大型汽轮发电机通风系统研究综述

为满足汽轮发电机不断地向大型化发展地需要，必须对大型汽轮发电机的通风系统进行优化设计，以提高其通风冷却效果。为此，国内外对影响汽轮发电机通风冷却状况的主要因素如冷却介质的流动与传热特性、不同通风系统的通风计算方法、通风系统的结构等进行了一系列理论分析和试验研究，并取得不少具有实际应用价值的成果。在对现有成果的分析和总结的基础上，指出了有待进一步研究之处。     

Cooling load reduction in office buildings of hot-arid climate,combining phase change materials and night purge ventilation

Night purge ventilation is a well-known passive technique for conserving cooling energy by storing night coolth in the thermal mass of the building fabric. We study the effect of phase change materials (PCM) as a light thermal mass, on the cooling load of a typical office building with HVAC system and night purge ventilation in hot-arid climate. In this paper the proper conditions to start night ventilation and the ventilation rate by fans is determined. Additionally, the effect of melting point temperature of the PCMs on the cooling load of the building is investigated. PCMs with proper melting temperature were applied to various building elements, and to the whole model. It was revealed that, application of PCMs will significantly contribute in reducing the cooling load, except for the floor on the ground, which resulted in an increase of the load.     

一种新型永磁磁力耦合器导风散热片的仿真研究

本研究针对一款新型永磁磁力耦合器导风散热装置的导风散热片进行仿真分析。首先设计单因素实验,对其部分几何参数进行研究,利用Fluent软件进行流固耦合模拟,得出几何参数对最高温升及阻力距的影响关系,为正交实验提供合理的参数范围。然后设计正交实验,利用极差分析得出合理的参数组合。最后利用上文参数组合建模,模拟安装不同导风散热片个数的散热效果,寻找合适个数。并与未安装导风散热片的模型进行对比,得出此新型导风散热片设计合理,具有一定的实用价值。     

Climatic potential for passive cooling of buildings by night-time ventilation in Europe

Due to an overall trend towards less heating and more cooling demands in buildings in many European countries over the last few decades, passive cooling by night-time ventilation is seen as a promising technique, particularly for commercial buildings in the moderate or cold climates of Central, Eastern and Northern Europe. The basic concept involves cooling the building structure overnight in order to provide a heat sink that is available during the occupancy period. In this study, the potential for passive cooling of buildings by night-time ventilation was evaluated by analysing climatic data, without considering any building-specific parameters. An approach for calculating degree–hours based on a variable building temperature – within a standardized range of thermal comfort – is presented and applied to climatic data of 259 stations all over Europe. The results show a high potential for night-time ventilative cooling over the whole of Northern Europe and still significant potential in Central, Eastern and even some regions of Southern Europe. However, due to the inherent stochastic properties of weather patterns, a series of warmer nights can occur at some locations, where passive cooling by night-time ventilation alone might not be sufficient to guarantee thermal comfort.     

Review on free cooling of buildings using phase change materials

The concept of Green building is gaining importance in the present energy scenario and related environmental issues. Free cooling or ventilation cooling is truly a green concept since even 1 g of carbon is not burnt for the purpose of cooling. Also it ensures that a good indoor air quality is maintained in the building. In this paper a detailed review of work carried out by various researchers on free cooling or ventilation cooling is presented. In addition the major challenges and facts posed in the use of phase change material for free cooling system design such as thermal resistance of air and phase change materials, geometry of encapsulation are discussed in detail. Also the method of energy efficient charging and discharging, effect of phase change temperature, insulation and geographical location are also discussed in this paper. This paper also provides lists the PCM candidates used for free cooling.     

A decoupled method to identify affecting mechanism of crosswind on performance of a natural draft dry cooling tower

The natural draft dry cooling tower (NDDCT) has been increasingly used for cooling in power generation in arid area. As crosswind affects the performance of a NDDCT in a complicated way, and the basic affecting mechanism is unclear, attempts have been made to improve the performance of a NDDCT based on limited experiences. This paper introduces a decoupled method to study the complicated crosswind effects on the inlet and outlet of a NDDCT separately by computational fluid dynamics (CFD) modeling and hot state experiments. Accordingly, the basic affecting mechanism of crosswind on the NDDCT performance is identified. Crosswind changes the inlet flow field of a NDDCT and induces mainstream vortices inside the tower, so as to degrade the ventilation. Besides, low crosswind deflects the upward plume at the outlet to further degrade the ventilation, while high crosswind induces the low pressure area at the outlet to reduce the ventilation degradation.     

Passive cooling in a low-energy office building

In office buildings, the use of passive cooling techniques combined with a reduced cooling load may result in a good thermal summer comfort and therefore save cooling energy consumption. This is shown in the low-energy office building ‘SD Worx’ in Kortrijk (Belgium), in which natural night ventilation and an earth-to-air heat exchanger are applied. In winter, the supply air is successively heated by the earth-to-air heat exchanger and the regenerative heat exchanger, which recovers the heat from the exhaust air. In summer, the earth-to-air heat exchanger cools the ventilation air by day. In addition, natural night ventilation cools down the exposed structure which has accumulated the heat of the previous day. In this article the overall thermal comfort in the office building is evaluated by means of measuring and simulation results. Measurements of summer 2002 are discussed and compared to simulations with a coupled thermal and ventilation simulation model TRNSYS-COMIS. The simulations are used to estimate the relative importance of the different techniques. The evaluation shows that passive cooling has an important impact on the thermal summer comfort in the building. Furthermore, natural night ventilation appears to be much more effective than an earth-to-air heat exchanger to improve comfort.     

Improved cooling performance of large motors using fans

This paper studies the cooling performance by axial fans with forward-swept and inclined blades and a structure with low ventilation resistance for large-capacity open-type motors. The ventilation resistance of axial fans for motors is much greater than that of common fans for creating draughts. Flow separates remarkably on the blades' surfaces and fluid noise is large. We reduced the ventilation resistance inside an electric motor and adopted axial fans with forward-swept and inclined blades. We confirmed by wind tunnel experiment that the flow rate with this combination increases remarkably compared with the conventional ventilation structure and axial fans. Numerical fluid analysis was performed on the flow around the blade at this flow rate. It was confirmed that no flow separation appeared for the air flow along the blade surfaces. This was also observed in a flow visualization experiment. Furthermore, an actual motor with both the low-ventilation-resistance structure and axial fans with forward-swept and inclined blades showed that the flow rate of cooling air increased by 80% compared with that of conventional machines, and the average temperature rise of stator windings decreased by 30%. Thus, the cooling performance was greatly improved.     

Energy conservation in large air-conditioned buildings: Use of evaporative roof cooling in hot and dry climates

Energy conservation potential of the evaporative roof cooling technique for a cinema house in a composite climate (characterized by Delhi) has been evaluated. Thermal loads due to heat conduction through the building envelope, the required ventilation and the occupants have been taken into account. Life-cycle-cost analysis has been employed to evaluate the cost effectiveness of this energy conservation technique. It is seen that evaporative cooling on the roof leads to a net saving of 14% in the initial investment and 17% in the annual cost.     

An experimental tool for research and educational applications on HVAC systems

This paper describes an experimental tool elaborated at the building sciences laboratory (LASH/DGCB). The objective of this tool is to develop control strategies for heating, cooling and ventilation, and test them on heating, ventilating and air conditioning equipment. The tests are conducted in a large room of the laboratory equipped with a double-flow ventilation system and a global control/data acquisition system. The tool is used for research and some experiments are led by engineering students. It enables the identification of optimal parameters for each developed control strategy, in order to reach good thermal comfort, acceptable indoor air quality and good stability of actuators at the least energy cost. In this paper we present an example of global control strategy for heating and cooling periods based on interior temperature control (fuzzy regulator). This strategy includes an indoor air quality controller (proportional integral or fuzzy regulator) based on indoor CO₂ level control. A measurements campaign during an occupied period is shown with an overview of the actuators’ behaviour. This tool also highlights the key role of advanced control techniques to manage heating, cooling and ventilation systems.     

Experimental investigation of effect of ventilation strategies on the performance of cold storage

Fresh fruits and vegetables are living organisms that require fresh air to survive while being stored. Respiratory gases can build up and damage produce if there is not enough ventilation during storage. Ventilation is required to prevent an excessive build-up of respiratory gases and to maintain the freshness of produce. In hot and dry areas, air ventilation of refrigerated storage can have a negative impact on food produce quality and affect storage performance. An indoor experimental study was carried out to investigate the air ventilation of the cold room during various modes of air supply. The energy recovery device (ERD) with and without evaporative cooling arrangement is used in the air supply and the performance enhancement is compared. The ERD reduces the air ventilation load by more than 50% compared to direct ventilation of the cold room and consequently, it reduces the total power consumption of air ventilation. Furthermore, the overall cooling performance of the system is improved by up to 45.7% when the ERDs are used compared to the direct supply of fresh air during air change mode and the use of energy-saving equipment has also proven improvements in the desired air conditions for food production.     

瓦斯发电机房通风降温问题研究

叙述了针对瓦斯发电机房隔声与通风降温之间产生的矛盾,对通风量计算的依据、过程以及各种通风降温方式的比较结果。     

Numerical investigation of free-cooling system using plate type PCM storage

Free cooling night ventilation is the process of storing the coolness in the night time and releasing this coolness in hot day time. In this paper, a numerical study was carried out to simulate and to find out the optimum design for plate type storage filled with phase change material (PCM) which is used in night ventilation systems. The effect of different parameters such as thickness of PCM-plates, inlet air temperature and air mass flow rates on melting front, cooling power, outlet temperature and thermal performance of heat exchanger was studied. The results showed that cooling power can be increased by increasing the mass flow rate. Also, the thickness of the plates in the storage device plays an important role in the thermal performance of the unit and has a linear relation with the melting process duration of PCM for considered configuration.     

Effect of ventilation strategies on air contaminant concentrations and energy consumption in buildings

Considering the diversity of indoor contaminant characteristics and generation patterns, finding an appropriate ventilation strategy that can secure acceptable indoor air quality with minimum energy consumption is a challenging task for HVAC system designers and operators. This study theoretically models and investigates the impact of various ventilation strategies on contaminant concentration behaviour and corresponding ventilation cooling energy requirements for a single‐zone enclosure. Two types of contaminants are considered; carbon dioxide as an occupancy dependent and formaldehyde, which is independent of occupancy. An airflow model is used to predict space pressure and air leakage rates across the enclosure envelope, and an air quality model is used to predict time‐varying contaminant concentrations. In addition, a building energy simulation model is utilized to predict the corresponding ventilation cooling energy requirements under hot climatic conditions. Results from this study show that acceptable contaminant concentrations during occupied periods can be achieved by different ventilation strategies but at substantially different ventilation energy requirements. More than 50 per cent reduction in ventilation energy requirements can be obtained while maintaining acceptable IAQ if proper ventilation strategy is employed. Copyright © 2001 John Wiley & Sons, Ltd.     

Enhancement of natural ventilation in a solar house with a solar chimney and a solid adsorption cooling cavity

This paper presents a parametric analytical study on the enhancement of natural ventilation in a solar house induced by a solar chimney and a solid adsorption cooling cavity. Some details on sizing such a system are also provided. Theoretical analyses are carried out to investigate the ventilation in the solar house with solar chimney alone, cooling cavity alone or with combined solar chimney and solar adsorption cooling cavity, without considering the wind effects. It is found that on a typical day, the solar house comprising of a 2.5 m² solar chimney, is able to create an airflow rate of more than 150 kg/h for the studied house. In addition, the ventilation rate at night is also increased by about 20% with the solar adsorption cooling cavity. It is expected that the proposed concept is useful to be incorporated with a stand-alone building or with a cluster of buildings for some favorable climates.     

Integration of variable refrigerant flow and heat pump desiccant systems for the cooling season

Energy saving and indoor air condition enhancing potentials by integrating the variable refrigerant flow (VRF) and heat pump desiccant (HPD) systems were investigated in a field performance test during a cooling season. Three different operating modes: non-ventilated, HPD ventilation assisted and HPD ventilation–dehumidification assisted VRF systems were investigated. The HPD systems operated in the ventilation–dehumidification mode dehumidify the outdoor air and supply it to the indoor air during the ventilation. It was found that the VRF systems provided an average of 97.6% of the total cooling energy for the HPD ventilation assisted mode. The remainder was the recovered cool by the HPD systems during ventilation. The VRF systems provided an average of 78.9% of the total cooling energy for the HPD ventilation–dehumidification assisted mode. The remainder was covered by the HPD systems which provided additional sensible and latent cooling. Overall, among the three operating modes, it is concluded that the HPD ventilation–dehumidification assisted VRF outdoor units consume less energy than the HPD ventilation assisted ones, but more than the non-ventilated ones, while providing the best indoor thermal comfort and indoor air quality conditions. For the total system, the HPD ventilation–dehumidification assisted VRF systems consume less energy than the HPD ventilation assisted ones.     

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.     

Path Analysis of Energy-Saving Technology in Yangtze River Basin Based on Multi-Objective and Multi-Parameter Optimisation

The Yangtze River Basin in China is characterised by hot-and cold-humid climates in summer and winter, respectively. Thus, increased demand for heating and cooling energy according to the season, as well as poor indoor thermal comfort, are inevitable. To overcome this problem, this study focused on the influence of passive design and heating, ventilation, and air conditioning equipment performance on the energy performance of residential buildings, and explored potential energy-saving technology paths involving passive design and improved coefficient of performance through a multi-objective and multi-parameter optimisation technique. A large-scale questionnaire survey covering a typical city was first conducted to identify family lifestyle patterns regarding time spent at home, family type, air conditioner use habits, indoor thermal comfort, etc. Then, the actual heating and cooling energy consumption and information of model building were determined for this region. Subsequently, the design parameters of an individual building were simulated using Energyplus to investigate the cooling and heating energy consumption for a typical residential building with an air conditioner. The results indicated an improvement of approximately 30% in energy efficiency through optimisation of the external-wall insulation thickness and the external-window and shading performance, and through use of appropriate ventilation technology. Thus, a multi-objective and multi-parameter optimisation model was developed to achieve comprehensive optimisation of several design parameters. Experimental results showed that comprehensive optimisation could not only reduce cooling and heating energy consumption, but also improve the thermal comfort level achieved with a non-artificial cooling and heating source. Finally, three energy-saving technology paths were formulated to achieve a balance between indoor thermal comfort improvement and the target energy efficiency(20 kWh/(m2?a)). The findings of this study have implications for the future design of buildings in the Yangtze River Basin, and for modification of existing buildings for improved energy efficiency.     

侧向风对自然通风直接空冷塔性能影响的数值分析

采用多孔介质简化模型分析了在不同风速情况下300 MW自然通风直接空冷系统空冷塔内的流场和各凝汽器换热量.结果表明:在没有侧向风时,流场是均匀对称的,此时塔内空气流量最大,而各凝汽器换热量均匀;当有侧向风时,由于空冷塔底部气流存在漩涡,使空冷塔内空气回流,空气流量减小;在风速大于4 m/s时,各凝汽器换热量差异较大,随着风速增加,这种现象加剧.     

Night cooling and ventilation design for office-type buildings

The suitability of night ventilation for cooling is first discussed by presenting a plot of summer weather conditions on the bioclimatic chart and by reporting on the results of energy and ventilation simulations of a typical UK office module. The development of a simplified design tool suitable for the early stages of design process is then described. For this model, user input is limited to a few key variables and the technique allows the designer to explore rapidly the effects of a range of design variables including variable external temperatures, internal gains and ventilation rates during the day and night.