Alternatives to Ozone Depleting Refrigerants in Test Equipment

Madeleine R. Johnson AGMC/MAEL 813 Irving Wick Drive West Newark AFB, Ohio 43057-5149 This paper describes the initial results of a refrigerant retrofit project at the Aerospace Guidance and Metrology Center (AGMC) at Newark Air Force Base, Ohio. The objective is to convert selected types of test equipment to properly operate on hydrofluorocarbon (HFC) alternative refrigerants, having no ozone depleting potential, without compromising system reliability or durability. This paper discusses the primary technical issues and summarizes the test results for 17 different types of test equipment: ten environmental chambers, two ultralow temperature freezers, two coolant recirculators, one temperature control unit, ·one vapor degreaser, and one refrigerant recovery system. The post-conversion performance test results have been very encouraging: system capacity and input power remained virtually unchanged. In some cases, the minimum operating temperature increased by a few degrees as a result of the conversion, but never beyond AGMC's functional requirements. INTRODUCTION The repair of aircraft inertial navigation and guidance equipment requires the use of environmental chambers, coolant recirculators, and other types of test equipment which contain refrigeration systems. There are more than 70 different types of test equipment used for processing or evaluating the inertial and navigational devices that are repaired at AGMC. Each type uses at least one of the following refrigerants: R-12, R-13, R-500, R-502, and R-503. All of these refrigerants are classified as stratospheric ozone depleting substances under the Montreal Protocol. 1•2 This paper describes the interim results of the refrigerant retrofit project at AGMC. The goal is to modify various types of existing test equipment to properly operate on alternative refrigerants that have no ozone depleting potential without compromising system reliability or durability. Selecting a replacement refrigerant and lubricant for a given application involves the consideration of several factors including thermodynamic performance (cooling capacity and power consumption), environmental properties, materials compatibility, system reliability and durability, refrigerant and lubricant availability, chemical stability, flammability, and toxicity. Moreover, the equipment conversions must be technically feasible, cost effective, and the converted units must be safe to operate. At a time when many equipment suppliers are marketing new products using hydrofluorocarbon (HCFC) refrigerants which have low ozone depleting potentials (primarily R-22 and mixtures based on R-22), this project focuses solely on hydrofluorocarbon (HFC) refrigerants that have no ozone depleting potential. This paper describes the technical approach and the primary lessons learned from the conversions completed prior to April I, 1994. REFRIGERANTS CFC Refrigerants The Montreal Protocol and the subsequent upgrades of this historic international agreement require the near-term phase out of chlorofluorocarbon (CFC) refrigerants including: R-11, R-12, R-113, R-114, and R-115. These same regulations also affect some commercially important azeotropic refrigerant mixtures3: CFC-500 CFC-12 (74 percent) and HFC-152a (26 percent)