Numerical analysis and experimental validation of an innovative process for catalytic hydrogen water heaters

Residential heating with hydrogen is a possible strategy for decarbonization where electrification is difficult due to constraints of the building or of the infrastructure. Hydrogen water heaters can have a catalytic combustor operated with an ultralean mixture to reach net-zero emissions and have an inherently safe process. This work numerically analyzes and experimentally validates the performance of an innovative process for a catalytic hydrogen water heater. The process enables the achievement of high efficiencies through the recirculation of reaction products, the preheating of fresh air, and the injection of hydrogen upstream of the fan. These characteristics are a novelty on a catalytic hydrogen water heater and the process presented is also patented. The numerical analysis of the process is carried out with a model, while the experimental validation involves the construction of a full-scale laboratory prototype. The theoretical thermal efficiency in the nominal operational condition producing 25 kW power is equal to 105.8%, with respect to the lower heating value at 15 °C. Moreover, the theoretical efficiency in the test condition is equal to 102.7% when accounting for the conversion of the fuel. Ultimately, the full-scale prototype is operated in the test condition achieving a measured efficiency of 102.6%.