Investigation of the flexibility of a residential net-zero energy building (NZEB) integrated with an electric vehicle in Hong Kong

Abstract

The flexibility of a net zero energy/emission building (NZEB) in the cooling dominated area is quantitatively investigated in this research. Flexibility sources include the renewable energy, i.e. building integrated photovoltaics (BIPVs) and wind turbine, and thermal energy storages, i.e. air handling unit cooling storage tank (ACST) and domestic hot water tank (DHWT). Parametric analysis has been conducted based on all proposed flexibility indicators with respect to the renewable energy capacity, the volume of both the ACST and the DHWT, and the set point temperature for recharging the DHWT. From our results, to meet the annual energy balance, this NZEB should be equipped with BIPVs and an 8 kW wind turbine, while these BIPVs should be installed on four walls and the roof (totally 306 m2 BIPVs). Considering the grid feed-in tariff in Hong Kong, the NZEB will get the net annual operational income at 646.3 HK$/m2.a. Flexibility factors indicate the flexibility of the energy storage systems for storing the surplus renewable energy (REe) and fulfilling the building demand. During the charging process, the increase of the REe capacity shows positive impact on flexibility factors of both the ACST and the DHWT. In the case when BIPVs are on four walls, with respect to the increase of the rated wind turbine capacity from 0 to 8 kW, the flexibility factor of the ACST increases from 0.49 to 0.58 during the charging process, whereas it decreases from -0.51 to -0.59 during the discharging process. Meanwhile, the flexibility factor of the DHWT increases from 0.32 to 0.57. Moreover, with respect to the increase of the ACST volume from 0.5 m3 to 2.5 m3, the flexibility factor increases from -0.23 to 0.17 considering both the charging and the discharging processes. With respect to the increase of the DHWT volume from 1 m3 to 3 m3, the flexibility factor increases from 0.32 to 0.74. With respect to the increase of the set point temperature for recharging the DHWT from 65 ºC to 100 ºC, the flexibility factor increases from 0.32 to 0.82. Moreover, in comparison with the nighttime interaction between the building and the vehicle, the daytime interaction will reduce the reliance on the grid for charging the EV. Moreover, the energy interaction between the building and the vehicle will be enhanced.