Experimental investigation of a novel desiccant cooling system (original) (raw)
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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
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.
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.
Nowadays, the increasing demand of summer cooling is typically covered by electric chillers, often determining electric peak loads and blackouts. Thus, a wide interest is spreading in small scale natural gas-fired cogenerators driving desiccant-based airconditioning systems, which represent interesting alternatives to conventional systems based on vapor compression cooling only. In this article, experimental tests performed on an air handling unit (AHU) equipped with a desiccant wheel (DW), coupled to a small scale cogenerator and an electric chiller are described. A new layout of the desiccantbased AHU is investigated, considering a third flow (the cooling air), besides the process air flow and the regeneration one. A cross-flow heat exchanger between process air and cooling air is used; the cooling air, cooled by an adiabatic humidifier, is aimed to precool the process air exiting the DW. The relevant influence of the heat exchanger and of the humidifier, as well as that of the chiller performance, on global primary energy requirements, water consumption and CO 2 equivalent emissions of the system is experimentally evaluated.
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:
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.
ENHANCEMENT OF THE PROCESSES OF DESICCANT AIR CONDITIONING SYSTEM
An experimental study was carried out to evaluate the liquid desiccant system performance during dehumidification and humidification processes using air injection through the liquid desiccant solution (Calcium Chloride). The air flows cross the desiccant solution with different air mass flow rates. The system is studied at different operating condition (air flow rate, temperature, humidity ratio and solution levels). The effectiveness of the proposed system for both dehumidification and humidification processes were evaluated. Also, the cooling effect and mass transfer coefficient was obtained. It is found that the system effectiveness reached 0.75 in the dehumidification process and 0.7 in the humidification process. Mass transfer coefficient depends on the air mass flow rate and the desiccant solution level in the tank Economical Results of the presented system is estimated
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 ...
2016
To date, the application of liquid desiccant air conditioning systems in built environment applications, particularly small scale, has been limited. This is primarily due to large system size and complexity, issues of desiccant solution leakage and carry-over and equipment corrosion. As a result, a novel integrated desiccant air conditioning system (IDCS) has been developed. The system combines the regenerator, dehumidifier and evaporative inter-cooler into a single membrane based heat and mass exchanger. This paper presents an evaluation, based on experimental data, of the novel IDCS operating with a potassium formate (CHKO2) desiccant working fluid. A range of tests have been completed to characterise the performance of the dehumidifier, regenerator and complete IDCS. Cooling output in the range of 570 to 1362W and dehumidifier effectiveness in the range of 30 to 47% are presented. An issue encountered has been an imbalance between moisture removal rate in the dehumidifier and moisture addition rate in the regenerator. As a result, an adjusted thermal COP (COPth,adj) value has been calculated. COPth,adj values of 1.26 have been achieved with an average of 0.72. Electrical COP (COPel) values of 3.67 have been achieved with an average of 2.5. The work demonstrates that the novel IDCS concept is viable and has provided progress to the field of liquid desiccant air conditioning technology for building applications. Further work is required in order to address the main issue of mass imbalance between the dehumidifier and regenerator. Keywords: Liquid desiccant, air conditioning, integrated design, building application, potassium formate.