Saturday, September 16, 2017

Does Your Cold Room or Chamber Need a Backup Cooling System? Part One

cold room in laboratory facility
Laboratory Cold Room
The applications for refrigerated space are extensive and varied. Materials, products, and processes are housed in cold cabinets (refrigerators) and rooms because the stored contents will deteriorate or otherwise be rendered useless through exposure to elevated air temperature. Cold spaces have some sort of system or arrangement that maintains the interior temperature below that of the surrounding space. The continuous operation of that system is essential to keeping the space cold and protecting the stored material. There is risk of loss associated with the operation of the equipment. Properly evaluating the probability and extent of a loss due to equipment failure is a key element in determining whether to invest in a backup cooling system for a cold space. The first step in the evaluation process is to define what constitutes failure.

Define failure in quantitative terms.

In order to make good decisions about how to proceed, or even if you should proceed at all, it is useful to describe failure conditions in a way that can be put to use in designing a solution that reduces the risk associated with it. "The cold room is not cold" is an accurate, yet insufficient description of a failure condition. It sheds little light on what should be done with the mechanical or control systems to reduce risk. Stakeholders tend to think of performance and failure in terms of the product or process contained within the cold space. It is most useful to describe failure in terms of system operation or performance, since these items can be used to develop a workable design or plan to address the risk. Here are some suggestions of things that might be included in your description of failure.
  • Temperature Excursion - Define an unacceptable deviation from setpoint conditions in terms of time and temperature. For example, "Temperature five or more degrees above setpoint for greater than seven minutes." This description provides a quantified design target. Your concern may be stored material temperature, rather than cold space air temperature, but control systems are most likely to measure and regulate air temperature. Describing a temperature excursion in terms of air temperature is most useful.
  • Equipment Operation - Most cold space temperature excursions are preceded by an event involving equipment or component malfunction. Establishing a list of equipment performance requirements necessary for proper operation can be useful in evaluating how deeply you may want to pursue the  reduction of risk. A simple example, confirming the refrigeration machinery is operating in response to a controller command, can be used to reduce risk of temperature excursion because the machinery failure can be detected before the temperature excursion is evident. An in depth analysis of equipment operation can produce a stunningly large list of events that must occur for proper operation. Not all will be candidates for action.
  • Improper Operation - This category includes things that the user may do, or coincidental things that may happen, that negatively impact system operation and will lead to failure. Some examples include over or improper loading of the space, failure of building support systems or utilities, and allowing excessive infiltration of air from the surrounding space (leaving the door open). Once again, a careful examination will produce a large list of possibilities which must be pared down to a workable few that can deliver cost effective protection.
It will be effective to bring in a cold room or refrigerator specialist and make them part of your evaluation team. As you can probably see, there are some fairly technical issues involved once you get beyond a description of temperature excursion. A specialist can help bring the technical issues into focus and provide explanation of each that stakeholders can use to make informed decisions.

In the next post, I will cover some strategies for reducing risk for cold space stakeholders. Share your cold storage and process requirements and challenges with equipment experts, leveraging your own knowledge and experience with their expertise to develop effective solutions.

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