Fuel cell cathode balance of plant freeze strategy

A fuel cell system with a cathode subsystem, said cathode subsystem comprising:

• a fuel cell stack;
• a cathode inlet line that provides cathode inlet air to the fuel cell stack;
• a cathode exhaust line that exhausts a cathode exhaust gas out of the fuel cell stack;
• a water vapor transfer unit that transfers humidity from the cathode exhaust gas to the cathode inlet air;
• and
• a charge air cooler that is located in the cathode inlet line and that feeds into the water vapor transfer unit, said charge air cooler being cooled by a coolant loop, wherein a pressure sensor is positioned on the charge air cooler such that the pressure of the cathode inlet air is measured after the air is cooled by the charge air cooler and the pressure of the cathode inlet air is measured before the water vapor transfer unit adds water to the cathode inlet air.

A fuel cell system with a cathode subsystem, said cathode subsystem comprising:

• a fuel cell stack;
• a cathode inlet line that provides cathode inlet air to the fuel cell stack;
• a cathode exhaust line that exhausts a cathode exhaust gas out of the fuel cell stack;
• and
• a by-pass line that selectively directs cathode inlet air to the cathode exhaust line using a by-pass valve, said by-pass valve located near the cathode inlet line in the by-pass line, said by-pass line including at least one turn downstream of the by-pass valve that prevents water in the cathode exhaust line from back splashing against the by-pass valve.