ASHRAE Journal - February 2009 - (Page 34) Electronic Expansion Valves Vs. Thermal Expansion Valves By Renato Lazzarin, Daniele Nardotto, and Marco Noro, Ph.D. S toring cold and frozen foods uses approximately 40% to 50% of electricity in supermarkets. Open vertical display cabinets, in particular, are large users of electrical energy. Many refrigerating machines use thermostatic expansion valves (TEVs). TEVs are the most widespread expansion device, but they have some characteristics that can limit versatility and performance of the machines. For example, this valve requires a minimum pressure drop between condensation and evaporation. This prevents possible advantages of low condenser pressure for air-cooled condensers. A minimum amount of superheating must be provided to avoid possible hunting of the valve. Some plants are more sensitive to negative aspects of TEV regulation because of plant specifics, type of duty, or distribution of cooling load during the year. Refrigerating machinery in supermarkets is just a characteristic example. One solution to the problems of TEV 34 ASHRAE Journal are both at the outlet of the evaporator. The two signals are elaborated by a regulator that controls, in real-time mode, the valve opening. To evaluate the possibilities of using EEV versus TEV, a large supermarket located on the Tirrenic coast of Italy, not far from Pisa in North Italy, was retrofitted with the EEVs installed in parallel to the TEVs to operate the plant alternately with the two technologies.4 A simulation model was developed to compare the two technologies on an annual basis from the energy and economic point of view under different conditions. The comparison was made for three climates: Milano, Roma and Trapani (for which hourly test referAbout the Authors Renato Lazzarin, is a professor at the Department of Management and Engineering, University of Padova, Italy, President AICARR (Italian Society of Heating Refrigerating and Air-Conditioning Engineers) and Commission E1 IIR. Daniele Nardotto, is a doctoral student and Marco Noro, Ph.D., is a researcher at the Department of Management and Engineering, University of Padova, Italy. is the electronic expansion valve (EEV). This electrically driven control device has been studied experimentally and theoretically in recent years,1,2,3 and it is widely available. It controls the refrigerant flow at the evaporator by means of a pressure sensor and a temperature sensor, which ashrae.org February 2009 http://www.ashrae.org
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