**1. Introduction**

The increasing population, technological advancements, and materialistic living standards have significantly increased the energy demand for cooling devices in last few decades. Almost 15% of world's total energy is consumed by air conditioning systems. The human thermal comfort conditions are described in terms of efficient control of sensible and latent load. The basic function of an air conditioner is to simultaneously control temperature,

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humidity, and quality of supply air as shown in **Figure 1**. Generally, in order to provide thermal comfort conditions to the occupants, an air conditioning system should maintain indoor air temperature of 18–26°C and relative humidity of 40–70%. The accurate and effective control of humidity becomes more crucial for applications where less moist environment is required.

the performance of liquid desiccant cooling systems because of lower heat input required for its regeneration. The desiccant cooling system can either be solid or liquid depending upon the type of desiccant material used. Liquid desiccants have advantage over the solid desiccants that these only requires low-temperature heat source to drive the system. The available

Renewable and Sustainable Air Conditioning http://dx.doi.org/10.5772/intechopen.73166 123

The development of desiccant-based cooling technology is a topic of interest now a day and has been widely investigated. Most recently, Rafique et al. [2] investigated the thermal and exergetic performance of a newly developed absorption type desiccant dehumidifier. The aim of this study was to lower the required regeneration temperature by employing liquid desiccant instead of solid desiccant materials. The computed results show that better supply air conditions can be obtained to provide human comfort in the hot and humid climate with effectiveness of the system largely dependent on air flow rate, wheel width, and humidity ratio of the process air. The annual average value of dehumidification performance is found to be 0.55 which shows that system can control the latent load efficiently throughout the year. In another study, Rafique et al. [3] studied the performance of desiccant assisted cooling system for five different sites in Saudi Arabia. The coefficient of performance (COP) of the system was observed to vary from 0.275 to 0.476 for different locations. Kabeel et al. [4] the performances of a solar energy assisted desiccant air conditioning system with different types of storage

In other studies the development of new configurations [4, 5], parametric and statistical analysis [6, 7], second law and anergy analysis [7, 8], exergoeconomy [9] and different other advancements [10] for desiccant cooling systems have been studied. The desiccant-based technology is on path of development but still a lot of work needs to be done in order to

configurations of the desiccant cooling system are shown in **Figure 2** [1].

materials are numerically investigated.

**Figure 2.** Different configurations for various desiccant systems [1].

The term sensible heat ratio is used to determine the performance of an air conditioner in terms of its ability to control sensible and latent load. Smaller the value of sensible heat ratio larger is the value of latent cooling loads. The value of sensible heat ratio is about 0.75 for the commonly used conventional vapor compression air conditioning system. The vapor compression air conditioning system controls the latent load by condensation process. The air is cooled below its dew point temperature to remove the moisture and then reheated again to desired supply temperature. A considerable amount of energy is wasted during this process of overcooling and reheating which lowers the system overall coefficient of performance. Moreover process of condensation creates an environment for the growth of harmful fungi and bacteria. Because of the high energy cost of these conventional systems and poor control of latent load, need arises for some alternative cooling devices.

To avoid the excessive waste of energy, an alternative way to achieve desired moisture reduction is the use of desiccant dehumidification system in which a desiccant material absorbs moisture from the humid air. Thermal energy is used to regenerate the desiccant material and cycle continues. The system is both cost-effective as well as environmental friendly. Since no refrigerant is used in these systems so depletion of ozone layer is minimized. Lowtemperature heat sources, like waste heat from engine or solar heat, can be used to operate the system.

A good desiccant should have better moisture absorption capability and lower temperature of regeneration. Different types of new desiccant materials with high dehumidification performance have been proposed in past few years. These materials have the potential to improve

**Figure 1.** The basic functions of an air conditioner.

the performance of liquid desiccant cooling systems because of lower heat input required for its regeneration. The desiccant cooling system can either be solid or liquid depending upon the type of desiccant material used. Liquid desiccants have advantage over the solid desiccants that these only requires low-temperature heat source to drive the system. The available configurations of the desiccant cooling system are shown in **Figure 2** [1].

humidity, and quality of supply air as shown in **Figure 1**. Generally, in order to provide thermal comfort conditions to the occupants, an air conditioning system should maintain indoor air temperature of 18–26°C and relative humidity of 40–70%. The accurate and effective control of humidity becomes more crucial for applications where less moist environment

The term sensible heat ratio is used to determine the performance of an air conditioner in terms of its ability to control sensible and latent load. Smaller the value of sensible heat ratio larger is the value of latent cooling loads. The value of sensible heat ratio is about 0.75 for the commonly used conventional vapor compression air conditioning system. The vapor compression air conditioning system controls the latent load by condensation process. The air is cooled below its dew point temperature to remove the moisture and then reheated again to desired supply temperature. A considerable amount of energy is wasted during this process of overcooling and reheating which lowers the system overall coefficient of performance. Moreover process of condensation creates an environment for the growth of harmful fungi and bacteria. Because of the high energy cost of these conventional systems and poor control

To avoid the excessive waste of energy, an alternative way to achieve desired moisture reduction is the use of desiccant dehumidification system in which a desiccant material absorbs moisture from the humid air. Thermal energy is used to regenerate the desiccant material and cycle continues. The system is both cost-effective as well as environmental friendly. Since no refrigerant is used in these systems so depletion of ozone layer is minimized. Lowtemperature heat sources, like waste heat from engine or solar heat, can be used to operate

A good desiccant should have better moisture absorption capability and lower temperature of regeneration. Different types of new desiccant materials with high dehumidification performance have been proposed in past few years. These materials have the potential to improve

of latent load, need arises for some alternative cooling devices.

is required.

122 Sustainable Air Conditioning Systems

the system.

**Figure 1.** The basic functions of an air conditioner.

The development of desiccant-based cooling technology is a topic of interest now a day and has been widely investigated. Most recently, Rafique et al. [2] investigated the thermal and exergetic performance of a newly developed absorption type desiccant dehumidifier. The aim of this study was to lower the required regeneration temperature by employing liquid desiccant instead of solid desiccant materials. The computed results show that better supply air conditions can be obtained to provide human comfort in the hot and humid climate with effectiveness of the system largely dependent on air flow rate, wheel width, and humidity ratio of the process air. The annual average value of dehumidification performance is found to be 0.55 which shows that system can control the latent load efficiently throughout the year. In another study, Rafique et al. [3] studied the performance of desiccant assisted cooling system for five different sites in Saudi Arabia. The coefficient of performance (COP) of the system was observed to vary from 0.275 to 0.476 for different locations. Kabeel et al. [4] the performances of a solar energy assisted desiccant air conditioning system with different types of storage materials are numerically investigated.

In other studies the development of new configurations [4, 5], parametric and statistical analysis [6, 7], second law and anergy analysis [7, 8], exergoeconomy [9] and different other advancements [10] for desiccant cooling systems have been studied. The desiccant-based technology is on path of development but still a lot of work needs to be done in order to

**Figure 2.** Different configurations for various desiccant systems [1].

make this technology with market friendly. In this regard, the major aim of this chapter is to introduce with the concept of alternative cooling technology, its need and recent developments. Different cooling cycles which can be employed for better performance of the system have been described in this chapter. Based on the developed mathematical model, a comparison has been made between two different configurations of desiccant cooling system.
