TIAGO

HVAC

10.1.4 HVAC SYSTEM LAYOUT AND WORKING

WORKING

The HVAC system is similar to a conventional auto-

motive HVAC system. It consists of a Compressor, a

Condenser, and an evaporator. System wise it can

be divided as low pressure side and the high pres-

sure side, which is divided at the evaporator, more

precisely at the expansion valve housed in it.

REFRIGERANT CYCLE

The compressor compresses the refrigerant R134a,

increasing its pressure and temperature. This high

pressure hot vapor is then made to pass through the

condenser

(condenser is cooled by the passing am-

bient air),

where it gives its latent heat to turn to

liquid, the drop in temperature is small, as most of

the heat lost will be latent heat resulting in change of

state to liquid

A receiver drier which is integrated in the condenser

is used to filter out the moisture and also allows only

liquid to flow further to the Thermal Expansion Valve

valve). The high pressure low temperature liquid

then expands in the TXV Valve where the refrigerant

pressure drops considerably, which also results in a

drop of temperature.

This cold low pressure liquid is circulated through the

evaporator coil, where it absorbs the heat of the am-

bient air made to pass through it by forced circulation

of the blower. The liquid refrigerant absorbs the la-

tent heat required to change to vapour state and

turns to vapour. There is no considerable change in

temperature as the heat absorbed by the refrigerant

is only latent heat. This vapour then flows to the

compressor and the cycle continues.

ENGINE COOLANT FLOW

A small amount of hot coolant from the engine is

made to pass through the heater coil keeping it at a

higher temperature all the time. From the heater coil

the coolant is flows to the water pump and again cir-

culated through the Engine.

AIR FLOW

The air is drawn in through the inlet duct due to the

suction created by the blower. The blower forces

either the ambient air or the cabin air depending on

the mode selected

(Fresh Air mode or Recirculation

mode)

to flow over the evaporator which lowers the

temperature of the ambient air. The incoming air also

gets dehumidified as the moisture condenses when

the air flows over the cold evaporator fins. This cold

de-humified air is then mixed with the hot air (

if re-

quired)

to attain the temperature selected by the

occupant; the mixing control is done by the heater

door opening