Application potential of solar air-conditioning systems for displacement ventilation

Solar air-conditioning can have higher application potential for buildings through the strategy of high temperature cooling. In recent years, displacement ventilation (DV), which makes use of the indoor rising plumes from the internal heat gains, provides a more effective supply air option than the traditional mixing ventilation (MV) in terms of both thermal comfort and indoor air quality. As it is possible to raise the supply air temperature to 19 °C for DV, it would enhance the competitive edge of the solar air-conditioning against the conventional vapour compression refrigeration. Through dynamic simulation, a solar-desiccant-cooling displacement ventilation system (SDC_DV) was developed for full-fresh-air provision, while a solar-hybrid-desiccant-cooling displacement ventilation system (SHDC_DV) for return air arrangement. The latter was further hybridized with absorption chiller (AB) to become SHDC_AB_DV, or adsorption chiller (AD) to be SHDC_AD_DV, in order to be wholly energized by the solar thermal gain. Benchmarked with the conventional system using MV, the SDC_DV had 43.3% saving in year-round primary energy consumption for a typical office in the subtropical climate; the SHDC_AB_DV had 49.5% saving, and the SHDC_AD_DV had 18.3% saving. Compared with their MV counterparts, the SDC_DV, the SHDC_AB_DV and the SHDC_AD_DV could have 42.4%, 21.9% and 30.3% saving respectively.     

Improvement of solar-electric compression refrigeration system through ejector-assisted vapour compression chiller for space conditioning in subtropical climate

In this study, improvement was made for the solar-electric compression refrigeration system by incorporating the ejector design to a conventional vapour compression chiller within the system. Through year-round dynamic simulation, the performances of the ejector-assisted vapour compression chiller (EAVCC) were evaluated under the intermittent and changing supply of solar energy in the subtropical climate. In addition, the effect of three common refrigerants, R22, R134a and R410A on the EAVCC was assessed and compared. It was found that the coefficient of performance of the chiller was increased and the total primary energy consumption of the system was decreased for all the three refrigerants, in which the degree of enhancement from R134a was the most significant. It was also noted that the effect of R410A on EAVCC was not apparent, and the overall system energy improvement was marginal. With appropriate ejector design and refrigerant selection of the solar-electric compression refrigeration system, the reduction potential of year-round primary energy consumption could be more than 5%. This would be certainly helpful in promoting the application of solar air-conditioning for building use in the subtropical climate.     

Performance analysis of liquid desiccant based air-conditioning system under variable fresh air ratios

In conventional air-conditioning system, fresh air volume is always restricted to save energy, which sacrifices indoor air quality (IAQ) to some extent. However, removing the latent load of air by liquid desiccant rather than by cooling is an alternative way of reducing energy consumption. Therefore, IAQ can be improved by increasing the volume of fresh air introduced into an air-conditioning system. In this paper, a liquid desiccant based air-conditioning system is studied, with the system performance under various fresh air ratios analyzed using simulation tests. In addition, the proposed system and a conventional system are compared. In the proposed system, with the increase in fresh air ratio, the heating load for solution regeneration rises, the dehumidification efficiency increases and the regeneration efficiency drops. The coefficient of performance (COP) of the liquid desiccant based system decreases sharply when the fresh air ratio exceeds 60%. The results also show that the proposed system can save power notably. The maximum power saving ratio is 58.9% when the fresh air ratio is 20%; however, the ratio drops when the fresh air ratio increases. These findings will be beneficial in the selection of fresh air ventilation strategies for liquid desiccant based air-conditioning systems.     

Feasibility study of desiccant air-conditioning system in Thailand

The objective of this study was to conduct an experimental analysis to investigate the performance and energy saving of the well-known desiccant air-conditioning system in Thailand. The system was composed of a silica gel bed, a split type air-conditioner (1.5 ton refrigeration) installed in a room of volume 76.8 m³, air ducts and a blower. Its design allows us to adjust the percentages of return air, outdoor air and indoor air mixed to the air leaving the desiccant, and desiccant bed thickness as well. Tests were conducted on several days with relatively similar ambient conditions. Under the test conditions used here, a 5 cm bed thickness is recommended with a maximum adsorption rate of 473 g/h. The optimum percentages of air ratios are as follows: 15% outdoor air, 15% return air (mixed together at the desiccant bed inlet) and 70% of indoor air mixed to the dry air leaving the desiccant. The corresponding electricity saving was about 24%. As expected, simple economic analysis indicated that the desiccant air-conditioning is only viable for large cooling capacities and central air-conditioned buildings. The payback period is about 4 yr.     

太阳能液体除湿处理热湿地区冷却顶板新风湿负荷

以广州为例分析了热湿地区冷却顶板空调系统新风冷负荷的特点,显示夏季空调期新风湿负荷占新风总负荷的90%以上.提出了利用太阳能液体除湿处理冷却顶板空调系统新风湿负荷的方案,并将其与常规的冷却除湿方案进行了比较.结果显示,冷却顶板空调系统新风湿负荷的太阳能液体除湿方式比冷却除湿方式节能40%以上,静态投资回收年限为2.2年,认为冷却顶板空调系统新风湿负荷的太阳能液体除湿方式要优于冷却除湿方式.     

蒸发冷却与溶液除湿复合空调系统的应用

根据长江流域高温高湿的气候条件,构建了两级蒸发冷却与溶液除湿相结合的复合空调系统。介绍了复合空调系统的流程,根据该地区的气候条件和相关的空调设计参数,比较了复合空调系统与一次回风空调系统的能耗。在设计工况下,复合空调系统的能效比为2.6,相比于一次回风空调系统的节能率为47.2%。     

香港地区溶液除湿与蒸发冷却复合系统的节能分析

本文提出了溶液除湿与蒸发冷却相结合的复合系统,并根据香港地区的气候条件和相关的空调设计参数,将该复合系统的能耗与一次回风空调系统的能耗进行对比.计算结果表明,在设计工况下复合系统的节能率为21.3%.当采用太阳能、地热等可再生能源或其它废热时,系统的节能率更大.结果表明该复合系统在香港具有较好的运用前景.     

New type of fresh air processor with liquid desiccant total heat recovery

A liquid desiccant total heat exchanger and small capacity refrigeration cycle combined fresh air processor is proposed here in this paper, in order to improve indoor air quality and decrease the energy consumption of the air-conditioning system. Operating principles of both the total heat recovery device and fresh air processor using liquid desiccant are presented in details. Experimental tests of the fresh air processor installed in a hospital show that energy efficiency ratio (EER) is around 6.3–7.3 in the summer experimental conditions and 4.7–5.0 in the winter experimental conditions. Hour-by-hour simulation, which is based on the climate data in Beijing, shows that the average EER is 5.3 and 4.3 in summer and winter period, respectively. Liquid desiccant has the potential to remove a number of pollutants, avoiding cross contamination. Furthermore, in summer fresh air is dehumidified by contacting liquid desiccant instead of 7 °C chilled water, which avoids wet surfaces in the air-conditioning system and much higher indoor air quality can be achieved.     

The effect of heat-pipe air-handling coil on energy consumption in central air-conditioning system

A study was carried out to investigate the effect of heat-pipe air-handling coil on energy consumption in a central air-conditioning system with return air. Taking an office building as an example, the study shows that compared with conventional central air-conditioning system with return air, the heat-pipe air-conditioning system can save cooling and reheating energy. In the usual range of 22–26 °C indoor design temperature and 50% relative humidity, the RES (rate of energy saving) in this office building investigated is 23.5–25.7% for cooling load and 38.1–40.9% for total energy consumption. The RES of the heat-pipe air-conditioning system increases with the increase of indoor design temperature and the decrease of indoor relative humidity. The influence of indoor relative humidity on RES is much greater than the influence of the indoor design temperature. The study indicates that a central air-conditioning system can significantly reduce its energy consumption and improve both the indoor thermal comfort and air quality when a heat-pipe air-handling coil is employed in the air-conditioning process.     

Energy savings potential of a desiccant assisted hybrid air source heat pump system for residential building in hot summer and cold winter zone in China

In hot summer and cold winter zone in China, air conditioning system has four running modes yearly including cooling with dehumidification, cooling, dehumidification and heating in residential buildings. The conventional air source heat pump (ASHP) system is not designed to independently control temperature and humidity, and is not very suitable for the dehumidification mode in the view of building energy consumption. A novel ASHP system combining radiant cooling/heating for residential buildings was presented. The main feature of this hybrid ASHP system is that desiccant wheel and cooling coil accomplish dehumidification process together, and the regenerative heat needed by the desiccant wheel is supplied by the condenser dissipated heat. Based on simulation studies and performance analysis, this paper predicts the primary energy consumption of the hybrid ASHP system in comparison with the conventional ASHP system during the cooling and heating seasons. It was found that primary energy requirement can be reduced by more than 8% in cooling with dehumidification mode, by 50% in dehumidification mode, and by more than 14% in heating mode. The study results prove that the hybrid ASHP system can keep great energy saving and running cost saving yearly, especially in the dehumidification process.     

Proposal for a new hybrid control strategy of a solar desiccant evaporative cooling air handling unit

Correctly controlled solar desiccant evaporative cooling is an interesting option for achieving savings in building air-conditioning consumption. The operation of this system (open loop cooling cycle) is strongly influenced by indoor and outdoor air conditions. This influence is characterized using numerical simulations. First the air conditioned room and the cooling system are simulated using a validated model of the desiccant wheel. Then the influence of each parameter of the desiccant air handling unit is evaluated. The third step is to assess the system cooling power for each operating mode with fluctuating outdoor and indoor air conditions. This allows for making relevant choices for a new control strategy taking into account both indoor and outdoor air conditions. This control strategy is tested for a whole cooling season and compared to a reference compression system with promising results, allowing for energy savings of about 40% for French climate.     

Energy saving through evaporatively cooled condenser air in conventional air-conditioning units

A theoretical study of the feasibility of evaporative cooling of the condenser air of a conventional vapour compression air-conditioning system to upgrade the rating of an air-cooled air-conditioning unit and consequent energy saving in the Delhi climate is presented. A brief review of the heat rejection option in an air-conditioning unit has been given and a theoretical background analysis for evaporative cooling of condenser air has also been presented. For illustration, one specific air-cooled package unit, whose performance characteristics as given by the manufacturers are available, has been used for calculations. Temperature variation data for New Delhi in the months of May and June 1991, obtained from the Meteorological Department, has been used. With the basic data, the upgradation of cooling capacity, power requirement and average energy consumption with and without evaporative cooling of condenser air has been calculated and the reduction in peak load and saving in the average energy consumption was predicted. Typical calculations of the water requirements for pre-cooling of condenser air were also predicted and compared with the corresponding requirements for water-cooled and evaporative condensers. It is concluded that there is an excellent and exciting possibility of reducing energy consumption (and consequent enhanced energy saving) in air-conditioning at national level.     

太阳能固体除湿空调系统的影响因素及方案优化

本文首先阐述了太阳能固体除湿空调系统的原理,从转轮除湿机性能、转轮式除湿系统和太阳能热水系统等3方面分析了本系统的影响因素。而后对除湿前混合的一次回风系统、除湿后混合的一次回风系统和二次回风系统进行了对比,并以一实例进行了分析计算,得到了除湿效率、COP热、太阳能集热器面积随潜热占余热的比例的变化规律。最后,探讨了本系统的运行模式及其优缺点。     

新型排风能量回收装置的分析与研究

作者从全铝制板翅式换热器与凝结水间接蒸发冷却联合应用的试验获得的结果出发，对该换热器应用于集中空调系统的能量回收做出了计算，并且进行较为详尽的分析，计算结果表明全新风空调系统使用该能量回收装置后，可以节省机组装机容量50％，节省运行费用一半；这对需要大量新风的厂房，医院的特殊病区等有很好的节能效果；而普通的舒适性空调系统，应用该能量回收装置后也可以节省装机容量20％；这表明在集中空调系统中应用全铝制板翅式换热器既能改善室内空气品质又能回收排风能量，是集中空调系统节能和人性化行之有效的措施：     

Performance analysis on a hybrid air-conditioning system of a green building

This paper presents the performance analysis on a hybrid air-conditioning system according to the hybrid building energy system of the green building demonstration project in Shanghai, in which a 150 m² solar collector is used to power two 10 kW adsorption chillers, a vapor compression heat pump is used to cool air in the evaporating end while the condensing heating at about 80 °C is fully used to regenerate a liquid desiccant dehumidification system. In the hybrid system, the sensible cooling to the air is treated mainly by solar adsorption cooling and vapor compression cooling, whereas the latent heat is treated by the liquid desiccant dehumidification system with regeneration from the condensing heat of the heat pump. The results show that the performance of this system is 44.5% higher than conventional vapor compression system at a latent load of 30% and this improving can be achieved by 73.8% at a 42% latent load. The optimal ratio of adsorption refrigerating power to total cooling load for this kind of hybrid systems is also studied in this paper.     

超高层建筑标准层空调设计

在空调设计中内外区较为复杂,尤其是超高层建筑,对此,本文指出了直接从室外引进新鲜空气供冷,对减少回水管运行时间、节能及全天候空调空气质量是有利的,并以上海、北京某工程为例指出相应方案。     

转轮除湿与单元式空调机相结合的空气处理系统

本文介绍了转轮除湿与直接膨胀式单元机组相结合的复合空调系统的2种紧凑型组成形式:前置预冷与后置冷却,并在几种不同室外工况下,针对应用于独立新风系统,对比分析了这2种典型组成方案的性能特点。结果表明,这2种除湿方式在4种典型工况下的制冷能耗相差不明显,在10%以内;但后置冷却除湿在高温高湿工况下难以实现较大的单位除湿量,且再生空气温度高;而前置预冷除湿系统采用较小的除湿转轮尺寸,结构更紧凑,可明显降低初投资,且再生空气温度较低。因此,前置预冷除湿系统在较小流量空气处理应用方面更具优势,更具商品化发展潜力。     

A combined system of chilled ceiling,displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.     

蒸发冷却空调新风系统的全年应用研究

结合干热、严寒或寒冷地区全年气候特点及冬夏季建筑能耗特性,通过逐时新风能耗模拟计算,得到设置热回收装置的全年用蒸发冷却空调系统冬季新风节能量远大于夏季节能量,选用热回收装置时应重点关注冬季热回收效率,各类热回收装置中转轮热回收装置全年节能量最大,节能效果最好。基于此,深入分析了蒸发冷却空调系统冬夏季新风加湿需求、新风量变化范围和水系统管径选择,给出了全年用蒸发冷却空调机组冬季运行的防冻措施。     

江阴市某商业综合楼太阳能空调热水系统设计

给出了江阴市某商业综合楼太阳能吸收式空调的设计及计算方法,详细地阐述了该吸收式空调系统的运行原理、负荷计算、空气处理过程、太阳能集热器的设计计算和布置方式、空调系统冷热源的选择、冷水机组的选型及依据等,并分析了连续阴雨天生活热水的保障问题以及储热、储冷水箱选择的依据,阐明了该系统运行的可行性,并通过满负荷计算的方法比较了改造前传统空调系统的耗电量与改造后太阳能吸收式空调系统的耗电量,得出太阳能吸收式空调节能约42%,太阳能吸收式空调具有一定的发展前景。