Energetic analysis of electronic vs traditional expansion valves in air conditioning

Adopting electronic expansion valves in air conditioners enables an appreciable energy saving with respect to the same installations equipped with traditional thermostatic expansion valves. This is due to the fact that electronic valves allow a lower condensation pressure in systems equipped with air cooled condensers, which is adjusted to variations in outside air temperature. Furthermore, PID control over the superheating leads the best use of evaporator under every condition (lower mean superheating), thus increasing the refrigerating capacity of the equipments. This paper reports on the energetic analysis of the operation of eight direct expansion air conditioners (total capacity 120 kW) installed at the Telecom Italia plant control room of Corticella (Bologna, Italy). Air conditioners are equipped with both thermostatic and electronic expansion valves, alternatively activated by solenoid valves on a daily basis, in order to compare the two systems at the same environment and similar load conditions. The annual analysis is done by means of a transient simulation program to simulate the behaviour of the air conditioners with the two systems, also taking into account energy savings obtained by the PID control of the plant introduced with the electronic valves. It is also reported the first results of a campaign of measurements that will extend from February to December 2006.