As a leader in the field of air conditioners, DENSO has been at the forefront of environmental technology. In 2002, DENSO introduced the world’s first carbon dioxide (CO2) air conditioning system for Toyota’s fuel cell hybrid vehicle (FCHV-4). The GWP of CO2 is extremely low – about 1/1,300 of that of HFC-134a. DENSO currently produces the following components.
Compressor
The compressor for the CO2 air conditioning system is unique. It is designed to withstand high pressure and reduce its power consumption to improve the coefficient of performance (COP)* of the system.
The compressor used for Toyota’s fuel cell hybrid vehicle (FCHV-4) is a scroll type and is driven electrically rather than by an engine via a belt. The electric compressor can be made airtight, which makes refrigerant leakage unlikely. In addition, since the compressor can be controlled by a motor regardless of the engine speed, the CO2 air conditioning system works efficiently in all driving conditions, providing comfortable air to passengers.
COP = cooling capability/compressor consumption
Gas Cooler
The gas cooler corresponds to a conventional condenser and cools the CO2 refrigerant discharged from the compressor at a high pressure.
Because of this high pressure, the tubes in which refrigerant flows and the tank for distributing the refrigerant into the tubes of the gas cooler are strengthened compared to a conventional heat exchanger. Specifically, each tube is made five to 10 times stronger than a conventional tube by optimizing the hole diameter and wall thickness. The tank is reduced in size in order to decrease the area that receives high pressure, without losing the capability to uniformly distribute the refrigerant into the tubes.
In addition, the gas cooler uses a unique tank structure, which allows refrigerant to flow more efficiently in the gas cooler to exchange heat with air.
Internal Heat Exchanger
The CO2 air conditioning system incorporates an internal heat exchanger that is installed between the outlet of the gas cooler and the evaporator. The internal heat exchanger, which is not equipped with the conventional HFC-134a, helps to further cool the CO2 refrigerant by exchanging heat with refrigerant flowing at the low-pressure side of the system. The internal heat exchanger increases the amount of liquid refrigerant flowing into the evaporator to increase the cooling performance, resulting in increased the coefficient of performance (COP = cooling capability/compressor consumption) of the system.
The internal heat exchanger is integrated with the accumulator and the expansion valve so that the structure of the CO2 air conditioning system becomes simple and easy to install.