Tenant units have fire standard doors to the hallway, but if they're propped open - the fire would not be contained.It's up to me to get an air conditioner if I want to be cooler, according to the landlord, but I regularly prop open my door, just like my neighbors do, in order to stay cool.  

Fish tanks, computer equipment, lighting, heating pads, portable air conditioner, electric blankets, power tools, just on and on. 

But, as unlikely as fires are, I couldn't live with myself if a tenant died because they couldn't escape out the window:https://www.amazon.com/BLACK-DECKER-BPACT08WT-Portable-Conditioner/dp/B01DLPUWL2/ref=sr_1_1?

As far as a tenant installing an air conditioner, I'm not worried about that too much as it's not a complicated process.

She had decided the air conditioner of a nearby unit that had been there for a full year where she had no problem with it - was all of a sudden intolerable and she wanted us to tell that tenant they had to remove their air conditioner. 

For cooling, we rely on seven window unit air conditioners and free-standing window units. 

Add a few window air conditioners you don’t have enough power.  

They did "2 things you should never be without..." and when the person visited the website it talked about you should never be without an Air Conditioner...

(short tangent below)I recently had a house that had a window air conditioner in the wall to cool the dining room. 

In that case I would purchase four window style air conditioner/heaters to mount into two of the windows per unit.That means each apartment will have two units they can control and this will be more than enough to heat and cool 1000 sf or less providing you purchase them to accomadate the correct square footage.The pros and cons of going this route:Pros:Cost.