Automotive Adsorption Air Conditioner Powered by Exhaust Heat. Part 1: Conceptual and Embodiment Design

Abstract

The significant power used by the mechanical compressor of an automobile (12-17 per cent during commuting for subcompact to mid-size cars) can be eliminated by powering the air conditioner with otherwise wasted exhaust heat. In the present work the conceptual and embodiment design of an exhaust-powered adsorption (desiccant-vapour) air conditioner are traced. The design is preceded by detailed discussion of automotive cooling requirements and the typical driving scenario on which the design is based. Adsorption cooling is then compared with other thermally powered cooling technologies [Stirling, absorption (liquid-vapour), and thermoelectric (i.e. Peltier)], demonstrating that adsorption is the best alternative in terms of size and mass. Next are described inventions to boost specific cooling power (SCP) in kW cooling per kg of air conditioner beyond the state of the art described in the literature while maintaining an adequately high coefficient of performance for cooling (COPc). The adsorbent is heated and cooled by light oil which in turn is heated and cooled by exhaust and fresh air. Such indirect heating and cooling achieves the required COPc, permits optimum placement of components in the vehicle, and allows the use of phase-change material (e.g. wax) to store exhaust heat, shortening the time needed to recharge the refrigerant reservoir which provides immediate cooling after start-up of a cold engine.