4.9.2 Road vehicles Refrigerated road vehicles fall into two basic categories. Firstly, there are large semi-trailers, with refrigeration units that can be run independently of the tractor unit. Secondly, there are rigid-bodied vehicles of various sizes, which may have independent refrigeration units, or may have units driven from the vehicle engine or axles, or may depend on eutectic storage media. Semi-trailers are used for long-distance or bulk movements, generally with only one or a few destinations Journey times may vary from two hours for supermarket distribution to several days for fresh produce transportation. A typical arrangement is shown in Fig. 4.6 Whilst most such vehicles use diesel engine drives with optional electric alternatives, some use total-loss refrigerant tanks (liquid nitrogen or carbon dioxide)to reduce both capital cost and noise levels in sensitive areas In most developed countries, semi-trailers are designed for use in ambient mperatures of 30C or above, with thermal insulation with overall value of 0.7W/m*K or better. If frozen goods may also be carried, insulation of less than 0.4 W/m*K would be used. Increasingly, multi-purpose multi-compartment vehicles are being produced, capable of carrying frozen, chilled and fresh produce simultaneously in different compartments Rigid-bodied vehicles vary from large vehicles very similar in use to the emi-trailers to small delivery vehicles for multiple deliveries of chilled foods to corner shops. Refrigeration units may be driven by diesel or electric motors, or by hydraulic drive from the vehicle chassis, or may be based on either total-loss or eutectic systems. The latter two are more often used for frozen food transport being relatively difficult to control at chilled temperatures. Delivery vehicles may require walk-in access for order selection from fixed shelving, and may ave to operate with large numbers of daily door openings. Legislation such as the UK food safety regulations(Anon. 1995a) has provided the impetus for much development of vehicle design to meet increasingly stringent temperature requirements Air cooler Air supply duct (canvas) 吧 refrigerant condenser Air return Fig. 4.6 Schematic arrangement of refrigerated semi-trailer4.9.2 Road vehicles Refrigerated road vehicles fall into two basic categories. Firstly, there are large semi-trailers, with refrigeration units that can be run independently of the tractor unit. Secondly, there are rigid-bodied vehicles of various sizes, which may have independent refrigeration units, or may have units driven from the vehicle engine or axles, or may depend on eutectic storage media. Semi-trailers are used for long-distance or bulk movements, generally with only one or a few destinations. Journey times may vary from two hours for supermarket distribution to several days for fresh produce transportation. A typical arrangement is shown in Fig. 4.6. Whilst most such vehicles use diesel engine drives with optional electric alternatives, some use total-loss refrigerant tanks (liquid nitrogen or carbon dioxide) to reduce both capital cost and noise levels in sensitive areas. In most developed countries, semi-trailers are designed for use in ambient temperatures of 30ºC or above, with thermal insulation with overall value of 0.7 W/m2 K or better. If frozen goods may also be carried, insulation of less than 0.4 W/m2 K would be used. Increasingly, multi-purpose multi-compartment vehicles are being produced, capable of carrying frozen, chilled and fresh produce simultaneously in different compartments. Rigid-bodied vehicles vary from large vehicles very similar in use to the semi-trailers to small delivery vehicles for multiple deliveries of chilled foods to corner shops. Refrigeration units may be driven by diesel or electric motors, or by hydraulic drive from the vehicle chassis, or may be based on either total-loss or eutectic systems. The latter two are more often used for frozen food transport, being relatively difficult to control at chilled temperatures. Delivery vehicles may require walk-in access for order selection from fixed shelving, and may have to operate with large numbers of daily door openings. Legislation such as the UK food safety regulations (Anon. 1995a) has provided the impetus for much development of vehicle design to meet increasingly stringent temperature requirements. Fig. 4.6 Schematic arrangement of refrigerated semi-trailer. 92 Chilled foods