Unit 26


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Unit 26

  1. 1. Heating, Ventilating, A ir-C onditioning & Refrigeration Technology
  3. 3. UNIT OBJECTIVES After studying this unit, the reader should be able to• Describe the different types of display equipment• Discuss heat reclaim• Describe package versus remote condensing unit applications• Describe mullion heat• Discuss walk-in refrigeration applications• Describe basic vending machine operation• Describe basic refrigerated air-dry unit operation
  4. 4. REACH-IN REFRIGERATION MERCHANDISING• Available in high-, medium-, and low- temperature ranges• Open cases – Less efficient but are more appealing to the customer• Closes cases – More efficient but are less appealing to the customer
  5. 5. Reach-in refrigerators with doorsOpen display case
  6. 6. SELF-CONTAINED REACH-IN FIXTURES• Heat is rejected back into the store (good in the winter, bad in the summer)• Equipment can be moved around easily• Since each unit is separate, if one system breaks down the others are not affected• Condenser cleaning and condensate removal need to be addressed• Condensate can be used to help cool the compressor
  7. 7. Self-contained boxes have their own condensing unit
  8. 8. INDIVIDUAL CONDENSING UNITS• Only one system is affected when a breakdown occurs• Condensing units can be located outside or in an equipment room• Air temperature in the equipment room can be controlled with dampers• Rejected heat can be reused to heat the store in the winter
  9. 9. MULTIPLE EVAPORATORS AND SINGLE- COMPRESSOR APPLICATIONS (ADVANTAGES)• Compressor motors are more efficient• System heat can be captured for use in heating the store (heat reclaim)• First-stage heat controls the three-way heat reclaim valve• Parallel and series heat reclaim systems
  10. 10. Multiple evaporatorsconnected to a single compressor
  11. 11. Rooftop air cooled condenser Duct mounted coil Receiver 3-way heat reclaim valveLiquid line Compressor
  12. 12. Rooftop air cooled condenser Receiver Heat exchanger PumpLiquid line Compressor Water tank
  13. 13. Return air from the structureDampers Cooling coil Supply air to structure Mixed air Filters Blower Outside air Heat reclaim coil Primary heat source
  14. 14. MULTIPLE EVAPORATORS AND SINGLE- COMPRESSOR APPLICATIONS (DISADVANTAGES)• Refrigeration load cannot be easily matched• Starting of large compressors draws higher locked rotor amperage• Short cycling of large compressors• Increases power consumption• Small increases in load may cause large compressor to cycle on
  15. 15. PARALLEL COMPRESSOR SYSTEMS• Often referred to as rack systems• Uses two or more compressors• Connected with common suction and discharge headers and receiver• Compressors cycle on an off to satisfy the load of the system• If there are three compressors connected in parallel, only one compressor will operate during the lowest load period
  16. 16. Vent line Oil strainers Oil reservoir Oil separator Suction tocompressors Discharge from Oil level regulators compressors
  17. 17. ADVANTAGES OF PARALLEL COMPRESSORS• Load matching• Diversification• Flexibility• Higher efficiencies• Lower operating costs• Less compressor cycling
  18. 18. DISADVANTAGES OF PARALLEL COMPRESSORS• Leaks affect the entire rack – Large leaks will result in the failure of multiple remote units• Compressor burnouts affect the entire rack – One motor burnout can result in the formation of acid in the entire system – Extensive cleanup procedure required
  19. 19. LOAD MATCHING• As the load changes, the common suction pressure entering the compressor will vary• Actual load is sensed by a pressure transducer• Compressors will cycle on, cycle off, load, or unload depending on the load on the system• Systems can be even (same size compressors) or uneven (different size compressors)
  20. 20. SYSTEM PRESSURE REGULATORS (SPR)• Located between the condenser and the receiver• Utilizes a parallel receiver instead of a series receiver• Controls the amount of liquid in the active refrigeration system• On hot days, the SPR causes refrigerant to enter the receiver to maximize the condenser’s effective surface area
  21. 21. SECONDARY FLUID REFRIGERATION SYSTEMS• Primary HFC or HCFC refrigerant used to cool a secondary refrigerant• Secondary fluid is usually an antifreeze solution and is always a liquid• Secondary fluid is circulated to individual fixtures to absorb box heat• Heat exchange process then takes place between primary and secondary fluids
  22. 22. CondenserSecondary refrigerant (water)circuit Evaporator Pump Heat exchanger Primary refrigerant circuit SECONDAY FLUID REFRIGERATION SYSTEM (SIMPLIFIED)
  23. 23. ADVANTAGES OF SECONDARY REFRIGERANT SYSTEMS• Uses less refrigerant• Easier to install with less critical piping• Lower superheat in primary refrigerant circuit• Less complicated defrost cycles• Less maintenance• Only low-pressure fluid is located in the customer area of store
  24. 24. DISADVANTAGES OF SECONDARY REFRIGERANT SYSTEMS• Higher initial equipment costs• Added cost of secondary refrigerant pumping• Thicker and better insulation required on secondary loop• Higher cost for low-temperature secondary fluids
  25. 25. PRESSURIZED LIQUID SYSTEMS• Uses a small centrifugal pump to pressurize the liquid in the liquid line• Saturation temperature is raised while liquid temperature remains the same• Liquid will not flash into a vapor if it experiences a pressure drop in the line• Leads to lower condensing temperatures, head pressures, and compression ratios which increase efficiency
  26. 26. CondenserCentrifugal pump Compressor Evaporator
  27. 27. UNITARY STAND-ALONE REFRIGERATION SYSTEMS• Multiple compressor modules located close to display cases• Condensers are cooled by a closed loop fluid cooler• Can be used as to reclaim heat for heating the space or hot water• Refrigerant usage is reduced• Less piping required, fewer solder joints, reduced leak potential
  28. 28. EVAPORATOR TEMPERATURE CONTROL• Multiple evaporators may not operate at the same temperature• Evaporator pressure regulators can be used to maintain different pressures• EPR valves are located on all of the higher temperature evaporator circuits
  29. 29. INTERCONNECTING PIPING IN MULTIPLE EVAPORATOR INSTALLATIONS • Liquid and suction lines need to be run to remote condensing units • Suction lines need to be insulated • Lines can be run in a pipe chase • Lines can be run through individual plastic pipes for ease in replacement in case of a leak
  30. 30. Refrigerated caseCondensate System piping piping Piping chase
  31. 31. TEMPERATURE CONTROL OF THE FIXTURE – MEDIUM TEMPERATURE• Can be accomplished without interconnecting wiring between box and condensing unit• Planned off cycle defrost can be controlled from equipment room• Defrost for the boxes can be staggered so each box is defrosted at a different time
  32. 32. TEMPERATURE CONTROL OF THE FIXTURE – LOW TEMPERATURE• Heat must be furnished to each evaporator (either electric or hot gas)• Defrost cycles can be staggered• Heat from other boxes is used for hot gas defrost• Electric heat defrost is easier to troubleshoot
  33. 33. HOT GAS DEFROST• Discharge gas from the compressor is directed to the evaporator being defrosted• The other evaporators can remain in the cooling mode while one evaporator is being defrosted• Three-way valves are used to direct the hot gas to the defrosting evaporator• The evaporator in defrost is piped in parallel to the condenser
  34. 34. CoolingCoolingCooling Solenoid open Receiver Accumulator
  35. 35. CoolingCoolingDefrost Solenoid closed Receiver Accumulator
  36. 36. CHEST-TYPE DISPLAY FIXTURES• Reach-in equipment can have lids or be open type• Fresh vegetables and meat are usually in open-type cases• Evaporators are usually mechanical draft and are at the bottom of the display• Chest-type cases can have remote condensing units or be self-contained units
  37. 37. BACK-TO-BACK CHEST-TYPE DISPLAY CASES Evaporator coils Plenum Plenum
  38. 38. CLOSED-TYPE CHEST FIXTURES• Normally low-temperature boxes for ice cream and frozen foods• Lids are a barrier to the customer and are not popular• Upright, closed display with glass doors allow customer to see the product• Upright displays can often be loaded from inside the walk-in cooler
  39. 39. DISPLAY CASE/WALK-IN COOLER (PLAN VIEW) Merchandising displays Product Storage Walk-in cooler Customer access to product
  40. 40. CONTROLLING SWEATING ON THE CABINET OF FIXTURES• Sweating forms when the cabinet is below dew point temperature• Small (mullion) heaters prevent moisture from forming• Heaters can be controlled based on the humidity level in the store• Stores are kept cool to reduce load on the refrigeration equipment
  41. 41. MAINTAINING STORE AMBIENT CONDITIONS• In warm weather, the air-conditioning systems remove moisture• Less humidity in the store means less moisture on the evaporator coils• Reduced defrost time since less ice will form on the coils
  42. 42. WALK-IN REFRIGERATION• Permanently erected – Not intended to be moved – Larger walk-in boxes are permanently installed• Knock-down type – Constructed of insulated metal panels – Can be disassembled and moved if necessary – Equipped with interior safety catches to prevent someone from becoming locked inside
  43. 43. EVAPORATOR LOCATION IN A WALK- IN COOLER • Can be piped to remote condensers or can be package units • Located in the box so the cold air does not blow out when the door is opened • Some have a fan switch to turn the fan off when the door is opened • Some systems pump down when the door is opened
  44. 44. CONDENSATE REMOVAL• Drain pan should be piped to the outside of the cooler• On low-temperature applications, the drain line needs to be heated• Drain lines should be pitched downward to prevent trapping condensate
  45. 45. Heat tape keeps the line warm Condensate lineCondensate line pitched run to the downward outside of the cooler
  46. 46. REFRIGERATION PIPING• Standard installations require fittings, soldering, leak checking, evacuating• Line sets are pre-charged flexible lines with quick-connect fittings• Condensing unit and evaporator are also pre- charged and have quick-connect fittings• No soldering or evacuation is required• Long line sets can be coiled horizontally to aid in oil return
  47. 47. Quick-connect fitting onunit Pre-charged tubing line with quick-connect fitting
  48. 48. VENDING MACHINE REFRIGERATION• Self-contained refrigerated dispensing machines• Equipment is similar to domestic refrigerators• Evaporators operate below freezing• Usually equipped with low-ambient controls• Some have self-contained, removable systems• When a breakdown occurs, the entire unit can be replaced• Health switch – device that will disable the unit if the temperature of the storage area is too high
  49. 49. WATER COOLERS• Water dispensed through a bubbler• Can use bottled or city water as a source• Pressure-type systems use supply water pressure to dispense water• Water pressure regulator can be adjusted for proper flow• Evaporator is a small tank with the refrigeration lines wrapped around it• The water that goes down the drain is used to either cool incoming water or the refrigerant in the liquid line
  50. 50. REFRIGERATED AIR DRIERS• Process of dehydrating air, removing moisture• Air used in pneumatic controls must be dry• Air is cooled down below dew point to allow the moisture to condense• The evaporator in the heat exchanger operates just above freezing• Hot gas bypass provides a false load on the system to prevent freeze ups• The hot gas bypass is usually controlled by the suction pressure of the system
  51. 51. SUMMARY• Refrigerated cases can be either open or closed• Closed cases are more efficient than open cases• Self-contained units have their own compressor and are not affected if other systems fail• Larger compressors can be used to service multiple units and evaporators• Heat from multiple evaporator systems can be used to heat the store or domestic water• Parallel compressor (rack) systems use a bank of compressors to control multiple systems
  52. 52. SUMMARY• Compressors cycle on an off to satisfy the load of the system• Rack systems are more efficient than multiple units with individual compressors• Leaks in a rack system affects the entire system• Rack systems have the advantage of load matching• System pressure regulators utilize parallel receivers to adjust the amount of refrigerant in the active circuit• Secondary refrigerant systems use an HFC or HCFC refrigerant to cool a secondary liquid (usually a water/antifreeze mixture)
  53. 53. SUMMARY• Secondary fluid is circulated to the remote units• Heat exchanges take place between the remote unit and the secondary refrigerant as well as between the primary and secondary refrigerants• Secondary refrigerant systems require less maintenance than conventional refrigeration systems• Pressurized liquid systems use small centrifugal pumps to pressurize the liquid in the liquid line• Pressurized liquid systems operate with lower condensing temperatures, head pressures, and compression ratios which increase efficiency
  54. 54. SUMMARY• Evaporator pressure regulators can be used to maintain different pressures in multiple evaporator systems• Suction and liquid lines need to be field installed to connect the evaporator to the condensing units• Refrigerant lines can be run in pipe chases to provide access for servicing and repair• Medium temperature systems can be defrosted by random, planned or off cycle methods• Low temperature systems can be defrosted by hot gas or by external electric heaters
  55. 55. SUMMARY• Cabinet sweating can be reduced by mullion heaters• Evaporators should be located so that cool air is not blown from the box when the door is opened• Walk-in refrigeration systems can be permanently erected or knock-down units• Condensate must be removed from the box• Drain lines on low temperature systems should be heated to keep them warm• Condensate lines should be pitched to aid in the condensate removal
  56. 56. SUMMARY• Refrigerant piping can be accomplished with pre-charged line sets• Refrigerated vending machines are self- contained units• Evaporators on water coolers are small tanks with refrigeration lines wrapped around it• Refrigerated air driers are used to remove moisture from air used in pneumatic controls systems