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HVACR317 - Refrigeration

HVACR317 - Refrigeration. Refrigerant Cycle. Refrigerants. Compressors are not meant to run in a vacuum. Running a compressor in a vacuum will damage the windings. Refrigerants provide the cooling for compressors. Refrigerants. At atmospheric pressure, water boils at 212 ° F.

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HVACR317 - Refrigeration

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  1. HVACR317 - Refrigeration Refrigerant Cycle

  2. Refrigerants Compressors are not meant to run in a vacuum. Running a compressor in a vacuum will damage the windings. Refrigerants provide the cooling for compressors.

  3. Refrigerants At atmospheric pressure, water boils at 212°F. If the pressure drops, the boiling point will drop as well - for example, in higher altitudes.

  4. Refrigerants All refrigerants have a specified boiling point temperature at a specified atmospheric pressure. Example 1: R134A at 0 psig will boil at -14°F. Example 2: R12 at 0 psig has a boiling point of -20°F. So, knowing the boiling point is at 0 psig, a chart can be created to show the boiling point at other pressures.

  5. Using Temp / Pressure Chart The chart on the next slide is the temperature / pressure chart. Find the column for R134A, and locate .1 psig on the column. Look to the left and find the temperature. R134A boils at -15°F at atmospheric pressure. Most systems do not need to run at temperatures this cold so the pressures are increased (by the use of a compressor), which makes the boiling point increase.

  6. Temperature Pressure Chart

  7. CFCs and HCFCs CFCs ChloroFluoro Carbons Old refrigerants being phased out. Contain chlorine HCFCs HydroChloroFluoroCarbons Less harmful Contains some hydrogen

  8. HFCs and Oils HFCs HydroFluoroCarbon Newer refrigerants No damage to Ozone layer Refrigeration Oils Lubrication for compressors Polyol Ester & Alkyl Benzene are synthetic oils.

  9. Refrigerant Containers Color Coded Containers Refer to your handout from National Refrigerants. You must know the colors for R22, R134A, R410A, R409A, R502 and R12. The oils used are specific for the type of refrigerants. Take care not to use the wrong oil with the refrigerant.

  10. System Components System Components Consist of the Following: Compressor Condenser Metering Device Evaporator Coil Liquid Line Suction Line Filter Drier Sight Glasses

  11. Compressor Compressor Pumps or circulates the refrigerant through the system. The compressor converts low pressure vapor refrigerant to high pressure vapor refrigerant. The compressor does not pump liquid.

  12. Condenser • Condenser: • Rejects heat from the system. • Condenses high pressure vapor into high pressure liquid refrigerant approximately 30F above ambient temperature.

  13. Metering Device Metering Device: Controls the flow of refrigerant entering the evaporator. Restricts the flow of refrigerant which starts the boiling process. (Almost like a resistor in electrical circuits). TXV is a type of metering device. TXV stands for Thermostatic Expansion Valve.

  14. Evaporator Coil & Liquid Line Evaporator Coil: Absorbs heat from the medium being cooled. Evaporates the refrigerant into a 100% low pressure vapor. Liquid line: Carries the high pressure liquid refrigerant from the condenser to the metering device.

  15. Suction Line Suction Line: Carries the low pressure vapor from the evaporator to the compressor inlet.

  16. Filter Dryer Filter Dryer: Located on the liquid line and removes the moisture and/or debris from the system. The drier material is made out of Silica gel or a molecular sieve which both filter and absorb moisture. The liquid line filter should be replaced any time the system is opened.

  17. Filter Dryer Filter Dryer, cont’d Special cleanup driers and suction line “core type” driers are usually installed on systems that are badly contaminated. Make sure you are aware of the direction of the arrow on filter driers. Most are not bi-directional.

  18. Sight Glasses Sight Glass Located in the liquid line. Allows a view of the refrigerant flowing in the system. Some sight glasses have a moisture indicator on them to let you know if moisture is in the system. Do NOT rely on the sight glass to charge a system. A clear sight glass can mean the system is either empty or full.

  19. System Components Sight Glass, cont’d DO NOT charge or diagnose a system by the sight glass. Always use the gauges. Customers will call and complain about “seeing bubbles in the sight glass” and assume it is a low charge. You cannot rely on that. The only correct way to diagnose a refrigeration system is with Superheat and subcooling.

  20. Refrigerant Cycle Sequence Refrigerant leaves the compressor as a high pressure vapor in the discharge line. Heat from the compressor and the refrigerant is released in the condenser coil. At this pressure, the boiling point is MUCH higher than the outdoor temperature (ambient air).

  21. Refrigerant Cycle Sequence As the heat is removed from the refrigerant, it starts to condense to a liquid state. This is the heat of condensation. Once the refrigerant is 100% liquid, a sensible heat change occurs as the liquid subcools.

  22. Refrigerant Cycle Sequence The liquid line now carries the refrigerant to the metering device. The refrigerant is forced through the pinhole in the metering device. Flash gas occurs (80% liquid, 20% vapor) as the refrigerant exits the metering device into the evaporator coil.

  23. Refrigerant Cycle Sequence Latent heat of evaporation now occurs in the evaporator coil as the refrigerant boils off. When the refrigerant is 100% vapor, a sensible heat increase will further heat the vapor (this is superheat). The refrigerant returns to the compressor through the suction line.

  24. Superheat Defined Superheat: A sensible heat change that occurs in approximately the last pass of the tubing in the evaporator coil. It is a sensible heat gain once the latent heat change has been completed. The latent heat change is the liquid changing to gas. When superheat is normal the heat transfer in the evaporator coil is working properly.

  25. Subcooling Defined Subcooling: Sensible heat change in the condenser coil following the change of state. After the condenser coil completely condenses the high pressure - high temperature vapor to high pressure liquid, the temperature should drop an additional 10 - 20°F as it enters the liquid line. This additional drop is called "subcooling."

  26. Additional Notes Flash Gas: Right after the metering device. 80% liquid and 20% vapor. Saturation Point: The point at which the refrigerant is 100% liquid or 100% vapor. The liquid saturation point is in the condenser. The vapor saturation point is in the evaporator.

  27. Additional Notes It is important to remember that refrigerant is NEVER used up. If it is not in the system, there must be a leak.

  28. Refrigerant Cycle Diagram Compressor Filter Drier Evaporator Metering Device Condenser

  29. Refrigerant State Diagram VAPOR Filter Drier LIQUID

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