Adiabatic cooling: technical differences between mobile and fixed rooftop solutions
Adiabatic cooling is a technology based everywhere on the same physical principle: the evaporation of water to capture heat from the air. But the architecture of the solution (mobile floor-mounted or fixed roof-mounted) radically changes its actual performance, installation constraints and total cost. This guide deciphers the differences that commercial data sheets overlook.
Overview
The same technology, two radically different architectures
Biocooling and evaporative cooling belong to the same technological family: adiabatic cooling. The physical principle is invariable. Warm air is brought into contact with evaporating water. This change of state captures thermal energy and lowers the air temperature, which is then diffused into the space to be treated.
This technology offers an alternative to conventional air conditioning, with an energy impact 6 to 10 times lower. But the architecture of the system changes everything. Two main approaches coexist on the BtoB market: fixed adiabatic solutions installed on the roof, and mobile adiabatic solutions installed directly on the floor of the building being treated. These two approaches do not produce the same results.
The two structuring differences at a glance
There are six technical differences between mobile and fixed roof solutions:
(roof exterior vs. recycled floor interior)
(a few hours vs. about 90 minutes)
(stable vs progressive)
(heavy work vs. 24-48h deployment)
(mandatory frost protection vs. simple storage)
(roof access, external filters vs. ground maintenance)
These six differences do not carry the same weight in an industrial decision. Two of them alone account for most of the differences in actual performance observed between the two architectures: the origin of the intake air and the time taken to cool down. These two points are discussed in detail below. The other four differences, as well as a 5-year TCO comparison table and an analysis of the disadvantages of adiabatic cooling according to each architecture, are developed in the PDF guide downloadable at the end of this page.
The decisive physical point: the origin of the intake air
A fixed solution installed on the roof draws in outside air. A mobile solution installed on the ground in the treated space draws in air from inside the building. This difference may seem secondary. But it is the key to real efficiency.
On a fixed rooftop installation, during a heatwave, the outside air drawn in is the hottest air available. There are no shaded areas, no protection, no thermal masking effect. The equipment must therefore cool 35, 38 or 40°C supply air to produce fresh air for the building. Performance depends entirely on the difference between outside temperature and dew point temperature.
On a mobile floor-mounted system, the equipment draws in air already present in the building, which is cooler than the outside air thanks to the thermal effect of the walls and floor. As the machine cools the treated area, the air it draws in itself becomes progressively cooler. The system enters a virtuous circle: the more the area is cooled, the fresher the air drawn in, and the better the performance.
This difference explains why a mobile industrial adiabatic cooler reaches its optimum operating speed after around 90 minutes, with gradual and lasting temperature gains. A fixed rooftop solution, on the other hand, remains stable throughout the day, with efficiency only beginning to improve in the late afternoon, when the outside temperature begins to drop.
The second decisive point: temperature descent time and thermal mattress
In an industrial building with a significant ceiling height, heat follows the physical law of stratification. Warm air rises, cool air sinks. The result is what thermologists call a “thermal mattress”: a layer of very hot air stored at the top of the building, often between 6 and 10 meters high.
This thermal mattress is of no operational use. Operators work downstairs, machines produce downstairs, workstations are downstairs. The hot air above is thermal waste.
A fixed roof solution distributes its fresh air from above, via ducts or bulk distribution. It must therefore first “attack” this thermal mattress before the fresh air descends to the useful zones. As a result, the time it takes to bring the temperature down to the workstations often exceeds the duration of a full working day.
A mobile floor-mounted solution, on the other hand, distributes air directly to the operators. Fresh air arrives where it’s needed. Downtime is around 90 minutes, making the solution compatible with early-morning shifts.
This difference in temperature descent time is the second criterion that explains the differences in performance observed in the field. For a full comparison of the 4 main solution families (including the two adiabatic architectures), see our air cooler comparison.
Bio-air conditioning and ecological air conditioning: terminological clarifications
The terms “bio-air-conditioning” and “ecological air-conditioning” are frequently used in commercial discourse to designate the two adiabatic architectures. They do not refer to separate technologies, but to the same physical principle of evaporative cooling.
The real question is not “bio-air-conditioning vs. conventional air-conditioning”, but “mobile adiabatic architecture vs. fixed rooftop adiabatic architecture”. It’s this distinction that determines actual performance, operating constraints and TCO over 5 years.
Download the complete guide: the 4 other differences + 5-year TCO
This page has detailed the two most decisive physical differences between the two architectures. The full PDF guide covers all 6 differences and provides the decision-making tools needed to decide:
The 4 differences not covered on this page (installation, winter operation, maintenance, daily energy efficiency)
A 5-year TCO comparison table for the two architectures on a typical 2000 m² site
A complete analysis of the disadvantages of adiabatic cooling for each architecture
Two technical diagrams: thermal stratification and temperature descent cycle
A decision matrix to identify the most appropriate architecture for your site
A case study: a plastics plant that compared the two solutions
To find out more about your project
If you would like to take a closer look at your decision, see also :
They put their trust in us
