Lots of hardware…
Full rack of VOIP/PBX equipment
Half Rack of network switch / patch equipment
Management console PC for the PBX
Plus the electric meters for 30 apartments and the house panels for the floor.
When the room was built I requested a vented door and an air handler to circulate the conditioned air from the common area through the room; that would at least keep it reasonable year round. My employer refused due to cost.
It is an interior room with concrete walls on 2 sides, drywall on the other two. It’s comfy in winter, but in summer can get well over 80. Amazing we have not lost any equipment in 6 years of operation.
This is a residential building, not a commercial enterprise.