• Energy Research

Conventional energy consumption in refrigeration is one of the important reasons in global warming. Solar cooling systems are becoming more compact, having lower costs, and are potential alternative technologies, especially in hot and sunny climates. The adsorption, absorption, and dissociative evaporative cooling (DEC) are the technologies used for sorption machines, which are discussed in this review paper. Various multi-criteria performance indicators appearing in the previous studies are discussed, followed by evaluating the benefits and drawbacks of distinguishing sorption solar thermal cooling systems. Market research is conducted to prove the capacity of these technologies. The review shows that compared to other technologies, the solar absorption system is more efficient, so it is very commonly used for cooling applications in various locations. An important topic was also presented using phase change materials and nanofluids in solar sorption systems, that need more research. It is noted from this that most solar cooling systems are hybrid in terms of source and there are multiple applications (cooling - heating and electricity generation). The software packages to study these systems are introduced. Further research is required on desiccant materials that can be regenerated under lower temperatures that would augment the extent of solar desiccant cooling application.

This study presents a techno-economic comparison of four alternatives (experimental prototype of concentrating solar power tower system, photovoltaic (PV) system, collapsible vertical axis wind turbine and diesel generator) to supply electrical energy for a small compound of buildings. Among the services needed in the compound are the provision of an adequate drinking water, health centre for immunization purposes, and learning centre. The result of this study shows that the amount of electrical energy needed to meet the basic power requirements is 7.3 kWh/day. Detailed analysis and design requirements of the four alternatives are presented. Dynamic indicators (life cycle cost, annualized life cycle cost and cost of energy production) were applied to evaluate the economic-effectiveness of these energy supply systems. The cost of energy was $1.06/kWh, $1.18/kWh, $1.19/kWh and $2.98/kWh for the PV system, solar power tower system, diesel generator system and wind turbine system, respectively. Providing electricity to the compound buildings using solar power tower and PV systems is very beneficial and competitive among the other types of energy sources.

A numerical study of a charging process of thermal energy storage (TES) system with solar tower receiver was investigated under real environmental condition of Jeddah area, where molten salt was considered as the working fluid of the TES tank. Incident heat flux data which was computed from beam radiation data of Jeddah area with ray tracing technique is used as an input power to the TES system. The Cranck–Nicolson numerical technique is used to model the transient temperature profile of the TES system, while the classic empirical equation is incorporated in the numerical modelling to consider the heat loss from the tank. Hourly variation in efficiency of the solar tower receiver, the transient temperature profile of the TES at different position of the tank, the transient profile for the average temperature of the TES system, and the transient energy storage profile of the storage tank was investigated in this study.

A solar tri-generation system comprises of photovoltaic thermal collectors that are used for the production of electrical power and domestic hot water simultaneously. This study presents the performance analysis of a micro-solar tri-generation system that fulfills the requirements of an off-grid single-family lodging. The main functions of this system include domestic hot water, electrical power, and cooling power production. A set of five photovoltaic thermal panels were modeled together. The electrical power generated was stored in a battery, while the hot water generated was passed through a flow diverting valve. This valve directed some of the hot water to an absorption chiller, while the remaining portion was sent to an insulated thermal storage tank for later use. Energy and exergy analyses were performed to evaluate the extracted energy’s quality and efficiency. The overall thermal energy efficiency achieved was 50.53%. The extracted energy in the form of hot water was 3777.5 W. The electrical power generated was 2984.6 W, which was sufficient for the small single-family lodging. The coefficient of performance of the absorption chiller was found to be 0.6152. The exergy efficiency achieved was 36.88%. The exergy extracted by hot water was 234.3 W, while the electrical exergy generated was 2984.6 W. The exergy extracted during refrigeration was found to be 91.22 W. Furthermore, varying wind speeds and tilt angles affected both the energy and exergy efficiencies. The tilt angle must be kept at less than 45°, and the optimum wind speed was determined to be 35 km/h.

Abstract Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Spiral fin exhaust pipes were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NO x ), carbon dioxide (CO 2 ) and carbon monoxide (CO). In addition, O 2 concentration in the exhaust was measured. The two designs adopted in this study were exhaust pipes with solid and hollow fins around them. The first type uses air flow around the fins to cool the exhaust gases. The second type consists of hollow fins around the exhaust pipe to allow cooling water to flow in the hollow passage. Different combinations and arrangements of the solid and hollow fins exhaust pipes were used. It was found that decreasing the temperature of the EGR resulted in reductions in the oxides of nitrogen (NO x ) and carbon dioxide (CO 2 ) but increased the carbon monoxide (CO) in the exhaust gases. In addition, the oxygen (O 2 ) concentration in the exhaust was decreased. As a general trend, the percentages of reduction in the NO x gas concentrations were lower than the percentages of increase in the CO emissions as a result of cooling the EGR of a Diesel engine by a heat exchanger. Using water as a cooling medium decreased the exhaust gases temperature and the amount of pollutants more than did air as a cooling medium. In a separate series of tests, increasing the cooled EGR ratios decreased the exhaust NO x but increased the particulate matter concentrations in the exhaust gases.

Energy is essential to achieve thermal comfort; however, energy consumption leads to environmental degradation. This study analyzed the energy consumption of two masjids in the Kingdom of Saudi Arabia (KSA) and identified opportunities for rationalizing energy consumption. A photovoltaic (PV) system was used to ensure that the conditions of nearly zero bill building (nZBB) or nearly zero energy building (nZEB) were fulfilled. The energy use intensities of the Al-Jamil and Al-Omar masjids were 111 kWh/m2 and 121 kWh/m2, respectively. The average electricity consumption per worshiper for the Al-Omar masjid was 1.35 kWh/prayer and that for the Al-Jamil masjid was 1.03 kWh/prayer. The end-use energy was the highest for cooling, accounting for 72–74 % of the total consumption; lighting accounted for 11–12 % of the total consumption at the two masjids. Approximately 60 % of the air-conditioning (AC) energy load was saved by improving the envelope; the electricity requirement for ACs increased by up to 30 % as the ambient temperature increased from 32 °C to 46 °C. Changing the set-point temperature from 20 °C to 27 °C afforded electrical energy savings of approximately 27 % for a summer day. The environmental benefits of using solar energy were also identified.

A mathematical model for predicting thermal efficiency, heat gain, and outlet air temperature of a covered plate attic solar collector under steady conditions was developed. The model presented in this paper utilizes the basic principles and relationships of heat transfer to simulate the behavior of the solar air heaters under various conditions. The model was validated by comparing the predicted outlet air temperatures and collector efficiencies to those measured during drying operation of an attic solar collector. The effect of the air speed inside the collector and wind speed above the collector on the collector efficiency were investigated using the mathematical model.