Desiccant Based Air Conditioning Research Articles

Water Vapor Adsorption on Desiccant Materials for Rotary Desiccant Air Conditioning Systems

In order to determine the water vapor adsorption performance of a rotary desiccant-based air conditioning system, the behavior of water adsorption on cylindrical pores of different sizes was studied by using classical density functional theory (CDFT) based on perturbated chain statistical associating fluid theory (PC-SAFT). Firstly, the structural parameters of the desiccant material were characterized by scanning electron microscopy (SEM), X-ray Energy Dispersive Spectrum (EDS), and N2 adsorption/desorption isotherms, as well as adsorption equilibrium measurements of water vapor at temperature range 293–308 K. Secondly, the potential energy equation of water molecules in cylindrical pores was determined, and contribution of various terms of PC-SAFT for simulating fluid in cylindrical pores were established. Finally, the pore size distribution (PSD) of the desiccant materials is determined by the PC-SAFT kernel. Moreover, water vapor condensation was investigated with the PC-SAFT model in micropores. The results indicate that the rotary desiccant materials have a large number of micropores with a volume of 0.3669 cm3/g and the amount of water adsorption is about 0.285 g/g. The condensation pressure and the pore width corresponding to the saturated pressure P0 grow with an increase in the temperature, signifying that adjusting the PSD of the material has a significant effect on improving the dehumidification performance. The research concludes that the PSD range of the oxide cylindrical pore between 1.09 and 1.53 nm is particularly beneficial for dehumidification. This study provides valuable theoretical guidance for optimizing dehumidification materials.

Energy retrofit of public office building through liquid desiccant assisted dedicated outdoor air system with fuel cell in Korea

Zero-energy buildings have been mandated in many countries to reduce carbon emissions from buildings. Existing buildings are no exception, and should be retrofitted with renewable energy to be ZEBs. Fuel cells are attracting increasing attention owing to their high efficiency and lack of limitations on the installation area compared to photovoltaic panels. However, a fuel cell simultaneously generates heat and electricity; therefore, it is important to use heat efficiently when using a fuel cell. To achieve this, this study proposes using a liquid desiccant-based air conditioning system when the fuel cell is used for energy self-sufficiency in an existing office building. The configuration of an air conditioning system called thermoelectric and liquid desiccant-assisted dedicated outdoor air system (TELDOAS) is designed, and its annual control logic is established for cooling and heating season operations. To reveal the energy performance of the proposed system, detailed energy simulation models were developed by integrating all mathematical and empirical models of each component using MATLAB. The results revealed that 24.7% of the annual primary energy could be saved by adding a fuel cell to the current air conditioning system consisting of a heat pump and an enthalpy rotary ventilator (ERV). Moreover, the results showed that using TELDOAS instead of ERV could save an additional 32.3% of the annual primary energy by efficiently reclaiming waste heat from the fuel cell. The heat recovery ratios of each system are analyzed to prove the advantage of using TELDOAS, and heat recovery is increased from 37.1% to 51.2% by using heat during the cooling season.

Investigation of angular aspects of a novel four-sector rotary dehumidifier configuration for HVAC applications

In buildings and industries, different humidity and temperature ranges may be required to fulfill the requirement. Desiccant-based air conditioning is more widely used to control the latent load using solar or waste heat efficiently. This work divides a rotary solid desiccant wheel into four sections: two process sections and two regeneration sections. Air from one process section (P1) is used in a cooling application with the aid of a cooling unit, while air from the other process section (P2) is used for warm and dry air applications. Furthermore, the input conditions and positioning of the regeneration sections (R1 and R2) are such that there is less carryover heat to the P1 section and more carryover heat to the P2 section, which is advantageous for both applications. The major objective of the present work is to investigate the optimal angular divisions of these four sections using a two-dimensional mathematical model. The developed mathematical model results are reported in good agreement with the experimental results of the literature. The optimal rotational speed of the wheel is computed as 15 revolutions per hour, and the optimal regeneration angles for R2 and R1 of the desiccant wheels are 100–110° and 115–125°, respectively.

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.

New multiple regression and machine learning models of rotary desiccant wheel for unbalanced flow conditions

In this study, five Multiple Linear Regression, three Multilayer Perceptron Regressor, seven Decision Tree and four Support Vector Machine models were constructed to predict outlet temperature and humidity ratio of silica gel desiccant wheels using eight input parameters for unbalanced flow condition. The effect of different kernel functions of Support Vector Machine algorithms, on the modeling of desiccant wheel was investigated for the first time in the open literature. Detailed validation of the developed models showed that the Response Surface model outperformed other Multiple Linear Regression models, and the Support Vector Machine model with Pearson VII Universal kernel was the best among all models. The determination coefficient and root mean square error for temperature were found to be 0.9791 and 1.2832 °C for the Response Surface model and, 0.9984 and 0.3511 °C for the Support Vector Machine model with Pearson VII Universal kernel, respectively. In the case of humidity ratio, the corresponding statistical parameters were 0.9763 and 0.5672 g/kg for the former and, 0.9976 and 0.1810 g/kg for the latter. The proposed models can be used reliably in the analysis of solid desiccant-based air conditioning systems for design and energy analysis.

Progressive Development and Challenges Faced by Solar Rotary Desiccant-Based Air-Conditioning Systems: A Review

A rotary desiccant-based air-conditioning system is a heat-driven hybrid system which combines different technologies such as desiccant dehumidification, evaporative cooling, refrigeration, and regeneration. This system has an opportunity to utilize low-grade thermal energy obtained from the sun or other sources. In this paper, the basic principles and recent research developments related to rotary desiccant-based cooling systems are recalled and their applications and importance are summarized. It is shown that with novel system configurations and new desiccant materials, there is great potential for improving the performance and consistency of rotary desiccant systems; at the same time, the use of solar energy for regeneration purposes can minimize the operating cost to a great extent. Some examples are presented to demonstrate how rotary desiccant air conditioning can be a promising solution for replacing traditional vapor-compression air-conditioning systems. Recent advances and ongoing research related to solar-powered hybrid rotary desiccant cooling systems are also summarized. The hybrid systems make use of a vapor-compression system in order to have better operational flexibility. These systems, although they consume electrical energy, use solar energy as the principal source of energy, and hence, significant savings of premium energy can be obtained compared to conventional vapor-compression systems. However, further research and development are required in order to realize the sustainable operation of solar rotary desiccant air-conditioning systems, as solar energy is not steady. Reductions in capital cost and size, along with improvements in efficiency and reliability of the system is still needed for it to become a player in the market of air conditioning.

Development and performance evaluation of a passive solar liquid desiccant regenerator

Vapour Compression Refrigeration (VCR) cycle that consumes electrical energy dominates airconditioning market today. Production of electrical energy is generally associated with fossil fuel consumption, emission of greenhouse gases and pollution. Air conditioning systems that use waste or renewable energy sources should be investigated as an alternative solution. Liquid desiccant-based air conditioning system (LDAC) is one such a potential candidate. The heat from a solar thermal collector can be supplied to the regeneration process of LDAC systems. A novel solar collector with the goal of no electrical power consumption, simplicity, low cost, and high efficiency was developed in this work for the regeneration of LD (aqueous calcium chloride solution). Condensate output in this device used for water desalination was 3.7 kg/m2, which is comparable with the best in the literature. An area of 7.5 m2 of such a device with no parasitic power would be needed per kW of latent cooling.

Mathematical Model Development of a Solar Assisted Liquid Desiccant Air Conditioning System with Fin Coil Dehumidifier

A novel scheme of a solar assisted, liquid desiccant supported comfort air conditioning system has been proposed in this paper. The primary intent of the system is to supply air at 25°C and 52% relative humidity, even during the hot and humid summer months prevailing in the plains of sub-tropical countries like India. A mathematical model has been put forward to predict the output air temperature, humidity ratio and the effectiveness of dehumidifier as well as the regenerator. The predicted air humidity ratio has been validated against data available in the literature. The model has been used to predict the optimum mass flow rates required to achieve the desired output conditions for the selected location (Kolkata). The study thus strengthens the need and feasibility of solar assisted desiccant based air conditioning systems for the sub-tropical climates as a replacement of the traditional VCR (vapor compression refrigeration) systems.

Study on Solid Desiccant-Based Air-Conditioning for Wet-Markets

Study on Solid Desiccant-Based Air-Conditioning for Wet-Markets

Study on Desiccant and Evaporative Cooling Systems for Livestock Thermal Comfort: Theory and Experiments

The present study considers evaporative cooling and desiccant unit-based air-conditioning (AC) options for livestock AC application. In this regard, proposed systems are investigated by means of experiments and thermodynamic investigations. Air-conditioning requirements for animals are theoretically investigated and temperature-humidity index (THI) is estimated. A lab-scale heat mass exchanger based on the Maisotsenko-cycle evaporative cooling conception (MEC) is set up and its performance is evaluated at different ambient air conditions. In addition, a desiccant-based air-conditioning (DAC) unit is thermodynamically evaluated using a steady-state model available in the literature. The study focuses on the ambient conditions of Multan which is the 5th largest city of Pakistan and is assumed to be a typical hot city of southern Punjab. The study proposed three kinds of AC combination i.e., (i) stand-alone MEC, (ii) stand-alone desiccant AC, and (iii) M-cycle based desiccant AC systems. Wet bulb effectiveness of the stand-alone MEC unit resulted in being from 64% to 78% whereas the coefficient of performance for stand-alone desiccant AC and M-cycle based desiccant AC system was found to be 0.51 and 0.62, respectively. Results showed that the stand-alone MEC and M-cycle based desiccant AC systems can achieve the animals’ thermal comfort for the months of March to June and March to September, respectively, whereas, stand-alone desiccant AC is not found to be feasible in any month. In addition, the ambient situations of winter months (October to February) are already within the range of animal thermal comfort.

Demonstration of Liquid Desiccant Based Air Conditioning System using Solar Energy and Waste Heat

Objectives: The objective of the current work is to demonstrate Liquid desiccant based air conditioning (LDAC) systems to reduce energy consumption and cater to latent cooling load more effectively. Methods/Statistical Analysis: This work describes three different projects undertaken to demonstrate efficacy of LDAC systems. One of the project demonstrated regeneration of liquid desiccant in a simple but economical solar thermal collector along with integrated liquid desiccant (LD) heat exchanger. Two other projects demonstrated regeneration using waste heat source and dehumidification of air in an internally cooled LD-air contacting device. Experiments were carried out in city of Vadodara in summer months of year2017 and encouraging results are found. Findings: The passive solar regeneration project showed that a latent cooling rate of 96 W can be provided using an LDAC system per m2 area of solar thermal collector. Another useful utility in form of distilled water could be produced at a rate of 1.7 liters in a day per m2 area in this collector. The internally heated device used for demonstrating use of waste heat for LD regeneration could provide moisture removal rate of around 3.0 kg/h from air using aqueous solution of calcium chloride as LD with an average concentration of 37.7%.In the internally cooled air-LD contacting device, 2.0 kW of latent cooling along with 0.3 kW sensible cooling could be provided for air entering at around 34.7o C temperature and 47.5% relative humidity with an average chilled water temperature of 9.5o C and LD concentration of 40.0%. These experiments have thus demonstrated and established efficacy of LDAC system to provide effective dehumidification with use of energy sources with nominal recurring costs and reduced pollutant emission. Application/ Improvements: Reducing heat losses in solar collector, air bypasses in the contacting device and higher residence time of LD in contacting device can help improve these results further. Keywords: Air Conditioning, Dehumidification, Energy Conservation, Liquid Desiccant, Solar Energy, Waste Heat

Preliminary Investigations on a Novel Rotating Media Liquid-air Contacting Device without Liquid Pool

Abstract Contacting device is a system that bring air and water in contact with each other in evaporative cooling systems while it brings liquid desiccant and air in contact with each other in case of liquid desiccant-based air conditioning systems. They should provide high surface area density for heat and mass transfer and also provide high heat and mass transfer rates in smaller volume with lower electrical power consumption. A novel design of contacting device is presented in this work, where plastic porous cylindrical contact media is used and unlike previous designs, the liquid pool in lower part of the device is eliminated. This would help to utilize the contact surfaces more effectively and reduce power consumption of motor used for rotation of the media as compared to earlier designs in literature. The novel contacting device and the experimental set up were developed and preliminary testing was done. The contact media is 230 mm long with diameter equal to 145 mm, providing surface area density equal to 445 m 2 /m 3 . In a preliminary experiment, the device provided evaporative cooling rate up to 288 W and effectiveness of 33.1%. The performance can be further improved by increasing mass flow rate of water for better wetting, increasing surface density by decreasing porosity and increasing path length of air.

Performance Evaluation and Parameter Analysis on a Composite Solid Desiccant based Air Conditioning System

Performance Evaluation and Parameter Analysis on a Composite Solid Desiccant based Air Conditioning System

Three years experimental comparative analysis of a desiccant based air conditioning system for a flower greenhouse: Assessment of different desiccants

This paper presents three years experimental comparative analysis of a desiccant-based and a traditional air conditioning system for a flower greenhouse in the winter season. Two identical neighbouring flower greenhouses were equipped with a traditional and an innovative air conditioning system respectively. The innovative air conditioning system is based on the Ventilated Latent Heat Converter (VLHC) AGAM 1020 that consists of a dehumidification and a regeneration unit. Heat recovery is performed on the desiccant regeneration process to warm up the dehumidified air coming back into the greenhouse.Comparative analysis was carried out for three years using three different desiccants in the VLHC: H2O/LiCl in 2010, H2O/KCOOH in 2011 and H2O/LiBr in 2012. The greenhouse equipped with a sorption unit exhibits an energy saving of 9.6% in 2010, 11.7% in 2011, and 15.1% energy saving in 2012. The comparative analysis gives the opportunity for the assessment of the hygroscopic salt solutions currently used as desiccants. Although H2O/LiBr desiccant exhibits the best performance, the solution H2O/KCOOH seems to be very promising as “desiccant of the future”.

Experimental performance study of a proposed desiccant based air conditioning system

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.

Liquid Desiccant based Solar Air Conditioning System with Novel Evacuated Tube Collector as Regenerator

Growing demand for air conditioning and pollution concerns related with production of electrical energy have compelled researchers to investigate new technologies for air conditioning. Liquid desiccant based air conditioning technology is adaptable to pollution-free renewable energy source like solar energy. It has additional advantages like air washing and high density energy storage. Use of solar energy for air conditioning is logical as higher availability of solar radiation matches with higher demand for air conditioning in summer. A novel evacuated tube collector (ETC) with heat pipes is developed in the Heat Pump Laboratory at IIT Bombay (HPL_IITB). In spite of being a not-tracking type, temperatures much beyond the range of flat plate or conventional ETC can be achieved and liquids can even be boiled in this collector. This collector was used as regenerator for liquid desiccant based solar air conditioning system. Objective of this work was to demonstrate and investigate performance of this solar collector with in-situ regeneration. Liquid desiccant was preheated in solution heat exchanger and pumped into the solar regenerator. Steam and regenerated liquid desiccant at outlet of collector were separated and steam was condensed downstream to the collector. Average thermal COP of 0.82 over 5 h experiment period could be achieved with single stage regeneration and insolation range from 509 to 752 W/m2. Parasitic power consumption was less than 40 W, which works out to be 1.5% of the regeneration duty. Solar collector efficiency up to 44.7% was achieved at 117 °C regeneration temperature and 719 W/m2 global radiation along with distilled water production of 5.14 kg/h.

Investigation of solar energy utilization in a novel desiccant based air conditioning system

In this study, a novel desiccant based air-conditioning system was considered. This system consisted of a desiccant wheel, heat exchangers, fans, evaporative cooler, electric heater unit to simulate solar energy, and refrigeration unit. A model was developed to investigate the utilization of solar energy in the system. In the model, the temperatures obtained from the experiments over the cooling season of 2008 and solar radiation data measured by the State Meteorological Affairs (DMI) between 1986 and 2006 years for Adana were utilized. The increase in the regeneration air temperature due to solar energy assistance for the days, on which the experiments were carried out, was calculated using the model. The results obtained from the model and the experiments were also compared with each other. It may be concluded that utilization of solar energy in the system increases the coefficient of performance (COP) between 50% and 120%.

Experimental analysis on the dehumidification and thermal performance of a desiccant wheel

The advantages of desiccant-based air conditioning systems, compared to conventional ones based on the dehumidification by cooling, have been highlighted in many research papers. The energy saving and the reduction of the environmental impact are higher when the desiccant material is regenerated by using “free” thermal energy (for example, waste heat from cogenerators or solar energy). Further investigation on the performance of the desiccant wheel is useful: therefore, in this paper, an experimental analysis on this component is presented, with particular attention to the variation of the performance as a function of the process and regeneration air flow rates. The desiccant material is regenerated by means of low-temperature thermal energy (about 65 °C) from a microcogenerator. Both the experimental results obtained by the authors and the data provided by the manufacturer have been used to calculate some performance parameters, and a satisfactory agreement has been obtained. The performance parameters have been evaluated as a function of the regeneration temperature, the inlet process air humidity ratio and temperature and the ratio between the regeneration and process air flow rates, in both the cases of fixed regeneration temperature and fixed regeneration thermal power: the results show that higher influence on the dehumidification process is due to the regeneration temperature rather than to the regeneration air flow rate. Moreover, the process air humidity ratio and regeneration temperature influence the desiccant wheel performance more than the process air temperature.

Optimisation of a desiccant cooling system design with indirect evaporative cooler

Solar desiccant-based air-conditioning has the potential to significantly reduce cost and/or greenhouse gas emissions associated with cooling of buildings. Parasitic energy consumption for the operation of supply fans has been identified as a major hindrance to achieving these savings. The cooling performance is governed by the trade-off between supplying larger flow-rates of cool air or lower flow-rates of cold air. The performance of a combined solid desiccant-indirect evaporative cooler system is analysed by solving the heat and mass transfer equations for both components simultaneously. Focus is placed on varying the desiccant wheel supply/regeneration and indirect cooler secondary/primary air-flow ratios. Results show that for an ambient reference condition, and 70 °C regeneration temperature, a supply/regeneration flow ratio of 0.67 and an indirect cooler secondary/primary flow ratio of 0.3 gives the best performance with COP e > 20. The proposed cooling system thus has potential to achieve substantial energy and greenhouse gas emission savings.

Experimental investigation of a novel desiccant cooling system

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.