RACA Journal I March 2026 www. refrigerationandaircon. co. za 15
TECH TALK
Medium-temperature rooms – such as dairies or produce stores – typically use 4mm fin spacing to maximise surface area and heat transfer. Freezers, operating at much lower temperatures and higher humidity, require 7mm spacing to reduce frost build-up and allow longer intervals between defrosts.“ The closer the fins, the greater the heat transfer – but also the quicker the icing,” La Grange warned.
Misunderstanding the temperature regime can be costly. A butchery cold room around 0 ° C is
The SAIRAC Cape Town Centre TechTalk commences. medium-temperature, but a freezer holding meat or ice cream must maintain at least-18 ° C. One These are popular because technicians can inspect them client, he recalled, stored frozen pineapple juice at-10 ° C; the easily for frost build-up. The compromise is shorter air throw, enzymes remained active and burst the drums within weeks. making them better suited to beverage displays or small rooms than large freezers.
MATCHING CONDENSERS AND EVAPORATORS Evaporator selection cannot be separated from condenser choice. In practice, contractors and consultants often select both. The same logic and correction factors apply: refrigerant, material and operating temperatures determine the adjusted duty.
For instance, an R134a system( F1 = 0.91) with copper fins( F2 = 1.03) yields an overall correction of 0.94, meaning the coil delivers 94 % of its nominal capacity. Using the Eurovent charts, if the room is 0 ° C and suction-8 ° C( ΔT = 8K), the nominal rating can be applied directly.“ Once corrected, you simply choose the model that meets or slightly exceeds the required capacity,” he said. A Thermocoil TE-MB 025 B3-4, a three-row twin-fan coil with 4mm fins, for example, delivers about 2.7kW against a 2.55kW need, comfortably within margin.
Physical fit and maintenance access often dictate the final choice. Compact bakeries or narrow freezer rooms may require low-profile, angled coils from the HDR or HCR ranges.
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“ The starting point, La Grange explained, is understanding nominal duty – the amount of heat the coil must remove to maintain the desired room temperature.”
RACA Journal I March 2026 www. refrigerationandaircon. co. za 15