Recent Developments in Coating Technologies for Adsorption Heat Pumps: A Review

Abstract

The use of adsorbent heat pumps as heating and cooling systems is particularly relevant thanks to their ability to exploit low-grade heat (e.g., below 90 °C) from renewable energy sources and waste energy streams with prospective applications in several fields, e.g., industrial and residential. Their development began in the 20th century and is still in full evolution. The great interest in their improvement and optimization was determined by some key factors inherent to their sustainability compared to traditional refrigeration systems (e.g., low electricity consumption and the low environmental impact of the employed refrigerants). Recently, strong efforts have been dedicated to increasing the achievable heating/cooling power density of this technology through the development of innovative adsorbent coating technologies. Indeed, the deposition of thin coatings on the surface of the heat exchanger could reduce the heat transfer resistance existing on the adsorbent material side, thus increasing the overall adsorption dynamics. Three main approaches have been assessed, namely a thick consolidated bed, binder-based composite coatings and in situ directly crystallization coatings. This paper provides a brief overview of some of the main achievements related to adsorbent coating technology developments for adsorption heat pump applications.

Zeolite NaY-Copper Composites Produced by Sintering Processes for Adsorption Heat Transformation—Technology, Structure and Performance

“…. 95 • C 850 Function [57], data [58] Specific heat capacity of binder in J/(kg*K) 1000 estimated Specific heat of copper in J/(kg*K) 382 [59] Specific heat of aluminum 900 [59] STM = C p,tot M sorb (11) If we compare the adsorbent mass per composite volume of sample we55 with the adsorbent bed density of 524 kg/m 3 (Granules) it can be stated that the additional copper fibers are almost entirely placed in the void space between the particles. However, the STM of the composite is more than twice as high as the adsorbent specific heat capacity.…”

“…They are, however, still not widespread in the market because of deficiencies regarding costs and efficiency in comparison to conventional vapor compression heat pumps. In order to overcome those limitations intensive research and development activities have been undertaken regarding the development of new adsorbents with high adsorbing ability [5][6][7] and thermodynamic features matching the working conditions, highly efficient evaporation and condensation elements [8,9], and more efficient heat exchanger designs [10,11].…”

“…Among those, the highest technological readiness level was reached for zeolites and zeo-type materials like SAPO-34 [1,4,12]. All those adsorbents are characterized by a low intrinsic thermal conductivity [10,11]. In order to obtain high power densities of the adsorption systems, the adsorbent is combined with heat exchanger structures, typically made from metals like aluminum, copper, or steel.…”

“…Since the adsorption process is a coupled heat and mass transfer process, it is important to minimize all transport resistances in order to achieve a high power density of the adsorption heat exchanger [10]. Various designs have been developed over the past years [11,13,14].…”

Materials research and development needs to enable efficient and electrified buildings

“…Recent efforts have investigated coating the adsorbent in a thin layer onto the heat exchanger surfaces to improve heating/cooling power density by reducing heat transfer resistance. 67 Developing novel adsorbent formulations and processing techniques optimized for coating heat exchangers could lead to important improvements in adsorbent heat pump technology.…”