A multi-purpose building with different applications such as residential, office, cultural, restaurant, parking, etc. is analyzed in this research. The facilities in many multi-purpose buildings in developing countries are considered having old energy systems with high energy consumption. Application for national energy labeling require optimizing the energy consumption. However, many such buildings in Iran are not awarded the above-mentioned label. The present study aims to assess a multi-purpose building which is not able to get standard energy label with existing situation. To reduce energy consumption in such buildings, solutions such as applying phase-change materials (PCM) in exterior walls, installation of photovoltaics (PV), employing building energy management system (BEMS), and switching the central system to gas engine-driven heat pump (GEHP) were analyzed. The reduction of energy consumption due to PCM, PV, BEMS, and GEHP solutions were 2, 6, 23, and 63%, respectively. The use of PCM, PV, and BEMS failed to enabling the building to receive energy label. Instead, the E category energy label was received only by switching the central heating system to the GEHP system. The payback period for switching the facilities to GEHP system lasted 7.5 years. This method of energy labeling can be used for all of the past multi-purpose Buildings.