I've officially applied for "extreme project rabbit hole" therapy 
I'm finally wrapping things up with this project having run the HRV drain hose (to a nearby laundry drain), done the rough wiring and installed inline electric heaters to condition cooler supply air. The Hubitat hub is running the show pretty much completely.
In normal operation, total power use is about 28 watts for the two EC fans (in the 50 CFM profile), and I'm adding in about 150 watts of post-heat when outside temps drop below 25 F. One of the perks of a system like this is that when the system calls for 60, 75 or 90 CFM, the EC motors are dialled up individually based on actual flow testing at the HRV.
Two zigbee dimmer modules limit power to the heaters, modulating their output based on supply and delivery temps. It's a pretty slick setup.
Still lots of work to do, but the EC fan control switches and inline heater switches are wired up (under the welcome sign). They allow manual control if required. The missus is not a fan of visible technology so a sweater or two on the hooks will hide the switches. They are managed by automation so if someone hits a switch, it won't be an issue. I want them there so I can give them a quick visual to make sure all it working as advertised. If the automation system is off for some reason, the switches can control the system as well.
The inline heaters can raise the fresh air supply temps 40 F, but the typical requirement will be about 10-15 F as outside temps fall below -10 F. I ended up doing this as the fresh air "dump" is into our main living area and even at 80% efficiency, with outside temps dipping well below freezing, the supply temps tend to cool down the space.
There are five levels of safety built in to the heating setup: 1. The PTC heater by design uses less power as it heats up. 2. If the unit itself exceeds 220 F or so, the integrated thermal switch turns it off. 3. I've added thermal fuses inline in the junction box for the housing 4. The remote bulb line level thermostat cuts power if the heater housing hits 70F 5. The automation system modulates power and turns on/off the heaters based on the HRV mode.
Finally, I've added manual switches to cut power if needed.
These PTC heaters are all of $17 each.
This remote bulb (part number A19ABC-12C) line level thermostat can manage the heaters just fine if required. Right now it's just there as a third level of safety. If the housing exceeds 70 F, power is cut to the system. It's 100% old school manual, so no power is required to operate it.
The automation bits are all working surprising well. The system defrosts itself depending on outside temps which amounts now to this routine:
- Close outside air dampers (which opens internal recirc damper)
- Switch to the 75 CFM profile for x minutes (based on outside temps) to warm up the unit/core.
- Stop for a minute (to allow any water to drain with neutral air pressures inside the HRV)
- Open the dampers and dial back the EC motors (mainly to 50 CFM).
- Turn on and modulate the inline heaters if required.
Everything is done in Rule Machine 5.1
Now I have to make it all pretty
