Warm air passes through water. It comes out cooler.
Evaporative cooling doesn't manufacture cold: it uses the energy water absorbs as it evaporates. The same phenomenon as wet skin in the wind — at the scale of a hall.
Warm air is drawn in
A fan pulls ambient air through the unit. The hotter and drier it is, the stronger the effect.
It passes through wet pads
A pump lifts water from the tank onto honeycomb pads, where it spreads before running back. The air passes through them: the water evaporates and takes its heat.
Cool air is blown into the space
A steady flow that puts the space under slight positive pressure: the air already there, with its odours and dust, is pushed out through the openings.
What it gives
The temperature of the air blown in, humidity included.
The drier the outside air, the greater the drop; in muggy weather it shrinks. The manufacturer's table gives the temperature of the air blown in, in degrees, according to the temperature and humidity of the outside air.
| Outside air | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|
| 20 °C | 12 | 13 | 14.5 | 15.5 | 16.5 | 17.5 | 18.5 | 19.2 |
| 25 °C | 16 | 17 | 18.5 | 20 | 21 | 22 | 23 | 24 |
| 30 °C | 19.5 | 21 | 22.5 | 24 | 25 | 26 | 28 | 28.9 |
| 35 °C | 23 | 25 | 26.5 | 28.5 | 29 | 30 | 32.5 | 33.7 |
| 40 °C | 25.6 | 28.1 | 30.4 | 32.3 | 33.9 | — | — | — |
Manufacturer's catalogue. Above 35 °C the table stops at 60% humidity: air that is both very hot and very humid does not occur. The manufacturer adds that moving air feels 1 to 2 °C cooler than the supply temperature. These figures are for the air leaving the machine — the temperature reached in a building depends on its volume, its heat gains and its openings, and that is what the survey establishes.
Honestly
Three pluses, three minuses.
No compressor
Only the fan and the pump draw power. An air conditioner, by contrast, drives a compressor.
No refrigerant gas
Water and air. No refrigerant to handle, declare or top up.
Fresh air, not recirculated
The system works on fresh-air supply. That's what makes it possible in open spaces.
Depends on humidity
The effect is greatest in hot, dry air and weaker in muggy weather. We say so before, not after.
It needs openings
The air blown in has to be able to leave again. With no way out, humidity builds up in the space and the effect fades.
It needs a water supply
Connection or tank, depending on the unit and the place. Checked during the study.
What it consumes
Eleven kilowatts against one hundred and eight.
With no compressor, only the fan and the pump draw power. The manufacturer compares the three ways of treating the same building; his assumptions are below the table.
| For the same building | Evaporative cooling | Air conditioning | Ventilation only |
|---|---|---|---|
| Capacity of one unit | 20,000 m³/h | 400,000 BTU/h | 40,000 m³/h |
| Power of one unit | 1.1 kW | 54 kW | 1.1 kW |
| Units installed | 10 | 2 | 8 |
| Installed power | 11 kW | 108 kW | 8.8 kW |
| Annual consumption | 34,320 kWh | 336,960 kWh | 27,456 kWh |
| Share of the air conditioning | 10.1% | 100% | 8% |
| What it does | Cooled fresh air; the hot air leaves | Recirculates the indoor air | Moves the air without cooling it |
The manufacturer's basis: a 1,000 m² building 4 metres high, 30 air changes per hour, 10 hours a day, 26 days a month, all year round. The air conditioning recirculates the air instead of renewing it. The price of electricity is not part of this basis: it depends on the contract.