Semester 3 CB303 Ventilation and Air Conditioning Note Lec 6 (Air Distribution)

1. SUPPLY DEVICES
AND ROOM AIR
DISTRIBUTION

2. SUPPLY DEVICES AND ROOM AIR DISTRIBUTION
• Heating, Ventilation and Air
Conditioning
• Provides comfort for people
• Allows humans to exist under
adverse conditions.

3. Comfort
• Comfort is primary intent
of HVAC systems.
• Productivity
• Building Durability
• Health
• Mold

4. Supply Devices and Room Air
Distribution
• One way to condition air is to use a fan to move the
air over the conditioning space.
• The components that make up the forced-air system
are :
 Blower (fan)
 Air supply system
 Filter
 Balancing damper
 Return air system
 Grillers
 And registers where the circulated air enters the room and returns to
the conditioning equipment

5. Basic HVAC Equipment
• Fans / Blowers
• Furnace / Heating unit
• Filters
• Compressor
• Condensing units
• Evaporator (cooling coil)
• Control System
• Air Distribution System

7. Types of fans
• The fan or blower as it is sometimes called, can be
described as a device that produces airflow or
movement.
• The fan provides the pressure
difference to force the air into the
duct system, through grilles and
registers and into a room.
• Several different types of fans produce this
movement such as propeller fan, axial-flow fans and
centrifugal fans.

8. THE PROPELLER FAN
• The propeller fan is used in exhaust-fan and condenser-
fan applications.
• It will handle large volumes of air at low pressure
differentials.
• The propeller fan can be cast iron, aluminum or stamped
steel and is set into a housing called a venturi to
encourage airflow in a straight line from one side of the
fan to the other(Figure above).
• The propeller fan makes more noise than the centrifugal
fan so it is normally used where noise is not a factor.

9. THE CENTRIFUGAL FAN
• The centrifugal fan has characteristics that make it
desirable for duct work.
• It builds more pressure from the inlet to the outlet
and moves more air against more pressure.
• This fan has a forward curved blade and a cutoff to
shear the air spinning around the fan wheel (Figure
above).
• The centrifugal fan is very quiet when properly
applied.

10. AXIAL FAN
• The axial-flow fans have blades that force air to move parallel to
the shaft about which the blades rotate.
• Axial fans blow air along the axis of the fan, linearly, hence their name.
• This type of fan is used in a wide variety of applications, ranging from
small cooling fans for electronics to the giant fans used in wind tunnels
• Axial flow fans are applied for air conditioning and industrial process
applications.
• Standard axial flow fans have diameters from 300-400 mm or 1800 to
2000 mm and work under pressures up to 800 Pa.

11. System Types and Common Terms
• Packaged Rooftop
Unit
• Split System
• Heat Pump
• Geothermal
• Air to Air
• Hydronic (water)
• PTAC / PTHP
Constant Volume
Variable Volume
Indoor Air Quality
Direct Expansion

12. Packaged Rooftop Units

13. FURNACE
A/C UNIT
Ductwork
Heating
and Cooling
Equipment
Temperature &
Humidity Controls
Split System

14. Heat Pump
• Operate on simple
refrigeration cycle
• Reversing the cycle
provides heating
• Temperature
limitations
• Air to air
• Water source
• Geothermal
• Lake coupled

15. Geothermal Heat Pump Systems

16. Variable Air Volume
T T
Variable Speed
Return Fan
ReturnAir
Return Ducts
Zone Thermostat
Reheat Coil
VAV Box
Supply Ducts
Variable Speed
Supply Fan
Filters
CoolCoilw/TempReset
HeatCoilw/Temp
Reset
HVAC-16

17. Terminal Units
Variable volume:
Parallel
Constant volume:
Series

18. Hydronic systems
• Pumps
• Piping
• Valves

19. Control Devices
• Thermostats
– Manual
– Programmable
• Optimum Start
• DDC Systems
• Variable Speed Drives
• Automatic Valves and Dampers
• Outdoor Sensors

20. Major Equipment
• Chillers
• Boilers
• Cooling Towers

21. Economizers
Air Side Water Side

22. Economizers
Free cooling source: When available, use cool outdoor air instead
of mechanically cooled air.
55 oF
80 oF
Minimum supply of
outside air
Normal Operation
Outside air dampers are positioned to
provide the minimum outside air
Economizer Operation
Outside air dampers are fully open.
Maximum outside air is provided
80 oF
55 oF and up
85%
outside air
85%
exhaust
HVAC-22

23. Zoning and Economizers
• Economizers provide “free cooling”
when outdoor conditions are optimal
• Proper orientation & zoning yields
comfort & efficiency
N
S
W ECore
HVAC-23

24. Air Distribution
• Ductwork
– Metal
– Flexible
– Ductboard
• Grilles, Louvers,
& Registers
• Dampers
– Shut off
– Fire
– Smoke
• Sealants
• Supports

25. Return Plenum Problems
HVAC-25

26. Additional Equipment
• Energy Recovery Units
• Desiccant Systems

27. Additional Equipment
• Heat Exchangers
• Humidifiers
• Silencers

28. Mechanical Dehumidification
Return air is mixed with ventilation air
Cold coil condenses moisture
Heat is added back (electric or gas) so that room air is not over
cooled- Reheat
Filter

29. Historical Minimum Ventilation Rates
(cfm/person)
0
10
20
30
40
50
60
70
1835
1842
1849
1856
1863
1870
1877
1884
1891
1898
1905
1912
1919
1926
1933
1940
1947
1954
1961
1968
1975
1982
1989
1996
Tredgold
1836
Nightengale
1865
Billings
1895
Flugge
1905
Yaglou
1938
ASHRAE
62-73
ASHRAE 62-81
Smoking 62-81
ASH-
RAE
62-89
Smoking 62-89

30. Improved Ventilation Effectiveness
• Mechanically provide filtered and
dehumidified outdoor air to the
breathing space
• Vary ventilation based on the number
of occupants and process loads -
changes in occupancy can be
measured by CO2 sensors
• Consider designs that separate
ventilation and space conditioning
• Utilize heat recovery systems to reduce
system size and ventilation energy
costs

31. Improved Ventilation Effectiveness
• Effective mixing of ventilation
air within space
• Net positive pressure in the
southeast; exhaust from
appropriate spaces
• Provide clean outdoor air,
avoid:
– loading docks
– exhaust vents
– plumbing stacks
– waste collection
– stagnant water

32. Additional Information / Resources
• ASHRAE – The American Society of Heating,
Refrigerating and Air-Conditioning Engineers
– www.ashrae.org
• Southface Energy Institute www.southface.org
• Geothermal heat pump consortium
www.geoexchange.org
• www.buildingscience.com
• www.energycodes.gov