NPC Based Design Optimization for a Net Zero Office Building in Hot Climates with PV Panels as Shading Device
Hot areas of the world receive a high amount of solar radiation. As a result, buildings in those areas consume more energy to maintain a comfortable climate for their inhabitants. In an effort to design net-zero energy building in hot climates, PV possesses the unique advantage of generating electrical energy while protecting the building from solar irradiance. In this work, to form a net-zero energy building (NZEB), renewable resources such as solar and wind available onsite for an existing
... lding have been analyzed in a hot climate location. PV and wind turbines in various configurations are studied to form a NZEB, where PV-only systems offer better performance than Hybrid PV Wind systems, based on net present cost (NPC). The self-shading losses in PV placed on rooftop areas are analyzed by placing parallel arrays of PV modules at various distances in between them. The effect on building cooling load by rooftop PV panels as shading devices is investigated. Furthermore, self-shading losses of PV are compared by the savings in cooling loads using PV as shading. In the case study, 12.3% saving in the cooling load of the building is observed when the building rooftop is completed shaded by PV panels; annual cooling load decreased from 3.417 GWh to 2.996 GWh, while only 1.04% shaded losses are observed for fully shaded (FS) buildings compared to those with no shading (NS), as PV generation decreases from 594.39 kWh/m 2 to 588.21 kWh/m 2 . The net present cost of the project has been decreased from US$4.77 million to US$4.41 million by simply covering the rooftop completely with PV panels, for a net-zero energy building. Energies 2018, 11, 1391 2 of 20 the European Directive 2020  , and national directives such as Vision 2030 of Saudi Arabia [8, 9]. The Paris Accord seeks to limit the increase in global average temperatures to 1.5 • C in 2030, and to achieve net-zero emissions by 2070. The European Union directive focuses on buildings, targeting 20% onsite energy generation, 20% more energy efficiency, and 20% less greenhouse gas emissions from all buildings by 2020. Saudi Arabia announced a plan under Vision 2030 to create a sustainable city, Neom, by the Red Sea on the border of Jordon in Tabuk province. Saudi Arabia also plans to generate 9.5 GW of renewable energy by 2023 [10, 11] . In recent years, renewable energy resources are becoming more economically feasible through the development of new technologies. In the past one year, 157 GW of renewable power systems have been installed at a cost of 279.8 billion US$, while 70 GW of fossil fuel energy systems have been decommissioned. China installed an astonishing 53 GW of solar energy systems at a cost of 86.5 billion US$  . Even the Middle East countries such as UAE and Egypt have spent 2.2 and 2.6 billion US$ respectively on solar energy plants. Currently, photovoltaic systems lead the energy production of renewable energy resources in the world  . Saudi Arabia awarded a 300 MW project to a ACWA Power, a private investor, in February 2018, with an initial capital cost of 300 million US$ ; in March 2018, KSA signed a memorandum with Softbank Group Crop to develop a 200 GW solar plant in multiple phases, with an enormous investment of 200 billion US$ . A lot of research is going on to increase the efficiency of renewable energy resources [15,16]. The research on PV was started analytically in 1950s. Now the dream is to print high energy efficient solar panels on flexible polyethylene terephthalate (PET) substrate, using printed electronics technologies at room temperature and in atmospheric pressure, which can last 25 years [17,18] and retain their efficiencies. The efficiencies of crystalline PV, III-V cell PV, and thin film PV cells have increased to 27.6% , 33.3%  and 21.7%  respectively. Since 2005, PV cell efficiencies have increased at a good rate, as presented by the NREL efficiency chart  and review articles [23,24]. PV and Wind energy system prices are decreasing, and producers are finding it difficult to deliver orders on time. This cost is declining as new competitors from Asia have entered this market. The price of solar panels has decreased by 77% from 2010 to 2017    . The cost of solar energy systems comprises the system design, panels, inverters, and skilled labor cost. New designs in wind energy with bigger turbines are decreasing technology prices, as these machines have higher power coefficients, which means that they can convert more wind energy into electrical energy. Innovative designs have reduced the use of steel in towers, and methods for making a floating tower for off-grid turbines to place them in deep water are currently in research  . The Middle East has abundant renewable resources [10, 28, 29] , and these countries should transform from fossil to renewable. The Kingdom of Saudi Arabia (KSA) is the largest oil exporting country, but huge domestic energy requirements are halting its economic growth  . The load profile of Saudi Arabia is unique, as peak load in summers is two times that of winter, because of huge cooling loads of buildings [31, 32] . The country has very hot and dry weather  . The KSA government has increased electricity prices by 260% from 0.008 US$/kWh. The solution to KSA's load problems is to curtail building load through the use of onsite renewable resources for buildings. Net-zero energy building (NZEB) can be achieved by generating electrical energy onsite, so that the net energy bought from the grid is equal to the energy sold to the grid. Developed countries have already started to design and build net-zero buildings     , in which smart techniques have been adopted to provide good insulation for buildings, reduce the load by effective use control of heating, ventilation, air conditioning (HVAC), and appliances, and to employ renewable energy systems [38, 39] . Modern buildings use both AC and DC energy systems in lighting and appliances to enhance efficiencies and eliminate conversion losses from AC to DC and vice versa [40, 41] . Off-grid energy systems require huge capital investment; during periods in which energy from renewable resources is unavailable, energy is taken from storage devices, whereas in net-zero energy systems, backup depends upon the grid. Off-grid systems require more installed capacity to meet the load, and store energy to use later. Energies 2018, 11, 1391 3 of 20 Energies 2018, 11, 1391 4 of 20 Case Study Analysis KSA has set a target of generating 9.5 GW of electrical energy from renewable energy resources by 2023, and of building a sustainable city by the Red Sea [8, 9] under the kingdom Vision 2030. KSA has already awarded ACWA Power, a private energy developer, a contract to develop the first 300 MW solar power plant, with an initial capital of 300 MUS$ in February 2018  . KSA and Softbank Group Corp signed a memorandum to develop a 200 GW solar plant with an investment of 200 billion US$  . In order to design and develop future renewable energy systems in KSA and fill thousands of jobs, Saudi students have to be well prepared to handle the huge task at hand. Universities are the ideal places to develop and understand the potential and methods of utilization of renewable energy resources and their application on loads such as buildings, to create a net-zero energy building (NZEB), and then spread the knowledge. In this work, the existing building of the College of Engineering, Majmaah University, is taken as a case study. The building of the College of Engineering has five floors and is located at 25.890302 N and 45.35629 E in Majmaah City in Riyadh province, Kingdom of Saudi Arabia (KSA), at a height of 722 m from sea level. The covered area of this building is 4859 m 2 , with parking space at the front and back of the building. The satellite image and building model are shown in Figure 1 . The CoE building working hours are from 8 a.m. to 8 p.m., where the electrical loads include heating and cooling systems, lighting, office equipment, and water heating systems. The annual daily average load is shown in Figure 2b , where a dip occurs at 12 p.m. for lunch break, and another at 2 p.m., when clerical staff leave the building. The annual load in Figure 2a shows the rise of the load with the rise in ambient temperature. The summer holiday months are from mid-June to mid-August; this results in a curtailment of the load. The system has been designed based on summer peak load, as a high load is observed in summer, and the designed system will work well in the winter as well. The KSA government has developed a data collection station to measure renewable resources throughout the kingdom for design and analysis of future renewable energy system projects for the targets set out in Vision 2030. The Majmaah station for renewable sources measurement is located in Majmaah University (MU). This measurement station is a Tier II station with uncertainty in data up to ±5%; the sensors are cleaned twice a week.