Since Evaporative cooling is related to humidity level, the following chart shows how much cooling you can get from evaporative Air coolers based on Outside ambient air temperature and humidity.
Here is the Bad news , as we all know Dubai weather is humid, so you can’t Expect much from evaporative cooling during the most humid month. But since Air coolers can move a lot of air, you can get in addition to cooling from Evaporative cooling , you’ll feel more cooling from the huge air flow fan.
The best thing about Evaporative air coolers that they use much less energy than conventional air conditioners, and can provide much more air flow.
Actually for outdoor cooling application there is no better way to do it than Evaporative cooling, because the need of huge air flow in open areas.
On the other hand, for Indoor cooling, temporary cooling or spot cooling, The conventional portable AC is best option to go. This applies to backup data center or tent cooling which is a common in Dubai and other Emirates.