# Assessment of the Potential of High-Performance Buildings to Achieve Zero Energy: A Case Study
## 1 Introduction  
A zero-energy building is a building with greatly reduced energy needs through efficiency gains such that the balance of the energy needs can be supplied by renewable energy generated on site on an annual basis [1; 2; 3]. Achieving zero energy is an ambitious yet increasingly achievable goal thanks to the recent advances in building technologies. A variety of governments, e.g., the European Union and the United States, have established policies and targets for new buildings to become zero-energy in the next ten years [4; 5; 6]. However, transforming the existing buildings into zero energy is as important as building new ones. The proliferation of low- and very-low-energy buildings in recent years presents great opportunities for such transformation. A number of studies have explored the technical and economic viabilities. [PERSON] et al. [7] investigated the possibility of converting a small low-rise public building located in a hot climate into a net-zero-energy building. An earlier retrofit had brought down annual energy consumption by 27% (659 MWh), and the simulation results indicated that an additional 33.6% savings (821 MWh) could be achieved by a set of energy efficiency measures (EEMs), which would make the building zero-energy ready. Three potential solutions to convert the building into a zero-energy building were discussed. The first solution would use only the photovoltaic (PV) system that utilizes the entire roof; the second solution would use less PV with the replacement of existing chillers with more efficient ones; the third solution would combine the PV and a solar cooling system. Simulationresults showed that the first solution could achieve the zero-energy goal on an annual basis, while the other two solutions could achieve the zero-energy goal on both an annual and a monthly basis. [PERSON] and [PERSON] [8] studied a three-story public building in Cyprus. A variety of strategies was simulated to explore the energy-saving potential, including integrating additional insulation materials, using light sensors to reduce unnecessary lighting consumption, increasing the U-value of the windows, etc. The simulation results implied that nearly 30% annual energy savings could be realized through retro-commissioning with approximately 11% from lighting and 9% from the HVAC system. The zero-energy goal could be achieved by integrating photovoltaic panels on 23% of the roof area. [PERSON] et al. [9] explored a LEED (Leadership in Energy and Environmental Design) -certified building with a total floor area of 2902 m\({}^{2}\) in Ohio, USA. They assessed two alternatives to reach the net-zero energy target. The first option was to add only PV panels to achieve zero energy on an annual basis; the other one was to add PV panels to meet all summer loads and solar thermal units to meet the heating needs. They concluded that the first option was more cost-effective. [PERSON] et al. [10] discussed a six-story university building in Spain. Natural ventilation was proposed in lieu of a conventional air conditioning system to meet the cooling needs. For the winter period, eliminating thermal bridges, using air-to-air heat recovery systems, and improving the windows' performance in the north facade showed potential energy savings of 62%. Their study indicated that with these measures, the building had the potential to become zero-energy ready. Some other studies reported similar findings with regard to transforming existing buildings into zero energy buildings [11; 12; 13; 14]. [PERSON] et al. [15] discussed retrofitting a single-family house in a rural area in Italy to achieve zero energy. A variety of approaches and technologies, such as natural ventilation, adaptive thermal comfort, advanced lighting, and a high-performance facade, were investigated. [PERSON] et al. [16] evaluated which HVAC technology was the most efficient for a residential building in the mixed-humid climate to achieve zero energy.