How Does a Ripening Air Cooler Work

Ripening air cooler is a dedicated direct‑expansion evaporator unit cooler for fruit ripening rooms (banana, avocado, tomato). Its core difference from standard cold‑storage coolers: operate at higher evaporating temperature, small coil‑to‑air temperature difference (ΔT) to keep high room humidity, avoid fruit dehydration while removing respiration heat generated by ripening fruits.

Main Components

• Evaporator coil (tube‑fin heat exchanger)

• Fans (EC variable‑speed or AC fans)

• Electronic expansion valve (EEV)

• Defrost system (hot‑gas or electric defrost)

• Drain pan & drain pipe

Step‑by‑Step Working Principle

1. Refrigeration cycle heat absorption Low‑pressure low‑temperature liquid refrigerant flows into the evaporator coil. It absorbs heat from circulating room air and evaporates into gas.

Ripening mode key point: Evaporating temperature is kept high (e.g. +7 °C for banana storage), so coil surface is only slightly colder than room air. Small ΔT limits water‑vapour condensation on fins; most moisture stays in the air to maintain 90‑95% RH.

2. Air circulation by fans Fans draw warm humid room air (loaded with fruit respiration heat) across the cold coil. Air is gently cooled, then blown back into the ripening room and circulates around fruit pallets. EC fans continuously adjust rotation speed: keep low air velocity (0.5‑1.5 m/s) over fruits to prevent surface moisture loss, while ensuring uniform temperature and ethylene gas distribution across the whole room.

3. Remove fruit respiration heat Ripening fruits release large amounts of respiration heat. The cooler continuously takes away this heat, stabilises room temperature and prevents local hot spots which cause uneven ripening.

4. Condensate drainage Only limited water vapour condenses on coil fins. Condensed water flows down into insulated drain pan and drains out through drain pipe, preventing water dripping onto fruits (mould risk).

5. Defrost cycle (when coil builds frost) Under high‑humidity ripening conditions, thin frost may form on fins over time.

• Hot‑gas defrost (preferred): Hot high‑pressure refrigerant gas from compressor discharge is diverted into the coil to melt frost gently. Fans stop or run at low speed during defrost. Minimum temperature & humidity fluctuation inside room.

• Electric defrost: Electric heaters heat the coil to melt ice, but causes obvious RH drop.

6. Expansion valve controls evaporating temperature EEV precisely adjusts refrigerant flow rate to hold stable evaporating temperature. When switching fruit types (banana / avocado / tomato), the controller changes EEV setting to get target Te and ΔT.