Load Of Air Conditioning System Research Articles

Air-conditioning load characteristics and grey box predicting model in subway stations

With the continuous expansion of metro, energy conservation of air-conditioning system in subway stations draws the attention of the whole world. Most of the researches are focused on improving the energy efficiency of the system, while the load characteristics of subway stations are paid little attention. The inaccurate load prediction in the designing of air-conditioning system results in redundancy and low operating efficiency. Therefore, accurately predicting the air-conditioning load is crucial for energy saving in subway stations. In this paper, an innovative three-stage subway air-conditioning load test method was proposed and implemented in nine subway stations in Qingdao. Based on the test data, the special air-conditioning load characteristics of subway stations as underground buildings were analyzed. The results showed that electrical equipment load accounted for the largest part, reaching 53.7 %, while only 42 % of the equipment power was converted into air-conditioning load. The positive role of the envelope should not be ignored, especially in the case of entrance and exit walls, which bore almost all of the fresh air load. Based on the three-stage test, a grey box model was established and the error was validated to be within 6 %. With this model, the load of air-conditioning system can be calculated by inputting passenger flow, power of electrical equipment and public area. This paper provides a reference for the design and operation of air-conditioning system in subway stations.

Study on Dynamic Load of Air-Conditioning System in Subway Station Based on Hourly Passenger Flow

The research focuses on the air-conditioning system in a public area of a subway station. To address this, an optimization model based on the grid time segmentation method was constructed, specifically a GM (1,1) model. We explored the influence of the hourly passenger flow fluctuation on the load of the subway air-conditioning system, obtained the dynamic change law of the air conditioning system load in the subway station, and then dynamically adjusted the air conditioning system according to the dynamic change law to reduce the operation energy consumption of the system. Through the analysis of the simulation results, the model predicted that compared with the actual passenger flow data, the average maximum relative error was 14.97%. On this basis, the change law of the dynamic load of the subway air-conditioning system which caused by the change in passenger flow from time to time could be calculated and analyzed. Compared with the calculated load of the air conditioning system, the working day load was decreased by 1469.77 kW, or 22.00%. The findings indicate that in response to the dynamic load of fluctuations, timely adjustment of the air supply parameter of the air-conditioning system offers a significant reference point for optimizing energy efficiency in subway stations.

Preparation and Thermal Model of Tetradecane/Expanded Graphite and A Spiral Wavy Plate Cold Storage Tank

A cold storage unit can store the cold energy off-peak and release it for building cooling on-peak, which can reduce the electricity load of air conditioning systems. n-tetradecane is a suitable cold storage material for air conditioning, with a phase change temperature of is 4–8 °C and a phase change enthalpy of 200 kJ/kg. However, its low thermal conductivity limits the application of n-tetradecane for high-power cold storage/release. This paper prepares a tetradecane/expanded graphite (EG) composite phase change material (CPCM), whose thermal conductivity can be increased up to 21.0 W/m·K, nearly 100 times over the raw n-tetradecane. A novel model to predict the maximum loading fraction of paraffin in the EG matrix is presented, with an error within 1.7%. We also develop a thermal conductivity model to predict the thermal conductivity of the CPCM precisely, with an error of less than 10%. In addition, an innovative spiral wave plate cold storage tank has been designed for the tetradecane/EG composite. The power and energy density of the cold storage tank are significantly improved compared to that of raw tetradecane. The energy density reaches 40 kWh/m3, which is high among the organic PCM thermal storage tank. This paper shows the significance of thermal conductivity enhancement in designing a cold storage tank.

An analysis into the alternative strategies of substantial energy saving for the facilities of University of Jeddah, Khulais branch

The main objective of this study is to develop strategies which aim to improve the energy saving and the sustainability at the University of Jeddah (UJ) - Khulais branch. The energy saving can be improved by reducing -indirectly- the cooling load, while the sustainability can be improved by recycling the sewage water, generating energy from the solar irradiance and improving land-use efficiency. Initially, the main reasons for increasing energy consumption in the buildings were identified. The most important reasons were large heat gain through the flat rooftops and sidewalls, infiltration and exfiltration, partial damage to the insulation materials of walls and ceilings, and thermal mass. To reduce the heat gained through buildings' rooftops, it is proposed to shade the rooftops by tilted and ventilated airgap Building Integrated Photovoltaic (BIPV). BIPV also help to improve the shading efficiency, land use efficiency, natural cooling of the rooftops and PV modules, Energy Efficiency Rating (EER) of the air-cooled ac system, and efficiency of night ventilation system. To reduce heat gained through the sidewalls, it is proposed to shade the walls by planting long-stemmed trees (Eucalyptus) around the buildings. Irrigating the trees by gray water will improve the sustainability and improve Leed Credit Point. Previous studies and current measurements of solar radiation under shaded surfaces have shown that shading the building is an appropriate strategy to reduce solar heat gain. Startup load of air conditioning system is another source of increasing energy use and it forms around 10-20% of the total cooling load due to high indoor temperature at the morning. As the buildings are not occupied after 3:00 PM, and during weekends, it is proposed to use mechanical night ventilation to reduce the indoor temperature and to improve the air quality. Connecting the ventilation system with a separate control system and the BMS at the buildings help to reach to the possible minimum indoor temperature.

Analysis on influencing factors and energy saving potential of photovoltaic curtain wall preheating fresh air system in severe cold area

In the general building air conditioning load, the fresh air load accounts for more than 30%, especially in the severe cold areas in the north, with long winter and large indoor and outdoor temperature difference, the fresh air heat load will account for a larger proportion in the air conditioning system load. Making full use of renewable energy can effectively reduce building energy consumption. In this paper, the air flow field distribution in the ventilation duct of photovoltaic curtain wall is numerically simulated by fluent simulation software, and the air distribution form and temperature field distribution in the system cavity under different ambient temperature, cavity thickness and tuyere position are analyzed and compared, so as to obtain the influence of different influencing factors on the performance of the fresh air preheating system, and combine the photovoltaic curtain wall preheating fresh air system and electric heating system to explore its energy-saving potential. The results show that when the cavity thickness is greater than 400mm, the reduction range of photovoltaic curtain wall temperature becomes smaller, and the overall temperature distribution of the cavity tends to be uniform. When the ambient temperature is different, with the increase of ambient temperature, after the fresh air passes through the photovoltaic curtain wall preheating system, the temperature difference at the inlet and outlet of the air flow channel decreases, and the maximum temperature difference decreases from 4.6k to 3.4K.The combination of photovoltaic curtain wall and electric heating is used to preheat the fresh air. Compared with the traditional method, the same fresh air load is treated, and the energy-saving rate is 60% ∼ 70%. It shows that using photovoltaic curtain wall to preheat the fresh air can achieve better results, which provides guidance for putting forward more appropriate, economic and energy-saving design schemes in the project.

Impact of Rooftop PV Shading on Net Electrical Energy Demand of Buildings in Pakistan

This work performs a quantitative assessment of the impact of rooftop PV installation on building’s net energy demand using model of roof structure and steady state thermal simulations. For this purpose, roof structure typically used in Faisalabad, Pakistan is modeled with and without the shading effect due to a 395 W commercial rooftop PV setup. The simulated parameters include the impact of PV module’s dimensions, mounting position/angle alongside roof size and ambient conditions on heat load of air-conditioning system to maintain a temperature of 25 °C within building’s top floor. During the daylight hours of July, the heat load added by the roof on average reduces from 150.87 BTU/h/m2 without PV to 118.16 BTU/h/m2 with PV structure. This 20.05% reduction in energy demand has been achieved with July’s maximum daytime solar and infrared irradiances of 792.2 W/m2 and 466 W/m2 recorded at an average ambient temperature of 35.5 °C and wind speed of 2.75 m/s. This study provides valuable data on optimization of roof layer structure during building’s construction in anticipation of PV system installation at a later stage. Also developed techniques/methods to reduce building’s energy budget due to PV installation, can be valuable input for construction industry as well.

Characteristic studies of heat sources and performance analysis of free-cooling assisted air conditioning and ventilation systems for working faces of mineral mines

High temperature heat hazard at mineral mine becomes more and more serious as the increase of mining depth. Heat sources at working faces of mineral mines are complex and are of different characteristics, presenting new challenges for air conditioning systems. In this paper, heat sources at four types of working faces are summarized and their characteristics are investigated. Based on this, simplified equations, which are linear with length of working faces, are proposed to calculate heat dissipation rates. So that the main heat sources of different working faces can be found, and cooling load of air conditioning systems can be calculated. Then, considering main heat sources of coal mines, a typical working face is designed to investigate performances of different ventilation systems and air conditioning systems. Simulation results show that segmented ventilation systems (SC) and heat shield assisted centralized ventilation systems (CCHS) can realize much better temperature distributions at working faces. However, cooling load can be greatly reduced for CCHS, when untreated air is supplied to the coal seam side. Based on this, free cooling assisted air conditioning systems are designed, and annual average energy efficiency ratio (EERann) of the systems are investigated and compared between direct evaporate cooling and indirect evaporate cooling (IEC). For SC, as compared with scenarios without free-cooling, IEC can increase EERann by 15%–23% and 22%–32% under Benxi and Datong ambient conditions, respectively. Besides, to ensure high EERann, CCHS is preferred and it is essential to increase thermal insulation of air ducts.

The techno-economic and environmental analysis of genetic algorithm (GA) optimized cold thermal energy storage (CTES) for air-conditioning applications

Thermal energy storage can be employed for air conditioning system load management, i.e., load shifting and leveling, to serve the peak electricity demand for the air-conditioning system with high capacity utilization. Ice and phase change material-based thermal energy storage systems were modeled and optimized for air-conditioning applications. The mathematical modeling involved energy, exergy, environmental and economic analysis of both the systems at full and partial operating modes. The system is then optimized for a commercial building to give maximized exergy efficiency and minimized total annual investment and operating cost over five different system temperatures as decision variables. The full operating mode strategy resulted in a higher exergy efficiency for both systems, whereas partial operating mode proved to be a more economical operating strategy. The multi-objective genetic algorithm-based optimization is carried out with two different refrigerants (R134a and R717) in the vapor compression refrigeration cycle of the systems. A single system design point is then selected using a multi-criteria decision-making technique. The electricity consumption while utilizing the thermal energy storage based system was lower as compared to the conventional system for air-conditioning applications. The two modeled systems are compared based on storage media, operating strategies, and the refrigerant used.

Accurate heating, ventilation and air conditioning system load prediction for residential buildings using improved ant colony optimization and wavelet neural network

Accurate prediction of the building load is crucial to ensure the energy saving and improve the operational efficiency of the heating, ventilation, and air conditioning (HVAC) system. In this study, the heating load (HL) and cooling load (CL) of buildings are analyzed using the Spearman method considering eight influencing factors: relative compactness, surface area, wall area, roof area, overall height, orientation, glazing area, and glazing area distribution. The ant colony optimization (ACO) method is used to optimize the ability of a wavelet neural network (WNN) to predict the HL and CL values of residential buildings. The linearly decreasing inertia weight and self-adaptive mutation operator are introduced to improve the optimizing capability of the ACO. An improved ACO-WNN (I-ACO-WNN) model is proposed to achieve a high-precision building load forecasting, and the formulas including the influence factors of the building load, are proposed. The regression coefficient values of the proposed forecasting model of HL and CL are 0.9714 and 0.9783, respectively. Compared to the traditional WNN model, the root mean square error values of HL and CL predictions by the I-ACO-WNN model are decreased by 66.01% and 73.28%, respectively; while the mean absolute error values are decreased by 82.44% and 84.82%, respectively; also, the mean absolute percentage error values are reduced by 81.21% and 85.31%, respectively; lastly, the mean square error values are reduced by 88.44% and 92.86%, respectively. The proposed prediction model can be used as a reliable tool for HL and CL estimation in future intelligent urban planning.

Exploration of interactive thermal influence characteristics of power and air conditioning system based on 1D/3D coupling calculation in electric vehicle underhood

The thermal problems in the underhood are serious in the integrated thermal management of electric vehicles. The interaction of the heat dissipation components in the underhood affects the heat exchange and working performance, which affects its driving range and safety. This paper takes the interactive thermal influence into consideration between the battery, motor and air conditioning system, builds an underhood thermal management system framework of electric vehicles, and establishes a 1D/3D coupling model for the integrated systems. Only the components in the underhood are studied in 3D. The impact of load change of the air conditioning system and power system on heat transfer performance of another system is studied under different heat exchanger layouts. The results show that the cooling effect of the power system decreases with the load of the air conditioning system increasing when the condenser is placed in front of the radiators. When the condenser is behind the radiators, the air conditioning system load change has no significant effect on the heat dissipation effect of the power system. For both arrangements, the load change of the power system has an evident influence on the refrigeration process of the air conditioning system. The dissipated heat of the condenser decreases as the power system load increases, and the COP increases gradually. At the same time, the cooling performance number is introduced to evaluate the heat dissipation capacity of the power system and the air conditioning system. The smaller the cooling performance number, the stronger the heat dissipation capability of the system, and vice versa, the worse the heat dissipation capability. So it can further optimize the cooling characteristics and safety of the entire electric vehicle by comprehensively considering the arrangement or the targeted optimization of the heat exchangers to improve the integrated thermal management system of EVs.

The role of structure cooling to reduce the effect of urban heat island in Mumbai

ABSTRACTIn India, for centuries, structure cooling principles have been part of strong architectural heritage. Buildings like Taj Mahal, Gol Gumbaz and temples of Hampi are a few notable examples of naturally cooled buildings. Some have used thermal mass, some have used water, while others use the combination of both to provide thermal comfort in the building as well as outside the building. Anthropogenic activities in urban areas increase usage of devices like air conditioning for human comfort inside a building. Typically, these principles discourage any external and/or induced forms of cooling. Less use of artificial systems means less heat and emitting less greenhouse gases in the environment. In an illustrative experiment, structural cooling system is introduced in a commercial building in Mumbai (hot and humid climate) to reduce the cooling load of the conventional air-conditioning system reducing overall heat load. An air-conditioning system typically adds ∼30% more heat from the compressors. This increases the ambient temperature of the area. In dense urban environments, this process escalates till a heat island is formed [Oke, T. (1982). The energetic basis of the urban heat island. Journal of the Royal Meteorological Society, 108(455), 1–24; Weng, Q., Dengsheng, L., & Schubring, J. (2004). Estimation of land surface temperature – vegetation abundance relationship for urban heat island studies. Remote Sensing of Environment, 89, 467–483]. A combination of structure cooling and an air conditioner can be used to significantly reduce load on the air conditioners. It will drastically reduce the energy consumption and resultantly the pollution in the environment. In Mumbai, India’s largest city, the ambient temperatures are sometimes 40–45°C in peak summers. To reduce the cooling load of the air-conditioning system, the structural cooling system was introduced as an innovative technique to reduce heat inside the structure and also in the environment. Application of such technique will be very useful on the structures like airport, station areas and commercial complexes to reduce the heat and pollution in the environment.

B-30 状態空間モデルによる空調負荷予測

B-30 状態空間モデルによる空調負荷予測

Phase Change Material Coating on Autoclaved Aerated Lightweight Concrete for Cooling Load Reduction

This work is focused on enhancing the thermal effectiveness of autoclaved aerated concrete (AAC) by the application of phase change material (PCM) as a coating. The dynamics of heat transfer and the cooling load of air conditioning system in the two tested houses with different wall materials (AAC and AAC with PCM coating) were investigated. The work demonstrated that by coating phase change material onto the exterior surface of the building materials a significant increase in the thermal effectiveness of the building materials was achieved and determined by comparing the lower interior surface temperature, heat flux evolution and room temperature. The increase in thermal effectiveness was applied to the AAC. It was demonstrated that the cooling load and power consumption of air conditioning system in buildings using the wall-PCM coating combination can be reduced variously by about 25 %.DOI: http://dx.doi.org/10.5755/j01.ms.23.2.15451

A method to calculate wall heat fluxes of electrical equipments based on overdetermined linear equation

Cooling load of air-conditioning systems in underground space mainly refersto heat released from multitudinous electrical equipments. Calculation of the total amount of heat release is of great importance to the underground ventilation and air conditioning systems during design stage for indoorthermalenvironment. A method based on overdetermined linear equation is applied to calculate heat release fluxes of equipment surfaces in an underground space. Firstly, a field test in an underground hydropower station was carried out. Temperatures of electrical equipment surfaces, walls, underground indoor air and dimensions of electrical equipments were obtained. Conventional methods based on heat transfer theory can obtain the results with a standard error of 0.59, which is a relatively high value. On basis of overdetermined linear equation, the method combines on-site temperature measurements with numerical simulation to calculate wall heat fluxes. When seven testing points are selected in the on-site temperature measurements for calculation, the heat release fluxes of three equipment surfaces can be obtained with a standard error of 0.07. The method based on overdetermined linear equation is an effective way to determine wall heat fluxes of electrical equipments in air conditioned space.

The study of the dynamic load forecasting model about air-conditioning system based on the terminal user load

The energy-saving optimization control strategies of central air-conditioning system widely used now is according to the operation parameters of the cold source side to adjust the load supply. But the operation parameter describes the centralized and hysteresis effect about the central air conditioning system in current load. The effects can’t well reflect the actual change about the user load and ensure the comfort of all users. It will be better if directly regulate the cold source of central air conditioning load according to the needs of the terminal users. Based on this idea, the study calculates the load of the terminal air-conditioning equipment according to its operating parameters, and then the dynamic load forecasting methods is used to establish the forecasting model that can forecast in real-time the load demand in the next time. The load forecasting methods do not need to analyze the factors that directly affect indoor load changes and to establish the load changes physical model. It use “the degree of load changes” to describe the load variation influence so to avoid the randomness and uncertainty about the change of the air-conditioning system load. The experimental results show that the forecasting model has well prediction effect. With the support of network control technology, all the terminal user load demand can be got, so the total load about the central air-conditioning based the terminal user forecasting load can be got. The better energy-saving optimization control strategies of central air-conditioning system will be get to use the forecasting load as the basis of the energy saving control for the central air conditioning cold source system.

Simulation and Comparison of Heating and Cooling Load between a Zero-energy Building and a Common Building in Severe Cold Region

In order to grasp the energy-saving potential of air conditioning system in severe cold region, choosing a nearly zero energy consumption building in Shenyang of China as research object. The concepts of green building and passive building, and many building energy efficiency technology such as phase change energy storage, exhaust air heat recovery, tunnel wind, low-e glass, outside wall insulation, are used in the process. Using the DeST software to establish a physical model and though simulating the heating and cooling load of building air conditioning system to research the Air conditioning system load variation and influencing factors and compare with the same type of conventional building energy consumption. Nearly zero energy consumption building's winter heating load has reduced 73.72% compared with the common building, and the comprehensive energy saving rate is up to 55.22%. The air conditioning system has great energy saving potential.

Simulation Analysis on Dynamic Load of Air-Conditioning System of Ocean-Going Ship

In this paper, a dynamic load mathematic model for ship’s multifunctional cabins was developed using the “black box model” theory. The multifunctional cabins’ dynamic loads for a ship navigating in a typical Eurasian route were calculated through this mathematic model. The research results show that the air-conditioning load of cabins varies with navigation areas and sailing time significantly. Ventilation load accounts for 51.92% of the total load, while heat conduction and radiation load only account for 7.47% and 6.68%, respectively. For a same navigating area, the maximum load for different cabins is 2.648 times of the minimum load at the same time. In addition, the impact factors were analyzed by regression analysis method, and that the 91.72% of variation of the dynamic load results from the outside temperature changing

Calculation of Coach Body Heat Transfer Coefficient for the High-Speed Railway Train in China

The coach body of the high-speed railway train is required to have a good thermal insulation performance. It can keep a comfort passenger environment and decrease demand for the cooling load of air-conditioning system. The determination of coach body heat transfer coefficient (K-value) is critical for the efficient design of vehicle air-conditioning system. A heat transfer coefficient calculation model is especially proposed for the typical aluminum section thermal insulating wall structure of high-speed trains coach body in china, on the basis of the fin heat transfer mechanism. For the train type of CRH3G, the calculating coach body heat transfer coefficient is in good agreement with the experimental value. So the proposed calculation method can significantly improve the computational efficiency of the K-value for the high-speed railway trains which have the typical aluminum section insulation wall structures, and provide a trustable basis for the coach body structure optimization design.

Study on Energy Materials with the Impact of Using Chilled Water Storage Systems on the Performance of Air Cooled Chillers

In the air conditioning (AC) industry chilled water storage (CWS) systems are one form of cool thermal storage technology that can be used to time shift the electrical load of the system from the peak day periods to off peak night time periods. In this paper the data for the actual exported and generated electrical energy obtained for the power stations has been used to estimate the electrical energy consumption and the peak electrical load of AC systems. It is estimated AC systems represent about 62% of the peak electrical load. The results demonstrate that CWS can reduce the peak electrical load of a chiller in an air cooled AC system by up to 100% and reduce the nominal chiller size by up to 33% depending up on the operating strategy adopted. This is achieved with only a 4% increase in power consumption of the chiller for all CWS strategies except for full storage where the energy consumption actually decreases by approximately 4%.

The Experiment and Simulation of Solid Desiccant Dehumidification for Air-Conditioning System in a Tropical Humid Climate

The aim of this research was to study and design a solid desiccant dehumidification system suitable for tropical climate to reduce the latent load of air-conditioning system and improve the thermal comfort. Different dehumidifiers such as desiccant column and desiccant wheel were investigated. The ANSYS and TRASYS software were used to predict the results of dehumidifiers and the desiccant cooling systems, respectively. The desiccant bed contained approximately 15 kg of silica-gel, with 3 mm average diameter. Results indicated that the pressure drop and the adsorption rate of desiccant column are usually higher than those of the desiccant wheel. The feasible and practical adsorption rate of desiccant wheel was 0.102 kgw/h at air flow rate 1.0 kg/min, regenerated air temperature of 55?C and at a wheel speed of 2.5 rpm. The humidity ratio of conditioning space and cooling load of split-type air conditioner was decreased to 0.002 kgw/kgda (14%) and 0.71 kWth (19.26%), respectively. Consequently, the thermal comfort was improved from 0.5 PMV (10.12% PPD) to 0.3 PMV (7.04% PPD).