Energy saving with total energy system for cold storage in Italy: Mathematical modeling and simulation, exergetic and economic analysis

With the aim of energy saving in cold storage in Italy, an integrated system (Total Energy System - TES) was considered for production of cold air, obtained by assembling compression system, absorption system and cogeneration unit (CHP) fuelled with methane-gas, in two different plant solutions: 1) TES consisting of the CHP, mechanically coupled with the compression refrigerating machine and thermically with the absorption system both designed to cool the air in the store rooms; 2) TES* characterized by the CHP, mechanically coupled with the compression refrigerating machine, designed to cool the air in the store rooms, and thermically with the absorption system designed to cool the air in a pre-refrigeration plant. A mathematical modeling and a consequent computer simulation of the behavior of both integrated system (TES and TES*) and both related conventional systems (CES consisting of a compression machine to cool the air in the store rooms and CES* characterized by two compression machines, the first cooling air in the store rooms, the second cooling air in a pre-refrigeration plant) was carried out. As an overall results, an energy saving of 21÷16% was calculated. Considering the difficulty of comparing the different types of energy involved, an exergetic analysis was also carried-out, confirming a better exergetic efficiency of TES vs. CES. Finally, an economic evaluation was also conducted with a very attractive profitability index for TES and TES* systems fuelled with natural gas. The economic analysis showed that the use of bio-methane, in the TES system, is profitable up to a bio-methane cost of 0.46 €/m3.