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## Exhaust Air Heat Exchanger 

In z14 servers, all water-cooled models have two Exhaust Air Heat Exchanger units that are installed on the rear of the A and Z frames, as shown in Figure 2-32. These units remove heat from the internal system water loop and internal air exits the server into the hot air exhaust aisle. 

<img src='content_image/971698.jpg'>

In addition to the PU SCMs cold plates, the internal water loop circulates through these two heat exchangers. These exchangers are in the path of the exhaust air in the rear of the frames. These heat exchangers remove approximately 65% of the residual heat from the I/O drawers, PCIe I/O drawer, the air-cooled logic in the CPC drawer, and the power enclosures. The goal is for two-thirds of the total heat that is generated to be removed from the room by the chilled water. 

If one client water supply or one WCU fails, the remaining feed maintains PU SMCs cooling. The WCUs and the associated drive card are concurrently replaceable. In addition, the heat exchangers can be disconnected and removed from the system concurrently. 

