Fan-cooled equipment: forced industrial cooling and heating

What is the difference between a chiller, a unit heater and a dry cooler?

The chiller cools a process fluid with a refrigeration circuit; the unit heater conditions the temperature of a space; the dry cooler dissipates heat from a fluid directly outdoors without a refrigeration circuit.

All three types use forced air convection but serve very different purposes. The chiller incorporates a refrigeration circuit (compressor, air condenser, expansion and evaporator) to produce cold and cool a process fluid circulating in a closed circuit — it is the equivalent of a refrigeration circuit in an air conditioning unit, but for industrial use. The unit heater has no refrigeration circuit: it takes thermal energy from a heat transfer fluid (steam, hot water or hot glycol) and transfers it to the ambient air of a working space to heat it; in its cooling version, it reverses the process (cold glycol or chilled water to cool the space air). The dry cooler also has no refrigeration circuit: it takes heat from the process fluid (which may come from cogeneration, compressors or machinery) and dissipates it directly outdoors through a tube-and-fin battery with fans. The selection depends on whether the function is producing cold (chiller), conditioning a space (unit heater) or dissipating process heat (dry cooler).

Can fan-cooled equipment operate outdoors and in warm climates?

Yes, they can be designed for outdoor operation, but effective thermal capacity decreases as ambient temperature approaches the process fluid temperature.

All three units can be installed outdoors. The fundamental thermal limitation is that ambient temperature is the heat sink: as the ambient warms up (summer, warm climates), the ability to dissipate heat or cool the process fluid decreases. For installations in Mediterranean or arid climates, BOIXAC sizes equipment using maximum annual temperatures at the location (typically 35–40°C), not average temperatures. In very warm climates, the battery can be oversized, air flow increased (larger fans or fans in parallel) or an adiabatic pre-cooling system for inlet air can be added.

Does fan-cooled equipment require periodic maintenance?

Yes, mainly cleaning the heat exchange battery and checking the fans. The circuit does not require water treatment.

The main maintenance consists of periodic cleaning of the tube-and-fin battery, which can accumulate dust, cotton fibres, pollen or organic debris that reduce air passage and the transfer coefficient. In rural, agricultural or tree-lined environments, cleaning frequency may be high (every 3–6 months). Fans require bearing inspection and blade balance checks during extended operation. The great advantage over a cooling tower is that there is no open water circuit: no Legionella treatment is needed, no limescale builds up and there are no discharge risks. BOIXAC specifies the recommended maintenance plan in the technical documentation of each unit.

Can the output of fan-cooled equipment be regulated?

Usually yes, via variable frequency drive on fan motors, where rotation speed adjusts to actual thermal demand.

Power regulation is a standard feature in modern fan-cooled equipment. The main options are: (a) Variable frequency drive (VFD) on fan motors: enables continuous air flow adjustment based on the fluid or space outlet temperature, achieving significant energy savings at partial load. (b) Stage on/off control (on/off per fan in multi-fan units): step-by-step control, less energy efficient but more economical. (c) Variable blade pitch in high-efficiency axial fans: enables air flow adjustment without changing motor speed. BOIXAC specifies the appropriate regulation system for each application based on the process load profile.

What is the typical power range of industrial fan-cooled equipment?

From a few kW for building unit heaters up to tens of MW for dry coolers in cogeneration or heavy industry.

The power range is very wide and depends on the type. Unit heaters for industrial buildings cover 10 kW to 200–300 kW per unit, with several units installable in parallel. Industrial chillers with air condensation range from 5 kW to several hundred kW. Dry coolers for cogeneration, air compressors or heavy industry can reach 1 MW or more per unit, and are configured as multi-unit arrays for large-scale projects. BOIXAC analyses process thermal requirements and specifies the right solution in capacity, dimensions and configuration for each installation.

Can fan-cooled equipment replace a cooling tower?

In many cases yes, especially when eliminating water consumption and the risks associated with open circuits.

The dry cooler is the solution that directly replaces the cooling tower in heat dissipation circuits. The advantages over the tower are: zero make-up water consumption, elimination of Legionella risks and biocide treatment requirements, no discharges, lower maintenance and operation in cold climates without risk of open circuit freezing. The main limitation is that the minimum achievable process fluid temperature with a dry cooler is always above ambient temperature (typically 5–10°C above outdoor dry bulb temperature), whereas a cooling tower can reach temperatures 2–4°C above wet bulb temperature. In most industrial applications where the process admits the return temperature of a dry cooler, the replacement is direct and economically favourable.