The energy and exergy streams of a trigeneration system (combined generation of heat, cooling and power) consisting of a biogas steam reformer, a water gas shift reactor, a high temperature proton exchange membrane fuel cell (HT-PEMFC) and a Li-Br absorption chiller are investigated in this work. Combined liquid and internal air cooling are applied to recover the heat from HT-PEMFCs. The effects of the temperature, pressure, anode stoichiometric ratio and cathode stoichiometric ratio on the efficiency, power production, net power consumption and cell performance are analyzed. The highest exergy efficiencies for electricity generation and also for combined generation of heat, cooling and power are achieved at elevated cell temperature, atmospheric pressure and at the anode stoichiometric ratio of 1.35 and the cathode stoichiometric ratio of four. The lowest exergy efficiency of all units in the HT-PEMFC based trigeneration system is obtained for the afterburner.