– The Approach and Experiences in ICC - Department of Building ...

CPD Technical Seminar, CIBSE (Hong Kong Branch), ASHRAE
(Hong Kong Chapter) and HKIE (BS division)
17, March 2010, Hong Kong
Building Energy Saving through Optimization
and Life-cycle Commissioning
– The Approach and Experiences in ICC
Shengwei Wang (王盛衛 王盛衛 王盛衛) 王盛衛
Chair Professor of Building Services Engineering
Department of Building Services Engineering
The Hong Kong Polytechnic University
A A Simple Simple View View of of Energy Energy Saving Saving Potentials Potentials for for Building
Building
HVAC&R HVAC&R Systems Systems in in Operation
Operation
- HVAC, lighting, lift, …
Design: Configuration,
Components selection, etc.
10~20%
Saving Potential
System operation and
Control Optimization
Building Building Building Energy Energy Saving
Saving
HVAC&R Systems
Energy Saving Potential
20~30%
Saving Potential
System, component and BAS
commissioning and diagnosis

Outline of Presentation
• Introduction to ICC building systems;
• Our roles in ICC project;
• The concept of “commissioning”
• Examples of commissioning efforts at design,
installation, T&C and operation stages;
• Saving Energy through Control Optimization
control strategies implemented
examples of control strategies
• Summary of energy benefits
• Summary of experiences in ICC
International Finance Centre (ICC)
Floor Area:
Hotel 70,000 (m 2 )
Office 286,000 (m 2 )
Commercial center
67,000 (m 2 )
Gross 440,000 (m 2 )
Six-star Hotel
High-rank
commercial
office
Commercial center and
basement
490 m
118 F

A
D
E
F
G
PCHWP-06-01
EVAPORAROR
WCC-06a-01
(2040 Ton)
COOLING
TOWER 1
FROM PODIUM & BASEMENT
TO PODIUM & BASEMENT
HX HX
(S-B) (S-B)
SCHWP-06-10 to 12
SCHWP-06-01 to 02
COOLING
TOWER 2
A
B
C
D
E
F
G
EVAPORATOR
COOLING
TOWER 3
B
COOLING
TOWER 4
FROM OFFICCE FLOORS(7-41)
TO OFFICE FLOORS(7-41)
EVAPORATOR EVAPORATOR EVAPORATOR EVAPORATOR
COOLING
TOWER 5
COOLING
TOWER 6
HX HX HX HX HX HX HX
PCHWP-06-02 PCHWP-06-03 PCHWP-06-04 PCHWP-06-05 PCHWP-06-06
WCC-06a-02
(2040 Ton)
Secondary water circuit for Zone 1
Secondary water circuit for Zone 2
Secondary water circuit for Zone
3 and Zone 4
Primary water circuit
Chiller circuit
Cooling water circuit
Cooling tower circuit
(S-B)
WCC-06a-03
(2040 Ton)
WCC-06a-04
(2040 Ton)
COOLING
TOWER 7
COOLING
TOWER 8
WCC-06a-05
(2040 Ton)
CDWP-06-01 CDWP-06-02 CDWP-06-03 CDWP-06-04
CDWP-06-05 CDWP-06-06
C
COOLING
TOWER 9
FROM OFFICE FLOORS (43-77)
COOLING
TOWER 10
TO OFFICE FLOORS (43-77)
WCC-06a-06
(2040 Ton)
CONDENSER CONDENSER CONDENSER CONDENSER CONDENSER CONDENSER
CT-06a-01 CT-06a-02 CT-06a-03 CT-06a-04 CT-06a-05 CT-06a-06 CTA-06a-01 CTA-06a-02 CTA-06a-03 CTA-06a-04 CTA-06a-05
CTA Towers (without heating coil)
SCHWP-06-03 to 05
HX
SCHWP-78-01 to 03
PCHWP-78-01 PCHWP-78-02
HX
SCHWP-42-04 to 06
FROM OFFICE FLOORS (79-98)
TO OFFICE FLOORSS (79-98)
PCHWP-78-03
HX
(S-B)
(S-B)
(S-B)
(S-B)
SCHWP-42-01 to 03
PCHWP-42-01 PCHWP-42-02 PCHWP-42-03 PCHWP-42-04 PCHWP-42-05 PCHWP-42-06 PCHWP-42-07
SCHWP-06-06 to 09
CTB Towers (with heating coil)
Our Our Our Our Our Roles Roles Roles Roles in in in in ICC ICC ICC ICC Project
Project
Project
Project
� Independent Energy Consultant
(Independent Commissioning
Agent)
� Developer of HVAC Energy
Optimization System (EOS)
and Energy Performance
Diagnosis System (EPDS)
COOLING
TOWER 11

� Summary of design power load of main HVAC
equipments
Chiller Pump Cooling Tower Fan PAU Fan AHU Fan Total
Number 6 36 11 29 152 234
Rated Power (kW ) 1346 152
Total load (kW ) 8076 4374 1672 513 4600 19235
Percentage 41.99% 22.74% 8.69% 2.67% 23.91%
� Annual electricity consumption of the central
air-conditioning system is about 50,000,000 kWh
Principle of Commissioning
(校核 校核 校核/校校 校核 校核 校核 校核 校核 校校 校校及及及及及及及及改進
校校 校校 校校 校校 校校 改進) 改進 改進 改進 改進 改進 改進
� Commissioning is the process throughout the
whole building lifecycle rather that one-off task.
� Commissioning is a valid means for
improving energy performance of
buildings and HVAC systems
throughout the building life cycle.

Categories of Commissioning
� Initial commissioning: Applied to a production of a new
building and/or an installation of new systems.
� Retro-commissioning: The first time commissioning
implemented in an existing building in which a documented
commissioning was not implemented before.
� Re-commissioning: Implemented after the initial
commissioning or the retro-commissioning when the owner hopes to
verify, improve and document the performance of building systems.
� On-going/continuous commissioning: Conducted
continually for the purposes of maintaining, improving and
optimizing the performance of building systems after the initial
commissioning or the retro-commissioning.
Life-Cycle Life ycle Commissioning
ommissioning
� The building profession in Northern American and
European countries has been promoting the new concept of
life-cycle “Commissioning” and role of “Independent
Commissioning Agent” over the last few years.
� Commissioning is the process throughout the whole
building lifecycle rather that one-off task as conventional
“Test and Commissioning”.
It is performed regularly throughout the whole building lifecycle from
early planning, design, construction and installation to operation
for ensuring that systems are designed, installed, functionally tested
and capable of being operated and maintained properly.
� Commissioning is an effective means for improving
energy performance of buildings and HVAC systems
throughout the building life cycle.
• An average payback period for commissioning of new
buildings is 4.8 years in United States.
• Average energy cost saving for periodical commissioning
of existing building is 15%.

Life-Cycle Life ycle Commissioning
ommissioning
� The building profession in Northern American and
European countries has been promoting the new concept of
life-cycle “Commissioning” and role of “Independent
Commissioning Agent” over the last few years.
� Commissioning ICC project is the is one process of the throughout very first the whole full scale
building trial lifecycle of the new rather concept that one-off of “Commissioning”
task as conventional
“Test and Commissioning”.
and “Independent Commissioning Agent” in
It is performed regularly throughout the whole building lifecycle from
early very planning, large design, and construction complex and building installation system to operation in
for ensuring that systems are designed, installed, functionally tested
and Asia. capable It of being is a very operated attractive and maintained contribution properly. to the
IEA Research programme Annex 47.
� Commissioning is an effective means for improving
energy performance of buildings and HVAC systems
throughout the building life cycle.
• An average payback period for commissioning of new
buildings is 4.8 years in United States.
• Average energy cost saving for periodical commissioning
of existing building is 15%.
Commissioning Commissioning and and and examples examples of
of
efforts efforts at at design, design, design, installation, installation, T&C
T&C
and and operation operation stages
stages

Development of Virtual Building System - Dynamic
simulation platform of the complex HVACR system
Load & status of AHUs
Zone airflow rates
Load & status of AHUs
On/Off
of AHUs
On/Off of AHUs
TYPE 49
Ma,i&Ta,in
On/Off of AHUs
TYPE 35
On/Off of AHUs Ma,i&Ta,in
On/Off of AHUs Ma,i&Ta,in
Pump & network Mw,i AHUs
TYPE 17 TYPE 63
Mw,i
Pump & network AHUs
TYPE 13 TYPE 21
Freq
Tao,i
PID control PID control
TYPE 43 TYPE 20
VPi
Pump sequence Npu PD
optimizer
TYPE 39
TYPE 7
PDset
Mixing
TYPE 60
Tw,in &Mw
HX sequence Nhx HX modeling
&mixing
TYPE 39
TYPE 41
Nhx
Pump & network
TYPE 14
Freq Mw,meas
Tw,out
PID control Mw,set PID control
TYPE 43 TYPE 43
Zone 1 Zone 1
Return pipe
TYPE 31
Pump & network Mw,i AHUs
TYPE 12 TYPE 63
Freq
Tao,i
PID control PID control
TYPE 43 TYPE 42
VPi
Pump sequence Npu PD
optimizer
TYPE 39
TYPE 6
PDset
Mixing
Zone 2
TYPE 48
Zone 2
Mw & Tw,rtn Mw & Tw,rtn
Mixing
TYPE 61
Mw,tot & Tw,rtn
Mw & Tw,rtn
Tw,rtn & Mw,tot
Mw,i
Pump & network AHUs
Freq
Tao,i
TYPE 18 TYPE 63
PID control PID control
Freq
Tao,i
TYPE 43 TYPE 42
PID control PID control
VPi
TYPE 43 TYPE 42
Pump sequence Npu PD
VPi
optimizer
TYPE 39 TYPE 62
Pump sequence Npu PD
PDset
optimizer
TYPE 39
TYPE 8
HX sequence Mixing
Load
PDset
TYPE 39 TYPE 47
Nhx
HX sequence Mixing
Pump & network HX modeling
Mw &mixing
TYPE 39 Nhx TYPE Zones 47 3&4 3&4
TYPE 15
TYPE 36
Freq Mw,meas
Tw,in
Pump sequence HX modeling
&mixing
TYPE 39
PID control
TYPE 37
TYPE 43
Mw Npu
Tw,sup
Mw,set
&Mw
Pump & network
PID control Mixing &
TYPE 16
TYPE 43
bypass
Freq Mw,meas
Tw,out
TYPE 19
PID control Mw,set PID control
Pump sequence
TYPE 43 TYPE 43
TYPE 39
Tw,rtn & Mw Mixing & bypass
Tw,sup & Mw TYPE 45 Zone 3&4
Tsup Supply pipe
TYPE 31
Mixing & Bypass
TYPE XX: Component type number
TYPE 67
T: Temperature
Tw,sup
Mw & PDmeas
Data Reader
TYPE 9
Twb&Tdb
Mw,tot& Trtn
Mw
Ma,i&Ta,in
Tsup
Chiller sequence controller
TYPE 50
Cooling tower controller
TYPE 3&54&55
Tw,out,i On/Off,i&Freq,i
On/Off
of AHUs
Tw,sup
Mw & PDmeas
Chiller One
TYPE 23
Chiller Two
TYPE 23
Chiller Three
TYPE 23
Chiller Four
TYPE 23
Mixing after chiller condensers
TYPE 4
Chiller Five
TYPE 23
Chiller Six
TYPE 23
CTA One CTA Two CTA Three CTA Four CTA Five CTA Six CTB One CTB Two CTB Three CTB Four CTB Five
TYPE 1 TYPE 1 TYPE 1 TYPE 1 TYPE 1 TYPE 1 TYPE 2 TYPE 2 TYPE 2 TYPE 2 TYPE 2
Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw
Mixing after cooling towers
TYPE 5
Tw,sup
On/Off
of AHUs
Tw,ch,out Tw,ch,out Tw,ch,out Tw,ch,out Tw,ch,out Tw,ch,out
Nch On/Off On/Off On/Off On/Off On/Off On/Off
Nch Tw,cd,out Tw,cd,out Tw,cd,out Tw,cd,out Tw,cd,out Tw,cd,out
Mw,tot&Tw,ct,in
Mw,tot&Tw,ct,out
Tw,cd,out
Load
Nhx
Mw
On/Off
of AHUs
Tw,cd,in
Tw,sup
Mw & Tw,in
Mw & PDmeas
Mw
Npu
M:
Load:
Freq:
N:
VP:
PD:
Subscript
w:
ao:
in:
rtn:
cd:
ct:
hx:
wb:
Water
Air outlet
Inlet
Return
Nhx
Tw,out
Number
Condenser
Tw,rtn& Mw
Water or air flow rate
Cooling load
Frequency
Valve position
meas: Measurement
Pressure differential
Cooling tower
Heat exchanger
Wet-bulb
a:
i:
Air
tot: Total
pu: Pump
sup: Supply
Mw,&w,in
Tw,rtn& Mw
Individual
set: Set-point
ch: Chiller
out: Outlet
db: Dry-bulb
Development of Virtual Building System - Dynamic
simulation platform of the complex HVACR system
Load & status of AHUs
Zone airflow rates
Load & status of AHUs
On/Off
of AHUs
On/Off of AHUs
TYPE 49
Ma,i&Ta,in
On/Off of AHUs
Mw,i
Pump & network AHUs
Pump & network Mw,i
TYPE 13 TYPE 21
AHUs
Freq
Tao,i
TYPE 12 TYPE 63
PID control PID control
Freq
Tao,i
TYPE 43 TYPE 20
PID control PID control
VPi
TYPE 43 TYPE 42
PD
VPi
Pump sequence Npu
optimizer
TYPE 39
TYPE 7
Pump sequence Npu PD
optimizer
PDset
TYPE 39
TYPE 6
Mixing
PDset
TYPE 60
Tw,in &Mw
Mixing
HX sequence Nhx HX modeling Zone 2
&mixing
TYPE 48
TYPE 39
TYPE 41
Nhx
Zone Zone 2
Pump & network
Mw & Tw,rtn Mw & Tw,rtn
TYPE 14
Freq Mw,meas
Tw,out
PID control Mw,set PID control
TYPE 43 TYPE 43
Mixing
Zone 1
TYPE 61
Zone 1
Mw,tot & Tw,rtn
Mw & Tw,rtn
Return pipe
Tw,rtn & Mw,tot
TYPE 31
On/Off of AHUs Ma,i&Ta,in
TYPE 35
Pump & network Mw,i AHUs
On/Off of AHUs Ma,i&Ta,in
TYPE 17 TYPE 63
Mw,i
Pump & network AHUs
Freq
Tao,i
TYPE 18 TYPE 63
PID control PID control
Freq
Tao,i
TYPE 43 TYPE 42
PID control PID Virtual
control
VPi
TYPE 43 TYPE 42
Pump sequence Npu PD
VPi
optimizer
TYPE 39 TYPE 62
Pump sequence Npu PD
PDset
optimizer
TYPE 39
TYPE 8
HX sequence Mixing
Load
PDset
TYPE 39 TYPE 47
Nhx
HX sequence Mixing
Pump & network HX modeling Building Mw &mixing
TYPE 39 Nhx TYPE Zones 47 3&4
TYPE 15
TYPE 36
Freq Mw,meas
Tw,in
Pump sequence HX modeling
&mixing
TYPE 39
PID control
TYPE 37
TYPE 43
Mw Npu
Tw,sup
Mw,set
&Mw
Pump & network
PID control Mixing &
TYPE 16
TYPE 43
bypass
Freq Mw,meas
Tw,out
TYPE 19 System
PID control Mw,set PID control
Pump sequence
TYPE 43 TYPE 43
TYPE 39
Tw,rtn & Mw Mixing & bypass
Tw,sup & Mw TYPE 45 Zone 3&4
Tsup Supply pipe
TYPE 31
Mixing & Bypass
TYPE XX: Component type number
TYPE 67
T: Temperature
Tw,sup
Mw & PDmeas
Mw,tot& Trtn
Mw
Ma,i&Ta,in
Tsup
On/Off
of AHUs
Tw,sup
Mw & PDmeas
Tw,sup
On/Off
of AHUs
Data Reader
Tw,ch,out Tw,ch,out Tw,ch,out Tw,ch,out Tw,ch,out Tw,ch,out
M: Water or air flow rate
TYPE 9
Chiller sequence controller Nch
TYPE 50
Nch
Cooling tower controller
TYPE 3&54&55
Tw,out,i On/Off,i&Freq,i
Chiller One Chiller Two Chiller Three Chiller Four Chiller Five Chiller Six
Load: Cooling load
TYPE 23 TYPE 23 TYPE 23 TYPE 23 TYPE 23 TYPE 23
Freq: Frequency
On/Off On/Off On/Off On/Off On/Off On/Off
N: Number
Tw,cd,in VP: Valve position
Tw,cd,out Tw,cd,out Tw,cd,out Tw,cd,out Tw,cd,out Tw,cd,out
PD: Pressure differential
Mixing after chiller condensers (updated throughout
Subscript
TYPE 4
Mw,tot&Tw,ct,in
Tw,cd,out
w: Water
a: Air
meas: Measurement i: Individual
ao: Air outlet tot: Total
in: Inlet
pu: Pump
CTA One CTA Two CTA Three CTA Four CTA Five CTA Six CTB One CTB Two CTB Three the CTB Fourentire
CTB Five process)
rtn: Return set: Set-point
TYPE 1 TYPE 1 TYPE 1 TYPE 1 TYPE 1 TYPE 1 TYPE 2 TYPE 2 TYPE 2 TYPE 2 TYPE 2
cd: Condenser ch: Chiller
Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw Tw,out & Mw
ct: Cooling tower out: Outlet
Mixing after cooling towers
hx: Heat exchanger sup: Supply
TYPE 5
Mw,tot&Tw,ct,out
wb: Wet-bulb db: Dry-bulb
Twb&Tdb
Load
Nhx
Mw
On/Off
of AHUs
Tw,sup
Mw & Tw,in
Mw & PDmeas
Mw
Simulated
Npu
Nhx
Tw,out
Tw,rtn& Mw
Mw,&w,in
Tw,rtn& Mw
Tw,sup
Tw,sup

A
D
E
F
Design Commissioning
The design commissioning mainly concerns the
future operation and control performance of HVAC
systems, and includes:
• Verification the system configuration and component
selection including the chiller system, water system
(primary/secondary system), heat rejection system
(cooling towers), fresh air system etc.
• Verification of the metering system for proper local
control, and the original proposed control logics at the
design stage.
• Proposal of additional metering system for implementing
supervisory control strategies and diagnosis strategies
and related facilities for implementing these strategies
( This is a typical energy-saving implementation from
the earlier design and installation phase)
HX-06
PCHWP-06-01
EVAPORAROR
WCC-06a-01
(2040 Ton)
FROM PODIUM & BASEMENT
TO PODIUM & BASEMENT
HX-06
(S-B) (S-B)
A Secondary water circuit for Zone 1 C
B Secondary water circuit for Zone 2
C
D Primary water circuit
E Chiller circuit
F Cooling water circuit
B
EVAPORATOR
FROM OFFICCE FLOORS(7-41)
TO OFFICE FLOORS(7-41)
HX-42
PCHWP-06-02 PCHWP-06-03 PCHWP-06-04 PCHWP-06-05 PCHWP-06-06
WCC-06a-02
(2040 Ton)
Secondary water circuit for Zone
3 and Zone 4
(S-B)
EVAPORATOR EVAPORATOR EVAPORATOR EVAPORATOR
WCC-06a-03
(2040 Ton)
WCC-06a-04
(2040 Ton)
WCC-06a-05
(2040 Ton)
FROM OFFICE FLOORS (43-77)
TO OFFICE FLOORS (43-77)
CDWP-06-01 CDWP-06-02 CDWP-06-03 CDWP-06-04
CDWP-06-05 CDWP-06-06
(S-B)
WCC-06a-06
(2040 Ton)
CONDENSER CONDENSER CONDENSER CONDENSER CONDENSER CONDENSER
From cooling towers
SCHWP-06-10 to 12
SCHWP-06-01 to 02
System Design Verification -
Secondary water loop systems of 3rd and 4 th zones
SCHWP-06-03 to 05
HX-78
SCHWP-78-01 to 03
PCHWP-78-01 PCHWP-78-02
HX-78
SCHWP-42-04 to 06
FROM OFFICE FLOORS (79-98)
TO OFFICE FLOORSS (79-98)
PCHWP-78-03
HX-78
(S-B)
(S-B)
(S-B)
SCHWP-42-01 to 03
PCHWP-42-01 PCHWP-42-02 PCHWP-42-03 PCHWP-42-04 PCHWP-42-05 PCHWP-42-06 PCHWP-42-07
HX-42 HX-42 HX-42 HX-42 HX-42 HX-42
SCHWP-06-06 to 09
Original Original Original Original System System System System
HX-78
SCHWP-78-01 to 03
HX-78
SCHWP-42-04 to 06
HX-78
FROM OFFICE FLOORS (79-98)
(S-B)
TO OFFICE FLOORSS (79-98)
HX-42 HX-42 HX-42 HX-42 HX-42 HX-42 HX-42
From Zone 3&4
SCHWP-06-06 to 09
To cooling towers
Primary pumps are omitted
(S-B)
To Zone 3&4
(S-B)
FROM OFFICE FLOORS (43-77)
(S-B)
TO OFFICE FLOORS (43-77)
SCHWP-42-01 to 03
Revised Revised Revised Revised System System System System
(operation (operation (operation (operation mode) mode) mode) mode)
Flow meter
Bypass valve

Pump power (kW )
1400
1200
1000
800
600
400
200
0
Comparison between Two systems
Original design
Alternative design
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time (h )
Typical sunnysummer
day
Annual Pump
Energy Saving is
1M kWh
System Design Verification-
Verification
Cooling tower system
• A very special cooling tower with large heat rejection
capacity and a very large dimension (4*10*9)
• High pressure drop through fill packing and silencer
• Energy consumption is about 3.6 million a year with
intended two-stage control
Annual saving potential of using variable speed
cooling towers is 2.4M compared with that
using constant speed towers. It is 1.4M
compared with that using two speed towers.
• Energy consumption is about 2.6
million a year with intended
VFD control from PolyU
• However, energy consumption
will increase greatly to about 5.0
million when single-stage is used
Silencer
100 Pa
Fill packing
300 Pa 50 Pa
Pressure drop
From chiller
To chiller

Example of CO 2 Sensor
Installation
Morgan
Stanley
CO CO22
CO CO22
CO CO22
CO CO22
CO CO22
CO CO22
AHU
Flow stations
CO CO2 2
CO CO22
CO CO22
CO CO22
CO CO22
AHU
CO CO22
CO CO22
CO CO22 CO2 CO2
Kaishing
� CO 2 sensor calibration and commissioning
CO2 concentration (ppm)
Measurement accuracy of CO 2 sensors directly affects
indoor air quality and energy performance of air side
system, which is therefore essential for implementing
optimal ventilation control strategy.
700
650
600
550
500
450
400
350
300
250
Before calibration
Fresh air (Measured) Return air (Measured)
Supply air (Measured) Supply air (Calculated)
200
9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00
Simple time (h)
CO2 concentration (ppm)
700
650
600
550
500
450
400
350
300
250
200
Empty
IC
After calibration
CO CO22
CO CO22
Fresh air (Measured) Return air (Measured)
Supply air (Measured) Supply air (Calculated)
CO CO22
BB
CO CO22
CO CO22
Empty
Empty
9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00
Sample time (h)

∆P
Q = A ⋅ v = A ⋅ 2∆P
Example of air flow
station Installation
Cooling Cooling tower tower site site operation operation issue issue
• We suggest all the cooling tower fans are equipped with
VFD for significant energy savings, and the variable
frequency range is from 50 Hz to 25 Hz at least.
• At the test stage, the manufacture
stated the minimum frequency is 37
Hz for cooling requirement of the
inside motor.
• The manufacture finally confirmed the
minimum frequency is 20 Hz ensuring
the normal operation of the fan.
This This This This low low low low frequency frequency frequency frequency increases increases increases increases the the the the
energy energy energy energy saving saving saving saving potential potential potential potential greatly greatly greatly greatly
at at at at partial partial partial partial load load load load conditions conditions conditions conditions !
! ! !

Cooling Cooling tower tower site site operation operation issue issue
• We suggest all the cooling tower fans are equipped with
VFD for significant energy savings, and the variable
frequency range is from 50 Hz to 25 Hz at least.
• At the test stage, the manufacture
stated the minimum frequency is 37
Hz The for cooling savings requirement is about 607,000 of the kWh , 2.86% of
inside motor.
annual energy consumption of chillers and
cooling towers due to the lower frequency limit.
• The manufacture finally confirmed the
minimum frequency is 20 Hz ensuring
the normal operation of the fan.
This This This This low low low low frequency frequency frequency frequency increases increases increases increases the the the the
energy energy energy energy saving saving saving saving potential potential potential potential greatly greatly greatly greatly
at at at at partial partial partial partial load load load load conditions conditions conditions conditions ! ! ! !
Low Delta-T Central Plant Syndrome
� Nearly all large primary-secondary chilled water
systems suffer from low chilled water temperature
difference, known as low delta-T central plant
syndrome, resulting in inefficient operation.
� When the low delta-T syndrome exists, a series of
operation problems will be resulted
� The inability to sufficiently
load chillers;
� Excess water flow demand;
� An increase in pump energy;
� Either an increase in chiller
energy or a failure to meet
cooling load; etc.
Water flow rate (L/s)
500
400
300
200
100
0
-100
-200
-300
-400
-500
Temp. difference after decouple
Water flow
Chiller operating number
0 12 24 36 48 60 72 84 96 108 120 132 144 156
0
168
Sample time (hour)
8
7
6
5
4
3
2
1
Chiller number and Temp. difference

Low Delta-T Central Plant Syndrome
� Nearly all large primary-secondary chilled water
systems suffer from low chilled water temperature
difference, known as low delta-T central plant
syndrome, resulting in inefficient operation.
Each phase in the life cycle of air-conditioning
systems, including design, equipment selection,
commissioning, operation and maintenance,
may result in low delta-T problems.
� When the low delta-T syndrome exists, a series of
operation problems will be resulted
� The inability to sufficiently
load chillers;
� Excess water flow demand;
� An increase in pump energy;
� applications.
Either an increase in chiller
energy or a failure to meet
cooling load; etc.
Temp. difference after decouple
400
300
Water flow
Some causes can be avoided, 200 but some
100
0
of them cannot be avoided in some
-100
� Potential solutions
Water flow rate (L/s)
500
-200
-300
-400
-500
Chiller operating number
0 12 24 36 48 60 72 84 96 108 120 132 144 156
0
168
Sample time (hour)
� The use of variable primary-only systems;
� The use of pressure-independent modulating
control valves;
� The use of bypass check valves;
� Advanced control and operation strategies.
8
7
6
5
4
3
2
1
Chiller number and Temp. difference

System Improvement by using a Check Valve
Check valve
Primary
pumps 01-06
CHILLER 01
CHILLER 02
CHILLER 03
CHILLER 04
CHILLER 05
CHILLER 06
FM
Secondary water
circuit for Zone 1
AHU
AHU
AHU
Secondary
Pumps 01-02
Secondary water
circuit for Zone 2
Secondary water
circuit for Zone 3&4
� Experimental validation prior to a check valve is really
installed
� by using a ‘conceptual’ check valve in the chiller
decouple ---- through fully closing down one of the
isolation valves in the chiller decouple when the
deficit flow was observed.
AHU
AHU
AHU
Secondary
pumps 03-05
� Summary of experimental results
Outlet air temp. of AHU 1 in L15 (°C)
Deficit flow (L/S)
12.5
12
50
0
-50
-100
-150
-200
-250
10:09:59
10:24:58
10:42:56
10:58:57
10:00:58
10:17:58
Closing the valve in
the decouple
10:36:58
10:51:59
11:10:59
11:06:59
11:19:04
5.5 °C set-point
11:23:01
11:39:01
12:03:03
12:21:03
12:35:00
13:00:01
11:32:56
11:54:58
12:14:56
12:29:58
13:14:04
12:48:56
13:07:58
Reopen the valve
in the decouple
5.0 °C set-point
13:29:01
13:43:58
13:56:59
14:13:58
14:38:58
14:52:04
15:02:58
15:16:57
15:33:04
15:47:59
16:06:59
16:23:01
13:24:59
Time
13:37:59
13:50:59
14:08:59
14:34:00
14:44:56
14:58:58
15:10:56
15:29:01
15:39:00
15:57:59
16:15:58
Cooling load of chiller(kW)
7000
6500
6000
5500
5000
4500
4000
200
0
10:17:58
10:36:58
Closing the valve
in the decouple
10:51:59
11:06:59
11:19:04
11:32:56
11:54:58
12:14:56
12:29:58
12:48:56
Reset supply water
temp. set point from
5.5°C to 5 °C
13:07:58
13:24:59
13:37:59
13:50:59
AHU
AHU
AHU
Secondary
pumps 06-08
14:08:59
14:34:00
Reopen the valve in
the decouple
Time
Time
Test procedure Cooling energy of chillers
Closing the valve
Reset supply water
Annual energy Reopen the valve in
in the decouple
temp. set point from saving potential by using the check
the decouple
1800
5.5°C to 5 °C
16
1600
15.5 valve in ICC is about 325,800 1400kWh
when compared
15
14.5
1200
1000
to that without using the check valve.
14
800
13.5
600
Using 'conceptual' check valve
with similar weather condition
by without using the check
13
400
valve
Total power (kW)
14:44:56
14:58:58
15:10:56
15:29:01
15:39:00
15:57:59
16:15:58
11:19:56
11:30:02
11:42:58
11:52:59
12:05:56
12:16:58
12:32:03
12:46:56
12:57:00
13:07:04
13:17:59
13:31:59
13:48:03
13:56:01
14:09:57
14:28:03
14:39:56
14:48:00
14:57:59
Supply air temperature Energy consumptions
Time

Online performance testing of control
optimizers and diagnostic tools on the
simulated virtual system
Control optimizers and diagnostic tools should be tested on the virtual
systems prior to site implementation
Virtual Plants
Simulated
Communication
Interfaces
IBmanager
Saving Energy through
Control Optimization
System Control Optimizer
Simplified
Models
Optimization
Strategies
Performance
Models
Diagnosis
Strategies
Performance
Prediction
Diagnostic Tool
Performance
Prediction

Optimization for HVAC&R systems
Optimization allows the of HVAC&R systems
provide expected quality of services (comfort and
health environment) with reduced energy
consumption by means of :
• Optimizing design configuration;
• Optimizing the selection and sizing;
• Optimal operation and control.
Optimal control strategies for central
air-conditioning air conditioning systems
� Chiller sequence, optimal start
Optimal chiller sequence - based on a more accurate cooling load
prediction using data fusion method, and considering demand limiting
Adaptive online strategy for optimal start - based on simplified subsystem
dynamic models
� Ventilation strategy for multi-zone air-conditioning
system
Optimal ventilation control strategy - based on ventilation needs of
individual zones and the energy benefits of fresh air intake
� Peak demand limiting and global electricity cost
management

Optimal control strategies for central
air-conditioning air conditioning systems (cont’d) (cont d)
� Chilled water system optimization
Optimal pressure differential set point reset strategy
Optimal pump sequence logic
Optimal heat exchanger sequence logic
Optimal control strategy for pumps in the cold water side of heat
exchangers
Optimal chilled water supply temperature set-point reset strategy
� Cooling water system optimization
Optimal condenser inlet water temperature set point reset strategy
Optimal cooling tower sequence
Optimal control of condenser
cooling water systems

Optimal control of condenser cooling water systems (cont’d) (cont d)
� Formulation of the optimal control strategy
It is designed using a model-based method
• The overall structure of the optimal control strategy
T wb, Q ev, N ch
Define the search ranges
for T w,cd,sup and N ct
T w,cd,sup& N ct
Online measurements
and control signals
Measurement filter
Simplified CTA and
Performance prediction
CTB tower models
Tw,cd,sup, NCTA, NCTB, Ma,, Pct , Freq
Cost estimation & optimization algorithm
Supervisory control strategy
Simplified chiller
model
Optimal control settings & cost
(T w,cd,sup , N CTA , N CTB , Freq , P ch +P ct ) Optimization process
N CTA
T w,cd,sup
N CTB
Interface
N ch &T wb
T w,cd,sup
Chiller plant control system
(BAS)
T w,cd,out
P ch
Freq
Q ev , N ch , T w,ev,in
It consists of :
Performance Performance predictor predictor
predictor
Cost Cost estimator estimator
estimator
Optimization Optimization tool
tool
Supervisory Supervisory strategy
strategy
• Objective function
N ⎛ ch NCTA
NCTB
J = minW
= ⎜
tot min⎜∑
Wch,
k + ∑WCTA,
i + ∑W
Tw,
cd , sup
Tw,
cd , sup ⎝ k=
1 i=
1
j=
1
CTB,
i
Optimal control of condenser cooling water systems (cont’d) (cont d)
• Parameters to be optimized
� The condenser water supply temperature set-point
� The number of CTA towers operating
� The number of CTB towers operating
• Optimization tool ---HQS (hybrid quick search) method
T
T
n,
o
w,
cd , sup
n,
o
w,
cd,
sup
= h
0
+ h T
1
wb
− ∆T
≤ T
⎛ Q
+ h ⎜ 2 ⎜
⎝ Qev,
w,
cd,
sup
ev
≤ T
des
⎞
⎟
⎠
n.
o
w,
cd,
sup
• Operating constraints
+ ∆T
Control setting
Upper limit
Search range
+Δx
-Δx
Low limit Search center (near optimal)
� basic energy and mass balances (i.e., flow, heat, etc.)
� mechanical limitations (i.e., fan speed, temperature, etc.)
Time
⎞
⎟
⎠

Temperature (°C )
Optimal control of condenser cooling water systems (cont’d) (cont d)
� Performance tests and evaluation
• Evaluation of control accuracy and computation performance
32.00
29.00
26.00
23.00
20.00
17.00
14.00
� Comparison between the HQS and GA-based strategies
Items
Seasons
Spring Mild-summer Sunny-summer
Typical working conditions
Qload (kW) 25520.11 31213.61 37547.74
Nch 4 5 6
Tw,ev,in (°C) 9.92 9.82 9.83
Tw,ev,out (°C) 5.50 5.50 5.50
Tdb (°C) 22.55 27.76 33.66
Twb (°C) 15.86 20.11 24.99
Mw,cd (L/s) 410.10 410.10 410.10
Items Tools
HQS GA HQS GA HQS GA
Optimization results
Wch (kW) 3628.07 3644.90 5004.21 4994.37 6794.24 6799.59
Wct (kW) 285.74 268.91 386.11 396.08 538.74 533.42
Wch+Wct (kW) 3913.81 3913.81 5390.32 5390.45 7332.98 7333.01
Optimal Tw,cd,sup (°C) 21.85 21.88 26.65 26.64 31.80 31.80
NCTA 6 6 6 6 6 6
NCTB 5 5 5 5 5 5
Freq (Hz) 25.99 25.35 29.33 29.62 33.39 33.26
Computational cost(s) 0.152 3.610 0.144 3.512 0.134 3.589
The computational cost saving is 96.0%
Dry-bulb Temp.
Wet-bulb Temp.
Optimal Temp. set-point
Near optimal Temp. set-point
Upper limit of set-point
Low limit of set-point
Optimal control of condenser cooling water systems (cont’d) (cont d)
• Evaluation of the Energy Performance
� Comparison of condenser water supply temperature setpoints
using HQS-based strategy and near optimal strategy
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (h )
Optimal temperature set-point
Spring Spring case case
38.00 Dry-bulb Temp.
Wet-bulb Temp. Sunny
Optimal Temp. set-point
35.00 Near optimal Temp. set-point
Upper limit of set-point
32.00 Low limit of set-point
Temperature (°C)
29.00
26.00
23.00
20.00
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (h )
Near-optimal temperature set-point
Sunny-summer summer case case
case

Power difference ( kW )
Optimal control of condenser cooling water systems (cont’d) (cont d)
� Comparison of the hourly-based power consumptions using
different control methods
40
30
20
10
0
-10
-20
Optimal strategy
Near optimal strategy
Fixed approach
-30
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (h )
HQS-based strategy
Spring case
Spring case 210
Optimal strategy Sunny
180 Near optimal strategy
Power difference ( kW )
150
120
90
60
30
0
-30
Fixed
approach
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (h )
Near optimal strategy
Sunny-summer summer case
case
Optimal control of condenser cooling water systems (cont’d) (cont d)
� Comparison of daily and annual power consumptions of the
condenser cooling water system using different control methods
• Daily power consumptions
Operation
Strategies
Fixed approach
Wct+Wch
(kWh)
Near optimal strategy
Wct+Wch Saving Saving
(kWh) (kWh) (%)
HQS-based strategy
Wct+Wch Saving Saving
(kWh) (kWh) (%)
Spring 51,738 51,623 114.53 0.221 51,404 334.30 0.646
Mild-summer 71,289 70,668 621.49 0.872 70,560 729.36 1.023
Sunnysummer
91,653 90,878 775.44 0.846 90,356 1,297.50 1.416
• Annual power consumptions
Operation
strategies
Wch
(kWh)
Wct
(kWh)
Wcd,pu
(kWh)
Wtot
(kWh)
Saving
(kWh)
Saving
(%)
Fixed approach 18,464,812 1,882,583 4,210,690 24,558,085 --- ---
Near optimal 18,715,458 1,501,701 4,210,690 24,427,849 130,236 0.530
HQS-based 18,715,134 1,448,765 4,210,690 24,374,589 183,496 0.747

Operation modes
Plume Control and Energy Benefits
Decision
maker
Platform for predicting
plume occurring possibility
Cooling
Water
Temp Setpoint
Operating Condition Power Consumption
Cooling
Tower
Number
Cooling
Tower
Freq
Normal operation when there is
no predicted plume occurs
At first-level warning, increase airflow rate
by 20% when plume potential is marginal
At second-level warning, increase airflow
by 40% when plume potential is high
Start heating using heat pumps when
visual plume is observed
Chiller
Power
Cooling
Tower
Power
Additional energy consumption for
plume control could be reduced from
Total
Power
Difference
°C - Hz kW kW kW kW %
Reference
First-level warning
22.7 3 26.51 856.2 59.1 32.8% to 5.5% or 1.5% at low Load
21.3 3 30.74 836.2 93.0
915.35
929.2
--
14.0
--
1.5
Second-level warming 20.1 3 35.52 819.9 145.9 965.8 50.6 5.5
Using heat pumps 22.7 3CT+1HP 26.51 856.2 59.1 1215.2 300 32.8
Chiller Plant Sequencing Control
of Enhanced Robustness
Using Data Fusion Technique

Types of chiller sequencing control
� Return chilled water temperature based sequencing
control
Background (1)
Chiller sequencing control
� Aims to determine how many and which chillers are to be
put into operation according to building cooling load
� Plays a significant role for building energy efficiency
� Bypass flow based sequencing control
� Direct power based sequencing control
� Total cooling load based sequencing control
Background (2)
Total cooling load based chiller sequencing control
� Building cooling load measurement
� Maximum cooling capacity
� Optimal number of chillers to be put into operation
N c = φ(Q cl, Q max)
Problems
� Building cooling load cannot be measured accurately
� Chiller maximum cooling capacity vary with the
operating conditions

Fused Cooling Load Measurement
Cooling load measurement
� Direct measurement of building cooling load
Q dm = c pwρ wM w(T w,rtn-T w,sup)
where c pw is the water specific thermal capacity; ρ w is the
water density; M w is water flow rate; T w,rtn,T w,sup are
chilled water return/supply temp.
� Indirect measurement of building cooling load
Q im = f(P com,T cd,T ev)
where f is the chiller inverse model; P com is chiller power
consumption; T cd,T ev are chiller condensing/evaporating
temperature
Robust building cooling load measurement technique
� Data fusion to merge “Direct measurement” and
“Indirect measurement” improving the accuracy and
reliability of building cooling load measurement
T sup
Advanced soft measurement system
Q dm
Direct
measurement
T rtn M w
Chiller
Model 1
Chiller
Model 1
Q im,1
P com,1 T ev,1 ,T cd,1
Data Fusion
Engine
+
…
Q im,n
P com,n,T ev,n,T cd,n
Central Chilling Plant
Chiller
Model n
Chiller
Model n
Q f
γ f

Robust Chiller Sequencing Control Building Cooling Load
Measurement Technique
Direct
measurement
Parameters
setting
Periodical
analysis
Central chilling
plant
Indirect
Measurement
Data Fusion
Engine
Robust Cooling Load
Measurement
Building Automation
System
Alarming
subsystem
Chiller sequencing
control
Temperature
set-point
Database
Optimal Control of Variable Speed Pumps
� Speed control of pumps distributing water to
To terminal
units
heat exchangers
� Original implemented
strategy --- differential
pressure controller by
resorting to the
modulating valve
Secondary side of HX Primary side of HX
From terminal units
Temperature
set-point
TM T
Temperature
controller
HX
HX
Water flow
set-point
TM
Water flow
controller
From cooling
source
To cooling
source
Temperature Temperature
set-point controller
Modulating
valves
Secondary side of HX Primary side of HX
From terminal units
To terminal
units
T
T
Temperature
controller
HX
HX
M
M
Pressure
differential set-point
ΔP
Differential
pressure
controller
From cooling
source
To cooling
source
� Proposed strategy
--- cascade controller
without using any
modulating valve

� Performance test and evaluation
� Site practically test showed that the proposed
strategy can provide stable and reliable control.
Compared to original implemented strategy, about
22.0% savings for pumps before heat exchangers in
Zone 1 was achieved.
� Due to the low load of Zone 1 in ICC at current
stage, a simulation test of annual energy savings by
using PolyU strategy is performed.
Pumps
Number
(standby)
Energy consumption (kWh)
Original
strategy
(kWh)
Energy saving of primary pumps before
heat exchanges due to the use of
PolyU strategy is about 250000 kWh.
Alternative
Strategy
(kWh)
Saving
(kWh)
Primary pumps in Zone 1 1(1) 528,008 456,132 71,876
Primary pumps for Zones 3&4 3(1) 921,235 795,830 125,405
Primary pumps in Zone 4 2(1) 401,008 346,420 54,588
Total saving of the primary pumps 251,869
Optimal Outdoor air Ventilation Control
Static pressure
set point
Static pressure
Static pressure
controller
P
The 7 th floor
………….
The 1 st floor
Outdoor air
controller
Set point
Adaptive DCV
strategy
Model-based
outdoor air flow rate
Control strategy

W
Energy-based outdoor air flow rate set-point
resetting scheme
cost
= W
fan
Q
+
COP
outdoor
Iterative
algorithm
= C
k
v
⋅ M
k
out,
set
Outdoor Air Optimal Scheme
+
Least Square Algorithm
Set point trails
Cost function
estimator
Optimal set point Range of set point
Supervisor Constrains
Parameter estimators
Parameter identification of the fan model
Real process of the multi-zone
air conditioning system
M
Model-based
predictor
k
out,
set
⋅(
H
k
out
COP
− H
� Site Implementation and Validation of Optimal
Ventilation Strategy for Fresh Air Control
� CO2-based occupancy detection
Number of occupancy
� Site counting the number of
occupancy in the typical floor
100
90
80
70
60
50
40
30
20
10
Demand-controlled Ventilation control
Counted
Predicted
0
8:30 9:30 10:30 11:30 12:30 13:30 14:30 15:30 16:30 17:30 18:30
Time (hour)
k
rtn
� Comparison
between counted
and predicted
occupancies
)

� Practically test and validation of the ventilation
control strategy
Tests aimed at validating the actual operational performance of the
ventilation control strategy and also for verifying whether the control
settings provided by PolyU strategy can be properly sent to the ATC
system and further be used in practical control.
AHU1
AHU2
Study cases
Control strategy
Fixed flow PolyU Fixed flow PolyU
About 662,000 Primary fan energy kWh consumption energy savings can be
612.29 607.99 794.60
761.92
Site test case
(kWh)
(PolyU strategy achieved only applied to by Primary using fan energy saving PolyU (%) - ventilation +0.70 - control +4.11
typical floor)
(Nov., 2009)
Energy saved due to fresh air
7.90 3.04 4.96
2.81
strategy for all cooling floors (kWh) per year in Zone 2!
Estimation case
(PolyU strategy applied to all
floors in Zone 2)
Summer case
(PolyU strategy applied to all
floors in Zone 2)
Primary fan energy consumption
(kWh)
Primary fan energy saving (%)
Primary fan energy consumption
(kWh)
Fresh air cooling energy
consumption (kWh)
Total energy consumption (kWh)
Total energy saving (%)
612.29
-
612.29
4754.4
5366.7
-
288.3
+52.9
288.3
1915.2
2203.5
+58.9
794.60
-
794.60
2985.6
3780.2
Site Implementation of The
Control Strategies
-
324.5
+59.2
324.5
1725.6
2050.1
+45.8

Implementation Strategy of Optimal Control and Diagnosis
Tools in ICC
BACnet SDK
Control
Parameters
Optimizer
Control Setting
from PolyU
Diagnosis
Control Setting
from ATC
Decision Supervisor
ATC
VAV Box
Overall KVA, etc.
Manual
Control
Chiller Plant Control Optimizer
and Diagnosis
LAN
Supply air control
optimizer
IBmanager
AHU PAU
Building
Management
System
Fresh air control
optimizer
Fresh air
terminal
Intelligent building management system
-- based on IBmanager
� IBmanager is an open and integrated management platform. It
employs standard middleware and web-service technologies to
support the integration and interoperation among distributed BASs.

Summary of Energy Benefits
• 1,000,000 kWh energy consumption is saved due to the
modification on the secondary water loops of Zone 3 & 4;
• 2,360,000 kWh , (about 5.1% of annual energy
consumption of chillers and cooling towers) of the cooling
system can be saving due to the change from single speed
to variable speed using VFD.
• 607,000 kWh , (about 2.8% of annual energy consumption
of chillers and cooling towers) of the cooling system will
be wasted when the lowest frequency is limited at 37 Hz.
• 3, 500,000 kWh (about 7%) of the total energy
consumption of HVAC system) can be saved using PoyU
control strategies based on the original design;
Summary of Energy Benefits
• 1,000,000 Saving Saving Saving Saving by by by by kWh Commissioning Commissioning
Commissioning
Commissioning energy consumption (Improving (Improving (Improving (Improving is saved the the the the due system system system system to the
modification on the secondary water loops of Zone 3 & 4;
configuration configuration configuration configuration and and and and selection selection selection selection – compared with the
• 2,360,000 kWh , (about 5.1% of annual energy
original design.
consumption of chillers and cooling towers) of the cooling
system can be saving due to the change from single speed
to variable speed using VFD.
• 607,000 kWh , (about 2.8% of annual energy consumption
of chillers and cooling towers) of the cooling system will
be wasted when the lowest frequency is limited at 37 Hz.
• 3, Saving Saving Saving 500,000 by by by kWh Control Control Control (about Optimization
Optimization
Optimization 7%) of the total energy
consumption of HVAC system) can be saved using PoyU
case
control
when
strategies
the HVAC
based
system
on the original
operates
design;
correctly
Saving by Control Optimization – compared with the
according to the original design intend.

Summary of Energy Benefits
• 1,000,000 Saving Saving Saving Saving by by by by kWh Commissioning Commissioning
Commissioning
Commissioning energy consumption (Improving (Improving (Improving (Improving is saved the the the the due system system system system to the
modification on the secondary water loops of Zone 3 & 4;
configuration configuration configuration configuration and and and and selection selection selection selection – compared with the
• 2,360,000 kWh , (about 5.1% of annual energy
original design.
consumption of chillers and cooling towers) of the cooling
system can be saving due to the change from single speed
to variable speed using VFD.
The annual total energy
• 607,000 kWh , (about 2.8% of annual energy consumption
of chillers saving and cooling is towers) about of the 7.0M cooling kWh system will !
be wasted when the lowest frequency is limited at 37 Hz.
• 3, Saving Saving Saving 500,000 by by by kWh Control Control Control (about Optimization
Optimization
Optimization 7%) of the total energy
consumption of HVAC system) can be saved using PoyU
case
control
when
strategies
the HVAC
based
system
on the original
operates
design;
correctly
Saving by Control Optimization – compared with the
according to the original design intend.
Summary of Experience in ICC
• Significant energy saving can be achieved by
allowing the system as good as the design intention
by identifying and correcting the errors at different
stages;
• Significant energy saving can be achieved by
making the system better than the design intention
by enhancing and optimizing the systems at different
stages;
• The involvement of a professional energy consultant
(commissioning agent) does not introduce troubles
to the building construction project, but instead it
facilitates different parties involved to support each
other to do their jobs smoothly and correctly.