An improved design of wind towers for natural ventilation and passive cooling

A design is proposed to improve the performance of wind towers (or Baud-Geers) for natural ventilation and passive cooling. Under similar climatological and design conditions, the new design is capable of delivering air to the building at higher flow rates. It can also cool the air evaporatively to lower temperatures. Higher airflow rates and the evaporative cooling capability of the new Baud-Geer design can be fully utilized at nigh in summer to cool the building mass to lower temperatures.Momentum, mass and energy analyses are carried out for the proposed design. The results are presented in graphical forms which may be used as guidelines for employing the design for specific applications in the hot, arid areas of the world. An example is worked out to show the use of the results.     

On the development, optical properties and thermal performance of cool colored coatings for the urban environment

This paper reports the measured solar spectral properties and the thermal performance of 10 prototype cool colored coatings, developed at the National and Kapodistrian University of Athens, using near-infrared reflective color pigments in comparison to color-matched, conventionally pigmented coatings. These coatings are developed to be used in the urban environment to fight the heat island effect. The spectral reflectance and the infrared emittance were measured and the solar reflectance of the samples was calculated. The surface temperature of the coatings when applied to concrete tiles was monitored, using surface temperature sensors and a data logging system, on 24 h basis from August to December 2005 in an effort to investigate the ability of the cool colored coatings to maintain lower surface temperatures than conventionally pigmented color-matched coatings. The data obtained has been extensively analysed and indicate significant success in the development of these cool colored coatings. It was found that all the coatings containing infrared reflective pigments have solar reflectance values higher than those of standard coatings. Furthermore, it was demonstrated that cool colored coatings maintain lower surface temperatures than color-matched conventionally pigmented coatings. This temperature difference is mainly due to differences in solar reflectance. These cool colored coatings can be used on buildings (roofs and walls) and other surfaces in the urban environment. Thus, at building scale, the use of cool colored coatings with increased solar reflectance can improve building comfort and reduce cooling energy use, and at city city-scale it can contribute to the reduction of the air temperature due to the heat-transfer phenomena and therefore improve outdoor thermal comfort and reduce the heat-island effect.     

Design of a solar heating and cooling system for CSU solar house II

This paper describes the design of a solar air heating and night/day exchange cooling system with emphasis on the operational modes. In this type of system the collector absorbs solar energy and converts it to heat for space heating and domestic water heating. Cooling is accomplished by using the cool night air available in dry climates) to cool a pebble-bed storage unit and subsequently using the cool pebbles to lower the air temperature in the building during the day. Circulation is from the solar system to the building in the same manner as most modern heating and air conditioning units but uses air as the medium for heat transfer. The air system is particularly suited for climatic regions where heating loads are high and cooling requirements are moderate. The system utilized in Solar House II operates in either the heating or cooling mode as selected through a seasonable change-over switch. Solar preheated hot water is furnished for domestic use in either mode.     

焙烧竖窑熟料的冷却及余热回收

本文详尽地介绍了在矾土焙烧竖窑底部熟料冷却段,采取下鼓上抽的联合通风方式冷却熟料,抽出的热风通过普通的空气加热器,反向换热,加热采暖循环水。该装置经过实践运行与测试,证明它一方面有效地解决了熟料的冷却,也延长窑底钢梁、推料杆以及熟料运输机的寿命,并改善了操作环境,另一方面又回收了大量热能于建筑物采暖。     

An experimental investigation into a solar assisted desiccant-evaporative air-conditioning system

In this experimental investigation a solar assisted open adsorption cooling system has been designed and tested under the local weather conditions of Basrah, Iraq. Data were obtained from June to September, inclusive, 1984. Tests were carried out hourly with a directly supply of hot air from a corrugated absorber solar air heater for regeneration. Also, tests were conducted at a constant regeneration temperature of 70°C using auxiliary heat. Adsorption was carried out by a rotary disk of silica gel. Three mass flow rates of process air were employed without recirculation. The performance of the solar air heater was obtained for both seasons, and the instantaneous efficiency was evaluated experimentally and analytically with results compared. Daily and seasonal coefficients of performance were obtained for the cooling system for the mass flow rates employed. A maximum seasonal average value of 2.8 was obtained for a mass flow rate of 0.075 kg/s. The system performance improved with higher regeneration temperature, higher process air mass flow rate and dry weather. It was possible to generate a cool supply of air at satisfactory conditions using solar energy only for all clear days under the local weather conditions.     

On the efficiency of night ventilation techniques for thermostatically controlled buildings

A new, integrated method to calculate the energy contribution of night ventilation techniques to the cooling load of a building is presented in this paper. The method is based on the principle of “Balance Point Temperature” and permits the calculation of the energy required to cool a building to acceptable comfort conditions when night ventilation techniques are used. It also permits the calculation of the energy contribution of night ventilated buildings compared to conventional air conditioned buildings. The proposed method is successfully validated with data from an extended and detailed simulation procedure using the TRNSYS simulation programme to calculate dynamically the thermal performance of buildings using night ventilation techniques. It is found that the method is of sufficient accuracy and can be used during the predesign as well as the design phase of a building to access the performance of night ventilated buildings.     

A multi-stage down-draft evaporative cool tower for semi-enclosed spaces: Aerodynamic performance

A multi-stage down-draft evaporative cool tower (DECT) was developed as an improvement to a previously developed single-stage design. The new tower incorporates a secondary air inlet, added to reduce the water consumption required to produce a desired cooling output in a tower of given maximum cross-section and primary inlet geometry. The secondary air, which may be drawn from the interior space being chilled, is cooled by evaporation in the lower section of the tower. This paper reports on the results of experiments conducted to establish the aerodynamic performance of the design prior to installation of a water spraying system. Design of the water spraying system and experiments on cooling performance are discussed in a companion paper.     

An ice thermal storage computer model

In hot humid countries such as Thailand, air conditioning plant is installed in most commercial and industrial buildings. A conventional air conditioning system, which is normally operated when cooling is required, is the most favored option. Ice thermal storage on a large scale, used to provide a cool reservoir for use in peak periods, is however an attractive financial option for large buildings to supply coolness. There are two means of operating ice thermal storage systems, namely full storage and partial storage.In this paper, a computer model has been developed in order to compare energy use in conventional air cooling systems and ice thermal storage systems. Under Thailand electricity tariff rates, the results from the simulations show that the full ice thermal storage can save up to 55% of the electricity cost required for cooling per month when compared with the conventional system. It is also found that using full storage option can reduce the total energy consumption by 5% for the selected building.     

Assessment of solar assisted air conditioning in Central Queensland's subtropical climate,Australia

Australia has a very sunny climate, with a very high demand for air conditioning. Implementing solar assisted air conditioning is an ideal option to achieve a high solar fraction which leads to a significant amount of energy and greenhouse gas emission savings. Solar assisted air conditioning systems are environmentally friendly by being constructed in a way that minimises the need for chlorofluorocarbons CFC, Hydro chlorofluorocarbons HCFC or Chlorofluorocarbons HFC refrigerants and by using a low grade thermal renewable energy, therefore, making them energy efficient and environmentally safe. They can be used either as stand-alone systems or with conventional AC, to improve the indoor air quality. Solar cooling is a new and a fast growing technology compared to other fields of solar energy applications. On the other hand most of the current solar cooling applications are demonstration projects in nature; the technologies are advancing yet still need a lot of additional design, planning, development, and research efforts. T now solar assisted air conditioning's main obstacles are the high installation costs, and the lack of knowledge and familiarity with this technology between designers, developers and architects.In this paper a feasibility study is carried out to assess a solar assisted air conditioning system for an office building under three of Queensland's subtropical climates; Rockhampton, Gladstone, and Emerald. The technical aspects of a proposed solar cooling system are investigated. Cooling load profile for a proposed reference building was obtained using TRNSYS software under the influence of these different climates. An electric vapour compression pump, with 2.5 coefficient of performance (COP) for cooling is used as a reference system to assess the primary energy consumption, assuming 80% of primary energy consumed by the reference conventional system is replaced by solar energy. The results of analysing the proposed system indicated that an 80% of the primary energy savings can be achieved by installing 50 m² of solar collectors and 1.8 m³of hot water's storage tank under the three selected climates.     

A ventilated courtyard as a passive cooling strategy in the warm humid tropics

The paper investigates the potential of a courtyard for passive cooling in a single storey high mass building in a warm humid climate. The inclusion of an internal courtyard in building design is attributed to the optimization of natural ventilation in order to minimize indoor overheating conditions. However, the efficiency of this strategy greatly depends on the design details of the building composition in providing appropriate airflow pattern to the courtyard. From the results of thermal measurements, a significant correlation between wall surface temperatures and indoor air temperatures is evident. A reduction of indoor air temperature below the levels of ambient is seen as a function of heat exchange between the indoor air and high thermal mass of the building fabric. However, this behavior is affected by indoor airflow patterns, which are controlled through the composition between envelope openings and the courtyard of the building.From a computational analysis, several airflow patterns are identified. A relatively better indoor thermal modification is seen when the courtyard acts as an air funnel discharging indoor air into the sky, than the courtyard acts as a suction zone inducing air from its sky opening. The earlier pattern is promoted when the courtyard is ventilated through openings found in the building envelope. The computational simulation utilizing the standard k-ε turbulent model with isothermal condition agrees closely with the measurements taken from the field investigation.     

Influence of different outdoor design conditions on design cooling load and design capacities of air conditioning equipments

Outdoor design conditions are important parameters for energy efficiency of buildings. The result of incorrect selection of outdoor design conditions can be dramatic in view of comfort and energy consumption. In this study, the influence of different outdoor design conditions on air conditioning systems is investigated. For this purpose, cooling loads and capacities of air conditioning equipments for a sample building located in Adana, Turkey are calculated using different outdoor design conditions recommended by ASHRAE, the current design data used in Turkey and the daily maximum dry and wet bulb temperatures of July 21st, which is generally accepted as the design day. The cooling coil capacities obtained from the different outdoor design conditions considered in this study are compared with each other. The cost analysis of air conditioning systems is also performed. It is seen that the selection of outdoor design conditions is a very critical step in calculation of the building cooling loads and design capacities of air conditioning equipments.     

Properties and performance of advanced reflective paints to reduce the cooling loads in buildings and mitigate the heat island effect in urban areas

High reflective coatings and paints spread on the roof and walls can be very useful to reduce the cooling loads in buildings to ensure thermal comfort in the built environment. The solar reflectance of construction and cooling materials was measured with a spectrophotometer. A surface temperature monitoring campaign compared the thermal profiles of typical Italian construction materials with an innovative sustainable white paint, obtained with a special mixture of milk and vinegar of very high solar reflectance. Two building-integration cool-roof campaigns were run in the experimental building, Casa Intelligente of ENEA, in which indoor and outdoor air temperature and roof surface temperatures were monitored. This campaign, run in the summer of 2005 and 2006, allowed us to verify the influence of cool roofs to mitigate indoor air temperatures and to compare the behaviour of different cool-roof technologies.     

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.     

夏季降温的太阳房实验分析

对建造在南宁市西郊的一座被动式太阳房在夏季运行时的实验数据进行了分析，其屋顶集热表面在夏季夜间能产生一定的致冷效果。所制取的冷空气不但在夜间可以对该太阳房起到降温的作用，并且可以储藏起来以供白天降温使用。     

Viability of wind towers in achieving summer comfort in the hot arid regions of the middle east

Operation of conventional wind towers, or Baud-Geers, are described. Wind towers maintain natural ventilation through buildings due to wind or buoyancy effects. The tower structure is cooled externally through radiative transfer with the sky, and internally with the cool ambient air, circulated through the building and the tower during the night. During the day, the warm ambient air is partially cooled by the tower structure before entering the building. When passed over moist surfaces, air is cooled evaporatively. However, sensible and evaporative cooling potentials of conventional wind towers, which depend on the tower design, are limited. Another disadvantage of the conventional wind towers is the admittance of dust into the building.Two modern designs of wind towers are considered which eliminate the above disadvantages. One design incorporates one-way dampers in the tower head and a wetted column in the tower. This design, which is particularly suitable in areas with good winds, evaporatively cools the hot-dry ambient air before admitting it into the building. The other design incorporates evaporative cooling pads at the tower entrance. This design is particularly suitable in areas with very little or no winds.This latter design may be incorporated into the existing minarets of the mosques and shrines, church towers, or other existing tall towers, to supply evaporatively-cooled air into the space.Conventional and the modern versions of wind towers can be incorporated aesthetically into the designs of modern buildings in the hot-arid regions of the Middle East, and other areas of the world with similar climate, to provide summer thermal comfort with little or no use of electricity.     

Cooling subsystem design in CSU solar house III

The use of cool storage in conjunction with residential lithium bromide absorption chillers allows for improved operating conditions of the cooling subsystem. Significant performance degradation in the absorption cooling capacity is evident whenever the chiller cycles on and off during periods of low cooling demand. The capability of providing storage for the chiller out-put prevents short-term cycling of the absorption machine and significantly improves the seasonal average coefficient of performance of the cooling system. Cool storage can also be utilized to allow for a lower cooling capacity of the absorption unit (lower tonnage), without decreasing the ability of the subsystem to meet the cooling demands of the building. The size of cool storage can, in fact, be optimized by evaluating the ability of the cool storage component to minimize cycling of the absorption machine and in meeting the cooling demands on a smaller tonnage chiller.     

夏季工况条件下空调/冷柜一体机性能实验研究

空调冷柜一体机系统是通过中间冷却器将空调与冷柜耦合,可以将空调系统中的部分制冷剂节流至中间冷却器对冷柜系统中的制冷剂进行过冷以提升其系统性能。实验研究了夏季工况条件下冷柜温度、室外环境温度及质量流量比对一体机系统制冷量及COP的影响。实验结果表明:在夏季工况条件下,冷柜系统的制冷量和COP随质量流量比的增大而增大,但质量流量比大于12%后其增速放缓;空调系统制冷量随质量流量比的增大而减小,而其COP随质量流量比的增大而略有增大。综合分析认为夏季工况条件下,质量流量比控制在8%～12%时可以提高空调及冷柜系统COP,同时空调器制冷量衰减也较小。     

Theoretical analysis of ammonia-water absorption cycles for refrigeration and space conditioning systems

This paper presents an investigation of an ammonia-water absorption cycle for solar refrigeration, airconditioning and heat pump operations at higher heat supply temperatures. The system consists of a solar driven generator, rectifier, condenser, evaporator, absorber and heat exchangers for preheating and subcooling within the system. A steady state thermodynamic cycle analysis based on mass and heat balances along with the state equations for the thermodynamic properties of the ammonia-water mixture has been carried out. A numerical computer simulation of the system with input component temperatures, refrigerant concentration/mass flow rate and effectiveness of the heat exchangers has been made to evaluate the relative heat transfer rates (i.e. coefficients of performance) and the mass flow rates for the cooling/heating modes. It is found that unlike the low generator temperature behaviour the coefficients of performance for both cooling and heating modes are reduced at higher generator temperatures. However, an increase of condenser temperature for each mode of operation improves the performance of the systems at higher generator temperatures. A choice for keeping the absorber temperature equal to/lower than that of the condenser is also predicted at lower/higher generator temperatures, respectively. In general the results are more pronounced for the refrigeration mode than for the heat pump mode and are least effective for the airconditioning mode.     

Optimal roof structure with multilayer cooling function materials for building energy saving

Both cool roof and phase change thermal storage are promising technologies in decreasing building energy consumption. Combining these two technologies is likely to further enhance the thermal comfort of the building as well as reduce air condition loads. In this paper, the cooling performance and energy-saving effects of four types of roof (normal roof, phase change material [PCM] roof, cool roof, and cool PCM roof [cool roof coupled with PCM]) were investigated under a simulated sunlight. Experimental results indicate that compared with normal roof, the other three roofs are able to narrow the indoor temperature fluctuation and decrease the heat flow entering into the room. Among them, cool PCM roof gave the best energy-saving effect that can lower the indoor temperature and heat entering into rooms by 6.6°C and 52.9%, respectively. Besides, the PCM location, PCM thickness, and insulation thickness exerted great impacts on the cooling performance of the roof. Placing the PCM on the internal layer beneath the extruded polystyrene (XPS) insulation board can make the indoor temperature 1.2°C lower than that on the middle layer. Although thicker PCM panels or insulation boards can provide a better thermal insulation, 5 mm in PCM thickness and 20 mm in insulation thickness are enough to guarantee the indoor temperature of cool PCM roof system at a comfortable range (22°C-28°C) for a whole day. These findings will give guidance in designing buildings with a light and compact roof structure to decrease energy consumption and improve comfort level.     

Cool Thermal Discharge by Melting Ice and Producing Chilled Air

This article deals with the time histories of the air flow rate required and the temperature of chilled air produced during cooling of air by melting ice with specified heat flux at the free liquid surface. The equations for estimating the required mass flow rate of air to maintain a specified heat flux removal of cool thermal discharge by direct contact of air with melting ice to produce chilled air were derived from an analysis of the heat transfer coupled with the moving boundary. Numerical examples are illustrated in which the inlet air temperatures were either specified or varied with time to simulate practical systems.