Experimental performance analysis and modelling of liquid desiccant cooling systems for air conditioning in residential buildings

The paper presents a new desiccant cooling cycle to be integrated in residential mechanical ventilation systems. The process shifts the air treatment completely to the return air side, so that the supply air can be cooled by a heat exchanger. Purely sensible cooling is an essential requirement for residential buildings with no maintenance guarantee for supply air humidifiers. As the cooling power is generated on the exhaust air side, the dehumidification process needs to be highly efficient to provide low supply air temperatures. Solid rotating desiccant wheels have been experimentally compared with liquid sorption systems using contact matrix absorbers and cross flow heat exchangers. The best dehumidification performance at no temperature increase was obtained in an evaporatively cooled heat exchanger with sprayed lithium chloride solution. Up to 7 g kg⁻¹ dehumidification could be reached in an isothermal process, although the surface wetting of the first prototype was low. The process then provides inlet air conditions below 20 °C for the summer design conditions of 32 °C, 40% relative humidity. With air volume flow rates of 200 m³ h⁻¹ the system can provide 886 W of cooling power.A theoretical model for both the contact absorber and the cross flow system has been developed and validated against experimental data for a wide range of operating conditions. A simulation study identified the optimisation potential of the system, if for example the surface wetting of the liquid desiccant can be improved.     

The potential of solar energy use in desiccant cooling cycles

The use of heat produced by solar thermal collectors is an interesting option for thermal driven air conditioning processes. A thermal driven cooling technique which fits well to non-tracking solar collectors is the desiccant cooling technique. Recently several projects have been carried out which focus on the connection of desiccant cooling systems with solar thermal energy for regeneration of the sorbents. This communication deals with three main topics: (1) experiences achieved in a realized system which is coupled to a solar collector are discussed, (2) a new concept is presented, in which a solar air collector is integrated into the desiccant cooling cycle as the only heat source and (3) a comparative study is presented which compares system performance for different system configurations and different climatic situations.     

太阳能/余热固体除湿冷却系统研究

提出并研制一种太阳能／余热驱动除湿冷却系统。系统包括2台内冷却紧凑式固体除湿器、热交换器、蒸发冷却器等部件。在不同工况下对系统的性能进行模拟计算，分析再生温度、热交换器效率及蒸发冷却器效率对系统性能的影响。     

Indoor temperature variations resulting from solar desiccant cooling in a building without thermal backup

The performance of a once-through solar desiccant cooling system, for air-conditioning a commercial office space, was modelled using the TRNSYS computer simulation software package. The study particularly focused on the potential for designing and operating a desiccant cooling system, without any thermal backup provided to mitigate for intermittent solar availability in three Australian cities.Increasing (i) indirect evaporative cooler effectiveness, (ii) air flow to the office space, and (iii) solar collector area were all shown to reduce the frequency of high temperature events inside the building occupied space. In the warm temperate climate of Melbourne (and to a lesser extent Sydney), high ventilation rates enabled comfort conditions to be maintained at or near acceptable levels in the occupied space, without the use of a backup thermal source.The synergy between evaporative cooling and solar desiccant cooling, observed in the warm temperate climates, was not evident in the tropical Darwin climate, suggesting that the selected ventilation desiccant cooling cycle is not appropriate for tropical climates.     

Performance analysis of a solar cooling plant based on a liquid desiccant evaporative cooler

Summer air conditioning represents a growing market in buildings worldwide, with a significant growth rate observed in European commercial and residential buildings. Available heat driven cooling technologies can be used in combination with solar thermal collectors to reduce the load caused by air conditioning on the electric utilities and to reduce the environmental impact. This work reports a performance analysis of an open cycle solar cooling plant. The plant, installed in Northern Italy, is based on a liquid desiccant evaporative cooler coupled with a solar field. Experimental tests run during summer show average primary energy ratio and primary energy saving index of about 1.6 and 30%, respectively. Though this performance is satisfactorily, the regeneration unit always operated near the lower bound of the nominal temperature range. Therefore, optimization of the solar system design could lead to higher performance.     

干燥地区住宅建筑蒸发冷却通风空调技术的应用研究

居住建筑是人们在生活中停留时间最久的场所之一,所以给其提供一个较好的空气品质尤为重要。传统的家用空调只能解决室内热湿负荷,不断去处理循环风,人们在室内停留时间过长可能会导致"空调病",为了避免以上情况,我们采用可以补充新风的蒸发冷却空调给室内降温~([1])。其中,可应用于住宅建筑的蒸发冷却设备有移动蒸发式冷风扇、窗式直接蒸发冷却器、热回收新风换气机和露点间接蒸发冷却空调,对相关工程进行实测分析,其温湿度均满足舒适性要求。     

蒸发式空调应用于我国农村住宅的前景初探

结合我国农村住宅建筑的特点和农村地区室内热舒适性,阐述蒸发式空调在农村住宅应用的意义和可行性。对用于农村住宅的蒸发式冷风扇、窗式蒸发空调器、柜式蒸发空调器和分体式蒸发空调器4种形式的蒸发式空调的特点和工作原理加以分析,指出蒸发式空调适用于气候条件适宜、经济欠发达的农村地区住宅。     

Development of solar cooling load factors for fenestration in Thailand

Abstract

This article describes the development of solar cooling load factors (SCL) for calculating cooling load from the fenestration part of the building envelopes in Thailand using Bangkok weather data. The Bangkok weather data are selected from 12 years of data collected by the meteorological department. Two sets of weather data are chosen based on dry bulb temperature of 0.4% annual cumulative frequency of occurrence and based on dry bulb temperature of 0.4% hourly cumulative frequency of occurrence and solar radiation obtained from the ASHRAE mathematical model. The building parameters that have effects on the room thermal response are studied. 288 different room types were checked. The values of amplitude and delay based on solar weighting factors are analyzed. Then, rooms with similar thermal response are grouped together and represented by a single point for the group. Each group is defined as a single zone type. Four different zone types are established. For each set of weather data, the values of solar cooling load factors for each zone type are developed.     

Use of compound desiccant to develop high performance desiccant cooling system

The paper is aimed to develop a high performance rotary solid desiccant cooling system using a novel compound desiccant wheel (DW). The unique feature of the desiccant wheel is that it can work well under a lower regeneration temperature and have a higher dehumidification capacity due to the contribution of the new compound desiccant materials. Experimental results indicate that the novel desiccant wheel under practical operation can remove more moisture from the process air by about 20–40% over the desiccant wheel employing regular silica gel. A mathematical model that is used to predict the system performance has been validated with the test results. By integrating the desiccant wheel with evaporative cooling, heat recovery and heating for regeneration sections, a solid desiccant cooling system can be formed. Simulation results show that because of the use of the new compound desiccant, the desiccant cooling system can work under much lower regeneration temperature and have a relative high COP, thus low grade thermal energy resources, such as solar energy, waste heat, etc., can be efficiently utilized to drive such a cooling cycle.     

除湿蒸发冷却空调系统的优化设计

设计一种可利用低品位热能的溶液除湿蒸发冷却空调系统。对此空调系统进行理论分析,得出如下结论：在溶液除湿蒸发冷却空调系统的多种实现形式中,新风经除湿后与回风混合比新回风混合后再除湿节能;将室内排风返回溶液再生器,进行热湿交换,既可加疆对处理空气的预冷,回收排风冷量,又可提高再生器的效率,降低系统能耗;把回热器吸收除湿浓溶液中的部分热量用于溶液再生器的稀溶液预热,可以提高溶液的再生性能。为除湿蒸发冷却空调系统的优化设计提供理论依据。     

住宅建筑电气设计规范征求意见稿

在住宅建筑电气设计中应贯彻执行国家的技术经济政策,做到安全可靠、经济合理、技术先进、整体美观、维护管理方便,由中国建筑标准设计研究院主编的工程建设行业标准《住宅建筑电气设计规范》的征求意见稿已完成,目前广泛征求意见阶段已经结束,预计2009年的下半年正式颁布。本文摘录了此规范意见稿中的有关住宅建筑（小区）的智能化集成系统和信息设施系统部分,敬请关注。     

Energy storage in open cycle liquid desiccant cooling systems

Energy for air dehumidification and cooling can be stored efficiently and non-dissipatively in liquid desiccants. For optimal storage capacity, new dehumidifiers have been developed and tested, dehumidifying air by a cooled microflow of a hygroscopic aqueous salt solution, e.g. LiClH₂O in an almost isothermal absorption process. A small, theoretically sufficient solution flow of about 0.21 l/(hm²) could be distributed uniformly over a cooled exchanger surface. An air dehumidification of 5.5 g/kg and a storage solution has been measured under steady state ARI^∗ conditions with an experimental dehumidifier for an air flow of 1000 m³/h.     

Assessment of adsorption-desorption characteristics of adsorbents for adsorptive desiccant cooling system

The performance of various dehumidification materials was assessed in terms of effective adsorption amount of water vapor based on the adsorption isotherms to find a suitable dehumidification element for an economical adsorptive desiccant cooling system being developed. The effective adsorption amount is an important factor for regeneration at lower temperatures. Three types of silica gels, S(a), S(b), and S(c), with different pore volumes and pore size distributions, and zeolite with various molar ratios of Si/Al, 5.6, 29, 47, 91, and 220, prepared from a Y-type zeolite treated with hydrochloric acid, an activated carbon with silica gel added to improve the hydrophobic surface, and MCM-41 were examined. Silica gels having effective adsorption amounts of 0.25 g/g, and activated carbon with silica gel added were assessed to be candidate desiccant materials.     

Experimental study on a two-stage rotary desiccant cooling system

The objectives of this study were to evaluate the performance of a novel two-stage rotary desiccant cooling (TSRDC) system and to obtain useful data and experiences for practical application. Newly developed compound desiccant (silica gel–haloids) was adopted in the system. An experimental set-up was built and used to test the system performance under three typical environmental conditions. System performances were evaluated in terms of moisture removal D and thermal coefficient of performance COP_th. It has found that the required regeneration temperature of TSRDC system is low and COP_th of the system is high. Regeneration temperatures from 65 °C to 80 °C, 65 °C to 75 °C and 80 °C to 90 °C were recommended for each environmental condition. In addition, the effects of some important operating parameters, such as inlet temperature and humidity ratio of process and regeneration air, on system performance were also investigated in this study.     

开式循环吸附制冷过程的实验研究

本文对基于开式循环的吸附除湿空调制冷系统进行了实验研究。实验证明,该空调制冷系统可用８５℃以上的热源作动力,制冷效率可以超过４０％ 。这样,可利用太阳能或工业余热驱动该制冷系统, 减少常规蒸汽压缩式制冷产生的氟里昂及热岛对空气的污染。本文取得的实验数据为开式吸附空调制冷系统的进一步完善及中试设计提供了可靠依据。     

Assessment criteria for solar cooling systems

Solar cooling systems should be able simultaneously to generate refrigeration and save conventional energy. An assessment of the potential of various cooling systems as refrigerators and energy savers is presented in the paper. For this purpose, a solar cooling system has been considered as a combination of an energy conversion and a refrigeration subsystem. Overall efficiencies of the various solar cooling systems are defined for direct quantitative comparison of different systems.     

Materials selection for thermal comfort in passive solar buildings

This paper presents the results of a combined analytical, computational, and experimental study of the key parameters for selecting affordable materials and designing for thermal comfort in passive solar buildings. The heat transfer across the walls of buildings is modeled using a simple heat diffusion model. In this way, the passive heat storage from the sun (passive solar) and the heat load from internal heat sources are stored in the walls of buildings that provide internal cooling during the day and internal heating at night. The simple analytical model of heat diffusion is used to identify the merit indices for the optimization of affordable passive solar performance. The time dependence of wall/internal temperature is then simulated using a simple finite difference model. The results from the analytical model and finite difference model are validated by conducting temperature measurements in two affordable housing complexes in Egypt. The implications of the results are then discussed for the design of thermal comfort in affordable housing.     

Evaluation of the completeness of LCA studies for residential buildings

Clean Technologies and Environmental Policy - Although life cycle assessment (LCA) is intensively employed in the residential building sector, the incompleteness problem threatens the reliability...     

冷凝热回收型制冷机组在住宅类建筑中的适用性研究

模拟全国4个气候分区内住宅类建筑的夏季空调冷负荷特性,并分析其生活热水使用特点,将两者对比,分析冷凝热回收型制冷机组在住宅类建筑中同时供冷和供热的可能性。结果显示,冷凝热回收型制冷机组在住宅类建筑中值得推广应用。