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

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

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

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  1. 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

  2. Contents • Five Basic Subsystems • Classification of Air Conditioning Systems • System Selection

  3. Five Basic Subsystems • Five subsystems or loops • Air-side • Chilled water • Refrigeration equipment • Heat rejection • Controls

  4. 27 oC 33 oC 25 oC 33 oC, 28 oC Conditioned space

  5. 27 oC 33 oC 25 oC 33 oC, 28 oC 13 oC 13 oC Air side system

  6. 27 oC 33 oC 25 oC 33 oC, 28 oC Chilled water system 12 oC 12 oC 7 oC 7 oC 13 oC 13 oC

  7. 27 oC 33 oC 25 oC 33 oC, 28 oC Refrigeration equipment 12 oC 10 oC 49 oC 12 oC 7 oC 38 oC 7 oC 3 oC 13 oC 13 oC

  8. 27 oC 33 oC 25 oC 33 oC, 28 oC Heat rejection 12 oC 10 oC 49 oC 35 oC 12 oC 35 oC 29 oC 7 oC 38 oC 7 oC 3 oC 29 oC 13 oC 13 oC

  9. 27 oC 33 oC 25 oC Control Loop 33 oC, 28 oC 12 oC 10 oC 49 oC 35 oC 12 oC 35 oC 29 oC 7 oC 38 oC 7 oC 3 oC 29 oC 13 oC 13 oC

  10. 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

  11. 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

  12. 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)

  13. Individual room air-conditioning system

  14. Primary air fan coil unit system

  15. Water-source heat pump system

  16. 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

  17. Variable-air volume (VAV) package system

  18. VAV reheat box VAV box Fan-powered VAV box

  19. 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

  20. A single-zone CV clean room system

  21. A dual-duct VAV central system

  22. A dual-duct VAV central system: Mixing VAV box and operating diagram

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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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