SUPPLY DEVICES AND ROOM AIR DISTRIBUTION

SUPPLY DEVICES AND ROOM AIR DISTRIBUTION

• Heating, Ventilation and Air Conditioning

• Provides comfort for people

• Allows humans to exist under adverse conditions.

Comfort

• Comfort is primary intent of HVAC systems.

• Productivity• Building Durability• Health

• Mold

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

Basic HVAC Equipment

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

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.

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.

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.

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.

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

Packaged Rooftop Units

                                                 

FURNACE

A/C UNIT

Ductwork

Heating and Cooling Equipment

Temperature &Humidity Controls

Split System

Heat Pump

• Operate on simple refrigeration cycle

• Reversing the cycle provides heating

• Temperature limitations

• Air to air• Water source• Geothermal• Lake coupled

Geothermal Heat Pump Systems

Variable Air Volume

T T

Variable Speed Return Fan

Re

turn

Air

Return Ducts

Zone Thermostat

Reheat Coil

VAV Box

Supply DuctsVariable Speed Supply Fan

Filt

ers

Co

ol C

oil

w/T

emp

Res

et

He

at

Co

il w

/Tem

p

Re

set

HVAC-16

Terminal Units

Variable volume: Parallel

                                       

Constant volume: Series

Hydronic systems

• Pumps• Piping• Valves

Control Devices

• Thermostats– Manual

– Programmable

• Optimum Start

• DDC Systems

• Variable Speed Drives

• Automatic Valves and Dampers

• Outdoor Sensors

                                                         

Major Equipment

• Chillers

• Boilers

• Cooling Towers

Economizers

Air Side Water Side

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 OperationOutside air dampers are positioned to provide the minimum outside air

Economizer OperationOutside air dampers are fully open. Maximum outside air is provided

80 oF

55 oF and up

85%outside air

85%exhaust

HVAC-22

Zoning and Economizers

• Economizers provide “free cooling” when outdoor conditions are optimal

• Proper orientation & zoning yields comfort & efficiency

N

S

W ECore

HVAC-23

Air Distribution

• Ductwork– Metal– Flexible– Ductboard

• Grilles, Louvers, & Registers

• Dampers– Shut off– Fire– Smoke

• Sealants• Supports

Return Plenum Problems

HVAC-25

Additional Equipment

• Energy Recovery Units• Desiccant Systems

Additional Equipment

• Heat Exchangers• Humidifiers• Silencers

                                                             

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

Filt

er

Historical Minimum Ventilation Rates (cfm/person)

0

10

20

30

40

50

60

70

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

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

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

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