Three different situations
If cooling air exhausts freely into the room, much of the heat stays inside. With exhaust ducted directly outside, the main concerns are residual heat and the required incoming air. With water cooling, some heat leaves through the water circuit, but the room still needs assessment. The share depends on the design and arrangement of the specific package.
The fan must overcome resistance
The heat balance determines flow, not automatically the right fan. Ducts, bends, louvres, filters and silencers create resistance. Verify the fan's available external static pressure and prevent recirculation of its own hot exhaust. Waste heat recovery can change the balance, but operation without heat demand must still be addressed. Winter operation must respect the equipment's minimum allowable temperatures.
What to check in practice
- Determine the heat actually released into the room.
- Use a relevant summer inlet temperature, not the annual average.
- Verify grille free area and pressure losses along the whole path.
Example scenario
For a room heat load of 20 kW and allowable air temperature rise of 10 K, using a density of 1.2 kg/m³ and specific heat capacity of 1,005 J/(kg·K) gives approximately 6,000 m³/h. This is an illustrative heat balance, not a fan selection.
What to watch out for
- Confusing total input power with residual room heat when exhaust is ducted outside.
- Sizing a grille by its outside dimensions without considering free area.
- Enclosing a compressor to reduce noise without ensuring cooling.
What if it is hotter outside than the allowable room temperature?
Ventilation with outdoor air alone cannot meet that requirement. The supply source must change, heat must be removed another way, or suitable active cooling must be used. More airflow alone cannot cool below the inlet temperature.