Effective energy management through on-line monitoring and control: A case study in cooling chambers of a Blood Center

Cooling systems are widely used for the preservation of food products, chemicals, pharmaceuticals, blood derivatives and in many other industrial applications. To avoid spoilage, products must always be kept in a suitable temperature range, with the lowest possible temperature fluctuation. As these devices have to be kept constantly energized, its share of contribution to the total energy consumption is generally very significant. An effective control of temperature variations for each cooling unit by means of a continuous monitoring system, in real time, turns possible the tracing of the temperature at which each product was actually submitted and thereby ensure that the quality of the product has been maintained (or not). A feedback control system, duly designed and tuned, implies reduction of temperature variations and consumed energy besides improving the cooling condition and the product quality. This paper presents the results of a system capable of providing the monitoring and control of industrial refrigeration equipment using a dedicated platform in which measurements of the electrical current and of the internal and external temperatures are continuously taken. From these measurements, dynamic models, correlating the internal temperature of the chamber and the electric current, were established and an automatic control system implemented. Results of the application of this management system to the Blood Centre of the State of Minas Gerais (Hemominas) are presented. The use of energy is more intense in air-conditioned environments in the spaces used for collection and processing of blood and in cold chambers for storage of products. It has been observed that changes in inventories and in the external temperature have substantial impact on these loads. In order to check which variables or conditions affect the thermal and energy profile, special computer routines have been used to establish the existing correlations among the energy consumption, the air temperature and the thermal load, to which the refrigeration chamber is subjected.