HVAC Introduction

HVAC is an acronym that stands for Heating Ventilating Air Conditioning. HVAC is for Controlling temperature and humidity to bring comfort to occupants inside the certain spaces such as Office Buildings, Residential Towers etc.

 Air Conditioning refers the cooling and dehumidification of indoor air for thermal comfort. Air Conditioning is based on the principles of Thermo dynamics, Fluid Mechanics and Heat Transfer.

 Refrigeration Cycle is more important for Air Conditioning System. 

The dome-like curve represents saturated conditions for the refrigerant. On the left half of the dome, the refrigerant exists as a saturated liquid and on the right as saturated vapor. Both liquid and gaseous refrigerant coexist inside the dome in saturation. To the left of the dome, the refrigerant is a sub cooled liquid and to the right of the dome, it is a superheated vapor.

The numbers (1 through 4) represent significant points in the flow of refrigerant as it makes its circuit in the cycle. The refrigerant working fluid undergoes thermodynamic changes between these points.

Point 1-2 (Evaporation): Since this is inside the d

ome, constant pressure (21.5 psia) and temperature (-5°F) are maintained, i.e., saturation. When heat is transferred at saturation, the result is a change in phase.

Point 2-3 (Compression): Compressing the gaseous Freon from 21.5 to 141 psia (6.5 to 126 psig) produces a concomitant increase in thermal energy represented by a rise in the enthalpy and the temperature of the Freon from 5° to 125°F. This is the heat of compression resulting from the added energy to the Freon vapor. Compression provides the thermal driving head to sustain the flow of Freon through the cycle.

Point 3-4 (Condensation): In passing through the dome from the right side to the left, the refrigerant cools from 125° to 105°F and changes phase from a superheated vapor to a slightly subcooled liquid.

Point 4-1 (Expansion): The refrigerant is expanded by passing through an expansion valve where its pressure is reduced from 141 psia to 21.5 psia. In the process of expanding, the Freon cools from 105° to -5°F (cold of expansion) and crosses into the dome where both saturated liquid and gaseous Freon can coexist. About 25% of the fluid vaporizes into a gas during the process.

The typical Refrigeration Cycle would be as follows

The following are the Components of Refrigeration System.

Evaporator/Chiller

Compressor

Condenser

Receiver

Thermostatic Expansion Valve (TXV)

The refrigerant will be used in the refrigeration system. 

Evaporaor to be located in the space to be refirgerated or cooled.

Compressor is used to compress the refrigerant to achieve heat transfer.

Condenser in which refrigerant rejects its heat to cooling medium either air or water.

Expansion Valve is used to bring down the pressure of refrigerant before entering into evaporator.