Microturbines and trigeneration: Optimization strategies and multiple engine configuration effects

This paper investigates energy savings and economic aspects related to the use of micro-turbine generators in commercial buildings either for cogeneration (electricity+heat) or for trigeneration (electricity, heat and cold). In all calculations, reference is made to a 25 k W-el-class commercial microturbine generator (MTG), tested by the authors. Various plant schemes are considered, based on one or several MTG sets. The possibility of generating heat and/or cold also by an electrically driven inverse-cycle air-to-water heat pump/chiller system is also considered. Calculations are based on the simulation code TRIGEN developed by the authors. The code provides detailed energy, economic and emission yearly balances. The plant operating mode is optimized in each time interval. The results indicate that, due to large load variations, (i) the optimum turbine nominal output is in the range of about 70% of the electric peak demand, (ii) energy savings are marginal, (iii) advantages related to splitting the overall capacity on more than one unit are marginal, and (iv) the addition of an absorption machine improves the plant economics.