Application Summary
The medical supply industry typically stores a wide variety of drugs in special air-conditioned warehouses before they are shipped to distributors. The chill room temperatures in these warehouses must be controlled and flawlessly maintained to within 2° to 8°C to ensure that the products are well preserved. Although they are in storage for a relatively short time, millions of dollars worth of drugs depend on such extremely close temperature control.

The refrigeration units are typically quite reliable and do not usually require much monitoring instrumentation. But sometimes a compressor failure occurs for obscure reasons and the situation calls for special data acquisition systems to log certain variables within the cooling system. Frequently, the instrumentation must be located on a rooftop next to the compressor while marginally protected against the hazards of the outdoor environment for days or weeks at a time.

IOtech’s Solution
Recently, a major pharmaceuticals company experienced several compressor problems, including a failure in a new installation for reasons that were quite vague. The building engineer responsible for the well being of the facility and the predictive maintenance technician quickly installed an IOtech ZonicBook next to the unit and connected several thermocouples to the compressor and refrigerant lines to measure temperature. They also monitored vibration, motor current, refrigerant, and pressure. The eZ-TOMAS program on the ZonicBook measured and logged these process variables.

During three weeks of monitoring, the data showed that the compressor tripped off several times, usually during the night. Moreover, the ZonicBook detected high discharge line temperature before these events. From these data, it was determined that the compressor’s minimum design load limit was exceeded. This produced a low refrigerant flow in the compressor, which uses the refrigerant for both cooling and lubrication. In addition, a bypass recirculation line modification is being investigated to help correct the problem.

The ZonicBook detected another fault while monitoring the compressor’s operating parameters; the motor current showed an abnormal voltage transient during the time the motor breaker was opening. Inspection revealed that the breaker relay had a burned contactor. The relay was replaced and the problem was solved.

Soon after the ZonicBook finished monitoring the first compressor, it was used on two similar units that experienced abnormal, frequent trips. After several weeks of testing, the first unit’s sister was found to have developed the same problem. This compressor had already failed once before and was overhauled within its first few months of operation.

During the time these tests were run, the ZonicBook was located on the roof in a chiefly unprotected environment next to the compressor. It survived the spring and summer weather and severe thunderstorms, which are typical in the Midwest. One time, the ZonicBook was exposed to a storm generating 85-mph winds, 1.25 in. of rainfall, and 100% humidity.

Later in the summer, the roof surface temperature reached about 130°F while the air temperature hovered around 85° to 95°F. The ZonicBook survived these extreme conditions for weeks without a single problem, but several sensors, cables, connectors, and transducers failed during the same period. The laptop computer was connected to the ZonicBook via an Ethernet cable and was located about 150 feet away in a well-protected room. It was decided to continuously monitor the condition of the refrigerant compressors and protect the contents of the warehouse even if it meant sacrificing the ZonicBook. However, in the end, the ZonicBook withstood the extremely hazardous environment and provided the building engineer and preventative maintenance technician with the data they needed to convince the compressor system designer and supplier that a redesign was crucial.

Conclusion
A reliability engineer at a medical supply warehouse used a ZonicBook to troubleshoot a failure of its chill-room air conditioning unit. The ZonicBook recorded excessively high compressor temperatures that resulted from low coolant and lubrication flow. From these data, the engineer and technician determined that the refrigerant system was improperly sized to handle low load conditions. The compressor system designer and supplier are currently making the modifications needed to remedy the problems detected by the ZonicBook.

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