Truck-Trailer Refrigeration Equipment

1. CHAPTER Truck-Trailer Refrigeration Equipment 13 Instructor Name:(Your Name)

2. Learning Objectives • Describe air circulation through the cargo area. • List three different forms of short cycling. • Explain the operation of the thermostat. • Describe the refrigeration unit operation. • Explain the reasons for pre-cooling trucks and trailers. • Explain loading procedures to ensure proper circulation .

3. Learning Objectives (continued) • Describe cargo floor construction. • Explain a pre-trip inspection. • Describe the advantages of multi-temperature refrigeration units.

4. Trailer Refrigeration Unit

5. System Components • Engine- Typically a four cylinder diesel. • Compressor- Range from 2 to 4 cylinder. • Condenser- Dissipates heat from trailer to ambient air. • Thermostatic Expansion Valve- Fixed orifice, externally equalized. • Evaporator- Absorbs heat in the trailer. • Microprocessor- Brain of unit. Controls all aspects of refrigeration and heating process.

6. Typical Refrigeration Engine and Microprocessor

7. System Components (continued) • Box Temperature- The actual temperature in the storage unit. • Set Point- Optimum temperature to maintain product. • Thermostat- Sets the temperature that the equipment will maintain. • Refrigerant- Chemical used to absorb and dissipate heat in the storage area.

8. Trailer Refrigeration System Layout

9. Trailer floor Construction • Fabricated from Aluminum • Forms ductwork under cargo for air circulation • Must be kept free from debris that can impede air flow

10. Multi Temperature Refrigeration Units • May have up to three units. • Each unit has its own evaporator and thermostat. • Unit can store fresh, frozen and dry goods together.

11. Multi Temperature Trailer

12. Pre Cooling Products • Product must be cooled to the holding temperature prior to loading trailer. • Trailer refrigeration equipment is designed to maintain temperature of product not cool it down. • Pre cool the trailer prior to loading. • Shut down refrigeration unit while loading to prevent refrigerated air from escaping.

13. Proper Loading Procedures • Pallets must be loaded so skids allow air flow fore and aft in trailer. • Product must be kept away from walls to allow air flow around all sides. • Ample air space must be allowed between load and ceiling. • Air space must be left between cargo door and cargo. • Air space must be left between front bulkhead and cargo.

14. Proper Pallet Placement

15. Proper Cargo Loading Technique

16. Improper Loading of Cargo

17. Short Cycling • Cargo is blocking units discharge air flow. • Cold air is routed back to air inlet. • Thermostat thinks it has reached set point and switches to heat mode. • Warm air flow is blocked and routed back to air inlet. • Thermostat thinks it has reached set point and switches to cool mode. • Process continues over and over, “Short Cycling.”

18. Auto Stop/Start • Auto stop/start used by most equipment today. • Constant run mode still available. • Constant run mode, unit cycles between heat and cool mode. • Auto stop/start mode, unit will shut down once set point is reached and programmed parameters are met. • Programmed parameters- unit must run long enough to charge battery and warm the engine. • Unit stays off until box temperature reaches preset temperature.

19. Summary • Microprocessors control all aspects of refrigeration and heating cycles. • Modern advances in technology allow distribution to market fresh fruit and vegetables any time of year. • Loads must be pre cooled to remove residual heat and humidity. • The box must be pre cooled to remove residual heat and humidity.

20. Summary (continued) • Correct loading is essential to product quality. • Discharge air must be able to circulate freely around all side of the product. • Rising fuel costs have contributed to the technology for auto stop/start. • The auto stop/start feature is a huge financial savings for the company using it , as well as a way of conserving our natural resources.