Liquid Desiccant Air Conditioning System Research Articles

Numerical and experimental study on the regeneration performance of a liquid desiccant system coupled with rotating packed bed and vacuum

High moisture load generated during the air quality control process introduces a considerable energy consumption, liquid desiccant air-conditioning system has some constrains during the application although it provides an opportunity to save energy. Therefore, a novel regeneration system of liquid desiccant coupled with rotating packed bed (RPB) and vacuum technique was proposed in this study. A numerical model of RPB was developed and validated in order to characterize the heat and mass transfer process during the regeneration and correlate to its performance, furtherly, an experimental rig was built to study its feasibility of RPB application in regenerators. To facility the investigation, the moisture removal rate was introduced to evaluate the regeneration performance and thereafter the effects of three key factors, rotating speed, regeneration pressure and initial concentration of liquid desiccant, were investigated accordingly. The results show that the moisture removal rate increases with the rotating speed for which the maximum of 17.395 g·L-1·min−1 was reached; meanwhile it decreases with the regeneration pressure and initial concentration of desiccant, among which the concentration has a greater impact on moisture removal rate. Compared to traditional packed bed regenerators, the rotating packed bed can significantly enhance the heat and mass transfer rate. In overall, the proposed system can reduce the energy consumption by 10.6%, the regenerate performance was improved significantly, and the feasibility of proposed system was verified to prompt its application.

Energy, exergy, exergoeconomic and enviroeconomic (4E) assessment on a liquid desiccant air-conditioning system using green deep eutectic solvent of ethaline

Despite the recognition of its energy-saving potential, the promotion of liquid desiccant air-conditioning system is limited by the drawbacks of existing desiccants in long-term or large-scale use. Deep eutectic solvent with good bio- and eco- friendliness has not yet been tested for systematic study in air-conditioning system. In this paper, a deep eutectic solvent, ethaline, is utilized in a heat pump driven liquid desiccant air-conditioning system, whose energy, exergy, exergoeconomic and enviroeconomic performances are studied. Under basic condition of ambient temperature of 35 ℃ and relative humidity of 80%, its systematic coefficient of performance reaches 1.406 with exergy efficiency of 32.65%. Meanwhile, 52.36% CO2 emission can be reduced compared with conventional condensation dehumidification air-conditioning system. The payback period of such system at basic condition with 20 kW cooling load is 14.4 years, and it can be significantly reduced in applications with larger cooling load. Parametric analyses for different requirements and environments are conducted as well. The energy and environmental superiority of ethaline is more significant under more latent loads, higher supply air flow rate and lower fresh air ratio. Under ambient temperature ranging from 28 ℃ to 40 ℃, the effect of CO2 emission reduction for ethaline reaches to extents of more than 38%. The advantages of ethaline are further illustrated in comparison with other potential desiccant candidates, in aspects of toxicity, price and corrosiveness. The potential performance improvement approach for ethaline used as liquid desiccant is also proposed and discussed. The results in this paper demonstrate the promising prospect of ethaline quantitatively, and provide enlightening for exploration of new liquid desiccant. In pace with the broadening application of air-conditioning system, liquid desiccant air-conditioning system using such green desiccants can be promoted, which brings out great prospects in energy saving and CO2 emission reduction.

Progressive development in hybrid liquid desiccant-vapour compression cooling system: A review

Over the past few decades, the air-conditioning (AC) sector has seen significant growth in liquid desiccant air-conditioning (LDAC) system technologies. The LDAC system has been considered as a viable substitute to vapour compression system (VCS) as a result of its exceptional temperature and humidity control and energy-saving ability. This study provides an overview of the developments associated with the incorporation of liquid desiccant technologies into VCS units to date. Various configurations of dehumidifiers and hybrid technologies have been compiled and analysed according to economic and environmental considerations. The operating principle of dehumidification and the regeneration process of a LDAC system are initially discussed. Afterwards, the numerous advancements in materials for liquid desiccant and dehumidifiers, which play a crucial part in the dehumidification and regeneration processes, are discussed. Numerous studies have demonstrated that by incorporating liquid desiccant systems with the VCS units, a comfort level of cooling can be achieved by employing a dehumidification process while providing 40–80% energy savings. This review article is beneficial to researchers since it identifies research gaps and explores prospective future research techniques to further enhance the performance of hybrid liquid desiccant-vapour compression systems..

A comparative study on the regeneration performance of traditional heating and heat localization methods

Liquid desiccant air-conditioning (LDAC) system is a promising alternative to the traditional vapor compression system. The most energy-consuming part of LDAC system is desiccant regeneration. An urgent issue that needs to be addressed is the inefficiency of traditional regeneration method. Solar heat localization is a novel and high-efficiency strategy for seawater desalination. However, the wide application is confined due to the low-efficient of water condensation and harvesting. In this work, the regeneration performance of heat localization method was investigated and an electric heating sheet was adopted to circumvent the effect of solar reflection. Compared with traditional heating method, the regeneration performance can be significantly improved by heat localization method. The regeneration efficiency of desiccant with 40 % concentration was significantly improved by 6 times (about 23.15 %) through heat localization method. Heat localization method allows immediate concentration of high-concentration desiccant with a low-temperature rise of regenerated desiccant. The low-temperature rise is beneficial for LDAC system due to less cooling energy is needed. This work is expected to extend the application of solar heat localization and provide some new information for liquid desiccant regeneration.

Economic and Experimental Assessment of KCOOH Hybrid Liquid Desiccant-Vapor Compression System

A liquid desiccant dehumidification cooling system is a promising, energy-saving, high-efficiency, environmentally friendly technology that maintains thermal comfort effectively indoors by utilizing renewable energy sources or waste heat to enhance system efficiency. In this research, a small-scale (6 kW cooling capacity) hybrid liquid desiccant air-conditioning system (HLDAC) is proposed to evaluate the dehumidification performance of a non-corrosive potassium formate (KCOOH) solution. For this, four input parameters, namely, inlet air flow rate, inlet desiccant temperature, inlet desiccant concentration, and inlet specific air humidity, were selected. Moreover, the different combinations of experiments were designed by employing response surface methodology (RSM) to evaluate the dehumidification performance parameters, namely, dehumidifier latent heat load, coefficient of performance of hybrid system, and moisture removal rate (MRR). Further, a comparative performance analysis between the hybrid system and a standalone vapor compression system (VCS) unit was carried out. The result showed a remarkable increase in coefficient of performance, which was observed at about 28.48% over the standalone VCS unit. Furthermore, the economic assessment of the proposed hybrid system is presented in this paper. Finally, from the economic analysis, it was concluded that the hybrid system had a payback time of 2.65 years compared to the VCS unit.

A state-of-the-art review on the liquid properties regarding energy and environmental performance in liquid desiccant air-conditioning systems

Liquid desiccant air-conditioning system (LDAS) becomes an attractive option for reducing the energy consumption of conventional air-conditioning systems. Despite lots of published papers on LDAS in various aspects, there is not yet a comprehensive and up-to-date review on the properties of liquid desiccants, while the selection of liquid desiccant plays essential role in the overall performance of LDAS. In this paper, a state-of-the-art review on the properties in regard of energy and environmental performance is delivered for present and potential liquid desiccants, including vapor–liquid equilibrium, specific heat capacity, safety concerns. The current situations and future concerns of liquid desiccant investigation can be obtained, while different kinds of liquid desiccant candidates can be compared and evaluated comprehensively. Existing liquid desiccant of halide salt faces severe drawback of corrosiveness in long-term use. Compared with existing liquid desiccants, the candidates of weak acid salt, ionic liquid and deep eutectic solvent behave low toxicity and friendly corrosiveness, whereas their weak moisture absorption ability, high cost or high viscosity is the bottleneck for further applications. Therefore, the mixture of them can be regarded as a promising candidate in LDAS applications, but the fundamental properties are urged to be measured. The work in this paper provides momentous reference and guidance for the exploration of new liquid desiccant as well as the evaluation of future prospect of LDAS.

Performance investigation of the solar direct-driven wood regenerator in liquid desiccant air-conditioning systems

Liquid desiccant air-conditioning (LDAC) systems are one of the most promising alternatives to conventional air conditioning systems due to the high energy efficiency. The most energy-consuming part of LDAS system is desiccant regeneration, while traditional regeneration methods often fail to balance the energy grade and energy efficiency. Inspired by solar heat localization for seawater desalination, the regeneration performance of this novel method has been investigated. Here, we fabricated a wood-based regenerator by drilling holes and spaying Chinese ink, which features high sunlight absorption and strong water transportation ability. Owing to the high hydraulic conductivity of drilled holes and low thermal conductivity of wood substrate, liquid desiccant can be regenerated efficiently with a low-temperature rise. Even for 40 wt% CaCl2 solution at 30 °C, the regeneration rate and efficiency can reach 0.64 kg·m−2·h−1 and 43.2 %. Comparisons between solar interfacial regeneration method and other traditional regeneration methods were also conducted. Results show that the solar interfacial method can significantly improve the regeneration rate at the same temperature. Given the low manufacturing cost and operating cost, high regeneration rate and efficiency, superior salt-rejecting property, and low-temperature rise, the wood regenerators based on solar interfacial regeneration show great potential in LDAC systems.

Design and energy analysis of 100% fresh air based hybrid liquid desiccant air conditioning system – A case study of a thermal power plant TG building

Turbine generator (TG) buildings in thermal power plants require chilled water air conditioning systems (CWAS) to control the temperature and humidity of heat dissipated rooms, which are energy-intensive and non-eco-friendly. As an alternative, a novel refrigerant-free 100% fresh air (FA)-based hybrid liquid desiccant air conditioning system (HLDAS) is proposed and presented the methodology to design it for a case study of TG building of 2X660 MW power plant in the most humid climate. The cooling and heating requirements for HLDAS are met with a cooling tower and potential waste heat from the plant. To assess the saving potential of the proposed system, annual energy consumption for the HLDAS, 10% FA-based CWAS (CWAS-1) and 100% FA-based CWAS (CWAS-2) are quantified and compared. The results revealed that HLDAS consume 55% and 31% of CWAS-1 and CWAS-2 power consumption, respectively. Low-grade potential waste heat from the plant is estimated and found to be sufficient for solution regeneration. The proposed system is extremely energy efficient for 100% FA applications where low-grade waste heat is available. In addition to this, since there are no ODP gases associated with the proposed system, the proposed HLDAS is recommendable in view of environmentally friendly technology and indoor air quality (since it is a 100% FA-based system). This work will support HVAC engineers and researchers in designing the LDAS for a given air conditioning application.

Hybrid liquid desiccant air-conditioning system with a direct expansion evaporative cooler

There is a need to control air temperature and humidity in humid regions, especially when fresh air is demanded. This study investigates the performance of a hybrid liquid desiccant (LD) air-conditioning system with a direct expansion (DX) evaporative cooler. Temperature, relative humidity, and power consumption were measured and reported using a wireless data-logging system at the air conditioning unit's key locations. The results showed that the hybrid unit reached a 34 % saving in the cooling load. In addition, the air hybrid liquid desiccant air-conditioning system with the direct expansion evaporative cooler saved about 32% in power consumption, compared to an uncooled desiccant air conditioning system that saved 23%.

Study on the performance of solar interfacial evaporation for high-efficiency liquid desiccant regeneration

Liquid desiccant air conditioning system (LDAS) was considered a promising air conditioning system due to the advantages of low-grade heat utilization, effective humidity control and environment-friendly. The performance of LDAS significantly depends on the heat and mass transfer components, namely dehumidifier and regenerator, while the regeneration process of traditional regenerator is energy-inefficient. Inspired by the high-efficiency solar interfacial evaporation which can produce drinking water from seawater, this method was introduced in this work for liquid desiccant regeneration to overcome the inefficiency of the regeneration process. Wood was prepared as the regenerator by alkali-assisted method and surface carbonization. The regeneration performance of solar interfacial regeneration was experimentally investigated and compared with that of packed-bed tower regeneration and membrane distillation regeneration. Results show solar interfacial regeneration is very competitive due to the high regeneration rate and efficiency, which can reach 0.57 kg m−2 h−1 and 42.5% for 40% LiCl solution under 1-sun irradiation. Moreover, the low temperature rises of concentrated solution, cheap construction costs and operating costs make LDAS more energy-saving. This work is expected to supply a novel method for liquid desiccant regeneration.

Experimental Investigation of Thermal Performance Parameters of Drying Air Unit with a Different Flowrate of Liquid Desiccant Solution

Liquid desiccant air-conditioning systems remove directly the latent load from moist air and remove indirectly sensible load of this air by using an indirect evaporative cooling process. The liquid desiccant must subsequently be regeneration once again with a low-grade heat source like solar energy. In this study, calcium chloride solution was used as a desiccant. For the desiccant solution regeneration process, a flat plate solar collector was employed. Different variables, such as the primary airflow rate and desiccant flow rate, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant systems such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the flow rate of primary air increases, the moisture removal rate, sensible heat ratio, and the mass transfer coefficient increase. For example, from 0.006 m/s to 0.0125m/s when the mass airflow rate increased from 0.1 kg/s to 0.18 kg/s.

Experimental performance of a three-fluid desiccant contactor using a novel ionic liquid

• Novel Ionic Liquid that is not corrosive to aluminum is used as liquid desiccant. • New three-fluid fin-tube desiccant contactor fabricated using aluminum. • Experimental performance of the fin-tube contactor using IL solution is investigated. • The fin–tube contactor showed superior performance than the packed bed contactor. • Lower solution flow rates and pumping power is expected using the fin–tube contactor. The experimental performance of a new three-fluid fin–tube contactor using a novel ionic liquid desiccant solution is investigated and compared with those of an adiabatic packed bed contactor with LiCl solution for liquid desiccant air conditioning system applications. Owing to the compatibility of the ionic liquid solution with aluminum, a fin–tube contactor is manufactured to exploit internal cooling from a third fluid. The results indicate the superior dehumidification performance of the fin–tube contactor, which yielded an outlet air humidity ratio of 10.5 g w ·kg da -1 at a solution mass flux of 3.06 kg·m −2 ·s −1 , as compared to a similar humidity ratio at a solution mass flux of 4.98 kg·m −2 ·s −1 achieved by the packed bed contactor. In terms of cooling performance, the outlet air temperature of the fin–tube contactor is 21.9 °C, which is lower than that of the packed bed contactor even at its highest solution mass flux. This indicates that the cooling performance of the fin–tube contactor has minimal dependence on the solution mass flux in achieving cooling effect, owing to the cooling medium flowing inside the tubes. Relatively lower solution pumping power than that of the packed bed contactor can be expected from the fin–tube contactor, in addition to the ability to achieve comfortable and hygienic indoor air at a cooling medium temperature of 17 °C or higher, the ionic liquid desiccant and three-fluid fin–tube contactor pair for liquid desiccant air conditioning system is elevated a step higher as an alternative to vapor compression air conditioning system.

Liquid Desiccant Air Conditioning System for Flat Plate Solar Collector with Nanofluids Regenerator

This paper deals with liquid desiccant air conditioning using solar flat plate collector. The problem in the use of liquid desiccant air conditioning is energy utilization for regeneration, corrosiveness and carryover. To overcome these developments of a dehumidifier for corrosion- resistant and solar regenerated are advised. A dehumidifier is made of stainless steel tubes of 316L type and stacked in aluminium fins to maintain the desiccant solution temperature. In this experiment, calcium chloride solution (CaCl2 -H2 O) is used. The solar flat plate collector is used for heating water using closed-loop of thermosiphon as regeneration. The flow rate for air is fixed at 10CFM and concentration of calcium chloride is 35% by mass is used. The inlet parameters considered are in the experiments solution volume flow rate, inlet temperature, inlet relative humidity, regeneration temperature, and desiccant solution temperature. The performance parameters are the absolute humidity reduction, outlet temperature and dehumidifier and enthalpy effectiveness. The experiments show that for a fixed Ta, inlet and RH% as solution volume flow rate increases, there is increase in absolute humidity reduction. The temperature of the dehumidified air is reduced compared to that of inlet air, if this air is passed over the pad used for the evaporating cooler. It is seen that the increase in relative humidity from 68.88% to 92.8% for the flow rate of 20 L/min and fixed inlet air temperature, increases absolute humidity reduction from 5.56 to 13.3 g/kg. The increase in solution temperature reduces the absolute humidity reduction due to solution vapor pressure increases and dehumidifier effectiveness. When the solution temperature changes from 31.5 to 34 0 C, there are reductions in the absolute humidity reduction and dehumidifier effectiveness by 34.4% and 13.04% respectively

Performance study of heat and mass transfer in a counterflow liquid to air membrane-based parallel-plate dehumidifier

Liquid to air membrane energy exchanger (LAMEE) is the most important component in a liquid desiccant air conditioning system. Three main configurations of LAMEE are presented in the literature: co-current, counterflow, and cross-counter flow. In this paper, we evaluated the performance of a counterflow LAMEE dehumidifier in terms of its cooling capacity (CC) and moisture removal rate (MRR). A numerical model was developed and validated with experimental results. The impact of solution properties and inlet air characteristics on the LAMEE’s performance were investigated. Simulation results show that CC and MRR are enhanced by decreasing the temperature and increasing the concentration of the liquid desiccant simultaneously. In order to obtain an optimal performance of the LAMEE, the solution mass flow rate should be equal to or slightly higher than the inlet air mass flow rate. On the other hand, we found that both CC and MRR increase with increasing inlet air temperature and relative humidity. Even though solution properties and inlet air characteristics affect the MRR and the CC, they have a negligible effect on the required air sensible cooling to meet the supply air condition (Qsen). The characteristics of outlet air provided by the LAMEE are in a stable state condition, which proves that the LAMEE has a wide range of adaptability in different operating conditions.

Performance investigation on electrodialysis regeneration of potassium formate desiccant solution for liquid desiccant air-conditioning systems

In this work, the ED regeneration experiments were conducted using KCOOH (potassium formate) liquid desiccant, which is attracting attention due to its non-corrosiveness and low toxicity. Varying solution concentration, solution temperature, and current density, effect of the operating conditions on overall transport number, overall hydration number, overall osmotic coefficient, and area-specific resistance (ASR) was analyzed. In particular, effect of the solution temperature on the ASR, which was frequently ignored in previous research, was evaluated. As the solution temperature increased from 21 °C to 30 °C, the ASR decreased 21% and 17% at different concentration conditions. Additionally, the overall transport number of the KCOOH was compared with experimental data of different liquid desiccants in other research. The result showed that at low solution vapor pressure condition, KCOOH recorded the largest overall transport number so that it has a potential to be an energy-efficient working fluid for ED regeneration system. Furthermore, the analysis results and the regression equations can be utilized in developing a system modelling of the liquid desiccant regeneration using ED with KCOOH desiccant in future research.

Performance analysis of different air conditioning systems in apartment buildings under different climates in China

Liquid desiccant air conditioning (LDAC) system and solid desiccant air conditioning (SDAC) system have strong dehumidification capability. To evaluate and compare their feasibility and applicability, performance analysis of these two air conditioning systems and the conventional split air conditioning (AC) system in apartment buildings was conducted under different climates in China. Results show that SDAC system has the best temperature control and LDAC system has the best relative humidity control with the same requirements. In hot and humid cities, 45% relative humidity can be reached and stably maintained by LDAC system in summer when the relative humidity set point is 50%. While for apartment building controlled by split AC system and SDAC system, indoor air relative humidity could even reach 65% in summer. LDAC system is most efficient in hot and humid cities. In cold and dry cities, split AC system performs better than other two systems. Moreover, a dividing line between areas where LDAC system is more efficient and areas where split AC system is more efficient is developed in this paper. Areas where LDAC system is more efficient are mainly distributed in the coastal areas, Yangtze River basin and south of the Yangtze River.

Comparative Analysis on Dehumidification Performance of KCOOH–LiCl Hybrid Liquid Desiccant Air-Conditioning System: An Energy-Saving Approach

Conventional air conditioners (AC) operate on vapor compression refrigeration (VCR) technology, which is a heavy consumer of electricity, and the used refrigerants harm the environment. In humid and hot areas, a liquid desiccant AC system integrated with a VCR system has been proposed as a better alternative to traditional standalone VCR system, as it is an energy-efficient system that can remove latent air load, air pollutants from the processed air, and it is energy-saving. In this study, a hybrid liquid desiccant air conditioning (LDAC) system with a capacity of 5.5 kW was designed and developed by integrating these two different technologies, and the vapor pressure of potassium formate (KCOOH) solution at different solution temperatures and concentrations were monitored experimentally to determine the optimal concentration range. Moreover, a comparative study was conducted to analyze the dehumidification performance of lithium chloride (LiCl) and KCOOH solutions. Experiments are designed by using Minitab 19 software, which employs the design of an experimental technique through full factorial design by considering four variables, namely, type of desiccant, inlet air flow rate, inlet desiccant temperature, and inlet air humidity. To study and compare dehumidification characteristics of both solutions, three responses were considered, i.e., the coefficient of performance of a hybrid system, the heat load of dehumidifier, and specific humidity change. Experimental results revealed that 70% of KCOOH solution exhibited comparable vapor pressure to that of 36% LiCl solution. Additionally, the dehumidification ability of the KCOOH solution was better than that of the LiCl solutions.

A current efficiency model coupled with desiccant molecular weight for electrodialysis regeneration in liquid desiccant air-conditioning systems

Liquid desiccant air-conditioning system is an energy-efficient choice for heat and moisture independent treatment in buildings, especially for the large dehumidification load. Electrodialysis regeneration is a novel and reliable regeneration method for liquid desiccants, which is suitable for hot and humid climates. In this paper, the performance of the electrodialysis regenerator for regenerating lithium chloride and lithium bromide solutions was studied experimentally, and the current efficiency of the electrodialysis regenerator for regenerating these two solutions was compared. Through analysis, the solute molecular weight was coupled into the current efficiency model, and a new current efficiency model of electrodialysis regenerator for regenerating these two solutions was established, which considers the solute molecular weight of liquid desiccant and can be extended to more liquid desiccants in the future. Furthermore, the performance of the liquid desiccant air-conditioning system using electrodialysis regeneration with these two solutions is compared based on this model. The results show that when lithium chloride solution is applied as liquid desiccant, the system performance coefficient (COP, ratio of cooling capacity to energy consumption) is between 1.16 and 4.49, while the performance coefficient of the system is between 2 and 8.3 when the system uses lithium bromide solution.

Inactivation of airborne microbial contaminants by a heat-pump-driven liquid-desiccant air-conditioning system

The COVID-19 pandemic has led to increasing interest in controlling airborne virus transmission during the operation of air-conditioning systems. Therefore, beyond an examination of the ability of liquid-desiccant material itself to inactivate microbes, a heat-pump-driven liquid-desiccant air-conditioning system was proposed and constructed to experimentally investigate the effect of liquid-desiccant solution on the inactivation of airborne bacteria and fungi in various air-conditioning processes. The proposed system comprises a liquid-desiccant unit to dehumidify or humidify process air using a desiccant-solution and heat-pump unit to cool or heat it and accommodate solution thermal loads. The decrease in the concentration of airborne bacteria and fungi before and after passing through the system (i.e., inactivation efficiency) were compared for the base, summer, and winter operating modes. The results indicated that airborne fungi were less inactivated than bacteria because they possess more stress-resistant cellular structures that resist inactivation. During the air-conditioning processes in both the summer and winter operating modes, the bacterial and fungal inactivation efficiencies improved compared to the base mode owing to the contact with desiccant solution. The higher solution flow rate and solution temperature improved the bacterial inactivation efficiency by 27% for the winter compared to the summer mode. Conversely, because of possible growth of fungi in the heated and humidified supply air in the winter, the fungal inactivation efficiency improved by only 1.5% for the winter compared to the summer mode. In conclusion, the proposed system can contribute to control the airborne transmission of microbial contaminants while operating air-conditioning systems.

Performance Analysis of a Passive Mixing Strategy assisted Heat-Pump-driven Liquid-Desiccant Air-Conditioning System

In liquid desiccant systems, an operating strategy of mixing small fractions of weak and strong solutions integrated with a closed-loop operating strategy has drawn attention for its ability to improve the system energy performance. This study proposed a passive mixing strategy integrated with the closed-loop strategy for a heat-pump-driven liquid-desiccant (HPLD) air-conditioning system and experimentally analysed its operating performances. Based on the density difference between the weak solution in the absorber sump after dehumidification process and the strong solution in the regenerator sump after regeneration process, the proposed passive mixing strategy can practically mix them without moving parts. The results showed that the passive mixing strategy was found to be feasible to properly maintain the solution temperatures and concentrations of both absorber and regenerator within the target range in the operation of the system. Therefore, the converged dehumidification rate was shown to be 4.3 g/kg and the converged cooling capacity was shown to be 5.4 kW, which satisfied the target performance. Consequently, the closed-loop and the proposed passive mixing strategy can be concluded to be applicable to the HPLD air-conditioning system.