Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Part II D. Yogi Goswami, Frank Kreith, Jan F. Kreider Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering

D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering  In hot and humid regions of the world experiencing significant latent cooling demand, solar energy may be used for dehumidification using liquid or solid desiccants.  By pretreating the ventilation air with a desiccant system, proper indoor humidity conditions could be maintained and significant electrical energy could be saved.  In a desiccant air-conditioning system, moisture is removed from the air by bringing it in contact with the desiccant and followed with sensible cooling of the air by a vapor compression cooling system, vapor absorption cooling systems, or evaporative cooling system.  In order to regenerate the desiccant for reuse, the desiccant is heated, which increases the water vapor pressure on its surface.  Two types of desiccants are used: solids, such as silica gel and lithium chloride; or liquids, such as salt solutions and glycols. Chapter 6: Solar Cooling and Dehumidification Solar Desiccant Humidification 6.2 Solar Desiccant Humidification

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Vapor pressure versus temperature and water content for dessicant and air. Vapor pressure versus temperature and water content for dessicant and air. Solar Desiccant Humidification

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering  The two solid desiccant materials that have been used in solar systems are silica gel and the molecular sieve, a selective absorber.  Note that the molecular sieve has the highest capacity up to 30 percent humidity, and silica gel is optimal between 30 and 75 percent. Chapter 6: Solar Cooling and Dehumidification Solid Desiccant Cooling System Equilibrium capacities of common water absorbents. Equilibrium capacities of common water absorbents.

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Solid Desiccant Cooling System Schematic of airflow of a dessicant cooling ventilation cycle  The desiccant bed is normally a rotary wheel of a honeycomb type substrate impregnated with the desiccant.  Simultaneously, a hot air stream passes through the opposite side of the rotating  wheel which removes moisture from the wheel.  The hot and dry air at state 2 is cooled in a heat exchanger wheel to condition 3 and further cooled by evaporative cooling to condition 4.  Air at condition 3 may be further cooled by vapor compression or vapor absorption systems instead of evaporative cooling.

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Solid Desiccant Cooling System Dessicant cooling ventilation cycle process on a psychromatic chart. Dessicant cooling ventilation cycle process on a psychromatic chart.  The return air from the conditioned space is cooled by evaporative cooling (processes 5 and 6), which in turn cools the heat exchanger wheel.  This air is then heated to condition 7.  Using solar heat, it is further heated to condition 8 before going through the desiccant wheel to regenerate the desiccant.

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Liquid Desiccant Cooling System A conceptual liquid dessicant cooling system  Liquid desiccants offer a number of advantages over solid desiccants.  The ability to pump a liquid desiccant makes it possible to use solar energy for regeneration more efficiently.  Since a liquid desiccant does not require simultaneous regeneration, the liquid may be stored for later regeneration when solar heat is available.  A major disadvantage is that the vapor pressure of the desiccant itself may be enough to cause some desiccant vapors to mix with the air.

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Liquid Desiccant Cooling System Exchange of humidity and moisture between dessicant and air in the tower.

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Liquid Desiccant Cooling System Exchange of humidity and moisture between dessicant and air in the tower.

Principles of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering D. Y. Goswami, F. Kreith, J. F. KreiderPrinciples of Solar Engineering Chapter 6: Solar Cooling and Dehumidification Liquid Desiccant Cooling System Exchange of humidity and moisture between dessicant and air in the tower.