What Size Dehumidifier Do You Need in the UAE?
It is the most common question we get asked, and it is almost always asked the wrong way round. People ring up and say “I need a dehumidifier for a 200 square metre warehouse, what size?” Floor area alone cannot answer it. Two buildings of identical size can need units differing by a factor of five, depending on what is happening inside them and how well they are sealed.
This is a practical guide to what actually determines the answer, and what you can work out yourself before you speak to a supplier.
The capacity figure on the box is conditional
Dehumidifier capacity is quoted in litres of water removed per day. What is easy to miss is that the figure is only meaningful alongside the conditions it was measured at.
A refrigerant dehumidifier works by cooling air below its dew point so moisture condenses out. The warmer and more humid the incoming air, the more water there is available to condense, and the more the machine removes. Cool the air down and the same machine removes considerably less.
This is why a unit rated at, say, 50 litres per day at 30 degrees and 80 percent relative humidity will not deliver anything close to that in a 20 degree store room at 55 percent. Manufacturers do not always test at the same conditions either, so two units with identical headline numbers can perform quite differently in your building.
When comparing units, check the rating conditions. If a supplier cannot tell you what conditions a figure was measured at, that figure is not much use to you.
What actually drives the size you need
A proper calculation is a moisture balance. You are working out how much water is entering the space per day, and specifying a machine that can remove at least that much while pulling the humidity down to where you want it.
The volume of the space, not the floor area
Air is what holds the moisture, so volume matters, not footprint. A warehouse with a ten metre eaves height contains far more air than a workshop of the same floor area with a three metre ceiling, and it needs correspondingly more capacity.
Air changes: how much outside air gets in
This is usually the largest single factor and the one most often ignored. Every cubic metre of outdoor air entering the building brings its moisture with it. In the UAE that load is substantial for most of the year.
Air gets in through mechanical ventilation, through doors opening and closing, and through leakage in the building envelope. A sealed, well constructed cold store might see a fraction of an air change per hour. A warehouse with roller shutters standing open through the working day might see several. The difference between those two cases can be larger than every other factor combined.
Moisture generated inside
Then there is whatever the building itself produces. Open water surfaces evaporate continuously, and a swimming pool is by far the biggest source most buildings will ever have. Wet processes, washing down, cooking and drying all release vapour. Curing concrete and drying plaster release a great deal during construction. People contribute too, though in an industrial space they are usually a rounding error next to the process.
The gap between where you are and where you need to be
Pulling a space from 80 percent relative humidity to 60 is a different job from holding it at 40 or taking it to 30. The lower the target, the harder the work and the more capacity you need, and below a certain point refrigerant technology stops being the right tool at all.
Be honest about the target. People often ask for a lower humidity than the application actually requires, and pay for capacity and running cost they never needed.
How quickly you need to get there
A construction drying job that has to be finished in a week needs far more capacity than the same building being held at a stable humidity indefinitely. Sizing for a deadline and sizing for maintenance are different calculations.
What you can work out before you call
You do not need to do the engineering yourself, but gathering these five things will get you a useful answer on the first conversation rather than the third.
1. Measure the space properly. Length, width and height. Height especially, because it is the one people leave out.
2. Measure what the humidity is actually doing. A cheap hygrometer is enough. Take readings at different times of day and on different days, because humidity swings considerably between a closed-up morning and a busy afternoon with the doors open. One reading tells you very little.
3. Decide what you actually need to hold. Not what sounds safe. If the requirement comes from a standard, a customer specification or an insurer, find the number. If it is about preventing mould and condensation, that is a different and generally easier target than a process requirement.
4. List the moisture sources. Any open water, any wet process, how often the doors open, whether the slab is new, whether the space is below ground.
5. Look honestly at the envelope. Are there gaps around doors? Is there a shutter that stands open all day? Is the ventilation system pulling in outside air continuously? Take photographs. This is the part that most often changes the recommendation.
Sealing the space usually beats buying a bigger machine
This is the single most useful thing in this article, so it is worth stating plainly. A dehumidifier fighting a continuous stream of humid outdoor air through an open shutter will run permanently, cost a fortune to operate, and still not reach setpoint. Adding a second machine does not fix it either.
Before specifying capacity, it is almost always cheaper to reduce the load: fit door seals, close or curtain openings that stand open unnecessarily, add an air curtain to an entrance that has to stay open, check that ventilation is balanced rather than pressurising the building with outside air, and address any obvious envelope leakage.
We have been to sites where the correct answer was a smaller dehumidifier than the client expected plus a properly specified door, and the running cost difference over a year was substantial.
Temperature decides the technology, not just the size
Once you know the load, the temperature of the space decides which type of machine should carry it.
In a normally occupied building in the UAE, a refrigerant dehumidifier is the efficient choice. It is working in exactly the warm, moisture-rich conditions it is designed for.
In a cold store, a chilled process area, or anywhere you need to hold humidity very low rather than merely comfortable, refrigerant units lose their advantage. There is less moisture available to condense and the coil is at risk of frosting. That is where a desiccant machine takes over, because it is largely indifferent to temperature.
Getting this wrong is a more expensive mistake than getting the capacity slightly wrong, because a refrigerant unit in a cold application does not underperform gracefully. It frosts, defrosts, and spends much of its time not dehumidifying at all.
Five sizing mistakes worth avoiding
Using floor area alone. It ignores height, which is often the biggest variable in industrial buildings.
Comparing headline litres per day between brands. Without matching test conditions, the comparison is meaningless.
Sizing for the average rather than the peak. If the doors are open every morning for deliveries, that is the condition the machine has to cope with.
Oversizing “to be safe”. An oversized unit short cycles, which wastes energy, wears the compressor and can drive humidity lower than intended, which brings its own problems with static and materials drying out.
Forgetting the drain. A unit sized correctly but left draining into a collection tank that nobody empties stops working the moment the tank fills. Any permanent installation should be plumbed to a drain or fitted with a condensate pump.
What we need in order to size it for you
Send us the dimensions including height, what the humidity is reading now, what you need it to hold, what is generating moisture, how the space is used and how often it is opened, and the temperature it runs at. For a pool, the water surface area and the water and air temperatures.
Photographs of the space and its openings are genuinely useful, often more useful than the numbers, because they show us the load you have not thought to mention.
Call +971 54 574 2443 or email info@climatech.ae and we will size it properly rather than guessing from floor area.
For the equipment itself, see our industrial dehumidifiers, the industrial and commercial range in portable, floor standing and ceiling ducted formats, swimming pool dehumidifiers for pool halls, and desiccant dehumidifiers for low temperature and low humidity applications.