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					BBSE3004: Air Conditioning and Refrigeration
        http://www.hku.hk/bse/bbse3004/




  Air Conditioning Systems
                  Dr. Sam C M Hui
         Department of Mechanical Engineering
             The University of Hong Kong
                E-mail: cmhui@hku.hk
Contents

• Five Basic Subsystems

• Classification of Air Conditioning Systems

• System Selection
Five Basic Subsystems

• Five subsystems or loops
  •   Air-side
  •   Chilled water
  •   Refrigeration equipment
  •   Heat rejection
  •   Controls
        33 oC, 28 oC




33 oC                  27 oC


   25 oC




                               Conditioned space
        33 oC, 28 oC




33 oC                  27 oC


   25 oC




        13 oC          13 oC



  Air side system
        33 oC, 28 oC
                               Chilled water
                                  system
33 oC                  27 oC

                               12 oC
   25 oC
                                         12 oC




                                    oC
                                         7 oC
                                7


        13 oC          13 oC
        33 oC, 28 oC
                                                Refrigeration
                                                 equipment
33 oC                  27 oC

                               12 oC              10 oC
   25    oC
                                        12 oC               49 oC




                                   oC
                                        7 oC           oC
                                                            38 oC
                               7                   3


        13 oC          13 oC
        33 oC, 28 oC

                                                               Heat rejection
33 oC                  27 oC

                               12 oC           10 oC
   25    oC
                                       12 oC           49 oC     35 oC
                                                                         35 oC




                                       7 oC            38 oC             29 oC
                               7 oC            3 oC              29 oC


        13 oC          13 oC
        33 oC, 28 oC                                   Control Loop


33 oC                  27 oC

                               12 oC           10 oC
   25    oC
                                       12 oC           49 oC   35 oC
                                                                       35 oC




                                       7 oC            38 oC           29 oC
                               7 oC            3 oC            29 oC


        13 oC          13 oC
Five Basic Subsystems

• Remarks:
  • Not all systems use all five loops
     • Such as DX (direct expansion) has no chilled water
  • Heat and humidification are part of the Airside
  • Temperatures are representative only
Classification of A/C Systems

• Three generic types:
  • Centralised all air systems
     • Such as CAV, VAV, dual duct
  • Partially centralised air/water systems
     • Such as FCU, induction units, chilled beams/ceilings
  • Local systems
     • Such as window-type units, Split-type packages
• Number of zones: single zone or multi-zone
Classification of A/C Systems

• Classification proposed by Mr. S K Wang
  • Individual systems (no air duct), such as
     • Room air-conditioners
     • Package terminal air-conditioner (PTAC) systems
  • Space (Space-conditioning) systems, such as
     • Two-pipe or four-pipe fan coil systems
        • Often with separate outdoor ventilation air & heat recovery
        • Standard sizes 02, 03, 04, 06, 08, 12 (200-1200 cfm)
     • Water-source heat pumps (WSHP)
Individual room air-conditioning system
Primary air fan coil unit system
Water-source heat pump system
Classification of A/C Systems

• Classification proposed by Mr. S K Wang
  • Packaged systems
     • Air is cooled directly by DX (direct expansion) coil and
       heated by direct-fired gas or electric heaters
     • Rooftop, split and indoor units
        •   Single-zone CAV packaged systems
        •   VAV packaged systems
        •   VAV reheat packaged systems
        •   Fan-powered VAV packaged systems
     • Common in USA/Canada
Variable-air volume (VAV) package system
VAV box   VAV reheat box




             Fan-powered
               VAV box
Classification of A/C Systems

• Central systems
  •   Single-zone CAV central systems
  •   Single-zone CAV clean room systems
  •   CAV zone-reheat central systems
  •   VAV central systems
  •   VAV reheat central systems
  •   Fan-powered VAV central systems
  •   Dual-duct VAV central systems
  •   Dual-duct CAV central systems
A single-zone CV clean room system
A dual-duct VAV central system
   A dual-duct VAV central system:
Mixing VAV box and operating diagram
Classification of A/C Systems

• Other systems
  • VRV or VRF (variable refrigerant volume/flow)
    systems
       • Similar to multi-split systems
  •   Displacement ventilation
  •   Underfloor air conditioning
  •   Ice-storage or chilled-water systems
  •   Desiccant cooling systems
  •   Chilled beams and ceilings
System Selection

• Selection criteria
   •   Temp., humidity, space pressure requirements
   •   Capacity requirements
   •   Redundancy
   •   Spatial requirements
   •   First cost
   •   Operating cost
   •   Maintenance cost
   •   Reliability
   •   Flexibility
   •   Life cycle analysis
System Selection

• System constraints
  •   Performance limitations (temp., humidity, etc)
  •   Available capacity
  •   Available space (for plants & distribution)
  •   Available utility source
  •   Building architecture
  •   Construction budget
  •   Noise levels
  •   Aesthetics and visible components
System Selection

• Selection report to address
  •   Design goal(s)
  •   Criteria for selection
  •   Important factors
  •   Other goals
• HVAC system selection matrix (see examples)
  • Score and grading for each design option
System Selection

• System analysis & selection
   • Central and decentralised systems
   • Primary equipment
      • Refrigeration plant
      • Air and water delivery
      • Heating equipment (if any)
• Space requirements
   • Equipment rooms (4-9% of floor area), e.g. for chillers
   • Fan rooms, vertical shafts
   • Equipment access
System Selection

• Design considerations
  • Air distribution methods
       •   Upward or downward air flow
       •   Perforated ceiling
       •   Side wall inlets
       •   Use of jet nozzles
  •   Ceiling plenums
  •   Pipe systems & insulation
  •   Heat rejection methods (air-cooled/water-cooled)
  •   Controls (stand alone or BEMCS)

				
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