Application of terminal box optimization of single‐duct air‐handling units

Terminal boxes maintain room temperature by modulating supply air temperature and airflow in building heating, ventilation and air‐conditioning (HVAC) systems. Terminal boxes with conventional control sequences often supply inadequate airflow to a conditioned space, resulting in occupant discomfort, or provide excessive airflow that wastes significant reheat energy. In this study, the procedure for the optimal minimum airflow setpoint was developed to improve thermal comfort and reduce energy consumption. The determined minimum airflow setpoint was applied in an office building air‐conditioning system. Improvements in indoor thermal comfort and energy reduction were verified through measurement. The results show that the minimum airflow reset can stably maintain room temperature, satisfy comfort standards and reduce energy consumption compared with the conventional control. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy‐saving evaluation of a thermosyphon heat recovery unit for an air‐conditioning system

The energy‐saving effect and economic benefits of a thermosyphon heat recovery unit installed in a shopping mall are investigated. To evaluate the thermal performance of the heat recovery unit in a season, a seasonal temperature effectiveness is advanced, and its calculation formula is deduced referring to the calculation method of seasonal energy efficiency ratio (SEER) for an air conditioner. The annual operating energy‐saving effect of the unit is analyzed by using the seasonal temperature effectiveness while the static economic evaluation method is applied for the economic benefits analysis of the unit. The analysis results indicate the seasonal temperature effectiveness of the unit is 66.08% in the winter and 55.43% in the summer. The energy‐saving effect of the unit is quite remarkable, and the payback time is about 2.65 years. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21049     

A performance comparison between an air‐source and a ground‐source reversible heat pump

In this study, the performance of a reversible ground‐source heat pump coupled to a municipality water reticulation system, is compared experimentally and with simulations to a conventional air‐source heat pump for space cooling and heating. A typical municipality water reticulation system comprises hundreds of kilometres of pipes designed in loops that will ensure adequate circulation of water. This results in a substantial heat exchanger with great potential. Indirect heat transfer occurs between the refrigerant and ground via the municipality water reticulation system that acts as the water‐to‐ground heat exchanger. The experimental and simulated comparisons of the ground‐source system to the air‐source system are conducted in both the cooling and the heating cycles. Climatalogical statistics are used to calculate the capacities and coefficients of performance of the ground‐source and air‐source heat pumps. Results obtained from measurements and simulations indicate that the utilization of municipality water reticulation systems as a heat source/sink is a viable method of optimizing energy usage in the air conditioning industry, especially when used in the heating mode. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance criterion of an indirect dry air‐cooled condenser for small modular reactor based on pressure transition temperature

In terms of reducing the environmental pollution caused by effluent water from typical condensers and the water dependency of small modular reactors, indirect dry air‐cooled condensers (IDACs) are being considered an ultimate heat sink. While the performance of air‐cooled heat exchangers has been investigated thoroughly for decades, evaluations of the condenser performance rely primarily on empirical data. Thus, a method for precisely determining the performance of the IDAC under various environmental and thermal‐hydraulic conditions has not yet been understood. The objective of this study is to experimentally investigate the critical parameter that initiates the deterioration of the condenser performance by varying the cooling duty and water velocity. The investigation is also extended to a parametric study of the air‐cooling conditions using a best‐estimate thermal hydraulic analysis code called multi‐dimensional analysis of reactor safety (MARS‐KS) to suggest a method for designing an IDAC system. Results showed that, for a given cooling duty and water velocity, the condenser exhibited an insufficient performance above a certain cooling water temperature. The temperature was defined as the pressure transition temperature (PTT) that initiates the increase in pressure inside the condenser. The calculation results of MARS‐KS were analysed based on the PTT and was used to suggest methods for designing an appropriate IDAC for the cooling duty and environmental conditions of given target site.     

Performance of passive heat removal by an air‐cooling panel from a high‐temperature gas‐cooled reactor

An experiment was performed to simulate an air‐cooling panel system for passive decay heat removal from a high‐temperature gas‐cooled reactor to investigate the performance of decay heat removal and the temperature distributions of components of the system. The experimental apparatus consisted of a pressure vessel 1 m wide and 3 m high. Nineteen simulated standpipes containing heaters with a maximum heating rate of 100 kW simulated residual heat of the core, and the cooling panels surrounded the pressure vessel. An analytical code (THANPACST2) was applied to the experimental data to investigate the validity of the analytical method and the model proposed. Under the conditions of helium gas at a pressure of 0.64 MPa and temperature of 514 °C in the pressure vessel, the predicted temperature distribution in the pressure vessel was estimated and was within ?10 to +50 °C as compared to the experimental data. The analysis indicated that the heat transferred to the cooling panel was 15.4% less than the experimental value. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 665–677, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10061     

Research on heat dissipation performance and flow characteristics of air‐cooled battery pack

With the depletion of fossil fuels and the aggravation of environmental pollution, the research and development speed of electric vehicles has been accelerating, and the thermal management of battery pack has become increasingly important. This paper selects the electric vehicle battery pack with natural air cooling as the study subject, conducts simulation analysis of the heat dissipation performance of battery packs with and without vents. Then this paper researches on the influence of internal flow field and external flow field. Field synergy principle is used to analyze the effect of velocity field and temperature field amplitude. The results show the following: it is found that the maximum temperature rise and the internal maximum temperature difference of the battery pack with vents are reduced by about 23.1% and 19.9%, raising speed value can improve the heat dissipation performance, and raising temperature value can decrease the heat dissipation performance. Reasonable design of the vents can make the inner and outer flow field work synergistically to achieve the best cooling effect. Then the reference basis for the air cooling heat dissipation performance analysis of electric vehicle, battery pack structure arrangement, and air‐inlet and air‐outlet pattern choosing are offered.     

A feasibility study of using thermal energy storage in a conventional air‐conditioning system

An Erratum has been published for this article in International Journal of Energy Research 2004; 28 (13): 1213. This paper deals with the simulation of thermal energy storage (TES) system for HVAC applications. TES is considered to be one of the most preferred demand side management technologies for shifting cooling electrical demand from peak daytime hours to off peak night hours. TES is incorporated into the conventional HVAC system to store cooling capacity by chilling ethylene glycol, which is used as a storage medium. The thermodynamic performance is assessed using exergy and energy analyses. The effects of various parameters such as ambient temperature, cooling load, and mass of storage are studied on the performance of the TES. A full storage cycle, with charging, storing and discharging stages, is considered. In addition, energy and exergy analysis of the TES is carried out for system design and optimization. The temperature in the storage is found to be as low as 6.4°C after 1 day of charging without load for a mass of 250 000 kg. It is found that COP of the HVAC system increases with the decrease of storage temperature. Energy efficiency of the TES is found to be 80% for all the mass flow rate of the discharging fluid, whereas exergy efficiency varies from 14 to 0.5%. This is in fact due to the irreversibilities in a TES process destroy a significant amount of the input exergy, and the TES exergy efficiencies therefore become always lower than the corresponding energy efficiencies. Copyright © 2004 John Wiley & Sons, Ltd.     

Validation of a methodology for thermal stratification analysis in sodium‐cooled fast reactors

Thermal stratification phenomena usually occur in the upper plenum after a scram of sodium‐cooled fast reactors, which should be closed concerned in the fields of structural integrity assessment and residual heat removal capacity. A 2‐dimensional analysis program under cylindrical coordinate was developed for predicting the in‐vessel thermal hydraulics. Non‐orthogonal block‐structured grids were generated to resolve the problems with complex structures. A second‐order discrete scheme based on midpoint rule was applied to the spatial discretization of convection and diffusion terms. Two sets of experiments characterized by distinct shapes of their apparatuses were used for the validation, mainly from the viewpoints of vertical temperature distribution and rising behaviors of the stratification interface. Results show that RANS‐type turbulent models make the significant impacts on different flow regimes. In the calculation of a scaled model with plenty of stagnant sodium in the upper region, the realizable k ? ε model (RKE) considering the mean deformation rate gives better outcomes than the standard k ? ε model (SKE). For the plant‐type upper plenum with considerable flow rate along the entire height, buoyancy modeling is the crucial issue to follow the upward movement of the interface and the relaxation process of the temperature gradient. In this case, employment of the turbulent Prandtl number reflecting the damping effect by incorporating the local Richardson number well reproduced the experimental results.     

Design and characterization of a cylindrical,water‐cooled heat sink for thermoelectric air‐conditioners

Thermoelectric air‐conditioners (TEACs) are becoming much concerned due to their many advantages, but the low COPs limit their broad applications. The two key factors to raise the COPs of TEACs are both the improvement of thermoelectric materials and the optimum design of hot side heat sinks. This paper provides a thermoelectric air‐conditioning system with a water‐cooled sleeve heat sink in the hot side of the thermoelectric pellets, and compares the overall heat transfer rates q_t, the total heat resistances R_t between the water‐cooled and air‐cooled heat sinks as well as the optimum fin length, the optimum fluid flow velocity and the optimum fin gap distance. The simulation results show that the overall heat transfer rate of water‐cooled heat sink is more than 20 times that of air‐cooled heat sink under the other same circumstances, as a result of the improvement of heat sink, the optimum COP of the thermoelectric air‐conditioning system with the water‐cooled heat sink proximately doubles that with the air‐cooled heat sink. This novel system could be simply installed and applied all the year round for cooling in summer and heating in winter. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of the near‐wake between actuator‐line simulations and a simplified vortex model of a horizontal‐axis wind turbine

The flow around an isolated horizontal‐axis wind turbine is estimated by means of a new vortex code based on the Biot–Savart law with constant circulation along the blades. The results have been compared with numerical simulations where the wind turbine blades are replaced with actuator lines. Two different wind turbines have been simulated: one with constant circulation along the blades, to replicate the vortex method approximations, and the other with a realistic circulation distribution, to compare the outcomes of the vortex model with real operative wind‐turbine conditions (Tjæreborg wind turbine). The vortex model matched the numerical simulation of the turbine with constant blade circulation in terms of the near‐wake structure and local forces along the blade. The results from the Tjæreborg turbine case showed some discrepancies between the two approaches, but overall, the agreement is qualitatively good, validating the analytical method for more general conditions. The present results show that a simple vortex code is able to provide an estimation of the flow around the wind turbine similar to the actuator‐line approach but with a negligible computational effort. Copyright © 2015 John Wiley & Sons, Ltd.     

Cooling load density characteristics of an endoreversible variable‐temperature heat reservoir air refrigerator

The performance optimization of an endoreversible air refrigerator with variable‐temperature heat reservoirs is carried out by taking the cooling load density, i.e. the ratio of cooling load density to the maximum specific volume in the cycle, as the optimization objective in this paper. The analytical relations of cooling load, cooling load density and coefficient of performance are derived with the heat resistance losses in the hot‐ and cold‐side heat exchangers. The maximum cooling load density optimization is performed by searching the optimum pressure ratio of the compressor, the optimum distribution of heat conductance of the hot‐ and cold‐side heat exchangers for the fixed total heat exchanger inventory, and the heat capacity rate matching between the working fluid and the heat reservoirs. The influences of some design parameters, including the heat capacitance rate of the working fluid, the inlet temperature ratio of heat reservoirs and the total heat exchanger inventory on the maximum cooling load density, the optimum heat conductance distribution, the optimum pressure ratio and the heat capacity rate matching between the working fluid and the heat reservoirs are provided by numerical examples. The refrigeration plant design with optimization leads to a smaller size including the compressor, expander and the hot‐ and cold‐side heat exchangers. Copyright © 2002 John Wiley & Sons, Ltd.     

Numerical investigation on the flow field of an axial flow fan in a direct air‐cooled condenser for a large power plant

The flow field of an axial fan in a direct air‐cooled condenser for a large power plant is modeled numerically. In order to improve the efficiency of heat exchange of the air‐cooled condenser, methods of increasing the rotational velocity of the fan and laying out the guide blade at the outlet of the fan are adopted. Results show that increasing the rotational velocity of the fan can effectively increase the flux of the fan, and can improve the efficiency of an air‐cooled condenser; laying out the guide blade at the fan outlet can ameliorate the flow field in an A‐flame. This causes the rotational kinetic energy to change into static pressure at the fan outlet, so the ability of the heat exchange of the air‐cooled condenser is improved. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21027     

Experimental and numerical analysis of oxy‐fuel combustion in a porous plate reactor

The present work focuses on studying experimentally and numerically the oxy‐fuel combustion characteristics inside a porous plate reactor towards the application of oxy‐combustion carbon capture technology. Initially, non‐reactive flow experiments are performed to analyze the permeation rate of oxygen in order to obtain the desired stoichiometric ratios. A numerical model is developed for non‐reactive and reactive flow cases. The model is validated against the presently recorded experimental data for the non‐reacting flow cases, and it is validated against the available literature data for oxy‐fuel combustion for the reacting flow cases. A modified two‐step oxy‐combustion reaction kinetics model for methane is implemented in the present model. Simulations are performed over wide range of operating oxidizer ratios (O₂/CO₂ ratio), from OR = 0.2 to OR = 0.4, and over wide range of equivalence ratios, from φ = 0.7 to φ = 1.0. The flame length was decreased as a result of the increase of the oxidizer ratio. Effects of CO₂ recirculation amount on the oxy‐combustion flame stability are examined. A reduction in combustion temperature and increase in flame fluctuations are encountered while increasing CO₂ concentration inside the reactor. At high equivalence ratio, the combustion temperature and flame stability are improved. At low equivalence ratio, the flame length is increased, and the flame was moved towards the reactor center line. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance enhancement of gas turbines by inlet air‐cooling in hot and humid climates

In this paper, a model to study the effect of inlet air‐cooling on gas turbines power and efficiency is developed for two different cooling techniques, direct mechanical refrigeration and an evaporative water spray cooler. Energy analysis is used to present the performance improvement in terms of power gain ratio and thermal efficiency change factors. Relationships are derived for an open gas turbine cycle with irreversible compression and expansion processes coupled to air‐cooling systems. The obtained results show that the power and efficiency improvements are functions of the ambient conditions and the gas turbine pressure ratio. The performance improvement is calculated for, ambient temperatures from 30 to 50°C, the whole range of humidity ratio (10–100%) and pressure ratio from 8 to 12. For direct mechanical refrigeration air‐cooling, the power improvement is associated with appreciable drop in the thermal efficiency. The maximum power gain can be obtained if the air temperature is reduced to its lowest limit that is the refrigerant evaporation temperature plus the evaporator design temperature difference. Water spray cooling process is sensitive to the ambient relative humidity and is suitable for dry air conditions. The power gain and efficiency enhancement are limited by the wet bulb temperature. The performance of spray evaporative cooler is presented in a dimensionless working graph. The daily performance of the cooling methods is examined for an ABB‐11D5 gas turbine operating under the hot humid conditions of Jeddah, Saudi Arabia. The results indicate that the direct mechanical refrigeration increased the daily power output by 6.77% versus 2.57% for the spray air‐cooling. Copyright © 2005 John Wiley & Sons, Ltd.     

A study on the integration of micro‐reformer and high‐ temperature PEM fuel cell

This study presented an integration platform for a methanol reformer and high‐temperature proton exchange membrane fuel cell (PEMFC). The methanol micro‐reformer was combined with the catalytic reaction section and reforming section, whereas the catalytic reaction section with Pt catalysis maintained the constant temperature environment for a reforming process. SRM reforming results showed that 74 to 74.9% hydrogen and 23.5 to 25.7% of carbon dioxide in the mixture product, and less than 2% of carbon monoxide, was produced. Using the reforming product of low carbon monoxide concentration and the highest methanol conversion rate, a micro reformer link with a fuel cell integration experiment was performed. Results showed a high temperature PEMFC with 3 to 4 W power output under methanol flow rates of 15 ml/hr. Due to the lower hydrogen pressure supplied from the micro reformer, the fuel cell power output may become unstable. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20322     

Passive thermal management of the lithium‐ion battery unit for a solar racing car

In this study, a three‐dimensional numerical model is developed to investigate the thermal and electrical characteristics of 18 650 lithium‐ion battery cells that are used in the solar racing car of Dokuz Eylül University, i.e., SOLARIS. The Newman, Tiedemann, Gu, and Kim (NTGK) battery model of ANSYS Fluent software is implemented to resolve the coupled multiphysics problem. In the analysis, only the discharging period of the battery is considered. Before going through parametric studies under variable weather conditions, time‐wise variations of the cell temperature and the battery voltage are evaluated both experimentally and numerically under two different ambient conditions of 0°C and 25°C. Comparative results revealed that reasonable predictions are achieved with the current battery model, and the difference between the predicted battery surface temperature and experimental data is less than 1°C. Following the model validation, the battery performance is numerically examined by applying the battery model to a real race procedure of SOLARIS. Phase change materials (PCMs) with different amounts and melting temperatures are implemented around the batteries, and transient analyses are conducted under real weather conditions. The current study aims to keep the battery temperature of a solar racing car above a certain limit to prevent the overcooling and maintain higher charging capacity. Implementation of PCM with a melting temperature of 26°C yields 3.15% of capacity increment, and such a performance improvement corresponds to 15.51 Wh of extra energy that can be extracted from an individual battery.     

A feasibility study of a solar desiccant air‐conditioning system—Part II: Transient simulation and economics

In this paper, a solid desiccant cooling system with a backup vapour compression system is simulated using TRNSYS and the performance of the system is evaluated in four cities in the United States with different climates. Economic analysis is performed in order to assess the feasibility of these systems and to determine the relevant economic parameters such as life cycle costs, life cycle savings and payback periods. Results show that the system has higher COP values for the locations with more latent loads. The air conditioner was able to meet the cooling demand in all four regions, but it needed more auxiliary energy in the Eastern and Mountain regions than in the Central region, because of the higher solar fraction in the Central region. The simulation also showed that the desiccant cooling system by itself was capable of meeting the cooling demand and hence the requirement of a backup system may be eliminated. Thermal and economic parameters were analysed for varying solar subsystem sizes which proved helpful in optimizing the design of the solar system. Recommendations to minimize the auxiliary energy costs using different methods for supplying the thermal energy for desiccant regeneration are described. Copyright © 1999 John Wiley & Sons, Ltd.     

State‐of‐charge estimation of power lithium‐ion batteries based on an embedded micro control unit using a square root cubature Kalman filter at various ambient temperatures

The development of a novel method to estimate the state of charge (SOC) with low read‐only memory (ROM) occupancy, high stability, and high anti‐interference capability is very important for the battery management system (BMS) in actual electric vehicles. This paper proposes the square root cubature Kalman filter (SRCKF) with a temperature correction rule, based on the BMS of a common on‐board embedded micro control unit (MCU), to achieve smooth estimation of SOC. The temperature correction rule is able to reduce the testing effort and ROM space used for data table storage (189.3 kilobytes is much smaller than the storage of the MPC5604B, with 1000 kilobytes), while the SRCKF is adopted to achieve highly robust real‐time SOC estimation with high resistance to interference and moderate computing cost (68.3% of the load rate of the MPC5604B). The results of multiple experiments show that the proposed method with less computational complexity converges rapidly (in approximately 2.5 s) and estimates the SOC of the battery accurately under dynamic temperature condition. Moreover, the SRCKF algorithm is not sensitive to the high measuring interference and highly nonlinear working conditions (even with 1% current and voltage measurement disturbances, the root mean square error of the proposed method can be as high as 0.679%).     

A feasibility study of a solar desiccant air‐conditioning system—Part I: psychrometrics and analysis of the conditioned zone

A desiccant dehumidifier in conjunction with evaporative coolers can reduce air conditioning operating costs significantly since the energy required to power a desiccant cooling system is small and the source of this required energy (solar, waste heat, natural gas) can be diverse. Such a solid desiccant cooling system with a backup vapour compression system is simulated and the performance of the system is evaluated to study its feasibility in four cities in the United States. This paper describes the relevant psychrometric calculations and analyses of the conditioned zone required for simulating the transient performance of the system. Copyright © 1999 John Wiley & Sons, Ltd.     

A novel experimental study on discharge characteristics of an aluminum‐air battery

In order to explore the discharge characteristics of aluminum‐air battery and find out the best discharge performance of aluminum‐air battery under the optimum working conditions, this paper studies discharge performances of an aluminum‐air battery under various ambient temperature and battery discharge conditions. The relationship between the temperature rise of the battery electrolyte and the discharge current density was studied by an experimental method. Effects of the electrolyte concentration and the ambient temperature on the battery discharge voltage were investigated. In addition, a novel method for calculating the efficiency of the aluminum‐air battery was proposed. Results show that the temperature of the aluminum‐air battery electrolyte gradually increases as its discharge current density increases and the electrolyte temperature rise could reach as high as 10°C after 60 minutes with a constant 35 mA cm^?2 discharge current density. The specific energy and the specific capacity of the aluminum‐air battery first increase and then decrease as the current density increases. When the current density is 25 mA cm^?2, the specific energy has a peak of 3105 Wh kg^?1 for the condition of the chamber temperature 40°C and the electrolyte concentration 2 mol L^?1 (2 M), while the specific capacity has a peak of 2207 Ah kg^?1; furthermore, its efficiencies under various conditions increase first with the current density, reach a peak range of 19.6% to approximately 36% at 25 mA cm^?2, and then decrease. These experimental results could be used as a technical guidance for the optimization in thermal management designs of the aluminum‐air battery under various operating conditions.