The research and development of the key components for desiccant cooling system

An air conditioning option, that is, desiccant cooling system (DCS) in which alternative energy source, such as solar energy, nature gas and rejected heat, can play their part for the benefit of environment and saving energy is constructed by regenerative dehumidification component combined with heat exchanger (recuperator) and evaporative cooler.The mathematical model of an rotary desiccant wheel that can be used to calculate the performance of stationary or rotary bed and transient or steady state operation is founded by considering many terms. A computer program for this new model has been compiled and some results of computer simulation compared with experimental value, they are good in agreement.The performance of evaporator is estimated by computer. We developed some kinds of evaporator of which the COP is about 1015 to decrease the room temperature and clean the air in drier climates. Using a new kind of chemical refrigerant invented by Zu-She Liu, the air conditioner will be simple in construction and very efficient (COP > 30).     

A methodology for the performance evaluation of an experimental desiccant cooling system

An experimental investigation was conducted in an open cycle desiccant cooling system (DCS) operating on the ventilation mode in the laboratory site [M. Yıldırım, An experimental investigation on heat and mass transfer in a desiccant cooling system, PhD thesis, Gaziantep University, Turkey (2002). [1]]. Although the operation of DCS is presumably affected by the design of primary components of rotary regenerator (RR) and desiccant wheel (DW) the methodology used in the analysis of experimental data is presented in this paper to set a different approach for the performance evaluation of similar systems.

The rotational speeds of RR and DW (N_RR and N_DW), air mass flow rate (m_a) in process and regeneration lines, and the regeneration temperature (T_R) were defined as operation parameters. Meanwhile coefficient of performance (COP) and cooling capacity (CC) of the system were called as the performance parameters. The system operation with a variety of experimental conditions resulted in an extensive data set covering the ranges of N_RR, N_DW, m_a and T_R as 5 rpm ≤ N_RR ≤ 20 rpm, 0.1 rpm ≤ N_DW ≤ 0.4 rpm, 0.05 kg/s ≤ m_a ≤ 0.139 kg/s and 60 °C ≤ T_R ≤ 90 °C, respectively. The interactive influence of the operation parameters was determined through the realization of the psychrometric cycle in deviation from an ideal cycle. A dimensional analysis based on a trial and error procedure was followed to determine the functional relationship of COP and CC.

The proposed correlations between COP and CC and the introduced system performance parameter (PP) were determined to be a sole function of m_a independent of N_RR, N_DW and T_R in their covered ranges.     

Effect of ambient conditions on the first and second law performance of an open desiccant cooling process

An open desiccant cooling process is presented and applied to ventilation and recirculation modes of the system operation. The cooling system consists of a desiccant wheel, a rotary regenerator, two evaporative coolers, and a heating unit. Certain ideal operating characteristics based primarily on the first law of thermodynamics are assumed for each component. The system with indoor and outdoor ARI conditions has a thermal coefficient of performance (COP) of 1.17 in ventilation mode and 1.28 in recirculation mode. A second law analysis is also performed and at ARI conditions, the reversible COP of the system is determined to be 2.63 in ventilation mode and 3.04 in recirculation mode. Variation of the first and second law based COP terms and cooling load with respect to ambient temperature and relative humidity are investigated in both modes of the system operation. The results of the analysis provide an upper limit for the system performance at various ambient conditions and may serve as a model to which actual desiccant cooling systems may be compared. As an additional study, a non-ideal system operation is considered and it is determined that both the COP and cooling load decrease with increasing ambient temperature and relative humidity, and they approach zero at high values of ambient temperature and humidity.     

Dynamic hygroscopic effect of the composite material used in desiccant rotary wheel

In this study, silica gel (SG), calcium chloride (CaCl₂) and composite desiccant (SG–CaCl₂) applied to a corrugated paper (CP) based desiccant rotary wheel are compared for their abilities to remove moisture from wet air. The experimental data shows that the CP–SG–CaCl₂ material could attain equilibrium within a very short period, and its hygroscopic capacity is much higher than that of CP–SG. Also, it exhibits a remarkable increase in moisture removal compared with the silica gel wheel.     

Construction and initial operation of the combined solar thermal and electric desiccant cooling system

This paper reports the constructed combined solar thermal and electric desiccant cooling system - its initial operation and operational procedures. The system, as designed, can be operated during nighttime and daytime. The nighttime operation is for thermal energy storage using the auxiliary electric heater, while the daytime operation is for solar energy collection and desiccant cooling. Ongoing experimental evaluation is being undertaken to observe and determine the long-term performance of the system.     

Development and construction of the novel solar thermal desiccant cooling system incorporating hot water production

This paper reports the development and construction of the novel solar cooling and heating system. The system consists of the thermal energy subsystem and the desiccant cooling subsystem. The system utilizes both the cheaper nighttime electric energy and the free daytime solar energy. The system is conceptualized to produce both cooling during summer daytime and hot water production during winter. Testing and evaluation of the system had been done to determine its operational procedure and performance. Based on the results, the thermal energy subsystem functioned to its expected performance in solar energy collection and thermal storage. The desiccant cooling subsystem reduced both the temperature and the humidity content of the air using solar energy with a minimal amount of back-up electric energy. The system however, needs further investigation under real conditions.     

Comparison of the modeling of a solar absorption system for simultaneous cooling and heating operating with an aqueous ternary hydroxide and with water/lithium bromide

This paper compares the theoretical performance of the modeling of a solar absorption system for simultaneous cooling and heating operating with water/lithium bromide and alternative aqueous ternary hydroxide mixtures. Aqueous ternary hydroxide working fluid consists of sodium, potassium and cesium hydroxides in the proportions 40 : 36 : 24 (NaOH : KOH : CsOH). Plots of Carnot coefficients of performance and enthalpy-based coefficients of performance are shown against the evaporator temperature. The results showed that, in general, the system with the hydroxide mixture may operate with higher coefficients of performance than the system with the lithium bromide mixture. Also it was shown that the system with the hydroxide may operate with a higher range of temperatures.     

Solar and geothermal heating and cooling of the European Centre for Public Law building in Greece

The European Centre for Public Law in Legraina near Athens in Greece is heated and cooled by a combined solar and geothermal system. The main components of the system are a saline groundwater supplying well, water storage tank for 6 h autonomy, inverter for regulating geothermal flow, heat exchanger, two electrical water source heat pumps placed in cascade, fan coils, air handling units, as well as solar air collectors for air preheating in winter. In addition, hot water is supplied to the building hostel by solar water heaters. Monitoring of the energy system during heating showed excellent energy efficiency and performance.     

Development of a PEM stack and performance analysis including the effects of water content in the membrane and cooling method

For the use of proton exchange membrane (PEM) fuel cell systems to become widespread, the components required to build one should be minimized. Because a PEM fuel cell has a limited operating temperature range, it requires some kind of cooling method. In this study, different cooling methods were investigated experimentally. A PEM fuel cell stack with an active area of 100 cm² and 8 cells in series was developed and used in this research. When 50% relative humidity inlet gases were supplied (at 15 A of current discharge and 70 °C), cell temperatures at the center increased from around 60 °C to 85 °C, and cell voltage dropped from 4.8 V to 3.2 V because of membrane drying (insufficient cooling). When fully hydrated inlet gases (100% relative humidity) were supplied to the PEM stack at the same test conditions, the cell temperature remained around 65 °C, and stack voltage remained around 5.7 V at 15 A of current discharge. Fully hydrated inlet gases play a positive role both for water transport (when the proton moves from the anode to the cathode) and to maintain the fuel cell stack temperature to prevent stack drying.     

The impact of the projected changes in temperature on heating and cooling requirements in buildings in Dhaka,Bangladesh

Dhaka, the capital of Bangladesh, is a fast growing megacity with a population of 12.8 million. Due to its tropical location, dense urban morphology and higher than average density of population, buildings in Dhaka are likely to be adversely affected by the projected changes in climate, in particular by the increases in temperature. Buildings play a vital role in most aspects of our lives and their energy consumption patterns affect climate change mitigation and adaptation strategies. It is important to understand the likely impact of the projected increases in temperature on cooling and heating requirements in buildings in future climates. In this research, global projections on changes in temperature are temporally downscaled using a statistically averaged baseline present-day hourly weather data to generate future weather data in three timeslices: 2020s, 2050s and 2080s. Time series data for the present-day and future climates are analyzed as well as heating and cooling degree-days are calculated.     

Numerical simulation of cooling energy consumption in connection with thermostat operation mode and comfort requirements for the Athens buildings

A model and a corresponding numerical procedure, based on the finite-difference method, have been developed for the prediction of buildings thermal behavior under the influence of all possible thermal loads and the “guidance” of cooling control system in conjunction with thermal comfort requirements. Using the developed procedure analyses have been conducted concerning the effects of thermostat operation mode and cooling power in terms of the time, on the total cooling energy consumption for the ideal space cooling, as well as for various usually encountered real cases, thus trying to find ways to reduce cooling energy consumption. The results lead to suggestions for energy savings up to 10%. Extensive comparisons between the ideal and various real cooling modes showed small differences in the 24-h cooling energy consumption. Because of the above finding, our detailed ideal cooling mode predictions gain considerable value and can be considered as a basis for comparison with real cases. They may also provide a good estimate of energy savings obtained if we decide to increase thermostat set point temperature. Therefore, as the extent of cooling energy saving is a priori known, one can decide if (and how much) it is worthy to increase thermostat set point temperature at the expense of thermal comfort. All results of the study, which refer to the Typical Athens Buildings during the typical Athens summer day, under the usual ranges of thermal loads, may be applicable to other regions with similar conditions.     

Comparative study between parallel and counter flow configurations between air and falling film desiccant in the presence of nanoparticle suspensions

A comparative numerical study is employed to investigate the heat and mass transfer between air and falling film desiccant in parallel and counter flow configurations. Nanoparticles suspensions are added to the falling film desiccant to study heat and mass transfer enhancements. The numerical results show that the parallel flow channel provides better dehumidification and cooling processes of the air than counter flow configuration for a wide range of pertinent parameters. Low air Reynolds number enhances the dehumidification and cooling rates of the air and high air Reynolds number improves the regeneration rate of the liquid desiccant. An increase in the channel height results in enhancing the dehumidification and cooling processes of air and regeneration rate of liquid desiccant. The dehumidification and cooling rates of air are improved with an increase in the volume fraction of nanoparticles and dispersion factor. Copyright © 2003 John Wiley & Sons, Ltd.     

Investigating the effects of injection and induction modes of hydrogen addition in a CRDI pilot diesel-fuel engine with exhaust gas recirculation

This work compares the outcomes of different flow rates of hydrogen added by induction and injection methods in three different flow rates (3, 9, and 15 LPM) through the intake manifold of a constant speed CRDI diesel engine operated at 1500 rpm. The premixed air and hydrogen mixture was ignited by injecting diesel fuel at 23? bTDC. Hydrogen addition reduced CO, HC, and smoke in both the techniques, but efficiency was decreased at a higher percentage of hydrogen induction, whereas it increased with the injection technique. The higher calorific value and flame velocity helped proper combustion and improved brake thermal efficiency by 7%, and the brake-specific energy consumption was reduced by 10.7%. In addition, CO, UHC, and Smoke were decreased by 15.8, 29.7, and 15% compared with neat diesel at full BMEP. Nitrogen oxides decreased by 5.6% for 15 LPM of hydrogen injection compared to the induction method with the same flow rate but higher than diesel fuel by 35.9%. Three different EGR percentages (5, 7.5, and 10%) were used to reduce the higher NOx emission. Though the injection process was complex compared to the induction method, the injection process can provide promising results even at higher hydrogen flow rates.     

A new cooling circuit and its control strategies for the thermal management of PEMFC in rapid startup application

This paper presents an experimental study of a new liquid cooling circuit and its control strategies. The objective is to meet the heat management requirements of a Proton Exchange Membrane Fuel Cell during startup. The cooling circuit creates an alternate flow through the stack. The cell heat generation is achieved by inserting heating pads enabling the study of the heat transfer behavior independently of the electrochemical reaction. New circuit control strategies are compared to reference strategies for no flow circulation or unidirectional flow. The alternate flow duty cycle is adjustable, and the stages where fluid is at rest in the fuel cell can be included. We show that this new cooling system can ensure a temperature rise of 26 °C in 85 s. A maximum temperature difference between the bottom and top part of the cells of 1 °C and 3 °C along the stack is observed.     

Assessment of the energy utilization efficiency in the Turkish transportation sector between 2000 and 2020 using energy and exergy analysis method

Energy and exergy utilization efficiencies in the Turkish transportation sector over the period from 2000 to 2020 are evaluated in this study. A comparison of the overall energy and exergy efficiencies of the Turkish transportation sector with the other countries is also presented. Energy and exergy analyses are performed for four transport modes, namely roadway, railway, airway and seaway, while they are based on the actual data for 2000 and projected data for 2020. Roadway appears to be the most efficient mode when compared with railway, air and seaway. It is projected that about 15% of total energy resources will be used in this sector during 2020. The energy utilization efficiencies for the Turkish transportation sector range from 23.71% in 2000 to 28.75% in 2020, while the exergy utilization efficiencies vary from 23.65% to 28.85% in the same years, respectively. Exergetic improvement potential for this sector is estimated to be 700 PJ in 2020, with an average increase rate of 4.5% annually between 2000 and 2020. Road transport and oil-fuelled combustion engines offer the principal scope for exergetic improvement in the coming decades. It may be concluded that the methodology used in this study is practical and useful for analyzing sectoral energy and exergy utilization to determine how efficiently energy and exergy are used in the sector studied. It is also expected that this study will be helpful in developing highly applicable and productive planning for energy policies.     

A 3D CAD-based simulation tool for prediction and evaluation of the thermal improvement effect of passive cooling walls in the developed urban locations

As a passive cooling strategy aimed at controlling increased surface temperatures and creating cooler urban environments, the authors have developed a passive cooling wall (PCW) constructed of moist void bricks that are capable of absorbing water and which allow wind penetration, thus reducing their surface temperatures by means of water evaporation. Passive cooling effects, such as solar shading, radiation cooling and ventilation cooling can be enhanced by incorporating PCWs into the design of outdoor or semi-enclosed spaces in parks, pedestrian areas and residential courtyards. The purpose of the present paper is to detail the development of a 3D CAD-based simulation tool that can be used to predict and evaluate the thermal improvement effect in urban locations where PCW installation is under consideration. Measurement results for the surface reduction effect of a PCW are introduced in the first part of the paper. In the second part, thermal modeling of a PCW is proposed based on analysis results of experimental data. Following that, a comparison study that integrates the proposed thermal modeling was conducted to validate the simulation method. In order to demonstrate the applicability of the developed simulation tool, a case study was then performed to predict and evaluate the thermal improvement effect at an actual urban location where PCWs were installed. Simulations were performed by modeling the construction location in two scenarios; one where the PCWs were composed of dry bricks, and another where the bricks were wet. The results show that, in terms of surface temperature and mean radiant temperature (MRT), this simulation tool can provide quantitative predictions and evaluations of thermal improvements resulting from the installation of PCWs.     

Multi-year application of the three-dimensional numerical generation of response factors (NGRF) method in the prediction of conductive temperatures in soil and passive cooling earth-contact components

A recently developed method named the three-dimensional numerical generation of response factors NGRF (Zoras and Kosmopoulos, 2009) was claimed to be fast, accurate and flexible as a result of incorporating elements of the response factor method into a finite volume technique based numerical model. The presented paper reports on the application of the NGRF method for the numerical prediction of temperatures within and around structural passive cooling components over multi-year temperature profiles. Once the numerical temperature response factors time series of an earth-contact component’s grid node had been generated then its future thermal performance due to any surrounding temperature variation can be predicted fast and accurately. The NGRF method was, successfully, applied through an intermodel testing procedure to simulate soil and structural earth-contact passive cooling component temperatures for multiple years.     

Similarity between the spiral arms of Galaxy M51 image and the interface curve of Yin-Yang balance in the Ancient Tai-Chi diagram

The particle paths of the Lagrangian flow field between two cylinders simulate well the spiral arms of Galaxy M51 image [1] and the interface curve of the Yin-Yang balance in the ancient Tai-Chi diagram [2]. The particle paths of the Lagrangian flow field involve four parameters. The normalization of the system of equations significantly simplifies the formulation of the flow process and reduces the original four parameters to only one parameter. Furthermore it provides the similarity between the formulation of the spiral arms of Galaxy M51 and that of the interface curve of the Yin-Yang balance in the ancient Tai-Chi diagram. Dedicated to Professor Dr. Jürgen Zierep, University of Karlsruhe, Germany, for his 80^th birthday in January 2009     

微燃机与小燃机在南方地区分布式联供系统中的应用比较

建立了考虑设备最大最小出力限制、温度和出力对设备性能影响的分布式联供系统优化运行混合整数非线性规划（MINLP）问题求解方法。在负荷确定的条件下,可对不同配置的分布式联供系统进行优化运行计算及经济、节能减排、调峰特性分析。针对我国南方地区气候及能源价格特点,对办公楼、商场、医院和宾馆四类典型城市建筑比较了分别由微燃机和小燃机为主机组成的分布式联供系统的适用性。计算结果表明,与冷、热、电分供形式相比,除办公楼外,由微燃机和小燃机为主机组成的分布式联供系统均具有较好的经济性;分布式供能系统节能减排、调峰性能优越;微燃机联供系统和小燃机联供系统经济性相当,但小燃机系统一次能源利用率较高。