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Outdoor thermal comfort has been receiving more and more attentions due to the increased demand of outdoor activities during last decades. People require good thermal comfort when they are exposed ...

A liquid desiccant-indirect evaporative cooling (LD-IEC) system has been proposed. The design is able to dehumidify and cool the product air simultaneously in one unit. A computational model has been developed to determine the performance of the heat and mass transfer process. The validation of the model demonstrated good agreement with the experimental data to within 10%. The detailed air treatment process has been theoretically studied. The thermal performance of the LD-IEC has been evaluated. Simulation results showed that the outlet temperature and humidity ratio were influenced by the liquid desiccant film length, intake air temperature, and intake air humidity ratio. For a specific inlet temperature and humidity ratio condition, a desired outlet condition can be obtained by adjusting the length of the liquid desiccant film.

A hybrid evaporative pre-cooled air-conditioning system is introduced for tropical climate applications. The indirect evaporative heat exchanger is employed to pre-cool the ambient humid air before passing through the vapor compression system. A computational model has been developed for the evaporative pre-cooling process. We validated the model by comparing the simulated outlet air temperature against experimental data. The validated model is then used to investigate the performance of the indirect evaporative heat exchanger in terms of the air temperature and humidity profiles. The pre-cooling process is able to reduce the product air temperature and condense water in the product channel. Consequently, the hybrid evaporative pre-cooled air-conditioning system is able to achieve a potential energy saving due the pre-cooling effect and the improvement of the chiller’s efficiency.

In recent years, Northern China suffers severe winter haze, which is attributed to extensive residential coal combustion for warm in winter. Chinese government presented proposals of the electrical energy substitute of the fossil fuels to solve the problem. However, the wide applications of electric heating utilities expose the reliability of the electrical grids on the production and transmission side particularly in extreme cold days. In this paper, we studied heating loads and electric load behaviors of an air source heat pump of a case-study suburban residential building of Beijing, China in wintertime in 2016. Firstly, we choose three characteristic days for heating loads analysis, i.e. the coldest, the warmest, and the medium day. Secondly, heating loads of the case-study building were calculated by a building energy simulation program, which is based on a coupled weather data and the building energy transfer. Hourly heating loads of the case-study building in the three characteristic days were studied based on the weather analyses. Thirdly, the electric load behaviors of the air source heat pump used for room heating were investigated. The COP of the heat pump under different operating conditions was calculated. The peak loads and the electric load fluctuations of the heat pump in wintertime were analyzed. This work provided a valuable database on heating loads and electric loads for warm in suburban area in Beijing, so as to help to achieve the electric grid safety.

To solve the severe air pollution problem, Chinese government presented proposals of the electrical heating substitute of the coal combustion for warm. The heat pump is the most economic electrical heating utility. From the start to steady operation of a heat pump, its electrical power is changed with the transient temperature rising of the heated room. Thus, the study of the transient room temperature rising is crucial to evaluate electrical power change of the heat pump. This paper presented a novel numerical simulation method to simulate transient temperature rising of a HVAC room. In this method, velocity of hot air blown off by a fan coil was not constant as usually was, and it was changed with the transient room temperature. This novel simulation method can simulate the real room heating process. The 3-dimensional transient room temperature model was built in a commercial software Fluent. Velocity of hot air blown off by a fan coil was the boundary condition of the model. Hot air velocity was first calculated by the lumped parameter method (LPM), and then it was applied as initial boundary condition of the transient room temperature model. Using this method, the transient temperature rising of a HVAC room was simulated under different outdoor temperatures. Before the heat pump started, the room temperature was assumed to be 3℃ higher than the outdoor temperature. The room was heated until its temperature reached the required temperature. Then, the heat pump steps into the operation state. The time-history of the room temperature from start to steady operation of the heat pump are obtained and analyzed. The results show the novel method can expedite the computation speed. For each time step, the results converged only after 2~3 iterations.

This study focused on the effect of inserting fins into metal foam on the solidification rate. To this aim, a well-designed experimental system with solid-liquid interface visualization was built. ...

This study presented an experimental investigation on heat transfer performance of a shell-and-tube heat exchanger with and without circular fins. Particular attention has been paid to the effect of injection flow rate of heat transfer fluid (HTF) on the thermal performance of the heat exchanger. A purposely-designed apparatus was built for experimental observation. Results showed that the application of fins had a great effect on improving phase change heat transfer and the full charging time was significantly reduced. Injection flow rate of HTF was found to have little influence upon the performance of the heat exchanger.

The evaporative cooling is an energy-saving and environmentally-friendly air-conditioning method. A cross-flow regenerative indirect evaporative heat exchanger (IEHX) has been designed and fabricated. In the proposed IEHX, the working air is gradually diverted into the wet channels through the holes distributed along dry channels. This arrangement allows the working air to be pre-cooled before entering the wet channel. The experimental study was carried out to investigate the performance of the IEHX under specific inlet conditions. Measurements have been conducted during steady-state operating conditions. Experimental results have demonstrated that the product air can be gradually cooled along its flow direction by transferring its heat to the working air. In addition, the proposed cross-flow IEHX is able to reduce the air temperature below wet-bulb temperature.

The lithium ion battery has been widely applied in the fields of electric vehicles and electronic products due to its advantages of high power density, long lifespan and low self-discharging, etc. In this study, two lithium ion batteries are adopted to explore the effects of different thermal conditions on battery’s performance. One of thermal conditions makes battery close to adiabatic condition similar to the thermal condition of battery pack without any thermal management system. Another thermal condition is constant temperature condition employed to simulate the thermal condition of battery pack with thermal management system. The experimental results show that (i) next chargeable capacities of these batteries are dependent on the previous dischargeable capacities for all thermal conditions; (ii) dischargeable capacities of these batteries markedly decrease with the increase of the discharge rates under 20°C constant temperature condition; (iii) dischargeable capacities are independent on discharge rates under close to adiabatic condition because the obvious battery temperature rise can offset the adverse effects of higher discharge rates on battery’s performance. Although higher battery temperature is conductive to weaken or eliminate the adverse effects of higher discharge rates, excessively high temperature can also accelerate battery aging and easily cause battery thermal runaway, which indicates that it is necessary for battery pack with thermal management system to control thermal conditions of batteries.

The sewage flow rate of the urban drainage system is relatively large and generally stable, its sewage temperature range varies relatively lightly and maintains 10~15℃ in winter. The sewage in the drainage system can be the low grade thermal source for building heating and cooling. Sewage source heat pump technology can efficiently extract or discharge the amount of heat from the sewage in the drainage system for building heating or cooling. The field test of the actual operation thermal performance of the sewage source heat pump were carried out and investigated. The sewage source heat pump system were continuously measured for 72 hours. Based on the test datum, the average COP of the heat pump was 4.5. The relationship between energy consumption of system and energy consumption of transportation are analyzed. The analysis shows that the pump of this system cannot match the load change well and the use of variable frequency pump can improve the energy efficiency of the system. Before the use of the sewage source heat pump system, the traditional coal-fired boiler and air-cooled chiller are the heating and cooling system of this building. Compared with the traditional coal-fired boiler and air-cooled chiller, the advantages of sewage source heat pump system in energy saving, economy and environmental protection are analyzed. The results show that: Compared with the original system, direct heat exchange type sewage source heat pump system can save 53% of the primary energy consumption, reduce the annual operating cost by 11%, increase the initial investment by a factor of 14.3%, and the payback period of incremental investment is about 4.7 years. This method not only has better energy saving, saving capital benefit, but also can reduce the local pollutant emission, and has better environmental emission reduction benefits.

This study presented experimental investigations on the thermal performance of a thermal energy storage (TES) unit with coil tubes. A designed test rig was built and the melting heat transfer characteristics (melting front and temperature distribution) inside the TES unit were examined. The effects of charging flow rate on the overall phase change process were examined. The results showed that natural convection accelerated the thermal energy transport in the melt phase in the top region, but weakened the heat transfer in the bottom region; this resulted in the unmelt PCM at the bottom. The melting heat transfer was overall enhanced by the increase in inlet flow rate, indicating that the full charging time can be shortened by a larger flow rate.

This study presented an experimental investigation on solidification behavior of fluid saturated in highly porous open-cell copper foams. Particular attention has been made on the effect of pore parameters (pore density and porosity) on the solidification behavior. A purposely-designed apparatus was built for experimental observations. Results showed that the copper foam had a great effect on solidification and the full solidification time can be saved up to 50%, especially preventing the decrease in solidification rate during the later stage of phase change. The smaller the porosity is, the faster the solidification rate will be. Pore density was found to have little influence upon the solidification rate. In addition, the local natural convection does exist but it has a slight effect on solidification, leading to the slant of the solid-liquid interface.

The polyethylene glycol (PEG-1000) was selected as phase change material (PCM) and the expanded perlite (EP), the granular activated carbon（GAC）, the powdered activated carbon (PAC) and the expanded graphite (EG) were selected as porous adsorption materials. The composite phase change material (CPCM) was prepared by the physical adsorption method. The composite phase change materials compound with the polyethylene glycol and the expanded graphite were picked by comparing and analyzing the adsorption capacity of such four types of porous materials. And then the composite building material for thermal storage mixed with the CPCM and the cement, water-reducer, early strength agent was prepared in the pressure condition of -0.05Mpa and the constant temperature condition of 70℃. Its thermal physical properties, the structural stability and the compression resistance capability of different quality proportion specimens were experimental researched. The results show that such composite building materials with CPCM appears light density, high thermal conductivity, large heat storage capacity and good stability, and its compression resistance capability can satisfy the requirement of ordinary mortar building material.

The ancient architectures of tower buildings type are representative in ancient architectures in Beijing, and compared with other types of ancient architectures, they are characterized by long distance from ground, high height of building itself, and large inner space. For the ancient architectures of tower buildings type, a proposal using floor-type fan coil air-conditioner for control of physical environment is suggested, and simulation calculation for indoor temperature field for one ancient architecture of tower building in Beijing is done using CFD software, with calculation content comprising the indoor temperature field and velocity field when the system is used in summer. The result shows that: adopting floor-type fan coil air-conditioner for summer conditions and adjusting blast amount of fan coil and blasting parameters can make air temperature agreeable and comfortable.

Biomass hot blast stove is one energy source which is aimed to provide clean hot air, it is widespread and has great potential for being generated from biomass. Under the equal condition of heating load between biomass hot blast stove and natural gas blast stove, this paper investigated the economic feasibility and adaptability of a method that using biomass hot blast stove instead of natural gas blast stove. Based on the technological process and the design parameters demand such as air supply temperature, heating capacity, air flow volume of the existed natural gas hot blast stove heating project, the mathematical model and some indexes for evaluating the technical and economic feasibility of the biomass heating way were established, the difference of the technical maturity, initial investment, annual operating cost, operation maintenance, operational risk and allowance policy within the two heating way were comparative analysed, the sensitivity of factors influencing annual total investment of the biomass hot blast stove was analysed. The results show that, the ratio represented by QZs/QZt of annual total investment between biomass hot blast stove and natural gas hot blast stove was only 0.56 under the equal heating load, the sensitivity of factors influencing annual total investment of the biomass hot blast stove was the biomass fuel, and the many problems about biomass hot blast stove like the technology is still immature, operational risk is relatively large, policy direction is unclear, regional differences and other factors were existence. If the operation of the biomass hot blast stove is safety and the biomass fuel of the biomass hot blast stove is plenty, we will recommend using biomass hot blast stove when the ratio of QZs/QZt was less than 1, and using natural gas blast stove when the ratio of QZs/QZt was more then 1.

Fog and haze weather has seriously affected many important aspects of human life and physical fitness. In order to improve air quality, local government has transformed coal-fired heating into clean energy heating in Beijing rural areas. This paper introduces three typical clean energy heating systems which are low temperature air source heat pump (LTASHP), thermal storage heater (TSH) and wall-mounted gas furnace (WGF), researches and tests the practical operation situation of three heating systems in the field. To compare technical and economic feasibility of three heating systems, the paper takes such residence where energy-saving standard of building palisade structure is approximately 50% as the research object, and establishes technical and economic mathematical analysis models, compares primary energy consumption and carbon dioxide emissions of three heating systems. This paper adopts annual cost approach, comprehensively takes into account power capacity increasing tariff and gas pipe network construction fee, and compares initial investment, operation cost and annual cost of three heating systems respectively from the perspective of users and government. The results show that LTASHP is the most energy-saving and its annual cost is lowest in the three heating systems. LTASHP is the most suitable alternative solutions to coal-fired heating in the three heating systems in rural Beijing.

This study focuses on the heat transfer between the vertical concentric tubes buried underground and the medium-deep rock-soil geothermal energy. The numerical simulation based on an in-house FORTRAN computation program was performed to analyze the mechanism of heat exchange underground. The program was shown to predict the test results of outlet water temperature and heat gain very well under the corresponding operating conditions when engineering data of an actual geothermal well were obtained to validate the numerical scheme. The effects of inlet water temperature and flow rate on the heat exchanger performance were also analyzed in detail. The comparison indicated that the present numerical scheme is able to predict the heat transfer performance of extremely long ground-coupled heat exchanger subject to various geothermal conditions.

The reed valve impact is the main reason leads to the valve fatigue failure, the valve noise and energy consumption of the rotary compressor. This paper built up a three dimensional fluid-structure interaction (FSI) model of the dynamic behaviour of the reed valve in a rotary compressor with the rotational speed of 4800 rpm. Then the P-θ diagram inner the cylinder was tested in an experiment to validate the FSI model. By the FSI model, the impact process, the impact stress and the impact velocity respectively for the reed impact against the retainer and the seat were investigated. It was found that for the reed impact against the retainer, the impact occurred at some local spots moving from the neck to the outer edge of the reed head in sequence rather than at all spots on the whole reed head simultaneously. The whole impact process finishes within the rotation angle of 1 o . The highest impact velocity as well as the highest impact stress happens at the outer edge of the reed head. The research results are helpful to the design and failure diagnosis of the reed valve, as well as to energy saving of the rotary compressor.

Energy losses in district heating pipeline networks can be reduced considerably using insulation materials. In this study, the optimum insulation thickness of direct burial laying used in district heating pipeline networks, energy savings, and payback periods are calculated for various pipe diameters, fuel types and soil depth in the city of Xi’an/China by software MATLAB depending on Life Cycle Cost Analysis (LCCA) method. The results show that optimum insulation thicknesses vary between 0.060 and 0.121 m, energy savings vary between 36.395 $/ m and 194.682 $/m, and payback periods vary between 0.445 and 1.691 years. When the rock wool is used as the insulation material and the soil depth is 1 m, the highest value of energy savings is reached in 500 mm nominal pipe size for fuel-oil fuel type, while the lowest value is obtained in 100 mm for geothermal energy. Therefore, the selection of optimum thickness for different pipes diameters and fuels types is particularly vital for the economic and environmental advantages.

This study presented a pore-scaled numerical simulation on the melting phase change heat transfer of a phase change material (PCM) impregnated in open-cell metal foam. Idealized tetrakaidecahedron was selected as the representing unit cell (UC) to mimic the real foam microstructure and an assembly of tetrakaidecahedron UCs with six lines and three rows was built for computation. Phase change heat transfer in PCM and coupled heat transfer between PCM and metallic ligaments were directly simulated. To address the contribution of natural convection in the melting phase to the overall melting time and pore-scaled melting interface, natural convection in the interstitial fluid was modeled and compared with the conduction-dominated case. Results demonstrated that micro-foam can significantly accelerate the melting phase change rate and further enhancement was observed at pore scale when natural convection in the melting phase was triggered on.

Latent heat thermal energy storage (LHTES) is a promising way to smooth the discrepancy between energy supply and demand, and it is now becoming increasingly significant in the heating and cooling of buildings. However, the low thermal conductivity of the available PCMs require more efficient configuration of LHTES system in reducing the melting time. In order to evaluate the dynamic thermal performances of LHTES unit in shell and tube heat exchanger, the two-HTF-passage configuration and single-pass configuration are numerically investigated. The results show that the central and annular injection in two-HTF-passage configuration has little influence on the transient melting interface location and temperature in the PCM domain and both can effectively enhance the phase change heat transfer, but the HTF tube injection in single-pass configuration shows a significantly poor performance.

The construction of eco-city is a hot spot nowadays, aiming to build harmony between human and nature. Ecological city is able to deal with the relationship between human and the environment, whose key point is to establish a comfortable outdoor thermal environment. To evaluate the built microclimate environment, a campus area located in Northwest China was selected. Different scenarios with extra greening, high albedo pavement materials, water body and their combinations were numerically analyzed through Universal Thermal Climate Index (UTCI) incorporated in the software ENVI-met V4.0. Results demonstrated that the scenarios with water body or high albedo materials was found to have little contribution to reduce UTCI, while the green scenario significantly reduced the UTCI peak (6.9 C) and also the duration (4.5 hours) of heat stress. The present study may be used as a guide for urban planning and construction for ecological city.

The modern development of electric vehicle requires higher power density to be packed into a battery pack. It is always expected that the battery can be arranged as much as possible, however, which leads to the serious thermal management issue due to the heat generation inside the battery packs. As extreme temperature affects performance, reliability, safety and lifespan of batteries, thermal management of battery system is critical to the success of all electric vehicles. The objective of this study is to explore the air cooling capability on the temperature uniformity and hotspots mitigation of a compact battery pack subject to various air flow paths, airflow rates. The numerical results show that the improvement of effective heat transfer areas between air-coolant and battery surfaces is able to obviously lower the maximum temperature and improve the maximum temperature difference in the densely-packed battery box.

This paper evaluates the economy of gravity heat pipe exchanger used for cooling communication base station to replace air conditioning in winter and transition seasons. The experimental data were analyzed, which proved that the gravity heat pipe exchanger can reduce running time and operating cost of air conditioning system. Based on the practical applications, the yearly cooling loads of a typical communication base station were calculated for five cities which represent the typical weather conditions of the five climatic zones in China. The results showed that the energy saving by using the gravity heat pipe exchanger is significant. The annual electricity-saving rate is the highest in Kunming, about 48.6%, while the annual electricity-saving rate is the lowest in Guangzhou, about 18.7% among the five climatic zones.

Absorber is a critical component of an absorption air-conditioning system. Its performance influences directly the overall efficiency and volume. In this paper, the commercial simulation software CFD-FLUENT was used to simulate the falling film absorption process of the coolant LiBr/H 2 O solution. This research attempts to know the effects of various Reynolds number on the absorption progress. The simulation results indicated that there was an optimized Reynolds number of liquid film which leads to an averaged maximum mass flux of 2.9×10 -3 kg·m -2 ·s -1 at the interface. The local interfacial mass transfer coefficient arrives at the maximum at the inlet, then decreases rapidly along the flow direction and approaches to a constant value gradually. It is also find that the local interfacial mass transfer coefficient increases with the increase of Reynolds number while the local heat transfer coefficient exhibits the opposite trend.

Indoor environmental control has been proved to be critical for long-term preservation for artifacts in archaeology museums. However, it is usually a very energy intensive process to sustain a steady condition continuously throughout the year for the whole exhibition hall. In this study, an energy efficient strategy that only controls the local environment for the preservation area is proposed. A laboratory room with a funerary pit was constructed to simulate a large open exhibition hall. Experimental investigations using the test pit, with radiant panels and air curtain system for control of the local environment for the funerary pit, validated this management strategy for the preservation of relics in archaeology museums. The results show that using both an air curtain and a radiant heating system provides a feasible and energy-saving strategy for controlling the preservation environment independently.