I have 2 Lifebreath HRV's and two furnaces in my house. Each furnace covers a different zone. I assumed these HRV's were both independent for each furnace. However, I noticed that the two HRV's are connected to each other via their terminals.
Namely, there are black & white wires connecting the RED and HI terminals (and by extension the ON terminal via the jumper between the RED and ON terminals) on the first HRV to the COM and NO terminals on the second HRV. (Diagram attached)Capture.JPG
I would just like to understand why the two are connected. The reason is I am interested in replacing both HRV controllers with dry contact WiFi relays to control the fan hi, low and dehumidistat functions. I just want to understand everything before I potentially screw anything up.
I'm not sure why they connected the HRV wiring together if they are 2 independent systems.
Usually ON(2) and RED(3) are jumpered when mechanical timers are used.
The COM(7) and NO(8) are used to interlock the HRV and furnace, so the furnace fan runs when the HRV starts.
I usually use the 3 wire method and wire NC(9) as well. In some cases the AC can back feed and start with the 2 wire method. See attached pic.
I would expect to see each HRV interlocked to the furnace that is part of the zone. It seems that HRV #2 would start HRV #1 and also furnace #1 fan when it starts.
If you use an Ecobee thermostat to control the HRV's it will take care of the interlocking so you don't need that wiring anyway.
A bit more background info - I moved into this house and it originally had a Honeywell Prestige IAQ kit for both systems, with the equipment interface modules. I wanted to replace these with Ecobees so I had an HVAC company come in and do the installation.
They told me that the Ecobee could only handle one accessory - either the HRV or the humidifier. I opted for the Ecobees to control the humidifiers. They installed separate mechanical timers (99-DET02) for the HRV's in the utility room next to the units themselves. This was a disaster - the tech told me that setting it to 20 would run the HRV for 20 minutes every hour, when in fact it was just a timer that ran for 20 minutes and then stopped until the button was pressed again. I then replaced those timers with the digital controls (DXPL02) so it would actually run 20 min every hour.
I guess there's no NC(9) connection since the Ecobees aren't controlling the HRV's.
I suppose the best course of action is to remove this wiring connecting the two units, and then figure out how to interlock HRV 2 with the furnace of the same zone?
I use the Presitge 2.0 at home as it will control both HRV and humidifier. I use the Redlink gateway to access it with an App but the downside is the App controls everything but the HRV. That is setup in the thermostat and runs the HRV whenever it's ASHRAE algorithm tells it to.
The NC(9) terminal should be on the HRV and is used to interlock the furnace using the 3 wire method. You use the 2 wire method but don't seem to have issues so I wouldn't worry about the NC(9).
That's what I would do. Remove the wiring between HRV #1 and #2 and install the interlock wiring from HRV #2 to its furnace.