200 Meat refrigeration 品品杀工 8642 Amount of infiltration Fig 9.5 Heat extracted by the refrigeration plant during the standard journey for a well, and a poorly sealed van(source: Gigiel, 1998) door is closed is a relatively small proportion of the total refrigeration load In this vehicle, fitted with a nominal 2kW cooling system, the state of the seals did not cause the temperature of the food to increase to more than 5° C during the journey 9.3.4.3 Weight of fittings and thermal mass of lining The weight of the fittings and the thermal mass of the lining form a size able refrigeration load and take a finite amount of time to cool. However, n a sales van this normally takes place late in the evening or in the early hours of the morning when ambient temperatures are low and no other loads are imposed on the van. The load is therefore smaller than the size of the refrigeration plant fitted and the short pull down time from 28 to 5C would not warrant keeping the refrigeration system running all night. However, if the vehicle was in continuous use for the transport of foods at different temperatures(chilled and frozen) then pull-down times between changing loads could be a serious disadvantage. 9.3.4.4 Door openings The heat extracted from a closed van is very small(Fig. 9.6). Door open ings greatly increase the heat load and, when the van engine drives the refrigeration system, this extra heat must all be removed during the period when the van is moving. Several factors interact when the number of door openings increases. The complete journey takes longer and during the extended journey the ambient temperature and the solar radiation on the van is different from the early part of the journey. If the length of time that he door is left open at each stop is also increased from 5 to 10min then the temperature of the air around the food in the van increases more during each stop. The refrigeration plant therefore operates at a higher evaporatdoor is closed is a relatively small proportion of the total refrigeration load. In this vehicle, fitted with a nominal 2 kW cooling system, the state of the seals did not cause the temperature of the food to increase to more than 5 °C during the journey. 9.3.4.3 Weight of fittings and thermal mass of lining The weight of the fittings and the thermal mass of the lining form a size￾able refrigeration load and take a finite amount of time to cool. However, in a sales van this normally takes place late in the evening or in the early hours of the morning when ambient temperatures are low and no other loads are imposed on the van. The load is therefore smaller than the size of the refrigeration plant fitted and the short pull down time from 28 to 5 °C would not warrant keeping the refrigeration system running all night. However, if the vehicle was in continuous use for the transport of foods at different temperatures (chilled and frozen) then pull-down times between changing loads could be a serious disadvantage. 9.3.4.4 Door openings The heat extracted from a closed van is very small (Fig. 9.6). Door open￾ings greatly increase the heat load and, when the van engine drives the refrigeration system, this extra heat must all be removed during the period when the van is moving. Several factors interact when the number of door openings increases. The complete journey takes longer and during the extended journey the ambient temperature and the solar radiation on the van is different from the early part of the journey. If the length of time that the door is left open at each stop is also increased from 5 to 10min then the temperature of the air around the food in the van increases more during each stop. The refrigeration plant therefore operates at a higher evaporat- 200 Meat refrigeration 20 18 16 14 12 10 8 6 4 2 0 good bad Amount of infiltration Heat extracted (MJ) Fig. 9.5 Heat extracted by the refrigeration plant during the standard journey for a well, and a poorly sealed van (source: Gigiel, 1998)