INTRODUCTION TO DESICCANT BASED AIR CONDITIONING (original) (raw)

A Review of Desiccant Cooling Systems

This paper describes recent published design advances that have been made in desiccant cooling systems. In desiccant cooling cycles, the desiccant reduces the humidity of the air by removing moisture from the air. Then the temperature is reduced by other components such as heat exchangers, evaporative coolers, or conventional cooling coils. The main advantage that desiccant cooling systems offer is the capability of using low-grade thermal energy. Desiccant cooling systems for residential and commercial applications are now being used to reduce energy-operating costs. However, the initial costs are comparatively high. The focus of research for the past decade has been to develop desiccant systems with a high coefficient of performance. Recent studies have emphasized computer modeling and hybrid systems that combine desiccant dehumidifiers with conventional systems. Introduction Almost all materials have the capacity to adsorb and hold water vapor, but commercial desiccants have significant capacity for holding the water. A commercial desiccant takes up between lOand 1100 percent (ASHRAE, 1989)of its dry weight in water vapor, depending on its type and moisture available in the environment. Desiccants remove moisture from the surrounding air until they reach equilibrium with it. This moisture can be removed from the desiccant by heating it to temperatures between 50 and 260 °C and exposing it to a scavenging air stream. The desiccant is then cooled so that it can adsorb moisture again. The transfer of moisture is due to the difference in vapor pressure at the desiccant surface and that of the surrounding air. When the vapor pressure at the desiccant surface is less than that of air, the desiccant attracts moisture and releases it when its vapor pressure is greater than that of air. Desiccant cooling systems are particularly useful when the latent load is large in comparison to the sensible load. Des-iccants also can remove contaminants from airstreams to improve indoor air quality (Relwani, 1986). A thermal energy input is used to regenerate the desiccant. Regeneration energy is equal to the heat necessary to raise the temperature of the desiccant to make its surface vapor pressure higher than the surrounding air plus the heat necessary to vaporize the moisture that it contains. A small amount of energy also goes into desorption of the water from the desiccant. The major advantages of desiccant cooling are:

Application of Desiccant in Modern Air Conditioning Systems

Cooling load component which comprises most of the consumed electrical load in hot seasons is mostly used by countries located in hot regions of the earth. Vapor compression cooling system (VCS) is currently the most common method of providing refrigeration and air conditioning process known as one of the major causes of Ozone depletion and takes considerable size of electrical charges. Cooling loads in air conditioning systems are divided in two groups of sensible and latent load. Cooling process in compressed cooling system can be done by reaching air temperature to the saturation temperature. Such a saturated air is reheated until suitable temperature provided for comfort conditions. Energy can be saved through eliminating latent load. A desiccant is a substance that has a high affinity for water and can be utilized to extract moisture from the air. The desiccant is regenerated after becoming saturated with moisture. Desiccants are classified as either liquid or solid. Application of desiccant air conditioner systems, are proposed an alternative solution for reducing energy consumption and green house gas emission, in hot and humid locations. In this paper, the principles operations of desiccant cooling systems are recalled and their actual technological applications are discussed.

Desiccant cooling air conditioning: a review

In this paper, the principles underlying the operation of desiccant cooling systems are recalled and their actual technological applications are discussed. Through a literature review, the feasibility of the desiccant cooling in different climates is proven and the advantages it can offer in terms energy and cost savings are underscored. Some commented examples are presented to illustrate how the desiccant cooling can be a perfective supplement to other cooling systems such as traditional vapour compression air conditioning system, the evaporative cooling, and the chilled-ceiling radiant cooling. It is notably shown that the desiccant materials, when associated with evaporative cooling or chilled-ceiling radiant cooling, can render them applicable under a diversity of climatic conditions. q

Experimental investigation of a novel desiccant cooling system

Energy and Buildings, 2010

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.

ADVANCEMENT IN DESICCANT AIR-CONDITIONING TECHNOLOGY

IRJMETS Publication, 2021

Due to the current energy crisis and high energy costs, various air conditioning systems are being investigated. Desiccants are a type of adsorbent substance with a strong attraction to water vapour. Desiccant air conditioning technology delivers improved indoor air quality with comparatively less power consumption. A brief overview on the working principle along with different types of desiccant evaporative cooling systems has been provided. The advancement is demonstrated through a literature analysis. Different types of desiccant materials and obstacles for the acceptance in recent market is summarized in the review.

Review on Recent development in Desiccant Cooling

International Journal of Energy Resources Applications

Due to its sustainable cooling design and inexpensive operation, desiccant based dehumidification and cooling systems have been popular in recent years for humid areas. In general, the desiccant cooling used in conjunction with evaporative cooling as two separate types of configurations according to direct or indirect cooling. The relative humidity of moist outside air can potentially be controlled by both the systems during dehumidification and cooling to produce indoor thermal comfort. The solid desiccant-assisted evaporative cooling technologies may enable the use of the technique in a wider variety of climates, including those with high humidity. The development of innovative desiccant materials, improvement of the structure and material of the dehumidifier setup, desorption consumption rate and operating strategy of the system are some of the potential research possibilities and recommendations that were made. According to this review study, the desiccant integrated innovative ...

Application of Liquid Desiccant Cooling Technology in Built Environment: A Review

International Journal of Modern Studies in Mechanical Engineering, 2020

The role of the desiccant used in the dehumidifier is to remove water vapor from the conditioned air due to vapor pressure difference between the hot desiccant and the supply conditioned air. The desiccant can be categorized mainly into the two categories as solid adsorption and liquid absorbent desiccant materials. Several other types of solid materials are available in nature that can hold water vapor to the great extent to its weight, e.g., silica, polymers, zeolites, alumina and mixtures. Other commonly used liquid desiccant materials are calcium chloride, lithium chloride, lithium bromide, triethylene glycol and an equal mixture between calcium chloride and lithium chloride. These liquid desiccants have many thermo-physical properties, but their requirements cannot be fully described by any single desiccant. These requirements include low vapor pressure, low crystallization point, high density, low viscosity, low reactivation temperature, and economy [1]. The moist air is dehumidified by being brought into contact with strong liquid or solid desiccant, after this to provide sensible cooling to dehumidification process, traditional vapor compression, and vapor absorption, direct or indirect evaporative cooler units used. When the solution is weakened by absorption of moisture, it provided for the regeneration process that can loses its moisture content due to external thermal source. This called as reactivating the saturated desiccant material [2]. Thermal energy, at a temperature as low as 46-72°C required for reactivating of the liquid desiccant can efficiently obtained using a particular type of air or water solar collector or other primary heat renewable source [3]. The typical cycle of the desiccant is made up by three processes as shown in Figure 1and Figure 2 depicts the fundamental deviation among traditionally used air conditioner and novel desiccant assisted dehumidification and cooling process [4]. The traditionally used vapor-compression cycle is now the foundation of the world air conditioning industry and will remain so for many years in conjunction with other hybrid cooling systems. The following problems are being addressed through a number of approaches including: (1) More efficient designs for household and commercial air conditioners, (2) More efficient buildings that require minimum or zero cooling, (3) The conversion Abstract: Liquid-desiccant assisted dehumidification and cooling system has been proved to be an effective method to extract the moisture of air with relatively less energy consumption, especially compared with conventional vapor compression system. To date, the conventional dehumidification mode with desiccant solution has been improved or replaced by newly emerged energy-saving systems with better performance. This paper gives a detailed account of the general features of the various components used in desiccant dehumidification and cooling techniques; meanwhile, the effect of various operating parameters on system performance also highlighted. Moreover, a summary of the experimental and analytical studies to evaluate the system performance has been made. Some new hybrid systems that greatly expand the desiccant dehumidification technique in industrial and residential applications, as well as effectively promoting the single system's performance, are also reviewed through literature. Through a literature review, the feasibility of the desiccant cooling is proven by its comparison with conventional vapor compression system in terms of energy and cost savings are underscored. Finally, future study and application for liquiddesiccant dehumidification techniques are concluded.

An overview of solid desiccant dehumidification and air conditioning systems

Renewable and Sustainable Energy Reviews, 2015

To address the importance of desiccant airconditioning (DAC) systems, this paper discusses the comparison between DAC and conventional vapor compression airconditioning (VAC). Performance and economic feasibility (PEF) of the system is conferred with reference literature to correlate the types of DAC system from the perspective of energy saving and system payback period. The present study provides three examples of existing desiccant cooling systems namely (i) standalone DAC system, (ii) single-stage hybrid DAC system, and (iii) two-stage hybrid DAC system, which highlight their importance under different environmental conditions. This study provides scientific and experimental supports on how the standalone or hybrid desiccant cooling can be a supplement to the exiting VAC system.

A Study of Desiccant-Based Cooling and Dehumidifying System in Hot-Humid Climate

International Journal of Materials, Mechanics and Manufacturing, 2013

The objective of this study is to investigate the feasibility of using desiccant cooling system as an alternative HVAC solution in buildings to achieve thermal comfort. This solution is more attractive when the solar energy is used to regenerate the desiccant wheel. An extensive experimental study has been performed in Tohoku University in Japan. A TRNSYS model of the desiccant cooling system combined with the heat wheel and heat source has been simulated and compared with the experimental data. The results of the simulation show that such system is feasible for cooling building in hot-humid climates.

A review on desiccant based evaporative cooling systems

The air conditioner should control the building sensible and latent load properly in order to provide the indoor comfort conditions. The conventional mechanical vapor compression system usually controls the latent load by the process of condensation of water vapor in which air is cooled below its dew point temperature and then reheated again up to the required supply conditions. The conditions where latent load is dominant these two processes i.e. overcooling and then reheating again will increase the consumption of electrical energy and emission of CO 2 remarkably. To avoid this wastage of primary energy and emission of harmful gases, desiccant based evaporative cooling system is a good alternative to traditional air conditioning system which is cost effective as well as environment friendly. It can be driven by thermal energy which makes a good use of solar energy which is free as well as clean. In this paper, a review of desiccant based evaporative cooling systems has been presented. The present study is undertaken from variety of aspects including background and need of alternative cooling systems, concept of conventional and desiccant based evaporative coolers, system configurations, operational modes, as well as current status of the desiccant based evaporative cooling technology. The review work indicated that the technology of desiccant based evaporative cooler has a great potential of providing human thermal comfort conditions in hot and humid climatic conditions at the expense of less primary resources of energy as compared to conventional cooling systems. Some modified and modern evaporative coolers have also been introduced in this paper.