The XL15C controller may be configured for up to 10 Control Loops. In the simplest form, a Control Loop reads a sensor (that is, the control sensor) and calculates an output to maintain the sensed value at a user defined set-point. There are many variations of this. For inputs, the user can configure control, reset, recovery, occupancy, enable/disable, and TOD bypass sensors. For outputs, the users may configure up to 4 modulating analog outputs, up to 4 stages for each analog output and an auxiliary digital output for controlling a fan or pump.
The control portion of the loop is an Enhanced PID (EPID) algorithm. The user
configures control algorithm type (PID or Non-linear), bias (position of set point within
the proportional band (that is, 0% or 50%), direct/reverse acting output, which sensor and
outputs to use, throttling range, integral time, derivative time, start up ramp time,
recovery, reset and sequencer parameters, set points, minimum on, off and bypass times,
DLC shed bump and lead/lag.
Flexible loops are enhanced proportional integral derivative (EPID) control loops.
A control (main) sensor must be configured for the flexible loop to be considered configured.Various external (that is, network variables) conditions can influence how the flexible loop controls.
Select the alogirthm type - PID or Non-linear
PID - Proportional Integral Derivative (PID) control.
A control algorithm that enhances the PI control algorithm by adding a component
proportional to the rate of change (derivative) of the deviation of the controlled
variable. PID compensates for system dynamics and allows faster control response
rate-reset. Standard PID control loops can be used in most HVAC applications. PID is the
primary choice, but if there is a problem achieving a stable loop, then the nonlinear
algorithm could be the solution.
Non linear - An alternative to the PID algorithm. Provides a more stable output when PID creates instability. The nonlinear algorithm is more successful for loops with output stability or where overshoot is not desirable. The nonlinear algorithm develops an error signal and makes relative corrections to reach and maintain zero offset. The main advantage over PID is that the non-linear algorithm cannot make large changes in the output.
Override Priority - The options for occupancy override priority are Network Wins (default) and Last In Wins.
With Network wins, nviManOcc has priority. If nviManOcc is some other value than OC_NUL, then the result is the value on nviManOcc. When nviManOcc is OC_NUL, then nviBypass has priority. If nviBypass is SW_OFF/SW_NUL then the wall module override is evaluated. Both nviManOcc and the wall module override use the internal bypass timers. nviBypass depends upon the timer of the other node to control the duration of the bypass. The Excel 15C keeps the loop bypass_timer running while nviBypass is SW_ON. If nviBypass goes away before the timer expires, then the loop remains in bypass for the balance of the timer.
With Last in Wins, the last bypass source is used to determine the state. If multiple sources change the state in the same second, they are evaluated in order: nviManOcc, nviBypass, wall module override. Each second the algorithm looks for an update to either nviManOcc, a change of state to nviBypass, or the wall module override being pushed. If any of these occur, then appropriate action is taken. Else, the bypass timer is checked for expiration and the current state returned.
This configuration takes the setpoints used by the flex loop control objects during the occupied, unoccupied and standby periods.
Engineering Units - Select the engineering unit of the main sensor.
Bypass Time - The time duration for which the control loop will be in Bypass state. The duration can be entered in 1 minute increments from 0 to 1080 minutes.
Disable in Unoccupied - If the selection is onDuringOccupied, it infers normal operation of the flexible loop during unoccupied periods. If the selection if OnDuringOccupied, it infers that if the flexible loop is unoccupied, the loop state is set to HVAC_OFF.
Flexible loops allow reset of the setpoint(occupied only) either in the direction of increased energy savings or in the direction of the increased comfort. Reset amount (+/-) is positive or negative to accomodate energy savings versus comfort. The reset of a control loop is dependent on the anlaog reset sensor input.
Engineering units - Select the engineering unit of the reset sensor.
Zero Reset Sensor Value - This is the minimum value above which the reset action occurs. The engineering unit is the reset sensor engineering unit
Max Reset Sensor Value - This is the maximum value below which the reset action occurs.
Max Reset amount - This is the value added to subtracted from the setpoint when the setpoint is reset as per the reset sensor input.
The recovery of the control loop is dependent on the analog recovery sensor input.
Engineering units - Select the engineering unit of the recovery sensor.
Min Recovery sensor value - The recovery sensor value representing full load (design) conditions.
Max Recovery sensor value - The recovery sensor value representing no load condition.
Min Recovery Ramp Rate - The recovery rate at full load condition.
Max Recovery Ramp Rate - The recovery rate at no load condition.
Intelligent Setback Ramp Rate - Flexible loops allow intelligent recovery to be either a step or ramp-up to the next setpoint. Recovery shall occur from unoccupied to standby, unoccupied to occupied, standby to occupied, occupied to standby. Flexible loops allow a setback of the setpoints prior to unoccupied.The transition from occupied to standby can either be a ramp or a step. The transition from standby to unoccupied is always a step. If the value is 0, then the setpoint will step change from occupied to standby. If it is non-zero, the setpoint will ramp change from occupied to standby.
Recovery step - This selection denotes whether the setpoint recovery will be ramped or a step.
The control parameters have different configurations based on the algorithm type.
Control Action - The control loop can be direct acting (cooling) or reverse acting (heating).
Bias - The available selections are zero percent (the command percentage nominal value is zero percent) or fifty percent (the command percentage nominal value is fifty percent). This option is enabled only if the algorithm type is PID.
Analog Limit - The options available are No Limit, Low Limit and High Limit.
Throttling Range - This value is the throttling range of the EPID.
Integral Time - This value is the integral time of the EPID. This option is available only if the algorithm type is PID.
Derivative Time - This value is the derivative time of the EPID. This is available only if the algorithm type is PID.
Setpoint Bump - This value is the amount that gets added to the occupied setpoint.
Max Drive - The maximum drive percent for the flex non-linear loops.This option is available only for the non-linear flex loops. Calculate the percentage by dividing the execution speed of the control loop by the motor speed in seconds.
Dead Band - The deadband (0-100) for non-linear loops.
Startup Ramp - Ramp Time - This is the time from start up to full controlled output. The resolution is 1 second. The range is 0 to 65530 seconds.
Start value - This is the primary analog (EPID) initial output value. The resolution is 1 percent. The range is 0-100 percent.
DeadBand - This is shown only if the algorithm type is selected as Flex PID.
% of Throttling Range -This value is the dead band in percent of the throttling range. Its range is 0 to 100%. The resolution is 1%
Delay Time - This value is the dead band delay in seconds. Its range is 0 to 65530 seconds. The resolution is 1 second.
Aux D.O. - The options available are Continuous and Intermittent for occupied and standby modes. Always intermittent for unOccupied mode
On Time - This is the minimum ON time for the auxiliary digital output . It has a range of 0 to 254 minutes with a resolution of 1 minute
Off Time - This is the minimum OFF time for the auxiliary digital output . It has a range of 0 to 254 minutes with a resolution of 1 minute.
This page allows the user to configure the setpoint alarms.
Alarm Pre Delay - This quantity represents the required time the main sensor input value must be outside the range set by the Alarm Delta Above setpoint or Alarm Delta Below setpoint before the SET_POINT_LOOP_ALARM is set. The range is 0 to 65460 seconds with a resolution of 1 second.
Alarm Post Delay - This quantity represents the required time the main sensor input value must be inside the range set by the Alarm Delta Above setpoint or Alarm Delta Below setpoint before the SET_POINT_LOOP_ALARM return to Normal is set. The range is 0 to 65460 seconds with a resolution of 1 second
Alarm Delta above setpoint - This value establishes the Alarm high limit for the main sensor input . If the main sensor input value increases above the effective setpoint value plus the Alarm Delta Above Setpoint Value and remains above for Alarm pre-delay time period a SET_POINT_LOOP_ALARM is set.
Alarm Delta below setpoint - This value establishes the Alarm low limit for the main sensor analog input. If the main sensor input value decreases below the effective setpoint value minus the Alarm Delta Below Setpoint value and remains below for Alarm pre-delay time period a SET_POINT_LOOP_ALARM is set.
Sequencer 1 (Heat) Start - This field represents start (x) percent of Sequencer 1.
Sequencer1 (Heat) End - This field represents end (y) percent of Sequencer 1.
Sequencer2 (Econ)Start - This field represents start (x) percent of Sequencer 2.
Sequencer2 (Econ) End - This field represents end (y) percent of Sequencer 2.
Sequencer3 (Cool) Start - This field represents start (x) percent of Sequencer 3.
Sequencer3 (Cool) End - This field represents end (y) percent of Sequencer 3.
Sequencer configuration values x1, x2, y1, and y2 determine the conversion from the
flexible control loop primary (EPID) analog output to the 3 sequencer analog outputs.
The sequencer takes the primary (EPID) analog output value and splits it up into three
separate analog outputs. Each of the sequenced analog outputs has a range of 0 to 100%
over a smaller range of the primary analog output. Typical uses include controlling
heating, economizer and cooling or converting the primary EPID analog output into more
stages.
An example sequencer configuration data is:
Sequencer 1 (Heat)Start : x = 0% y = 100%.
Sequencer 1 (Heat)End : x = 33% y = 0%.
Sequencer 2 (Econ)Start : x = 33% y = 0%.
Sequencer 2 (Econ)End : x = 66% y = 100%.
Sequencer 3(Cool)Start : x = 66% y = 0%.
Sequencer 3 (Cool) End: x = 100% y = 100%.
Minimum On Time - This is the minimum ON time for each staged digital output at a resolution of 1 minute. Range is 0 to 254 minutes.
Minimum Off Time - This is the minimum OFF time for each staged digital output at a resolution of 1 minute. Range is 0 to 254 minutes.
Interstage On Time - This is the interstage ON time for the staged digital outputs at a resolution of 1 minute. It is the time a lower numbered stage must be ON before the next stage can turn ON. Range is 0 to 254 minutes.
Interstage Off Time - This is the interstage OFF time for the staged digital outputs at a resolution of 1 minute. It is the time a higher numbered stage must be OFF before the next stage can turn ON. Range is 0 to 254 minutes.
Lead Lag selection - This quantity indicates whether lead lag should be used. Lead/Lag is used to share the run time of the equipment equally among the stages.The EXCEL 15C keeps track of run time to the nearest hours by counting ON time every minute.
Disabled – Lead Lag is not used. Stages are turned ON/OFF starting with the first stage every time.
First On / First Off – The first stage ON will be the first stage OFF. This is a rotating scheme.
Equal Runtime – The stage with the lowest amount of runtime is turned ON first. In the event two or more stages have equal amounts of runtime, the lowest numbered stage is selected first. The stage with the most runtime is turned OFF first.
Note:
Any change in the configuration needs to be downloaded to the controller. Until then, the objects would be marked as "Stale".This is an indication that these changes need to be downloaded to the controller.Invoke "Download" to download the configuration changes to the controller.