CO2 Air Conditioning Systems - 图文

Contact: Marlene Goldsmith

(248) 372-8222

marlene_goldsmith@denso-diam.com

FOR IMMEDIATE RELEASE March 4, 2002

CO2 Air Conditioning Systems

Concerns regarding the effect of global warming have been growing in recent years.

Refrigerant of car air conditioning systems was switched from CFC-12 to HFC-134a in many countries for ozone layer protection. However, the global warming potential of HFC-134a refrigerant is still high, and car air conditioning systems are required to use a more

environmentally benign refrigerant to prevent global warming. For the future, carbon dioxide (CO2) refrigerant is considered to be one of the most promising alternatives.

Features of CO2 Refrigerant

Extremely Low Global Warming Potential Value (GWP)

The global warming potential value of CO2 is extremely low, which is about 1/1300 of HFC-134a. Therefore, even if CO2 is leaked from an air conditioner system when it is used as refrigerant for the system, the effect caused by leakage to the environment is negligible.

CO2 Air Conditioning Systems Page 2 of 7 High Operating Pressure

CO2 has a critical temperature*1 lower than that of HFC-134a and a critical pressure*2 higher than that of HFC-134a. Therefore, in air conditioning systems adopting CO2 refrigerant, a high-pressure side temperature exceeds the critical point. This results in a high operation pressure that is 7 to 10 times larger than that of HFC-134a.

*1) Critical temperature is the temperature above which a substance cannot exist in the liquid state regardless of the pressure.

*2) Critical pressure is the equilibrium pressure of a fluid that is at its critical temperature.

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CO2 Air Conditioning Systems Page 3 of 7

DENSO CO2 Air Conditioning System

DENSO, which is a global leader in air conditioning systems with the world’s top market share of 24 percent, has developed a CO2 air conditioning system resistant to high operation pressure.

DENSO’s CO2 air conditioning system shown in FIGS. 1 and 2 differs from a conventional air conditioning system using HFC-134a mainly in the following points: ?

A gas cooler, which corresponds to a conventional condenser, cools CO2 refrigerant discharged from the compressor. Because CO2 refrigerant exceeds the critical point of CO2 at the high-pressure side, CO2 refrigerant is not condensed by the gas cooler. Instead, the expansion valve condenses a part of the CO2 refrigerant as a result of adiabatic expansion. ?

As shown in FIG. 1, an inner heat exchanger is provided between the gas cooler and the heat exchanger to further cool the CO2 refrigerant, discharged from the gas cooler, by exchanging heat with refrigerant flowing at the low-pressure side of the system. The inner heat exchanger increases the liquid refrigerant at the inlet of the evaporator to increase the cooling performance, resulting in increased Coefficient of Performance (COP) of the system. ?

The accumulator is disposed at the low-pressure side since the refrigerant pressure at the high-pressure side is about 10MPa or more, which is much higher than that of the

CO2 Air Conditioning Systems Page 4 of 7

conventional system. Because the accumulator is integrated with the internal heat exchanger and the expansion valve, the structure of the CO2 air conditioning system becomes simple and is easy to install in the vehicle. ?

Each component is designed to enable resistance to high operation pressure.

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CO2 Air Conditioning Systems Page 5 of 7

FIG. 1 Basic Structure of CO2 Air Conditioning System

Gas/Cooler Inner Heat Exchanger Compressor Accumulator Expansion valve Evaporator HVAC Unit

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