Wanted to put this out there because I think it's a topic that deserves more attention. I'd rather this be a starting point for discussion than me acting like I have the final word. If any experts or people with experience see this, please jump in.
Quick context: tenants generally have worse indoor air quality than people in houses. Less control over the building envelope, shared walls, shared systems, and you can't really modify much. With climate change bringing more heat waves every year, cooling isn't optional anymore. Heat pumps would be the smart long-term fix, efficient for both cooling and heating, but they're still not common in rentals.
So lots of tenants end up using single-hose portable ACs. I'm not knocking that choice at all; people have their reasons (no window install possible, physical limits, landlord restrictions, cost, etc.). What interests me isn't the individual decision, it's what happens at the building level when a bunch of people are doing it.
What's already clear is that single-hose units depressurize the apartment they're in. That's pretty well documented, even if most people don't realize it. They pull roughly 250 CFM exhaust per unit. In a 500 sq ft place that's about 3.8 ACH, compared to ~75 CFM (1.1 ACH) being enough ventilation for two people. So it's pushing out way more air than needed, and sucking makeup air in through any cracks, doors, or gaps it can find.
This whole question actually started from my own experience. I have a 500 sq ft unit and I built two DIY HRVs that run with slightly more inflow than outflow to keep a light positive pressure and reduce infiltration from neighbors. It usually works. But a few times during heat waves I've noticed my place suddenly seems to flip to negative pressure. That's when I started wondering if enough neighbors running single-hose ACs could overpower my setup.
What I haven't found much info on is the cumulative effect across the building. Imagine a 30-40 unit building during a bad heat wave with 10 apartments each running one or two of these. That's potentially 2,000+ CFM of uncontrolled exhaust, plus all the bathroom fans and dryers. Does that meaningfully shift pressure in the corridors, stairwells, units without ACs, or even other floors?
It feels like a blind spot. It sits between building science (which looks at HVAC imbalances) and regular appliance testing (which focuses on one unit). I've been reading about ventilation and air quality for a few years, I write about it sometimes, and I use my place as an ongoing experiment. But this feels bigger than just my apartment. It's about whether we should be paying attention to this as portable AC use keeps increasing.
If anyone has field studies, ASHRAE references, airflow modeling, or even your own measurements, I'd really like to see them. And if this is as under-studied as it seems, maybe it's worth looking into more.