Engine-driven hybrid air-conditioning system

A hybrid air-conditioning system that combines an engine-driven chiller with desiccant dehumidification was configured and experimentally tested to provide reliable data for energy consumption and operation cost. The engine performance and the desiccant wheel performance were measured and a numeric model previously set up for dehumidification capacity prediction was validated. For a reference building, the results based upon measured data show that under present electricity/gas price ratio, more than 40% of operation cost can be saved by the hybrid system.     

太阳能溶液除湿空调(下)

五太阳能溶液蓄能太阳能是分布广泛、使用清洁的可再生能源,但太阳辐射的不连续性和不稳定性,成为太阳能利用的关键问题。太阳能溶液除湿空调系统可吸收太阳能,并以空调能力的形式储存于除湿剂浓溶液中,是一种有效的蓄能方式。太阳能溶液除湿空调循环中,浓溶液在除湿     

太阳能制冷讲座(8) 太阳能溶液除湿空调(上)

介绍了太阳能溶液除湿空调的工作原理及特点。详述了系统主要部件除湿器、太阳能集热再生器的构成,介绍了太阳能溶液蓄能原理,并对太阳能溶液除湿空调的研究进展和应用前景进行了总结。     

Performance analysis of solar absorption-subcooled compression hybrid refrigeration system in subtropical city

Solar absorption-subcooled compression hybrid refrigeration system is a new type of efficient and economical solar refrigeration device which always meets the demand of cooling load with the change of solar irradiance. The performance of the hybrid system is higher due to the improvement of evaporator temperature of absorption subsystem. But simultaneously, the variation of working process as well as performance is complicated since the absorption and compression subsystems are coupled strongly. Based on the measured meteorological data of Guangzhou, a subtropical city in south China, a corresponding parametric model has been developed for the hybrid refrigeration system, and a program written by Fortran has been used to analyze the performance of the hybrid system under different external conditions. As the condensation temperature ranges from 38°C to 50°C, the working time fraction of the absorption subsystem increases from 75% to 85%. Besides, the energy saving fraction also increases from 5.31% to 6.02%. The average COP of the absorption subsystem is improved from 0.366 to 0.407. However, when the temperature of the absorption increases from 36°C to 48°C, the average COP of hybrid system decreases from 2.703 to 2.312. Moreover, the working time fraction of the absorption subsystem decreases from 80% to 71.7%. The energy saving fraction falls from 5.67% to 5.08%. In addition, when the evaporate temperature increases from 4°C to 14°C, the average COP of the absorption subsystem decreases from 0.384 to 0.365. The work of the compressor decreases from 48.2 kW to 32.8 kW and the corresponding average COP of the absorption subsystem is improved from 2.591 to 3.082.     

Comparative study of different solar cooling systems for buildings in subtropical city

In recent years, more and more attention has been paid on the application potential of solar cooling for buildings. Due to the fact that the efficiency of solar collectors is generally low at the time being, the effectiveness of solar cooling would be closely related to the availability of solar irradiation, climatic conditions and geographical location of a place. In this paper, five types of solar cooling systems were involved in a comparative study for subtropical city, which is commonly featured with long hot and humid summer. The solar cooling systems included the solar electric compression refrigeration, solar mechanical compression refrigeration, solar absorption refrigeration, solar adsorption refrigeration and solar solid desiccant cooling. Component-based simulation models of these systems were developed, and their performances were evaluated throughout a year. The key performance indicators are solar fraction, coefficient of performance, solar thermal gain, and primary energy consumption. In addition, different installation strategies and types of solar collectors were compared for each kind of solar cooling system. Through this comparative study, it was found that solar electric compression refrigeration and solar absorption refrigeration had the highest energy saving potential in the subtropical Hong Kong. The former is to make use of the solar electric gain, while the latter is to adopt the solar thermal gain. These two solar cooling systems would have even better performances through the continual advancement of the solar collectors. It will provide a promising application potential of solar cooling for buildings in the subtropical region.     

Analysis on a hybrid desiccant air-conditioning system

Hybrid desiccant-assisted preconditioner and split cooling coil system, which combines the merits of moisture removal by desiccant and cooling coil for sensible heat removal, is a potential alternative to conventional vapor compression cooling systems. In this paper, experiments on a hybrid desiccant air-conditioning system, which is actually an integration of a rotary solid desiccant dehumidification and a vapor compression air-conditioning unit, had been carried out. It is found that, compared with the conventional VC (vapor compression) system, the hybrid desiccant cooling system economizes 37.5% electricity powers when the process air temperature and relative humidity are maintained at 30 °C, and 55% respectively. The reason why the hybrid desiccant cooling system features better performance relative to the VC system lies in the improvement brought about in the performance of the evaporator in VC unit due to desiccant dehumidification. A thermodynamic model of the hybrid desiccant system with R-22 as the refrigerant has been developed and the impact of operating parameters on the sensible heat ratio of the evaporator and the electric power saving rate has been analyzed. It is found that a majority of evaporators can operate in the dry condition even if the regeneration temperature is lower (i.e. 80 °C).     

Effect of neutral temperature on energy saving of centralized air-conditioning systems in subtropical Hong Kong

Higher room temperature can still let the occupants have a neutral thermal sensation if higher air speed is provided. With a suitable scheme of neutral temperature and comfort air speed, reduction of energy consumption of the central chiller plant may surpass the additional energy requirement of the air side equipment, then both energy saving and thermal comfort can be achieved for the entire air-conditioning system. To evaluate this, the energy consumptions of a centralized air-conditioning system using the common air side alternatives were studied for the subtropical Hong Kong. The alternatives are variable air volume (VAV) system, constant air volume (CAV) system and fan coil (FC) system. Each of them was associated to a central chiller plant to serve a high-rise office building. The studying range of the room air temperature was from 23 °C to 30 °C. It is found that the VAV and FC systems can provide both thermal comfort and energy saving for higher room temperature, but CAV system is not feasible when the room air temperature is above 27 °C. If the indoor air speed threshold is considered, the neutral temperature can be brought up to 26.5 °C, and the energy saving potentials of VAV and FC systems would be 12.9% and 9.3% respectively.     

Exergy analysis of a liquid-desiccant-based,hybrid air-conditioning system

We present the applicable exergy analysis and estimate irreversible losses that are generated during operation of a hybrid air-conditioning cycle with emphasis on a partly closed solar regenerator that is used to regenerate weak desiccant. The desiccant mass-flow rate has been chosen as the fundamental parameter for analysing the system. We find an optimum mass-flow rate for minimum irreversibility, i.e. maximum exergy. Large irreversibilities occur for high ambient vapor pressures, which tend to decrease the system exergy and overall performance of the regenerator.     

Solar panel cooling system with hollow fibres

Photovoltaic (PV) panel overheating drastically reduces their efficiency and lifespan. Overheating also has the potential to form electric arcs which can melt metal fixtures and burn away the module’s insulating materials. Due to these phenomena, the introduction of water-cooling or, more generally, liquid-cooling systems inside the PV panel appears reasonable. Hollow fibre cooling system consisting of plastic tubes of a small diameter (less than 1 mm) was tested as a simple solution. Fibres can be placed in contact with the back surface of a PV panel and coolant flowing through provides efficient and uniform cooling. Heat removed from the panel may be used for domestic or industrial needs or released to the surroundings. Hollow fibres have very thin walls (about 0.1 mm) to transfer heat easily, and the system is light, compact and resistant to corrosion. Experiments confirmed that such system can cool the PV panel, removing up to 1 kW of heat and lowering the module temperature from 90°C to about 50°C. It was observed that cooling improves the electric efficiency of PV cells by about 50%.     

Solar-powered systems for cooling, dehumidification and air-conditioning

This paper describes current trends in solar-powered air conditioning, which has seen renewed interest in recent years due to the growing awareness of global warming and other environmental problems. Closed-cycle heat-powered cooling devices are based mainly on absorption chillers, a proven technology employing LiBr–water as the working fluid pair. Recent developments in gas-fired systems of this type make available double- and triple-effect chillers with considerably higher COP than their single-effect counterparts, which makes it possible to reduce the amount of solar heat required per kW of cooling. These systems require, however, high-temperature solar collectors. The principles of multi-staging absorption systems are described. An economic comparison is provided which shows the total system cost to be dominated by the solar part of the system. At current prices, the high COP, high temperature alternative is still more costly than the low temperature one. Open-cycle desiccant systems employing either solid or liquid sorbents are described. While the main thrust in research on novel closed-cycle absorption systems has been toward increasing the operating temperature in order to improve efficiency through multi-staging, open-cycle absorption and desiccant systems have been developed for use with low temperature heat sources such as flat plate solar collectors. A novel open-cycle (DER) system is described, which makes it possible to use the solar heat at relatively low temperatures, for producing both chilled water and cold, dehumidified air in variable quantities, as required by the load.     

聚光式太阳能动力与制冷联合热发电系统

1前言从20世纪90年代到现在,国内外聚光式太阳能热发电系统是以聚光式太阳能锅炉取代矿物燃料锅炉,并联辅助常规能源锅炉和蓄热器进行发电的。太阳能热发电系统在热力学原理上也是按朗肯循环或勃莱顿循环运行的,而卡诺循环效率η_卡是工作于两个一定温度之间的所有热机效率η_(热机)的理论     

On the performances of a hybrid air-conditioning system in different climatic conditions

In previous papers the authors demonstrated that significant energy savings can be achieved in air-conditioning through the use of a hybrid plant in which a vapor-compression inverse cycle is integrated with an air dehumidification system working with hygroscopic solution and hydrophobic membrane. The advantage of this system lies in the fact that the refrigeration device operates at a higher evaporation temperature than that of a traditional system, in which dehumidification is achieved through condensation.In the proposed hybrid system the supplied air is simultaneously cooled and dehumidified in an air-solution membrane contactor. The LiCl solution is cooled by means of a vapor-compression inverse cycle. The solution is regenerated in another membrane contactor by exploiting the exhaust air and the heat rejected by the condenser.The paper reports a study of the steady-state behavior of the system in summer climatic conditions on varying some significant climatic parameters, such as the latent load of the conditioned space and the outdoor and indoor relative humidity. The performances of the hybrid system are compared with those of a traditional direct-expansion air-conditioning plant. Results of the simulations reveal that energy saving may exceed 60% when the latent load in the conditioned environment is high.     

Study on hybrid ground-coupled heat pump system for air-conditioning in hot-weather areas like Hong Kong

The ground-coupled heat pump (GCHP) system is becoming attractive for air-conditioning in some moderate-weather regions due to its high energy efficiency and reliable operation capability. However, when the technology is used in buildings where there is only cooling load in hot-weather areas like Hong Kong, the heat rejected into the ground by the GCHP systems will accumulate around the ground heat exchangers (GHE). This heat accumulation will result in degradation of system performance and increment of system operating costs. This problem can be resolved by using the hybrid ground-coupled heat pump (HGCHP) system, which uses supplemental heat rejecters to reject the accumulated heat. This paper presents a practical hourly simulation model of the HGCHP system by modeling the heat transfer process of the system’s main components. The computer program based on this hourly simulation model can be used to calculate the hour-by-hour operation data of the HGCHP system. As a case study, both a HGCHP system and a traditional GCHP system are designed for a hypothetic private residential building located in Hong Kong, and the economic comparisons are conducted between these two types of systems. The simulation results show that the HGCHP system can effectively solve the heat accumulation problem and reduce both the initial costs and operating costs of the air-conditioning system in the building.     

Analysis of solar desiccant cooling system for an institutional building in subtropical Queensland,Australia

Institutional buildings contain different types of functional spaces which require different types of heating, ventilating and air conditioning (HVAC) systems. In addition, institutional buildings should be designed to maintain an optimal indoor comfort condition with minimal energy consumption and minimal negative environmental impact. Recently there has been a significant interest in implementing desiccant cooling technologies within institutional buildings. Solar desiccant cooling systems are reliable in performance, environmentally friendly and capable of improving indoor air quality at a lower cost. In this study, a solar desiccant cooling system for an institutional building in subtropical Queensland (Australia) is assessed using TRNSYS 16 software. This system has been designed and installed at the Rockhampton campus of Central Queensland University. The system's technical performance, economic analysis, energy savings, and avoided gas emission are quantified in reference to a conventional HVAC system under the influence of Rockhampton's typical meteorological year. The technical and economic parameters that are used to assess the system's viability are: coefficient of performance (COP), solar fraction, life cycle analysis, payback period, present worth factor and the avoided gas emission. Results showed that, the installed cooling system at Central Queensland University which consists of 10 m² of solar collectors and a 0.400 m³ of hot water storage tank, achieved a 0.7 COP and 22% of solar fraction during the cooling season. These values can be boosted to 1.2 COP and 69% respectively if 20 m² of evacuated tube collector's area and 1.5 m³ of solar hot water storage volume are installed.     

太阳能制冷讲座(3) 太阳能固体转轮式除湿空调(下)

<正>四基于太阳能空气集热器的转轮除湿空调1工作原理典型的基于太阳能空气集热器的转轮除湿空调如图7所示,经太阳能空气集热器加热后的热风,直接流经转轮再生区,再生干燥剂。集热系统主要包括太阳能空气集热器、风机、流量调节与控制部件     

武汉地区中央空调系统节能的优化策略

根据武汉的地域特征 ,以节能、能源利用与保护环境为原则 ,讨论和分析了围护结构、冷热源、空调输送装置系统及经济运行等多种中央空调的节能对策。     

Simulation of an integrated hybrid desiccant vapor-compression cooling system

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 activate a desiccant dehumidification cycle. The hybrid system consists of 4 major components: a compressor, an evaporator and 2 desiccant, integrated condensers/dehumidifiers. The equations governing the transport of heat and mass in the desiccant, integrated condenser/dehumidifiers are formulated considering air as the working fluid in the process stream and a refrigerant stream, which is cooled from superheated vapor to subcooled liquid, as the heat source during desorption; a water stream is used to remove the heat generated during adsorption. The governing equations are nondimensionalized and solved for both sorption processes using an explicit finite-difference scheme. The performance of a first generation prototype desiccant, integrated, hybrid, vapor-compression cooling system is then evaluated at ARI conditions.     

Solar hybrid heating systems for greenhouses

Theoretical prediction of the total heat requirements of a greenhouse using several solar hybrid systems under various representative Jordanian ambient conditions have been carried out. Either an air-source heat pump, a water-source heat pump, a boiler, and electric-resistance element system or a combination of these was considered as the heat source. The operation-cost analysis which was carried out indicated that for the given ambient conditions the hybrid solar heat-pump system was in general the most economic.