Pre-Cool and Free- Cool Fan Control

Transcription

1 5/26/2014 Pre-Cool and Free- Cool Fan Control ArcticCool Chillers ArcticCool Chillers Limited Authored by: Casey Smith

2 ArcticCool Chillers Limited Pre-Cool and Free-Cool Fan Control Sequence of Operations Document Casey Smith ii

3 ArcticCool Chillers Limited Table of Contents Introduction... 1 How this document is organized...1 Who should read this document... 2 Terms and definitions... 2 References and Revisions... 2 Hardware Configuration... 3 Direct IO...4 Inter-Controller Communications T3C...6 Modbus Communications - MB...7 Program Parameters...7 Control Strategy... 9 Full Mechanical Mode...9 Mechanical Mode...9 Pre-Cool Mode...9 Free-Cool Mode Implementation System Enable Parameters Inputs Outputs Sequence Mechanical Mode Idle State Parameters Inputs Outputs Sequence Starting State Parameters Inputs Outputs Operational State Parameters Inputs Outputs Sequence Free-Cool Mode Free Cool/Mechanical Mode Arbitration Parameters Inputs iii

4 ArcticCool Chillers Limited Outputs Sequence Valve/Fan Arbitration Fan Control Parameters Inputs Outputs Sequence Valve Control Parameters Inputs Outputs Sequence List of Figures Figure 1: Typical Wiring Diagram (using MCX152V)... 4 Figure 2: Free Cool - Fan and Valve Control Zones List of Tables Table 1: Glossary of Terms... 2 Table 2: Reference Documentation... 2 Table 3: I/O Listing... 4 Table 4: Data from T3C Controller... 6 Table 5: Parameter List... 7 iv

5 ArcticCool Chillers Limited Revision History Revision Synopsis 1.0 Design Phase for review 1.1 Update for first build, Pump Control Added 1.2 Pump Control Removed 1.5 First Release with product based on version 1.1 ArcticCool Fan Controller version 1.1. Graphics and details added. v

6 Introduction This document describes the design of the control and logic to supplement the capabilities of the Danfoss Turbocor T3C Standard Chiller Control Software. This Sequence of Operations design is based on T3C version This specification includes: 1. Fan Control: a. Condenser Fan b. Free-Cooling Fan 2. Cooling Coil By-pass Valve Control. How this document is organized This Sequence of Operations Document has the following sections: Introduction this section. o Document organization o Who this document is designed for. o Glossary of terms o Document history and sources Hardware Setup o Wiring Considerations and options o Communications to other devices Control Strategy o Full Mechanical mode o Mechanical mode o Pre-Cool Mode o Free-Cool Mode o Pump Control Implementation o System Enable o Mechanical mode o Pre-Cool Mode o Free-Cool Mode o Pump Control January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 1

7 Who should read this document Arctic Cool Chillers Limited The sequence of operations design document is meant for all personnel associated with the chiller design and any programmers building controls for the chiller. This document can then be part of the larger IOM document as part of the delivery package of the chiller. Terms and definitions Table 1: Glossary of Terms Term What it means UI or HMI The User Interface a display is provided with the controller. Glyph A small graphical display with a specific function. Fan Bank 1-6 fans comprise a fan bank and the fan bank is dedicated to 1 refrigeration circuit. A fan bank operates as a unit and is controlled to the same speed. References and Revisions Table 2: Reference Documentation Document Description Revision T3C chiller standard software MCX Turbocor Compound Capacity Controller user manual, Filename: AC_T3C_DKRCC.PS.RI0.B5.02_520H7630 May 2013 January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 2

8 Hardware Configuration Arctic Cool Chillers Limited The design calls for either the MCX61V or MCX152V. Project size will dictate. The specifications for this revision are: 1. Chiller with 2 refrigeration circuits expandable to 4 (4 circuits requires MCX152V). 2. Includes Free Cool Fluid Cooler. This control has the following data sources: 1. Direct connect IO 2. Data from the main controller (T3C) via CAN bus. 3. Data from fans/pumps via Modbus (MB). 4. BMS Control via Modbus from HMI. This control allows for some selectability for sources of input information; i.e., raw IO or communicated IO. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 3

9 Figure 1: Typical Wiring Diagram (using MCX152V) Direct IO Table 3: I/O Listing INDEX DESCRIPTION TYPE OR POLARITY ANALOG INPUTS 1 Ambient Temperature NTC-10K 2 Chilled Leaving Water Temperature NTC-10K DIGITAL INPUTS 1 On/Off N.C. 8 General Alarm N.O. ANALOG OUTPUTS January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 4

10 1 Cooling Valve Position 0-10 V 2 Fan Bank 1 Speed Reference 0-10 V 3 Fan Bank 2 Speed Reference 0-10 V DIGITAL OUTPUTS 1 Alarm N.O. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 5

11 Inter-Controller Communications T3C to ArcticCool Fan Controller This set of data leverages the functional capabilities of the T3C Chiller software to which this controller is designed to be companion controller. Table 4: Data from T3C Controller Name Type Notes a07 Cooling enable Parallels with Digital input for auto enable. t01 Compressor Max Power Used with Calculated Total Power to provide current capacity t17 Bypass Solenoid Delay Used to delay fan Start up to Operation State Change a10 Control Setpoint For Free Cooling Control a41 Compressor 1 actual state Fan State is controlled to match c08 Discharge Pressure DTC1 Used to derive SDT, Process Value for condenser control c14 Calculated Total Power DTC1 Used in capacity Calculation a44 Compressor 2 actual state Fan State is controlled to match d08 Discharge Pressure DTC2 Used to derive SDT, Process Value for condenser control d14 Calculated Total Power DTC2 Used in capacity Calculation a47 Compressor 3 actual state Fan State is controlled to match e08 Discharge Pressure DTC3 Used to derive SDT, Process Value for condenser control e14 Calculated Total Power DTC3 Used in capacity Calculation A50 Compressor 4 actual state Fan State is controlled to match f08 Discharge Pressure DTC4 Used to derive SDT, Process Value for condenser control f14 Calculated Total Power DTC4 Used in capacity Calculation January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 6

12 Modbus Communications - MB Arctic Cool Chillers Limited Modbus has 2 prime functions: 1. Communicate bi-directionally with the HMI so that the HMI can: a. Display information from the controller. b. Set parameters in the controller. 2. Communicate with the Fan Array (Future current incompatibilities exist between fan controller and MCX controller. At this time all fan communications are via Analog output): a. Collect Status and Alarm data from each fan. b. Send Speed Commands to each fan. Program Parameters The following table shows the parameters used by the program. All values are modifiable with the appropriate access code. Table 5: Parameter List LABEL DESCRIPTION MIN MAX VALUE UNIT ADU StU General > Setup HOA Hand/Off/Auto Hand 3001 UOM Unit of Measure Select US 3002 y07 Restore default parameters NO 3003 ALA General > Configuration BUZ Buzzer activation time min 3004 AdL Alarm relay activation delay s 3005 AOF Alarm relay active if unit in OFF YES 3006 SEr General > Serial settings SEr Serial address (Modbus and CAN) bau Serial baudrate (Modbus) COM Serial settings (Modbus) E PAS General > Password L01 Password level L02 Password level L03 Password level TEM Unit config > Temperature control SEt Setpoint deg 3013 dif Differential deg 3014 XOT Fan - Valve Crossover Timer s 3015 FCL Unit config > Free Cooling Configuration January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 7

13 LABEL DESCRIPTION MIN MAX VALUE UNIT ADU FCE Free Cooling Enable Enable 3016 FMN Fan Minimum Speed % 3017 FMx Fan Maximum Speed % 3018 FPG Free Cool Fan PID Loop Proportional Gain FPI Free Cooling Fan PID Integral Factor s 3020 LTH Free Cool Enable Threshold deg 3021 UTH Free Cooling Disable Threshold deg 3022 FCV VLP VLI VMx VMn CND Unit config > Free Cooling Valve Configuration Bypass Valve PID Loop Proportional Factor Bypass Valve PID Loop Integral Factor Bypass Valve Maximum Open Position Bypass Valve Minimum Open Position Unit config > Condenser Cooling Configuration s % % 3026 CLA Condenser Minimum Approach deg 3027 CHA Condenser Maximum Approach deg 3028 CSN Condenser Minimum Setpont deg 3029 CSX Condenser Max Setpoint deg 3030 CPC Condenser Power Compensation Enable 3031 Enable FST Fan Start Speed % 3032 CMN Condenser Fan Speed Minimum % 3033 CMX Condenser Fan Speed Maximum % 3034 CPG Condenser Fan PID Loop Proportional Gain CPI Condenser Fan PID Loop Integral s 3036 FFL Sensor Failure Default Fan Speed % 3037 CTL Parameters > Fan Unit Control VHA Free Cooling Bypass Valve Off 3038 Hand/Off/Auto VSP Bypass Valve Manual PositionSetting % 3039 F1C Fan Bank 1 Hand/Off/Auto Control Auto 3040 F2C Fan Bank 2 Hand/Off/Auto Control Auto 3041 F3C Fan Bank 3 Hand/Off/Auto Control Auto 3042 F4C Fan Bank 4 Hand/Off/Auto Control Auto 3043 F1S Fan Bank 1 Manual Speed Setting % 3044 F2S Fan Bank 2 Manual Speed Setting % 3045 F3S Fan Bank 3 Manual Speed Setting % 3046 January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 8

14 LABEL DESCRIPTION MIN MAX VALUE UNIT ADU F4S Fan Bank 4 Manual Speed Setting % 3047 Control Strategy This section details the functional components of the controller: 1. Chiller Mode Full Mechanical. 2. Chiller Mode Pre-Cool. 3. Fan Mode Mechanical. 4. Fan Mode Free Cool. Full Mechanical Mode Full Mechanical mode is enabled when the ambient temperature is above the mechanical mode threshold. In this mode the modulating bypass valve is in the full bypass position and no fluid is flowing through the fluid cooler coils. All compressors, refrigeration circuits and fans are set to provide mechanical cooling Mechanical Mode Mechanical mode, at a circuit level, indicates that all cooling capacity is provided by the compressor. The fans in the associated fan bank provide condenser cooling only. Pre-Cool Mode In pre-cool mode, the ambient temperature is such that surroundings provide some of the cooling capacity which is then topped up by the compressors. The fans in this case provide some fluid cooling and some condenser cooling. The 3-way valve is set to full flow through the fluid cooler. This a combination mode, the fans only really function in either Mechanical mode or Free Cool mode. Pre-cool mode allows the fan banks to operate independently such that some of the fan banks provide free cooling and others provide mechanical cooling. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 9

15 Free-Cool Mode Free Cool mode indicates that the ambient air provides enough cooling capacity without the need to engage the compressors at all. In this mode, the fans and 3-way valve modulate to control the LWT temperature at setpoint. Implementation This section details the sequence of operations for fan control in the 2 modes of the chiller: 1. Mechanical Mode 2. Free-Cooling Mode Note: From the fan control perspective there are only the 2 modes and the pre-cool mode is a combination including both Mechanical and Free Cool modes working in concert. All modes are dependent on the System Enable. System Enable The Fan Control program has a System Enable function that is a global control. See the following sections for details. Parameters The System Enable function has the following parameters: Inputs 1. Hand/Off/Auto control settable by display 2. Free-Cool Temperature Threshold. 3. Mechanical Temperature Threshold. The System Enable function has the following inputs: Remote Enable IO or T3C (Cooling Enable). Ambient Temperature IO or T3C. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 10

16 Outputs The System Enable function has the following outputs: When system is disabled then all outputs are set to safe state. Sequence The following describes the System Enable Function: 1. Hand/Off/Auto set to Off System is disabled. 2. Hand/Off/Auto set to Hand System is enabled. 3. Hand/Off/Auto set to Auto: a. Remote Enable or Cooling Enable on System is enabled. b. Remote Enable and Cooling Enable off System is disabled. The following describes the sequence while the system is enabled: 1. Mode Setting is determined by Ambient Temperature 2. Ambient Temperature greater than Mechanical Threshold: a. 3-way Valve set to full fluid cooler by-pass. b. Chiller set to Mechanical Mode Cooling capacity is provided by compressors under the control of the T3C software. c. Fan banks are controlled according to Mechanical Mode below. 3. Ambient Temperature less than Free-Cool Threshold: a. 3-way Valve set to engage fluid cooler and is under the control of LWT and its setpoint. b. Controller is set to Free-cool mode cooling capacity is provide by both fluid coolers and mechanical cooling where fluid coolers are allowed to provide as much capacity as they are capable of. The mechanical cooling then provides the balance required to meet setpoint. Fan banks are controlled in the following manner: i. Idle circuit fan banks are controlled by the LWT setpoint providing free cooling capacity. ii. Fan banks on circuits providing mechanical cooling are controlled according to mechanical mode below. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 11

17 Mechanical Mode In Mechanical Mode, the fans work in banks where a bank is assigned to each refrigeration circuit. Each circuit has 1 Turbocor compressor and the fan bank for each circuit is controlled to provide the most efficient combination of fan power and compressor power. All banks and circuits work independently but controlled by the same algorithm. NOTE Fan Banks and the Bypass Valve have Hand and Off Modes: Off No fan or valve operation. Fan Bank State shows Off Hand fan bank speed and valve bypass position are controlled by user entry. Fan Bank State shows Hand Figure 2: Condenser Cooling Control page For this control mode there are 4 States: 1. Off System enable is off, no Fan Function 2. Ready System is enabled and fans are available 3. Start proceeds from Ready and normally continues to operational but can return to idle. 4. Cooling proceeds from starting and returns to Ready While chiller is in Full Mechanical mode the fluid cooler is completely by-passed, no fluid flows through the fluid cooler. NOTE Any fan banks that are Ready are available to Free Cool Mode control. Ready State The Ready state is the resting state. The fans are in Ready when the compressors are off and the chiller is in full Mechanical mode. In this state the output to the fan bank is 0%. The Fan Ready state is active under the following compressor states: January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 12

18 Absent (enumerated Value 0) Off-Line (enumerated Value 1) Idle (enumerated Value 2) Stopping (enumerated Value 6) Fault (enumerated Value 8) Time-out (enumerated Value 9) Parameters The Ready State has the following parameters: Arctic Cool Chillers Limited Hand/Off/Auto control. Inputs The Ready State has the following inputs: Compressor State T3C. System Enable Internal. Outputs The Ready State has the following outputs: Fan Speed % - MB. Sequence The following describes the Ready State Function: 1. System is enabled 2. Fan Banks are in Auto Mode 3. Set fan bank output to 0%. Start State The Start state is dictated by the T3C software when a requirement for compressor to start occurs. Start State for fans follows Start state for compressors. Parameters The Start State has the following parameters: Hand/Off/Auto control. Fan Start Speed Setpoint % January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 13

19 Inputs The Start State has the following inputs: System Enable - Internal. Compressor State T3C. Fan bank Status MB. Bypass Solenoid Delay Time T3C. (Used as Start to Cooling State Change delay) Outputs The Start State has the following outputs: Fan Speed % MB. Sequence In the Start state has the following steps: 1. System is enabled 2. Fan Banks are in Auto Mode 3. Fan Control is in Ready or Free COOL (Condenser Cooling takes precedence over free cooling) 4. Fan Controller monitors T3C Compressor State, when Start detected, the fan control changes to Start also. 5. Fan bank output is set to Start Speed setpoint. 6. When Compressor changes to Operational, the delay timer starts. 7. When the delay timer completes, state changes to Cooling. Cooling State In the Cooling state, the controller modulates the speed of the fans to optimize the performance of the compressors. The Cooling state for fan control includes the following compressor states: Operational (enumerated Value 3) Hold (enumerated Value 4) Retreating (enumerated Value 7) January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 14

20 Parameters The Cooling State has the following parameters: Inputs Hand/Off/Auto control. Saturated Discharge Temperature Setpoint Dynamic, based on the following (see Setpoint Control section for details): o Maximum SDT setpoint. o Minimum SDT Setpoint. o Maximum Approach. o Minimum Approach. Mechanical Cooling PID Loop Gain Factor. Mechanical Cooling PID Loop Integral Factor. Maximum and Minimum Speed. Capacity Compensation Enable/Disable. Figure 3: Condenser Control Setup The Cooling State has the following inputs: System Enable. Compressor State T3C. Fan bank Status IO/MB. Saturated Discharge Temperature (SDT Calculated from DTC discharge pressure and refrigerant) T3C. Compressor Capacity. Ambient Temperature. Outputs The Cooling State has the following outputs: Fan Speed % MB. Sequence In the Cooling state has the following steps: 1. System is enabled 2. Fan Banks are in Auto Mode 3. Fan Control is in Starting and delay timer has expired 4. Fan Controller monitors T3C Compressor State, when Operational, Hold or Retreating state is detected, the fan control changes to Operational also. This state is maintained until an Idle, Fault, Absent, Offline, Timeout, Lockout or Stopping state condition is detected. (See Idle State section). January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 15

21 Temperature Arctic Cool Chillers Limited 5. Fan bank output is controlled by a PID loop to maintain compressor relative speed. Ideally, this algorithm keeps the compressor speed at minimum but allowing for maximum compressor turn down. Chiller is at its most efficient when the compressor is running close to the surge speed. The SDT setpoint is active based on Ambient Temperature and Approach temperature. In turn, the approach temperature in conditioned by the compressor capacity. Setpoint Control The controller recalculates the saturated discharge setpoint continuously based on ambient temperature and optionally compressor capacity. Therefore, there are 2 modes of setpoint control: 1. No Compensation 2. Capacity Compensation The mode is controlled by the Capacity Compensation Enable/Disable parameter. A dynamic setpoint keeps the SDT as low as possible allowing the compressor to run as efficiently as possible and yet allow the compressor its highest turn-down capability. Figure 4: Circuit 2 Setpoint Control No Compensation The No Compensation mode Saturated Discharge Temperature setpoint is very simple: SDT SP = AmbientTemp + Max_Approach The chart to the right tracks the SDT setpoint versus the Ambient Temperature. For this chart the Maximum Approach was 25 F. Notice that at the extremes of the chart, the maximum (125 F) and minimum (65 F) setpoint parameters are in force Uncompensated SDT Setpoint Ambient SDT SP No Comp January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 16

22 Temperature Temperature Arctic Cool Chillers Limited Capacity Compensation Compensated SDT Setpoint 50% Load Ambient SDT SP Compensated SDT Setpoint With Variable Load Ambient Load SDT SP Free-Cool Mode Free Cool mode uses the ambient air and fluid coolers to provide some or all of the cooling capacity of the chiller. This chiller is equipped with 2 independent coils, the Fluid Cooler coil and the Condenser Coil configured such that air flow passes the fluid cooler coil first then the condenser coil. The chilled fluid path is directed via modulating valve through the fluid cooler coil then into the evaporator barrel. If the ambient conditions and load are such that leaving fluid temperature from the fluid cooler coil is at setpoint then no mechanical cooling is required. This is referred to January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 17

23 as full Free Cool operation. If the fluid cooler is not capable of producing enough capacity to satisfy the setpoint then Mechanical cooling is added to top-up the capacity. This state is called Pre-cool operation. When controller is in Free Cool mode the fans operate in either Mechanical or Free Cool modes. If the setpoint cannot be satisfied by free cooling alone then the chiller provides additional mechanical cooling; in this case, the following is true: Fan banks are aligned to refrigeration circuits and are controlled as a bank they are all running or stopped as required. Fans are controlled to provide the most energy efficient balance between compressor power and fan power. Fan banks on circuits in mechanical cooling mode provide condenser cooling. Fan banks on circuits Idle provide free cooling to achieve LWT setpoint. The Fluid Cooler bypass valve and fans work in concert to provide constant LWT at setpoint. The following figure shows the relative contribution of the fans and by-pass valve in Free Cool mode. LWT Temperature Fan Control Area LWT Setpoint Valve Control Area 100% Fan Control 0% 100% Valve Control 0% Figure 5: Free Cool - Fan and Valve Control Zones January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 18

24 Free Cool/Mechanical Mode Arbitration Arctic Cool Chillers Limited The controller uses ambient temperature and 2 threshold settings to arbitrate when to enable free cooling control of fans and when to return to a full mechanical mode. Parameters The Free Cool/Mechanical arbitration function has the following parameters: Free Cool Enable threshold Free Cool Disable threshold System Enable Inputs The Free Cool/Mechanical arbitration function has the following inputs: Ambient Temperature IO or T3C Outputs The Free Cool/Mechanical arbitration function has the following outputs: System internal control Free Cool Mode / Mechanical Mode Sequence The Free Cool/Mechanical arbitration function has the following sequence of operations: 1. Temperature is less than Free Cool Enable threshold Set Mode Free Cool. 2. Temperature is greater than Free Cool Disable threshold Set Mode Mechanical. 3. If temperature is between the threshold values mode setting is not changed and Default is Mechanical mode Valve/Fan Arbitration Refer to Figure 5: Free Cool - Fan and Valve Control Zones. The controller monitors the LWT and provides fan air flow in increasing amounts as the LWT rises above Chiller Setpoint. As the LWT drops below setpoint, the fans shut off (0% speed) and the valve modulates towards a full bypass position as the LWT gets farther from setpoint. The controller provides a hysteresis control using timers. The Valve delay starts when fans are at 0% speed and the LWT temperature is below setpoint. The Fan delay timer starts when the Valve is in the full fluid cooler flow position and the LWT is above setpoint. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 19

25 Fan Control Fans in this controller are controlled as a group called a fan bank. Each fan bank is dedicated to a refrigeration circuit and is controlled independently. This allows the chiller to function in a combination mode, or pre-cool, where some fan banks are providing condenser cooling and the rest are providing free cooling. Parameters The Free Cool Fan Control function has the following parameters: Free Cool Fan PID Gain factor. Free Cool Fan PID Integral Factor. Fan/Valve delay timer. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 20

26 Inputs The Free Cool Fan Control function has the following inputs: Remote Enable internal System Mode Free Cool enable. Chiller Setpoint T3C. Outputs The Free Cool Fan Control function has the following outputs: Fan Bank Speed MB or IO. Sequence The following describes the Free Cool Fan Control Function: 1. System Enabled 2. Free Cool Mode Enabled. 3. Valve position is 100% bypassed all chiller flow is through the free cooling coils. 4. LWT is above Chiller Setpoint. 5. Fan Delay is instantiated. a. Timer continues while above remain true. 6. Fan delay has expired. 7. Fan Bank not required for mechanical cooling Circuit (Turbocor Compressor) is Idle. 8. Fan bank is started. 9. Control Fan Bank Speed to achieve Chiller Setpoint on leaving water temperature (LWT). a. All fan banks not in use for mechanical cooling in free cooling mode are controlled to the same speed. Valve Control In extreme conditions, the ambient temperature is low enough that passive flow through the cooler coils is more than capable of satisfying the load. In this case, the controller uses the modulating bypass valve to operate and allow some flow to bypass the fluid cooler to maintain the setpoint and not drop too far below. Parameters The Free Cool Valve Control function has the following parameters: Free Cool Valve PID Gain factor. Free Cool Valve PID Integral Factor. Fan/Valve delay timer. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 21

27 Inputs The Free Cool Valve Control function has the following inputs: Remote Enable internal System Mode Free Cool enable. Chiller Setpoint T3C. Outputs The Free Cool Valve Control function has the following outputs: Valve Position IO. Sequence The following describes the Free Cool Valve Control Function: 1. System Enabled 2. Free Cool Mode Enabled. 3. Valve is set to free cool position all flow is directed through the cooling coils prior to flowing through the evaporator. 4. Free Cool Fan Speed is 0%. (Mechanical Cooling should be disabled at this point if not, other settings should be checked). 5. LWT is less than Chiller Setpoint. 6. Valve Delay is instantiated. a. Timer continues while above remain true. 7. Valve delay has expired. 8. Control Valve bypass position to achieve Chiller Setpoint on leaving water temperature (LWT) by allowing entering water flow to bypass the cooler coils. January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 22