Temperature Control Pointers
Keep these tips in mind when selecting the control for a process chiller.
|A chiller is a compressor-based cooling system that is used to remove heat from water and transfer it to air or water.|
A chiller is a compressor-based cooling system that is used to remove heat from water and transfer it either to air or water. Many different sizes and configurations are available, so the setup is dependent upon the specific process requirements. Typical components found in a chiller include a temperature controller, a compressor, a recirculating pump and a reservoir.
The reservoir is filled with the fluid to be recirculated, and modern units are supplied with green, environmentally friendly (non-ozone depleting) refrigerants.
The choice of compressor is important and should be based upon the application, required temperature, ambient conditions and other parameters. For example, scroll compressors used in certain applications can offer improvements in efficiency, enhanced reliability and quieter operation through the inherent design of fewer moving parts.
Here are 10 tips to remember when selecting a temperature controller.
Size is going to be an important factor. Faceplate size and depth will impact the final dimensions of the control panel. Common industry size is 1/16 DIN with a depth of ~3.54" (90 mm) or less. A 1/16 DIN faceplate typically will have up to a four-digit display for the process value (PV). This is useful if you want precise indication of the temperature down to a one-tenth (0.10) of a degree.
Chiller performance can degrade if the filter system is not properly maintained. Temperature indication of the running setpoint (SP) is important feedback to the operator so he can visually see that the chiller is working as intended.
Controllers often come with the ability to configure alarm and event strategies. Alarms indicate to the operator when the process is going out of control. You should be able to select from a number of alarm options, including rate of change, deviation band, high and low.
|Typical components found in a chiller include a temperature controller, a compressor, a recirculating pump and a reservoir.|
Programming simple alarms usually can be done through the front panel, or you can use a PC wizard to configure a complex strategy. Events also can be set up to allow for special cases such as boost cooling when time-to-temperature is critical.
Improvements in display technology allow the use of scrolling messages even on a small 1/16 DIN display. This aids in communicating precisely - using actual words - the nature of an alarm and does not leave to chance whether the operator can interpret an alarm code. By enabling each function to have a scrolling text message, faster response and presumably process control can be achieved. Many controls manufacturers offer the ability to provide messages in several common languages such as English, French, German, Italian or Spanish.
Temperature overshoot and undershoot of the desired setpoint can sometimes occur when using on/off control or poorly tuned PID controllers.
|A correctly setup controller will also aid the long-term reliability of the chiller.|
This can potentially lead to problems with the primary process and reliability issues with the chiller. Select a controller with the amount of control needed to effectively manage the chiller and process.
Take advantage of the autotune facility that is standard on many controllers in order to tune your process quickly and accurately.
Some chiller manufacturers use a separate timer for a purge function. Today’s controllers have an internal timer that can replace this piece of hardware.
The chiller is an ancillary piece of equipment and typically is operated in combination with a primary process. The ability to use digital communications (Modbus RTU) allows for easy connection to a master controller such as a PLC. A remote setpoint feature is useful if the chiller is required to change to different temperature setpoints depending on the process being run.
It is important to not only select the controller but also the controller supplier. Be sure the supplier can support you and its product in the field. Assess the level of warranty you require - this can vary from out of the box to multiple years.
With the additional capabilities of 1/16 DIN controllers, it would be useful to have an easy configuration process. The latest controllers typically use short codes to enable “out of the box” operation.
The temperature controller provides the “brain” in that it precisely controls the process. A correctly setup controller will aid the long-term reliability of the chiller. PC