18 May 2017

P.1.3.8 Optimum hybridization of wind turbines, heat pumps, and thermal energy storage systems for nearly zero-exergy buildings (NZEXB) using rational exergy management model

The definition Nearly-Zero Exergy Building (nZEXB) is a new concept regarding 4DE (Fourth-Generation District Energy) systems. It recognizes different energy exchanges between the district and the building at different exergy levels. In nZEXB systems, a multitude of sustainable systems and renewable energy resources are mobilized. Their optimum bundling in design and load allocation is a complex problem and must be based on a robust platform of a common objective, which in this case is the minimization of exergy destruction that eventually leads to additional CO2 emissions. An optimization model was developed for a ground-source heat pump with thermal energy storage coupled to a wind turbine. Coefficient of performance (COP) and Primary Energy Ratio (PER) were redefined in terms of exergy to serve the objective function of minimizing exergy destructions. In developing the optimization model, the Rational Exergy Management Model (REMM) was employed, which aims to increase the balance among the supply and demand exergies and helps to establish a circular exergy flow. The impact of several design variables like the type of terminal units, the size and efficiency of the wind turbine, reservoir temperature, and the split of the turbine electricity between the heat pump and the building were investigated. It has been concluded that heat pumps play a major role in achieving nZEXB status provided that an optimum bundling with other sustainable systems and equipment is achieved.