When Cold is Critical (June 2000)
Keeping Equipment CoolDedicated-precision, or process, fluid chillers and self-contained indoor precision chillers possess a number of distinct advantages as opposed to building or central system installations for a variety of industrial and medical applications. For example, total cooling control, reliability, corrosion resistance, continuous operation, energy efficiency, and application flexibility are all key benefits of a dedicated chiller system.
Fluid-cooled medical and industrial process equipment are sensitive to fluctuations in temperature, and lack of a continuous supply of cooling fluid could result in major downtime due to equipment failure and component damage.
There are a number of dedicated-process chiller systems available that are designed specifically to prevent unanticipated equipment downtime or component damage due to improper cooling. Dedicated-process chillers, in particular, are one of the most effective solutions to this type of problem since these units are designed to provide specific, capacity-matched cooling protection, proper temperature/water flow, and year-round operation for industrial equipment and other fluid-cooled systems. Unlike central system chillers, dedicated-fluid chillers can provide fail-safe reliability through a variety of designed-in mechanisms.
For this reason, it is imperative for specialized medical equipment and laboratory instrumentation to have adequate chiller protection for functions that require it. Not only do such units improve process integrity and accuracy, they also extend equipment life and boost operational economies since they significantly reduce downtime. Needless to say, chiller downtime means equipment downtime, which, in turn, means loss of revenue. In addition to reducing downtime, dedicated chillers also help medical/lab facilities comply with increasingly stringent EPA regulations governing the discharge of contaminated wastewater, by incorporating closed-loop designs within the system.
Choosing the Right Chiller SystemCentral building chiller systems possess inherent disadvantages. For example, a central building chiller is usually designed to operate on a specific schedule when night or seasonal setbacks are programmed to increase water temperature for energy conservation. This will adversely impact any process that depends on lower water temperatures. In most cases, there is no provision for winter operation; and if there is such a provision, it soon becomes disproportionately expensive to operate a large central chiller for long periods simply to supply the relatively small cooling needs of an individual piece of equipment. With a building chiller, energy consumption for the pumps alone may exceed the total energy consumption of a dedicated chiller.
Building-wide chiller systems normally do not provide the high level of monitoring and control capabilities characteristic of dedicated chillers. While there is a general trend in the hvac industry towards having equipment communicate to building management systems, dedicated chillers allow for increased flexibility, such as switchover schemes.
And as opposed to a building system, dedicated chillers can be customized to specific applications. In some cases, they can be designed with emergency alarm capabilities that allow backup procedures to become activated if a water source faulted. Thus, for troubleshooting purposes, a dedicated chiller can be customized with a variety of options that augment basic capabilities. In short, the process becomes wholly dependent on what the building system can or cannot do, while the dedicated system can be customized to specific applications.
Good Equipment HealthUnlike building chillers, precision chillers are dedicated to specific medical/lab facility fluid-cooled process equipment operations. These systems are precision-matched to the cooling needs of this equipment or process function and they cool only that equipment. In addition, the process chiller operates year-round, independent of the building chiller. Thus, it cools equipment whether the central building system is operating or not and whether the ambient temperature surrounding the equipment is hot or cold.
Dedicated-process chillers also provide precise temperature control since they are designed to react to changing loads more readily than central systems. Thus, more precise temperature regulation is an inherent feature of a dedicated chiller. The central chiller must allow for not only normal temperature rise between chiller and processor, but must also take into consideration a variety of outside influences such as flow rates which are subject to change.
Medical/lab equipment can be adversely affected by seemingly minor fluctuations in temperature that can result in unanticipated downtime, premature equipment failure, and increased maintenance costs. Fluid-cooled process equipment can be extremely susceptible to such conditions because these systems demand a continuous supply of cooling fluid. For this type of medical/lab process application, small, rugged chillers are needed for instrument components considering their operating environment, and they must be able to operate in low ambient temperatures as well as be able to circulate a wide variety of fluids.
In addition to these concerns, more stringent EPA legislation on dumping wastewater has mandated recirculation. As a result, users prefer to use closed-loop systems that are typical in a dedicated-process chiller unit. The increase in demand for sophisticated medical/lab instrumentation has created a commensurate demand for ancillary chillers due to the fact that such units are increasingly being used to improve overall equipment reliability. And improved reliability means reduced downtime and increased operational revenues.
Dedicated-process fluid chillers and processor cooling units provide precise temperature control for fluid-cooled equipment in industrial environments, medical facilities, and laboratories. This type of equipment needs properly chilled fluid systems in order to operate reliably. And for medical equipment applications, for example, the dedicated-process chiller provides a clean, nonferrous cooling loop required by sensitive systems.
As an example, process chillers are close-coupled to MRIs, CT scanners, PET scanners, linear accelerators, electron microscopes, cryogenic compressors, or other sensitive medical equipment to provide proper levels of protection. The dedicated chiller is matched to the cooling needs of the equipment and cools only that equipment, it is not cooling the room, or building, or any other area as is the case with building chillers. Close coupling allows for precise temperature control and ensures that clean water circulates around the cooled equipment. The dedicated-chiller system is also factory-tested and packaged to ensure fast on-site installation.
Features to Look ForStandard features of dedicated chillers can include Nationally Recognized Testing Laboratory (NRTL) approval that allows for quick and easy inspection and building code conformance certification. Certain systems are also available in three fluid types (water, ethylene glycol, or propylene glycol) while capacity and fluid flow rates can be precision-matched to the user’s system needs.
Some chillers are fabricated with a stainless steel fluid reservoir to reduce temperature fluctuations due to rapidly changing loads. In addition, precise temperature control is ensured with a hot gas bypass valve that balances varying heat loads for precise control. Because the valve reduces compressor cycling, it also reduces component wear.
Optional features include an emergency water bypass or an emergency bypass system, each of which automatically switches operation to separate water supplies in case of flow or temperature problems. The emergency bypass option meets EPA guidelines for systems using glycol solutions since it isolates the chiller from the fluid source so as not to deleteriously affect the environment. The key to this function is that it separates the backup source from the dedicated-process cooling loop, thus preventing the water and glycol from being mixed.
Another type of chiller, a self-contained, indoor-precision chiller, features built-in dependability, energy efficiency, and application flexibility. This type of system can also be designed to use redundant modules with switchover capabilities. This type of equipment cooling unit provides constant, fail-safe protection for water-cooled computers and related apparatus. Dual chiller modules with automatic switchover capabilities provide backup in the event of failure. With this function, no single component failure can interrupt overall system operations. These cooling units are also application-matched to the temperature stability requirements of water-cooled processors.
With a self-contained, indoor-precision chiller, both coolant flow and temperature are precisely regulated to keep processing temperatures within specification parameters. At the heart of this type of system is a semi-hermetic compressor that extends service life and has the highest energy efficiency ratios in the industry. It is also able to unload capacity for better temperature control. Some models can also be equipped with capacity controls that enable the chiller to increase or decrease its cooling capacity to match a change in equipment. This is accomplished without repiping, rewiring, or replacing any components and allows expansion of equipment components without an unnecessary energy usage penalty.
Thus it can be seen that a dedicated-process chiller or processor cooling unit offers distinct advantages over central building systems for reasons of economy, productivity, reduced maintenance/downtime, and compliance with EPA mandates concerning wastewater disposal. Any one of these considerations would legislate in favor of a dedicated-process chiller or cooling unit when selecting a system for particularly demanding applications. ES