H. Bagheri-Esfe, M. Shahriar,
Volume 19, Issue 6 (6-2019)
Abstract
One of the main concerns of the world today is of energy resources and rising prices. To counter this, most countries in the world are looking for new solutions to reduce the need for energy in various fields. Energy consumption in buildings has a significant share of the annual energy consumption of countries. About 40% of energy consumption of Iran is annually consumed in heating, cooling, and other building needs. Therefore, this sector has a significant potential for improving infrastructure and reducing energy consumption. One of the building components that plays a significant role in the loss of thermal energy is . Using multi-glazed windows filled with ideal gases, a lot of wasteful energy in the building can be reduced. In this paper, the effect of using different multi-glazed windows to reduce building heat losses has been investigated. Effect of number of layers, kind of ideal gas and its thickness, and also kind of frame in this paper. To investigate these factors, thermal losses of a typical building in the Carrier software. Also, heat flux passing through multi-glazed windows for different filling gases is calculated by Fluent software. Based on the results, three-glazed window with Krypton gas has the best performance in reducing heat loss of the building and its application improves thermal performance of a single-pane window up to 66%.
M. Taheri, M. Afzalian, S.a. Zolfaghari, H. Hassanzadeh,
Volume 19, Issue 12 (12-2019)
Abstract
Particle pollutants in the indoor environment are a serious threat to human health. Therefore, it is necessary to recognition, investigation, and controls of the distribution of these particles in the indoor environment. In the present research, the effect of air inlet angle of swirling diffusers in UFAD systems has been investigated on micron particles pattern distribution by considering the thermal comfort condition. For analyzing the fluid flow and particle distribution, the development of OpenFoam solver by the Eulerian-Lagrangian method has been used. The two-node model of Gauge has been used for predicting the thermal comfort conditions. Inlet angles are set in three cases of 30, 45 and 60. Based on the results, in all three cases, the TSENS index is in the thermal comfort zone. However, by changing the swirling angle from 30 to 60, the vertical temperature difference can be reduced about 1℃. Investigation of changing the inlet angle shows that at inlet angle of 30 and 60 degrees, the percentage of particles exited with 2.5 micrometers diameter were 32% and 55% of the total particles, respectively. In other words, increasing the inlet air angle can lead to exit more amount of any size of particles from the room. In addition, by increasing particles size, larger particles removed faster from the breathing zone, and smaller particles will remain longer time in the air. Therefore, smaller particles have a greater impact on indoor air quality.
M. Sharjerdi, H. Safikhani,
Volume 19, Issue 12 (12-2019)
Abstract
In this article, technical-economical investigation of heating and cooling loads in faculty of engineering of Arak university, Iran has been investigated. The tradiational and modern conditioner systems such as CAV, VAV, fan coil systems (all three systems are tested with direct fired absorption chiller and screw chiller), VRF system, split system and evaporative cooling system (in total 9 different systems) are designed for this faculty and are compared technically-economically. In this article, the costs of water, electricity and gas, purchase of systems and equipment, maintenance and repair of equipment of the examined systems are calculated and are compared with each other and then this work is done in different cooling loads, so that the results are not limited to the technical faculty of Arak university and can be used for all existing systems throughout the country. In the end, it is shown, that the evaporative cooling system has the lowest current and initial cost among the other systems. however, since this systems do not have the ability to determination of the amount of humidity and ideal temperature for the desired space can not be considered as an ideal and standard system. Also it is shown, that the current and initial costs of compression chiller are less than of absorption chiller and VAV systems have the better performance than CAV and fan coil systems, and the VRF system, after the evaporative cooling system, has the lowest current and initial cost among the examined systems, especially the split system. Due to the intelligent and optimal control of this system, it can be selected as an ideal system.
A. Heidary, M.a. Ehteram,
Volume 20, Issue 2 (1-2020)
Abstract
In the present paper, the performance of a shell and tube heat exchanger in which its cold working fluid is water and its hot working fluid is flue gases from natural gas-fueled internal combustion engine with working power of 15.4 kW was investigated. At first, with changing temperature and flow rate of inlet water, the performance of heat exchanger in both condensation and non-condensation situations was experimentally studied in the laboratory in order to have a criterion for validation of the simulations results in future. By comparing different simulation models in Aspen B-JAC software, the least error simulation model was chosen to do the other costly and impossible analyzes numerically in the laboratory environment. The study of the effect of the tube’s inner diameter on the heat exchanger’s performance in condensation situation showed 5.4% increase in the heat transfer while inner diameter decreases from 7 to 6 mm. The separation of the different heat transfer stages showed 26.4% of the latent heat transfer in the maximum discharge experiments for the inner diameter of 6 mm. Finally, the engine/heat exchanger set was assessed as micro combined heat and power and assumed that the heat exchanger is used for providing hot water for a 4-person family house in Tehran and the combustion engine is used for generating electrical power. This set was able to provide hot water during 9 warm months of a year by 1-hour work per day with 29% decrease of fuel consumption in comparison with traditional burners and at the same time, this set provides almost twice the electrical power requirements.
H. Safikhani, M. Loloee ,
Volume 20, Issue 3 (2-2020)
Abstract
In this paper, multi-objective optimization of the cooling and heating systems at the faculty of engineering of Arak University is investigated to increasing comfort and reducing the cost of energy. In the first step, the faculty building with 4 floors, 11800 square meters of infrastructure and 122 classrooms and rooms is modeled and the comfort and cost of the faculty are calculated. In the next step, a database of 2,000 faculties with different design variables was created and analyzed. Between the formed databases, buildings with the best objective functions are selected and presented in a Pareto front. Design variables are the 11 geometrical and non-geometrical factors affecting the comfort and cost of the faculty. The objective functions are the comfort, cost, and energy consumption. The results indicate that both absorption and compression systems have the ability to achieve acceptable levels of comfort, but the amount of energy consumed in the absorption chiller is higher than the energy consumption of the compression system, which indicates the necessity of using absorption systems in conditions of waste heat. Also, the results indicate that the absorption system, despite the higher energy consumption than the compression system, has lower energy consumption costs due to the difference between electricity and gas tariffs in Iran country and should be corrected.
M. Fallah, Z. Medghalchi,
Volume 20, Issue 6 (6-2020)
Abstract
Recent energy-saving policies in Iran led to more insulation implementation in buildings. Therefore, the occurrence of anti-insulation increases in the building industry. The anti-insulation phenomenon is the reverse function of insulation that causes cooling energy increment rather than energy saving. This phenomenon is an important and effective factor in energy consumption and the resident’s comfort. However, it has not been considered in thermal insulation studies worthily. Therefore, in this study, the anti-insulation occurrence temperature set-point is detected under eight climates of Iran by simulation in the EnergyPlus software. Four thickness of polystyrene insulation is evaluated under three insulating methods including external, mid and internal insulation. Results indicate that the anti-insulation occurs in six climates of Iran. Furthermore, cold and marine climates are more likely to anti-insulation occurrence than hot climates. The anti-insulation happens at a lower temperature by increasing the insulation thickness. In external insulation, due to usage of the wall’s thermal mass, anti-insulation occurs in high temperatures compared with mid and internal insulation methods.
Alireza Etemad, Ashkan Abdalisousan, Mahdi Aliehyaei,
Volume 22, Issue 2 (1-2022)
Abstract
A significant portion of world energy consumption belongs to building sector, And HVAC systems have an important share in building energy usage. In this research, a novel HVAC system has been proposed which is based on three technologies of combined heating and power, ice thermal energy storage, and solar heating. The system is named CCHP-ITESS as an abbreviation of previously mentioned technologies. This system was modeled on a case study building in Tehran, to obtain energy consumption, costs, and payback results in comparison with conventional HVAC systems. In order to realize the effect of energy prices on the economical results, the same system and building were simulated for the city of Los Angeles,California,US. The results showed that both scenarios will lead to significant reduction in net source energy consumption, which is 36.87% reduction in Tehran and 40.28% reduction in Los Angeles. However, the system is not economically reasonable in Tehran because of the low energy prices and has a 39 years of payback period, but is absolutely feasible in Los Angeles with ab payback period of less than 3.5 years. As a result, application of this system is feasible in Los Angeles and not feasible in Tehran.
Elham Eskandari, Ebrahim Hajidavalloo, Mohammad Reza Saffarian, Saeed Mohaghegh, Omid Adibi,
Volume 24, Issue 9 (8-2024)
Abstract
Application of vertical air curtain refrigerators in commercial stores has gained popularity due to easy access of products by the customers. However, energy consumption of these refrigerators is approximately %50 higher than that of refrigerators with doors. This paper experimentally investigates the effect of ambient temperature variation on the performance of these refrigerators. Experimental measurements include parameters such as temperature, pressure, relative humidity, velocity, and power consumption in both air cycle and refrigeration cycle. Moreover, parameters such as compressor power, refrigeration effect, total load, coefficient of performance, pressure ratio, thermal entrainment coefficient, refrigeration capacity, volumetric and mass flow rates of air in the evaporator and condenser, refrigerant mass flow rate, condenser heat, air curtain thermal efficiency, Richardson number, Reynolds number, and deviation modulus under different ambient conditions were calculated. The experimental results show that the refrigeration performance is affected by ambient air temperature, which directly influence on the infiltration rate of ambient air into the refrigerator compartment and on the return air temperature to the evaporator. Therefore, the return air temperature is crucial indicator for assessing the efficiency of the refrigerator. With increasing ambient temperature, compressor power increases, while the refrigeration effect and COP decrease. The results also indicate that as ambient temperature rises, air curtain efficiency decreases somehow that temperature difference between front and rear of the shelves may reach up to 4.6°C. For every 1°C increase in ambient temperature, compressor power consumption increases by approximately %0.64, while refrigeration effect and COP decrease by %0.06 and %1.77, respectively
Yousef Shahsbi, Erfan Mirshekari,
Volume 25, Issue 1 (12-2024)
Abstract
This research examines the optimization of expansion loops in steam pipeline systems using a neuro-fuzzy network. Stress analysis was conducted based on the ASME B31.3 design code using CAESAR II software. Additionally, a neuro-fuzzy network was developed and optimized in MATLAB. The results indicate that the neuro-fuzzy network outperforms traditional methods and the MLP neural network. Combining this network with the Bee Colony Optimization algorithm led to the identification of an optimal loop that minimizes pipeline length and reduces static and thermal stresses. The optimized loop obtained from the Perceptron network increased the loop length by 20 cm (1.14%) and reduced the total sum of standard stresses by 14.6%. In contrast, the optimized loop from the neuro-fuzzy network reduced the loop length by 120 cm (6.78%) and decreased the total sum of standard stresses by 9.5%. These findings demonstrate that the application of artificial intelligence techniques in expansion loop design significantly reduces thermal stresses and enhances design efficiency
