Test Results: Cycled Settings on Temperature Control Units

Modality Solutions provides insight into the performance and influence of cycled settings on temperature control units.  

What is the impact of the cycled setting? We have results to share. While running a series of controlled tests for a client, the TCU was inadvertently set to cycle mode allowing us to compare and contrast the results of a “continuous” versus “cycled” setting.

Most if not all carriers of temperature sensitive pharmaceutical products have clear instructions to set the temperature control unit (TCU) to run in “continuous” operation.  

Why? The fan and compressor unit remain active and operating at all times to minimize the temperature differentials within the trailer. But, the TCUs have an alternate setting for fuel saving. In this mode, the fan and compressor will cycle off when the set point temperature is achieved. The TCU will “wake up” when the thermostat temperature reads 3 to 5 degrees from the set point.

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Temperature controlled storage

The temperature of the air passing through the supply vent of the trailer is an indirect measurement of the mode of operation of the TCU. In continuous mode the extreme in temperature variation is plus or minus 3 degrees of the set point. In cycle mode, the lag time to activate the TCU can result in temperature spreads of over 5 degrees from the set point. 

  There is additional variance in the cycle mode because the fan operation also contributes to the overall distribution of temperatures within the trailer. The chart below is an example of cycle mode for a CRT at a cold exposure. The temperature variations violate both sides of the CRT limits. 

Clearly, the cycle mode will not meet the tight tolerance for refrigerated (5C) shipments. Controlled room temperature (CRT) shipments are also placed in jeopardy depending on the specific definition of CRT.

 The chart below is an example of continuous mode for a refrigerated (5C) shipment at a cold exposure. The temperature variations are well within normal limits. 

The results shown are only for the cold tests. The hot tests results were similar. The fuel savings between the two modes are less than $20 for a 24-hour period. These savings cannot justify the risk of wider trailer temperatures for either refrigerated or CRT pharmaceutical products.

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 If the cycle mode is used at all, it would only be for frozen shipments when the setpoint is safely set well below the critical high temperature. 

In regards to locating the most compatible warehouses and cold storage facilities, Gary Hutchinson outlines four key steps of the decision making process.

(1) engage in the strategic network design of cold chain logistics operations;

(2) offer deep market knowledge of 3PL providers, thermal packaging suppliers, and compliant monitoring approach and technologies;

(3) recommend 3PLs and facilities to ship and store commercial drug product to wholesalers and distributors; and

(4) follow-up by assessing GDP compliance of key supply chain partners.