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HVAC Air Conditioning Engineering

HVAC Systems Design and Engineering

HVAC Air Conditioning Engineering
W.P. Jones
MSc, CEng, FlnstE, FCIBSE, MASHRAE
531 Pages

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Preface:

Air conditioning (of which refrigeration is an inseparable part) has its origins in the fundamental work on thermodynamics which was done by Boyle, Carnot and others in the seventeenth and eighteenth centuries, but air conditioning as a science applied to practical engineering owes much to the ideas and work of Carrier, in the United States of America, at the beginning of this century.

Although the fundamentals of the subject have not altered since the publication of the last edition there have been significant changes in the development and application of air conditioning. Among these are concerns about indoor air quality, revision of outside design data and the expression of cooling loads arising from solar radiation through glass by the CIBSE. The phasing-out of refrigerants that have been in use for many years (because of their greenhouse effect and the risks of ozone depletion) and the introduction of replacement refrigerants are far-reaching in their consequences and have been taken into account. The tables on the thermodynamic properties of refrigerant 22 have been deleted and new tables for refrigerants 134a and ammonia substituted. There have also been new developments in refrigeration compressors and other plant. Advances in automatic controls, culminating in the use of the Internet to permit integration of the control and operation of all building services worldwide, are very important. Revisions in expressing filtration efficiency, with an emphasis on particle size, have meant radical changes in the expression of the standards used in the UK, Europe and the USA. The above developments have led to changes in the content, notably in chapters 4 (on comfort), 5 (on outside design conditions), 7 (on heat gains), 9 (for the refrigerants used), 12 (automatic controls) and 17 (on filtration standards).

Two examples on heat gains in the southern hemisphere have been included. As with former editions, the good practice advocated by the Chartered Institution of Building Services Engineers has been followed, together with the recommendations of the American Society of Heating, Refrigerating and Air Conditioning Engineers, where appropriate. It is believed that practicing engineers as well as students will find this book of value.

TOC

Chapter 1.
The Need for Air Conditioning
The meaning of air conditioning 1
Comfort conditioning 1
Industrial conditioning 2

Chapter 2.
Fundamental Properties of Air and Water Vapor Mixtures 3
The basis for rationalization 3
The composition of dry air 3
Standards adopted 5
Boyle's law 6
Charles' law 7
The general gas law 9
Dalton's law of partial pressure 11
Saturation Vapor pressure 12
The Vapor pressure of steam in moist air 13
Moisture content and humidity ratio 16
Percentage saturation 18
Relative humidity 19
Dew point 20
Specific volume 21
Enthalpy: thermodynamic background 22
Enthalpy in practice 23
Wet-bulb temperature 25
Temperature of adiabatic saturation 28
Non-ideal behavior 30
The triple point 33

Chapter 3
The Psychrometry of Air Conditioning Processes 38
The psychrometric chart 38
Mixtures 39
Sensible heating and cooling 42
Dehumidification 44
Humidification 48
Water injection 52
Steam injection 54
Cooling and dehumidification with reheat
Pre-heat and humidification with reheat
Mixing and adiabatic saturation with reheat
The use of dry steam for humidification
Supersaturation
Dehumidification by sorption methods

Chapter 4
Comfort and Inside Design Conditions
Metabolism and comfort
Bodily mechanisms of heat transfer and thermostatic control
Metabolic rates
Clothing
Environmental influences on comfort
Other influences on comfort
Fanger's comfort equation
Synthetic comfort scales
Measuring instruments
Outdoor air requirements
Indoor air quality
The choice of inside design conditions
Design temperatures and heat gains

Chapter 5.
Climate and Outside Design Conditions
Climate
Winds
Local winds
The formation of dew
Mist and fog
Rain
Diurnal temperature variation
Diurnal variation of humidity
Meteorological measurement
The seasonal change of outside psychrometric state
The choice of outside design conditions

Chapter 6
The Choice of Supply Design Conditions
Sensible heat removal
The specific heat capacity of humid air
Latent heat removal
The slope of the room ratio line
Heat gain arising from fan power
Wasteful reheat
The choice of a suitable supply state
Warm air supply temperatures

Chapter 7.
Heat Gains from Solar and Other Sources
The composition of heat gains
The physics of solar radiation
Sky radiation
Definitions
The declination of the sun
The altitude of the sun
The azimuth of the sun
The intensity of direct radiation on a surface
The numerical value of direct radiation
External shading
The geometry of shadows
The transmission of solar radiation through glass
The heat absorbed by glass
Internal shading and double glazing
Numerical values of scattered radiation
Minor factors affecting solar gains
Heat gain through walls
Sol-air temperature
Calculation of heat gain through a wall or roof
Air conditioning load due to solar gain through glass
Heat transfer to ducts
Infiltration
Electric lighting
Occupants
Power dissipation from motors
Business machines

Chapter 8
Cooling Load
Cooling load and heat gains
Cooling load for a whole building
Partial load
Cooling load offset by reheat
The use of by-passed air instead of reheat
Face and by-pass dampers
Cooling in sequence with heating
Hot deck--cold deck systems
Double duct cooling load
The load on air-water systems
Diversification of load
Load diagrams

Chapter 9
The Fundamentals of Vapor Compression
Refrigeration
The basis of Vapor compression refrigeration
Thermodynamics and refrigeration
The refrigerating effect
The work done in compression
Heat rejected at the condenser
Coefficient of performance
Actual vapor-compression cycle
Pressure-volume relations
Volumetric efficiency
Thermosyphon cooling
Refrigerants
Ozone depletion effects
Global warming
Other methods of refrigeration
Safety

Chapter 10.
Air Cooler Coils 279
Distinction between cooler coils and air washers
Cooler coil construction
Parallel and contra-flow
Contact factor
Heat and mass transfer to cooler coils
Sensible cooling
Partial load operation
The performance of a wild coil
Sprayed cooler coils
Free cooling
Direct-expansion coils
Air washers

Chapter 11
The Rejection of Heat from Condensers and
Cooling Towers 311
Methods of rejecting heat
Types of cooling tower
Theoretical considerations
Evaporative condensers
Air-cooled condensers
Automatic control
Practical considerations

Chapter 12
Refrigeration Plant
The expansion valve
The distributor
Float valves
Evaporators for liquid chilling
Direct-expansion air cooler coils
The reciprocating compressor
The air-cooled condensing set
Condensing set-evaporator match
The control of direct-expansion cooler coils and condensing sets
The performance of water chillers
The screw compressor
The scroll compressor
Centrifugal compressors
The water-cooled condenser
Piping and accessories
Charging the system

Chapter 13
Automatic Controls
The principle of automatic control
Definitions
Measurement and lag
Measurement elements
Types of system
Methods of control
Simple two-position control
Timed two-position control
Floating action
Simple proportional control
Refined proportional control
Automatic valves
Automatic dampers
Application
Fluidics
Control by microprocessors and Building Management Systems (BMS and BEMS)

Chapter 14
Vapor Absorption Refrigeration
Basic concepts
Temperatures, pressures, heat quantities and flow rates for the lithium
bromide-water cycle
Coefficient of performance and cycle efficiency
Practical considerations

Airflow in Ducts and Fan Performance
Viscous and turbulent flow
Basic sizing
Conversion from circular to rectangular section
Energy changes in a duct system
Velocity (dynamic) pressure
The flow of air into a suction opening
The coefficient of entry (CE)
The discharge of air from a duct system
Airflow through a simple duct system
Airflow through transition pieces
Airflow around bends
Airflow through supply branches
Flow through suction branches
Calculation of fan total and fan static pressure
The interaction of fan and system characteristic curves
The fan laws
Maximum fan speed
Margins
Power-volume and efficiency-volume characteristics
Fan testing
The performance of air handling units
Methods of varying fan capacity in a duct system
The effect of opening and closing branch dampers
Fans in parallel and series

Chapter 16
Ventilation and a Decay Equation
The need for ventilation
The decay equation
An application of the decay equation to changes of enthalpy

Chapter 17
Filtration
Particle sizes
Particle behavior and collection
Efficiency
Classification according to efficiency
Viscous filters
Dry filters
Electric filters
Wet filters
Centrifugal collectors
Adsorption filters
Safety