By Eamonn Ryan
At a SAIRAC Cape Town Centre TechTalk, Marius la Grange – general manager of Thermocoil Cape Town and a past SAIRAC president – took delegates through the fine art of choosing the right evaporator. This is part three of a three-part series.
For a freezer room at -18°C suction -25°C using R404A and a 3.05kW duty, redundancy is key. A single-fan evaporator could suffice, but two smaller fans ensure continued operation if one fails – crucial when product loss could be catastrophic.
In a 5m² ice-cream freezer at -22°C, the corrected nominal duty might reach 2kW, yet coil size and airflow remain critical. Even small installations must balance spatial fit, circulation and defrosting intervals to prevent temperature swings.
Fin material determines corrosion resistance and hygiene. Aluminium fins are cost-effective and standard; copper suits corrosive environments such as spice processing; hydrophilic coatings improve condensate drainage and inhibit corrosion while preventing droplets from spitting. “Hydrophilic fins act like a treated car windscreen, water slides straight off,” La Grange said.
Air velocity above 2.5m/s can eject droplets into the room, wetting product and wasting cooling energy. Remedies include lowering fan speed via delta wiring or using multi-fan units to distribute airflow and reduce velocity across each coil.
Integrating design, comfort and maintenance
Selecting the right evaporator extends beyond the mathematics of nominal duty and correction factors. It requires awareness of the physical environment, the products stored and the people using the space. Dual fans offer redundancy; dual discharge designs improve worker comfort; easy-access coils simplify maintenance.
Compressor matching is another step: once the corrected evaporator duty is known, the compressor can be sized to maintain the required suction conditions. Regular cleaning is essential to prevent fouling, though aggressive chemicals should be avoided on aluminium or coated fins.
La Grange reminded engineers that refrigeration design lives as much in the field as on paper. “Your catalogue and your ΔT tables give the numbers, but the real skill lies in reading the room – literally. Watch how air moves, how people work, how frost forms. That’s what separates good systems from great ones.”
Ultimately, evaporator selection is an exercise in balance: between nominal duty and practical performance, between theory and site reality. By combining accurate load calculations with understanding of ΔT, refrigerant behaviour, airflow, material and maintenance constraints, engineers can design cold rooms that are efficient, reliable and comfortable. Whether cooling a prep area, a general freezer or a precision ice-cream store, applying these principles ensures optimal product integrity and long-term system durability.
As La Grange concluded, “When you get the evaporator right, everything else in the system follows.”