Energy zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Vol. 13, No. 4, pp. 333-342, 1988 0360-5442/88 $3.01) + 0.00 Printed in Great Britain. All rights reserved Copyright Q 1988 Pergamon Press plc zyxwvu ZEOLITE HEAT PUMP FOR DOMESTIC HEATING? G. RESTUCCIA, V. RECUPERO, G. CACCIOLA, and M. ROTHMEYER C.N.R. Institute for Transformation and Storage of Energy, Salita S. Lucia sopra Contesse. 39 98126 Pistunina-Messina, Italy zyxwvutsrqponmlkjihgfedcbaZYXWVU (Received 27 July lY87) Abstract-Various applications are discussed for the civil use of a device based on the adsorption/desorption of water vapour in a zeolite. Experimental work carried out with a testing system is described. Technical and economical development of such a system depends mainly on the solution of heat- and mass-transfer problems. To assess these problems, a special heat exchanger was designed and tested in a small-scale demonstration unit. We also describe the design procedure for a prototype heat exchanger and provide a description of a shell and finned-tube heat exchanger located in a zeolite bed. Details of plant assembly and experimental results are included. INTRODUCTION Gas adsorption in a solid is an exothermic process and desorption is endothermic. Conse- quently, by carrying out adsorption and desorption at different pressures, it is possible to pump heat between various temperature levels, provided that heat exchange with the external environment is carried out in a cyclical manner. For gas-solid adsorption processes, the water vapour/zeolite system is attractive in the construction of a heat pump for domestic or industrial heating and cooling. l-3 The fundamentals of operation and the thermodynamic parameters are well known for this system, but their technical and economical development depends on the solution of crucial issues of which the most important are heat and mass transfer. Since zeolites are solids with relatively low thermal conductivity, heat transfer from the thermal source towards the load via an intermediate device is the limiting factor for high specific power and economic feasibility of the system. Further, the zeolite-water adsorption heat storage is a closed-loop cycle where the mass transfer depends upon the differential vapour pressure between the water and the zeolite located in containers. Mass transfer is optimized by minimizing the pressure drop due to the zeolite packed bed or to the plant configuration. Altogether, the solution of the heat and mass transfer problems requires careful design of the plant components. OPERATIONAL MODES For domestic use, it is possible to envisage that an adsorption machine can be used both as a heat storage device with heat pump effect and as a cooling system. For both applications, there are two essential components (Fig. 1): a condenser/evaporator and a tank containing the solid adsorbent, which acts alternately as a generator or adsorber. As mentioned above, the system exchanges heat with the environment, thus the generator/adsorber and the condenser/ evaporator are provided with heat exchangers. The work cycle can be separated into two steps: the charge and discharge phase. During the former, the solid adsorbent is dehydrated by heat Q,, furnished by an external source, and the water vapour is condensed at temperature 7; into the condenser releasing heat to the user. The differential vapour pressure between generator and condenser acts as the driving force for mass transfer. In the discharge phase the evaporation of water takes place at temperature 7’, in the evaporator, generally near ambient temperature. Water vapour flows from the evaporator towards the zeolite bed, where the tWork supported by Progetto Finalizzato Energetica II CNR-ENEA, sottoprogetto “Accumulo e distribuzione del calore ,” CNR contract. EGY 13:4-c 333