by Jacques Gordon
The Internal Heat Exchanger – IHX – has been around for a long time in stationary air conditioning systems, but most automotive service technicians are hearing about it for the first time. It will be needed in vehicles that use R-1234yf refrigerant, but it’s already being used in the current model Toyota Sienna minivan filled with R-134a refrigerant.
An IHX is a liquid-to-vapor heat exchanger, with one inner chamber and one outer chamber. Hot liquid refrigerant from the condenser flows through the inside chamber, and it’s surrounded by cool refrigerant vapor flowing from the evaporator through the outer chamber. After the condenser removes enough heat to condense the refrigerant to a liquid, it’s still pretty warm. The IHX transfers even more heat out of the liquid refrigerant, “sub cooling” it below condensation temperature. Obviously this improves A/C system efficiency, but it’s important to understand some of the different ways engineers will ‘spend’ that improvement.
By getting a head start on cooling the refrigerant before it reaches the expansion device (orifice tube or thermal expansion valve), the IHX is utilizing cooling capacity that is otherwise wasted. A design engineer could use this “free” cooling capacity to reduce the size of the compressor, which could cascade into weight reduction and less load on the engine. Sure, these would be small improvements, but these days engineers are adding up all the little improvements they can get.
More significantly, the vapor that exits the evaporator almost always contains tiny droplets of liquid. It’s not enough liquid to damage the compressor, but it does reduce efficiency. By letting heat from the hot liquid refrigerant flow into that vapor, these droplets get one more chance to vaporize before they get to the compressor. This reduces the power needed to run the compressor, translating into reduced emissions and/or improved fuel economy.
However, the main reason the IHX is being used today is to get away with using less refrigerant. In the lab, an A/C system filled with R-1234yf is about 10% more efficient when equipped with an IHX. That means lower temperature at the vents for the amount of power consumed to run the compressor, reducing tailpipe emissions even further.
There are two basic types of Internal Heat Exchanger. On an orifice tube A/C system, the IHX may be built into the accumulator. On an expansion valve system, the IHX is more likely to be a separate part, a tube-within-a-tube that has a pair of inlet/outlet fittings on each end. There are no moving parts to wear out, so unless it’s hopelessly clogged or damaged in a collision, you’ll probably never replace one.
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When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.
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The 34th annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Power Up will take place January 16-18 2014 at the Sheraton New Orleans.