In most larger cities there are a number of companies that rent/lease portable units to data centers for emergency use. I saw one data center loose it's main ac unit and they brought in 12 portable units until the replacement part got there.
At my former office we turned a closet into a server room. When our AC went out one day I thought the door was going to catch on fire! Luckily, we rented a portable AC unit from Mobile Air, http://www.mobileair.com, until the regular AC was fixed.
is the portable cooling option for hire only or can you just keep an emergency cooling solution on site? how much time does one usually have in case the cooling system fails before the site has to be shut down?
i don't know about emergency cooling systems but i can tell yoy that if a data center is well designed with a higher ceiling(more that 9 feet) one usually has time before the room temperature starts to rise to dangerous level. it gives the data center operator enough time to turn off the equipments that produce the most heat.