SCHEMATICS OF HVAC & BATTERY COOLING SYSTEM (BCS) 5. WORKING The HVAC system is similar to a conventional automotive 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-pressure 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 vapour is then made to pass through the condenser (condenser is cooled by the passing ambient 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 (TXV). 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 ambient air made to pass through it by forced circulation of the blower. The liquid refrigerant absorbs the latent 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. BATTERY COOLING SYSTEM (BCS) After condenser ‘T’ joint is provided in the refrigerant line and refrigerant flows towards Chillier unit which is used for battery cooling system. 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 chillier unit, where it absorbs the heat of the coolant made to pass through it by forced circulation of coolant pump. The liquid refrigerant absorbs the latent heat required to change to vapour state and turns to vapour. Low pressure, super-heated refrigerant flows towards compressor suction. Before compressor suction, one ‘T’ joint is provided where superheated vapour refrigerant from cabin HVAC and BCS chillier comes together and flows towards compressor suction. FATC 6
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