(568b) Non-Vapor Compression Adsorptive Heating and Cooling Technology

Global warming is perhaps the largest threat facing mankind in the 21^st century. There are only a limited number of ways this global warming threat can be mitigated. One such way is to eliminate the use of HFC-134 as a refrigerant in air conditioning systems in various military, commercial and residential platforms. It is purported that water vapor can be used instead of HFC-134 as a refrigerant, but not as a replacement refrigerant in existing air condition systems. An entirely new non-vapor compression air conditioning system is proposed based on proven concepts borrowed from pressure swing adsorption (PSA) technology. This new technology is referred to simply as a PSA heat pump (HP).

PSA is commonly used in industry for the separation and purification of gas streams, like in the production of oxygen from air and in gas dehydration. Commonly, in PSA, an adsorbate fluid is moved into a substrate adsorbent. Gas species adsorb more to an adsorbent at higher pressures and desorb reversibly from the adsorbent at lower pressures. If the adsorbent is selective for one gas species over another, a separation or purification can be achieved. The same principle of adsorption to and reversible desorption from an adsorbent can be applied to the pressure swing cycling of a pure gas or vapor for energy storage or transfer. Hence, a PSA HP system utilizes water vapor under vacuum for cooling and heating applications with high efficiency.

It must be emphasized that this PSA HP system is not based on the traditional concept of an adsorption heat pump, where no mechanical pump is used. In that kind of system, the transport of the coolant (working fluid) is carried out instead by heating/desorbing at high pressure in one bed and by cooling/adsorbing at low pressure in another bed, thereby eliminating the need for a compressor or pump. The major problem with this traditional approach is the excessively small coefficient of performance (COP) (< 1.0) mainly due to electrical energy being required for bed regeneration during the heating/desorbing cycle step. In this new PSA HP technology, the adsorption/desorption phenomena do not replace the role of the pump; on the contrary, it requires and thus takes advantage of a pump being present. Hence, electric power is needed only to operate the pump, not for electrically heating the bed. What is identified as isothermal condensation in a traditional vapor compression HP system is carried out by adsorption at high temperature and pressure in this new PSA HP system, and what is identified as isothermal evaporation in a traditional vapor compression HP system is carried out by desorption at low temperature and pressure in this new PSA HP system.

This new non-vapor compression PSA HP cooling system cycles an adsorbate fluid such as water vapor between two adsorbent beds such as BPL activated carbon in a closed loop under vacuum. A vacuum pump is utilized to swing pressure between a high-pressure water vapor adsorbed state and a low-pressure water vapor non-adsorbed state. During the pressure swing process, when water transitions from a fluid state to an adsorbed state, heat is released (exothermically) during the adsorption process which can be ejected from the system to heat an object or space or be ejected to a thermal dump such as the atmosphere. During the pressure swing process, when water transitions from an adsorbed state to a fluid state, heat is absorbed (endothermically) during the desorption process which can be extracted from an object or space to cool the object or space. This presentation will describe this highly efficient means to transfer thermal energy to and from spaces for cooling and heating by cycling water vapor back and forth from a series of heat exchanger tubes filled with just BPL activated carbon via simulation with the UofSC dynamic adsorption process simulator (DAPS).