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

Creative cooling system designs, coupled with smart
controls, can improve cold room performance and reduce risk.

In Part One of this series, defining cold storage risk in quantifiable means was the major topic. Part Two illustrated that there are several operating schemes that can be employed to protect against mechanical failure in a cold storage facility, whether a reach-in cabinet or a building sized enclosure.

Effectively implementing a plan that reduces risk in cold storage facilities will require participants with more than just a familiarity with refrigeration system operation. Here is a list of some subjects of technical expertise that should be part of the solution.

• Refrigeration system operation - This seems obvious, but what is needed is a somewhat more detailed knowledge of how refrigeration systems work. The expertise is useful for developing a hierarchy of all the potential failure scenarios, how to detect them and respond.
• Refrigeration compressor failure - Risk reduction involves focusing on all the things that can go wrong. Not everyone is adept at doing this, but for the purposes of this project it is a useful skill. 
• Sensing and measurement technology - Cold space temperature failure only occurs after mechanical failure. Relying on temperature as the only indication of failure overlooks the benefits derived from direct monitoring of equipment operation.
• Control system complexity - Regulating and coordinating all the various facets of system operation is challenging when multiple cooling systems are involved. The control system must be capable of delivering proper cold space performance under a number of operating equipment scenarios. Two cooling systems could be active, or either of the single units in coordination with one another or alone.

The control system is the key to gaining the most advantage of any additional expense for backup refrigeration equipment. Monitoring equipment operation will enable early detection and alert for a number of indicators of impending or immediate equipment malfunction. Here is a short list of the essential performance parameters to monitor.

• Room temperature - Obvious, with no explanation needed.
• Refrigeration compressor motor current - This is easily and economically accomplished. It provides an indication of whether the compressor is operating in response to controller command, as well as key information about compressor performance.
• Refrigerant discharge and suction pressure - This can be used to assess system performance in relation to an established baseline. Additionally, there are numerous opportunities to utilize discharge and suction pressure relationships as indicators of refrigeration system health.
• Evaporator fan motor current - The fans that move air through the cold space are driven by one or more motors which are part of the equipment needed for expected performance. Motor health and performance can be determined using fan motor current.

There is plenty involved in deriving the maximum benefit from the additional cost for backup equipment. System control is easily accomplished with a properly programmed PLC. Understanding the interrelation of multiple systems operating on a single cold space is key to implementing a successful solution.

Share your cold storage concerns and challenges of any scale with equipment planning experts. Leverage your own knowledge and experience with their application expertise to develop an effective solution.

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

The usage pattern of a cold space will determine how
best to reduce the risk from mechanical failure.
Image courtesy of Percival Scientific

In Part One of this series, what may define failure in cold room or refrigerator operation was discussed, giving the reader a starting point in evaluating whether to incorporate a backup refrigeration system into a cold space design. Operational failure can, and does, arise from countless sources. Some can be expected and anticipated, others not. Regardless of the source of failure, though, having a backup plan in place can help avoid damage to cold stored materials in all but the most catastrophic of events.

Once a decision is made to establish a contingency or backup plan, the form of the backup strategy needs to be addressed.

All backup strategies have a common goal of keeping the cold material cold. A simple clear goal, but with numerous ways it can be achieved, and each option may provide its own array of additional benefits or attributes which make it more suitable for a particular facility, budget, or other constraint.

"Twins" - An obvious backup cooling strategy is to provide a copy of whatever system is required for full range operation of the cold space. While this option offers an easy decision, it is likely to be one of the more costly ways to proceed. Proper design of a cooling system is based upon a load calculation that accounts for all the heat gain to which the cold space will be exposed. The sum of the loads will determine the size of the cooling system. Some applications that require close temperature control, or are subject to excessive door opening time, large warm mass additions, fresh air induction, dehumidifier operation, or a host of other heat sources could have comparatively large cooling systems. Purchasing and installing a full capacity redundant cooling system, in these cases, should be considered only when full operational capability of the space is the only option. When one system fails, the backup can maintain the space conditions without any change needed to the way in which the space is used.

Relocate - When the amount of stored material is manageable and a suitable space can be identified, it may be most effective to maintain unused cold space that is designated for use in the case of equipment failure. This likely will apply best to installations of refrigerated cabinets (refrigerators), where stored materials can be easily moved from the failing refrigerator to the backup space. The backup space should be kept in operation continuously, so its proper operation is confirmed. This backup scheme may be well suited to facilities with numerous refrigerated cabinets in use. The common backup cold space serves multiple users. A challenge specific to this plan is keeping the backup cold space from being used as normal cold space by any user for any number of reasons.

Full Load / Base Load - If a cold space is to have two cooling systems, an alternate to the "Twins" scheme can be considered. An analysis of space usage may reveal patterns that can be adjusted in case of a failure of the primary system. If a change in space usage can be enforced during periods when the primary cooling system is inoperable,  a smaller capacity, lower cost cooling unit can be incorporated as the backup unit. This option can impose some additional control challenges, but also some potential energy saving benefits, which will be discussed in the next installment.

Half Load / Full Load - If there are substantial lengths of time during which the cold space faces a low and stable heat load, another operating scheme may be considered for providing backup cooling. The full heat load component of the design is split evenly between two cooling units. One of the cooling units will be sufficient to maintain cold space temperature during most of the day, with the second unit available to provide additional capacity when needed. The second unit also serves as a backup in case the primary fails. This scheme will require adjustment to room usage in the case of failure, similar to that of the Full Load / Base Load plan previously described.

There are numerous other risk reduction schemes that can be developed to deal with the potential of cooling system mechanical failure. Some schemes may provide energy savings during normal operation, as well. A key element of real risk reduction and maximizing the benefit of the additional equipment cost lies in the control system. The controls need to be capable of detecting failure and taking appropriate action in response to a large matrix of possible conditions. The takeaway from this article is that there is more than one solution to the challenge. Approach the problem with an analysis of how the cold space is utilized, before selecting equipment. The subject can be more complex than it appears, especially to those unfamiliar with control systems. Enlist the help of experienced equipment specialists to help identify the risks, assess cold space usage, and develop an effective plan.

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

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.

Full Featured Environmental Chamber Control System

The IntellusUltraConnect C9 adds a range of remote
connectivity functions to the operational functions of the
IntellusUltra C8.
Image courtesy Percival Scientific

Percival Scientific has a long history of designing and manufacturing environmental chambers and plant growth chambers for life science industries and institutions. Those years of experience are part of the IntellusUltra series of control units that serve as the user interface and operating unit of the company's line of environmental rooms and chambers.

Ease of use is the hallmark of the controllers. Some applications, especially those for plant studies, can require multi-step profiles that change temperature, humidity, lighting, and other functions. Entering or editing a profile with IntellusUltra is intuitive and simple.

In addition to a plethora of operational features, the "Connect C9" version offers a range of remote connectivity functions that can keep users in touch with their equipment and research anytime and anywhere. From the Percival Scientific website...

• Remote connectivity and monitoring with e-mail notifications.
• On-board USB connection allowing for real time data logging with up to four gigabytes of data storage. Simply use a portable USB stick to download your data to analyze on any other capable device.
• An on-board Ethernet connection allows direct monitoring and analysis of chamber conditions.
• Available remote monitoring software has been optimized to interface with the major web browsers.
• Ability to upgrade to our cloud-based service securely and confidently monitor and backup your research data

Solid control of environmental parameters, plus connectivity that enables access to the system from anywhere. More detail is provided in the document included below. Share your environmental room and chamber plans and challenges with experienced lab equipment professionals, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Plant Growth Chamber Environmental Controller from Atlantic Technology Group, Inc.