Free cooling
Also known as: natural cooling, compressorless cooling
Short definitionUsing cold outdoor air as a free source of cooling. When the air is suitable the compressor drops out, the work is left to the fan and pump, and the electricity bill shrinks noticeably in the cold months.
An extra finned coil is placed in front of the chiller’s condenser and the return water or glycol passes through it first. When the air is 1–2 K colder than the return water the coil pre-cools and the compressor does the rest. Once the gap widens and the air is 8–10 K colder than the required water, the compressor is not needed at all. In those hours consumption falls to a tenth, even a twentieth, of running on compressors.
In cold room work it does not pay off everywhere. In frozen storage and in rooms around 0 °C the gain is next to nothing; a processing hall at 10–15 °C and process water are where it belongs. In potato, onion and garlic stores the same idea is applied as night ventilation: if the outside is 2–3 K colder than the product and the humidity is suitable, the hatches open. The gain is calculated from hourly climate data. Glycol goes into the circuit so the outdoor coil does not freeze.