1. Air Conditioning Systems
BBSE3004: Air Conditioning and Refrigeration
Air Conditioning Systems
Dr. Sam C M Hui
Department of Mechanical Engineering
The University of Hong Kong

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

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

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

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

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

9. Control Loop 33 oC, 28 oC 27 oC 33 oC 25 oC 12 oC 10 oC 12 oC 49 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 ( 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 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

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)