Knowledge Base

Start by clearing up the most common misunderstanding: an evaporative cooler is not an air conditioner. There is no compressor inside, and no refrigerant. It cools by evaporating water, and the physics are worth stating precisely because they define the limits of the machine. One kilogram of water absorbs roughly 2,260 kilojoules of heat as it evaporates — about 540 kilocalories. That number tells you what this equipment can do, and just as importantly, what it cannot.

How the temperature actually drops

Open up an evaporative cooler and you will find four working parts: the cooling pad, an axial fan, a circulation pump with a water tank, and a control panel. The pump lifts water to the top of the pad, where it trickles down through corrugated fibre paper and forms a thin film across the surface. The fan pulls hot air through from the other side. As that air crosses the wet pad, sensible heat is absorbed by evaporation and converted into latent heat, so the dry-bulb temperature of the outgoing air falls.

The critical detail is that the process does not change the enthalpy of the air. It only shifts energy between sensible and latent form. How much cooler the supply air can be therefore depends entirely on how dry the incoming air is. In arid conditions the outlet can run 5 to 12°C below ambient, and in genuinely dry regions such as Xinjiang the gap can reach 15°C. Once relative humidity climbs above 70%, evaporation slows sharply and performance drops off. Above 80% humidity, you are essentially running an expensive fan.

Deciding whether it belongs in a commercial kitchen

This is where most selection mistakes happen. A commercial kitchen is typically hot, humid, and greasy, and two of those three conditions work directly against evaporative cooling.

Start with humidity and airflow. In a closed kitchen with no continuous exhaust path, blowing humid air inward simply stacks humidity higher. Staff stay uncomfortable, and food preparation surfaces get damp. In that setting the cooler must be paired with exhaust fans to create a proper supply-and-extract path; without it, the installation does nothing useful. For coastal kitchens in southern China, where relative humidity sits above 70% for most of the year, expectations need to be set correctly: the job of this equipment is targeted spot cooling plus ventilation, not holding the whole kitchen at 26°C.

Then consider grease. The cooling pad is a honeycomb of fibre paper. Once oil mist coats it, both water permeability and airflow drop, and evaporation efficiency follows them down. Kitchen-duty units should therefore be fitted with stainless steel or nylon pre-filters that catch coarse oil mist before it reaches the pad. Put an ordinary unit into a heavy-grease kitchen and the pad will be finished within a single summer.

The advantages are equally clear. Power draw runs roughly one fifth to one tenth that of a conventional air conditioner. A complete unit costs RMB 2,000 to 8,000 to install, while a central air conditioning system starts above RMB 50,000. On an eight-hour shift, an evaporative cooler consumes about 8.8 kWh, costing under RMB 10; air conditioning over the same area would exceed RMB 40. For open or semi-open spaces, or anywhere ductwork is impractical — factory floors, warehouses, canteen prep areas, temporary outdoor work zones — the arithmetic is compelling.

Three specifications matter, not one

Air volume comes first. As a working rule, every 100 square metres needs roughly 5,000 to 8,000 cubic metres per hour of airflow, which works out to at least one unit rated above 4,500 cubic metres per hour per 100 square metres. Measure both floor area and ceiling height, because heat load in a workshop with a 3.5-metre ceiling is nothing like one at 6 metres.

Second is tank capacity. Forty litres or more meaningfully reduces how often someone has to top it up, which matters in a kitchen running continuously. Otherwise a staff member will be babysitting the water level through the lunch rush.

Third is safety hardware. Low-water protection, dry-run shutdown, and tip-over cut-off are non-negotiable. Running the pump dry is the single most common cause of failure in these machines. A pump costs very little to replace; a burnt-out motor does not. Keeping one spare pump on the shelf is cheap insurance.

Routine care sets the performance ceiling

The condition of the pad and the water is effectively the condition of the machine.

Two jobs belong on the weekly list: clean sediment out of the tank, and check the water level sensor and float valve. Where water quality is poor, change the water weekly to prevent algae growth and scale blocking the distribution pipes. Once a month, check motor bearing lubrication and test pad permeability. Pour a little water along the top of the pad and watch whether it travels down evenly. Dry patches mean that section has compacted or clogged.

The pad itself is a consumable, generally replaced every one to two years. A 15-centimetre thickness gives the best cooling performance. If airflow drops, check the motor for dust build-up and inspect the filter before suspecting the pump. If the unit reports a leak, check whether the water level sensor has scaled up before assuming a cracked tank. Those two misdiagnoses account for most unnecessary service calls.

One last point: before shutting the unit down for winter, drain the tank and the piping completely. A single cold night in northern China is enough to crack a tank, and it is the most common repair request every spring.