Solar water heaters proposed for the British University in Egypt Bathrooms VS. Traditional electrical water

Transcription

1 Solar water heaters proposed for the British University in Egypt Bathrooms VS. Traditional electrical water Loai Sultan a, Hesham Safwat b, Ahmed Hussein a b* 1 Department of Mechanical Engineering, The British University in Egypt, El-Sherouk City, Cairo P.O. Box 43, Egypt Abstract For the past few years Egypt has been facing a crisis of electricity, which is expected to develop as a result of the increase in the population and temperature which will lead to an increase in the electricity consumption. In order to provide electricity and decrease the consumption of fossil fuels and electricity provided from the power plants, alternatives including solar energy must be considered. One way to benefit from the solar radiation is to use it in water heating applications. It is proposed to switch all the electric heaters installed in the British University in Egypt bathrooms with solar thermal water heaters to decrease the electricity consumption of the campus. After the completion of the campus there will be around 81 bathrooms located in 13 buildings. The installed traditional electric heaters can consume around 206,966 kwh in 6 month; instead, if the university implemented the solar thermal heaters, it would decrease the consumption to 41,391 kwh in the same period of time. Practical experiment is held inside the campus by installing one 300 liter solar thermal heater and comparing it with a traditional 30 liter electric heater. The experiment will test the efficiency of the solar system and if it would be successful to replace the traditional electric heater. Fully detailed economical study will be done to show all the costs of installing the new solar systems and how it would save both energy and money. Key words : solar water heating, British university in Egypt solar heaters, energy saving, traditional electric heaters, solar heating benefits. Nomenclature ṁ, Is the mass flow rate of the water flowing in the inner tank supplied from the network to be heated, Is the specific heat capacity of the cold water, Is the difference in temperatures between inlet temperature from the network and the outlet water temperature that exits the tank., Is the collector area G, Is the total incident radiation, Transmission coefficient of glazing, Absorption coefficient of plate, Collector overall heat loss coefficient, The average temperature of the collector, Is the ambient air temperature U, the overall heat transfer coefficient A, the heat transfer area, The logarithmic mean temperature difference

2 1. INTRODUCTION 1.1 solar technology in Egypt Due to the rise of the need for the sources of energy and the increasing costs of fuels, the use of solar energies is an attracting source that could be used for heating in many applications; twenty percent of the gross energy consumption goes for the water heating. By the use of solar energy, the solar heating device is made to heat water in order to produce steam for many applications that need it. There is an infinite quantity of sun radiation gained, when it fall over a collecting surface, it is directly converted to heat energy that will be used in many heating applications. (Jatin, Pragna and Kishan 2) The use of the solar energy will significantly decrease the dependency on the energy usage. It also helps in the reduction of the national reliability on the imported vitality sources. Solar energy is a very reliable energy source, which can be a substitute for any utility (Jatin, Pragna and Kishan 2) The main types of collectors used in Egypt for the domestic applications are the flat plate collectors. Also the industrial applications that require high temperatures can install evacuated tubes collectors that can give high range of temperatures. Unfortunately the solar energy technology is not widely used in Egypt, only around 10% of the touristic villages and hotels implements the solar technology, also very small number of universities uses the solar technology to produce electricity and for hot water applications. 1.2 Types of solar collectors in Egypt The first type of collectors is considered to be one of the most important and common type of all collectors, because it s efficiency can reach 70%, which is relatively high (Honeyborne, 2009). Therefore this type is almost implemented in industrial applications due to the high temperatures of water it can reach. one of the systems advantages, the tubes are cylindrical in shape, which allows the collector to be able to absorb radiation with minimum reflection as the radiation in perpendicular to the tube at all angle, this allows absorption all the time through the day with the same efficiency throughout the whole year. In addition to that, the plates are well insulated from the back and the sides which make it not affected by outside temperature. Another advantage of this type is the ease of installation and maintenance due to its lightweight and compatibility. Also the ability of changing one tube if a problem occurred in it without needing to change or alter the whole system. Figure 1 working principle of evacuated tube The second type is of solar thermal collectors is the flat plate collectors. This type is more often used in domestic applications, as its efficiency and temperatures it reaches is enough to satisfy the needs of domestic applications. Figure 2 evacuated tube collectors The construction of this type of collectors consists of dark, special coated, flat plate that is fixed at the back of the collector; the plate is well insulated at the back and the sides. As the plate is flat, the increase in dark area enhances the radiation absorption. This type of collectors in general has lower efficiency and larger design than other types. Figure 3 flat plate collectors

3 2. Scope of work The scope work is to install and practically test a solar central water heating system for a bathroom in the British university in Egypt. where first will study the components of the solar system(collectors, heat exchangers, expansion tanks, piping, valves and gages, auxiliary heat sources and control),after studying the component the method of connection of this system. The main objective of the project is to study the efficiency of the system through scheduled readings taken at different times to study how the system operate in different temperatures and conditions. A detailed study of the effect of the inlet water temperature on the other temperatures of the system will be provided. The most important part is the cost analysis, this part will show why this system should be implemented in all the bathrooms of the university and how the university will benefit from it through electrical savings and environmental impacts. 3. Methodology and equations Q= ṁ To validate the system, the calculations are used to compare between the temperatures provided by the manufacturer in the catalogue and the actual readings that was measured practically on the system installed in the university s bathroom. First thing is to calculate the heat gained by the cold water inside the tank at using the above equation at different actual measured temperature and compare it to the catalogue temperatures. The second step is to find average temperature of the hot fluid from the following equation: The heat energy supplied from the radiation of the sun is cleared in the equation above. This heat energy is much higher than the energy exchanged between the cold water and the hot water that flows inside the closed loop of the collector. So the calculated Q in the first step is divided by the efficiency of the collector to give the useful energy form the sun. Afterwards, all the data in the equation are constants as they are fixed specifications of the system, except the ambient temperature and also the Q that depends on the temperatures in the first parts. For each measurement the Q can be calculated and then the Q useful can be calculated and then the average temperature of the hot fluid inside the closed loop can be calculated and compared to the catalogue conditions. The third step is to calculate the outlet temperature of the hot fluid inside the closed loop by using the following equation: Q= The overall heat transfer coefficient considers all the resistances and the heat transfer that happens between open loop and the closed loop, as the heat transfer are is fixed and the Q is calculated, from the logarithmic mean temperature we can calculate the outlet temperature of the closed loop at all measured temperatures.

4 4. The British University In Egypt bathrooms case study 4.1 Building picture Figure 4 building A 4.2 System flow Figure 5 system flow

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6 4.3 System components & Measurement procedure As mentioned, the main objective of the project is to compare the solar thermal heater with the traditional electric heater. To do that, an electric meter is installed as shown in the picture to measure the electric consumption, two meters are installed, on with the solar heater and the other is installed with the electric heater. The measurements was taken at different times of the days for both systems, the reason for this was to study the variation in both the electric consumption and the outlet temperatures with the change in the ambient temperature. Each reading was taken at a time that can represent the average temperature of a single month in semester two. For example, the readings taken at 8 AM can represent the average consumption and the average outlet temperature of the cold water in March because the ambient temperature at this time is close to the average temperature in this month, while the 10 AM readings represents April and so on. The total daily consumption was divided into 6 portions for the 6 readings. Six different readings daily was measured for 15 days to decrease the errors and to have an estimate for the daily electrical consumption for both systems and also to measure the outlet temperature of the cold water. In the 15 days period of taking measurements, the consumption of water was very low as the year was almost finished. For this issue, a continuous consumption was applied for both systems with the equal amount of water to be consumed. The amount of water was calculated according to the no. of people that visits the bathroom daily and it will be described in details later. The electric heaters showed almost a constant consumption daily but for the solar system there was no any electrical consumption at all readings. The solar system is fitted was a 3 KW back-up heater that is fixed at 40 degrees, is the average temperature of the water inside the tank decreases below 40, the back-up electric heater will start compensate for the heat loss. This did not happen at any time. To prove the system s efficiency, 3 readings were taken at 4 AM which was the lowest temperature of the day and can represent the first semester at the university. The 3 readings was taken at different days, in each time the total daily consumption was continuously consumed, the result was that the temperature did not decrease below the 40 degrees so there was no electrical consumption. Opening the hot water tap and watching the water meter until it consumes the required consumption did the measurement. The inlet and outlet temperatures are measured while consuming the water. After consuming the specified amount, the electric meter is observed to count the kwh consumed during the reading. By the end of the day, the electric consumptions are added up to give the total daily electrical consumption. Figure 6 electric heater flow meter Figure 7 solar heater flow meter Figure 9 solar heater system Figure 10 electric heater set up Figure 11 solar heater set up Figure 12 auxiliary heater

7 Measuring instruments: Electricity meter Electricity meter is a device that measure the rate of usage of an business, house or powered devices from the electricity, where the electricity corporation put the electricity meter at the costumer place where through this device the company is able to measure the rate electricity usage rat of this place and then the corporation bill the costumer due to the electricity consumption of this person and one of the most common measuring devices is the electromechanical meter (watt/hour) meter (Anderson, 2013) Bimetallic thermometers Bimetallic thermometer is a device used to measure the temperature increasing or decreasing of water where inside this device bimetallic strips that convert the temperature values into mechanical department, where this strip consist of two different metallic material such as metal and brass where the connection method between each other through welding or brazing, where the strip is covered by coil one end is connected to the device and the other end drive the indicated arrow (Germanow (Anderson, 2013), 2013). Figure 13 electricity meter Figure 14 bimetallic thermometers 5. Energy analysis and discussion The following are examples for the measurements conducted in one day Date Tim e ( c) (c ) ( c) Electric consumption Date Time (c) (c) (c) Electric consumption (kwh) (kwh) x/5/ a.m x/5/ a.m a.m a.m TABLE 1 electric heater readings TABLE 2 solar thermal heater readings

8 From the previous measurements and by applying the energy equations, the following graphs are conducted to study the effect of varying the inlet temperature of the cold water on the average temperature of the closed loop inside the collector by applying the energy equations with different temperatures. Another graph is to study the effect of the inlet temperature on the outlet temperature of the water and also another graph to show the ffect on the outlet temperature of the closed loop. 1) graph between Tci and Tavg The graph above the relation between the cold inlet temperature and the average temperature of the inlet and outlet hot temperatures where by increasing the value of the cold inlet temperature that increases the average temperature of the inlet and outlet hot temperatures. 2) graph between Tci and Tco The graph shows the extrusive relation between the cold inlet temperature and the cold outlet temperature where by increasing the cold inlet temperature value that will increase the cold outlet temperature value.

9 3) graph between Tho and Tci The graph shows the extrusive relation between the cold inlet temperature and the hot outlet temperature where by increasing the cold inlet temperature value that will increase the hot outlet temperature value. 7.1 Diversity calculation This calculation is done to calculate the daily consumption of the water in floor no.3 - building A. This floor contains the following rooms with the no. of persons inside the rooms: Rooms Number of rooms No of persons Professors rooms Teacher assistants rooms 1 16 Classrooms The diversity calculation is considered under full capacity and maximum occupation for the rooms to be considering the worst case scenario. There are 150 students occupy the classrooms every 2 hours, so in one day 450 students can visit the classrooms. With only about 3 students that enters the bathrooms between sessions. So the no. of students enters the bathroom daily = 3 sessions/day *3 students* 6 classrooms= 54 students daily There are 16 teacher assistants staying in one room in this floor There are 26 Professors stays in 13 offices in this floor. The average consumption of one person according to the Egyptian code= 5 litres/person for washing hands

10 The readings will be measured at 6 different times per day at different ambient temperature to study the effect of solar radiation and the ambient temperatures at different times. So the total water consumption will be divided on 6 measurements. The daily water consumption = ( ) * 5 = 460 litres And for taking the measurements we will continuously consume around 75 litres each reading. 7.2 Annual electric consumption the following is a template of readings to calculate the daily consumption of electricity from the electric heater. 8 AM ( presents March ) DAY SOLAR HEATER (kwh) ELECTRIC HEATER (KWh) AVERAGE CONSUMPTION TABLE 3 example of electrical consumption of one month Consumption of One day in February = 2.25 * 6 = 13.5 kwh/ day The following table shows the daily electric consumption of the electric heater among the months of semester 1 Time Month presented Average consumption/reading Daily consumption (KWh) (KWh) 8 A.M. MARCH A.M. APRIL P.M. JULY P.M. JUNE P.M. MAY P.M. FEBRUARY TABLE 4 electric heater consumption in semester 2

11 7.3 Graphs The following graphs show a comparison between the solar heater and the traditional electric heater, the comparison is between the electrical consumption of both systems and the cost of the consumed electricity. kwh Electric consumption of solar heater V.S. Traditional electric heater solar heater traditional electric heater february march april May June July MONTH L.E. Cost of electricity of the solar thermal heater V.S. traditional electric heater Solar thermal heater Traditional electric heater February March April May June July MONTH As the electrical consumption of the solar water heating system is zero all the time it will result in zero costs. While for the traditional electric heater, there is a huge difference in electrical consumption between both systems. This difference will be calculated in the economical study.

12 6. Economical study The total consumption of semester 2 in one bathroom, from February to july = 1836 kwh The total cost of the electrical consumption of semester 2 in one bathroom = L.E. The electrical consumption of the solar thermal heater = 0 kwh The British university in Egypt contains 15 buildings, some buildings are under construction and some buildings are working. But, by the start of next semester, all the buildings will be working. Each building in the British university in Egypt contains 4 floors. Each floor contains 1 bathroom for males and 1 bathroom for females. The number of bathroom inside each building is 8 bathrooms. So, the total number of bathroom in the British university in Egypt = 120 bathrooms. The solar thermal heater cost 12,500 L.E. Including the plumbing work. The annual maintenance cost is 200 L.E. The cost of substituting the traditional electric heaters of all the 120 bathrooms = 12,500 * 120= 1.5 million L.E. And the annual electrical consumption of the 120 traditional electric heaters = * 2(semesters) * 120 (electric heaters) = L.E. The payback period of equipping all the bathrooms with thermal solar heaters Year Initial cost Annual profit 1-1,500, ,156, , , , By interpolation between year 5 and 6 The payback period = year

13 7. Conclusion Due to the rise of the need for the sources of energy and the increasing costs of fuels, the use of solar energies is an attracting source that could be used for heating in many applications. The use of the solar energy will significantly decrease the dependency on the energy usage. It also helps in the reduction of the national reliability on the imported vitality sources. Solar energy is a very reliable energy source, which can be a substitute for any utility. Each business that require the use of a lot of energy they should start installing solar thermal water heating system in order to save a lot of money and payback in the long term, solar thermal water heating system provides us with the amount of heating water needed. And we can see the impact environmentally and economically. References abdrabo, M. (2008). economic assessment of solar water heaters potentials in Egypt. Journal of commercial management and studies. Bay, K. (2013). Solar Geyser Technology. Egyptian code for hot water. (2005). Elalfy, N. (2016). Activiate application of solar water heating in Egypt. ARPN Journal of Engineering and Applied sciences. Herzog, A. V., Lipman, T., & Kammen, D. (2000). RENEWABLE ENERGY SOURCES. University of California, Berkeley, USA. Honeyborne, R. (2009). Flat plate versus Evacuated tube solar collectors. Imboden, O. (2016). Solar Power Energy Information, Solar Power Energy Facts. Retrieved from National Geographic: Jinping Li, X. L. (2012). Experimental research on indoor thermal environment of new rural. Matulka, R. (2013, April 19). Storage water Heaters. Retrieved from US department of Energy: Mazarrón, F. R., García, J. L., & Porras-Prieto, C. J. (2004). Feasibility of active solar water heating systems with evacuated tube collector at different operational water temperatures. Technical University of Madrid, School. Nayyar, M. (2000). Piping Handbook. Mcgraw-Hill. Nemet. (2012). ANALYSIS OF AN ACTIVE AND PASSIVE SOLAR WATER HEATING SYSTEM. Sixteenth International Water Technology Conference. Istanbul, Turkey. Origen. (2012). Ecovillage Solar System. Owen, M. (2015). The ASHRAE Handbook. P, S., Thangavel, & Somasundaram. (2014). Performance study on evacuated tube solar collector using therminol D-12 as heat transfer fluid coupled with parabolic trough. Reddy, S. (1995). Electrical vs solar water heater: a case study. Renewables, Z. (2008). Zen Renewables drain back heating system. Seai. (2007). Solar water heating application.