Unitec Refrigeration Services - Post-Harvest cooling technologies - hi humidity

By: Unitec Refrigeration Services  11-11-2011
Keywords: storage, Cooling, Relative Humidity

Airspray systems have been specially designed for quickly cooling most vegetables, fruit and flowers after harvesting or after ripening and then to maintain constant storage environments with ultra high humidities (96% to 98%). It is impossible to maintain these humidity levels with controlled humidifiers and conventional systems.

By nature, all freshly harvested produce at high temperatures deteriorates and dehydrates quickly; the need to immediately remove its field heat is vitally important if it is to keep its pre-harvested quality.  The Airspray post   harvest function of pressure cooling is designed to gain time by extending this life cycle enough for produce to arrive at the market and consumer in fresh and attractive conditions.

It is generally recognised that one hour lost in pre-cooling results in 8 to 24 hours lost in shelf life. Airspray systems are designed to remove field heat from the heart of produce in a cooling time within 1-6 hours with nominal cooling capacities from 8.5 kW to 160 kW to suit all growers’ requirements. Storage environments will be maintained with ultra-high humidities (96-98%) at constant room temperatures without any defrost period.

High humidity is the one common denominator for pre-cooling and storage of most fresh produce. It was thought, in the past, the 85% to 90% humidity levels, obtainable from conventional dry evaporation refrigeration systems, were adequate because of the common belief that a higher humidity would create mould and decay. This common misunderstanding arises from confusion of comparing free moisture against high humidity air. Produce being stored in a room at 90% humidity will lose moisture 6 times faster than in a room at 100%. Airspray Air Handlers are designed to achieve the essential 96-98% relative humidity levels that most varieties of fresh produce need.

Storage temperatures are maintained evenly throughout the chamber by positive air distribution. This is vital to prevent condensation on the produce and to prevent warm pockets collecting. Temperature fluctuations of several degrees that occur in storage atmospheres can cause condensation which very likely accelerates the incurrence of mould and decay. These fluctuations can usually be traced to evaporator defrosting and cycling of the refrigeration system, doors remaining open to the ambient atmosphere or to an overload of the refrigeration system due to a warmer incoming product. Only with carefully designed pressure cooling systems can these sensitive temperature fluctuations be avoided.


  • High capacity pressure cooling
  • High humidity storage rooms
  • Ripening Rooms (single and multi-tier)
  • De-greening rooms
  • S02 Gassing rooms
  • Cheese curing rooms
  • Mushroom growing rooms
  • Specialty Systems
  • Reduced weight loss
  • Even temperatures throughout storage rooms (Ducted air supply)
  • Pressure cooling capability
  • S02 scrubbing
  • Low noise operation 65-70 db (Backward curved fans)
  • Longer storage life
  • Fast product cooling

Keywords: Cooling, Relative Humidity, storage

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