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Proceedings of Insert Conference Abbreviation (Dissertation Review Sample)


concepts, merits, and demerits of presently available technologies on domestic solar heater systems

Proceedings of Insert Conference Abbreviation
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A literature review on the development of domestic solar water heating system 
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This paper analyzes the concepts, merits, and demerits of currently available technologies on domestic solar heaters systems, including the research problems, objectives, and future prospects. Also referred to as solar domestic water systems, solar water heaters offer affordable and reliable energy for heating water all year round. The systems can be utilized in any climate. Current technologies for solar water heating systems are solar collectors and storage tanks; active heating systems possess circulating controls and pumps, whereas passive solar water heating systems do not (Chen, et al., 2006) (1). The application of solar collector technologies for domestic hot water over the past three decades has illustrated that solar heating systems are currently being produced on a mature and reliable technology. Examples of technologies that are in application today include the use of evacuated-tube solar heating system using a two-phase evacuated-tube, the use of a two-phase thermosyphon solar water heater systems, and single-phase thermosyphon evacuated-tube collector systems. An analysis of the technologies demonstrates that the two-phase design is more sustainable than the rest of the technologies since it can be utilized to make the outside of buildings more attractive, yet ensure climate adaptability and energy efficiency.
Solar water heaters have continued to witness increased popularity across the globe (Chow, et al., 2013) (2). It is a fact that solar water heating represents the oldest domestic application of solar energy, according to Chen, et al. (2006) (1). . The process of heating water using solar energy typically makes greater "sense" economically than the entire house space heating since individuals require hot water throughout the year. Heating domestic water usually requires significantly less collector room than that required for space heating (Parent, Van Der Meer, & Hollands, 2012) (3). The opportunity to acquire a return on initial investment in the system every day of the year represents a distinct economic merit. Only temperate collector temperatures are necessary to cause effective system functioning across different technologies and solar water heater types (Chen, et al., 2006) (1). Consequently, heating domestic water is accomplished in less than idyllic weather conditions.
Heating water using the sun is critical to residential settings (Chen, et al., 2006) (1). Designs applicable to hot climates tend to be cheaper and much simpler, and are perceived as suitable technology for such places. Europe, India, Japan, and China dominate the international solar thermal market.
The solar water heating system is simply abbreviated as SWH and describes the entire mechanism that is used to tap and use the sun’s energy to heat fluids or water in homes. Evacuated-tube technology is a form of technology utilized to convert the sun’s energy into usable heat.
There are various technologies associated with solar water heating systems. These technologies are analyzed in the subsequent sections, including their advantages and disadvantages.
solar water heater technologies
Solar water heating technologies, simply abbreviated as SWH, represent a reliable, cost-effective and simple technique of harnessing energy from the sun to offer energy for the needs of businesses and homes (Parent, Van Der Meer, & Hollands, 2012) (3). Simply put, SWH systems essentially collect energy from the sun for heating a fluid or air. This fluid or air transfers solar heat either directly or indirectly to the premise’s water supply (Weiss, 2013) (4). Despite the systems have been in application for centuries, today’s technological progress means that SWH technologies can be affordably and efficiently operated in any climate. Regions whose temperatures fall below freezing tend to require the application of drain-back or direct systems, whereas sunnier, warmer climates can utilize a direct system, which heats the water to be utilized directly.
Active solar water heating systems
Active SWHs come in two forms: direct circulation systems and indirect circulation systems. Direct systems, also known as open loop systems, circulate water through collectors CITATION Wer03 \l 1033 (Weiss, 2003). The main advantage of this technology is that it is comparatively cheaper than other technologies. However, the technology possesses several disadvantages. First, they offer minimal overheat protection unless for those in possession of heat export pumps. Secondly, they have little or no freeze safeguards, unless the collectors utilized are freeze-tolerant. Finally, collectors can amass scale in hard water regions where ion-exchange softeners are not utilized. Until the introduction of freeze-tolerant solar collectors, this technology was not perceived as suitable for cold climates because a freeze could damage the collector and force pressurized water to gush from the collector.
On its part, an indirect or closed loop system utilizes a heat exchanger to separate potable or drinkable water from the fluid, which is known as HTF – heat-transfer fluid that circulates within the collector (Parent, Van der Meer, & Hollands, 2012) (3). This technology is slightly more expensive than conventional technologies. However, the technology is advantageous since it offers both overheat and freeze. Active systems utilize one or more pumps in the circulation and heating of fluid and water in the system. The main disadvantage of the system is its prohibitive cost, though it has several advantages (Weiss, 2013) (4). First, storage tanks can be placed lower than collectors, permitting increased liberty in system design and permitting the usage of pre-existing storage tanks. The system also has superior efficiency, permits usage of drain-back tanks, elevated control over the system, and permits situation of storage tanks in conditioned and semi-conditioned space, thereby reducing heat loss. Active systems permit the use of HTF between the storage tank and collector using solar power, and can utilize bubble or geyser pumps instead of the conventional electric pumps.
Passive direct systems
These systems, typically used in warm climates, are simple and reliable. The distinct feature of these systems is that, unlike other types of technologies, do not require the use of pumps and other electrical components. The thermosiphon (see image below) and integral collector storage mechanisms represent the most common passive systems. In addition, the two-phase technology offers low installation and maintenance costs, eliminates the need for ancillary control, and saves space since it does not require the use of storage tanks. Such systems also have the advantage of lasting longer (over thirty years) if they are regularly inspected.
Figure 1: The thermosiphon SWH (Kalogirou, 2013)
Evacuated tube collectors (ETC)
The use of the evacuated tube collector technology in modern SWH systems includes the single- and two-phase evacuated solar water heaters (Chow, et al., 2013) (2). The use of a two-phase evacuated tube contributes to freezing resistance, meaning it can be utilized in the cold regions. On their part, single-phase evacuated-tubes possess the advantage of their natural capacity for circulation at low costs. SWH systems that use the evacuated-tube technology possess competitive edge over the conventional gas and electric water heaters because of their economic benefits; they can be produced at cheaper costs.
Figure 2: Image showing the working principle of ET solar water heaters (Chow, Bai, Dong, & Fong, 2013 Solar Energy 98)
However, ET technology also poses some disadvantages. Most evacuated-tube collectors are manufactured from annealed glass, which is vulnerable to hail, disintegrating into golf ball-sized hail (Kalogirou, 2013) (5). Those collectors manufactured from "coke glass," possessing green tint, are more robust and less susceptible to lose their vacuum. However, their efficiency is significantly reduced because of the diminished transparency.
Formed or unglazed collectors
These are akin to fatal-plate collectors, but they are not physically cosseted by glass panels nor thermally-insulated (Weiss, 2003) (4). Consequently, such types of collectors are considerably less efficient for domestic application in water heating. However, for purposes of heating pools, the water that is getting heated is usually cooler than ambient roof temperature, a point at which the inexistence of thermal insulation permits extra heat to be derived from the immediate environment.
The use of a heat-pump heater with photovoltaic (PV) panels
The use of PV panels to power heat-pump heaters is very popular within residential areas that are characterized by low demands for hot water (Weiss, 2003) (4). The technology has several advantages, including being cheaper and simpler to install and maintain, enables the system to return extra energy to the grid to be used for domestic electricity purposes, and dehumidifies spaces.
Flat plate collector
This is an extension of the fundamental concept to put a collector in a glass box that looks like an "oven" in the sun’s direction (Weiss, 2003) (4). The largest part proportion of flat plate collectors involves the use of heat transfer technology. Overall, flat plate collectors are more efficient than evacuate-tube collectors in complete sunshine conditions are. However, flat plate collectors have reduced energy output as compared to evacuated-tube collectors in extre...
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