Design and development of solar water heating system experimental apparatus

Acquiring new instructional laboratory apparatus is a challenge due to typical budgetary limitations. In addition, the apparatus designed by companies specialising in education equipment may not exactly reflect the educational objective intended by the faculty. These obstacles had forced the author to seek and search different venues to acquire experimental laboratory apparatus for demonstrating heat transfer principles. It was concluded that such an apparatus can be designed, developed and constructed in house within a manageable budget. This can be successfully accomplished by taking advantage of the capstone senior design project and the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) Undergraduate Senior Project Grant Program. The purpose of this ASHRAE’s article is to fund equipment for undergraduate engineering senior projects on ASHRAE-related topics. Solar water heaters can operate in any climate [1-4]. The performance of these heaters varies depending on how much solar energy is available at that locality, and more importantly on how cold the water coming into the system is. The colder the incoming water, the more efficiently the solar water heating system operates. A large number of studies have examined the performance of solar water heating systems; see for example and the references cited therein [5-10]. Very recently, Jaisankar et al reported a comprehensive review on solar water heaters [11]. They reported that the efficiency of solar thermal conversion is about 70% when compared to solar electrical direct conversion system, which has an efficiency of only 17%. Owing to its ease of operation and simple maintenance, solar water heating systems play an important role in domestic, as well as industrial sector. Solar water heaters can be either active or passive. The active solar water heating system uses a pump to circulate the heated water through the system. On the other hand, a passive solar water heating system moves the heated water through the system without pumps. This type of a system does not have electric components to break, which makes it more reliable and easier to maintain than active systems. A thermosiphon solar water heater relies on warm water rising, a phenomenon known as natural convection, to circulate water through the solar collector and to the storage water tank. Temperature in the storage water tank is a function of the buoyancy-induced flow of heated water in from the water heater. In this type of installation, the storage water tank must be above the solar collector. As water in the solar collector heats up, it becomes lighter and rises naturally into the storage tank above. Meanwhile, cooler water in the tank flows down pipes to the bottom of the solar collector, causing circulation throughout the system. The water storage tank is attached to the top of the solar collector, so that thermosiphon effect can take place. Design and development of solar water heating system experimental apparatus Hosni I. Abu-Mulaweh Indiana University-Purdue University Fort Wayne Fort Wayne, Indiana, United States of America ABSTRACT: The design and development of experimental apparatus for demonstrating solar water heating is described in this article. This solar heating experimental apparatus was designed to meet several requirements: 1) the system is to operate using the thermosiphon concept, in which flow through the system is created by density differences in the fluid; 2) to increase the solar energy absorbed by the water and improve the educational value of the project, the solar collector must have the ability to rotate in order to maintain a position perpendicular to the sun’s rays; and 3) the experimental apparatus must be mobile. A prototype of a solar water heating system was constructed and tested. The solar collector rotated as the sun position/angle was changing, indicating the functionality of the control system that was design to achieve this task. Experimental measurements indicate that the water in the tank was heated by the solar energy being absorbed by the solar collector. Moreover, the water temperature measurements at different heights in the storage tank show the thermosiphon effect has been attained. Solar water heating utilising thermosiphon is attractive because it eliminates the need for a circulating pump. Keywords: Design, laboratory, solar heating brought to you by COREView metadata, citation and similar papers at provided by Opus: Research and Creativity at IPFW 100 The thermosiphon effect for solar hot water heating has been employed with solar collectors as the principal heating component. These solar heating systems use either direct heating by the collector itself as reported by Huang and Shieh [12] and Morison and Braun [13] or indirectly via a heat exchanger (Parent et al [14]). In these cases, the thermosiphon induced flow is a result of the incident solar radiation but is also affected by the hot water removal pattern. Recently, Kishor et al used a fuzzy model system to predict the outlet water temperature of a thermosiphon solar water heating system [15]. This article describes the design and development of an experimental apparatus for demonstrating solar water heating. This solar heating experimental was designed to meet several requirements: 1) the system is to operate using the thermosiphon concept, in which flow through the system is created by density differences in the fluid; 2) to increase the heat added to the water and improve the educational value of the project, the solar collector must have the ability to rotate in order to maintain a position perpendicular to the sun’s rays; and 3) the experimental apparatus must be mobile. DESIGN AND BUILDING PROCESS The design process that was employed in this research project is the one outlined by Bejan et al [16] and Jaluria [17]. The first essential and basic feature of this process is the formulation of the problem statement. The formulation of the design problem statement involves determining the requirements of the system, the given parameters, the design variables, any limitations or constraints, and any additional considerations arising from safety, financial, environmental, or other concerns. The following is a summary of these guidelines: • The solar water heating system must not require pumps. It should utilise thermosiphon effects. • Solar collector controls - the control system is used to achieve the optimal sun exposure of the solar collector. The system is based on the fact that maximum sun exposure is achieved when sunlight hits the solar collector at a 90° angle. A mechanical system will be designed to rotate and control the angle of exposure of the solar collector to achieve optimal exposure. This mechanical system will be designed such that a rotational motion device instigates the solar collector motion through an input from an electronic device. The electronic device (i.e. microcontroller or programmable logic controller (PLC)) instigates the motion based on information obtained about the position of the solar collector relative to the sun. • All components of the system must be visible, and must be instrumented with thermocouples and flow rate meters. This is essential because, as mentioned above, the finished product would serve as an instructional laboratory apparatus for demonstrating solar water heating and thermosiphon concept. • The material should endure flow and temperature variations, and should be resistant to corrosion. • The heating system components such as tubes and fittings must be standardised to lower the cost. • Mobility - the system will be used for demonstration purposes and will require direct sunlight. Therefore, the system must be mobile, allowing for placement in sunlight. The system must also be designed so that it can be stored when not in use. After the problem statement was formulated, several conceptual designs were considered and evaluated. Each design concept was evaluated by the following criteria: effectiveness, cost, safety and size. The solar water heating system experimental apparatus that was designed and constructed is shown in Figure 1. Solar Collector The solar collector was designed conceptually to have vertical runs of parallel pipe. The main restriction for the design of the solar collector was the size of the collector. This was due to the fact that it must remain portable and safe. Therefore, a custom size of 2 ft wide by 3 ft long was specified, producing an overall area of 6 ft2. The 2 ft width and 3 ft height allows for sufficient clearance in most doorways and would allow for safe transportation from storage to a testing environment. Along with the solar collector frame, other components such as the piping, absorber and glass needed to be determined. Since the width of the collector was set to be 2 feet, and typical solar collector piping is ½" copper, the number of pipes was determined to be seven. The piping was constructed of ½" nominal copper pipes that run lengthwise through the collector. The absorber was based on typical solar collector standards and was constructed of fiberglass. Like the absorber, the glass material was chosen based on industry standards. All of the solar collector components that would be exposed to the sun must be painted black in order to attract more sunlight. The glass cover over the absorber was constructed of low-iron, tempered glass. Storage Tank The tank that was selected from the design evaluation required that it must be of a vertical configuration. The tank also should be designed such that the water can enter and exit the tank and allow for the thermosiphon effect to take place. The tank also must be designed taking into account proper safety precautions. 101 Figure 1: Solar water heating experimental apparatus.