႔
Chapter-17 Chilled Water System Configurations
Chapter-17 Chilled Water System Configurations ၁၇.၁ Chilled Water Plant Basics Chilled water plant
(functional parts)
(၁) Chilled water
ၾ
chiller
(၂) Air Handling Units(AHU) ၊ Fan Coil Units(FCU) ၊ CRAC units (၃) Chilled water distribution pumps and pipes (၄) Condenser water pumps, pipes, and cooling towers (၅) Controls (operation of the mechanical components together as a system)
႔
၁၇.၁.၁ Chilled Water Temperatures Comfort cooling system
chilled water supply temperature
6.7°C (44°F)
ၾ
3.3°C (38°F)
chilled water temperature
ၾ (၁) Chilled water temperature
ၾ
(၂) Chilled water temperature
chilled water
(flow)
ၾ
(lower supply air temperature)
(air flow rate) (၃) Chilled water temperature
Air side ၾ
chilled water coil ၌
႔
(dehumidification) (၄) Chilled water temperature (၅)
system efficiency
ၾ
chilled water distribution system ၏ capacity
chilled water temperature Chilled water temperature
consumption)
Chilled water flow rate
(energy
system
(၆) Chilled water temperature
ၾ ၾ
chiller ၏
chiller
၏
(energy
႔
၏ system
၌ condensation (sweating) 17-1
Chillers and Chilled Water Systems
႔
insulation
Chilled water
34°F(1.1°C)
chiller
(sophisticated) evaporator
chiller control
(method)
၁၇.၁.၂ Effect of Chilled Water Temperature Chiller
leaving chilled water temperature
temperature
refrigerant
pressure
႔ refrigerant temperature
leaving chilled water
leaving chilled water
pressure
႔ ၾ
compressor work
၏
(energy consumption)
Chiller
system
၏
Leaving chilled water temperature
ၾ
chiller
pump
ၾ
temperature
(flow rate)
chilled water
ၾ
၁၇.၁.၃ Effect of Chilled Water Flow Rate Evaporator
heat exchanger
ၾ
Chilled water (erosion)၊ (flow rate)
chilled water
(flow rate)
(vibration) ၊
ၾ (noise)
heat transfer efficiency
(flow rate)
(water velocity)
ၾ
ၾ
႔ chiller performance
႔ ၾ
(minimum flow)
၁၇.၁.၄ Condenser Water Temperature chiller
enteri Design temperature
(lowest allowable temperature)
chiller condenser water temperature
၌
၁၇.၁.၅ Effect of Condenser Water Temperature Chiller pressure
entering
refrigerant temperature
႔
Entering condenser water temperature
(temperature)
(pressure)
consumption)
compressor
၏
Entering
(power consumption) (energy
ၾ
(power ၾ
Chiller
system
consumption) ၾ
refrigerant
၏
Entering
chiller efficiency
၁၇.၁.၇ Effect of Condenser Water Flow Rate Condenser
heat exchanger
(flow) (vibration) ၊ heat transfer efficiency (startup conditions) (specific range of limits) 17-2
ၾ
ၾ
(water flow rate)
(water velocity)
(noise)
႔ Chiller performance
condenser water flow
(erosion)၊ (flow rate) Chiller
ၾ ႔
႔
Chapter-17 Chilled Water System Configurations
ၾ
water velocity
(water hardness) tube
condenser tube
F
၌
၌
(water hardness)
velocity
3.51 ft/s (1.07 m/s)
၁၇.၁.၈ Chilled Water and Condenser Water Flow Rates Chilled water system
condenser water
(installation)
(flow rate)
ၾ
chilled water
(operation)
AHRI 550/590
flow rate •
2.4 gpm/ton [0.043 liter per second/kW] for evaporator water flow rate
•
3.0 gpm/ton [0.054 lps/kW] for condenser water flow rate flow rate
(temperature difference) 10°F(5.5°C)
Compressor efficiency 9.1°F(5.1°C)
condenser
(temperature difference)
10°F(5.6°C)
၁၇.၂ Single Chiller System Chiller configuration
single chiller system Chiller plant
chiller
ၾ
၁၇-၁ Chiller (
) Chiller
၏ condenser water loop ၾ
chiller ၏
system
chilled water
႔ ၾ ႔ single chiller system
system
၊
၊
(break down)
႔
Multiple chillers standby chiller
“
h
”
Standby chiller
chiller
(break down) ၾ
( ) Chiller
၊ data center
multiple chillers system
system Standby chiller
(break down)
computer center ႔
(application)
chilled water loop
ၾ Centrifugal compressor
load
chiller
႔ ၾ
chiller full load capacity ၏ 30% 17-3
Chillers and Chilled Water Systems
႔
Chilled water plant
chiller
“installed capacity”
၏
Peak load
“running capacity”
capacity
chiller
Running capacity
capacity
“
”
“capacity to load ratio” - chiller plant (500RT x 4)
500RT chiller (၄)
Peak load
1,500RT (500RT x 3)
install capacity
500RT chiller (၃) ႔ ၾ
2,000RT
running capacity
capacity to load ratio
0.75(1,500RT/2,000RT)
၁၇.၂.၁ Single Chiller System Advantages and Disadvantages Table 17-1 advantages and disadvantages of single chiller system (Advantages)
(Disadvantages)
– Lower first cost
– Inefficient at low load conditions
– Simple system for installation and control
– Lack of back-up and redundancy
၁၇.၃ Multiple Chiller System
၁၇-၂ Chiller configuration chiller
ၾ
chiller
ၾ
water cooled plant
system reliability
efficiency
႔
chiller
Multiple chiller system configuration configuration ၏ 95%
parallel configuration ၊ chiller
chiller 2011
႔
parallel
Chilled water
ၾ ၊ consultant
AHRI Standard 550/590-2011
AHRI
(contractor) ၾ
Reference AHRI 550/590-
“performance rating of water chilling packages using the vapor compression cycle” AHRI 550/590-2011 chiller
17-4
series configuration
Parallel configuration
Chiller ၾ
Chiller
chillers ၊ cooling towers ၊ chilled water pumps ၊ condenser water pumps ၊
piping ၊ accessories controls
plant
႔
(comply)
chiller
၊
႔
Chapter-17 Chilled Water System Configurations
Chiller ၏ parameter ၾ
chiller
(standard) ၏ efficiency (k
Load Value (IPLV)
၊
Non-standard Part Load Value (NPLV)
AHRI 550/590-2011 Chiller
performance
Integrated Part ႔
(standard)
S
(construction) E
15 “S R22
႔
(installation)
M h
R134a
psig
” chiller
၏ condenser
(pressure)
႔
Part load
chiller manufacturer
Chiller
(comply)
maximum capacity )
15
pressure vessel
(comply)
Underwriter Laboratory (UL) standard 465 Chiller
႔
ASME(American Society of Mechanical Engineering)
၏ boiler and pressure vessel code
(
evaporator
ၾ
Pressure vessel
႔
(
)
႔ ၾ
part load operating performance
Intergrated Part Load Value (IPLV)
Non-standard Part Load Value (NPLV)
(၂)
၁၇.၄ Parallel Chillers System Table 17-2 advantages and disadvantages of parallel chillers system (Advantages) – More efficient at low load conditions
(Disadvantages) – Increased first cost
– Provides back-up and/or redundancy – More difficult to control effectively, especially with different size chillers (should have computerized system) – More equipment to maintain h (၁) Primary only system (၂) Primary - Secondary system (၃)
၁၇.၅ P
O P
႔
S h
“primary only system”
P h
h
ၾ h
”
h
S ႔
h ႔
“ h ႔
h
h ႔
h secondary chill
17-5
Chillers and Chilled Water Systems
႔
၁၇-၄
၁၇-၅
chiller ၁၇-၆
h
h
႔
h h
၁၇-၆
၁
႔
၂
h
ch Dedicated
pump
h
႔ chiller
၁၇-၃ Primary only circuit
၁၇-၄ Common header system
၁၇-၅ One to one
႔
dedicated system
၁၇-၆ Primary only system with common header
၁၇.၅.၁ Primary Only System with Common Header ၁၇-၆)
primary only system
Primary
h
h
water ၆)
seconadry chilled
h production loop(primary ch
၁၇-
႔ 17-6
h
c ႔
h h
႔
Chapter-17 Chilled Water System Configurations
h
h
h
primary chilled water pump ႔
pump h
h
႔
h
h
႔
ၾ
႔
h
h
h
၊ ႔
h
၊
ၾ
evaporator
h
ၾ
h
h
co
(amount chilled water flow rate)
pressure drop)
႔
ၾ
h
ၾ h
chiller
႔
ၾ
႔ ၾ
h
h
႔ h ႔ (a
constant f
h
၊ h
h
၌
႔
h
h
၁၇-၇(
၌
) Schematic of the constant-flow rate primary system.
Primary chilled water pump ႔
h
h
S
ၾ
႔
h
h
h
႔
h
႔ P
h h
chille
h ၊
႔
(size ၊ 17-7
Chillers and Chilled Water Systems
႔
complexity)
႔
chiller
႔ ၾ
႔
႔ ႔
h
႔
ၾ
ၾ
h
common h
႔
h
h
h
႔
႔
h
const
၁၇-၇( ) Primary only system with one to one configuration with two way valve h h
၁
႔
႔ ၂
h ႔
flow rate)
၂ ႔
၅
၏ h
(chilled water
h ၾ
speed)
၁၇-၈ Primary only system with dedicated pump 17-8
႔
႔
Chapter-17 Chilled Water System Configurations
႔
h
chilled water flow rate) h
h
၏
႔
leaving chilled water temperature setpoint h
h h
၊
ၾ
၏
h
h
s
instability)
၁၇.၅.၂ Primary Only System with Dedicated Pump (၁၇-၈)
၏
(office 200RT AHU
၏ design load �
600 TR (100 tons of refrigeration each floor)
AHU
AHU 600RT
capacity
ၾ
Δ
1
Chiller
ၾ Chiller
၏
total installed capacity
� 200 tons capacity chiller (၃) � Chiller
၏ capacity
chilled water supply (CHWS) temperature 44°F
12°F)
(flow rate) 400 GPM ( 4 Δ
AHU ၏ cooling coil
Δ
x
h
12°F)
)
(flow rate) 200
GPM ( 4 Δ x 1 � Dedicated pump
၁၇.၅.၃ Primary-Only System ၏ (disadvantage) (၂) control
chiller staging
bypass
႔
(၁) Chiller
plant plant ၾ
(၂)
၊ chiller
plant
base load
chiller staging
bypass control system
plant
primary-secondary system
Fail-safe
operation
primary-secondary
system
Table 17-2 advantages and disadvantages of primary-only systems Secondary pump P
ၾ
႔
h ၏ ႔ 17-9
Chillers and Chilled Water Systems
႔
၁၇.၆ Primary - Secondary System ၁၇-၇) P
h
h
h
႔
“production pump”
Primary chilled water
“production circuit/loop” S
h
“distrubution pump”
Secondary chilled water
“distrubution circuit/loop” Primary- secondary pumping system loop
chilled water system
circuit
႔
loop
circuit
႔
ၾ
၌
neutral bridge (de-coupler) (၁) Primary circuit
chilled water
Primary pump
constant volume ၊ low head pump Chiller
primary pump
(၂) Secondary circuit
ၾ one to one configuration
႔
common header
chilled water distribution
Secondary circuit ၏
pumps ၊ Fan Coil Units (FCU)၊ Air Handling Units (AHU) terminal unit
ၾ
speed pump
Secondary pump
ၾ
(၃) De-coupler secondary
secondary loop
primary loop
secondary loop
၏
႔
၏
variable
(pressure drop)
ၾ
primary loop pumping
control valves
constant speed
Secondary circuit pump
(၂)
common pipe hydraulic
၊
႔
Primary-
(primary
secondary)
၁၇.၆.၁ Dedicated Pump and Manifold Pump (Common Header) ၁၇-၁
-
Primary-secondary
h
seconadry chilled water circuit
(distribution loop) c
h
Primary chilled wa
dedicated pump
h
၊
၂
၁၇-၉-
primary chilled water
circuit/
production loop (primary chilled water Dedicated pump
႔
႔
M
h
h ႔
17-10
h
secondary chilled water pump ႔
h
ၾ
dedicated pump
ၾ
h
႔
၁၇-၉(
Chapter-17 Chilled Water System Configurations
) Primary secondary with manifolded pumps (၁၇-၉)
( )Primary secondary with dedicated pumps
primary - secondary
႔
၏
common h ၾ
ၾ
၁၇-၉( ၁၇-၉- )
“D
”
variable secondary flow) system
chilled
၌
secondary circuit
h h
priamry chilled water
flow
secondary chilled water P
secondary circuit h
ၾ ၏
flow rate)
chilled water
႔ ၾ chilled water flow rate)
၌
၏
၊ 17-11
Chillers and Chilled Water Systems
႔
၁၇.၆.၂ Dedicated Pumps at Production Loop or Primary Chilled Water Circuit/Loop Pro h
h
၏
၌ “
၊
”
၊
၊
h
ၾ
႔
evaporator pre
chiller
ၾ
dedicated pump
h
P
h
(constant flow of
water
- 5
၅
(standard chilled water flow rate)
h
၏ stand
h
1,200 GPM (500R x .4 PM
႔ two-way modulating valve
h
႔ ၾ
h
h S
D
SD
႔
Variable Frequency Dirve (VFD)
Primary chilled water pump (production pump ႔
h
႔ pressure
႔ ၾ
loss)
ၾ
႔
h
၏
h
႔
h Primary chilled wa -
h P
side)
၁၇-၁ Production loop
၁၇-၁၁ Dedicated pumps at production loop (primary chilled water circuit/loop) 17-12
-
production loop (load
x
loa
distribution loop
၁၇-၁၂ M
႔
Common header at production loop
႔
Chapter-17 Chilled Water System Configurations
H
production
(chiller) loop
distribution (AHU/FCU) loop
control Primary secondary pumping arrangement pump
(၂)
distribution
Production
႔
AHU/FCU
pump (၂) (၂)
႔ Pump
၏
ၾ Production pump
chiller
႔
primary pump
production side
(pressure drop) Distribution
distribution system
AHU/FCU
pump ႔၏
(pressure drop) ၁၇-၁၃ Decoupled arrangement Chiller
(minimum flow rate)
bypass
bypass valve
၁၇.၆.၃ Bypass Line
႔
Decouple Line sizing
Primary–secondary
variable-primary-flow system (decoupled system) Bypass line
10%
15%
chiller ၏ VPF system
bypass line (flow rate)
bypass line
chiller
၏ (pressure loss) line
bypass
water velocity x
bypass line
bypass line (၁ )
႔
Bypass
valve
၁၇-၁၄ Decoupled system supply tee
Bypass Valve
Maintain a minimum chilled water flow rate through the chillers
Differential pressure measurement across each chiller evaporator
Flow meter preferred
Modulates open to maintain the minimum flow through operating chiller(s).
Bypass valve is normally open, but closed unless Min flow breeched
Pipe and valve sized for Min flow of operating chillers
High Rangeability (100:1 preferred)
PSID Ratings for Static, Dynamic, And Close Off = Shut Off Head of Pumps 17-13
Chillers and Chilled Water Systems
႔
Linear Proportion (Flow to Valve Position) Characteristic preferred
Fast Acting Actuator
Locate in Plant around chillers/pumps (preferrred) Energy saving
၁၇.၆.၄ Bypass Control Problems Bypass control ၾ
(complex
ၾ
Chiller
flow
Magnetic
flow meter
Magnetic flow meter flow meter
(
)
(accuracy)
Elbow
Signal transmitter ( )
Valve
flow meter
ၾ ႔
ၾ
valve calibration
(differential pressure across the valve) b
control loop tuning
႔
Pump chiller
(minimum flow rate)
၏ design flow rate
(half)
၌ differential pressure
System ၾ
chiller
low load
bypass valve
chiller Control loop
tune chiller ႔
plant
control loop
tuning
pressure independent control valve
Pressure independent control valve (constant differential pressure) ( )
(flow)
၊
system ႔
bypass control
control
control
- AHU
၊ AHU
bypass control
control (ဃ)
(complex) control system ႔
Bypass system
(nuisance) chiller trip
Manual reset ၾ
႔
reset (out of service)
(operator)
ၾ hydraulically decouple
production
distribution
႔
(flow rate) ၾ
(
) Bypass piping
( ) No-flow static head (from the building water column) ( ) Water 17-14
႔
ၾ Pumping system
႔
Chapter-17 Chilled Water System Configurations
D
h
chillers
႔ ၾ
chiller
(flow)
D
(number of operating
႔
bypass pipe
restriction
Bypass piping ၌
(zero pressure loss) bypass piping
႔
႔
(restrictions)
- check valve
၁၇.၆.၅ Production Loop/Circuit
႔
Primary Loop/Circuit Production loop
distribution loop
(independent chilled
water
Conventional
temperature
controller
၊
၊
၊ chiller (simplest)
႔ ၾ
chiller
leaving chilled water system temperature rise
၁၇-၁၅ Production loop Decoupled system
chiller
ၾ
chilled water temperature
chiller
Distribution pump
႔
distribution piping
secondary pump AHU/FCU
chiller water header
supply header water
႔
႔
terminal unit
႔
Distribution system
(၁၇-၁၆)
distribution system flow control
Cooling coil
configuration
flow control valve
ၾ
ၾ Load
cooling coil valve
three way valve Two-way modulating valve
ၾ
Chiller
f
႔ system
-
pump
(energy consumption) variable speed drive distribution pump
Decoupled system ၾ 17-15
Chillers and Chilled Water Systems
႔
AHU ၊ FCU ၊ CRAC unit
terminal equipment
(simultaneously) peak load load
load
(sum of the peaks load)
ၾ
ၾ
Variable flow system
႔ chiller ၊ pump
pump
pipe
(sizes)
load
႔
႔ ၾ
ၾ
႔
over pumping
(pumping energy) AHU ၊ FCU ၾ
peak
Return water temperature
႔
(return water temperature)
chilled water
cooling coil
႔
ၾ ႔
၌
ၾ
chilled
water return system
part load condition ၌ return water
Counter flow cooling coil
design temperature
coil
chilled water
Return water chiller
၏
၏ efficiency
Return water
system
configuration
၁၇.၆.၆ Secondary Loop Flow Control ၏
P configuration
ၾ Variable
terminal equipment
two-way automati
Variable Frequency Drive (VFD)
၊
farthest point or last control valve and terminal ၌ Primary/secondary system P
P
primary variable flow design
႔
two way
h
-
႔၏
႔
S set point
SD
h
P V D
17-16
၏
-h
႔
Chapter-17 Chilled Water System Configurations
h
ၾ
Pressure D
HVAC Controls and Building Automation Systems
S ၌
h
(minimum pressure
h
ၾ
S
pressure differential sensor
D ၏
signal
System demand
႔
ၾ
open
control valve
system pressure difference) ၾ
pump speed
Part Distribution syste ၾ
distribution flow
Δ Consta -
flow constant ႔
valve
h
bypass port
ၾ
ၾ
terminal heat transfer device
Constan
၊
Three way FCU
terminal heat exchange device (AHU/FCU)
ၾ
၌
ၾ ၏
supply temperature set point
S ၾ
ၾ
temperature difference
flow installation cost ႔
heat
ၾ
x h
ၾ
(temperature difference h
၏
pump System
efficienc
17-17
Chillers and Chilled Water Systems
႔
၁၇-၁၆ Constant flow primary/secondary chilled water system Variable flow distrib P
Δ
-
modulating two-way S
E ES
S
.1–1
S
. .4.1
-
SD
(၁၇-၁၆)
constant primary and constant variable system
Constant speed primary pumps
၁၇-၁၈ VSD control
Seconadry chilled water p
supply tee
load terminal
႔
႔
႔
ၾ
chilled water c water p
႔
၏ friction
၏h
seconadry chilled water c
h
AHU/
႔
seconadry chilled water pump ၾ
pump curve
AHU/FCU/CRAC u
h
Primary chilled water p h
၏
constant speed secondary pumps
၁၇-၁၇ Distribution loop and bypass pipe FCU/CRAC unit
D
႔၏
primary chilled water p s
၏h
primary
seconadry chilled
၏ friction
(
ၾ Primary chilled water pump ၏ Seconadry chilled water pump ၏ ၏ 17-18
h
၏ ၏
႔
Chapter-17 Chilled Water System Configurations
S
h
၏
chilled water flow rat
၏ cooling
၏ cooling ႔ ၾ
h
၏
h Seconadry
h
Variable S
Frequency Drive (VFD)
D
SD
speed (chilled w
S
႔
Variable
႔
၌
ၾ
h
၏
SD
part l
energy saving)
-
S
(pressure difference between the supply and return water piping)
va
variable sp ႔
differenti
Variable
Speed Drive SD
၁၇-၁၉(
)
႔
h
၁၇-၁၉( )
႔
high
႔
raise) ၏ cooling
႔၏
Cooling
-way control
h
way control valve
two႔
ၾ
differential pressure) seconadry chilled water pump (distribution pump ၏
speed)
distribution
႔ ႔
- ၁၇-၁၉- ) ႔
႔
multiple distribution pump configuration) East building (A) ၊ ၊ B
B
႔
17-19
Chillers and Chilled Water Systems
႔
႔
ၾ
x
႔
primary circuit (supply f
secondary circuit (demand f
႔
P ႔
h
ၾ ၾ
၁၇-၂ Secondary flow (1200 GPM
၁၇.၆.၇ Secondary (Demand) Flow Secondary flow (1200 GPM
primary flow (800 GPM)
Primary (Supply) Flow
႔
႔
primary flow (1200 GPM
႔
၁၇-
၂ (၁၇-၂ )
building cooling
water flow rate)
1
PM
Primary circuit (productio
1
h ႔ ၾ
1
PM
၃
ၾ
PM ႔
၌ chilled water
၁၇.၆.၈ Secondary (Supply) Flow Secondary flow (1200 GPM
17-20
4
p ၾ
၂၁)
(chilled
Primary (Demand) Flow primary flow (800 GPM
၁၇-
႔
Chapter-17 Chilled Water System Configurations
၁၇-၂၁ Secondary circuit (demand) 1200 GPM > Primary circuit (supply) 800 GPM
၁၇-၂၂ Secondary circuit (demand) 600 GPM < Primary circuit (supply) 800 GPM Secondary 1,
b
chilled water flow rate)
PM
P
1 ၾ
h
PM
pump (၂)
PM
႔ ၾ (1200GPM - 800GPM)
400
4
GPM
႔ ၾ 17-21
Chillers and Chilled Water Systems
႔
400 GPM
႔
S
chilled water flow(1200)
chilled water flow
PM
ၾ
h
႔
႔ h
h
ၾ
h
h
၁၇.၆.၉ Secondary (Supply) Flow
Primary (Demand) Flow
Secondary flow (600 GPM
primary flow (800 GPM
၁၇-၂၂ P
၏
Secondary circuit (de
h
PM
၏
(chilled water flow rate)
PM
႔ ၾ
GPM
(800-600)
႔ ၾ
GPM
secondary circuit (demand)
႔
S
chilled water flow chilled water flow (800 GPM)
PM ၾ
h
႔
႔
h h
h
႔
ၾ
h
h D
h
၁၇.၆.၁ Primary-secondary system ၏ Primary-secondary system ၏ (၁)
Evaporator
၌
(constant flow through evaporator)
Primary-secondary system
s
chiller ၏ evaporator
၌
႔ Chiller evaporator l
Primary-secondary system
႔ primary loop
control
staging sequence
17-22
(freezing)
Load
Primary flow decouple
(၂)
၌
(inadvertent shutdown) system flow
chilled water Chiller controls packages
Chiller
load
႔
(၃)
Chapter-17 Chilled Water System Configurations
Primary-secondary system
၊
႔ ၾ
system၊
system၊
ၾ (၄)
Total dynamic head
independent loop
၁၇.၆.၁၁ Primary/Secondary System
႔
၏
၏
(Disadvantages)
Primary-secondary system ၏ (၁)
Δ s Primary-secondary system
evaporator
႔ ၾ
chiller water flow rate
႔ ႔ ၾ
(actual flow) load
flow rate flow
chilled water return
temperature C
secondary pump VSD ၾ
Primary loop
decouple
႔
ၾ
bypass
chilled water supply
return water
return water temperature
(၂)
(၃)
pump speed ႔
system efficiency
(Capital investment)
(Higher operating and energy costs) Primary-secondary system Primary loop
constant speed constant flow
ၾ
Pump
(၄
variable speed pump off-peak load ၾ
(Requires more plant space) Primary pump
secondary pump
၁၇-၂၃ Primary secondary System
ၾ
၁၇-၂၄ Variable Primary Flow (VFP) system 17-23
Chillers and Chilled Water Systems
႔
Table 17-4 primary-secondary chilled water system ၏ Chiller flow
load flow
ၾ
႔ (temperature differential)
equipment
system Thermal storage system
(sophisticated) control system
Water side economizer
၁၇-၂၅ Variable primary chilled water plant
၁၇.၇ Variable Flow Primary (၁)
၂
chiller
(၂)
(Simplifies system design)
(၃)
(minimum flow)
variable flow modulating control valve
Bypass (၄)
(parallel)
႔
parallel or series design) 17-24
(series)
(System can be
႔
Chapter-17 Chilled Water System Configurations
Summary on Variable Primary Flow (VPF) Chillers
Pumps
Size equally with same WPDs (best)
Respect Min/Max Flows through chillers
Set Pump VSD Ramp function to about 10%/min (600 sec 0 to Max Speed)
Use Modulating Valves (preferred) on chiller evaporator headered pumping
Use 2 Position Valves (1 min stroke) on chiller evaporator dedicated pumping
VSD Controllers
Headered Pumping Arrangement (preferred)
Dedicated Pumping OK (over-size pumps)
2 Way Valves
Select for Static, Dynamic, Close-off ratings (PSID) equal to pump SOH (plus fill pressure)
Range-ability 100 to 200:1
If Bypass – fast acting, linear proportion
If Coils –
“O -O ”
1 -15 min
intervals) Controls
Set-point far out in index circuit (lower the value, the better the pump energy)
Set Ramp function in VSD Controller (10%/min average)
Run 1 more pump than chillers (when headered)
Chillers On by common Supply Temp, Load, Amps, Adj Flow (Adj for Low Delta T)
Chillers Off by Amps, Load, Adj Flow (Adj for Low Delta T)
Over-pump Chillers to combat Low Delta T and get Max Cap out of chillers
Bypass controlled by Min flow (preferred) or Min WPD of largest chiller (locate in plant for best energy, but can go anywhere in system)
၁၇.၇.၁ Variable Primary Flow Only (VPF) Advantages (၁)
Lower Capital Cost Installed (vs Primary/Secondary)
(၂)
No secondary pumps/piping/valves/electrical to buy and install
(၃)
Fewer piping and electrical connections – less field labor
(၄)
No large Common pipe, but smaller Bypass pipe/valve/flow meter/controls
(၅)
Lower CHW Pumping Energy
(၆)
Potential Savings, may reduce pump horsepower and initial cost.
(၇)
Reference ARTI (Air Conditioning & Refrigeration Technology Institute)
(၈)
Estimated energy savings of 3 to 8 percent
(၉)
Estimating initial cost saving of 4 to 8 percent
(၁ ) Estimating life cycling saving cost 3 to 5 percent (၁၁) Smaller Footprint (vs Primary/Secondary) (၁၂) More space available or better access to the other equipment (၁၃) Higher Reliability (၁၄) Fewer mechanical components (၁၅) Any pump can serve any chiller 17-25
Chillers and Chilled Water Systems
႔
(၁၆) Lower Capital Cost Installed (vs Primary/Secondary) (၁၇) No secondary pumps/piping/valves/electrical to buy and install (၁၈) Fewer piping and electrical connections – less field labor
၁၇.၇.၂ Variable Primary Flow Only (VPF) Disadvantages (၁) Potentially higher PSID rated 2-Way valves in system (၂) Requires more robust (complex and calibrated) control system (၃) Requires coordinated control of chillers, isolation valves, and pumps in sequencing (၄) Potentially longer commissioning time and start-up (ref ASHRAE Taylor article) (၅) Requires greater operator sophistication (၆) Sudden flow variation through the chiller (၇) More of an issue when additional machines are staged on (၈) More complexity with bypass control
၁၇.၈ Condenser Water Circuit h ႔ ၾ
h
၁၇-၂၆ Condenser water pump piping options ႔
condenser water piping arrangement
Option A Dedicate a pump for each condenser (၁၇-၂၆-A) Option B Provide a common header at the pump discharge and two-way automatic isolation valves for each condenser (၁၇-၂၆-B) Option C Provide a common header with normally closed (NC) manual isolation valves in the header between pumps (၁၇-၂၆-C) 17-26
႔
႔
Chapter-17 Chilled Water System Configurations
Option A -
(Advantages)
(၁) Chiller
condenser
Option A
head
(pressure drop)
pump
ၾ
option B drop
Option B
pump
chiller
ၾ
condenser pressure
၏ head
Pressure drop
balancing valve
(၂)
control Chiller
႔
Chiller
pump
pump
refrigerant
႔
ၾ
pump down
(၃) Pump
ၾ
ၾ chiller
pump
trip
chiller
ၾ
chiller
Pump
Option B
pump
chiller
chiller ၊
Option B -
(Advantages)
(၁) Redundancy
Option A Option B
(၂) Option B
pump
h
chiller
႔
႔(standby pump)
Option A
(standby pump)
႔
႔(standby pump)
Option B (၃) Isolation valve
condenser pump
chiller
(၄) Water side economizer
Water side economizer
(cold weather) (၅) Option C
headered pump
manual isolation valve
Option A
Capacity Option A
Chiller
chiller
standby pump
pump
(၆) Option A
Chiller ၾ
pump
manual isolation valve
(one to one)
Option C
Head pressure control
Option B
standby pump
Option B
၁၇.၈.၁ Refrigerant Head Pressure Control Chiller Screw chiller
၌ minimum refrigerant head (lift) evaporator
condenser
ၾ
minimum refrigerant head
Hermetic centrifugal chiller ၊ magnetic bearing chiller minimum refrigerant head
ၾ
(၂)
ၾ ၾ
refrigerant head pressure
17-27
Chillers and Chilled Water Systems
႔
Chiller
cooling tower basin chiller
ၾ
head pressure safeties
start-up head
ၾ
chiller
Low
Head pressure control
(manufacturer)
Water side economizer
minimum refrigerant head
Head pressure control temperature
၁၇.၈.၂
cold starts
cooling tower water
ၾ
head pressure
h
ၾ
Minimum Flow Rates Cooling tower
႔
distribute)
fill
႔
(uniformly
Fill (minimum flow rate) (minimum flow rate) ႔
႔
fill (dry surface)
႔
႔
႔
ၾ
(heat reject fill
၁၇-၂၇ Cooling tower cell isolation options Option A (left)
No isolation valve
Option B (center)
Auto-isolation valves on supply only
Option C (right)
Auto-isolation valves on supply and suction
Option A Option A
efficient
Cell Fan ၏
SD
(speed)
cooling tower
ၾ 25%
ၾ Option B Option B
automatic isolation valve
basin level
supply line
equalizer
- tower cell (၃) cell (၂)
17-28
၏
Duty (peak heat rejection)
equilizer isolation valve
Cell
Suction ၾ
cell
automatic
႔
Chapter-17 Chilled Water System Configurations
equalizer equalizer
cell
၏
(undersized) supply cell ) cell Overflow pipe ႔ ၾ
(overflow)
make up water valve
make up water
႔
ၾ
equalizer
Option C Option C ၌ automatic isolation valve
supply
suction line
Automatic valve equalizer
Valve ၊
၊
ၾ
Cooling tower
Option C equalizer
၁၇.၉ Low Delta – T Syndrome Chiller and leaving)
၏ capacity
flow rate
chilled water temperature difference (entering
႔၏
Constant-flow system
peak design condition
(flow rate)
∆T (difference between the chiller supply and return) Air-conditioning 1%
(applications)
႔
(operational hours) Three-way valve
ၾ
၏ 99%
Δ low Δ
ၾ
Bypass
operating temperature
(phenomenon)
HVAC industry
part load
chilled water bypass
chilled water return temperature differential
system
load (BTU/hr)
“
–
”
chiller
(rated)
capacity Chiller
chilled water leaving temperature
control
Cooling load
chilled water supply temperature ၊ chilled water return temperature ၾ
၁၇.၉.၁ Low Delta-
chilled water return temperature
Δ
- chiller 52°F
ၾ
႔
chiller ၏ loading
Syndrome ၏
Constant flow system temperature
chilled water flow
low Δ
ၾ
design return water temperature 55°F h
loading
႔ return water percentage (%
17-29
Chillers and Chilled Water Systems
႔
[ Where:
]
CHL (%): Percent chiller loading CWRTR: Real chilled water return temperature CWSTD: Design chilled water supply temperature CWRTD: Design chilled water return temperature
h
Δ
Design
= 55- 45
1 °
Δ
Actual
[ chiller
= 52 – 45 = 7°F: ]
rated capacity ၏ 70%
chiller
ၾ
Chiller
tower
pump
cooling
ၾ
၁၇.၉.၂ Chiller Performance centrifugal chiller
၏
performance (၁) h Evaporator
l
chilled water leaving temperature (relative humidity )
reset
65%
(၂) Condenser water entering temperature Chiller manufacturer (၃) Fouling factor 0.00025 h ft2 °F/Btu (0.000044 m2 °C/W)
Condensing surface fouling factor fouling factor
၊ tube cleaning
၊ outdoor air
brush cleaning system (၄) Evaporator ၏ surface area
condenser ၏ surface area
၊ condenser
chiller efficiency evaporator
contamination
႔ evaporator
(manufacturers) centrifugal chiller condenser
evaporator
ၾ
ၾ
condenser
compressor
minimum performance
႔ ၾ evaporator ၊ condenser
compressor
႔
၁၇.၁ Series Chiller System Chiller
(series)
Chiller
၏ flow rate
၏ evaporator chiller
17-30
single pass
mixing problem system flow
႔ flow rate (၂) ႔
႔
ၾ
chiller
႔
double pass
(series) ၾ
Chiller efficiency
႔
Chapter-17 Chilled Water System Configurations
၁၇-၂၈ Series chillers ၾ
upstream chiller
water
(warmer temperatures) return
ၾ ၾ
(pipe in series)
chiller
(pressure drop)
pressure loss
Low flow system ၾ
[9°C]
႔ ၾ
chiller
System
total system
(series) (temperature difference)
16°F
(pressure loss)
၁၇.၁ .၁ Advantages and Disadvantages of Series Chillers Table 17-5 advantages and disadvantages of series chillers Advantages
Disadvantages
– Easier to control with simple control systems
–
Increased pumping requirements for chilled
water – Effective with different size chillers
– Chillers may not be interchangeable
– Utilize one stand-by pump – Good for large temperature differential systems (၁၇-၂၈)
(၁၇-၂၉) ႔
multiple chiller
chiller (၂)
(၁) Chilled water coil
(series)
(series) (higher temperature rise)
(lower water flow
rate) (၂)
(series)
chiller
၏
(pressure drop)
pump head (၃) Part-load operation
control
(၄) Multiple-chiller plant
parallel
၁၇.၁ .၂ Series Counter Flow Series counter flow Downstream machine
energy
40°F [4.4°C] chilled water
Upstream machine
50°F 17-31
Chillers and Chilled Water Systems
႔
[10°C] chilled water
Downstream machine
Upstream machine
႔ 85°F [29.4°C] condenser water
႔ condenser water
5°
Condenser water ၾ
႔
Single large chiller condenser water circuit compressor
(pumping costs)
chiller
condenser water flow direction
5°
၌ lift
Chilled water
႔
ၾ
series-counter flow
duplex machine
Evaporator
duplex ၏
Efficiency
refrigerant circuit
ၾ
ၾ System reliability
၁၇-၂၉ Series counter flow chillers
၁၇.၁၁ Chiller Staging Multiple chiller plant
chiller
၊
႔
(staging the chillers, on
or off) (၁) Primary loop
chilled water flow rate
(၂) System load (၃) Chiller
chiller(s) staging chilled water pump
Chilled water system
17-32
secondary loop
၊ condenser water pump cooling load
cooling tower
၏
chilled water flow rate
႔
Chapter-17 Chilled Water System Configurations
Where: •
:
B
•D
h ……
h
:
. 4
•S :
1
•S :
h
h
•Δ : h
1B
-°F)
. .
- T supply water] in °F
fluid (water flow rate) density
specific gravity
HVAC OR (1 ton of refrigeration = Heat extraction rate of 12000 BTU/hr) - chilled water system Chilled water supply temperature capacity
၏ chilled water flow rate 42°F
return temperature
6,000 GPM 54°F
cooling
refrigeration ton
GPM = 6,000
Δ
Supply water temperature = 42°F
LF
12 °F (54°F – 42°F) 4 Δ
41
PM
Return water temperature = 54°F
( design load Chilled water pump
)
(
)
chiller ၏ flow rate
chiller
Chiller ၏ output capacity Cooling load demand
temperature range (Δ ) ၏ flow rate return water temperature
return water temperature
17-33
Chillers and Chilled Water Systems
႔
၁၇-၃ Chilled water plant
၁၇-၃၁ Chilled water plant with common header
၁၇-၃၂ Chilled water plant with common header (header pumps)
၁၇-၃၃ Chilled water plant (dedicated pumps) -End17-34
