Study of high temperature PEM fuel cell (HT-PEMFC) waste heat recovery through ejector based refrigeration

The incorporation of an ejector refrigeration cycle with a high temperature PEM fuel cell (HT-PEMFC) presents a novel approach to combined heat and power (CHP) applications. An ejector refrigeration system (ERS) can enhance the flexibility of a CHP system by providing an additional means of utilizing the fuel cell waste heat besides domestic hot water (DHW) heating. This study looks into the performance gains that can be attained by incorporating ejector refrigeration with HT-PEMFC micro-CHP (mCHP) systems (1 to 5kWe). The effectiveness of the ERS in utilizing fuel cell waste heat is studied as is the resulting enhancement to overall system efficiency. A test rig specially constructed to evaluate an ERS under simulated HT-PEMFC conditions is used to test the concept and verify modeling predictions. In addition, two separate analytical models were constructed to simulate the ERS test rig and a HT-PEMFC/ERS mCHP system. The ERS test rig was simulated using a Matlab® based model, while two residential sized HT-PEMFC/ERS mCHP systems were simulated using a Simulink® model. Using U.S. Energy Information Administration (EIA) air conditioning and DHW load profiles, as well as data collected from a large residential monitoring study in Florida, the Simulink model provides the results in system efficiency gain associated with supporting residential space cooling and water heating loads. It was found that incorporation of an ERS increased the efficiency of a HT-PEMFC mCHP system by 8 to 10 percentage points over just using the fuel cell waste heat for DHW. In addition, results from the Matlab ERS test rig model were shown to match well with experimental results.