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

Plot the multi-stage refrigeration cycle on a Pressure-enthalpy diagram, explain its operation and carry out performance calculations 
SAQA US ID UNIT STANDARD TITLE
9462  Plot the multi-stage refrigeration cycle on a Pressure-enthalpy diagram, explain its operation and carry out performance calculations 
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 5  Level TBA: Pre-2009 was L5  6 
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 does not replace any other unit standard and is not replaced by any other unit standard. 

PURPOSE OF THE UNIT STANDARD 
Explain the principles of operation and application of multi-stage vapour compression systems, plot the multi-stage refrigeration cycle on a pressure-enthalpy diagram and carry out performance calculations on multi-stage refrigeration cycles. 

LEARNING ASSUMED TO BE IN PLACE AND RECOGNITION OF PRIOR LEARNING 
  • Explain the operation of the vapour compression cycle, and identify and explain the operation of the components and the associated controls, safety devices and defrost systems.
  • Explain the function and operation of refrigeration circuits as applied to air-conditioning or refrigeration systems and select and explain the function of components, accessories and controls. 
    		•

    UNIT STANDARD RANGE 
    Compound and cascade systems. Compressors in multi-stage configuration.
    Air-conditioning and refrigeration applications 

    Specific Outcomes and Assessment Criteria: 

    SPECIFIC OUTCOME 1 
    Explain the purpose of multi-stage vapour compression and its principles of operation 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The difference between single and multi-stage compression is explained. 

    ASSESSMENT CRITERION 2 
    2. The reasons for multi-stage compression are listed and discussed. 

    ASSESSMENT CRITERION 3 
    3. The principles of operation of multi-stage compression are explained. 

    ASSESSMENT CRITERION 4 
    4. The operation of multi-stage systems with single-stage systems is compared and contrasted. 

    ASSESSMENT CRITERION 5 
    5. The influence of multi-stage compression on the performance of the plant is explained and relevant system performance calculations are carried out. 

    SPECIFIC OUTCOME 2 
    Discuss the various types of multi-stage vapour compression systems and their applications. 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. The various methods of multi-stage compression are listed and explained. 

    ASSESSMENT CRITERION 2 
    2. The applications of the various systems are discussed and merits and limitations of each system are explained. 

    ASSESSMENT CRITERION 3 
    3. The interface between the various stages of the multi-stage system and the rest of the refrigeration systems is identified and explained. 

    SPECIFIC OUTCOME 3 
    Plot the multi-stage vapour compression system on a pressure-enthalpy diagram. 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. Optimisation of intermediate pressures in multi-stage systems is explained in terms of multi-stage compression parameters. 

    ASSESSMENT CRITERION 2 
    2. The multi-stage compression cycles for various multi-stage compression methods are explained by plotting the relevant cycles on a pressure-enthalpy diagram. 

    ASSESSMENT CRITERION 3 
    3. The actual vapour compression cycle is drawn on the pressure-enthalpy diagram. Range : Line pressure drops, superheat and sub-cooling, actual and isentropic compression. 

    SPECIFIC OUTCOME 4 
    Carry out system performance calculations from pressure-enthalpy diagram. 

    ASSESSMENT CRITERIA     

    ASSESSMENT CRITERION 1 
    1. Calculations of the optimum interstage pressure/s are demonstrated and explained. 

    ASSESSMENT CRITERION 2 
    2. Specific thermodynamic properties of refrigerants are obtained from the pressure-enthalpy diagram. 

    ASSESSMENT CRITERION 3 
    3. System performance is derived from the pressure-enthalpy diagram. 
    ASSESSMENT CRITERION RANGE 
    Mass flow rates, coefficient of performance, compressor power requirements, refrigeration effect and heat rejection.
     


    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 
  • Understanding the operation of and applying various multi-stage compression systems.
  • Thermodynamics of multi-stage refrigeration. 
    		•


    Critical Cross-field Outcomes (CCFO): 

    UNIT STANDARD CCFO IDENTIFYING 
    Identify and solve problems
  • Identifying merits and limitations of multi-stage refrigeration systems 
    		•

    UNIT STANDARD CCFO ORGANISING 
    Organise and manage myself and my activities responsibly and effectively
  • Selecting suitable multi-stage systems for various applications 
    		•

    UNIT STANDARD CCFO COMMUNICATING 
    Communicate effectively
  • Communicating with members of the design team 
    		•

    UNIT STANDARD CCFO SCIENCE 
    Use science and technology effectively and critically
  • Plotting multi-stage system cycles on pressure-enthalpy diagram and carrying out relevant performance calculations 
    		•

    UNIT STANDARD CCFO DEMONSTRATING 
    Demonstrate an understanding of the world as a set of related systems
  • Understanding the impact of incorrect system selection on the operation of the refrigeration installation and consequently costs 
    		•

    UNIT STANDARD CCFO CONTRIBUTING 
    Learner and societal development
  • Understanding thermo dynamical and fluid mechanical principles as applied to refrigeration 
    		•

    UNIT STANDARD NOTES 
    Correct S.I. units are to be used. 

    QUALIFICATIONS UTILISING THIS UNIT STANDARD: 
      ID QUALIFICATION TITLE PRE-2009 NQF LEVEL NQF LEVEL STATUS END DATE PRIMARY OR DELEGATED QA FUNCTIONARY
    Elective  20722   National Diploma: Air Conditioning, Refrigeration and Ventilation  Level 5  Level TBA: Pre-2009 was L5  Passed the End Date -
    Status was "Registered"     		 2004-06-13  MERSETA 


    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.
     
    NONE 


    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.