Troubleshooting Cold Storage Problems


Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 202/732
Publication Date: 10/94
Order#: 94-083
Last Reviewed: 10/94
History: Original Factsheet
Written by: Hugh Fraser - Engineer, Horticultural Crop Protection and Post Harvest/OMAFRA

Table of Contents

  1. Introduction
  2. Problems

Introduction

There are hundreds of refrigerated storages in Ontario (Figure 1) used for short or long-term storage of fruits and vegetables (termed products in this Factsheet). Storages are used as a marketing tool to smooth out peaks and valleys in production, allow a more continuous supply to customers, and help maintain the quality of produce. Storages come in a vast array of sizes, layouts and construction methods, all of which are critical to their proper function.

This Factsheet lists some of the most common problems found in refrigerated storages, with possible causes and solutions.

Cold storage with some of the components discussed in this Factsheet.

Figure 1. Cold storage with some of the components discussed in this Factsheet.

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Problems

Problem: Some product is freezing

Possible Cause(s)
  • Heavy freezing air from evaporator coils is dropping on product
  • Poor airflow or container stacking arrangement, causing freezing, dead air spots
  • Product is touching, or is close to freezing walls
  • Product stacked too high near coils
Possible Solution(s)
  • Adjust coils to run at higher temperature; install baffles under coils to deflect cold air and allow it to warm up before hitting product.
  • Use smoke generator to find dead air spots; relocate coils or increase their fan capacity; install air tubes and/or extra circulation fans; layout containers to promote good air distribution.
  • Re-insulate, especially on concrete foundations; keep product away from cold walls.
  • Stack product lower, especially in direct airflow of evaporator coil fans.

Problem: Some product is shrivelling

Possible Cause(s)
  • Storage relative humidity too low
  • Vapour pressure differential too high; warm, moist product versus cold, dry air
  • Wooden containers and storage structure itself is drawing moisture out of the air and product
  • Products such as pome fruit appear wrinkled when slightly frozen
Possible Solution(s)
  • Install more coils so they can operate at a lower temperature difference between "cold" air leaving the coils and air that the product "feels"; this reduces air dehumidification; install humidification equipment that can supply ultra-fine or atomized mist; it's hard to put water back into desiccated product.
  • Remove field heat more rapidly and promptly after harvest so there is less vapour pressure difference between product and storage air, thus less incentive for moisture to leave the product, causing desiccation.
  • Wet the wooden containers before putting in long term storage; tests show that wooden bins can increase 10% in weight by absorbing moisture; wet plywood walls and floor as well.
  • See possible solutions under freezing; pome fruit that has been slightly frozen does not shrivel from moisture loss and will lose wrinkles when thawed.

Problem: Some product is sweating or has free water on it

Possible Cause(s)
  • Warm, moist air from recently placed product is hitting cold product
  • Outside air is hitting cold product after removal from storage
  • Defrost water from evaporator coils is dripping on produce
  • Humidification system droplets are too large
Possible Solution(s)
  • Keep "cold" product being stored for longer periods in separate room from "hot" product being cooled; install more refrigeration to reduce dramatic air temperature increases.
  • Allow product to warm up gradually; condensation is unavoidable if product is put directly into a warm, moist atmosphere.
  • Drain condensate away onto floor if possible to help humidify the storage.
  • Install humidification equipment that can supply ultra-fine or atomized mist.

Problem: Product is displaying premature ripening, discolouring, loss of leaves (plants)

Possible Cause(s)
  • Ethylene gas may be present
  • Storage temperature may be too high
Possible Solution(s)
  • Remove high ethylene producing fruits in storage area such as; apples, pears, cantaloupes, plums, peaches, apricots, muskmelons and tomatoes; avoid using forklifts that emit ethylene in the exhaust; thoroughly ventilate storage rooms before use.
  • Lower storage temperature.

Problem: Product has odours or off-flavours

Possible Cause(s)
  • Products nearby that readily transfer odours and/or off-flavours
Possible Solution(s)
  • Remove crops such as cabbage, rutabagas, celery, potatoes, onions, lettuce, or garlic.

Problem: Product is rotting

Possible Cause(s)
  • Product is too warm and is respiring and aging rapidly
  • Product damaged, overripe, or of poor quality before storage
Possible Solution(s)
  • Provide quick and uniform rapid cooling after harvest; maintain recommended temperature during the storage period.
  • Increase culling rates before storage; do not expect the storage to turn poor quality product into a top quality product with a long shelf life.

Problem: Walls and/or ceiling are condensating

Possible Cause(s)
  • Interior surfaces are colder than the room air hitting it.
Possible Solution(s)
  • Install more insulation to warm up wall surfaces above the room air's dew point; tighten up building; provide better airflow in these areas.

Problem: Walls and/or ceiling are mouldy

Possible Cause(s)
  • Surface temperatures and moisture level are ideal for mould growth
Possible Solution(s)
  • Install more insulation to warm up wall surfaces above the room air's dew point, tighten up building; provide better airflow in these areas; dry out room and clean and disinfect the cladding.

Problem: Walls and/or ceiling are rotting

Possible Cause(s)
  • Moisture migrating into wood cladding/structure
  • Improper installation of, or missing vapour barrier
Possible Solution(s)
  • Before reconstruction, determine why and how to prevent moisture from migrating in again.
  • Re-insulate if needed, possibly with different insulation; vapour barrier may not be advisable depending on use.

Problem: Ceiling is dripping

Possible Cause(s)
  • Poor attic ventilation allowing a build up of hot, moist air in attic
  • Insufficient attic insulation causing condensation which drips through the cracks
  • Improper installation of, or missing vapour barrier
Possible Solution(s)
  • Provide 1 m2 of unrestricted eave inlet area per 600 m2 of ceiling, with same unrestricted peak area, or mechanically ventilate @1 air change/2 minutes.
  • Add insulation to prevent the warm, attic side of the insulation from approaching the cold temperature of the storage below.
  • Vapour barrier location depends on vapour pressure drive direction; a vapour barrier may not be advisable depending on building use.

Problem: Floor is drying out even if floor is sprayed with water

Possible Cause(s)
  • Storage relative humidity is too low
  • Floors have cracks for water to escape
Possible Solution(s)
  • Install more coils so they can operate at a lower temperature difference between "cold" air leaving the coils and air that the product "feels"; this reduces air dehumidification; install humidification equipment that can supply ultra-fine or atomized mist; it is hard to put water back into desiccated product.
  • Flood floors to see if water runs away, especially along concrete foundation; seal if necessary.

Problem: Inside air temperature fluctuates during storage period

Possible Cause(s)
  • Thermostat not located properly and does not sense average room temperature
  • Airflow not uniform throughout storage
  • Evaporator coils have too large a temperature difference across them
  • Poor quality or insensitive thermostats
Possible Solution(s)
  • Install thermostats in average room airflow, usually in the return airflow to evaporator coils; relocate thermostats away from warm/cold walls, doors, lights, cold air leaving the coils, or hot product.
  • Use smoke generator to determine location of dead air spots; relocate evaporator coils or increase the capacity of their fans (if possible); install air tubes and/or extra fans; rearrange storage containers to allow more uniform airflow.
  • Lower the temperature difference across the evaporator coils; recognizing that this will result in a lower potential heat removal capacity.
  • Use good equipment since uniform temperature control is vital for maintaining product quality.

Problem: Inside air temperature is warmer than desired during storage period

Possible Cause(s)
  • Inadequate refrigeration
  • Insufficient insulation for summer use
  • Poor attic ventilation
  • Hot sunny days with dark, roof surface
  • Airflow not uniform or of insufficient capacity in storage
  • Poor thermostat location that senses cold temperatures
Possible Solution(s)
  • Install more refrigeration cooling capacity.
  • Install minimum R-20 in walls, R-24 in attic, R-12 on foundation; floors are seldom insulated in Ontario, but for year-round use, the cost can be justified.
  • Provide 1 m2 of unrestricted eave inlet area per 600 m2 of ceiling, with same unrestricted peak area, or mechanically ventilate at 1 air change/2 minutes.
  • Paint roof chalk-white and provide adequate attic ventilation, since attic temperatures can reach 60°C if the roof is a dark colour.
  • Use smoke generators to determine location of dead air spots; relocate evaporator coils or increase the capacity of their fans (if possible); install air tubes and/or extra fans; rearrange storage containers to allow more uniform airflow.
  • Install thermostats in average room airflow, usually in return airflow to evaporator coils; avoid locating thermostats on outside cold walls, near doors, or near the cold air leaving evaporator coils.

Problem: Inside air temperature is colder than desired during the storage period

Possible Cause(s)
  • Thermostat poorly located and senses warmer temperatures
  • Insufficient insulation for winter use
Possible Solution(s)
  • Install thermostats in average room airflow, usually in return airflow to evaporator coils; avoid location thermostats on outside warm walls, or near doors or lights.
  • Install minimum R-20 in walls, R-24 in attic, R-12 on foundation; floors are seldom insulated in Ontario, but for year-round use, the cost can be justified.

Problem: Inside air temperature is not uniform

Possible Cause(s)
  • Airflow not uniform or of insufficient capacity in storage
  • Short-circuiting of air directly back to the evaporator coils because of poor storage container arrangement
Possible Solution(s)
  • Use smoke generators to determine location of dead air spots; relocate evaporator coils or increase the capacity of their fans (if possible); install air tubes and/or extra fans; rearrange storage containers to allow more uniform airflow.
  • Avoid alleys/openings that allow air to simply by-pass product or storage containers; air will always take the easiest path and air must be forced to travel a meandering path to maximize cooling potential; use a smoke generator to inspect for short-circuiting.

Problem: The storage air smells bad or is difficult to breathe

Possible Cause(s)
  • Gases such as carbon dioxide or ethylene may be present in excessive quantities as a result of decay or respiration
Possible Solution(s)
  • Look for and dispose of decaying product; install a small exhaust fan that provides ventilation of 1 or 2 air changes/day; some newer storages (not built as Controlled Atmosphere storages) are very tight so there is no natural air-change ventilation.

Problem: Evaporator coils are icing up and run a lot of condensate

Possible Cause(s)
  • Coils running at too low a temperature
  • Defrost system not running properly
  • Storage relative humidity is high
Possible Solution(s)
  • Increase coil temperature; this may require larger capacity evaporator coils
  • Repair defrost system or install a more effective one.
  • Install more effective defrost method, since the relative humidity should be high for most cropsa.
  1. Some crops such as onions, garlic, or squash require lower humidities.

Problem: Electrical consumption is rising

Possible Cause(s)
  • Insulation is wet or missing
  • Higher volume of product being cooled than before
  • Product is entering storage hotter than in previous seasons
  • Building less tight or doors open more often
  • Malfunctioning refrigeration equipment
Possible Solution(s)
  • Correct moisture problem and re-insulate with an insulation that is more suitable for cold storages.
  • Install more refrigeration as crop production rises; one rarely has 'too much refrigeration capacity', but the system should be properly sized to reduce costs.
  • Earlier varieties and variable weather might mean harvested product is warmer, requiring more refrigeration capacity than before.
  • Re-tighten the building since they do become less tight over time; install flaps over access doors.
  • Get equipment serviced by a qualified refrigeration contractor familiar with the needs of farm produce.

For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca