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 two of a three-part series.
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. These are popular because technicians can inspect them easily for frost build-up. The compromise is shorter air throw, making them better suited to beverage displays or small rooms than large freezers.
La Grange added that design constraints frequently complicate maintenance: “In tiny bakery freezers, you sometimes have to remove the entire evaporator to replace a defrost heater. That’s not poor design – it’s just the reality of tight spaces.”
The importance of airflow
Airflow direction also affects performance. Drawing air through the coil, rather than pushing it, gives smoother, more uniform flow and better heat transfer: just as air-handling units place fans on the discharge side. “When air is drawn, it passes evenly through the coil instead of swirling around it,” he said.
Air movement must also serve people. In prep areas where staff work in light clothing, comfort matters as much as cooling capacity. A 30m² space at 15°C might require a 1.6kW duty, handled by a single-fan coil – but dual discharge models can distribute air more evenly, preventing drafts and cold spots.
Humidity adds another dimension. Air entering the coil typically has about 80% RH (Relative Humidity). Smaller ΔT values risk excessive dehydration of produce; larger ΔT values reduce moisture removal. Balancing ΔT maintains the right humidity for products such as lettuce or blueberries.