• Energy Research

Abstract One significant obstacle to the adoption of geothermal heat pump (GHP) technology is the installation costs of geothermal heat exchangers (GHE). Cost reduction through optimization of system parameter offers the potential for increased applications. In the current work, five major parameters are considered: length, radius, well numbers, the flow discharge inside the pipe, and the pipe's external radius for optimization using a genetic algorithm (GA) for a residential building in hot climatic conditions. In addition, system optimization is critical in determining values of design parameters for assessing the impact different circulating fluids on the energy consumption of GHP. A ten-year simulation is undertaken to evaluate the capacity of various circulating fluids and their effects on energy consumption reduction. The simulation shows a significant decrease in energy consumption based on varying levels of Ethylene glycol, Methanol, Potassium acetate, Sodium chloride, Freezium™ compared to pure Water in the GHP. The COP of the GHP system is also calculated with different circulating fluids. In addition, the circulating fluid with the highest performance loss during ten years of operation is identified. Based on the results, Ethylene glycol is selected as the preferred solution for use in the GHP. In the present study, we have also established the optimum configuration of GHEs according to a reliable evolutionary algorithm for investigating the effect of various circulating fluids on the system's energy consumption.

The effectiveness of using wetted cellulose pads on improving the performance of two conventional passive cooling systems has been evaluated. First, an experimental design was developed to determine the impact of using a wetted cellulose pad on the temperature and velocity of the airflow. A cellulose pad (7090 model) with a cross-sectional area of 0.5 × 0.5 m2 and three different thicknesses of 10, 15, and 30 cm were selected and tested. The results indicated that using wetted cellulose pads with thicknesses ranging from 10–30 cm decreased the outlet airflow temperature from 11.3 to 13.7 °C on average. For free airflow at velocity 3.5 m/s, the outlet airflow velocity from the wetted cellulose pad decreased to 0.9, 0.7 and 0.6 m/s, respectively, for cellulose pads with thicknesses of 10, 15, and 30 cm. By applying experimental results on a psychrometric chart, the humidity ratio of outlet airflow was obtained between 40–70%. The study established airflow velocity as the critical parameter in passive cooling systems. With the novel concept of combining wetted cellulose pads for passive cooling systems (i.e., wind catchers and induced ventilation), there is good potential to reduce the energy requirements for thermal comfort in buildings in regions with a hot and arid climate.

Abstract Geothermal heat is an energy source that is local, reliable, resilient, environmentally-friendly, and sustainable. This natural energy is produced from the heat within the earth, and has different applications, such as heating and cooling of buildings, generating electricity, providing warm/cold water for agricultural products in greenhouses, and balneological use. Geothermal energy is not dependent on weather or climate and can supply heat and electricity almost continuously throughout the year. It may even be possible to use geothermal projects as “thermal batteries”, wherein waste or collected heat is stored for future use, even seasonal use, making geothermal energy “renewable” at a time scale of years. Extensive research has been carried out on different technologies and applications of geothermal energy, but comprehensive assessment of geothermal heating and cooling systems is relevant because of changing understanding, scale of application, and technology evolution. This study presents a general overview of geothermal heating and cooling systems. We provide an introduction to energy and the environment as well as the relationship between them; a brief history of geothermal energy; a discussion of district energy systems; a review of geothermal heating and cooling systems; a survey of geothermal energy distribution systems; an overview of ground source heat pumps; and, a discussion of ground heat exchangers. Recognition and accommodation of several factors addressed and discussed in our review will enhance the design and implementation of any geothermal heating or cooling system.

Adaptive and flexible control techniques have recently been examined as methods of controlling flow and reducing the potential noise in vertical axis wind turbines. Two-Dimensional (2D) fluid flow simulation around rod-airfoil is addressed in this study as a simple component of the wind turbine by using Unsteady Reynolds Averaged Navier–Stokes (URANS) equations for prediction of noise using Ffowcs Williams-Hawkings (FW-H) analogy. To control the flow and reduce noise, the active controlling vibration rod method is utilized with a maximum displacement ranging from 0.01 C to 1 C (C: airfoil chord). Acoustic assessment indicates that the leading edge of the blade produces noise, that by applying vibration in cylinder, blade noise in 0.1 C and 1 C decreases by 22 dB and 35 dB, respectively. Applying vibration is aerodynamically helpful since it reduces the fluctuations in the airfoil lift force by approximately 48% and those in the rod by about 46%. Strouhal assessment (frequency) shows that application of control is accompanied by 20% increase. Applying vibration in the rod reduces the flow fluctuations around the blade, thus reduces the wind turbine blade noise. This idea, as a simple example, can be used to study the incoming flow to turbines and their blades that are affected by the upstream flow.

Passive cooling systems, such as wind towers, can help to reduce energy consumption in buildings and at the same time reduce greenhouse gas (GHG) emissions. Wind towers can naturally ventilate buildings and also can create enhanced thermal comfort for occupants during the warm months. This study proposes a modern wind tower design with a moistened pad. The new design includes a fixed column, a rotating and movable head, an air opening with a screen, and two windows at the end of the column. The wind tower can be installed on roof-tops to take advantage of ambient airflow. The wind tower’s head can be controlled manually or automatically to capture optimum wind velocity based on desired thermal condition. To maximize its performance, a small pump was considered to circulate and spray water on an evaporative cooling pad. A computational fluid dynamics (CFD) simulation of airflow around and inside the proposed wind tower is conducted to analyze the ventilation performance of this new design of wind tower. Thereby, the velocity, total pressure, and pressure coefficient distributions around and within the wind tower for different wind velocities are examined. The simulation results illustrate that the new wind tower design with a moistened pad can be a reasonable solution to improve naturally the thermal comfort of buildings in hot and dry climates.

Abstract The high geothermal heat exchanger (GHE) installation cost is the main challenge encountered in the widespread use of geothermal heat pump (GHP) systems, so its optimization is vital for reducing the costs. In the present study, five main parameters ─the radius, length, and the number of wells, the external pipe's radius, and the flow discharge inside the pipe─ are optimized by genetic algorithm (GA) for a residential building in Tehran. Moreover, sensitivity analysis of several design parameters, which are not considered in the objective function, indicates that pipe thermal conductivity, borehole thermal conductivity, soil thermal conductivity, and borehole distance parameters had the highest effects on entropy generation (EG), respectively. Therefore, this approach can help engineers to select the most efficient parameters for improving their design. Eventually, the optimized GHP is investigated by energy and economic viewpoints. One-year energy simulation of these systems is conducted to determine the energy consumption. Simulation results suggest that the annual energy consumption of the GHP with the coefficient of performance (COP) of 5.6 is 10.111 MWh; whereas, the annual consumption of heat pumps with an air-source heat pump equals 42.222 MWh, which is 4.17 times greater than that of the GHP. A simulation over a 10-year period is also performed to consider the drop in performance of the GHE over time. Furthermore, the economic analysis results suggest that the payback period of this system is about 7.4 years, and the energy subsidy paid by the government will be reduced annually to 14, 417, 839 Iranian Rial (IRR).

Abstract This research amplifies an environmentally-friendly refrigeration system which works by the combination of an ideal vapor compression system with a single-effect absorption system. At this hybrid absorption/recompression system, a booster compressor has implemented between the generator and condenser of absorption system and by adjusting pressure ratio tried to reach to the absolute heat transfer between generator and condenser coils in order to improve the efficiency of system and avoid the heat dissipation in condenser. This system has some advantages such as being environmentally-friendly, removing the need for the bulky condenser, and having about four-fold more efficiency than conventional absorption system. The objective of current study is to accommodate a quantitative description of the hybrid system to reach the optimum matching temperature of the generator, condenser, and evaporator. Furthermore, irreversibility and exergy destruction for different components of the system have been calculated and demonstrated that maximum exergy destruction occurs at condenser and generator. It is concluded that in generator temperature of 60 °C for the hybrid system, coefficient of performance becomes maximum (4.4) and the total exergy destruction is minimum. Non-crystallization working range of the hybrid system occurs at low generator temperature in comparison with single-effect absorption system.

In this study, a numerical and empirical scheme for increasing cooling tower performance is developed by combining the particle swarm optimization (PSO) algorithm with a neural network and considering the packing’s compaction as an effective factor for higher accuracies. An experimental setup is used to analyze the effects of packing compaction on the performance. The neural network is optimized by the PSO algorithm in order to predict the precise temperature difference, efficiency, and outlet temperature, which are functions of air flow rate, water flow rate, inlet water temperature, inlet air temperature, inlet air relative humidity, and packing compaction. The effects of water flow rate, air flow rate, inlet water temperature, and packing compaction on the performance are examined. A new empirical model for the cooling tower performance and efficiency is also developed. Finally, the optimized performance conditions of the cooling tower are obtained by the presented correlations. The results reveal that cooling tower efficiency is increased by increasing the air flow rate, water flow rate, and packing compaction.