Abstract
The Sultanate of Oman, being a petroleum-producing country, depends on fossil fuels for the majority of its power production. The fossil fuel sources are on the verge of extinction if they are used at the current rate. Globally, buildings are expected to generate the energy they demand using renewable energy sources and, if possible, feed it to the grid. Zero Energy Buildings (ZEBs) and Near Zero Energy Buildings (NZEBs) are put into action for the above purposes. With an average global solar irradiation of 5.56 kWh/m2/day and an average wind speed of 6.58 knots, solar and wind are the primary renewable energy sources that can be yoked in Oman. The solar and wind power plants that are being built in Oman are following the Grid Code Operations as of 2020. Buildings in Oman, newer ones and old ones, are constructed using traditional building materials, leading to poor performance of the building's peripheral enclosure and little or no emphasis on sustainability. This has led to thermally bungling building envelopes in Oman, contributing to high energy consumption for lighting and cooling buildings, which invariably adds to global warming. Extensive use of fossil fuels has also escalated the average global surface temperature. The main aim of this paper is to analyze the design and development of ZEB/NZEB technology to be used in an educational institute in Salalah, Sultanate of Oman, incorporating state-of-the-art techniques in harnessing renewable energy sources with Battery Storage Systems (BSS), construction/modification and orientation of buildings towards energy-efficient buildings, smart and energy-efficient systems and appliances, HVAC approaches, and automated real-time conservation practices using Internet of Energy (IoE).
Keywords:
- ZEB or NZEB
- IoE
- Battery Storage Systems
- Educational Institute
Introduction
The production capacity from renewable supplies in Oman has a target to increase 30% by 2030 (Tabook & Khan, 2021). Subsequently, the first wind farm was fixed in the south of Oman with a 50 MW capacity, and a 500 MW solar plant will be tied to the grid in 2021. To cope with renewable assembly projects, the grid code details a connection condition for verifying the fulfillment of renewable plants. As the requirement for energy is rising rapidly due to urbanization and industrialization across the world, concerns include greenhouse gas emissions causing environmental catastrophes and the exhaustion of fossil fuels (Todorovic, 2011). Therefore, the world is trying to substitute, conserve, or reduce fossil fuel usage by using renewable energy sources (Vergini & Groumpos, 2015) . As a result, many countries are adapting the idea of a ZEB, which can be a single house or a small community, with the purpose of producing their own energy to meet their own demand. The methodology adapted leads to ZEB or NZEB (Gong et al., 2020).
1. Related Works
Todorovic (2011) analyzes existing definitions, some of which are confusing, the approach to zero-energy buildings, and the problem of existing buildings that are not efficient and need to be refurbished. The analysis of the refurbishment of existing buildings in Belgrade is discussed, and possible energy achievements are estimated. This topic is of interest to researchers, energy specialists (heating, air conditioning), the entire building industry, and, of course, architects.
Vergini and Groumpos (2015) define the parameters that should be taken into consideration, and classifying ZEBs helps with that attempt. Energy management and intelligent control play a key role in the successful operation of a ZEB, improving its performance and reducing its consumption. The method of Fuzzy Cognitive Maps (FCMs) is appropriate for problems with many parameters where mathematical modelling and calculations have difficult or, in some cases, impossible solutions.
Gong et al. (2020) propose a hybrid energy storage system including batteries and a variable-power electric water heater that enables the NZE homes to behave like dispatchable generators or loads, thereby reducing the rate of change of the net power flow from the house. A cosimulation framework, INSPIRE+D, that enables the dynamic simulation of electricity usage in a community of NZE homes and their connection to the grid is enabled.
Hannan et al. (2018) present a critical review of the potential of an IoE-based Building Energy Management System (BEMS) for enhancing the performance of future generation building energy utilization. The detailed studies of the IoE architecture, typical NZEB configurations, different generations of NZEB, and smart building energy systems for future BEMS are investigated. The operations, advantages, and limitations of the existing BEMSs or NZEBs are illustrated. A comprehensive review of the different types of IoE-based BEMS technologies, such as energy routers, storage systems and materials, renewable sources, and plug-and-play interfaces, is then presented.
Irfan et al. (2018) mention that the change in climate is mainly due to the emission of Green House Gases (GHGs), which are produced from the emission of gases and the use of fossil fuels for the generation of electricity in Pakistan. Most of the energy is used in commercial buildings as well as in residential buildings. It is imperative that buildings be constructed in such a way that they consume less energy due to efficient design, generate on-site energy for own use, and export excess energy to the utility.
2. Energy Generation at NZEB in Oman
A building, either residential or commercial, is called a Zero Energy Building (ZEB) or Near Zero Energy Building (NZEB), if it generates energy for its own use within its limitations (Hannan et al., 2018; Samarji et al., 2012; Srinivasan et al., 2011). Renewable energy technologies, which are located near the building, produce the energy required (Irfan et al., 2018). Differences still exist in the interpretations of ZEB and NZEB (Roekrai & Khan-Ngern, 2020). In general, ZEB and NZEB can be expressed by Equation 1 as given below.
where, GE= Generated Energy and CE = Consumed Energy, over a period of time (Chandanachulaka & Khanngern, 2017).
A major share of renewable energy is from solar Photo Voltaic (PV) and squall energy, especially in Oman, which is a warmer country. Also, compared to other alternative energy sources, solar PV has the lowest components and is the most economical (Chandanachulaka & Khanngern, 2017). Moreover, the squall energy is limited to certain geographical locations only, and at the location of study, the possibility of harnessing is almost nil. The location of the study is in the heart of the city of Salalah, where the wind speeds are less than the minimum required for electricity production. The wind speed at the location of the study is marked at 8 to 10 km/h, whereas the minimum wind speed to start turning the wind turbine and generating electricity is generally 12 to 14 km/h. So, in this analysis, a solar PV system is the only source. The Global Horizontal Irradiation (GHI) and Photovoltaic Power Potential (PPP) of the Salalah region, for a period of 1999–2018, are given in Figures 1 and 2. Figure 1(a) shows 2 the daily total of GHI ranges from 5.6 to 5.8 kWh/m and 2 the yearly total ranges from 2045 to 2110kWh/m . The PPP ranges from 4.6 to 4.8kWh/kWp and the yearly total ranges from 1680 to 1753kWh/kWp as shown in Figure 1(b).
Figure 1. (a) Global Horizontal Irradiation, Oman (b) Photovoltaic Power Potential, Oman
Figure 2(a) gives the details of the number of sunny days in Salalah for the year 2021, and Figure 2(b) shows the average number of sunny hours for the year 2021. From the Figure 2(a), the total sun hour count is 3690, making an average of 307.5 hours, with the highest of 372 hours and the lowest of 93 hours seen in the month of July. Khareef season falls during the months of July and August, and this substantially reduces solar radiation. The total number of sunny days in the year 2021 is counted as 255, which contributes an average of 21.25 hours per month, as shown in Figure 2(b). The same dip in sunny days is observed during the months of July and August of 2021. The average sun hours and radiation data make a solar PV system feasible to be used in Salalah as an alternate energy source (World Weather Online, n.d.).
Figure 2. (a) Sun Hours & Sun Days in Salalah (2021) (b) Average Sun Hour in Salalah (2021)
The study is carried out in a staff room at the University of Technology and Applied Sciences-Salalah, Sultanate of Oman, one of the leading educational institutions in Oman. The sample room consists of two ACs, twelve fluorescent lamp assemblies (each with four 18-watt lamps), five computers, a printer, a photocopier, and several Data System Support Organization (DSSO). The college works from 8 AM to 6 PM, counting to 10 hours of power usage. Table 1 gives the daily electrical load details of the staff room.
Table 1. Daily Load Calculation of Staff Room
The paper is prearranged and the research is organized as solar panel design, battery storage system design, methods that should be adapted for energy efficient building construction, modification, and orientation, energy efficient systems and appliances that are to be used, HVAC approaches and conservation practices, and techniques of cost-effective control and conversion of energy. In the end the conclusions are discussed.
3. Solar PV System Design
As previously stated, renewable energy sources are the foundation of any ZEB or NZEB. Being a warmer country, the most suitable renewable technology in Oman is solar Photo Voltaic (PV) technology. The primary phase of converting the existing building to ZEB or NZEB is to design a solar PV system with battery storage, considering the special climatic conditions of Oman, especially in the Dhofar region, where the Khareef (monsoon) season drastically reduces the solar irradiance for almost 2 months, July and August. Most commonly available solar panels range from 100W to 400W with a nominal voltage of 12V or 24V for a single panel.
The average sun hour in Oman is estimated to be 6.5 hours, and the number of solar panels required is calculated using an efficiency of 80%.
The energy cost per unit in Oman is considered as 30 Baisa (Bz). One Omani rial = 1000 Baizas.
Panel output per day = 400W x 6.5h x 0.8 = 2080Wh
No of panels required = 109422Wh/2080Wh
= 53 Panels (Rounded)
The calculated energy bill to be paid to the energy providing agency is 109.422 kWh x 30Bz/unit x 365days
= 1198.17 Omani rial.
Saving in terms of energy consumption per year by implementing solar PV system is 109.422 kWh x 30Bz/unit x 300days = 984.798 Omani rial.
The cost of 53 PV panels along with an MPPT, charge controller, and inverter is estimated at 2400 Omani rials. The energy harnessed by PV panels is to be stored for later usage, which makes it vital for an efficient BSS.
4. Battery Storage System Design
BSS is an integral fragment of any ZEB or NZEB system and substantially contributes to the efficiency and storage of power harnessed from renewable energy sources. Deep cycle batteries are used to store the harnessed energy due to their efficient deep discharge and fast charging capabilities. Presently available deep-cycle batteries of 200 Ah at 24 V are considered for the design and study of this research. Calculations take into account one day of autonomy, a battery discharge level of 60%, and an efficiency of 85%.
Battery Capacity (Ah) = Total Daily Load * Days of autonomy/ (0.85 x 0.6 x nominal battery voltage)
= 109.422 KWh*1/ (0.85 x 0.6 x 24V) = 8939.7 AH
Required BSS = 8939.7 Ah /200 Ah = 45 Batteries
The cost of 45 batteries is estimated to be 1600 Omani rial, which when combined with the cost of solar PV modules totals 4000 Omani rial. The payback period is around 5 years, with a total savings of 984.798 Omani rial per year on electricity bills.
In Oman, solar power as a renewable source of energy is not yet widely used, despite the very high potential for such technologies. The annual average insolation on a horizontal surface in Halban, Oman (Latitude N 20 ° 23', Longitude E 55 ° 96') is at 2,241.1 kWh/m2/year and among the highest in the world (3). On the roof of the Eco House, a photovoltaic system with 38 modules of 327 Wp each has been installed at a tilt angle of 25 °. The total array capacity of 12.42 kWp has the potential to generate 20 MWh/a of electricity based on the available climate data. In addition, a roof installed solar thermal system with 4m2 panel area will cover 100% of domestic hot water demands with 55 - 60 °C hot water from a 200l tank. The Eco House will be connected to the campus grid, and as long the university grid consumes more electricity than the PV system can generate, it can feed into the grid. The Eco House is the first residential building in Oman to receive permission from the Authority for Electricity. It has a regulation to feed in PV-generated electricity and receives a feed-in tariff that is equal to the market price.
5. Battery Storage System Design
Painting the exterior wall with thermal insulation paints is the suggested primary modification in the subject under consideration. It is estimated that these paints absorb only 1.9% of solar heat compared to the 10 to 20 percent of absorption by normal paints. It is observed that the consumption of energy for cooling requirements is well conserved by the reduced hours of usage of AC.
According to observation, creepers and trees grown on the faces of the exterior walls of the building furthermore reduce the thermal conduction of the building, thereby reducing the interior temperature. Energy-efficient building envelopes, such as thermal insulation of walls, high-efficiency windows and door seals, etc., aid in maintaining the barrier between the unconditioned exterior and the conditioned interior. Using lighter and whiter shades on the walls will improve the reflection of light and reduce its absorption, thereby increasing the lighting efficiency. The study room is painted lighter and has light-colored floors, converting it to ZEB will not increase its cost. Projected window design increases the area of transparency, thereby inviting more natural lighting to the interiors and narrowing the artificial lighting requirement, along with energy-efficient systems and appliances.
6. Energy Efficient Systems & Appliances
One of the primary energy needs of any building is effective interior lighting, whether natural or artificial. The staff room under study is illuminated using artificial fluorescent lamps. Replacing existing fluorescent lamps with low-power LED lights will further reduce the energy requirement.
Total power consumed by existing fluorescent lamps is 12 x 6 x 18 = 1296 W/ hour
Energy consumed by existing fluorescent lamps is 12.96KWh/day = 12.96 units/day
Energy consumed per year =12.96 x 300 = 3888 units.
Total cost for power usage = 3888 x 30/1000= 116.64 Omani rial.
The 18 W fluorescent lamp gives 33 lux, considering a beam angle of 120 degrees at a height of 3.6meters. Total 72 existing lamps gives a total lux of 2376. Energy efficient 18W LED lamp will give 60 lux to meet the room lux of 2384, so need 40 LEDs.
Power consumption of LED per year = (40 x 18 x 10 x 300) / 1000 = 2160 kWh.
Energy saving per year=3888 kWh - 2160kWh
= 1728 kWh.
Cost saving in terms of energy consumption per year = 1728 x 0.03 = 51.84 Omani rial.
Estimated payback period is 8 months. The discussions are about the conservation approaches to be incorporated for further reduction in power usage.
7. HVAC Approaches & Conservation Practices
It is estimated that 50% of energy consumption in the subject area is used for cooling, using AC. The number of ACs in the room is four; each is normally working at a temperature of 18 degrees Celsius. Energy-efficient building modifications, as discussed in energy-efficient building modifications, allow keeping the air-conditioning system's temperature higher than the current setting of 18. According to observations, each degree increase in air conditioning saves 3% of energy consumption. That means an increase in the set temperature of the air-conditioning system to 22 will save a total of 12% of total energy consumption.
Energy saving per day = 12% of 2100W x 4 AC x 10 hours = 10080 kWh
Savings = 3024 x 30/1000 = 90.72 Omani rial.
8. Techniques of Cost-Effective Control & Conversion of Energy
Controlling the usage of power is an integral action towards achieving ZEB or NZEB, which is accomplished by Smart Energy Management Systems (SEMS) using IoE. The main function of IoE is to monitor, record, and control energy usage to create a balance between demand and supply of energy. The key to energy conservation is to integrate automation with smart devices to optimize energy usage.
The Internet of Energy (IoE) refers to the automation of electricity infrastructures to facilitate increased electricity efficiency and conservation of energy through a reduction in energy wastage, thereby advancing cost savings. Electrical equipment equipped with occupancy or motion sensors detects the presence of users and sends a control signal to dim or turn off lamps, fans, air conditioners, and so on.
The data in Table 2 given above depicts the energy savings per day by incorporating IoE and soft switching, which add up to a total savings per year of 23122.8 kWh and a cost savings of 693.684 Omani rials. The total estimated cost of soft switching equipment is 25.22 rials, 76 switches, or 1942.3152 Omani rials.
Table 2. IoE Based Energy Conservation Through Soft Switching
9. Results
Table 3. Consumption of Energy and Savings
Figure 3 shows the energy consumption from the grid before and after the installation of a solar PV system. Without implementing any of the conservation techniques discussed above, the grid dependency has decreased to nearly zero with the calculated load. The total cost incurred is 2710 Omani rial, with a payback period of 5 years.
Figure 3. Energy Consumption Before and After Solar PV Installation & Savings
The impact of the energy-efficient systems and appliances is detailed in Figure 4, in which a 56.25 percent reduction in energy consumption is observed. This provided a savings of 34.020 Omani rial per year, counting to a payback period of 8 months.
Figure 4. Energy Consumption Before and After Energy Efficient Systems and Appliances Installation & Savings
Figure 5 depicts energy conservation techniques, in which building modifications account for a 13.1% reduction in sunlight absorption, and using HVAC approaches and conservation practices, energy consumption for cooling purposes can be significantly reduced, with an estimated 12% reduction in power consumption, amounting to a 1512 kWh reduction when compared to previous practices.
Figure 5. Energy Consumption Before and After Solar PV Installation & Conservation Techniques, Cost Savings and Payback Period
In Figure 6, the percentage of energy saved is shown, with the highest savings of 100% by solar PV installation and the lowest of 12% using HVAC approaches.
Figure 6. Percentage of Energy Saved
10. Limitations
Salalah is well known for its Khareef season (monsoon season) during the months of July and August, when the average monthly sun hours fall to 100 hours from the normal average of 300 hours. So the grid dependency is needed, particularly during these months, which is a major limitation in this study. The installation of a solar PV system and a BSS is expensive at first, and when combined with the costs of building modifications and appliance cement, the Return On Investment (ROI) will be delayed. As an existing building, the provision for space for the installation of solar panels and BSS is limited.
Conclusion
The design and development of ZEB/NZEB technology to be used in an educational institute in Salalah, Sultanate of Oman was analyzed. Controlling the usage of power is an integral action towards achieving ZEB or NZEB, which is accomplished by smart Energy Management Systems (SEMS) using IoE. The IoE monitors, records, and controls energy usage to create a balance between demand and supply of energy. The key to energy conservation is to integrate automation with smart devices to optimize energy usage. Without implementing any of the conservation techniques discussed above, the grid dependency has decreased to nearly zero with the calculated load. Also, there is in the future, BSS can be replaced by super capacitors for better efficiency and control, reactive power control, power quality, frequency control, frequency range, voltage control, fault ridethrough, black start capability, a smart meter; smart and soft operating switches, auto sensors, etc. can be implemented.
Keep track of the energy audit and alter the usage accordingly towards cost control, periodic maintenance and repair of electrical appliances, use of a programmable thermostat, a detailed study of the entire building, peak shaving, which saves nearly 20% to 25%, bright lights, cleaning the lamp and fixture regularly as illumination level falls by 20 –30% due to dust collection, use of double doors, automatic door closers, air curtains, double-glazed windows, polyester sun film, etc. Reduce heat ingress and air conditioning load in buildings, and educate users on additional practices and user habits for additional savings and smooth system operation. This study, future scope, and suggestions will help to fill the research gap for future researchers.