A Novel Solar-assisted Membrane-based Liquid Desiccant Air Conditioning System for Hot and Humid Climatic Conditions

1. Introduction According to the energy statistics of India, building sector consumes 40% of electricity out of which nearly one third is consumed by heating, ventilation and air conditioning (HVAC) systems [1]. Currently, more than 90% of the HVAC systems are of vapor compression refrigeration type which are energy inefficient for humidity control [2]. Therefore, it is desirable to meet such HVAC demands using an alternative system which is not only energy efficient, but can also utilize the low grade energy sources such as solar or waste heat. The liquid desiccant system is one such prospective alternative which can utilize the solar energy for its desiccant regeneration. Such systems are classified as direct contact-packed bed system and indirect contact-membrane system. The latter is preferred to avoid problems associated with the desiccant carryover. The conventional membrane-based liquid desiccant air conditioning system (MLAC) contains adiabatic dehumidifier and regenerator. The temperature of the desiccant to the dehumidifier is maintained in such a way as to simultaneously cool and dehumidify the air. However, it cannot cool and dehumidify the air to the desired level due to resistance for heat and mass transfer in the intermediate membrane and the exothermic heat that is generated during absorption. Present study proposes a novel MLAC with an additional air cooling heat exchanger. Performance analysis of such a novel solar assisted MLAC is carried out for the hot and humid climatic conditions prevailing in the city of Chennai, India. 2. Methodology and Description The main components of MLAC are dehumidifier and regenerator. They are modelled and validated with the reported experimental data. The MLAC is designed to provide air conditioning for a room having low sensible heat factor (SHP) with loads of 3 kW sensible and 2 kW latent. Aqueous solution of lithium chloride is used as desiccant. Evacuated tube solar collector is used to harvest solar energy. Storage tank with three mixing zones and aspect ratio (L/D) of 4:1 is used. The year round performance of the MLAC is evaluated in terms of the room temperature, specific humidity and coefficient of performance. 3. Conclusions Results of the present study conclude that the proposed solar assisted MLAC is able to achieve better indoor conditions (24°C and 0.0097 kg/kgda) at approximately the same COP of the conventional MLAC. The recommended range of inlet desiccant temperature to the dehumidifier and regenerator are 16-19°C and 45-50°C respectively. The results of the present study are expected to be useful in optimum design of MLAC for the hot and humid climatic conditions. References 1. A technical report of energy and buildings by Centre for Science and Environment. Available at \u3c http://www.cseindia.org/userfiles/Energy- and -% 20 buildings. pdf \u3e [Accessed 5.6.2017]. 2. Alternatives to Vapor-Compression HVAC Technology, ASHRAE Journal Article. Available at \u3c https://www.ashrae.org/File%20Library/docLib/.../2014Oct012-023_ Goetzler. pdf \u3e [Accessed 15.12.2017]

A Comprehensive Review of Dehumidifiers and Regenerators for Liquid Desiccant Air Conditioning System

This is an Accepted Manuscript of an article published by Elsevier in Energy Conversion and Management on July 15, 2021, available at: https://doi.org/10.1016/j.enconman.2021.114234Peer ReviewedLiquid desiccant air conditioning systems (LDAS) are an energy-efficient and eco-friendly alternative to conventional air conditioning systems. The performance of a LDAS significantly depends on its simultaneous heat and mass transfer components, namely dehumidifier and regenerator. These components are referred to as liquid desiccant energy exchangers (LDEEs) since the working fluids (air and desiccant) exchange both heat and moisture. There has been a lot of research on LDEEs over the last two decades to improve their performance, thereby enhancing the efficiency of the LDAS. The main objective of this comprehensive review paper is to summarize the developments of LDEEs. The desiccant material, and design, operating, and performance parameters of LDEEs are explained in detail. Even though a lot of research has been done on LDEEs, they are not much utilized in the practical heating, ventilation, and air conditioning (HVAC) systems. To address this issue, future research should prioritize its focus on (i) practical problems of LDEEs such as cross contamination, and leakage and blockage of the membrane, (ii) long term performance study in the practical systems, (iii) noncorrosive and inexpensive solution, (iv) compatible material for efficient heat and mass transfer, and (v) generalized design and performance control methodology. The discussions presented in this communication will be useful to ascertain the crucial research gaps that need to be addressed by future research studies

Performance Evaluation Of Thermally Activated Glass Fibre Reinforced Gypsum Building Equipped With Desiccant System

According to International Energy Outlook 2017, the energy consumption of the building sector is expected to increase by 32% from 2015 to 2040. This is due to the accelerating demand for mechanical air conditioning system for maintaining the indoor comfort conditions and high embodied energy of the conventional building materials. Many solutions are proposed globally to address these problems. Thermally Activated Building System (TABS) is one such energy efficient alternative to the conventional mechanical air conditioning system for providing the desirable indoor comfort conditions. In TABS, copper pipes are embedded in its building structures namely ceiling, floor and walls. Chilled water circulated in the copper pipes cools the building structures which in turn cool the indoor environment by radiative and convective heat exchange methods. However, the TABS handles only the sensible load. Therefore, a solid desiccant system is used along with TABS for maintaining the desired indoor humidity. Glass Fibre Reinforced Gypsum (GFRG) is used as a building material which is made up of reinforced glass and gypsum. It is used in the present study due to its low embodied energy. The combination of TABS and GFRG building is named as Thermally Activated Glass Fibre Reinforced Gypsum (TAGFRG) building. Ventilation rate of the proposed TAGFRG is maintained according to the standards prescribed by ASHRAE. To appreciate the energy saving potential and feasibility of TAGFRG building, its thermal performance is compared with that of the conventional concrete building. Both TAGFRG and conventional concrete building are constructed with the same dimensions (1m (L) x 1m (B) x 1m (H)) for such comparison. The present study analyses the influence of various operating parameters on the performance of the proposed TAGFRG. The operating parameters considered are cooling water temperature, cooling surfaces and air velocity. The performance parameters used to evaluate the indoor thermal comfort of the proposed TAGFRG are indoor temperature and humidity, Predicted Percentage Dissatisfied (PPD) and Predicted Mean Vote (PMV). The decrease in supply water temperature and increase in radiant surface area, increase the thermal comfort level of the indoor. The results of the present study will be useful for predicting the optimum design of proposed TAGFRG which has the potential to reduce the energy consumption and carbon emission of the building sector

A transient numerical model for desiccant-coated fixed-bed regenerators and compensation for transient sensor errors

This is an Accepted Manuscript of an article published by Taylor & Francis in Science and Technology for Build Environment on 06-January 2022, available at: https://doi.org/10.1080/23744731.2021.2017236Natural Science and Engineering Research Council (NSERC), Tempeff North America Inc., Winnipeg, Canada (Project No: 533225-18), ASHRAE.Peer ReviewedDesiccant-coated fixed-bed regenerators (FBRs) can achieve high effectiveness due to high ratio of energy transfer area to volume, and therefore, they are favourable air-to-air energy recovery exchangers for HVAC systems. However, unlike other types of energy recovery exchangers, the air properties (i.e., temperature and humidity) at the outlet of FBRs vary with time. The variations in outlet airflow properties can cause errors in measurements because the measurements include the FBR and sensors transient responses. In this paper, a numerical model is developed to evaluate the performance of desiccant-coated FBRs and their transient operation. The model consists of an exchanger model (FBR model) and sensor (temperature and humidity) models to distinguish the actual performance of the FBR alone from the measured performance, which includes both the FBR and the sensor's response. The model is validated with experimental measurements and available results in the literature. The model can decouple the measured response of the FBR and sensors to predict the FBR performance. This paper's main contribution is an insight into the complex heat and mass transfer processes in desiccant-coated FBRs and measurement sensors. The results of this paper could be used to provide practical recommendations for humidity measurements of different types of desiccant-coated FBRs developed for HVAC applications. Furthermore, the measurement requirements in the current testing standards (ASHRAE 84 and CSA C439-18 standards) for FBRs are examined. Recommendations from this paper could be implemented in future versions of these standards