Greetings to all - happy to have found this forum.
My VisionPro 8000 t-stat recently failed and I upgraded to a Honeywell T10. The installer had it hooked up in a jiffy and it's working great. However, my home is equipped with an Bryant (Venmar) ERV (ERVBBLHU1200) that is controlled with a Bryant/Carrier wall controller (KLACN0101BLC). I'm using dual heat (Trane HP and CL90 propane furnace).
My installer cannot figure out how to use the T10 to control the ERV. The T10 has a pair of connectors that are just contact closure for a downstream unit - humidifier, ERV, etc.; the two terminals can be used wet or dry. I suggested to the installer that it would have to be dry because the t-stat would send 24vdc and the ERV controller board looks to be 12vdc.
My home really just needs the ERV to operate as a ventilator. I have a unique situation in that the house has an attached garden/atrium room. The house is sealed with foam and the attics are heated and cooled. In our area winter temps rarely dip below 20F and usually vary between 30F-45F. Without any humidification or de-humidification the house varies between 36% RH in the winter and 48% in the summer.
I need the ERV to bring in fresh air. The T10 has the ability to start the ERC using the contact closures on the two "U" terminals. The problem is the ERV is a two-speed motor and the logic circuit seems to control motor speed based on a resistance bridge. My installer's a great chap but mention stuff like this and his eyes roll... so I'm trying to help.
The wall controller connects to the ERV with 4 wires: black, green, yellow, and red. I believe black is ground and green is the control wire. I'm guessing that the red and yellow wire add to the control function by sending different voltage signals based on resistance. Bryant manuals don't explain any of this, but I found some references in Venmar documents. These suggest that shorting black and green with start the unit in high-speed mode and open the damper. Also, by installing a 3.9kohm resistor between black and green with trigger low-speed operation.
Rather than experiment with expensive control boards it seems better to ask the pros and pass this along to my installer. Any advice would be very welcome!
You're right. Setup the T10 ventilator option as dry contacts and wire the ERV B and G terminals to the T10 U & U terminals.
If you remove the B and G wires from the ERV controller and twist them together the ERV should start. The dry contacts will accomplish the same thing when the ventilator is turned on. The Y and R will not need to be used.
You will only be able to control the one ERV fan speed but that is usually not a problem.
I imagine the new thermostat can control the ERV interlock and start the furnace fan when the ERV starts. If so, and you have separate ERV interlock wiring then that could be eliminated as well.
Thanks for getting back - super duper.
Yes, the T10 has some pretty sophisticated settings for controlling the ERV based on ASHRAE calculations, humidity control, or simply a timer. The interlock is built in. It appears a lot more capable than the older Bryant controller and eliminates another box on the wall.
Just two more questions:
1. Is the damper energized when B and G are connected? I believe the damper is triggered whenever the fan motor is energized... just checking.
2. Will an inline resistor in the B-G connection bring the motor to the "low" setting?
This is very hard information to tease out so I'm very grateful for you help with this.
Yes, the internal damper would open anytime the ERV is turned on. Unless the ERV is in defrost mode.
I never bothered checking which fan speed is energized. My guess would be high speed. You can likely switch fan wires around inside the ERV to change to the speed you want.
I'm not sure what kind of voltage or signal triggers the different speeds but I think you're on to something with the resistor. That's essentially what the controller does.
Because Venmar made ERVs for many others firms (Bryant, Carrier, Broan, Rheem/Ruud, Honeywell, Lennox, Nutech,...) it's exceedingly difficult to know which wall controller signal goes to what. Everyone will have to investigate their own case. In my case, I can command "Low" only from the wall - when I do B-G sends 3.5vdc to the ERV logic board. When I set the humidity to a level that trips the ERV it demands high-speed and I see 12vdc going to the ERV board (I think from the yellow wire). Since the Honeywell T-10 can only command one-speed, I'll set it up to close the "U" terminals to send 3.5vdc to the ERV so it runs in low-speed. I say this while thinking whether it really matters. I think the speed differential between "high" and "low" is about 30% so fretting about whether to step down the B-G voltage or not might be a minor issue. The key thing is to let the ERV run to ventilate.
With my setup, the T-10 will turn on the ERV in parallel with either the cooling or heating loop while ensuring that at least 10% of an hourly cycle provides ventilation. I'll monitor RH and adjust that setpoint as needed. My home is designed for passive solar heating with a large south-facing window wall. In the winter with a sunny day the shades trees have dropped their leaves and we get a huge solar effect from that southerly exposure. The result is we wind up with around 75F in the house with nothing running on sunny cold days. The T10 will then run the ERV anyway to ventilate the house while giving the heating system a rest.
Hope this thread helps others with similar situations down the road. This forum rocks!
Forgot the add... the T10 has the ability to set temp thresholds as well. So on those very cold days (temps below freezing, for example) I can simply bypass ventilation and the defrost cycle won't be an issue.
Tryng to hook my ERV control to the T10. Jumping the B and G terminal doesn't start the unit. I'm using and old Flair/Venmar controller with 4 wires (B-G-R-Bk). Should I tie one of the other 2 wires to the B or G ?