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The humidifier plays a key role in a humidification–dehumidification (HDH) desalination system; it directly affects both the freshwater production efficiency and energy consumption ratio of the system. In this study, for a humidifier in an HDH system, a heat–mass coupled differential equation model of spray water and air on the surface of the packing material was established, and the effects of parameters such as the spray water temperature (tw), mass flow rate of spray water (mw), air temperature (ta), and air mass flow rate (ma) on the humidification performance of humidifiers composed of eight different types of packing materials were investigated. The results show the following: (1) Under the same inlet spray water and air conditions, the humidification performance of different packing materials from good to bad is as follows: cellulose paper, polypropylene, hackettes, saddles, snowflakes, wooden slats, polyvinyl chloride, gunny bag cloth. (2) Increasing the tw can significantly improve the humidification performance. To achieve higher humidification energy efficiency, it is recommended to increase the tw to above 80 °C. (3) With the increase in the mw, although the humidification efficiency (εhum) decreases slightly, the humidification rate (mhum) increases, and the specific humidification energy ratio (ηhum) decreases accordingly. To maintain a high mhum and a low ηhum, it is advisable to control the mw at not less than 0.5 kg/s. (4) Increasing the humidifier inlet ta can improve the mhum, εhum, and ηhum, although not as effectively as increasing tw. (5) Increasing the ma can improve mhum and εhum. However, it simultaneously increases the ηhum. The results of this study can provide theoretical guidance for the selection of efficient packing materials and the optimization of humidifier operating conditions in HDH desalination systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel approach to control CO 2 and H 2 O composition in an enclosed environment. • A cyclic CO 2 adsorption process and dehumidication units are considered. • The mathematical model shows superior performance of the proposed system. • Carbon footprint of the system is discussed with scale-up study. • Influence of parametric uncertainties in the model is discussed. Rapid growth in global energy consumption has raised concern on the environmental impacts such as ozone layer depletion and climate change. Enclosed space, such as commercial buildings, accounts for about 40% of global energy consumption and the demand is constantly increasing due to increasing population, urbanization, and economic development. The energy demands in the building sector calls for strategic measures to develop energy efficient technologies. This paper presents a strategy to decrease energy demands inside buildings by proposing a ventilation system which regulates the enclosed air quality resulting in reduced air conditioning. The system consists of multiple adsorption beds with zeolite 13X monoliths for CO 2 removal, and silica gel for humidity control, inside the enclosed space. The air conditioning system results in decrease in energy requirement and improvement in economics by 55% as compared with conventional ventilation system. The model is scaled up to the size comparable with total office inventory of New York City, and the reduction in carbon emissions by introducing the air composition control system for New York City is equivalent to replacing 57 million incandescent light bulbs by LEDs. This paper concludes that the air conditioning system proposed in this study results in the improvement in performance as compared to a conventional ventilation system and could reduce energy consumption inside commercial buildings. [ABSTRACT FROM AUTHOR]

Abstract: A one‐dimensional mathematical model is developed to evaluate the operating and design parameters of the desiccant wheel for air conditioning application. In this paper, dehumidification coefficient of performance (DCOP) and sensible energy ratio (SER) are adopted as a combined performance index to reflect the dehumidification and thermal performance of the desiccant wheel. The analysis of the results reveals that for lower SER, suitable wheel length, wall thickness, channel pitch, and channel height should be 100 mm, 0.2 mm, 3 mm, and 5 mm, respectively. These design parameters have been analyzed under different operating conditions and it was found that for higher DCOP, rotational speed, regeneration temperature, process and regeneration velocity should be 20 rph, 60°C, and 2 m/s. [ABSTRACT FROM AUTHOR]

The purpose of air-conditioning systems is to provide a suitable indoor environment with respect to temperature, humidity and fresh air. Liquid desiccant dehumidification constitutes an effective method for extracting moisture from humid air with less energy consumption. Current studies mainly focus on dehumidification system under certain heat and mass transfer ability (number of mass transfer units NTU m ). This paper will investigate NTU m of counter-flow packing tower and its influence on system performance. An experiment including a counter-flow packing tower was conducted. When the height of tower was 0.7 m, the volumetric mass transfer coefficient was between 1–4 kg/(m 3 ·s) and NTU m presented a range between 0.9–1.4, when air flow rate changes from 1 kg/(m 2 s) to 2.5 kg/(m 2 s). When the height changed to 2.1 m, the NTU m of the tower presented a variation from 3.3 to 4.3. Furthermore, a simulation model is developed, which is validated by experimental data and past research results. The influence of NTU m on total circulation flow path is mainly caused by heat and cold offset and an NTU m value approximately of 4 constitutes a suitable value of increasing heat and mass transfer ability. Comparing three typical flow paths, when NTU m is lower than 3.5, inter-stage circulation presents improved performance in system COP. When NTU m is large, total circulation is efficient. The system COP cross points of flow paths are caused by heat and cold offset and concentration difference of the solution circulation between the dehumidifier and the regenerator, which can be quantified by loss coefficient ε and χ respectively. The heat and mass transfer ability of the system should be considered in the designing process of flow path configuration to obtain an efficient performance for different range of NTU m . [ABSTRACT FROM AUTHOR]

This paper aimed to evaluate the applicability of adiabatic humidification in the heating, ventilation, and air conditioning (HVAC) systems of semiconductor cleanrooms. Accurate temperature and humidity control are essential in semiconductor cleanrooms and high energy consumption steam humidification is commonly used. Therefore, we propose an adiabatic humidification system employing a pressurized water atomizer to reduce the energy consumption. The annual energy consumption of three different HVAC systems were analyzed to evaluate the applicability of adiabatic humidification. The studied cases were as follows: (1) CASE 1: a make-up air unit (MAU) with a steam humidifier, a dry cooling coil (DCC), and a fan filter unit (FFU); (2) CASE 2: a MAU with the pressurized water atomizer, a DCC, and a FFU; and (3) CASE 3: a MAU, a DCC, and a FFU, and the pressurized water atomizer installed in the return duct. The energy saving potential of adiabatic humidification over steam humidification has been proved, with savings of 8% and 23% in CASE 2 and CASE 3 compared to CASE 1, respectively. Furthermore, the pressurized water atomizer installed in the return duct exhibits greater energy saving effect than when installed in the MAU. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews and surveys the available hybrid liquid-desiccant air-conditioning system technologies. These technologies are proposed as alternative to the traditional vapor-compression systems because of its advantages in removing air latent load, environment-friendly feature, ability to remove pollutants from the processed air, and ability to reduce electrical energy consumption. This paper first introduces the traditional air-conditioning system: vapor compression, vapor absorption, and evaporative cooling. In addition, the principles of liquid desiccants and liquid-desiccant dehumidification systems and the hybrid liquid-desiccant classifications are discussed. Next, combination of the liquid-desiccant systems with vapor compression, vapor absorption, and direct and indirect evaporative cooling units are outlined. Finally, conclusions and some important suggestions are presented based on the collected information. [Copyright &y& Elsevier]

Abstract: Air conditioning is essential for maintaining thermal comfort in indoor environments, particularly for hot and humid climates. Today, air conditioning, comprising cooling and dehumidification, has become a necessity in commercial and residential buildings and industrial processes. It accounts for a major share of the energy consumption of a building or facility. In tropical climates, the energy consumed by heating, ventilation and air-conditioning (HVAC) can exceed 50% of the total energy consumption of a building. This significant figure is primarily due to the heavy duty placed on cooling technologies to remove both sensible and latent heat loads. Therefore, there is tremendous potential to improve the overall efficiency of the air-conditioning systems in buildings. Based on today’s practical technology for cooling, the major components of a chiller plant are (1) compressors, (2) cooling towers, (3) pumps (chilled and cooling water) and (4) fans in air handling units. They all consume mainly electricity to operate. When specifying the kW/Rton of a plant, there are two levels of monitoring cooling efficiency: (1) at the efficiency of the chiller machines or the compressors which consume a major amount of electricity; and (2) at the overall efficiency of cooling plants which include the cooling towers, pumps for moving coolant (chilled and cooling water) to all air-handling units. Pragmatically, a holistic approach is necessary towards achieving a low energy input per cooling achieved such as 0.6kW/Rton cooling or lower by considering all aspects of the cooling plant. In this paper, we present a review of recent innovative cooling technology and strategies that could potentially lower the kW/Rton of cooling systems – from the existing mean of 0.9kW/Rton towards 0.6kW/Rton or lower. The paper, broadly divided into three key sections (see Fig. 2), begins with a review of the recent novel devices that enhances the energy efficiency of cooling systems at the component level. This is followed by a review of innovative cooling systems designs that reduces energy use for air conditioning. Lastly, the paper presents recent developments in intelligent air-control strategies and smart chiller sequencing methodologies that reduce the primary energy utilization for cooling. The energy efficient cooling technology, innovative systems designs, and intelligent control strategies described in the paper have been recently researched or are on-going studies. Several have been implemented on a larger scale and, therefore, are examples of practical solutions that can be readily applied to suit specific needs. [Copyright &y& Elsevier]

Abstract: This paper sets the viewpoint of air-conditioning system from heat sources and humidity sources, especially focusing on the temperature distribution of heat sources and how it influences the efficiency of air-conditioning system. For humidity sources, they are different from heat sources for their physical essence, which provides the possibility of separate treatment of heat and humidity. This paper establishes the ideal air-conditioning system of cooling and dehumidifying, based on the ideal treatment of heat sources, and humidity sources. Then the difference between ideal system and actual system are explored by a case study showing the decrease of efficiency step by step. The gap between ideal system and actual system can be concluded into three main imperfections: the method of treatment of heat sources, transmission temperature difference and heat exchange temperature difference, and the energy consumption of transportation. In the last, according to the actual influencing factors, some improving directions are proposed to improve the current system correspondingly. [Copyright &y& Elsevier]

Abstract: The performance of different HVAC systems varies when coupled with different buildings. This paper examines the relationship between building heating and cooling load and subsequent energy consumption with different HVAC systems. Two common HVAC systems in use throughout the UK office building stock, variable air volume (VAV) system and fan coil (FC) with dedicated outside air system, have been coupled with a typical narrow plan office building with and without daylight control and for both cellular and open plan. The results presented in this paper clearly indicate that it is not possible to form a reliable judgment about building energy performance based only on building heating and cooling loads. For the two investigated systems, variable air volume system and fan coil with dedicated outside air system, the difference between system demand and building demand varied from over −40% to almost +30% for cooling and between −20% and +15% for heating. If a heat recovery unit is used, the difference in heating performance is even greater, rising to −70%. [Copyright &y& Elsevier]

The paper presents a winter air-conditioning system which is suitable for regions with mildly cold but dry winters. The system modifies the evaporative air-cooler that is commonly used for summer airconditioning in such regions by adding a heating process after the humidification process. The paper describes a theoretical model that is used to estimate the system's water and energy consumption. It is shown that a 150-LPD solar heater is adequate for air-conditioning a 500 ft3/min (14.4 m3/min) air flow rate for four hours of operation. The maximum air-flow rate that can be heated by a single solar waterheater for four hours of operation is about 900-cfm, unless a solar water heater large than a 250-LPD heater is used. For the 500 ft3/min air flow rate the paper shows that the 150, 200, 250 and 300 LPD solar water-heaters can provide air-conditioning for 4, 6, 8 and 10 hours, respectively, while consuming less energy than the equivalent refrigerated-type air-conditioner. [ABSTRACT FROM AUTHOR]

Abstract: Building legislation along with environmental and comfort concerns are increasingly driving designers of building services and air conditioning equipment towards more energy efficient solutions. Heat pipe technology is emerging as a viable, efficient and environmentally-sound technology for applications in efficient air handling unit designs. In this paper, an experimental investigation on the thermal performance of an air-to-air heat exchanger, which utilises heat pipe technology, will be presented. The heat exchanger consisted of 7 loop heat pipes with finned evaporator and condenser sections. The heat exchanger was fully instrumented to test for the effect of the variation of heat load and the air velocity, through the heat exchanger, on the overall thermal resistance of the loops. The values of the effectiveness of the heat pipe heat exchanger are shown to vary with the air velocity as expected but the results also allow the prediction of effectiveness variation with the heat load and operating temperature (previously assumed to be constant). The results allow an interpretation of the overall thermal performance of each loop heat pipe as a function of the load and air velocity. The paper concludes with a theoretical analysis of the energy savings that would be expected when utilising the technology in a representative application. [ABSTRACT FROM AUTHOR]

Abstract: As dehumidification is one of the most important tasks of environment control of the building, it is necessary to know the energy efficiency of dehumidification processes. The energy efficiency can give the energy cost of drawing moisture from indoor air to the outside environment. This paper presents analysis of the ideal cost of dehumidification process by a liquid desiccant cycle. Formulas to calculate ideal efficiency of dehumidification process are obtained, which is determined by indoor temperature, outdoor temperature, and the temperature of the intersection point of the iso-relative humidity line of indoor air and the iso-humidity ratio line of outdoor air. The ideal efficiency of the condensing dehumidification method is lower than the ideal dehumidification process, due to the fact that condensing dehumidification method must dehumidify the air at the temperature of dew point. Results from this paper can be used as theoretical foundation for the further analysis of various dehumidification methods and the development of new dehumidification processes. [ABSTRACT FROM AUTHOR]

Desiccant dehumidification system is an alternate option against conventional dehumidification system in hot and humid climates. Conventional dehumidification systems have many drawbacks that include high power consumption and increase the chlorofluorocarbon (CFC) level in the environment and major contribute to depletion of ozone layer. This paper discuss the functioning of dehumidification, cooling and air-conditioning systems using various solid desiccant with focus on the use of solar energy for dehumidification of humid air and regeneration of solid desiccant wheel. A comparative study of various dehumidification, cooling and air-conditioning systems show that solid desiccant has low operating and maintenance cost and is environment friendly. [ABSTRACT FROM AUTHOR]

Abstract: Liquid desiccant dehumidification technology is becoming increasingly attractive due to its high efficient utilization of low-grade heat and its effectiveness in dehumidification. Using this technology, energy-efficient air conditioning systems have been developed, which demonstrated superiority over the traditional vapor compression type system by allowing both temperature and humidity to be controlled independently. This paper presented a state-of-the-art review of the research and development in this field, covering the topics of heat and mass transfer models, performance evaluation of liquid desiccant dehumidification and regeneration, and technology development of dehumidifiers and regenerators as the most important components of liquid desiccant systems. Meanwhile, many detailed systems using solar energy in desiccant cooling was reported, and some new applications of liquid desiccant dehumidification were also introduced. [Copyright &y& Elsevier]

Abstract: An experimental investigation on the performance of a proposed hybrid desiccant based air conditioning system referred as HDBAC is introduced in this paper. HDBAC is mainly consisted of a liquid desiccant dehumidification unit integrated with a vapor compression system (VCS). The VCS unit has a cooling capacity of 5.27kW and uses 134a as refrigerant. Calcium chloride (CaCl2) solution is used as the working desiccant material. HDBAC system is used to serve low sensible heat factor applications. The effect of different parameters such as, process air flow rate, desiccant solution flow rate, evaporator box and condenser box solution temperatures, strong solution concentration and regeneration temperature on the performance of the system is studied. The performance of the system is evaluated using some parameters such as: the coefficient of performance (COPa), specific moisture removal and energy saving percentage. A remarkable increase of about 54% in the coefficient of performance of the proposed system over VCS with reheat is achieved. A maximum overall energy saving of about 46% is observed which emphasizes the use of the proposed system as an energy efficient air conditioning system. [Copyright &y& Elsevier]

Abstract: A temperature and humidity independent control (THIC) system is a way to regulate indoor temperature and humidity separately through different approaches. Because of this distinction, THIC air-conditioning systems can satisfy the adjustment requirements of indoor temperature and humidity better than conventional systems can, and they show significant potential for energy conservation. In the past ten years, rapid improvements have been achieved in both theoretical research and the development of equipment related to THIC systems, and more and more applications are being put into use in non-residential buildings in China. This paper focuses on the development of THIC systems in China and reviews recent achievements and progress related to the main devices used for temperature and humidity control, including outdoor air handling dehumidification processors, sensible heat terminals, and high-temperature cooling sources. The energy performance of THIC systems is examined based on an analysis of established applications. Both the performance of key components and the energy consumption of entire systems indicate that THIC systems result in significant improvements in energy performance compared to conventional systems. Developmental trends and recommendations about design methodology, ways to improve the performance of handling devices, and feedback from applications of THIC systems are also discussed. [Copyright &y& Elsevier]

Air conditioning consumes a very large amount of electricity globally. Energy efficiency of the conventional vapor compression cooling is low in warm and humid climates due to water condensation. Membrane separation is viewed as one efficient process for air dehumidification. In this paper, we report the development of a novel thin flat sheet zeolite membrane for the air dehumidification application. The membrane is prepared by deposition of an ultra-thin H2O-selective zeolite membrane film (~3μm) on a thin (~50μm) porous metal sheet support. Under separation temperature of 32°C and feed air relative humidity (RH) of 90%, a quality membrane shows water permeance as high as 6.8×10−6 molm−2 Pa−1 s−1, which is about 1 to 3 orders of magnitude higher than the previously reported in the literature, and a water vapor/air separation factor over 300. In addition, this zeolite/metal thin-sheet membrane exhibits excellent stability as no apparent decline of separation performances is observed during 8-day continuous testing with humid in-house air. To simulate various climate conditions, the membrane is tested over a range of separation conditions which include temperature, feed air RH, and permeate pressure. It is estimated that 50% or higher energy efficiency gain over the conventional vapor compression system can be obtained when the membrane separation factor is above 200. The results suggest the possibility to develop an on-line, compact membrane dehumidifier for significant enhancement of air conditioning energy efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The temperature and humidity independent control (THIC) system, which controls indoor temperature and moisture separately, may be an attractive alternative to existing conventional HVAC systems for its prominent improvement on the overall system performance and utilization of low grade energy resources. In order to verify the effectiveness of THIC system, a pilot project has been implemented in an office building in Shenzhen, China. In the system, liquid desiccant fresh air handling units driven by heat pumps are utilized to remove the entire latent load of outdoor air supplied for the whole building, and chilled water at the temperature of 17.5°C from chiller is pumped and distributed into dry fan coil units and radiant panels to control indoor temperature. This paper presents the results of field test of the system, which shows that the system can provide a comfortable indoor environment even in very hot and humid weather. The COP of the entire THIC system can reach 4.0. According to the energy usage data recorded from the year 2009, the energy consumption of the THIC system in the tested office building was 32.2kWh/(m2 yr), which demonstrates magnificent energy-saving potential compared with the conventional air-conditioning system (around 49kWh/(m2 yr)). [Copyright &y& Elsevier]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: Desiccant based air conditioning systems are a suitable way to improve indoor air quality due to its superior humidity control. In this study, a novel desiccant based air conditioning system is designed and tested experimentally to improve the indoor air quality and reduce energy consumption. In the system studied, a heat exchanger, which is not used in this type of systems, for pre-heating the regeneration air with exhaust air is used. This paper reports results of initial operation and operational procedures. The performance of the system and its components is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Regeneration of dehumidizers is the most important stage in the working cycle of desiccant system. The lower regeneration temperature will be favorable for the energy efficiency of the whole system. Ultrasonic technology may be a promising method of dehydration applied to the regeneration of desiccant. As a non-heating method, the power ultrasonic may help lower the regeneration temperature and bring about energy savings. In the present paper, the mechanism of ultrasonic regeneration is set forth based on the ultrasonic theory as well as the mass transfer model in solid–gas and liquid–gas system. The recent studies related to ultrasonic dehydration are extensively reviewed, which is of significant reference to the study of desiccant regeneration assisted by power ultrasound. In addition, this work gives the basic ideas of ultrasonic dehydrator for solid/liquid-desiccant regeneration, which will promote the development of relevant equipments. Finally, some unexplored issues on this topic are addressed, including insight into the effects of ultrasonic on the regeneration, drying kinetics model for ultrasonic regeneration and the challenges possibly faced for the ultrasonic transducer development. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study to develop a new control algorithm to replace the traditional on–off control algorithm widely used by direct expansion (DX) air conditioning (A/C) systems, which are widely used in small to medium sized buildings. The new control algorithm, which enables both the compressor and the supply air fan in a DX A/C system to operate at high speeds when the indoor air dry bulb temperature setting is not satisfied and at low speeds otherwise, is termed the H–L control. Extensive experiments have been conducted with an experimental DX A/C system at simulated different climates under both H–L and on–off control. The results suggest that the use of H–L control would result in better control performance in terms of an improved indoor humidity level and a higher energy efficiency of the DX A/C system when compared to the use of the traditional on–off control. The H–L control is also simpler, and its associated hardware cost is much lower than that of the control algorithms based on variable speed technology. [Copyright &y& Elsevier]

• A novel SADC-HR system is proposed and analyzed. • Low grade cold energy of SSAR subsystem is produced and utilized in cascade. • An ACR cycle is integrated with a WCR cycle for cooling/heating without sunlight. • Lower power consumption occurs at optimized generating/evaporating temperature. • Energy-saving and economic performance of the novel system is proven to be better. The solar absorption refrigeration technology plays a major role in the building energy saving and emission reduction. According to the concept of energy cascade utilization, this paper proposes a novel solar absorption/dual compression hybrid refrigeration (SADC-HR) system, which consists of solar-driven single effect absorption refrigeration (SSAR) subsystem and power-driven dual-source dual-compression refrigeration (PDCR) subsystem. An air-cooled compression refrigeration (ACR) cycle is integrated with the water-cooled compression refrigeration (WCR) cycle to make up the PDCR subsystem, so as to satisfy the all-weather space cooling/heating demand. The SADC-HR system achieves the cascade production and utilization of cold energy for the temperature and humidity independent control air conditioning system. The thermodynamic model of the SADC-HR system is built to evaluate the system performance and operating parameters, and the comparisons with two conventional systems are also discussed. The results indicate that there are optimum generating temperature of 70 °C and optimum evaporating temperature of 18 °C for the SSAR subsystem to obtain the lowest power consumption at low solar intensity of 450 W/m2. The SADC-HR system also exhibits better economic performance, and its solar collector area is respectively 55.79% and 34.75% lower than that of the conventional SSAR system and solar absorption-compression cascade refrigeration (SA-CCR) system at low solar intensity of 450 W/m2. In addition, the proposed system shows the better energy-saving performance as well as a smaller environmental impact, whose power consumption is reduced by 61.47% compared with the conventional SA-CCR system at solar intensity of 800 W/m2, and the present case study demonstrates that total seasonal electricity consumption in the SADC-HR system decreases a value of 25.32% which corresponds to a decline of 21580.66 kg of CO 2 emission in comparison with the conventional ACR system. [ABSTRACT FROM AUTHOR]