Desiccant Air Conditioning

It is important to decrease the energy cost of heating, ventilating and air conditioning (HVAC) systems without compromising indoor air quality and comfort conditions due to the rising cost of fossil fuels and other environmental concerns. Liquid desiccant cooling systems are one of the alternatives in this regard which is not only environmental friendly (no use of any refrigerant which deplete ozone layer) but at the same time make a good use of alternative sources of energy like, solar, biomass etc. This paper presents different commercially available liquid desiccants and their composites which combines the properties of two or more desiccant materials for better performance. A good desiccant should have better moisture absorption capability and lower temperature of regeneration. This paper also includes the different configurations of liquid desiccant dehumidifiers and their advantages as well as drawbacks. Some new configurations of liquid desiccant dehumidifiers have been introduced which greatly improves the system overall performance. Moreover, a summary of the performance parameters has been made to analyze the system performance. This review is meaningful for the research and technical development process of liquid desiccant technology.

Cooling by solar energy is one of the key solutions to the global energy and environmental degradation issues. Solar liquid desiccant based on evaporative cooling is proposed as an eco-friendly alternative to the conventional vapour compression systems due to its huge untapped energy savings potential. In this paper, the recent works on solar assisted liquid desiccant cooling and its various applications combined with evaporative air-conditioning under different climates are reviewed and advantages the system may offer in terms of energy savings are underscored. A basic description of the principles of hybrid solar liquid desiccant with direct and indirect evaporative cooling is provided. Finally, solar regeneration methods and recent developments for the liquid desiccant air-conditioning system are presented.

The river current turbine is one of the clean decentralized renewable energy technologies potential in delivering locally the energy for the communities inaccessible by the electricity connection. In order to assist in optimizing a river turbine design and predicting its performance, a mathematical model can be one of the alternative methods. This study is a continuous work on developing a mathematical model for a river current turbine with a horizontal axis rotor arrangement. In present model, the effect of blade parameters is included, providing a widening understanding on the system behavior of the turbine. To develop the model, the Blade Element theory which is generally applied for the wind turbine is adopted. The result shows that, to run the model, instead of the water velocity, the turbine radius, the rotation and the specific mass of water, it requires additional input parameters of the number of blades, the cord length of the blade, the blade angle and the data of the lift...

In this study, a novel combined compact evaporative (CCEC) cooler is fabricated, and its cooling performance has been examined experimentally under various operating conditions. The prototype under study was a cross-flow, two-stage evaporative cooler combined with a desiccant dehumidifier. It consisted of a compact heat exchanger generating series of wet and dry channels utilizes thin film evaporation. The air was cooled sensibly by flowing through the dry channels, and then wet channels where evaporation took place. The desiccant was utilized to control the relative humidity of the air. Experimental results show that the prototype efficiency inversely proportional with inlet air mass flow rates and slightly influenced with variation inlet air temperature.

Craving for higher comfort and rise in living standards in various societies have led to higher demand for air conditioning. Energy consumption is related with climate change. Desiccant based air dehumidification systems can run with waste heat or renewable source of energy. Liquid desiccant (LD) based air conditioning systems are many times conceived as complicated and costly. A novel but simple internally cooled LDAD system is developed, integrated and tested in this work. Outdoor air was passed through the coil, thus making it essentially a study of fresh air enthalpy removal. Temperature range of 14 to 22oC was used for cooling water, which can be catered by a single stage vapour absorption refrigeration system on lower side or cooling tower on the higher side. The cooling capacity of the system increased up to 54%, compared to conventional chilled water coil. Latent heat fraction removed was also higher, showing usefulness of the system for higher latent load applications. Higher air velocity was found to give higher cooling capacity, while moisture removal per kg of air and effectiveness were higher at lower air velocities.

The liquid desiccant cooling system is found to be a good alternative of conventional air conditioning system for better control of both latent and sensible loads. The major component of a liquid desiccant cooling system is desiccant dehumidifier which controls the latent cooling load. In this paper a mathematical model for rotary type liquid desiccant dehumidifier commonly known as desiccant wheel has been presented. The desiccant wheel has a cylindrical shape with a number of identical narrow circular slots distributed uniformly over the rotor cross section. The slots are filled with a porous medium carrying the solution of liquid desiccant, to make the absorbing surface. The absorption and regeneration performance of the desiccant dehumidifier is discussed in this paper for different operating conditions. The wheel performance curves which help to determine the air outlet conditions and coefficient of performance (COP) of the system are drawn for a wide range of wheel thickness (0.06-0.6m), air mass flux (1-8 kg/m 2 .s), and regeneration temperature (60-85 o C). A reduction of about 30% in outlet humidity ratio is observed with an increase in the wheel thickness from 0.06 to 0.2m. The computed results show that better supply air conditions can be obtained to provide human thermal comfort in the hot and humid climate with effectiveness of the system largely dependent on air flow rate, wheel thickness and humidity ratio of process air.