What are liquid-cooled rear doors?

A liquid-cooled rear door, also known as a rear-door heat exchanger (RDHx), replaces the back door on a server rack or server cabinet with a water-cooled coil. Hot exhaust air from the servers passes through the coil and leaves the cabinet at or near room temperature, removing heat before it reaches the room. Passive doors rely on the servers’ own fans, while active doors add fans to handle higher rack loads. They are a popular way to add higher-density racks to an existing air-cooled room.