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Unit 26
- 1. Heating, Ventilating, Air-C onditioning & Refrigeration Technology
- 2. SECTION 5 COMMERCIAL REFRIGERATION UNIT 26 APPLICATION OF REFRIGERATION SYSTEMS
- 3. UNIT OBJECTIVES Afterstudying 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. 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. Reach-in refrigerators with doors Open display case
- 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. Self-contained boxes havetheir own condensing unit
- 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. MULTIPLE EVAPORATORS ANDSINGLE- 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. Multiple evaporators connected toa single compressor
- 11. Rooftop air cooledcondenser Duct mounted coil Receiver 3-way heat reclaim valve Liquid line Compressor
- 12. Rooftop air cooledcondenser Receiver Heat exchanger Pump Liquid line Compressor Water tank
- 13. Return air fromthe structure Dampers Cooling coil Supply air to structure Mixed air Filters Blower Outside air Heat reclaim coil Primary heat source
- 14. MULTIPLE EVAPORATORS ANDSINGLE- 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. 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. Vent line Oil strainers Oil reservoir Oil separator Suction to compressors Discharge from Oil level regulators compressors
- 17. ADVANTAGES OF PARALLEL COMPRESSORS • Load matching • Diversification • Flexibility • Higher efficiencies • Lower operating costs • Less compressor cycling
- 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. LOAD MATCHING • Asthe 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. 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. 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. Condenser Secondary refrigerant (water) circuit Evaporator Pump Heat exchanger Primary refrigerant circuit SECONDAY FLUID REFRIGERATION SYSTEM (SIMPLIFIED)
- 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. 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. 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. Condenser Centrifugal pump Compressor Evaporator
- 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. 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. INTERCONNECTING PIPING INMULTIPLE 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. Refrigerated case Condensate System piping piping Piping chase
- 31. TEMPERATURE CONTROL OFTHE 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. TEMPERATURE CONTROL OFTHE 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. 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. Cooling Cooling Cooling Solenoid open Receiver Accumulator
- 35. Cooling Cooling Defrost Solenoid closed Receiver Accumulator
- 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. BACK-TO-BACK CHEST-TYPE DISPLAYCASES Evaporator coils Plenum Plenum
- 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. DISPLAY CASE/WALK-IN COOLER(PLAN VIEW) Merchandising displays Product Storage Walk-in cooler Customer access to product
- 40. CONTROLLING SWEATING ONTHE 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. 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. WALK-IN REFRIGERATION • Permanentlyerected – 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. EVAPORATOR LOCATION INA 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. CONDENSATE REMOVAL • Drainpan 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. Heat tape keeps the line warm Condensate line Condensate line pitched run to the downward outside of the cooler
- 46. REFRIGERATION PIPING • Standardinstallations 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. Quick-connect fitting on unit Pre-charged tubing line with quick-connect fitting
- 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. WATER COOLERS • Waterdispensed 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. 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. SUMMARY • Refrigerated casescan 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. SUMMARY • Compressors cycleon 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. SUMMARY • Secondary fluidis 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. SUMMARY • Evaporator pressureregulators 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. SUMMARY • Cabinet sweatingcan 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. SUMMARY • Refrigerant pipingcan 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