Prepared by Roland Duquesne Thermo King Corporation

Presented by Ronnie Meechan: GEA Refrigeration Africa

Cool Chain Association

Introduction: Ingersoll Rand-Thermo King-GEA Refrigeration Africa

Heat sources

Some best practices

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GEA Refrigeration Africa

• Total staff complement of ±320

• 12 Branches

Objective of transport refrigeration

- Extend storage and shelf life of product

- Maintain quality of product

- Reduce the rate of decay

-Reduce deterioration by micro organisms

REMOVE HEAT

Main Heat sources

- Heat infiltration: Heat gain from outside the compartment

- Service load: Heat gain from doors openings, etc…

- Product load: Heat gain from cargo: respiration, etc…

- Pre-cooling equipment: Residual heat in the insulation, air in trailer, etc…

- Product Pre-cooling: Heat in product if not loaded at correct temperature

- Other factors

Heat Infiltration

Heat infiltration through the wall of the loading area through convection,

Q convection = k*A*ΔT/L = Kf*A*ΔT

Example of a std insulated trailer at ambient temp of 38c and inside 0c

Kf= 0.02/0.0762

A= 166.82 m2ΔT= (38-0)

Qtot= 1663 watts

Heat due to service load

1) Heat gain/loss due to air exchange with air outside

Example doors are left open

Qa = (8/b)*V* ΔT*D*E*F*A*G

Example: std trailer with same ΔT as previously and 10 single door opening of

5 minutes each

Qa= 1788 watts

Heat due to service load

2) Heat residual in the trailer or box if not pre-cooled

3 factors: Inner lining of body

Insulation of body

Air in body

Example std trailer parked at 38c ambient

-Inner lining: 2543 watts

-Insulation: 624 watts

- Air: 400 watts

Total: 3567 watts

Heat due to service load2) Product Pre-cooling/Heating

To bring a product past the freezing point the heat to be extracted is the sum of

Qproduct = Qunfrozen+Qlatent+Qfrozen

Heat extracted to bring product to freezing point

The latent heat to freeze the product

Heat extracted to bring product to its final temperature

Example: a refrigeration compartment with setpoint at +13c

is loaded with 3000 kg of mangoes at +30c

specific heat of mangos: 3.559J/kg*K

Heat need to be extracted in 2 hrs

Qproduct = 3000*3559*23/2= 34107 Watts !!!

or with same conditions with a std reefer unit we would need

6 hrs !!!

Heat due to Product LoadProduct continue to give off heat after harvest = heat of respiration

Fruit –vegetables take in oxygen , releasing carbon dioxide and heat (See

ethylene slide)

Qr = Mp*R

Example: a refrigeration compartment with setpoint at +0c

is loaded with 3000 kg of strawberries at +0c

Qr = 3000/1000*44.4 = 133 Watts

Heat due to other factors

Loading: - sealed docks?; time to load?

Defrost events: - capacity of unit used to extract water from the air

- loss of capacity due to unit defrosting

Air exchange: - Air need to circulate properly to avoid hot/cold

spots. Air carries the heat to the evaporator to

remove the heat from compartment

Product loading: - pallets, boxes, stacking

Air exchangeMake sure air is not restricted

Best practices : 6 directions

Humidity is not covered in this section

Reminder: Link between ethylene and respiration to be detailled

There is a link between internal ethylene and CO2 - respiration

There is a minimum of ethylene concentration needed to induct rippening of the

fruit

The skin of fruit and surface exposed to air influences the ethylene content as

well as the release of it.

a few hours after harvest fruit already have detectable ethylene quantities.

The ethylene content rises when fruit approach the respiratory climate

The deterioration peak is when the fruit have softened and changed in colour

This process is also directly associated to production of CO2

Reminder: Link between ethylene and CO2 release for mangos

THANK YOU