relay so when the "electric heating" device comes on in the zone it trips the relay and turns off the fan. If you don't know how are aren't prepared to reprogram your Evohome system I wouldn't touch it because the schedules messed themselves up a couple of times doing this. I cannot see how I could have done it and Resideo said it was probably just a bug like the ghost zone issue.

Not one installer I spoke to fully understood the cooling features when they came out and the sellers were mislabelling products they were selling such as the BDR91 relays confusing the A and T functionality. This wasn't helped by the fact that Honeywell / Resideo technical documentation contained incorrect technical information about the relays and lacked detailed setup instructions. I figured out how to do this myself and confirmed with Resideo that it was correct. They apologised for the documentation issues and mistakes of the seller and sent me a BDR91T for free so I have tested all functionality and know it can be done with just the BDR91A relay depending on firmware / manufacture date.

Thanks for taking the time to write this. It also doesn't help that a historical BDR91T was sold with the RF2 Packs, that has exactly the same functionality of the BDR91A and has been interchangeable for many years! They should have really renamed the BDR91 as P or C not to cause further confusion with installers and retailers. Resideo notifying everyone properly would have also helped, but I have gotten used to this over the years.