According to the International Energy Agency in 2012, HVAC systems in the building sector are the most energy consuming devices, contributing 10–20% of the final energy consumption in developed countries. Thus, the increase in energy efficiency for HVAC systems plays an important role in energy policies worldwide [1]. Providing cooling by utilizing renewable energy, such as solar energy, is one solution to address the energy issues. Desiccant-based solar cooling is one of the most promising methods of utilizing solar energy for the purpose of air conditioning. This system is a combination of dehumidification, refrigeration, cooling with the help of an evaporative cooler, and finally regeneration of the desiccant system by a heat source, in order to provide and maintain the desired room temperature and relative humidity with enhanced efficiency of energy use [2]. So, compared to conventional systems, desiccant-based air conditioning provides efficient control of room temperature along with relative humidity, while consume less electrical energy [3]. Almost all air-conditioning systems essentially handle two kinds of load, namely sensible load and latent load. The sensible load is due to temperature differences, while latent load is due to moisture [4]. Conventional air-conditioning systems do not have any separate arrangements for handling sensible and latent load. Here, the evaporator coil can handle both sensible as well as latent load. When handling latent load in conventional air-conditioning systems, it is necessary to maintain the temperature of the evaporator coil below the dew point temperature of the inlet air. So it is again required to reheat, which implies poorer energy efficiency. In desiccant-based air-conditioning systems, latent cooling is performed by desiccant dehumidification and sensible cooling by evaporative cooling or refrigeration. Thus, a considerable part of expensive vapor-compression refrigeration is replaced by inexpensive evaporative cooling.

The desiccant dehumidification and cooling system (DDCS) is the best alternative for the VC system as it overcomes the traditional system’s disadvantages and is more economical and easily accessible. The DDCS decreases the operational costs and work more significantly when powered by solar energy [5,6,7].

The conventional reheat system not only consumes excess electrical energy because of low energetic efficiencies, but it is also responsible for damaging our environment. These two reasons are responsible for the need to investigate the development of an alternative HVAC system which does not have any adverse effect on our environment, as well as being able to use low-grade sources of energy. Desiccant-based air-conditioning systems utilizing solar energy fulfil both the demands of researcher, so it is one of the most promising choices [8]. Several experimental setups have been built and tested across the world to study the feasibility and effectiveness of using solar-powered solid desiccant cooling systems instead of traditional VC systems. In hybrid systems, both solar-energy- and electricity-driven refrigeration systems are utilized, and progress has been made in making solar energy a primary energy source [9] This paper intends on discussing the various aspects of recent efforts in the field of desiccant dehumidification and cooling systems, and the use of solar energy in the regeneration process of desiccant wheels to improve the efficiency of its application. The study focusses on different advanced desiccant materials which may be considered as possible candidates for desiccant cooling systems, and on the progress and applications of solar technology in recent decades for the purpose of air-conditioning. At the same time, the obstacles and research and development requirements for future work are also summarized.

Desiccants are absorbents which have very high attraction towards water vapor. Desiccants are present either in solid form or in liquid form. Solid desiccants are extremely porous and use chemical adsorption processes in order to adsorb water vapor. Silica gel, activated alumina, synthetic polymers, natural zeolites and molecular sieves are some examples of solid desiccants. For the purpose of dehumidification and cooling Silica gels are used widely [10,11,12,13,14]. Liquid desiccants are commonly very strong solutions of ionic salts. Calcium chloride or lithium chloride, and nearly-organic liquids, such as tri-ethylene glycol are the common examples of liquid desiccants. Some widely used solid desiccants and their properties are discussed in the following sections.

In rotary desiccant-based air-conditioning systems, latent cooling is performed by desiccant dehumidification and sensible cooling is performed by a low-cost evaporative cooler. So, it is a combination of the dehumidification of the process air by passing it through the rotary desiccant wheel followed by cooling of the dehumidified air to the required indoor conditions. This system is made continuous by a regeneration process in which heated regeneration air is made to flow through the desiccant wheel so that the water vapor which is accumulated from the process air is removed and the wheel is made available to absorb water vapor from the process air in the next cycle. Therefore, the desiccant cooling system mainly contains three components: the desiccant dehumidification system, the cooling system, and the regenerative heating source.