Psychometric technoeconomic assessment and parametric studies of vapor-compression and solid/liquid desiccant hybrid solar space conditioning systems

This communication presents some studies on hybrid vapor-compression (V-C) and solid/liquid desiccant solar air-conditioning systems. Desiccants are used to bring the humidity within the comfort range by partially converting the latent heat load (LHL) into sensible heat load and then meeting this load with conventional V-C cycle. In both the options of hybrid systems consisting of vapor-compression and solid/liquid desiccant cycles, heat rejected from the condenser of the V-C cycle is used to regenerate the desiccants to improve the coefficient of performance (COP) of the systems. A thermodynamic assessment and technoeconomic feasibility study of hybrid V-C and solid/liquid desiccant solar air-conditioning systems have been presented. It is found that a hybrid system with desiccant cycle is more promising under high latent heat load and higher ambient humidity conditions and significant energy saving can be achieved over standard V-C cooling systems.     

An open cycle absorption heat pump

The absorption cycle can be also of the open type. This concept has been utilized in developing solar cooling absorption systems. Another possibility not yet investigated is an open cycle absorption heat pump. The system rests upon the utilization of a packed tower operating with liquid desiccants. The tower dehumidifies both the exhausted air of heating plant and the exhaust of a natural gas boiler. A conventional heater heats up the regenerator of the sorbent and the inlet air. Simulations give a PER of the system (the open cycle heat pump) higher than 1.3 with respect to the Gross Calorific Value of natural gas. This value is difficult to obtain with the more complex closed cycle absorption or vapour compression cycle motor driven heat pump.     

闭式循环太阳能空调系统热稳定性分析

闭式循环太阳能空调系统减少了蓄热水箱以及与之相关的热水循环泵,直接在太阳能集热器与制冷机组之间形成热水循环环路,系统得到简化的同时,降低了水泵功耗,具有明显的经济性和节能性。然而,由于系统水容量较低,闭式循环太阳能空调系统在运行过程中呈现出明显的波动性。通过研究主要过程参数的变化率,对系统运行的热稳定性进行了分析,并对系统的应用方式进行了探讨。     

沸石开式循环储能试验装置动态特性实验研究

１前言七十年代,澳大利亚的Ｃｌｏｓｅ［１－２］等人首次进行了利用固体材料吸／脱附循环实现低温热储存的研究,这种方法克服了传统储能方法的缺陷,为热能储存开辟了新天地。近年来国内外也相继对此开展了大量研究。以沸石～水为吸附对的吸附／脱附循环,因其无公害性而逐渐受到人们关注。以沸石～水为吸附对的闭式循环制冷／热泵装置,国内外均有报导,但开式循环却很少见诸报导。而开式循环可以直接利用湿空气作为水的载体,环境状态的空气流过系统,经吸附（或脱附）作用后又回到环境,这一特点是其他吸附对所不具备的。因此,本文提…     

Desiccant integrated hybrid vapor-compression cooling: Performance sensitivity to outdoor conditions

The performance of a desiccant integrated, hybrid, vapor-compression cooling system is modeled numerically. The concept of hybrid cooling investigated in this paper utilizes the waste heat rejected from a vapor-compression cycle to directly activate a solid desiccant dehumidification cycle. The hybrid system consists of four major components; a compressor, an evaporator and two desiccant integrated condensers/dehumidifiers. The performance sensitivity of a first generation prototype hybrid, vapor-compression cooling system to variable outdoor conditions is reported and compared to the performance of conventional vapor-compression systems.     

Micro cooling systems for high density packaging

Future 3D electronics packaging systems will require micro cooling systems that can be integrated and permit the continued use of air as a coolant. To achieve this, new types of silicon micro heat exchangers were made using an anisotropic etching process. Various heat exchanger configurations and sizes were made using sandwich and stacking techniques. They can be used either as a heat exchanger for direct cooling with compressed air or as a heat pipe and thermosyphon for indirect cooling with fan-blown air. The performance characteristics of the various cooling systems are stated. The micro-heat-pipe can be used for power loss densities of up to 3 W·cm⁻², the direct air cooling up to 15 W·cm⁻² and the thermosyphon up to 25 W·cm⁻². Cooling performances are achieved that are otherwise only possible with liquid cooling. The practical application of the micro cooling system is demonstrated using the example of the Pentium processor. With a power loss of 15 W, the high-performance micro cooling system is able to limit the increase in operating temperature to 15 K. The volume of the micro heat exchanger is 2.5 cm³ and therefore considerably smaller than that of standard heat sinks.     

Heat pipes for ground heating and cooling

Different versions of heat pipe ground heating and cooling devices are considered. Solar energy, biomass, ground stored energy, recovered heat of industrial enterprises and ambient cold air are used as energy and cold sources. Heat pipe utilization of air in winter makes it possible to design accumulators of cold and ensures deep freezing of ground in order to increase its mechanical strength when building roadways through the swamps and ponds in Siberia. Long-term underground heat storage systems are considered, in which the solar and biomass energy is accumulated and then transferred to heat dwellings and greenhouse, as well as to remove snow from roadways with the help of heat pipes and solar collectors.     

Hybrid model for evaluating the performance of open-cycle absorption systems for waste heat recovery

An analytical model has been developed to predict the performance of open-cycle absorption systems for waste heat recovery. The model is based on the integral control volume approach. The system conservation equations as well as constitutive relations are presented.Predicted results demonstrated the capabilities of the model and showed that the model compared well with other existing models and data.     

Effect of adsorbent heat and mass transfer resistances on performace of an open-cycle adiabatic desiccant cooling system

A mathematical model describing the heat and mass transfer processes that occur during sorption of water vapor in a dehumidifier consisting of parallel channels lined on either side width desiccant felt, is presented. The model includes both gas-side and solid-side resistances for thermal and mass transport. The moisture transport in the desiccant is expressed by considering both gas phase diffusion and surface diffusion. The heat and mass transfer in the desiccant matrix occurs simultaneously and is coupled by an equilibrium sorption relation which is applied locally within the desiccant. Solutions are obtained by using an explicit finite-difference scheme.The effect of heat and mass transfer Biot numbers and other system parameters on the performance of an adiabatic open-cycle cooling system are investigated.     

高性能太阳能固体吸附式制冷与供热联合循环研究

以电加热器为热驱动源,对所提出的太阳能供热与制冷联合循环的复合机系统进行了实际测试及性能分析。实验结果表明,供热与制冷联合循环的复合机装置,能有效地应用于太阳能为驱动源的固体吸附式制冷装置之中,并在制冷的同时对外供热,系统的总能利用得到了较大的提高,为太阳能制冷技术的有效利用作出了积极的探索。     

Interface investigation of planar hybrid n-Si/PEDOT:PSS solar cells with open circuit voltages up to 645 mV and efficiencies of 12.6 %

We have studied interface formation properties of hybrid n-Si/PEDOT:PSS solar cells on planar substrates by varying the silicon substrate doping concentration (N _D). Final power conversion efficiencies (PCE) of 12.6 % and open circuit voltages (V _oc) comparable to conventional diffused emitter pn junction solar cells have been achieved. It was observed, that an increase of N _D leads to an increase of V _oc with a maximal value of 645 mV, which is, to our knowledge, the highest reported value for n-Si/PEDOT:PSS interfaces. The dependence of the solar cell characteristics on N _D is analyzed and similarities to minority charge carrier drift-diffusion limited solar cells are presented. The results point out the potential of hybrid n-Si/PEDOT:PSS interfaces to fabricate high performance opto-electronic devices with cost-effective fabrication technologies.     

太阳能空调品质及评价方法

太阳能空调的服务对象是建筑,其最终目标是要为建筑营造舒适的室内热环境。因此,合理评价太阳能空调品质对保证空调效果,优化系统设计具有重要的意义。基于太阳能空调冷量输运过程参数,提出输冷过程热稳定性、冷冻水能质系数以及输冷过程匹配性三项指标,用来评价太阳能空调品质。根据实验数据对太阳能空调品质进行了评价与分析,并对系统的应用方式进行了探讨。     

Analysis of modified counter-flow cooling towers

Evaporative air cooling for human comfort and other applications, whenever possible and feasible, is less expensive than conventional air conditioning. A cooling tower is used in the centralised evaporative air cooling system. In the present study, the counter-flow cooling tower is modified to pre-cool the air at the tower inlet, either by the water after the cooling load, or the tower exit air. These two modified cooling towers are modelled and their thermal performances are compared with the conventional counter-flow cooling tower. For generality, the results are presented in terms of number of transfer units (NTU), a dimensionless number for a cooling tower indicating its size. The modified cooling towers are found to be better than the conventional one in lowering the tower approaches below about 2°C. These cooling towers seem to be distinctly advantageous when operating at low approaches, small ranges and large wet-bulb depressions, thus making them quite useful in evaporative air cooling applications.     

Studies on some solar collector/regenerator systems for open cycle absorption air conditioning/liquid desiccant cooling systems

This communication presents theoretical heat and mass transfer studies on solar collector/regenerator systems which determine the performance of open cycle absorption air conditioning system. Possible configurations viz. open inclined surface, forced flow and brine-still solar regenerators have been analytically modelled and a comparative assessment using a numerical model has been presented. The numerical model takes into account the flow length dependence of the solution temperature/concentration and the rate of water mass desorption in the regenerator. The effects of various operating and climatic parameters on the water mass desorption rate for the given working fluid have been studied.     

Effects of Chemical Heat Sink Generated by an Oxalic Acid Cooling Stream on Film-Cooling Effectiveness

Based on the theory of heat transfer enhancement, a novel film-cooling method for turbine blades that involves a chemical heat sink generated by the use of oxalic acid as a cooling stream has been proposed. Experiments were conducted on a flat plate with a row of 30° angled holes, and the conventional method using air as the cooling stream was examined for comparison. Overall, the results of this study demonstrate that the proposed cooling method involving an oxalic acid-induced chemical heat sink is more effective than the conventional method.     

Thermal optimization of high power LED arrays with a fin cooling system

In this paper, we describe an optimization process of thermal design for the light lamp which utilizes the Light Emitting Diode (LED) module as a lighting source. The thermal performance of the LED module was shown to significantly improve by the optimization process of cooling system attached with it. A wind circulating cooling system was designed for the LED arrays with the input power of 60?Watts and another heat pipe cooling system was designed for the input power of 144?Watts. The effects of design parameters such as air temperature and air velocity on the thermal performance of LED lamp were investigated. Thermal performance of the two cooling systems was compared for practical application.     

Performance and Exergy Analyses of a Solar Assisted Heat Pump with Seasonal Heat Storage and Grey Water Heat Recovery Unit

The main research objective of this paper was to compare exergy performance of three different heat pump (HP)-based systems and one natural gas (NG)-based system for the production of heating and cooling energy in a single-house dwelling. The study considered systems based on: 1. A NG and auxiliary cooling unit; 2. Solely HP, 3. HP with additional seasonal heat storage (SHS) and a solar thermal collector (STC); 4. HP with SHS, a STC and a grey water (GW) recovery unit. The assessment of exergy efficiencies for each case was based on the transient systems simulation program TRNSYS, which was used for the simulation of energy use for space heating and cooling of the building, sanitary hot water production, and the thermal response of the seasonal heat storage and solar thermal system. The results show that an enormous waste of exergy is observed by the system based on an NG boiler (with annual overall exergy efficiency of 0.11) in comparison to the most efficient systems, based on HP water–water with a seasonal heat storage and solar thermal collector with the efficiency of 0.47. The same system with an added GW unit exhibits lower water temperatures, resulting in the exergy efficiency of 0.43. The other three systems, based on air–, water–, and ground–water HPs, show significantly lower annual source water temperatures (10.9, 11.0, 11.0, respectively) compared to systems with SHS and SHS + GW, with temperatures of 28.8 and 19.3 K, respectively.     

热管喷射式空调系统中喷射器的研究

利用热管和喷射器复合所组成的空调系统是一种可利用太阳能和备类余热的无泵型新型空调系统。该系统利用喷射器代替压缩机,利用热管内的毛细芯实现工质循环。本文分析了喷射器的流动特性,采用一个简化的一维模型计算了喷射器的喷射系数。设计了一种专用的小型内置式喷射器,对一太阳能热管喷射式空调系统的制冷特性和性能系数进行了数值模拟。模拟计算表明,喷射器的结构和运行特性对热管喷射式制冷系统的性能有明显的影响。     

用于住宅建筑的太阳能吸收式空调性能分析

夏季太阳能辐射强度与空调负荷有很好的一致性,这使得太阳能辅助空调具有独特的优点。根据郑州地区夏季太阳辐射和空调负荷特点,针对某一太阳能辅助吸收式空调系统进行了理论分析,该系统供冷对象为200m2别墅,采用60m2平板式太阳能集热器和一个带有辅助加热装置的集热水箱作为热源。在发生器温度为70—100℃,蒸发温度5—15℃的范围内计算了系统性能系数和太阳能利用率。计算结果表明,在5—9月份,太阳能可以提供建筑冷负荷的76—122%。     

Absorption cycles. A review with regard to energetic efficiency

The improvement of energy conversion systems in order to decrease consumption of primary energy and to minimize negative impact on the environment which originates from industries with large cooling and heating demand is mandatory. We want to review the potential of absorption heat pump technology in this respect. Absorption systems are compared to conventional compression systems with regard to the consumption of primary energy. Different areas of application such as air-conditioning, refrigeration, heating, combined cooling and heating, and process heat recovery are treated. Absorption systems have a large potential for energy saving, especially when they are operated by heat from cogeneration systems or, of course, by waste heat. But even direct-fired systems can compete with compression machinery: highly efficient cycles which perform far better than comparable conventional machines are in development.