BASICS OF HVAC SYSTEM

HVAC SYSTEM• A HVAC System consists of a chain of

components designed to heat,ventilate or cool a specific area while maintaining a defined environmental cleanliness level.

To Control/Maintain Temperature - Heating

To Purify the Air - Ventilation

To Control/Maintain Humidity - Air Conditioning

PURPOSE OF AIRCONDITIONING

AIRCHANGES• The air change rate refers to the number

of times in a 1-hr period that the volume of air in a space is renewed.

Design Consideration The factors affecting air change rate are:• The presence of air pockets or dead space

in the Controlled area.• The relative positioning of Supply and

Return air grills.• Type of Machine and Equipments placed

inside the area.

FRESH AIR

CV

CV

T

TH

EXHAUST VENT

CONTROLLED ROOM

MACHINE

CV

legendCHILLED WATER

CHILLED BRINE

10 FILTER

HOT WATER

5 FILTER

HEPA FILTER

CONTROL VALVE

MANOMETER

CV

GENERAL LAYOUT OF HVAC SYSTEM

Defumigation Outlet

COMPONENTS OF THE HVAC SYSTEM

• AIR MOVING EQUIPMENTThe blowers / fans and their design characteristics govern the Amount of air flowing through the system and delivers theStatic pressure required to overcome resistance offered by Filters,Coils and ducting layouts. Centrifugal blowers driven by electric motors are widely usedSELECTION CRITERIA:• Volume of controlled space.• Desired air changes.• Desired environmental conditions.• Static pressure requirements based on specific layout.

COMPONENTS OF THE HVAC SYSTEM

• AIR COOLING AND HEATING SYSTEMS Central systems normally employ air-to-water cooling

systems using finned copper coils and air heaters for heating systems.For humidity control upto 50% chilled water is used as cooling media while for lower humidity levels chilled brine at -1C and or regenerative desiccant driers are used.

SELECTION CRITERIA:• Desired Environment Conditions.• Ambient Environment Conditions.• Heat load and Volume of space to be Conditioned.

COMPONENTS OF THE HVAC SYSTEM

• AIR DISTRIBUTION NETWORK It is the structural assembly whose primary function

is to convey air between specific points.Galvanized Iron or Anodized Aluminum is used to fabricate the ducting.

Based on air volumes and total pressures handled air ducts are classified as: High Pressure : 3” water gauge and upwards. Low Pressure : 0 – 2” water gauge. Components of air distribution network includes

ducting,insulation,diffusers,louvers and grilles.

COMPONENTS OF THE HVAC SYSTEM

• Dimensional stability.• Integrity at specified air volumes and pressures.• Vibration.• Noise.(Transmission and Generation)• Exposure to damage.• Support.• Compatibility with insulating,sealing or adhesive agents.• Resistance to air flow.• Air flow patterns inside the Controlled space.• Nature and type of sanitizing procedures.

SELECTION CRITERIA:

CLASSIFICATION OF FILTERS

• Air filters retain particles by various collection methods largely characterized by particle and aerosol behavior.

• Filters can be broadly classified as:• SIEVING FILTERS• DYNAMIC FILTERS

FILTERATION MECHANISM OF DYNAMIC FILTERS

• INERTIAL IMPACTION Particles are trapped by randomly oriented obstrucles.

Retention is due to the three dimensional array of filter matrix.Efficiency varies directly with particle diameter.

• DIRECT IMPACTION Particles are trapped by the porosity of the filter. Retention

is mainly due to collision of the particle with the filter fiber.Efficiency varies directly with particle dimensions.

FILTERATION MECHANISM OF DYNAMIC FILTERS

• DIFFUSION Retention by diffusion takes place with very small

particles owing to Brownian motion and the efficiency is a function of Avagadro’s number,air velocity and particle diameter.

INERTIAL IMPACTIONm

DIRECT IMPACTION 0.5-1.0m

DIFFUSION 0.2-0.3m

Dominant Retentive ActionParticle size

EVALUATION OF AIR FILTERS

CRITERIA• Airflow resistance• Collection efficiency• Service life• Arrestance

METHOD• Measuring Dp across filter• DOP test• Measuring Dp across filter• Area of filter media

CONSTRUTION OF HEPA FILTER

• FRAME Frame selection is based on chemical or fire resistance. Generally Stainless Steel or Anodized Aluminum is used.• FILTER MEDIUM Most common media in use today is glass microfibres.It can sustain air velocities upto 12 ft/sec and temperatures from 4C to 450 C .• SEPERATORS Used for supporting the media.Corrugated separators of

Aluminum alloy,Kraft paper are widely used.

CONSTRUTION OF HEPA FILTER

• ADHESIVES Used to bond the frame to the glass medium.Polyurethane foams are used for low temperature applications while silicate adhesives are used in high temperature applications.• GASKETS Used to seal the frame of the filter against the filter plenum. Closed cell neoprene foam is used for low temperature applications while Teflon is used for higher temperatures.