Heat dissipation using fresh air
Table 12 provides an example of the design calculation for a fresh air cooling system with an external air temperature of 35°C and a relative humidity of 70%. Since the heat generated by the air supply fan also needs to be taken into account, the total amount of heat that must be dissipated is increased by this value.
This results in a required fresh air volume of approximately 60 m³/min for each 40' container. Some shipping companies, for example, P&O Nedlloyd, specify values of 100 m³/min in their construction regulations, since the maximum incoming air temperature in regions such as the Suez canal can be greater than 35°C. Germanischer Lloyd recommends 75 m³/min in their latest set of ventilation regulations and thus also assumes external temperatures above 35°C.

Design of an air cooling system for refrigerated
containers with mechanical air supply

Sources of heat
Number of refrigerated containers 100
  Quantity of heat per container: 10 kW
Container heat to be dissipated: 1,000.0 kW
Fresh air flow per container 60.0 m³/min
Air flow: 360,000.00 m³/h
Approx supply air fan capacity (same for return air): 163.64 kW 2,200 (m³/h)/kW
Total quantity of heat to be dissipated: 1163.64 kW

Heat dissipation
Incoming air temperature: 35 °C   PDs    5,621.6 Pa
Moisture content 80.0 % PD    4,497.3 Pa
Enthalpy on entry 110.27 kJ/(1+x)kg x 0.029287621 kg/kg
Specific heat
(per kg of air):
10.30 kJ/kg

Exit temperature: 44.73 °C
Exit moisture: 47.6 % PDs    9,448.4 Pa
Exit enthalpy: 120.56 kJ/(1+x)kg PD    4,497.3 Pa
Exit dew point: 31.0 °C
Air density: 1.13 kg/m³
Quantity of dissipated heat: 1,163.64 kW

Overall energy requirements
For powering the fans: 163.6 kW
Total 163.6 kW

Table 12: Energy equation for cooling with air

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