Air Conditioning Systems 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 27 oC 33 oC 25 oC Conditioned space

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

Chilled water system 33 oC, 28 oC 27 oC 33 oC 25 oC 12 oC 12 oC 7 oC

Refrigeration equipment 33 oC, 28 oC 27 oC 33 oC 25 oC 12 oC 10 oC

Heat rejection 33 oC, 28 oC 27 oC 33 oC 25 oC 12 oC 10 oC 12 oC 49 oC

Control Loop 33 oC, 28 oC 27 oC 33 oC 25 oC 12 oC 10 oC 12 oC 49 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 reheat box VAV 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 Space requirements 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)