An apparatus to refrigerate the cargo space of delivery vehicles. It provides an
environmentally friendly alternative to conventional mechanical a / c and
refrigeration units. Cooling is provided by controlled
evaporation of a liquefied gas such as CO.sub.2 or
nitrogen. Defrost and heating requirements, if needed, are provided by hot engine
coolant or by electric heaters powered from the vehicle electrical
system.
Airflow for the
evaporator and for circulation in the temperature controlled space is provided by a blower which is mechanically or electrically driven from vehicle power. This invention can also be applied to multi-
temperature control applications. The apparatus is compact and is particularly suited for small inner city delivery vehicles. FIG. 1: The sketch shows an inner city delivery
truck for which this invention is most suitable. Refrigerated goods are placed in roller cages that are designed to maximize cargo hauled by use of roller cages that extend to within 2 inches of the ceiling. The
evaporator section of this invention is mounted at or near the front wall of the
truck and is separated from the cargo by a vertical bulkhead. The conditioned air is delivered at the bottom of the
truck to avoid top freeze of perishable cargo that is in close proximity to the ceiling. FIG. 2: This shows the
piping schematic and is similar to the invention described in U.S. Application Serial No. 60 / 238,929 (the '929 application) incorporated herein by reference. FIG. 2 shows the engine
coolant coil located ahead of the CO.sub.2 coil in the direction of
airflow. This prevents the coldest air from coming in contact with the engine
coolant--in the cooling mode the air leaving the CO.sub.2 coil can be as low as -50.degree. F. for frozen load applications and this may cause the engine coolant to start freezing. Arrangements must be made to circulate air between the two coils in defrost mode. One means to accomplish this is to place a
damper at the outlet of the
evaporator section and run the fans. The
damper would be closed during defrost. Another method is to place the engine coolant coil on the
discharge side of the CO.sub.2 coil and use a
cut-out switch if the engine
coolant temperature drops below a predetermined value. In this arrangement there is no need for the
damper arrangement as the heat will rise to melt any
frost on the CO.sub.2 coil. If electric heat is used for defrost and heating freezing of the engine coolant is not a concern and the heaters can be fastened to the
discharge side of the CO.sub.2 coil. An electric stand-by mode can be provided to power the
system for cooling, heating and defrost when the vehicle is parked with the engine off. A plug-in electrical cable can provide the power needed for the controls, the fans and for heating and defrost. The figure shows the electric heaters attached on the
discharge side of the CO.sub.2 coil. Operation: Detailed description is in the '929 application except for the following: The evaporator section is designed for vertical installation to maximize cargo space. Air is discharged at the bottom but may be a conventional top discharge if needed for specific applications. Conventional methods can be used to provide defrost and heating. If engine coolant is used for a heat source, it is preferable to thermally isolate the CO.sub.2 coil from the engine coolant coil to avoid freezing the coolant. The evaporator blower may be located on the inlet side of the coils rather than as shown in the figures. Unique Features: 1. Absence of a conventional condensing section on the exterior of the vehicle makes this an ideal
refrigeration unit for small inner city delivery vehicles. Many of the truck cabs are now almost full height (same as the truck body) and there is limited space for the condensing section. 2. Cold plates can be used and still maximize cargo cube. However, this invention has 30-40% less weight than comparable "
cold plate" systems. 3. Other features are described in the '929 application.]