14 www. refrigerationandaircon. co. za RACA Journal I March 2026
TECH TALK events and exhibitions
MASTERING EVAPORATOR SELECTION
By Eamonn Ryan
From nominal duty to practical application.
At the October 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. Far from a matter of simply picking a unit from a catalogue, he stressed, it’ s a disciplined balance of science, standards and experience. Correct selection determines not only how well a system cools, but how efficiently, reliably and comfortably it performs over its lifetime.
The starting point, La Grange explained, is understanding nominal duty – the amount of heat the coil must remove to maintain the desired room temperature. That begins with four fundamentals: the room set-point, the suction temperature, the refrigerant and airflow characteristics.
Consider a customer wanting to keep a space at 16 ° C. With a ΔT( difference between room and suction) of 10K, the suction temperature must be 6 ° C. Using the manufacturer’ s conversion tables, this yields a correction factor of 1.6. Thus, an evaporator rated at 2.4kW under standard conditions would easily handle the duty required for those conditions.
Every manufacturer’ s catalogue – be it Thermocoil, Heat Exchange Centre or Colcoil – follows the same Eurovent-certified method, which allows direct comparison between brands under identical laboratory conditions. Eurovent defines standard test points: SC2 for medium-temperature rooms( air in at 0 ° C, suction-8 ° C) and SC3 for low-temperature storage( air-18 ° C, suction-25 ° C). These nominal values are the baseline, to be corrected for the refrigerant used and the coil’ s material.
Two key correction factors apply: F1, which adjusts for the refrigerant’ s latent heat of vapourisation, and F2, for fin or tube materials. Multiply the nominal duty by both to find true coil capacity.“ Each refrigerant absorbs heat differently. A kilogram of R290, for example, removes almost twice the heat of R22 when it boils,” said La Grange.
COIL DESIGN AND APPLICATION Evaporator coils are fin-and-tube heat exchangers on the lowpressure side of a direct-expansion system. As liquid refrigerant evaporates inside the coil, it absorbs heat from the room air and exits as superheated vapour ready for compression and heat rejection at the condenser.
14 www. refrigerationandaircon. co. za RACA Journal I March 2026