HVAC PRO for Windows User s Manual 637.5 OEM Section Technical Bulletin Issue Date 1094 Reciprocating Chiller Reciprocating Chiller Page 3 Description 3 Theory of Operation 5 Overview 5 Control Sequence 5 Configuration Questions and Answers 7 Compressor Lead/Lag Control? 10 Stage Selection 11 Cooling Diagnostics 11 Reset Control Function 11 - No Reset 11 - Outdoor Air Reset 11 - Zone Temperature Reset 12 - Return Water Reset 13 - Remote Reset 14 - Ramping Strategy 15 Leaving Water Low Limit? 16 Outdoor Temperature Lockout? 16 Ice Mode Control? 16 Is a Demand Limiting Input Needed? 17 Select Pump Logic 17 - Single Pump Control 17 - Dual Pump Control 17 Flow Interlock Input? 18 1994 Johnson Controls, Inc. 1 Code No. LIT-6375220
Modes of Operation Page 18 - Occupied Mode 18 - Unoccupied Mode 19 - Select Method to Initiate Occupied Mode 19 - Shutdown Mode 19 - Select Method to Initiate Shutdown Mode 19 2 OEM Reciprocating Chiller
Reciprocating Chiller Description The AS-UNT33n-1 microprocessor-based leaving water controller performs multiple capacity steps of cooling from a single sensor. Its operation is based on an adjustable setpoint and control band. The controller can be used as a standalone controller or it can be connected to a Companion or Metasys Network. When connected to a network, the controller provides point and control information to the rest of the network and communicates over the N2 Bus. For a smaller facility, the controller can stand alone in conjunction with a Zone Terminal. The controller is configured using the HVAC PRO for Windows software tool, Release 4.00 or later. For certain specific original equipment manufacturers, this controller comes factory-configured. Figure 1: Reciprocating Chiller Controller OEM Reciprocating Chiller 3
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Theory of Operation Overview Operation of the reciprocating chiller controller is based on an adjustable setpoint and control band. If the leaving chilled water temperature begins to rise to the desired setpoint plus control band divided by two (upper limit), the first stage of cooling is energized. Additional stages of cooling follow, after a time delay for each stage, as long as the leaving water temperature remains above the upper limit of the control band. As the leaving water temperature begins to drop to setpoint minus control band divided by two (lower limit) cooling stages begin to de-energize--also with a time delay between each stage. 57 PB 47 45 43 LWSP DB DB Control Band algorthm.drw Figure 2: Leaving Water Control Algorithm Operation No stages energize or de-energize as long as the leaving water temperature is within the control band. Generally, anytime the leaving water temperature goes above the control band, stages energize. Conversely, when the leaving water temperature falls below the control band, stages de-energize. At initial start of the unit, a time delay occurs. There is a 60 second interstage on delay between stages. Each stage incorporates minimum on and off timers with a maximum cycle rate of six cycles per hour. Control Sequence Leaving Water is controlled to the Actual Leaving Water Setpoint. The Actual Leaving Water Setpoint is a function of what mode of operation the controller is in and if a reset option is used. The Control Band potentiometer (AI-6), located on the front of the controller, is used to determine the Actual Leaving Water Deadband and Prop Band. OEM Reciprocating Chiller 5
Actual Leaving Water Deadband: Control Band (AI-6) 2 Actual Leaving Water Prop Band: Actual Leaving Water Deadband Number of Stages Example: Control Band = 4 F Number of Stages = 6 Deadband = 4 2 = 2 F Prop Band = 2 * 6 = 12 F As the Leaving Water Temperature (AI-3) rises above the Actual Leaving Water Setpoint, but within the Actual Leaving Water Deadband, there is no increase in the Compressor Command. As the Leaving Water Temperature continues to rise above the Deadband and into the Prop Band, the Compressor Command increases. When Leaving Water Integration Gain is used, a Proportional plus Integral Command is calculated. As the Compressor Command increases, stages of cooling capacity energize. Minimum on/off, interstage times, and cycles per hour attributes control the outputs. As the Leaving Water Temperature decreases towards the Actual Leaving Water Setpoint, the Compressor Command decreases. Upon re-entering the Deadband, the current Compressor Command is maintained. If the Leaving Water Temperature falls below the Actual Leaving Water Setpoint minus the Deadband, the Compressor Command continues to decrease. 6 OEM Reciprocating Chiller
Configuration Questions and Answers The Reciprocating Chiller Control is configured by responding to a programmed sequence of questions using HVAC PRO for Windows. The flowchart explains the order of the questions. OEM Reciprocating Chiller 7
Start HVAC PRO for Windows Select File, New, OEM Applications,* Reciprocating Chiller Is Compressor Lead/Lag Control Desired? No Yes Method to Initiate Lead/Lag of Compressors? N2 Software Command BI Command Both (N2 Priority) Both (Equal Priority) Occupied Transition Compressor Runtime Compressor Starts Number of Stages? 1 through 8 AI Selectable 2/3/4 AI Selectable 4/6/8 Number of Stages? AI Selectable 4/6/8 2, 4, 6, or 8 Stages Cooling Diagnostics? Yes / No Select Reset of Chilled Water Option None Outdoor Air Reset Zone Temperature Reset Return Water Reset Location of Zone Temperature Value? Analog Input N2 Command Control from Return Water if Leaving Water Sensor is unreliable? Yes / No Is Leaving Water Low Limit needed? Yes / No Is Outdoor Temperature Lockout needed? Yes / No FLOW2A Go to A Figure 3a: Question and Answer Flowchart 8 OEM Reciprocating Chiller
A Is Ice Mode Control needed? No Yes Method to Initiate Ice Mode? N2 Software Command BI Command Both (N2 Priority) Both (Equal Priority) Is Demand Limit Input needed? Yes / No Select Pump Logic None Single Pump Dual Pump Is Flow Interlock needed? Yes / No Select Method to Initate Lead/Lag of Dual Pump N2 Software Command BI Command Both (N2 Priority) Both (Equal Priority) Select Method to Initiate Occupied Mode N2 Software Command BI Command Both (N2 Priority) Both (Equal Priority) Select Method to Initiate Shutdown Mode N2 Software Command BI Command Both (N2 Priority) Both (Equal Priority) Stop FLOW2B Figure 3b: Question and Answer Flowchart (Cont.) OEM Reciprocating Chiller 9
Following is an explanation of the questions along with a brief description of some of the corresponding control logic. Compressor Lead/Lag Control? If Lead\Lag Control is selected, four options to initiate the mode of operation are available: Binary Input (BI) N2 Command from FMS both BI and N2 with N2 priority both BI and N2 with equal priority Equal priority means first on, last off. An Automatic Lead\Lag control is also available. Each option is described below. If you choose the BI or N2 points, the controller changes the lead circuit depending upon the status of the input. A circuit is defined as a group of binary outputs. All odd number stages are considered part of circuit one and all even number stages are considered part of circuit two. If the Automatic control is selected, then an Automatic Enable (BD) point must be configured allowing the Automatic Control to turn on or off. When the BD point is enabled (by default), the control reverses the sequencing of refrigeration circuits based on these user selected trigger points: Occupied Transition--a change from Shutdown, Unoccupied or Ice Mode to Occupied mode Compressor Runtime--based on which circuit has the least cumulative compressor runtime Compressor Starts--based on which compressors have the fewest number of starts All comparisons are based on the actual activity of the lead compressor of each circuit. A monitor only Lead Circuit Index (BD) point indicating which circuit is currently leading is provided. If the Automatic Enable is off, the compressors sequence in numerical order. Note: The Lead\Lag reversing of circuits takes place only when all compressors are off. Changing the Lead Circuit BI or N2 command has no effect unless all stages are off. This means the BI could read Lead Circuit is two, and the Lead Circuit Index reads one. This means the controller is awaiting an opportunity to change the Lead Circuit. 10 OEM Reciprocating Chiller
Stage Selection Cooling Diagnostics Reset Control Function No Reset Outdoor Air Reset You choose the number of stages of cooling in one of two ways. First, you can select the exact number of stages available through the HVAC PRO for Windows software. One through eight stages are available. If this option is chosen, the only way to modify the number of controlled stages is by modifying the configuration. A read-only Number of Cooling Stages point displays the chosen number of stages. The second way allows you to select between two, three, or four stages, or four, six, or eight stages depending upon the position of DIP switches one and two (SW-1 and SW-2) associated with Analog Input number two. With SW-1 in the T position and SW-2 in the 2V position, the controller controls three or six stages. With SW-1 in the V position and SW-2 in the 2V position, the controller controls two or four stages. With SW-1 in the T position and SW-2 in the 10V position, the controller controls four or eight stages. A read-only point displays the chosen number of stages. Note: When you choose the multi-stage option, the number of stages desired must be set while the controller is de-energized. If the settings are changed after the controller is energized, any changes are ignored. Diagnostics of the Cooling Outputs are available when chosen with HVAC PRO for Windows. The Leaving Water Temperature sensor determines a drop in Leaving Water Temperature over time whenever an output is energized. Diagnostic Temp and Diagnostic Time are the two adjustable variables that are used to set up the change in temperature over time function. Each output has a read-only failure point associated with it that acknowledges when a failure occurs. Once a failure occurs for a particular output, the alarm can only be cleared by producing the change in temperature over time, or by cycling power. Available options for reset of controlled water temperature include: No Reset, Reset from Outdoor Air, Reset from Zone Temperature, Reset from Return Water Temperature, and Remote Reset. Each is described below. Leaving Water Temperature is controlled to the Leaving Water Setpoint which is adjustable from the front panel of the controller (AI-4). This adjustable setpoint is in effect during the Occupied mode of operation. Likewise, the Unoccupied Leaving Water Setpoint is maintained during the Unoccupied mode. If the Leaving Water Sensor (AI-3) becomes unreliable, the compressor command is forced to zero. An Outdoor Air Temperature (OAT) sensor (AI-1) is required when Outdoor Air Reset is chosen. Four variables are used to set up the reset ramp that calculates the Actual Leaving Water Setpoint. OEM Reciprocating Chiller 11
Leaving Water Setpoint (AI-4) (LWSP)0 Leaving Reset Band (AI-5) (LWRB) Outdoor Air High Limit (OAHL) Outdoor Air Reset Band (OARB) LWRB LWSP (OALL=OAHL-OARB) OALL OARB OAHL RESETS1 Figure 4: Outdoor Air Reset, OEM, Reciprocating Chiller As the OAT increases above the Outdoor Air Low Limit (OALL), the Actual Leaving Water Setpoint decreases from its Leaving High Limit (Leaving Water Setpoint + Leaving Reset Band) to the Leaving Water Setpoint. When OAT reaches the Outdoor Air High Limit, the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the OAT sensor is missing or unreliable, no reset occurs and the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the Leaving Water Sensor (AI-3) becomes unreliable, the compressor command is forced to zero. Zone Temperature Reset When this option is chosen, a zone temperature must be made available to the controller. There are two ways of letting the controller know the zone temperature. The first is through an adjustable Analog Data Float (ADF) point. With the use of a facility management system, a zone temperature, or average of multiple zone temperatures, can be shared with the controller. The second way is with the use of a zone temperature sensor hooked directly to the controller. Regardless of which method is used, the control strategy is the same. 12 OEM Reciprocating Chiller
Four variables are used to set up the reset ramp that calculates the Actual Leaving Water Setpoint: Leaving Water Setpoint (AI-4) (LWSP) Leaving Reset Band (AI-5) (LWRB) Zone Temperature High Limit (ZTHL) Zone Temperature Reset Band (ZTRB) LWRB LWSP (ZTLL=ZTHL-ZTRB) ZTLL ZTRB ZTHL RESETS2 Figure 5: Zone Temperature Reset, OEM, Reciprocating Chiller As the Zone Temperature increases above the Zone Temperature Low Limit (ZTLL), the controller decreases the Actual Leaving Water Setpoint from its Leaving High Limit (Leaving Water Setpoint + Leaving Reset Band) to the Leaving Water Setpoint. When zone temperature reaches the Zone Temperature High Limit, the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the zone temperature sensor is missing or unreliable, or if there is an unreliable zone temperature value at the ADF point, no reset occurs and the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the Leaving Water Sensor (AI-3) becomes unreliable, the compressor command is forced to zero. Return Water Reset When the Return Water Reset option is chosen, a Return Water Temperature (RWT) sensor (AI-1) is required. Four variables are used to set up the reset ramp that calculates the Actual Leaving Water Setpoint: Leaving Water Setpoint (AI-4) (LWSP) Leaving Water Reset Band (AI-5) (LWRB) Return Water High Limit (RWHL) Return Water Reset Band (RWRB) OEM Reciprocating Chiller 13
LWRB LWSP (RWLL=RWHL-RWRB) RWLL RWRB RWHL RESETS3 Figure 6: Return Water Reset, OEM, Reciprocating Chiller As the Return Water Temperature increases above the Return Water Low Limit (RWLL), the controller decreases the Actual Leaving Water Setpoint from its Leaving Water High Limit (Leaving Water Setpoint + Leaving Water Reset Band) to the Leaving Water Setpoint. When Return Water Temperature reaches the Return Water High Limit, the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the Return Water Temperature sensor is missing or unreliable, no reset occurs and the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the Leaving Water Sensor (AI-3) becomes unreliable, the compressor command is forced to zero. When Return Water Reset is chosen, a Fail Smart Logic option is also available. When chosen it has the following characteristics. If the Leaving Water Sensor (AI-3) becomes unreliable, the controller switches from Leaving Water control to Return Water control. Actual Return Water Setpoint equals Leaving Water Setpoint (AI-4) plus an adjustable Leaving Water Setpoint Offset. This value takes into account the temperature differential between leaving and returning water temperatures; typically, about 10 F. If both the Leaving and Return Water sensor are unreliable, the compressor command is forced to zero. Remote Reset This is not an option in HVAC PRO for Windows software for the reciprocating chiller path. This is an application where a customer wants to reset Leaving Water Setpoint from a remote signal, such as a 4-20 ma source, rather than Outdoor Air, Zone Temperature, or Return Water. 1. To offer this remote signal feature, select Outdoor Air Reset during the question and answer session. Answer all other questions. When finished, the Outdoor Air Temp input is AI1. 14 OEM Reciprocating Chiller
2. Double click on AI1 (Outdoor Air Temp) and change the name (i.e., Remote Signal). Change sensor type to voltage. Update input low range to 0V (0 ma) or 2V (4 ma) to input high range 10V (20 ma). Update output low range to 0 and output high range to 100. 3. Go to parameters and double click on Outdoor Air High Limit. Change the name to Remote Signal High Limit (RSHL). Change the value to 100. Remote Signal Low Limit (RSLL) remains at zero. 4. Double click on Outdoor Air Reset Band. Change name to Remote Signal RB (RSRB). Change value to 100. LWRB LWSP (RSLL=RSHL-RSRB) RS = Remote Signal RSLL RSRB Figure 7: Remote Signal Reset RSHL RESETS4 As the RS increases above the Remote Signal Low Limit (RSLL), the Actual Leaving Water Setpoint decreases from it s Leaving High Limit (Leaving Water Setpoint + Leaving Reset Band) to the Leaving Water Setpoint. When the RS reaches the Remote Signal High Limit, the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the RS sensor is missing or unreliable, no reset occurs and the Actual Leaving Water Setpoint equals the Leaving Water Setpoint (AI-4). If the Leaving Water Sensor (AI-3) becomes unreliable, the compressor command is forced to zero. Ramping Strategy The ramping strategy applies to all three reset options. When a reset function is used, a Ramping of the Compressor Command is also issued. Two adjustable variables setup the ramp as needed. These are Ramp Output and Ramp Time. The Ramp is used to meter the Proportional Command into the Sequencer when conditions don t require a quick startup of all stages. For example, if the Outdoor Air Temperature (OAT) is at Outdoor Air Low Limit (OALL), with OALL being equal to Outdoor Air High Limit minus Outdoor Air High Limit (OAHL). When the OAT is at OAHL, the Proportional Command is fed to the sequencer at the same rate as it is calculated. But if the OAT drops below the OAHL, the Proportional Command is ramped to the Sequencer. The allows for a slower start up of stages. OEM Reciprocating Chiller 15
Leaving Water Low Limit? Outdoor Temperature Lockout? Ice Mode Control? If the Leaving Water Temperature drops below an adjustable Leaving Water Low Limit for more than three seconds, the compressor command is forced to zero immediately. A Leaving Water Low Limit Alarm (BD) point triggers on. Once the Leaving Water Temperature rises above the Leaving Water Low Limit by an adjustable Leaving Water Low Limit Differential, a normal control sequence is initiated just as in startup. Default values are 15 F for the Leaving Water Low Limit and 5 F for the Leaving Water Low Limit Differential. Leaving Water Low Limit affects compressor commands only. All Pump logic, if used, remains unaffected. Outdoor Temperature Lockout, if chosen with the HVAC PRO for Windows software puts the controller into a Shutdown mode whenever it senses the temperature is below the adjustable Outdoor Temperature Lockout setpoint for more than five minutes. The Outdoor Temperature Lockout Status (BD) point is triggered. Once the Outdoor Temperature rises above the Outdoor Temperature Lockout by an adjustable Outdoor Temperature Lockout Differential, a normal transition from shutdown to the prevailing mode occurs. Outdoor Temperature Lockout affects any used pump control. Note: This feature requires an outdoor air sensor. If Ice Mode Control is selected, four options to initiate the mode of operation are available: Binary Input (BI) N2 Command from FMS Both BI and N2 with N2 priority Both BI and N2 with equal priority Equal priority means first on, last off. Upon entering the ice mode from either BI or N2 activation, the main PI control loop is disabled. The current Leaving Water Temperature is compared to the Ice Mode Setpoint. If it is above the setpoint, the Compressor Command is forced to 100%. When the Leaving Water Temperature drops below the Ice Mode Setpoint minus 0.1 F, the Compressor Command is forced to 0%. The Compressor Command is not a proportional change from 100 to 0%. These are the only two levels of Compressor Command during the Ice Mode. Once the Compressor Command falls to 0%, or the Ice Mode deactivates, the control returns to the Occupied or Unoccupied mode as required by binary inputs or software commands. The control does not cycle to maintain an Ice Mode Setpoint. The BI or N2 command that started the Ice Mode must be released and enabled to start the procedure again. Leaving Water Low Limit is not in effect during this mode. 16 OEM Reciprocating Chiller
Note: The feature may require chiller manufacturer to add/change the components to their system. Make sure manufacturer s representative and/or manufacturer is aware of this feature requirement. Is a Demand Limiting Input Needed? Select Pump Logic Single Pump Control Dual Pump Control If Demand Limit Input (AI-1) is selected with the HVAC PRO for Windows software, it affects the control strategy as follows. This input inversely limits the Compressor Command for external demand limiting control strategies. As the input goes from 0-10 VDC, the Compressor Command is proportionally limited from 100 to 0%. For example, if the Demand Limit Input is 5 VDC, the Compressor Command cannot exceed 50%. If 8 VDC is present, the maximum Compressor Commands is 20% and so on. The Demand Limiting function can operate when the control is in the Occupied or Unoccupied modes only. Demand Limiting does not occur while in the Ice Mode. A monitor-only Demand Limit Override (BD) initiates whenever the Demand Limit Input effects the Compressor Command. After answering yes or no to this question, you must then select pump type. Choose single or dual pumps control. When Single Pump Control is selected, a BO and BI point are assigned as Pump and Pump Status respectively. The pump is commanded on unless it is in the Shutdown or Restart mode, or the Outdoor Temperature Lockout is enabled. After the Pump is energized, an adjustable Pump Status Time Delay occurs allowing verification of Pump Status. If Pump Status is verified within this time period, normal control occurs. If Pump Status is not verified, a Pump Failure Alarm (BD) point initiates. The Pump remains energized. When dual pump control is selected, one BI point and two BO points are assigned as Pump 1 and Pump 2 Pump Status respectively. The user also has the option of controlling the lead pump through the BI or N2 command. The lead pump is commanded on unless it is in the Shutdown or Restart mode, or if the Outdoor Temperature Lockout is enabled. After the lead Pump is energized, an adjustable Pump Status Time Delay occurs allowing verification of Pump Status. If Pump Status is verified within this time period, normal control occurs. If Pump Status is not verified, a Lead Pump Failure Alarm (BD) point is initiated and the lead Pump de-energizes. As soon as a Lead Pump Failure is initiated, the lag Pump energizes. If Pump Status is verified within the Pump Status Time Delay, normal control occurs. If Pump Status is not verified within the Pump OEM Reciprocating Chiller 17
Status Time Delay, a Lag Pump Failure Alarm (BD) initiates. The lag pump, however, remains energized. Note: Dual Pump Control is limited to six stages of leaving water control. If the Lag Pump is operating due to lead pump failure, and the lead pump has been repaired, the only way to restart the Lead Pump, is to cycle power on the control or transition to shutdown and back again. This begins a normal startup sequence. If a Chilled Water Pump Control is selected, and the Pump is de-energized for any reason, and Pump Status remains on for more than one minute, a Jumpered Flow Switch Alarm (BD) is initiated. This condition puts the controller in a Shutdown mode where it remains until the Jumpered Flow Switch Alarm is cleared. This condition can be cleared by opening the Pump Status input or cycling power to the controller. Flow Interlock Input? Modes of Operation Occupied Mode If Pump Control is not selected with HVAC PRO for Windows, a Pump Status (BI) point can be assigned to monitor status of an independent pump. Regardless of how the Pump Status point is selected, it has the following characteristics. After a transition from Shutdown mode or Restart Delay, the controller waits an adjustable Pump Status Time Delay for a verification of Pump Status. If Pump Status is verified during this Pump Status Time Delay, normal control occurs. If Pump Status is not verified, a Pump Failure (BD) point is initiated. If Pump Status was previously verified and then lost for a period of three seconds, the Compressor Commands are forced to zero. If Pump Status is lost for a period of one minute, the Pump Failure Alarm is initiated. Once Pump Status is again verified, normal control occurs and the alarm is cleared. Up to four modes of operation are available in the control strategy including Shutdown, Ice Mode, Occupied, and Unoccupied. Each is described below in priority order, first to last. Occupied mode controls the Leaving Water Temperature to the Leaving Water Setpoint (AI-4) located on the front of the controller. If a reset option is used, the Actual Leaving Water Setpoint may vary depending on the reset variable. This mode can be enabled or disabled through a hardware (BI) or software (BD) point or both. Upon entering the Occupied mode from any other mode, the controller goes through an adjustable Occupied Time Delay. This allows a Pump to start and flow to be verified. It also allows for the water loop to equalize in temperature before deciding how much cooling capacity is needed. 18 OEM Reciprocating Chiller
Unoccupied Mode Select Method to Initiate Occupied Mode Shutdown Mode Select Method to Initiate Shutdown Mode Unoccupied mode controls the Leaving Water Temperature to the Unoccupied Leaving Setpoint. This mode can be enabled or disabled through a hardware (BI) or software (BD) point or both. If a reset option is used, it is disabled during this mode. You must choose No or one of the following: Binary Input (BI) N2 Command from FMS Both BI and N2 with N2 priority Both BI and N2 with equal priority Equal priority means first on, last off. Shutdown mode is a multi-purpose catchall mode of operation. It can be enabled or disabled using a hardware (BI) or software (BD) point, or both, depending on how it was configured with HVAC PRO for Windows. Other conditions that affect Shutdown are Outdoor Temperature Lockout, Leaving Water Low Limit, or a Pump Failure. When Shutdown mode is enabled, the compressor command is forced to 0%. Leaving Water Low Limit and Pump Failure has no effect on pump control. Shutdown mode is a multi-purpose catchall mode of operation. It can be enabled or disabled using a hardware (BI) or software (BD) point, or both, depending on how it was configured with HVAC PRO for Windows. Other conditions that affect Shutdown are Outdoor Temperature Lockout, Leaving Water Low Limit, or a Pump Failure. When Shutdown mode is enabled, the compressor command is forced to 0%. Leaving Water Low Limit and Pump Failure has no effect on pump control. OEM Reciprocating Chiller 19
Notes Controls Group FAN 637.5 507 E. Michigan Street HVAC PRO for Windows User s Manual P.O. Box 423 Printed in U.S.A. Milwaukee, WI 53201 20 OEM Reciprocating Chiller