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SOUTH AFRICAN QUALIFICATIONS AUTHORITY 
REGISTERED UNIT STANDARD THAT HAS PASSED THE END DATE: 

Explain the operation of the vapour compression refrigeration cycle, and identify and explain the operation of the components and the associated controls, safety devices and defrost systems 
SAQA US ID UNIT STANDARD TITLE
9388  Explain the operation of the vapour compression refrigeration cycle, and identify and explain the operation of the components and the associated controls, safety devices and defrost systems 
ORIGINATOR
SGB Air-conditioning Refrigeration and Ventilation 
PRIMARY OR DELEGATED QUALITY ASSURANCE FUNCTIONARY
-  
FIELD SUBFIELD
Field 06 - Manufacturing, Engineering and Technology Engineering and Related Design 
ABET BAND UNIT STANDARD TYPE PRE-2009 NQF LEVEL NQF LEVEL CREDITS
Undefined  Regular  Level 3  NQF Level 03  14 
REGISTRATION STATUS REGISTRATION START DATE REGISTRATION END DATE SAQA DECISION NUMBER
Passed the End Date -
Status was "Registered" 		 2001-06-13  2004-06-13  SAQA 0836/01 
LAST DATE FOR ENROLMENT LAST DATE FOR ACHIEVEMENT
2005-06-13   2008-06-13  

In all of the tables in this document, both the pre-2009 NQF Level and the NQF Level is shown. In the text (purpose statements, qualification rules, etc), any references to NQF Levels are to the pre-2009 levels unless specifically stated otherwise.  

This unit standard is replaced by: 
US ID Unit Standard Title Pre-2009 NQF Level NQF Level Credits Replacement Status
116709  Explain the operation of the vapour compression refrigeration cycle, and identify and explain the operation of the components and the associated controls, safety devices and defrost systems  Level 3  NQF Level 03  10   

PURPOSE OF THE UNIT STANDARD 
People credited with this unit standard have proven the ability to:
  • Explain the operation of an actual vapour compression refrigeration cycle as applied to direct expansion, flooded, liquid overfeed and reverse cycle systems and Identify and explain the function of the components and the associated controls, safety devices and defrost systems.
  • Give advantages and limitations of direct expansion flooded, liquid overfeed and reverse cycle systems.
  • Discuss applications of the various systems.
  • State principles of operation and internal and external factors affecting the operation and performance of refrigeration components and accessories in an actual vapour compression refrigeration system. 
    		•

    LEARNING ASSUMED TO BE IN PLACE AND RECOGNITION OF PRIOR LEARNING 
    Explaining the operation of the basic vapour compression refrigeration system. 

    UNIT STANDARD RANGE 
    Refrigeration systems:

    Air-cooled, water-cooled and evaporatively cooled plants of the DX (direct expansion), flooded, liquid overfeed (liquid recirculation) and reverse cycle type (heat pump), as applied to domestic, commercial and industrial systems. Single stage operation only, but including multi-evaporative and condenser systems and liquid circulation systems.

    Refrigerant control devices:

    Capillary tubes, internally and externally equalised thermostatic expansion valves (with different bulb charges), solenoid type expansion devices, two-way thermostatic expansion valves, expansion device for heat pumps, refrigerant distributor, hot-gas by-pass valves and cylinder unloaders, reversing valves, solenoid valves, high-pressure and low-pressure float valves.

    Controls and safety devices:

    The following controls and safety devices used in refrigeration systems (excluding systems in which ammonia is the refrigerant).
    Manual and auto-reset low pressure and high pressure controls, oil pressure controls, head pressure control systems, temperature controllers (incl. electronic types), temperature sensors, humidistats, flow switches, level switches, rupture discs, pressure relief devices, defrost timers.

    Defrost systems:

    Off-cycle defrosts, electric defrost and hot gas defrost systems terminated by time and/or temperature and/or pressure. 

    Specific Outcomes and Assessment Criteria: 

    SPECIFIC OUTCOME 1 
    Explain the differences in operation between the theoretical and the actual vapour compression 
    OUTCOME NOTES 
    Explain the differences in operation between the theoretical and the actual vapour compression refrigeration cycle. 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The differences between the theoretical and actual vapour compression refrigeration cycle are explained. 
    ASSESSMENT CRITERION RANGE 
    Sub-cooling, superheating, line pressure drop, non-isentropic compression.
     

    ASSESSMENT CRITERION 2 
    2. The effects of the actual operating conditions on refrigerant mass flow, COP, power requirements and heat transfer are explained. 

    ASSESSMENT CRITERION 3 
    3. A flow diagram of the actual vapour compression cycle is sketched and the cycle is drawn on a pressure-enthalpy diagram and compared with the basic cycle. 

    ASSESSMENT CRITERION 4 
    4. The cycle and its components are sketched and described when the system is used as heat pump. 

    ASSESSMENT CRITERION 5 
    5. Causes and effects of flash gas are explained. 

    SPECIFIC OUTCOME 2 
    Compare and discuss the various types of vapour compression refrigeration systems 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The operation of the various types of actual vapour compression refrigeration systems and the component functions are explained using a block flow diagram showing the various components of such systems. 

    ASSESSMENT CRITERION 2 
    2. The various systems and typical applications are listed, compared and discussed. 

    ASSESSMENT CRITERION 3 
    3. Advantages and limitations of the various systems are discussed. 

    SPECIFIC OUTCOME 3 
    Explain the effect of actual operating conditions on the performance of the various components 
    OUTCOME NOTES 
    Explain the effect of actual operating conditions on the performance of the various components in the actual vapour compression cycle. 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The effects of superheat and sub cooling on the operating conditions and the performance of components and accessories in the system are explained. 

    ASSESSMENT CRITERION 2 
    2. The effect of pipe pressure losses on the operating conditions and the performance of components and accessories in the system is explained. 

    ASSESSMENT CRITERION 3 
    3. The effect of non-isentropic compression on the operating conditions and the performance of components and accessories in the system is explained. 

    SPECIFIC OUTCOME 4 
    List, identify and state the purpose of refrigerant control devices 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The purpose of the refrigerant control devices in a refrigeration system is explained. 

    ASSESSMENT CRITERION 2 
    2. Typical examples of applications of refrigerant control devices in a refrigeration system are given. 

    ASSESSMENT CRITERION 3 
    3. The various methods of controlling refrigerant flow in a system are listed. 

    ASSESSMENT CRITERION 4 
    4. The various control devices are correctly identified and their position located on a refrigeration plant indicated. 

    ASSESSMENT CRITERION 5 
    5. The importance of the correct positioning of the control device in the system is explained. 

    ASSESSMENT CRITERION 6 
    6. The various types of control devices are listed. 

    ASSESSMENT CRITERION 7 
    7. The different makes and models of control devices are identified. 

    SPECIFIC OUTCOME 5 
    Explain the operation of refrigerant control devices 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The operation of the various control devices and their influence on system performance is explained. 

    ASSESSMENT CRITERION 2 
    2. Possible faults on metering devices during operation are listed and discussed. 

    ASSESSMENT CRITERION 3 
    3. The required adjustments to be made to the devices to ensure correct control action are explained. 

    ASSESSMENT CRITERION 4 
    4. The impact of control device operation on system performance is explained. 

    ASSESSMENT CRITERION 5 
    5. The importance of correctly matching the control device to the system is explained. 

    ASSESSMENT CRITERION 6 
    6. Component parts of control devices are listed and identified. 

    ASSESSMENT CRITERION 7 
    7. Installation procedures in accordance with manufacturer's specifications are explained. 

    SPECIFIC OUTCOME 6 
    Identify refrigeration plant control and safety devices 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. Each control device is correctly identified. 

    ASSESSMENT CRITERION 2 
    2. Each safety device is correctly identified. 

    ASSESSMENT CRITERION 3 
    3. The difference between and the purposes of control devices and safety devices are explained. 

    SPECIFIC OUTCOME 7 
    List the commonly applied controls and safety devices for refrigeration plants 
    OUTCOME NOTES 
    List the commonly applied controls and safety devices for refrigeration plants and explain their purpose and operation. 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The commonly used control and safety devices are listed. 

    ASSESSMENT CRITERION 2 
    2. The purpose of the control devices is stated and discussed. 

    ASSESSMENT CRITERION 3 
    3. The purpose of the safety devices is stated and discussed. 

    ASSESSMENT CRITERION 4 
    4. The operation of the control and safety devices is explained. 

    ASSESSMENT CRITERION 5 
    5. The method of determining the setting of the devices is explained. 

    ASSESSMENT CRITERION 6 
    6. The importance of selecting the right range for the devices is explained. 

    ASSESSMENT CRITERION 7 
    7. The consequences of not including safety devices or selecting the wrong instrumentation are stated and explained. 

    SPECIFIC OUTCOME 8 
    List the commonly used defrost systems and explain their purpose and operation 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The various methods of defrosting coils are explained and their purpose is stated. 

    ASSESSMENT CRITERION 2 
    2. The methods of initiating and terminating the defrost cycle are explained. 

    ASSESSMENT CRITERION 3 
    3. The sequence of events when defrosting coils is explained. 

    ASSESSMENT CRITERION 4 
    4. The consequences of no, insufficient or extended defrosting is explained. 

    ASSESSMENT CRITERION 5 
    5. The importance of heater tapes on the drip tray and the drain is stated. 


    UNIT STANDARD ACCREDITATION AND MODERATION OPTIONS 
    Any person wishing to be assessed against this unit standard may apply to an assessment agency, assessor or provider institution accredited by the relevant ETQA, who may appoint a moderator to be present at the assessment.
    The assessor must have knowledge and experience of air conditioning or refrigeration. 

    UNIT STANDARD ESSENTIAL EMBEDDED KNOWLEDGE 
    The names and functions of refrigeration systems, components, controls, safety devices and defrost systems.
    Types and principle of operation of various actual vapour compression systems.
    Description of operation of various systems.
    Various types of vapour compression systems and their application.
    Consequences of selecting incorrect system for application.
    Principles of thermodynamics and fluid mechanics. 


    Critical Cross-field Outcomes (CCFO): 

    UNIT STANDARD CCFO IDENTIFYING 
    Identify and solve problems:
  • Select correct refrigeration systems for particular application
  • Apply thermodynamic principles during design of vapour compression system
  • Identify different devices 
    		•

    UNIT STANDARD CCFO SCIENCE 
    Use science and technology effectively and critically:
  • Apply thermodynamic and fluid mechanic principles
  • Identification of devices and explaining their purpose 
    		•

    UNIT STANDARD NOTES 
    This unit standard has been replaced by unit standard 116709, which is "Explain the operation of the vapour compression refrigeration cycle, and identify and explain the operation of the components and the associated controls, safety devices and defrost systems", Level 3, 10 credits.

    Supplementary information:

    This unit standard covers the commonly applied vapour compressor refrigeration systems. 

    QUALIFICATIONS UTILISING THIS UNIT STANDARD: 
      ID QUALIFICATION TITLE PRE-2009 NQF LEVEL NQF LEVEL STATUS END DATE PRIMARY OR DELEGATED QA FUNCTIONARY
    Core  20720   National Certificate: Air-Conditioning, Refrigeration and Ventilation  Level 3  NQF Level 03  Passed the End Date -
    Status was "Registered"     		 2004-06-13  Was MERSETA until Last Date for Achievement 


    PROVIDERS CURRENTLY ACCREDITED TO OFFER THIS UNIT STANDARD: 
    This information shows the current accreditations (i.e. those not past their accreditation end dates), and is the most complete record available to SAQA as of today. Some Primary or Delegated Quality Assurance Functionaries have a lag in their recording systems for provider accreditation, in turn leading to a lag in notifying SAQA of all the providers that they have accredited to offer qualifications and unit standards, as well as any extensions to accreditation end dates. The relevant Primary or Delegated Quality Assurance Functionary should be notified if a record appears to be missing from here.
     
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    All qualifications and part qualifications registered on the National Qualifications Framework are public property. Thus the only payment that can be made for them is for service and reproduction. It is illegal to sell this material for profit. If the material is reproduced or quoted, the South African Qualifications Authority (SAQA) should be acknowledged as the source.