Energy Conserving Electrical Design and Analysis for Commercial Buildings

Transcription

1 J. Energy Power Sources Vol. 1, No. 2, 2014, pp Received: July 3, 2014, Published: August 30, 2014 Journal of Energy and Power Sources Energy Conserving Electrical Design and Analysis for Commercial Buildings Bezawit Teshome and Getachew Bekele Electrical and Computer Engineering, Addis Ababa Institute of Technology, Addis Ababa, Ethiopia Corresponding author: Bezawit Teshome Abstract: The electrical energy demand growth in Ethiopia has been enormous in the past few years as a result of economic growth and development. This sharp increase in demand of electricity is expected to continue in the years to come, which requires the generation of vast amounts of electricity. Therefore, more efficient use of energy has to be considered as one of the major options to achieve sustainable development. This study discusses the potential for efficient energy use in the commercial building sector of Ethiopia. It shows how much integrating energy conserving design concepts and methods into their design can play a significant role in reducing energy consumption and achieving sustainable energy structure for the society. Case studies are done on two typical commercial buildings located in Addis Ababa, Ethiopia in order to evaluate the energy consumption of conventional buildings and to select the appropriate energy conservation measures that can be implemented. This paper demonstrates the methodology followed including the modeling and simulation of the design. The potential energy saving is presented through the annual saving analysis. Life cycle cost analysis is also carried out to evaluate the economical aspect of the energy conserving design. In addition, obstacles to the full realization of energy-saving potentials in the nation s building sector are discussed. Key words: Energy conservation, commercial buildings, RETScreen. 1. Introduction Potentials for a successful use of renewable energy in Ethiopia are obvious. The country can harvest around 45,000 MW from hydropower, 10,000 MW from wind energy sources and around 5,000 MW from geothermal energy. However, the sole power provider, EEPCo (Ethiopian Electric Power Corporation) generates MW of electrical power from hydro power plants and diesel power generators. EEPCo categorizes national energy use in five broad sectors: domestic/residential, commercial, street light, industrial LV and industrial HV. The total number of customers connected to the national grid in the year 2010/2011 was 1,899, ,746 of these customers were from the commercial sector which is around % of the total. Total energy sale in that same year was 3, GWh. And energy usage of the commercial sector was GWh which is about % of the total energy consumption [1]. Economic growth will almost proportionally increase the electrical energy demand of the consumers. For instance, only on the last year about 24 % increase in energy demand has been observed in Ethiopia as a result of 11 % economic development. For the last few years, there has been a common situation of limited generation capacity addition facing a continuously growing demand. One effective way of offsetting the effect of this limited generation and transmission capacities is to increase the margin between system generation and load. There is an aim at raising generation capacity in Ethiopia by expanding the system. But in parallel with the expansion, energy saving strategies must also be considered at the demand side of the network through the implementation of well-designed energy conserving systems.

2 80 Energy Conserving Electrical Design and Analysis for Commercial Buildings Buildings are designed to respond to social and business needs and they inevitably have social and economic values. At the same time, the operation of commercial buildings accounts for about 25 % of the total electrical energy consumption of the country, which is a significant portion of the nation s energy use [1]. Despite these facts, almost none of the commercial buildings that are constructed in Ethiopia have a design that considered any kind of energy conservation mechanism. On top of this, these buildings are dependent on the energy supply from the grid except for their back up diesel generators. This study suggests where, when and how energy can be conserved in commercial building sector of Ethiopia. It provides a listing of the most feasible and practical energy conserving design strategies that can reduce energy consumption beyond conventional practice and produce cost savings over the life cycle of the buildings. It will promote the development of efficient use of energy and the use of renewable energy at the consumer level. 2. Methodology The key factors associated with the successful achievement of low energy building design are identified. Case studies are carried out to demonstrate current practices in specific sectors of commercial buildings. In choosing sample buildings due attention is given to identify which sector of the building industry will most likely implement energy conserving techniques. Then all the necessary data is collected from the selected existing buildings through interview, questionnaire and site visit. The gathered data is organized and analyzed to create the load profile of the buildings, to assess the potential for energy saving and to select the appropriate energy conserving strategies. System design, modeling and simulation is carried out to present and justify the practices which could be used relative to energy conservation and describes most efficient ways to design commercial buildings. A hybrid modeling, simulation and analysis is run using RETScreen software and excel spreadsheets to analyze the energy efficient design and the renewable energy system. Excel is used to organize the data and to calculate the required output. The RETScreen (Renewable-energy and Energy-efficient Technologies) is used to evaluate the annual energy savings and financial feasibility of the proposed energy conserving system. 3. Sample Case Study 3.1 Commercial Buildings in Addis Ababa Addis Ababa is the capital city of Ethiopia, having a total area of km 2. It is located at N E Coordinates at an elevation of 2,355 m. It has a Subtropical highland climate [2]. Buildings in Addis Ababa are categorized as residential buildings, public buildings, commercial buildings and industrial buildings. The city has recently been in a construction boom with tall buildings rising in many places. Various luxury services have also become available and the construction of commercial building has recently increased. A commercial building is a building that is used for retail use. It often combines functions, such as an office, bank, bar, coffee house, convention center, grocery store, hotel, restaurant, supermarket... Due to the specific nature of this paper two prototype buildings are considered as a representative of the commercial buildings, which are hotel and mixed use shop and office building. The hospitality and retail sectors are the fastest growing sectors in Addis Ababa as well as in Ethiopian building industry. These sectors are most likely in a better financial and awareness level to invest for energy conservation and energy management systems. 3.2 Case Study on a Hotel Building Building Description Beer Garden Hotel Beer Garden Inn is a three star B+G+6 hotel building located in Addis Ababa, Ethiopia. It has 32 hotel rooms, indoor spaces like restaurant, kitchen, bar/lounge,

3 Energy Conserving Electrical Design and Analysis for Commercial Buildings 81 steam, sauna, lobby/reception, bedrooms with bathrooms, restrooms and corridors and outdoor spaces like terrace, car parking and balcony with a total floor area of 3, m 2 [3]. It gives 24 hrs per day and 7 days per week service with 80 % average occupancy rate Building Electrical Design: Data Analysis Electrical power demand of this building was analyzed based on the design. The building has a total electrical power demand of kw which gives a total power demand per total floor Area of W/m 2. The electrical power end use percentage for each function is shown in Fig. 1 [3] Building Load Profile: Actual Load The base case electrical equipment and lighting patterns are studied using the building s electrical design and data collected during a visit of the building in order to create the load profile. The base case lighting pattern was analyzed by going through the types of lamps used in different areas of the building including their respective total quantity and wattage. The result shows that 703 lamps are used to light up the building with a total power demand of kw. Quantity and load of the electrical equipments were the other parameters studied. The equipments were binned in to five categories: pumps, fans & motors, kitchen equipment, water heater & boiler, laundry Fig. 1 Electrical power end use by function Beer Garden. machines, guest room & others and brewery. Their respective load is calculated to be kw, kw, kw, kw, kw and kw. All these electrical equipments have a total power demand of kw. This brings the total actual electrical demand of the building to kw Annual Energy Consumption Electric bills of 12 consecutive months (Jan.-Dec., 2011 G.C) have been collected and monthly energy consumption data has been extracted from these bills. Total annual energy consumption and monthly average consumption have been calculated to be 408,640 kwh for a total of 284, birr and 34, kwh for a monthly average of 23, birr respectively. Using the data from the design, the information obtained during a visit of the building and based on the data extracted from the electric bills, the base case energy consumption of the building has been analyzed. The annual electrical energy consumption of the lighting system and the equipments has been calculated to be 49, kwh and 460, kwh respectively. This brings the estimated total annual energy consumption of the building to 510, kwh. 3.3 Case Study on a Mixed Use Building Building Description Yerga Haile Shopping Mall Yerga Haile Mall is a mixed use 2 tower 2B+G+5 building located in Addis Ababa, Ethiopia. It has indoor spaces like shops, corridor, office space, restaurant with kitchen, restrooms, parking and outdoor spaces like terrace and balcony with a total floor area of 10,743.3 m 2 [3]. It gives 12 hrs per day and 6 days per week Service with 100 % average occupancy rate Building Electrical Design: Data Analysis Electrical power demand of the two mixed use buildings was analyzed based on the design. The result shows that the phase 1 building has a total electrical power demand of kw which gives a total power demand per total floor Area of W/m 2. And the phase 2 building has a total electrical power demand of kw which gives a total power demand per total

4 82 Energy Conserving Electrical Design and Analysis for Commercial Buildings Fig. 2 Electrical power end use by function Yerga Haile. floor Area of W/m 2. Overall, the two buildings have a total electrical power demand of kw which gives a power demand per floor area of 33.13W/m 2 [3]. The power demand percentage of each function is found to be as shown in the Fig Building Load Profile: Actual Load Based on the building s electrical design and data collected during a visit of the building the actual base case electrical equipment and lighting patterns are studied for both Yerga Haile Phase 1 and Phase 2 buildings. The base case lighting pattern was analyzed and the result shows that 748 lamps are used to light up the phase 1 building with a total power demand of kw and 416 lamps are used to light up the phase 2 building with a total power demand of kw. Electrical equipments in the building of Yerga Haile Phase 1 were binned in to two categories; pumps, fans & motors and others. Their respective load is calculated to be kw and kw. This shows that all the electrical equipments in the building have a total power demand of kw. This brings the total actual electrical demand of the building to kw. Similarly, the electrical equipments in the building of Yerga Haile Phase 2 were binned in to three categories; pumps, fans & motors, kitchen equipments and others. Their respective load is calculated to be 4.50 kw, kw and kw. And all the electrical equipments in the building have a total power demand of kw. This brings the total actual electrical demand of the building to kw. The resulting total base case electrical loads of the two Yerga Haile buildings shows that there are 1164 lamps used to light up the buildings with a total power demand of kw. And the total power demand of the electrical equipments in the buildings is kw. This brings the total actual electrical demand of the two buildings to kw Annual Energy Consumption Electric bills of 12 consecutive months (Jan.-Dec., 2011 G.C) for the two Yerga Haile buildings have been collected and monthly energy consumption data has been extracted from these bills. Total annual energy consumption and monthly average energy consumption have been calculated to be 451,120 kwh for a total of 316, birr and 37, kwh for a monthly average of 26, birr respectively. Using the design data, the information obtained during a visit of the building and based on the data extracted from the electric bills, the base case annual energy consumption of the two buildings has been modeled. The annual electrical energy consumption of the phase 1 building for the lighting system and the equipments has been calculated to be 152, kwh and 151, kwh respectively. And the total annual energy consumption of the building is found to be 303,980.76kwh. Similarly, the base case annual electrical energy consumption of the phase 2 building for the lighting system and the equipments has been calculated to be 91,772.68kwh and 64, kwh respectively. And the total annual energy consumption of the building is found to be 156,571.13kwh. This brings the estimated total annual energy consumption of Yerga Haile shopping Mall to be 460, kwh. 3.4 Solar Radiation Intensity of Addis Ababa The assessment of the solar radiation potential for Addis Ababa is done by taking data from 3 different sources. These sources are National Metrological

5 Energy Conserving Electrical Design and Analysis for Commercial Buildings 83 Agency of Ethiopia, NASA Surface meteorology and Solar Energy, and the RETScreen. The data available at the national metrological agency was the monthly average sunshine duration per day for the past eleven consecutive years (2001G.C. to 2011G.C.). This data is used to calculate the solar radiation intensity through mathematical approach [4]. To do so, the value of the two coefficients ɑ and b of Addis Ababa which are used to calculate average solar radiation, are taken to be 0.25 and 0.60 respectively [5]. The solar radiation is then calculated using these regression coefficients, n is the average sunshine duration and H o is the extraterrestrial radiation for the location which can be calculated its formula [4]. The monthly solar radiation data for each month of the 11 years and monthly and annual average solar radiation in MJ/m 2 are calculated. These values are then converted in to KWh/m 2 using the conversion relation 1 MJ is equal to Wh. Finally, the monthly and annual average solar irradiance in KWh/m 2 is obtained. The maximum monthly average solar radiation is on February with a value of 6.78 KWh/m2 and the minimum is on July and August with a value of 4.33 KWh/m2 and 4.29 KWh/m2, and this is because July and August are the months of the rainy season in Addis. The annual average solar radiation is found to be 5.87 KWh/m2, and this value indicates that the area has good potential for the implementation of PV (photovoltaic) system to cover some part of the electrical energy demand of a building located in the city. This value is used to analyze the power generation through a photovoltaic technology. 4. Energy Conserving Design, Modeling, Simulation and Analysis The two sample commercial buildings given in section 3 are taken for more detailed study, energy conserving redesign and analysis. RETScreen is used for assessing the technical and financial feasibility of the implementation of the energy conserving system through a comparison between a base case, which is the conventional technology, and a proposed case which is the energy conserving technology. 4.1 Design, Modeling & Simulation Energy Conserving Design Considerations Although a single technique for energy conservation cannot achieve a significant energy reduction, combined techniques could do it. Therefore, many combinations were assessed. The design techniques and technologies considered while modeling the systems include: The use of equivalent energy efficient CFL and LED lamps to replace the base case power consuming incandescent and fluorescent lamps; Using energy efficient lighting control systems, circuits controlled by the level of daylight using a luminosity sensors and dimmers, combined presence of an occupancy sensor and a photocell; Using ENERGY STAR equipments where possible; On site generation of electrical power by using solar photovoltaic panel and the use of solar water heater system installation for covering the hot water requirement of the building. By considering the energy efficient building design techniques and technologies that are mentioned above the original electrical system of the two sample buildings were redesigned Hotel Building Design In order to decrease the power demand and energy consumption of the lighting system in the building, replacement of the lamps in use by equivalent energy efficient lamps were proposed. To do so, the spaces in this building were divided in to 4 categories namely corridor, stairs, toilet and others. From the initial design which is the base case, there are incandescent and fluorescent lamps of different wattage used. In this case the total power demand of the lighting system is kw. In the proposed case, the energy efficient CFL and LED lamps are used to replace the incandescent and fluorescent lamps [6-10]. In this case the total power demand of the lighting system is 10.66

6 84 Energy Conserving Electrical Design and Analysis for Commercial Buildings kw resulting in a power saving of kw which is about % of the base case lighting system power demand. In the proposed energy efficient design the application of better lighting control systems are suggested. The use of an occupancy sensor + photo sensor+ dimmer for the lighting system of the corridor and an occupancy sensor for the lighting circuits of the toilet and the stair case will reduce the power consumption of the systems by 25 % and 35 % respectively by reducing the unnecessary operational hours and lumen outputs of the lamps [6, 11-13]. As a result, the power demand of the lighting system is reduced to 9.52 kw giving a total power saving of 1.14kw. The energy efficient lighting system design brings the total power demand from the base case kw to the proposed case 9.51 kw with a total power saving of kw which is about % of the base case lighting system power demand. In the proposed energy efficient case energy star equipments are to be used wherever possible [14]. The most energy efficient products were selected among energy star products and these appliances are used instead of the base case equipments. From the replacements of conventional model equipments with a total power consumption of kw, a reduction to kw has been achieved in the proposed case which means a power saving of kw. After these changes are made on the original design by the implementation of the proposed energy efficient design techniques and technologies, the resulting power saving that can be achieved is analyzed. From a total of kw of conventional design power demand a reduction to kw is achieved. This shows a power saving of % which is equal to kw. Part of the building s lighting system, corridor and stair lighting, is selected to be supplied by the PV system. According to base case information, power demand, daily and annual electricity consumptions of this lighting system are calculated to be 4.91 kw, kwh and MWh respectively. After the energy efficient design, power demand, daily and annual electricity consumptions of this lighting system is reduced to 1.41 kw, kwh and MWh respectively. Based on this data, PV system calculations were done. In this context, the first step was calculation of PV peak power required to deliver the energy and then BP 275, 75-Watt peak Mono-crystalline Photovoltaic Module was selected from the database to calculate the number of modules required. These data are entered in to the RETScreen software. 42 of these modules are used and 27 m 2 roof area is needed for the establishment of the PV panels in order to meet the required electricity load. The overall power saving analysis for the energy conserving design is carried out considering saving of both the energy efficient design and the onsite power generating PV system. The result shows that the power demand of this building reduced from kw to kw giving a percentage power saving of % which is equal to kw Mixed Use Building Design Yerga Haile Phase 1: The spaces in this building were divided in to 7 categories namely corridor, parking, stairs, toilet, shop, office and bank. From the initial design which is the base case, there are incandescent and fluorescent lamps used to light up these spaces. In this case the total power demand of the lighting system is kw. In the proposed case, the energy efficient LED and CFL lamps are used to replace incandescent and fluorescent lamps [6-10]. In this case the total power demand is reduced to kw resulting in a total power saving of kw which is about % of the base case lighting system power demand. The use of energy efficient lighting control systems, an occupancy sensor + photo sensor+ dimmer for the lighting system of the corridor, shop, office and bank and an occupancy sensor for the lighting circuits of the parking, toilet and the stair were proposed [6, 11-13]. As a result, the total power demand of the lighting

7 Energy Conserving Electrical Design and Analysis for Commercial Buildings 85 system for the 7 categories is reduced to kw giving a total power saving of 4.99 kw. This value brings the power demand of the energy efficient lighting system design from the base case 45.58kw to the proposed case kw with a total power saving of kw which is about % of the base case lighting system power demand. In the proposed energy efficient case, the most energy efficient products were selected among energy star products and these are used instead of the base case equipments [14]. From the replacements of conventional model equipments in the base case with a total power consumption of kw, a power consumption reduction to kw has been achieved in the proposed case by giving a total power saving of 0.90 kw. After the application of the proposed energy efficient design techniques and technologies, the resulting power saving that can be achieved is analyzed. From a total of kw of conventional design power demand a reduction to kw is attained. This shows a power saving of kw after the redesign which results in a percentage power saving of %. Corridor and parking lighting system of the building is selected to be supplied by the PV system. According to base case information, power demand, daily and annual electricity consumptions of this lighting system are calculated to be 13.8 kw, kwh and MWh respectively. After the energy efficient design, power demand, daily and annual electricity consumptions of this lighting system is reduced to 3.8 kw, kwh and MWh respectively. Based on this data, PV system calculations were done. 140 modules are used and 90 m 2 roof area is needed for the establishment of the PV panels in order to meet the required electricity load. The overall power saving analysis for the energy conserving design is carried out considering saving of both the energy efficient design and the onsite power generating PV system. The result shows that the power demand of this building reduced from kw to kw giving a percentage power saving of % which is equal to kw. Yerga Haile Phase 2: The procedure followed to design the energy conserving system for the phase 2 building was similar to the one used for the phase 1 building. The spaces in this building were divided in to 7 categories namely corridor, parking, stairs, shop, office, kitchen and restaurant. In the initial design which is the base case, there are incandescent and fluorescent lamps used to light up these spaces with a total power demand of kw. In the proposed case, energy efficient LED land CFL lamps are used to replace incandescent and fluorescent lamps [6-10]. In this case the power demand is reduced to kw resulting in a power saving of kw which is about % of the base case lighting system power demand. Energy efficient lighting control systems, an occupancy sensor + photo sensor+ dimmer for the lighting system of the corridor, shop, office kitchen and restaurant and an occupancy sensor for the lighting circuits of the parking and the stair were proposed [6, 11-13]. As a result, the power demand of the lighting system for the 7 categories is reduced to 7.44kw giving a power saving of 2.71 kw. This value brings the power demand of the energy efficient lighting system design from the base case kw to the proposed case 7.44 kw with a total power saving of kw which is about % of the base case lighting system power demand. From the replacements of conventional model equipments in the base case with a total power consumption of kw, with energy efficient/energy star products [6] in the proposed case, a power consumption reduction to kw has been achieved by giving a total power saving of kw. After the implementation of the proposed energy efficient design techniques and technologies, the resulting power saving that can be achieved is analyzed. From a total of kw of conventional design power

8 86 Energy Conserving Electrical Design and Analysis for Commercial Buildings demand a reduction to kw is achieved. This shows a power saving of kw after the redesign which results in a percentage power saving of %. Corridor and parking lighting system of the building is selected to be supplied by the PV system. After the energy efficient design, power demand, daily and annual electricity consumptions of this lighting system is reduced to 2.0 kw, kwh and MWh respectively. Based on this data, PV system energy calculations were done. 74 modules are used and 48m2 roof area is needed for the establishment of the PV panels in order to meet the required electricity load. The overall power saving analysis for the energy conserving design is carried out considering saving of both the energy efficient design and the onsite power generating PV system. The result shows that the power demand of this building reduced from kw to kw giving a percentage power saving of % which is equal to kw. Yerga Haile Shopping Mall Total: For the two mixed use buildings, a power demand reduction to kw is achieved from a total of kw of conventional design power demand. This shows a power saving of kw after the redesign which results in a percentage power saving of %. The overall power saving analysis for the energy conserving design is carried out considering both the energy efficient design and the onsite power generating PV system. The result shows that the power demand of this building reduced from kw to kw giving a percentage power saving of % which is equal to kw. 4.2 Energy Consumption and Annual Saving Analysis Hotel Building The proposed energy conserving design annual energy saving analysis is carried out for the hotel building. The result shows that a saving of MWh, a reduction from MWh to MWh is obtained from the lighting system and a saving of MWh, a reduction from to MWh is obtained from the rest of the electrical system in the building. This brings the total annual energy consumption from MWh to MWh saving % which is MWh of energy. The implementation of the PV system increases the overall annual energy saving to %, which is equal to MWh (see Table 1), a reduction of the overall annual energy consumption from MWh to MWh Mixed Use Building The proposed energy conserving design annual energy saving analysis has been carried out for the phase 1 building. The result shows that a saving of MWh is obtained from the lighting system and a saving of MWh is obtained from the rest of the electrical system in the building. This brings the total annual energy consumption from MWh to MWh saving MWh of energy which is 35.7 % of the total. After the implementation of the PV system the overall annual energy saving is increased to %, which is equal to MWh (see Table 2a), a reduction of the overall annual energy consumption from MWh to MWh. Similarly, the proposed energy conserving design annual energy saving analysis has been carried out for the phase 2 building. The result shows that a saving of MWh is obtained from the lighting system and a saving of MWh is obtained from the rest of the electrical system. This brings the total annual energy consumption from MWh to MWh saving MWh of energy which is 51.9 % of the total. After the implementation of the PV system the overall annual energy saving is increased to %, which is equal to MWh (see Table 2b), a reduction of the overall annual energy consumption from MWh to MWh. The annual energy saving of the energy efficient design for the two buildings is %, which is equal to MWh, a reduction of the annual energy consumption from MWh to MWh. The

9 Energy Conserving Electrical Design and Analysis for Commercial Buildings 87 Table 1 Energy saving Beer Garden. Description Energy saved Energy cost savings (MWh) ($) Corridor lighting Stair lighting Toilet lighting Other lighting Kitchen equipments Refrigerators Laundry machines , Other equipments Exaust fans Kitchen fan Total , Table 2a Energy saving Yerga Haile-1. Description Energy saved Energy cost savings (MWh) ($) Corridor lighting Parking lighting , Stair lighting Toilet and shop , Office and bank , Exhaust fans Total , Table 2b Energy saving Yerga Haile-2. Description Energy saved Energy cost savings (MWh) ($) Corridor lighting Parking lighting Stair lighting Shop lighting , Office, restaurant L Kitchen equipments Exaust fans Total , overall annual energy saving of the two buildings after the implementation of the PV system is increased to 45.8 %, which is equal to MWh, a reduction of the annual energy consumption from MWh to MWh. 5. Life Cycle Cost Analysis The life cycle cost analysis of both the energy efficient and the PV systems has been done using the RETScreen software. An average electricity rate of $40/MWh is taken to execute the analysis. 5.1 Hotel Building The proposed energy efficient system for this building brings with it an additional cost which is around $33,190. At the same time the implementation of this system will bring annual cost saving of $4786 by decreasing the annual energy cost from $16,110 to $11,324 [6-13]. The result of the financial analysis shows that this proposed system has a payback period of 6.3yrs. And the proposed PV system has an additional cost of around $6833 [15]. This system will bring annual energy cost saving of $164. The result of the financial analysis shows that this proposed system has a payback period of 18.7yrs. The overall proposed energy conserving system for this building brings with it an additional cost of $40,023. At the same time the implementation of this system will bring annual cost saving of $4950 by decreasing the annual energy cost from $16,110 to $11,160. The result of the financial analysis given in Fig. 3 shows that this proposed system has a payback period of 7.3 yrs. 5.2 Mixed Use Building The proposed energy efficient system for the phase 1 building brings with it an additional cost which is around $58,770 [6-13]. At the same time the implementation of this system will bring annual cost saving of $4340 by decreasing the annual energy cost from $12,159 to $7819. The result of the financial analysis shows that this proposed system has a payback period of 11.6yrs. And the proposed PV system has an additional cost of $20,767 [15]. This system will bring annual energy cost saving of $554. The result of the financial analysis shows that this proposed system has a payback period of 15.4 yrs. The overall proposed energy conserving system for this building has an additional cost of $79,537. At the same time, this system will bring annual cost saving of $4895 by decreasing the annual energy cost from $12,159 to $7265. The result of the financial analysis given in Fig. 4 shows that this proposed system has a payback period of 13.5 yrs.

10 88 Energy Conserving Electrical Design and Analysis for Commercial Buildings payback period of 10.7 yrs. 6. Conclusions Fig. 3 Cumulative cash flow graph Beer Garden Hotel. Fig. 4 Cumulative cash flow graph Yerga Haile Phase 1. Fig. 5 Cumulative cash flow graph Yerga Haile Phase 2. Similarly, the proposed energy efficient system for the phase 2 building brings with it an additional cost which is around $32,615 [6-13]. At the same time the implementation of this system will bring annual cost saving of $3250 by decreasing the annual energy cost from $6263 to $3012. The result of the financial analysis shows that this proposed system has a payback period of 8.9 yrs. And the proposed PV system has an additional cost of $11,278 [15]. This system will bring annual energy cost saving of $293. The result of the financial analysis shows that this proposed system has a payback period of 12.9 yrs. The overall proposed energy conserving system for this building has an additional cost of $43,893. At the same time, this system will bring annual cost saving of $3543 by decreasing the annual energy cost from $6263 to $2720. The result of the financial analysis given in Fig. 5 shows that this proposed system has a With concerns for energy supply security increasing, it is essential to find ways to reduce load, increase efficiency, and utilize renewable resources. Having sustainable environment starts with sustainable building to work or live in. This is not only a matter of choice but it s also a matter of insuring a better world for us and the upcoming generation. In the developed nations there is better awareness, knowledge, finance and technology compared to developing nations. But this doesn t mean that developing nations should do nothing to achieve energy efficiency, rather should do more. For Ethiopian buildings, attempt to incorporate energy conserving building concepts will give them big jump to the future science and technology race to attain sustainable development while the financial benefit is a plus to the 21 st century globalized economy of the world. It will not only save energy cost of the buildings for their life cycle but it will also have a huge support for the improvement of the electric energy access of the nation. When we save energy, that energy can be used for school, clinic, or a factory which couldn t have the access to electricity due to shortage. In simple words energy conservation is of national concern as it is a fundamental way of reducing poverty and one step closer to be developed nation with better living condition for all citizens. The potential for energy savings in the building sector is large. This study shows that, for commercial buildings in Ethiopia, it is economically realistic to reduce annual energy consumption by 25%-45% (see Table 3) or more if optimum mixes of low energy design strategies are implemented. If energy management systems are applied in the building when it is operational, the energy saving percentage will considerably increase even more. Energy conserving buildings cost more at first but yield much more over the entire life of the building as a result of savings in money

11 Energy Conserving Electrical Design and Analysis for Commercial Buildings 89 Table 3 Summary of energy saving analysis result. Base case Proposed case Fuel cost savings Building Energy rate Energy consumption Energy Energy consumption Energy Energy saved Energy (MWh) cost (MWh) cost (MWh) saved Energy cost savings Hotel $ $16, $11, % $ 4,950 Mixed Use Phase 1 $ $12, $7, % $ 4,895 Mixed Use Phase 2 $ $6, $2, % $ 3,543 that comes from more efficient use of energy. So, the stigma is between the knowledge of up-front cost vs. life-cycle cost. This study makes it apparent that there are substantial constraints in the technology of onsite energy generation sector in Ethiopia. Even for the available technology the price becomes an uphill battle to apply in the desired intensity. But considering energy efficiency concepts as much as possible will increase the saving and shorten the payback period of the whole energy conserving system. Acknowledgment The authors are grateful to Studio GP Consulting Architects and to the building managers/owners for their cooperation with the collection of all the necessary data. The authors would also like to thank the National Meteorological Agency for providing the required meteorological data. References [1] EEPCo, (accessed December 2011). [2] Wikipedia, the free encyclopedia, (accessed December 2011). [3] Studio GP Consulting Architects and Engineers, Official Design Drawing Files. [4] J.A. Duffie, W.A. Beckman, Solar Engineering of Thermal Processes, 2nd Ed., John Wiley & Sons, Inc. [5] F. Drake, Y. Mulugetta, Assessment of Solar and Wind Energy Resources in Ethiopia. I. Solar Energy, Solar Energy 57 (3) (1996) [6] (accessed December 2011). [7] Led Application Series: Linear Fluorescent Replacement Lamps, U.S. Department of Energy, Energy Efficiency & Renewable Energy. [8] (accessed December 2011). [9] (accessed December 2011). [10] (accessed December 2011). [11] V.N. Bill, D. Maniccia, A. Tweed, An analysis of the energy and cost savings potential of occupancy sensors for commercial lighting systems, /resources/pdf/dorene1.pdf (accessed August 16, 2000). [12] (accessed December 2011). [13] (accessed December 2011). [14] (accessed December 2011). [15] E.S. Abd, A. Nafeh, Design and Economic Analysis of a Stand-Alone PV System to Electrify a Remote Area Household in Egypt, Open Renewable Energy Journal 2 (2009)