technical bulletin Subcooler Control

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1 Overview technical bulletin The E2 now has support for controlling a Subcooler. Incorporating Subcooler control in the E2 eliminates the need for standalone Subcoolers that do not have network communication capability. The E2 Subcooler application provides control of the Leaving Liquid Temperature as well as control or monitoring of the Subcooler's superheat, therefore protecting the compressors by minimizing liquid floodback. A MultiFlex ESR8 board may be used to control the Subcooler expansion valve. Subcooler is a licensed feature application. Refer to the License Management section of this document for instructions on adding Subcooler control. E2 Subcooler Application Figure 1 - Typical Subcooler System Document Part # Rev 0 05-JUN Emerson Climate Technologies Retail Solutions, Inc.This document may be photocopied for personal use.

2 Application I/O Inputs The Subcooler application provides the following inputs: 1. Entering Liquid Temperature 2. Leaving Liquid Temperature 3. Suction Pressure 4. Suction Temperature 5. Enable (digital) Outputs The Subcooler application provides the following outputs: 1. EEV % Position (stepper valve) 2. Over-Close Active (digital) 3. Alarm Active (digital) Sequence of Operation Activation The Subcooler application has the ability to enable or disable the control of the expansion valve based on the Entering Liquid Temperature. When the Entering Liquid Temperature rises above your specified Control Enable setpoint, the application enables the control of the Leaving Liquid Temperature and superheat. When the Entering Liquid Temperature falls below the Control Enable setpoint minus your specified deadband, the application disables the control of the Subcooler and the expansion valve fully closes. The Subcooler application has a Master Enable digital input. If the application sees an OFF value on the input, the Subcooler is disabled and the valve fully closes. If this input is left disconnected, the application interprets that as an enable signal. Control Methods The Subcooler application allows you to choose one of two possible Subcooler control methods. The first method is called Floating SH and the second method is called Leaving Liquid. The parameter Control Type is used to select the control method to be used. Document Part # Rev 0 05-JUN-2012 Page 2 of 12

3 Floating Superheat (SH) Control Method The Floating SH control method primarily controls the Leaving Liquid Temperature by adjusting the superheat setpoint of the evaporator. The expansion valve is modulated to maintain the calculated superheat setpoint. The calculated superheat setpoint is not permitted to fall below your specified minimum setpoint to prevent liquid refrigerant from reaching the vapor injection ports on the compressors. 1. Leaving Liquid Temperature Control When the Subcooler application is enabled, the algorithm compares the Leaving Liquid Temperature to the Leaving Liquid Temperature setpoint. If the Leaving Liquid Temperature is above the setpoint, the active superheat setpoint is adjusted downward. If the Leaving Liquid Temperature is below the setpoint, the active superheat setpoint is adjusted higher. You have to specify the frequency at which this calculation is performed and it defaults to two minutes. You must also specify the amount of adjustment to the active superheat setpoint and it defaults to 0.5Δ F. The active superheat setpoint is not permitted to fall below your specified minimum superheat setpoint to prevent flooding of the evaporator. 2. Superheat Control When the Subcooler application is enabled, the algorithm controls the measured superheat to the active superheat setpoint by modulating the stepper expansion valve. This control is provided using a PI loop. Throttling range and integral gain parameters are provided to tune the PI loop. The active superheat setpoint is initially set to your specified starting superheat setpoint. However, as the algorithm monitors the Leaving Liquid Temperature, the active superheat setpoint is adjusted higher or lower to maintain the desired Leaving Liquid Temperature. 3. Recovery Mode When the Subcooler control is first enabled, the algorithm enters your adjustable timed recovery mode. The default duration is 30 seconds. During this mode, the valve opens to a specified percent (defaulting to 50%), filling the evaporator with refrigerant and thus providing a valid superheat reading. After the recovery mode times out, the algorithm controls the valve using the PI loop control. The integral accumulation of the PI loop is reset at the start of PI control. 4. Flood Failsafe If the current measured superheat falls below a Flood Failsafe level (defaulting to 1 F), the valve immediately closes to prevent liquid from exiting the evaporator. Normal control of the valve resumes when the measured superheat rises to 2 F above the Flood Failsafe level. While the valve is in Flood Failsafe mode, the PI control loop is suspended and upon resumption of normal control, the integral accumulation of the PI loop is reset. Document Part # Rev 0 05-JUN-2012 Page 3 of 12

4 Leaving Liquid Control Method The Leaving Liquid control method directly controls the Leaving Liquid Temperature by modulating the expansion valve to maintain the Leaving Liquid setpoint. The superheat is not maintained at any specific setpoint. However, the superheat is monitored to ensure that it does not fall below a minimum threshold. If the superheat does fall below this threshold, the expansion valve begins to close, even if the Leaving Liquid Temperature is above its setpoint. This forced closure is necessary to prevent liquid refrigerant from flooding back to the compressor(s). As the superheat rises above a threshold, the expansion valve is allowed to open again in order to maintain the Leaving Liquid Temperature at its setpoint. 1. Leaving Liquid Temperature Control When the Subcooler application is enabled, the algorithm uses PID to control the Leaving Liquid Temperature to maintain the Leaving Liquid Temperature setpoint. The output of the PID drives the expansion valve. As the Leaving Liquid Temperature rises above the setpoint, the PID output percentage increases, based on the TR and I-Gain parameter values. As the Leaving Liquid Temperature falls below the setpoint, the PID output percentage decreases. 2. Superheat Flood Control In the Leaving Liquid control mode, the superheat is not directly controlled. However, the superheat is monitored to ensure that it does not fall to zero degrees. To accomplish this, the algorithm applies a multiplier to the calculated PID output if the superheat falls below the Minimum Superheat SP. When the superheat equals the Minimum Superheat SP, the multiplier is 100%. As the superheat drops below the Minimum Superheat SP, the multiplier decreases to a value below 100%. If the superheat falls to the level specified by Flood Failsafe SP, the multiplier is zero. At all superheat values between the Flood Failsafe SP and Minimum Superheat SP, the multiplier is between zero and 100%. Document Part # Rev 0 05-JUN-2012 Page 4 of 12

5 Figure 2 - PID Multiplier The multiplier is used to modify the PID output percentage. The resulting valve percentage is calculated as: Valve % = PID% X Multiplier For example, if the PID output is currently at 75% and the multiplier is calculated to be 50%, then the resulting valve % is 37.5%. When the multiplier reaches zero percent, the Leaving Liquid Temperature control PID is disabled. The PID remains disabled until the multiplier rises to 100%, at which point the PID is re-enabled. Valve Over-Close The algorithm has an over-close routine that forces the valve to fully close once per day at a time specified by the parameter Valve Sync TOD. When the over-close routine starts, the OVER CLOSE output turns ON and the EXV % output goes to zero. The PID is disabled while the over-close routine is active. The over-close routine lasts for 60 seconds, after which the valve goes back to normal control and the OVER CLOSE output turns OFF. Document Part # Rev 0 05-JUN-2012 Page 5 of 12

6 Failure Modes The algorithm monitors the control sensors and takes additional action if a failure is detected. The failure modes are active for either control method that is selected. Entering Liquid Temperature Probe If the Entering Liquid Temperature probe fails (or is not configured), the algorithm continues to control the Subcooler. Leaving Liquid Temperature Probe If the Leaving Liquid Temperature probe fails, the algorithm controls the valve based on the starting superheat setpoint. Suction Temperature Probe If the Suction temperature probe fails, the algorithm is not able to monitor or control superheat and the expansion valve closes. Suction Pressure Transducer If the Suction pressure transducer fails, the algorithm is not able to monitor or control superheat and the expansion valve closes. MultiFlex ESR8 Board Offline If the MultiFlex ESR8 board loses communication with the E2, it moves the expansion valve to your specified failure position. Document Part # Rev 0 05-JUN-2012 Page 6 of 12

7 Application Modes The application provides a status output to indicate what general mode of operation the algorithm is in. The available modes are: Off Recovery Mode Flood Failsafe Off Critical Sensor Fail On Description Application is not enabled; either the Enable input is OFF or the Entering Liquid Temperature is above the Control Enable SP. The system has opened the expansion valve to a fixed percent to generate a valid superheat reading. The measured superheat has fallen below 1 F and the expansion valve is closed to prevent liquid from exiting the evaporator. This mode is only valid if the Subcooler is operating in Floating SH control mode. Either the suction temperature probe or the suction pressure transducer, or leaving liquid temperature probe, or input leaving liquid setpoint connection, has failed and the valve is closed. No valve control occurs until the sensors are repaired. The system is monitoring or controlling superheat and the Leaving Liquid Temperature by modulating the expansion valve. Table 1 - Application Modes Document Part # Rev 0 05-JUN-2012 Page 7 of 12

8 Application Alarms The following application alarms are supported. Leaving Liquid Temperature - High or Low Limit Exceeded Superheat - High or Low Limit Exceeded Leaving Liquid Temperature - Not Reaching Setpoint Superheat - Not Reaching Setpoint For the High and Low Leaving Liquid Temperature, there is a separate alarm and notice trip points. The High and Low Superheat alarm is configurable as an alarm or notice. Both alarms have their own alarm delay and priority parameters. The Not Reaching Setpoint alarms for both superheat and Leaving Liquid Temperature are configurable as either an alarm or notice and have their own alarm delay and priority parameters. The Superheat Not Reaching Setpoint alarm is disabled if the Control Mode is set to Leaving Liquid control. Alarm Output The Subcooler control application has an Alarm status output. This is a digital value that turns ON if any application alarms are active. License Management Some applications in the E2 are only available when activated with a license key that is obtained through Retail Solutions. Licensing allows the user to activate certain features in the E2. Subcooler is a licensed feature application. To obtain a license for the Subcooler application, go to the TCP/IP setup screen and obtain your E2 controller s MAC Address. Press + T, or from the Main Menu: 1. Press (System Configuration) 2. Press (Remote Communications) 3. Press (TCP/IP Setup) to open the TCP/IP Setup screen and locate your E2 s MAC address (circled in Figure 3 - TCP/IP Screen - Locating the Mac Address): Document Part # Rev 0 05-JUN-2012 Page 8 of 12

9 Figure 3 - TCP/IP Screen - Locating the Mac Address 4. Call Retail Solutions Customer Service at and have your MAC Address ready in order to obtain your unique license key. Once you have received your unique license key from Customer Service, you can now activate the licensed feature(s) from the License Report screen. The License Report screen displays that E2 controller s unit type and firmware version, the list of all licensed features on that E2, the current number and maximum number of each of those applications allowed, and which additional features, (that require a license key), have been enabled. From the Main Menu: 1. Press (System Configuration) 2. Press (Licensing) 3. Press (Add Feature) Document Part # Rev 0 05-JUN-2012 Page 9 of 12

10 4. Enter your license key to activate the desired feature: Figure 4 - Enter Your Unique License Key 5. Reboot the controller and open the License Report screen again to see the license key appear next to the activated feature (Figure 5 - License Report Screen): Figure 5 - License Report Screen Document Part # Rev 0 05-JUN-2012 Page 10 of 12

11 To access the License Report screen to see the Subcooler (after it has been licensed): Go to Main Menu Choose 7 (System Configuration) choose 9 (Licensing) To access the Subcooler application in the E2 (this screen would appear after it has been licensed): Go to Main Menu Choose 5 (Configured Applications) Choose Subcooler from the list Figure 6 - Subcooler s Status Screen Document Part # Rev 0 05-JUN-2012 Page 11 of 12

12 Figure 7 - Subcooler s General Setup Screen Document Part # Rev 0 05-JUN-2012 Page 12 of 12 This document may be photocopied for personal use. The contents of this publication are presented for informational purposes only and they are not to be construed as warranties or guarantees, express or implied, regarding the products or services described herein or their use or applicability. Emerson Climate Technologies Retail Solutions, Inc. and/or its affiliates (collectively Emerson ), reserves the right to modify the designs or specifications of such products at any time without notice. Emerson does not assume responsibility for the selection, use or maintenance of any product. Responsibility for proper selection, use and maintenance of any product remains solely with the purchaser and end-user JUN-2012 Emerson is a trademark of Emerson Electric Co Emerson Climate Technologies Retail Solutions, Inc. All rights reserved.