Pre-Cool and Free-Cool Fan Control - Arctic Chiller...

5/26/2014

Pre-Cool and Free-Cool Fan Control

ArcticCool Chillers

ArcticCool Chillers Limited

Authored by: Casey Smith


ii

Pre-Cool and Free-Cool Fan Control Sequence of Operations Document

Casey Smith


iii

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 ........................................................................................................................ 10

Implementation ................................................................................................................. 10 System Enable ........................................................................................................................... 10

Parameters ........................................................................................................................................... 10 Inputs ................................................................................................................................................... 10 Outputs ................................................................................................................................................. 11 Sequence ............................................................................................................................................... 11

Mechanical Mode ....................................................................................................................... 12 Idle State ............................................................................................................................................... 12

Parameters ........................................................................................................................................ 13 Inputs................................................................................................................................................ 13 Outputs ............................................................................................................................................. 13 Sequence .......................................................................................................................................... 13

Starting State ........................................................................................................................................ 13 Parameters ........................................................................................................................................ 13 Inputs................................................................................................................................................ 14 Outputs ............................................................................................................................................. 14

Operational State ................................................................................................................................. 14 Parameters ........................................................................................................................................ 15 Inputs................................................................................................................................................ 15 Outputs ............................................................................................................................................. 15 Sequence .......................................................................................................................................... 15

Free-Cool Mode ......................................................................................................................... 17 Free Cool/Mechanical Mode Arbitration ............................................................................................ 19

Parameters ........................................................................................................................................ 19 Inputs................................................................................................................................................ 19


iv

Outputs ............................................................................................................................................. 19 Sequence .......................................................................................................................................... 19

Valve/Fan Arbitration .......................................................................................................................... 19 Fan Control ......................................................................................................................................... 20

Parameters ....................................................................................................................................... 20 Inputs................................................................................................................................................ 21 Outputs ............................................................................................................................................. 21 Sequence .......................................................................................................................................... 21

Valve Control ....................................................................................................................................... 21 Parameters ........................................................................................................................................ 21 Inputs................................................................................................................................................ 22 Outputs ............................................................................................................................................. 22 Sequence .......................................................................................................................................... 22

List of Figures Figure 1: Typical Wiring Diagram (using MCX152V) ........................................................................ 4

Figure 2: Free Cool - Fan and Valve Control Zones ....................................................................... 18

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


v

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.

Arctic Cool Chillers Limited

January 2015 Pre-Cool and Free-Cool Controller SOO 1.5 pg. 1

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 1.715.100.

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



Who should read this document

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



Hardware Configuration

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.



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



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.



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


d08 Discharge Pressure DTC2 Used to derive SDT, Process Value for condenser control

d14 Calculated Total Power DTC2 Used in capacity Calculation


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



Modbus Communications - MB

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 0 2 1 - Hand 3001 UOM Unit of Measure Select 0 1 0 - US 3002

y07 Restore default parameters 0 1 0 - NO 3003 ALA General > Configuration BUZ Buzzer activation time 0 15 1 min 3004 AdL Alarm relay activation delay 0 999 0 s 3005 AOF Alarm relay active if unit in OFF 0 1 1 - YES 3006 SEr General > Serial settings

SEr Serial address (Modbus and CAN) 1 100 30 3007 bAU Serial baudrate (Modbus) 0 8 6 - 192 3008 COM Serial settings (Modbus) 0 2 1 - 8E1 3009 PAS General > Password L01 Password level 1 0 999 100 3010 L02 Password level 2 0 999 200 3011 L03 Password level 3 0 999 300 3012 TEM Unit config > Temperature control SEt Setpoint -20.0 90.0 45.0 deg 3013 dIF Differential 0.0 20.0 0.5 deg 3014 XOT Fan - Valve Crossover Timer 0 500 20 s 3015 FCL Unit config > Free Cooling

Configuration



LABEL DESCRIPTION MIN MAX VALUE UNIT ADU FCE Free Cooling Enable 0 1 1 - Enable 3016 FMN Fan Minimum Speed 0.0 100.0 5.0 % 3017 FMx Fan Maximum Speed 0.0 100.0 100.0 % 3018 FPG Free Cool Fan PID Loop Proportional

Gain 0.0 100.0 10.0 3019

FPI Free Cooling Fan PID Integral Factor 0 500 200 s 3020 LTH Free Cool Enable Threshold -40.0 100.0 35.0 deg 3021 UTH Free Cooling Disable Threshold -40.0 100.0 45.0 deg 3022 FCV Unit config > Free Cooling Valve

Configuration

VLP Bypass Valve PID Loop Proportional Factor

0.0 100.0 10.0 3023

VLI Bypass Valve PID Loop Integral Factor

0 100 250 s 3024

VMx Bypass Valve Maximum Open Position

0.0 100.0 100.0 % 3025

VMn Bypass Valve Minimum Open Position

0.0 100.0 0.0 % 3026

CND Unit config > Condenser Cooling Configuration

CLA Condenser Minimum Approach 0.0 100.0 5.0 deg 3027 CHA Condenser Maximum Approach 0.0 100.0 25.0 deg 3028 CSN Condenser Minimum Setpont 0.0 100.0 75.0 deg 3029 CSX Condenser Max Setpoint 0.0 150.0 115.0 deg 3030 CPC Condenser Power Compensation

Enable 0 1 1 - Enable 3031

FST Fan Start Speed 0.0 100.0 50.0 % 3032 CMN Condenser Fan Speed Minimum 0.0 100.0 0.0 % 3033 CMX Condenser Fan Speed Maximum 0.0 100.0 100.0 % 3034 CPG Condenser Fan PID Loop

Proportional Gain 0.0 300.0 25.0 3035

CPI Condenser Fan PID Loop Integral 0 500 250 s 3036 FFL Sensor Failure Default Fan Speed 0.0 100.0 100.0 % 3037 CTL Parameters > Fan Unit Control VHA Free Cooling Bypass Valve

Hand/Off/Auto 0 2 0 - Off 3038

VSP Bypass Valve Manual PositionSetting 0.0 100.0 0.0 % 3039 F1C Fan Bank 1 Hand/Off/Auto Control 0 2 2 - Auto 3040 F2C Fan Bank 2 Hand/Off/Auto Control 0 2 2 - Auto 3041

F3C Fan Bank 3 Hand/Off/Auto Control 0 2 2 - Auto 3042 F4C Fan Bank 4 Hand/Off/Auto Control 0 2 2 - Auto 3043 F1S Fan Bank 1 Manual Speed Setting 0.0 100.0 0.0 % 3044 F2S Fan Bank 2 Manual Speed Setting 0.0 100.0 0.0 % 3045 F3S Fan Bank 3 Manual Speed Setting 0.0 100.0 0.0 % 3046



LABEL DESCRIPTION MIN MAX VALUE UNIT ADU F4S Fan Bank 4 Manual Speed Setting 0.0 100.0 0.0 % 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.



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:

1. Hand/Off/Auto control – settable by display

2. Free-Cool Temperature Threshold.

3. Mechanical Temperature Threshold.

Inputs

The System Enable function has the following inputs:

Remote Enable – IO or T3C (Cooling Enable).

Ambient Temperature – IO or T3C.



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.



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.

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.

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:

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”

NOTE

Any fan banks that are

Ready are available to

Free Cool Mode control.

NOTE



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:

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:


Fan Start Speed Setpoint %



Inputs

The Start State has the following inputs:

System Enable - Internal.


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:



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)



Parameters

The Cooling State has the following parameters:


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.

Inputs

The Cooling State has the following inputs:

System Enable.


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:



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).

Figure 3: Condenser Control Setup



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.

No Compensation

The No Compensation mode Saturated Discharge

Temperature setpoint is very simple:

𝑆𝐷𝑇𝑆𝑃 = 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.

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Tem

per

atu

re

Uncompensated SDT Setpoint

Ambient SDT SP No Comp

Figure 4: Circuit 2 Setpoint Control



Capacity Compensation

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

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Tem

per

atu

re

Compensated SDT Setpoint 50% Load

Ambient SDT SP

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Tem

per

atu

re

Compensated SDT Setpoint With Variable Load

Ambient Load SDT SP



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.

Tem

per

atu

re

Fan Control

Valve Control

LWT Setpoint

LWT

100% 0%

100% 0%

Fan Control Area

Valve Control Area

Figure 5: Free Cool - Fan and Valve Control Zones



Free Cool/Mechanical Mode Arbitration

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.



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.



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.



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.

Pre-Cool and Free-Cool Fan Control - Arctic Chiller...

Documents

Transcript of Pre-Cool and Free-Cool Fan Control - Arctic Chiller...