The present study examines the effect of the number of objective functions on the optimal performance of an exhaust air heat recovery unit including a building integrated photovoltaic/thermal unit (BIPV-T) and a heat recovery wheel (HRW). The unit is able to precool/preheat the outdoor air and generate electricity. Four objective functions are introduced to optimize the performance of the system from energy, energy, economic and environmental perspectives and all the possible single-objective, two-objective, three-objective and fourobjective optimizations are conducted and the results are compared. Seven geometrical and operating variables consisting of the width, depth, and length of the BIPV-T channel, air mass flow rate, and rotational speed, length, and depth of the HRW unit are chosen as the decision parameters. The outcomes revealed that if a designer expects the examined unit to supply the entire energy and exergy required by building and the production of extra energy and exergy is worthless, then the optimization of unit performance based on the maximization of the amount of undischarged CO2 (Scenario 2) will be the best and the most effective scenario for the single-objective optimization of the unit.
