Development of a Compact Adsorption Heat Pump System for Automotive Air Conditioning System

In order to reduce the energy consumption of the automotive air conditioning system, adsorption heat pump (AHP) system is one of the key technologies. We have been developing compact AHP system utilizing the exhaust heat from the engine coolant system (80-100 °C), which can meet the requirements in the automotive application. However, AHP systems have not been practically used in automotive applications because of its low volumetric power density of the adsorber. The volumetric power density of the adsorber is proportional to sorption rate, packing density and latent heat. In general, the sorption rate is determined by mass transfer resistance in primary particle of an adsorbent and heat and mass transfer resistance in packed bed. In order to improve the volumetric power density of the adsorber, it is necessary to increase the production of the sorption rate and the packing density. In the present study, we suggest a compact adsorber which is characterized by honeycombed composite plates of an adsorbent with thermal conductive filler bonded to a plate-type heat exchanger. In the suggested adsorber, the heat and mass transfer can be controlled independently. The heat transfer resistance is controlled by the effective thermal conductivity and the thickness of the composite plate, and the mass transfer resistance is controlled by the effective diffusion coefficient and the wall thickness of the honeycombed structure. In addition, the packing density is controlled by the aperture ratio of the honeycombed composite plate. We found that the adsorption and desorption rate and the packing density were 1.33 times and 1.36 times larger than a reported coating-type adsorber respectively. The volumetric power density of our suggested adsorber is comparable to that of an mechanical compressor.