Potential of Carbon Dioxide in Two Refrigeration Applications Commonly Encountered in the Netherlands

An inventory study of the energy use in cold storage installations in The Netherlands showed that frozen storage and combined chilled storage and distribution are responsible for a substantial part of the energy consumption of the sector. Two reference complexes including a standard number of refrigerated rooms can represent these two categories of plants. These reference complexes are used to evaluate the potential of carbon dioxide transcritical or secondary cycles in these refrigeration applications. First a second law analysis of the existing reference plants is presented identifying the contribution of the different components to the total irreversibility of the system. Then the comparable irreversibility losses are predicted when C02 is to be used in the same plants as a primary (transcritical) or secondary refrigerant. Based on these results, the advantages and drawbacks of the two carbon dioxide options (transcritical I secondary) in such plants are compared taking the existing systems into account. INTRODUCTION An inventory study of the energy use in cold storage installations in The Netherlands (Bosma [1995]) showed that frozen storage, is responsible for about 60% of the energy consumption of the companies participating in the Dutch Cold Storage Association. Combined chilled storage and distribution represents only 10% of the energy consumption of the sector. In most of these cold stores, HCFC 22 is used in the refrigeration plant. When looking for substitutes for this non-zero ODP medium, carbon dioxide appears as a candidate. Two options are then available: the application of a transcritical carbon dioxide cycle or the application of carbon dioxide in a secondary loop with, for instance, ammonia in the primary loop. The purpose of this paper is to investigate the potential of carbon dioxide in reference cycles for the two types of cold storage applications representative for the sector in The Netherlands. The system performance calculation will be based on an exergy analysis. Exergy is a measure of the departure of the state of a fluid from that of the environment and is defined as (Moran & Shapiro [1993)): (1) The terms h0 and S0 represent the enthalpy and entropy values at the environmental temperature T 0 and pressure Po· Mostly the effects of motion and gravity can be neglected and eq. (1) reduces to