Fixed bed and rotatory desiccant systems have been widely studied and used for dehumidification; they suffer from decreasing sorption capacity as the desiccant’s temperature increases due to the released heat of adsorption. The desiccant coated heat exchangers (DCHX) overcome this limitation. Such heat exchangers are able to deliver combined heat and mass transfer between the process air and the working fluid. The process air can be cooled and dehumidified simultaneously by pumping cooling water/refrigerant in the DCHX. The DCHX has to be heated cyclically to regenerate the desiccant material. This paper presents a review on the studies conducted on air-to-liquid DCHX. It summarizes various modeling approaches used to simulate the performance of DCHX as well as the experimental studies conducted to validate these models. It also reviews the current and potential applications of these heat exchangers. Current work in this field consists of experiments conducted on the DCHX as standalone equipment (i.e. component level) as well as an integrated component into cooling and dehumidification systems (system level). The integration of the DCHX in such systems was found to improve the COP, leading to energy savings.

Energy use for space cooling has increased by 156% from 1990 to 2010 in the Canadian residential sector. In many parts of the country, the increasing use of electrically driven air-conditioners has begun to shift the peak load on the electricity grid from the coldest days of winter to the hottest days of summer. Many of Canada’s major electric utilities providers rely on fossil fuels to generate the additional capacity needed to meet the peak demand, resulting in significant greenhouse gas emissions. Solar-driven sorption chillers remain one of the possible solutions for shaving the peak loads experienced by the electricity grid. This paper presents a review of the recent developments in the research of adsorption and absorption chillers, as well as a comparison of the two technologies based on the latest published experimental results found in the literature. Adsorption chillers continue to evolve in their design, including the use of new consolidated and composite adsorbents, the integration of coated adsorbers into internal heat exchangers, and newly developed advanced cycles for heat and mass recovery. While the physical design of adsorption chillers continues to be advanced, the development of absorption chillers for solar cooling applications has largely been focused on optimizing the system as a whole through improved control strategies and the implementation of newly developed high performance solar collectors. Finally, the paper aims to assess the current state of development of solar-driven sorption chillers to provide insight into their applicability in the Canadian residential sector, as well as the remaining challenges facing this technology.

Trigeneration systems are closely associated with sorption cooling technology because prime mover waste heat can be recovered to produce cooling. The working pair and cycle type of the sorption cooling system needs to be matched to the waste heat temperature of the prime mover, as well as with the capacity and application of the trigeneration system. A residential trigeneration system with a 4 kW elec internal combustion engine, a 220 gallon (830 L) hot water tank and a 3 kW adsorption chiller powered by 70°C waste heat with separate sensible and latent cooling control strategy is presented in this study. Transient experiments were conducted under 5 day long hot water and space cooling load profiles from a simulated house to evaluate the performance from a practical perspective. The fuel consumption was measured and compared with that of two baseline systems. An analytical criterion was derived and discussed to further evaluate the trigeneration system with different loads under different climates. It was found that the presented residential trigeneration system could save about 30% of fuel consumption compared with conventional off-grid operation mode, but is not more fuel efficient than the conventional on-grid and vapor compression cooling combination.

A new concept for long-term solar storage is based on the absorption properties of aqueous calcium chloride. Water, diluted and concentrated calcium chloride solutions are stored in a single tank. An immersed heat exchanger and stratification manifold are used to preserve long-term sorption storage, and to achieve thermal stratification. The feasibility of the concept is demonstrated via measurements of velocity, CaCl 2 mass fraction, and temperature in a 1500 liter prototype tank during sensible charging. Experiments are conducted over a practical range of the relevant dimensionless parameters. For Rayleigh numbers from 3.4 × 10 8 to 5.6 × 10 10 and buoyancy ratios from 0.8 to 46.2, measured Sherwood numbers are 11±2 to 62±9 and the tank is thermally stratified. Convective mixing is inhibited by the presence of a steep density gradient at the interface between regions of differing mass fraction. The predicted storage time scales for the reported Sherwood numbers are 160 to 902 days.

Thermally activated systems based on sorption cycles, as well as mechanical systems based on vapor compression/expansion are assessed in this study for waste heat recovery applications. In particular, ammonia-water sorption cycles for cooling and mechanical work recovery, a heat transformer using lithium bromide-water as the working fluid pair to yield high temperature heat, and organic Rankine cycles using refrigerant R245fa for work recovery as well as versions coupled to a vapor compression cycle to yield cooling are analyzed with overall heat transfer conductances for heat exchangers that use similar approach temperatures for each cycle. Thermal-to-mechanical conversion efficiencies of ∼9%, upgraded heat delivered at 150°C, or cooling coefficients of performance of 0.5–0.7 are realized for source temperatures of 120°C, with a nominal 1 kW of heat extracted from the waste heat stream. Ambient sink temperatures of 35°C are used, as well as indoor return air temperatures of 27°C for cycles that produce cooling at 8°C. Comparative assessments of these cycles on the basis of efficiencies and system footprints will guide the selection of waste heat recovery and upgrade systems for different applications and waste heat availabilities. The increased implementation of such waste heat recovery systems in a variety of applications will lead to decreased primary source inputs and sustainable energy utilization.

A new IEA Task has recently been initiated to develop new storage materials. This Task is implemented as a Joint Task between the Solar Heating and Cooling (SHC) and Energy Conservation through Energy Storage (ECES) Implementing Agreements, and is entitled “IEA SHC/ECES 42/24: Compact thermal energy storage: material development for system integration”. The objective of this Task is to develop advanced materials for compact storage systems, suitable not only for solar thermal systems, but also for other renewable heating and cooling applications such as solar cooling, micro-cogeneration, biomass, or heat pumps. The Task will cover phase change materials, thermochemical and sorption materials, and composite materials and nanostructures, and will include activities such as material development, analysis, and engineering, numerical modelling of materials and systems, development of storage components and systems, and development of standards and test methods. The main added value of this Task is to combine the knowledge of experts from materials science as well as solar/renewable heating and energy conservation. The Task has officially started on January 1, 2009, and will last for four years.

The design a solar-sorption refrigerator to be used in the warm and humid climate of Mexico, the most critical environmental conditions and most demanding climatic zone for cooling technology, requires that the adsorption capacity of the composite sorbent to be characterize. It must be verified that the composite sorbent such as silica gel, calcium chloride and various natural zeolites, with different substances in a gaseous state as sorbate, (water, methanol and ethanol), has hydrogen bonds that can be united and broken easily, measuring the amount of energy required by the sorption-desorption mechanism.