Conventional Air Conditioning System Research Articles

Performance investigation of new design thermoelectric air conditioning system for electric vehicles

Conventional automobile air conditioning systems use environmentally harmful Chlorofluorocarbons. This method also makes noise and uses a lot of battery energy, making it unsuitable for electric vehicles. So in this paper, the performance of a newly designed cooling system based on the thermo-electric cooling technique installed on the vehicle's roof is proposed and investigated. A complete theoretical transient thermal model based on energy balances is constructed, solved, and validated. The results show an optimum value of the used number of thermoelectric modules, which depends on the input power. This value is 150 for an input power of 200 W and 100 for an input power of 1000 W. At an ambient temperature of 42 °C and without applying a cooling system, moving vehicle with three persons and closed windows, its cabin temperature reaches about 66 °C; in contrast, after applying the TEC system, this temperature reaches around 26 °C at input power 1000 W. The coefficient of performance of the system reduces from about 3 to about 0.85 by increasing the input power from 200 to 1000 W, respectively. Although the coefficient of performance of this system is lower than that of the conventional, it has advantages that make it competitive with conventional air conditioning systems. An economic study based on the Egyptian market shows that the annual cost of the thermo-electric cooling system is lower than that of the conventional one.

Retrofitting conventional chilled-water system to a solar-assisted absorption cooling system: Modeling, polynomial regression, and grasshopper optimization

This study aims to replace the current conventional chilled-water system with solar-assisted absorption cooling in a large pharmaceutical company in Amman, Jordan. Conventional heating, ventilation, and air conditioning (HVAC) systems were used to serve the existing 9000 m2 area of the pharmaceutical facilities. Two solar absorption chiller configurations were proposed and evaluated to investigate this replacement using TRNSYS® software. The auxiliary heater and storage tank were configured in series and parallel and evaluated based on actual data from the company. The effects of the evacuated tube collector (ETC) on the solar fraction, storage tank volume (STV), auxiliary heat required (Qaux), and heat loss (Qloss) were studied. The grasshopper optimization algorithm (GOA), a newly developed optimization technique, was used to optimize the storage tank volume with solar fraction (SF), Qaux, and average heat loss (kJ/h) on an hourly basis in parallel and series configurations. Mathematical equations involving the factor such as storage tank volume and Qloss responses in parallel and series configurations were developed using regression modeling (RM) over all experimental observations. The optimal factor values were then calculated using the GOA and regression models. The confirmation findings indicated that SF was maximized, and Qloss was effectively minimized. Under the 95 % confidence level with = 0.05, the p-value for all RMs was <0.05, indicating the significance of the RM. Furthermore, the RM matched the provided data well, with a low prediction error. The GOA indicated that the parallel system configuration was the superior connection that provided optimum results for SF, and Qaux at a storage tank of 2.8 m3. According to the GOA method, the optimal STV for a series layout was 2.0 m3 and for a parallel arrangement was 2.8 m3. In terms of SF, the parallel system configuration outperformed the series system, which increased by 12.34 %. The parallel system significantly decreases Qloss and Qaux by 4.04 % and 7.39 %, respectively. To compare the GOA with other meta-heuristic optimization approaches, conventional HVAC systems were optimized using particle swarm optimization (PSO). The results indicated that the GOA surpasses the PSO technique in terms of the required convergence speed and population size. Because the movement of agents depends on the positions of each agent inside the swarm, GOA differs from other optimization algorithms. The novelty of this study demonstrates that the GOA technique provides a higher probability of convergence with less computing effort than well-liked and popular optimization methodologies such as PSO for a variety of Qloss, Qaux, and SF issues. These results have significant reverberation for the potential of the GOA to minimize Qloss and Qaux, and maximize SF in the parallel and series configurations of the auxiliary heater.

Development and life cycle cost analysis of a solar hybrid HVAC system for use in buildings in tropical climates

Due to the high amount of energy used by conventional air-conditioning systems in hot/warm and humid climates, solar desiccant cooling systems (SDCSs) have emerged as an alternative with significant energy savings (ESs). The main challenge of these systems is their high initial cost compared to the percentage of energy saved. System optimization will enhance this percentage, making these systems economically viable. This study aims to develop a solar hybrid desiccant cooling system (SHDCS) and assess the life cycle cost of the innovative-optimized model. Three optimization potentials—the dehumidification, cooling, and regeneration air processes—are taken into account for developing an SHDCS. A new two-stage hybrid desiccant system is designed and simulated in TRNSYS software, using the aforementioned optimization potentials for a seminar room located at the National University of Malaysia—or Universiti Kebangsaan Malaysia (UKM)—Selangor, Malaysia, as a site study. The empirical setup validates the simulation model. The influence of optimization potentials on performance indicators such as the coefficient of performance (COP), the solar fraction (SF), ES, and CO2 emissions are evaluated. The results show that the innovative-optimized model can provide thermal comfort in the seminar room while saving ∼38% electricity compared to a conventional fan coil unit (FCU). The COP, SF, and payback period of the optimized system are respectively improved by 0.9, 1.5, and 7 years.

The impact of the wall insulation material and variable refrigerant flow system on building energy consumption and cost

The use of VRF system and insulation in building envelope are both considered as promising option to reduce energy consumption of a building. This study analysis energy saving potential of VRF system and building insulation using modelling and simulation of a typical office building. The model office building is simulated with the weather of Hyderabad, Sindh, Pakistan using EnergyPlus building simulation software. The simulation cases include conventional and VRF air conditioning systems with and without insulation to evaluate and compare the annual cooling and energy savings and payback period. Results showed that by replacing conventional air conditioner with VRF AC electrical power can be reduced by 42-45%. It is also noted that Cellulose, expanded polystyrene, extruded polystyrene and polyurethane insulations can save around 49.5, 51.4, 51.6, and 54.54% of electricity, respectively. In the case VRF air conditioner used with Cellulose, expanded polystyrene, extruded polystyrene and polyurethane insulation may reduce electricity consumption by 66.5, 67.4, 67.5 and 68.9 %, respectively. The payback period varies from 7 to 15 months. However, cellulose with VRF air conditioner has the least payback period of around 7 months. The longest payback period of around 15 months was noted for the un-insulated office building with VRF air conditioner. Despite having longer payback period, the combination of polyurethane insulation with VRF air conditioning system is the most efficient combination.

Design optimization and energy performance evaluation of a dedicated outdoor air system with dual cooling sources

Dedicated outdoor air systems can save cooling energy and improve thermal comfort compared to conventional air-conditioning systems. Although many studies have investigated the energy performance of dedicated outdoor air systems for a certain application, there is a lack of a modeling resource to investigate with how the designs of the system are coordinated with control strategies aiming to improve its energy efficiency. This paper aims to optimize dedicated outdoor air system designs and develop a flexible model to evaluate the performance of the system. First, two innovative energy-saving designs of dedicated outdoor air system with dual cooling sources were proposed. Alternative design 1 optimizes the structure of the fresh air unit, while alternative design 2 builds on alternative design 1 by coupling it with a heat recovery system. Then, the two innovative systems and a baseline design were modeled using the equation-based Modelica tool. Finally, the energy performance of the three systems was evaluated under a hot and humid climate. Results showed that the Modelica-based models are able to capture the transient control strategy details. Alternative design 2 was found to be the optimal design among the three designs, with the highest energy efficiency ratio of chiller plants at 5.3. Moreover, it can reduce the cooling load supply by 9.3% and save about 7.4% on the energy consumption of chiller plants compared to the baseline design. In addition, alternative design 2 has a payback period of only 2.7 years, compared to the baseline design. It reveals the benefit of the heat recovery system in reducing the energy consumption and the cost of the cooling system. The developed dedicated outdoor air system simulation model can provide an evaluation for further improving the system optimization design, control strategy, and equipment configuration in engineering applications.

Advanced Method of Variable Refrigerant Flow (VRF) Systems Designing to Forecast Onsite Operation—Part 2: Phenomenological Simulation to Recoup Refrigeration Energy

This paper focuses on the application of speed-regulated compressors (SRCs) to cover changeable heat loads with high efficiency in conventional air conditioning systems (ACS) as well as in the more advanced variable refrigerant flow (VRF)-type outdoor and indoor ACS. In reality, an SRC is an oversized compressor, although it can operate efficiently at part loads. The higher the level of regulated loads (LRL) of the SRC, the more the compressor is oversized. It is preferable to reduce the size of the SRC by covering the peak loads and recouping the excessive refrigeration energy reserved at decreased actual loads within the range of regulated loads. Therefore, the range of changeable loads is chosen as the object to be narrowed by using the reserved refrigeration capacity. Thus, the general fundamental approach of dividing the overall heat load range of the ACS into the ranges with changeable and unchangeable loads, as previously developed by the authors, is applied for the range of primary changeable loads. Due to this innovative step, the principle of two-stage outdoor air conditioning according to changeable and unchangeable loads, also proposed by the authors, has been extended over the range of primary changeable loads to reduce the level of refrigeration capacity regulation and SRC size. To realize this, part of the changeable load range is offset by the reserved refrigeration capacity, leading to a reduction in the changeable load range and the SRC size by approximately 20% for temperate climatic conditions.

A comprehensive study on the performance of vertical ground-coupled heat pumps

Vertical Ground-Coupled Heat Pump (VGCHP) systems are a green and sustainable alternative to conventional heating, ventilating, and air-conditioning systems. However, their main drawback is the high initial installation cost of the Vertical Ground Heat Exchanger (VGHE), which has hindered their widespread adoption. Improving the performance of VGCHP to reduce their installation and operating costs requires a comprehensive study that scrutinizes the long-term effects of various involving parameters on the performance of the system. This contribution presents a comprehensive study investigating various influential factors, including climate type, refrigerant type, borehole depth, and type of compressor and circulating pump, on the VGCHP system performance. For this aim, a detailed model of the VGCHP is developed that includes detailed heat pump modeling, fast and accurate VGHE analytical modeling, and recommended constraints of the ASHRAE standard. The developed heat pump model is compatible with both pure and refrigerant mixtures. The five-year operation of 180 cases is simulated. Based on five-year simulation results and sensitivity analysis, 90 cases are selected, and their 20-year operation is investigated. The results demonstrated that the heat pump type is the most influential parameter on the Coefficient of Performance (COP), and the climate type is the most influential parameter on the maximum thermal load provided to the building per VGHE unit length. Moreover, optimum design parameters are determined based on short- and long-term simulation results. Furthermore, the response surface method is implemented to develop predictive equations for COP and maximum thermal load as a function of influential factors.

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.

Dehumidification performance improvement by using liquid desiccant blends – An experimental study

To minimize global warming and consumption of electricity, a desiccant-based air conditioning system has been proposed as a better alternative to control air humidity, compared to the conventional air conditioning system. In the present study, the performance of the hybrid desiccant was compared with the pure LiBr and KCOOH solution. Blends of LiBr and KCOOH at different weight ratios were used as desiccants. The performance of the system was compared based on its moisture removal rate and dehumidification effectiveness. The performance of the system increased with increasing desiccant flow rate, the concentration of the solute and the airflow rate. From the tested concentrations, the blend of 40% LiBr and 10% KCOOH concentration showed the highest MRR and dehumidification effectiveness among all blends of LiBr and KCOOH. From the study, it can be concluded that by using an optimized blend of LiBr and KCOOH as a desiccant in place of neat LiBr, the limitations of pure LiBr can be partly resolved without sacrificing much on the dehumidification performance.

Comparative economic analysis of air conditioning system with groundwater source heat pump in general-purpose buildings: A case study for Kayseri

In this study, which aims to reduce energy consumption and dependence on fossil fuels in buildings, the use of an alternative air conditioning system instead of conventional air conditioning systems (CACS), which are widely used in general-purpose public buildings (GPPBs) with high energy consumption, is investigated. A groundwater source heat pump system (GSHPS) was selected as the alternative air conditioning system that exploits an underground water source used in Kayseri province (Turkey). GSHPSs were used both for heating and cooling of a sample GPPB and all costs were determined in detail in the study. In order to compare whether the GSHPS is economical or not, a commonly used CACS, which consisted of a central heating system with natural gas and an air-cooled cooling system was selected. After system components was selected according to the thermal loads of the building, the system costs were determined considering the initial investment cost and the operating costs. Results showed that the proposed GSHPS was more economical than the CACS in terms of initial investment cost and equivalent uniform annual cost by 22.68% and 11.09%, respectively, despite being 3.87% more expensive in terms of total annual operating costs.

Indoor Environmental Quality assessment of mixed-mode ventilation with ceiling fans in the tropics

Mixed-mode ventilation in buildings has a potential for significant energy savings. However, previous attempts in the tropics were unsuccessful due to the hot and humid weather. Indeed, there is little to no natural ventilation potential in tropical climates if conventional air conditioning systems are used. Additionally, existing studies typically do not consider the noise and air quality constraints while the performance of mixed-mode buildings is susceptible to outdoor conditions. Using elevated air movement has proven to be an effective strategy to offset the rise in the room temperature setpoint without sacrificing occupants’ thermal comfort as it helps dissipate body heat through the convective cooling effect. Hence, this study aims at investigating the total indoor environment quality (IEQ) performance of mixed-mode ventilation operations with various air speeds based on tropically acclimatized subjects. To this end, a testbed was designed and constructed in Singapore, consisting of a variable air volume (VAV) system, ceiling fans with continuous speed control, personal ventilation (PV) desks, and plenum acoustic windows. Five operating modes have been tested: fully air-conditioned (AC) mode using VAV alone, hybrid air conditioned (AC+PV) mode using VAV and PV desks, concurrent ventilation (CV) mode using PV desks with the windows partially opened, natural ventilation (NV) mode with the windows fully opened, and acoustic natural ventilation (Acoustic NV) mode with the windows partially opened. 57 subjects were invited to the experiment and asked to complete a comprehensive IEQ survey under 16 different indoor conditions, which are combinations of these operating modes and air speeds ranging from 0.10 to 1.15 m/s. Experiment results show that NV and CV in Singapore can achieve more than 90% thermal acceptability with adequate air movement. More importantly, the median standard effective temperature (SET*) for thermal neutrality is approximately 3°C higher when operating in NV as compared to AC+PV or CV modes, indicating adaptation even when the modes switches are within the same day.

Experimental Findings and Analysis of a Split Unit Evaporative Cooler for Efficient and Eco-Friendly Cooling Applications

As the global energy demand surges, there is a pressing need to develop energy conservation methods to ensure future comfort requirements are met sustainably. Traditional air conditioners, employing vapor compression refrigeration systems, consume substantial power (around 1.5KW) and entail high costs. Alternatively, evaporative coolers offer a cost-effective and lower-power option for comfort maintenance. However, their drawback lies in the excessive humidity in the cooled air, leading to discomfort for individuals. To address this issue, our article focuses on designing and manufacturing a split cooling unit that efficiently cools the air without increasing its humidity. By recirculating the air through the split unit, we aim to maintain optimal room conditions for comfort. This becomes increasingly vital as inefficient building designs in India contribute to 20-25% of electricity wastage in government buildings, resulting in significant annual energy-related financial losses. Conventional heating, ventilation, and air conditioning (HVAC) systems further exacerbate the problem, consuming about 50% of building energy, mostly sourced from fossil fuels, rendering them environmentally unfriendly and unsustainable. Our split cooling unit seeks to provide an eco-friendly and sustainable solution to tackle this energy challenge.

Numerical Analysis of dew point Indirect Evaporative Cooler

An indirect evaporative cooler that uses a Maisotsenko (M) Cycle has the potential to be a green and sustainable solution for managing a building’s cooling demand since it can attain sub-wet bulb temperature without humidification. This study presents the design and simulation analysis of a crossflow indirect evaporative cooler using the COMSOL Multiphysics software for various ambient conditions. The cooler’s performance was evaluated by varying the inlet air temperatures. The analysis was conducted using numerical simulations, and the outcomes were compared with experimental data. The simulation results demonstrated that the cooler could achieve significant temperature reductions at a minor energy consumption as compared to traditional air conditioning systems. This study delivers that this system reduces the temperature of inlet air up to 22°C as well as cooling capacity and coefficient of performance values are 3.699 kW and 27.40. Overall, the results demonstrate the potential of crossflow indirect evaporative coolers as an energy-efficient alternative to conventional air conditioning systems.

Development of Sky-source Heat Pump System

In order to realize a decarbonized society, which is an urgent global issue, the introduction of renewable energy is being expanded. Currently, renewable energy is mainly used to create electricity, such as via photovoltaic cells and wind turbines, while the high introductory costs of other renewable energy sources, such as solar and geothermal, is an impediment to its popularization. We have developed a high-efficiency, low-cost “Sky-sourced Heat Pump SystemⓇ (SSHPⓇ)” that utilizes renewable heat, and is operating at a demonstration site in eastern Japan. Unlike conventional air conditioning systems, our SSHPⓇ system is a unique water heat-sourced heat pump system which connects various renewable energy heat sources, such as solar, air, and geothermal heat, with air conditioning units and hot water heat pumps via a heat source water loop. Based on measurements taken from March 19 to August 28, 2022, and system simulations, primary energy consumption and CO2 emissions were significantly reduced by about 22%, or 32% when compared to typical electric heat pumps. The results indicate that the introduction of SSHP is highly effective.

An Investigation to Reduce Electricity Bills using Inverter AC in Pakistan

The cost affiliated with energy consumption of a conventional air conditioner is so high, an average salaried person cannot afford it. 5.8 m x 4.5 m x 3.6 m room is used for the energy assessment, in which the Inverter/VRF and Conventional air conditioning systems are used separately to attain a set temperature of 25 OC for the weather in Hyderabad, Pakistan. Through the simulated results, May has the highest energy use, with 467 kWh for conventional air conditioning and 310 kWh for inverter air conditioning. When compared to conventional air conditioners, inverter or VRF air conditioners can save up to 50% on energy. In Pakistan, according to NEPRA pricing, inverter air conditioners can have a payback time of 5 to 11 months for various brands of air conditioners, and they can reduce an ordinary consumer's annual electricity cost by up to 48 percent.

Wireless, AI-enabled wearable thermal comfort sensor for energy-efficient, human-in-the-loop control of indoor temperature

The conventional heating, ventilation, and air conditioning (HVAC) systems are based on a set-point control approach that only considers the temperature of the environment without reflecting the thermophysiological status of the occupant. This approach not only fails to fully satisfy individual thermal preferences, but it also makes an HVAC operation energy-inefficient. One possible solution is to control the indoor thermal condition based on an accurate prediction of the occupant's thermal comfort to prevent any unnecessary energy consumption. Here, we present an artificial intelligence (AI) wearable sensor-based human-in-the-loop HVAC control system that is operated on a real-time basis reflecting the thermophysiological condition of the occupant to automatically improve their thermal comfort while reducing the energy consumption of the building. The wristband-type, AI-based, three-point wearable temperature sensor offers excellent thermal comfort prediction accuracy (93.9%), enabling a human-centric HVAC control operation. A proof-of-concept demonstration of closed human-in-the-loop HVAC control using the AI-enabled wearable sensor system confirms both the accuracy of the thermal comfort prediction and the energy-efficiency of this approach, demonstrating its potential as a new solution that improves the occupant's thermal comfort and provides building energy savings.

System design and long-term field test for a novel multi-mode heating tower heat pump system in cold regions

Aiming at the shortcomings of the cooling and heating sources of conventional building air conditioning systems, a multi-mode regeneration HTHP system is proposed and the working principle and working mode in detail are described. The system is applied in the actual energy-saving retrofit project, and control strategies and evaluation calculation method are given. The cooling performance, heating performance, and moisture absorption characteristics of HTHP systems are calculated hourly, daily, and throughout the year. The results show that: the average comprehensive cooling efficiency is 4.34 when the average air temperature in summer is 30 °C and the average relative humidity is 67.1%, and the average comprehensive heating efficiency is 3.12 at the temperature of -1.52 °C and humidity of 77.3%. The annual comprehensive cooling and heating operation efficiency are 4.47 and 3.49. The average regeneration efficiency during the test is 4.34 kg/kWh, which is less affected by the external environment and operating conditions. During the operation in winter, the moisture between the solution and the air migrates in two directions: evaporation dominates at higher temperatures and lower humidity, and absorption is on the contrary. Comprehensive moisture absorption accounts for about 3.9% of the whole year.

Performance analysis of a novel dual-evaporation-temperature combined-effect absorption chiller for temperature and humidity independent control air-conditioning

Temperature and humidity independent control (THIC) air-conditioning (AC) systems are promising alternatives to conventional AC systems. A novel dual-evaporation-temperature combined-effect (DETCE) absorption chiller for THIC AC application is proposed. It can produce high-temperature (16–18 °C) and low-temperature (7 °C) chilled water with a thermal coefficient of performance (COP) above 1 by the deep utilization of heat source at around 100–120 °C. Theoretical models were established to investigate effects of generation temperature (Tgen), evaporation temperature and high-temperature cooling capacity ratio (HCR) on thermal performance of the novel chiller. The results show that the COP of the proposed chiller (COPch,prop) is largely affected by Tgen and HCR. The COPch,prop is 24.1 %-50.4 % larger than that of the conventional single-effect absorption chiller (SEABC) under typical HCRs (0.5–0.7). Performance comparison of the DETCE absorption chiller-based THIC AC system and the conventional SEABC-based AC system was also conducted under different room sensible heat ratios (RSHR), fresh air ratios (FR) and ambient conditions. It is found that the proposed system has a greater energy-saving potential when applied in an air-conditioned space with a large RSHR and FR. Under typical RSHRs (0.6–0.8), both the thermal energy saving rate (ESR) and the heating fluid saving rate of the novel system are over 20 %. Besides, the proposed system can achieve an average ESR of around 30 % under a wide range of ambient conditions. This study provides a novel solution for the deep utilization of solar energy or waste heat at around 100–120 °C to achieve efficient and environmentally friendly THIC AC.

Thermal performance of a directional heat radiation device utilizing the Monte Carlo ray tracing method

Conventional air conditioning systems heat and cool an entire space for the total volume but are deficient in terms of energy efficiency. Partial and personalized devices rarely take into account moving occupants and are deficient in terms of flexibility. To address these problems, a directional heat radiation (DHR) device was introduced. The effectiveness of the DHR device under heating conditions was verified by experiments and the thermal performance of the DHR device under three different arrangements was analyzed. Based on energy balance, the radiation distribution factor calculation model and the heat transfer model of the DHR device were established by combining the Monte Carlo ray tracing method and the thermal network method. The results showed that the thermal performance of the DHR device arranged level downward was best and twice that of the level upward arrangement. The mathematical model of the heat transfer process was verified by experimental data, and the relative error was within 2 %. The simulation results showed that the radiation temperature at different positions θdprt in the center of the room increased with increasing tube diameter and reflecting cover opening width and decreased with increasing tube spacing. Under simulated heating conditions, the optimal structure of the DHR device has a tube diameter of 16 mm, reflecting cover opening width of 60 mm, and tube spacing of 80 mm. The heat flux per unit floor area of the DHR device was approximately 56 W/m2, which reduced the heating capacity by 20 % compared to that without the reflector cover, while improving the local thermal environment of the space and increasing energy efficiency.

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.