If your process chiller malfunctions, lost production and lost profits may result. Why not consider a multicircuit chiller?

Dual, auto-change chilled water circulating pumps ensure continuous chilled water flow to the process. Pumps are supplied with isolation and check valves plus separate power disconnects to allow for rapid changeout of one pump while the other remains in operation.

Many industrial manufacturing processes require a continuous supply of refrigerated water. Some of these processes are "round the clock" operations. For other manufacturers, a loss of cooling water is critical or even disastrous in manufacturing and profitability terms.

Traditionally, water chillers have been treated simply as a plant service required by the manufacturing process, like electrical power. Unfortunately, water chillers are more complex than simply opening a water faucet or turning on a switch. They are self-contained electromechanical devices that include compressors, controls, refrigeration systems, pumps, piping and wiring. Any fault in a component can render a chiller inoperative and stop production, causing lost profit and a diminished return on investment. Even batch production processes (for example, batch cooling of cosmetics or pharmaceuticals) can lose a production run if a chiller fails to operate "on cue" for the required cooling cycle.

While the majority of industrial water chillers are dependable machines, additional redundant measures are required if any malfunction jeopardizes production and profitability. In any standard chiller, a refrigerant leak in the evaporator, condenser or piping will stop production for hours or even days. The same is true if the refrigeration compressor breaks a valve or suffers a burnt-out motor.

In a typical 100-ton chiller, four individual semihermetic compressors are fitted with cylinder unloaders for a total of eight stages of cooling. In conjunction with microprocessor staged controls, this provides very close control of water temperature without the use of hot gas bypass valves. (Optional laser/MRI controls can deliver a control band of setpoint +0.3oF.)

The solution requires a fundamental shift in philosophy. The same redundancy and reliability factors that are engineered into the production equipment also must be applied to the chiller. In this way, the process chiller becomes integrated into the continuous production process. For total chiller reliability, the chiller must be constructed with redundant, multiple circuits. These systems are equipped with multiple independent refrigeration circuits, auto-standby pumps, separate disconnects and microprocessor controls with remote controls. The cost of integrating the chiller into the continuous production process may be recovered with the avoidance of a single production stoppage.

Questions to ask when considering whether a multicircuit redundant chiller is necessary include:

  • If my manufacturing process chiller fails for any reason, what is the cost of lost production, sales and profit per hour? per shift? per day?

  • How much does it cost to repair or replace the chiller on an emergency basis (including nights or weekends)?

  • How much is a rental chiller (including mandatory minimum rental time, delivery and installation charges)?

This 150-ton water-cooled multicircuit chiller has four semihermetic compressors, each in its own independent circuit.

Consider the long-term benefits of a multicircuit, redundant chiller: It is more cost effective than duplicating complete chillers, except typically below 10-tons cooling capacity. Consider also that a multicircuit redundant chiller will consume less valuable floor space. It is most practical to utilize two independent refrigeration circuits from 10 to 25 tons capacity. Larger chillers from 30 to 150 tons can be split into four equal, independent refrigeration circuits. Completely independent refrigeration circuits are defined as separate compressors, each with its own evaporator, condenser and all attendant piping, valves and power wiring. Split evaporators, or multiple compressors in a common refrigeration circuit, cannot provide the required level of redundancy and are not recommended.

Additional redundancy can be obtained by selecting an oversized four-circuit chiller in which any three circuits can handle the total cooling load. In this case, even with one circuit down, a site repair can be implemented while the remaining three circuits handle the total load. Modern microprocessor controls can rotate the compressor circuits automatically, based on run time, to equalize individual component wear factors.

Four independent stainless steel plate evaporators provide added redundancy. They are fitted with isolation valves to allow for individual replacement without disturbing the remaining circuits.

The chilled water circulating pump generally is considered a reliable chiller component. However, a leaking mechanical pump seal or a simple pump motor failure will shut down production until it is repaired or replaced. It is a simple matter to add a redundant pump, piped and wired, which will start automatically and set an alarm in the event the lead pump fails. The pumps also may be rotated automatically by the microprocessor controller every time the chiller is started. Chillers with duplex pumps should always be fitted with a high quality pressure-differential switch, in preference to a paddle-type flow switch. Differential switches generally are more reliable and will eliminate false alarms.

An essential component of a multicircuit redundant chiller is the inclusion of individual power disconnects or manual circuit breakers for each compressor and pump. In this way, any major electrical component can be isolated, repaired or replaced while the chiller is still operational, and production can continue without a hitch.

In the past, electromechanical controls have been considered simpler for a production or maintenance operator to troubleshoot or repair, but these controls are limited in capability -- especially for alarms and remote control or remote monitoring. The latest generation of plug-in microprocessor controllers is designed to be replaced easily and quickly in the event of any malfunction. These controllers are available in modular plastic enclosures with DIN rail clip-on mounting and plug-in wiring terminals, making complete replacement possible in minutes.

This microprocessor-based control and alarm module snaps onto a panel-mounted DIN rail and has plug-in terminal connections for quick and easy replacement.

It is important to specify microprocessor controls with serial ports, which allow communication with central building management control systems via an RS232 or RS485 connection. This feature allows the operator to send and receive a remote alarm for any system malfunction -- or even control and monitor every aspect of the chiller operation from a remote location. Currently, the most widely used communication platform for central building management systems is Modbus, so a microprocessor that uses this platform is compatible with most central monitoring systems -- without the need for an expensive interface and without a requirement for shared protocol. High-end microprocessor controllers also are available with a plug-in web-gate connection. In this case, the chiller can be accessed from an Internet connection anywhere in the world.

Standard microprocessor controls should offer the following features:

  • Push-button chilled water temperature adjustment.

  • LCD display of chilled water temperature, critical functions and alarms.

  • Local visible and audible alarms for all critical functions.

  • Serial port for remote monitoring or control via RS232 or RS485.

  • World Wide Web connection port.

This differential switch is used for pump changeover and alarm.

The standard visible and audible alarms should include high chilled water temperature; low chilled water temperature; pump failed/standby pump running; and individual refrigeration circuit alarms that indicate compressor failure, high-pressure shutdown, low-pressure shutdown and freeze alarm/circuit shutdown.

Process chillers should be considered an integral part of continuous production equipment for all critical applications. They should be designed and built for redundant operation if the chiller downtime cost is prohibitive from a lost production standpoint. It can be a costly mistake to consider chilled water as a simple factory service without first making provisions to keep it flowing.