18SANIA ATIQUE

HVAC

WHAT IS HVAC

EATING ENTILATION IR CONDITIONING

HV

A

GOAL OF HVAC

The goal of the heating, ventilating, and air conditioning (HVAC) system is to create and maintain a comfortable environment within a building.

"Conditioned" air means that air is clean and odor-free, and the temperature, humidity, and movement of the air are within certain comfort ranges.

COMFORT REQUIREMENTS

TemperatureHumidityAir movementFresh airClean airNoise levelsLightingFurniture and work surfaces

COMFORT REQUIREMENTS BY HVAC SYSTEM

Comfort requirements that are typically impacted by the HVAC system include:

Dry-bulb temperatureHumidityAir movementFresh airCleanliness of the airNoise levelsSome HVAC systems address these comfort

requirements better than others.

FUNCTIONS OF HVAC

Control of air temperatureControl of moisture content in the airProper air movement. To hold the air contamination within

acceptable limits

FIVE SYSTEM LOOP

FIVE SYSTEM LOOP

The premise of this method is that any HVAC system can be dissected into basic subsystems.

These subsystems will be referred to as "loops/" There are five primary loops that can describe virtually any type of HVAC system.

Airside loop (yellow)Chilled-water loop (blue)Refrigeration loop (green)Heat-rejection loop (red)Controls loop (purple)

AIRSIDE LOOP

The first two comfort requirements mentioned were dry-bulb temperature and humidity.

In order to maintain the dry-bulb temperature in the conditioned space, heat (referred to as sensible heat) must be added or removed at the same rate as it leaves or enters the space.

In order to maintain the humidity level in the space, moisture (sometimes referred to as latent heat) must be added or removed at the same rate as it leaves or enters the space

COMPONENTS OF AIR LOOP

Conditioned space Supply fan and filter Cooling Coil.

CHILLED WATER LOOP

CHILLED WATER LOOP

A chilled-water applied system uses chilled water to transport heat energy between the airside, chillers and the outdoors.

COMPONENTS OF CHILLED WATER LOOP

The components of the chiller Evaporator Compressor An air- or water-cooled condenserExpansion device

REFRIGERATION LOOP

Recall that in the chilled-water loop, the evaporator allows heat to transfer from the water to cold liquid refrigerant.

liquid refrigerant at 38ºF (3.3ºC) enters the tubes of the shell-and-tube evaporator.

As heat is transferred from the water to the refrigerant, the liquid refrigerant boils.

The resulting refrigerant vapor is further warmed (superheated) to 50ºF (10ºC) inside the evaporator before being drawn to the compressor

COMPONENTS OF REFRIGERATION LOOP

COMPRESSORCONDENSOREXPANSION DEVICE

HEAT REJCTION LOOP

The fourth loop is the heat-rejection loop. In the refrigeration loop, the condenser transfers

heat from the hot refrigerant to air, water, or some other fluid. In a water-cooled condenser, water flows through the tubes while the hot refrigerant vapor enters the shell space surrounding the tubes.

Heat is transferred from the refrigerant to the water, warming the water.

Water enters the condenser at 85ºf (29.4ºc), absorbs heat from the hot refrigerant, and leavesat 100ºf (37.8ºc)

HEAT REJCTION LOOP

The water flowing through the condenser must be colder than the hot refrigerant vapor

A heat exchanger is required to cool the water that returns from the condenser—at 100ºF (37.8ºC)—back to the desired temperature of 85ºF (29.4ºC) before it is pumped back to the condenser.

When a water-cooled condenser is used, this heat exchanger is typically either a cooling tower or a fluid cooler (also known as a dry cooler).

COMPONENTS OF HEAT REJCTION LOOP

COOLING TOWERPUMP AND CONTROL VALVE

CONTROL LOOPS

The fifth, and final, loop of the HVAC system is the controls loop.

Each of the previous four loops contains several components. Each component must be controlled in a particular way to ensure proper operation.

Typically, each piece of equipment (which may be comprised of one or more components of a loop) is equipped with a unit-level, automatic controller.

In order to provide intelligent coordinated control so that the individual pieces of equipment operate together as an efficient system, these individual unit-level controllers are often connected to a central, system-level controller