That Bionaire appears to have the air inlet and outlet within a couple of inches of each other, that isn't going to do anything except waste electricity. You're just recirculating indoor air.
Real ERV/HRVs have ducting ports in both sides, and installing all the ducting and electrical is far more expensive than the $500~1000 the unit itself costs. That's why they're uncommon: Install is expensive and painful.
The window unit linked at the top doesn't appear to do heat recovery. Most of the decentralized single-room mechanical ventilation heat-recovery (MVHR) units reverse their fans every 60-70 seconds in order to operate their heat exchangers, such as this example.[0] That period should be long enough for the exhausted air to disperse far enough away outside that it won't just be sucked back into the house, unless the exterior exhaust is positioned in a really weird spot outside where wind is minimal and the air can't effectively disperse. Alternatively, they can also be paired with another unit so that one exhausts air at the same time the other brings in fresh air, allowing better airflow across/within the room.
The problem with this approach is that once you start ventilating multiple rooms with these small units (figure $500 per room with a single unit, twice that if two), the cost rapidly approaches that of a centralized unit with ducting. But if you're just looking to ventilate a room or two, they're likely a very cost-effective solution. I could also see them being used on a first floor living room/kitchen in conjunction with a centralized unit ventilating upstairs bedrooms with the ducting run through an attic. That'd probably be cheaper overall than trying to run an intake/exhaust duct downstairs or installing units in each room. Plus, each exterior penetration increases the opportunity for uncontrolled air leakage and, most importantly, water.
The other problem with this approach is that it is limited to 50% efficiency long-term. They claim "up to 90%", but it is only 90% efficient immediately after switching directions. The efficiency then drops to 0% before switching modes again.
They make vents that exhaust in a spiral from the center and intake from the sides so that the air flows are perpendicular. Might look funny on that unit but could help with that mixing problem.
> That Bionaire appears to have the air inlet and outlet within a couple of inches of each other, that isn't going to do anything except waste electricity. You're just recirculating indoor air.
Are you referring to the ports on the interior or exterior?
The unit is 26 in. wide for a use case (e.g. apartments) where the HRV avoids leaving a window open for simultaneous intake and exhaust. If the exterior wind direction doesn't locate the exterior outlet downwind of the intake, one could potentially install a short exterior duct to add separation, as in step 13 of this DIY HRV, https://www.loudawson.com/17884/how-to-build-air-cross-flow-.... For the interior ports, 45-degree angled vents can reduce overlap between the airflow directions. Without the HRV, air would be moving in and out of the same window anyway, without any structural separation.
Amazon reviews for the Bionaire reported both energy savings and air quality improvement, so it worked for some people.
The BluMartin FreshAir 100 and the Fresh-R series are both MVHR units that fit into existing walls: there’s a Fresh-R model that goes into a window frame too.
Commercial ERV/HRV units start around $500, https://www.greenbuildingadvisor.com/question/inexpensive-ef...
DIY counter-flow design with coroplast sheets, https://ecorenovator.org/forum/showthread.php?t=891&page=38#...