air conditioning and refrigeration(1).ppt

7/27/2019 Air Conditioning and Refrigeration(1).ppt

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

Dr. Sam C M Hui

Department of Mechanical Engineering

The University of Hong Kong

E-mail: [email protected]

Air Conditioning Systems


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Contents

Five Basic Subsystems

Classification of Air Conditioning Systems

System Selection


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Five subsystems or loops

Air-side

Chilled water

Refrigeration equipment

Heat rejection

Controls


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33 oC, 28 oC

27o

C33 oC

25 oC

Conditioned space


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13 oC 13 oC

33 oC, 28 oC

27o

C33 oC

25 oC

Air side system


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13 oC 13 oC

12 oC

7 oC

33 oC, 28 oC

7 oC

12 oC

27o

C33 oC

25 oC

Chilled water

system


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13 oC 13 oC

12 oC

7 oC 3 oC38 oC

49 oC10 oC

33 oC, 28 oC

7 oC

12 oC

27o

C33 oC

25 oC

Refrigeration

equipment


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13 oC 13 oC

12 oC

7 oC 3 oC38 oC

49 oC10 oC

35 oC

29 oC

33 oC, 28 oC

7 oC

12 oC

29 oC

35 oC

27o

C33 oC

25 oC

Heat rejection


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13 oC 13 oC

12 oC

7 oC 3 oC38 oC

49 oC10 oC

35 oC

29 oC

33 oC, 28 oC

7 oC

12 oC

29 oC

35 oC

27o

C33 oC

25 oC

Control Loop


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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


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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


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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)


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Individual room air-conditioning system


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Primary air fan coil unit system


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Water-source heat pump system


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Classification proposed by Mr. S K Wang

Packaged systems

Air is cooled directly by DX (direct expansion) coil andheated 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


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Variable-air volume (VAV) package system


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VAV box VAV reheat box

Fan-powered

VAV box


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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


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A single-zone CV clean room system


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A dual-duct VAV central system


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A dual-duct VAV central system:

Mixing VAV box and operating diagram


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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


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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


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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


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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


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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


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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)

air conditioning and refrigeration(1).ppt

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