Transcript Chilled-Water Systems

Chilled-Water Systems
Types of Chillers & System Design
© Trane
Air Conditioning Clinic TRG-TRC016-EN
Chilled-Water Systems
period one
Types of Water Chillers
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Air Conditioning Clinic TRG-TRC016-EN
Vapor-Compression Cycle
reject heat
D
C
condenser
compressor
expansion
device
energy in
A
evaporator
B
absorb heat
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Compressor Types
scroll
reciprocating
helical-rotary
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centrifugal
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Condenser Types
air-cooled
water-cooled
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Air-Cooled or Water-Cooled
water-cooled
air-cooled
0 tons
500 tons
1,000 tons
1,500 tons
2,000 tons
2,500 tons
3,000 tons
[0 kW]
[1,759 kW]
[3,517 kW]
[5,276 kW]
[7,034 kW]
[8,793 kW]
[10,551 kW]
chiller capacity
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air-cooled or water-cooled
Maintenance

Water treatment

Condenser tube brushing

Tower maintenance

Freeze protection

Makeup water
cooling tower
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Air Conditioning Clinic TRG-TRC016-EN
Part-Load Efficiency Rating

Integrated Part-Load Value (IPLV)
 Weighted-average
 Based
on an “average” single-chiller installation
 Standard

load curves
operating conditions
Non-Standard Part-Load Value (NPLV)
 Weighted-average
 Based
on an “average” single-chiller installation
 Non-standard
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load curves
operating conditions
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AHRI Standard 550/590 (Air-Cooled Chiller)
AHRI Definition of Integrated Part Load Value (IPLV/NPLV)
IPLV =
1
1%
A
+
42%
B
+
A = kW/Ton @ 95°F(30°C) @ 100% Load
45%
C
+
12%
D
B = kW/Ton @ 80°F(24°C) @ 75% Load
C = kW/Ton @ 65°F(18°C) @ 50% Load
D = kW/Ton @ 55°F(18°C) @ 25% Load
Temperatures: Expected Entering Air Temperature
AHRI Conditions: Chilled Water: 54°/44°F
Ambient Temperature: 95F
1% (95°F)
12%
55°F
99% of chiller
operation is at ambient
of ≤ 80°F!
80°F
65°F
45%
© American Standard Inc. 2001
42%
Is this true for your building profile?
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Real World Comparisons
Houston (Two Chiller Plant)
1
IPLV =
Custom Analysis versus Generic NPLV Estimates
16% of Operation
(IPLV = 45%)
45% of Operation
(IPLV = 42%)
1%
+
A
42%
+
B
45%
+
C
12%
D
36%
Operation
(IPLV = 1%)
3% of Operation
(IPLV = 12%)
© American Standard Inc. 2001
An Air-Cooled Chiller Example
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air-cooled or water-cooled
Comparison
air-cooled
water-cooled

Lower maintenance

Greater energy efficiency

Packaged system

Longer equipment life

Better low-ambient
operation
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Air Conditioning Clinic TRG-TRC016-EN
Chilled-Water Systems
period two
Chilled-Water System Design
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Chilled-Water System Components
cooling tower
cooling coil
pumps
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chiller
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Chilled-Water System
air-cooled
chiller
coil
pump
control
valve
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Load-Terminal Control Options

Three-way
modulating valve

Two-way
modulating valve

Face-and-bypass
dampers
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Three-Way Valve Control
airflow
three-way
modulating
valve
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bypass
pipe
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Two-Way Valve Control
airflow
two-way
modulating valve
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Face-and-Bypass Damper Control
bypass
damper
airflow
face
damper
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Load-Terminal Control Options

Three-way modulating valve
 Constant
 Variable

return-water temperature
Two-way modulating valve
 Variable
water flow (pump energy savings)
 Constant

water flow
return-water temperature
Face-and-bypass dampers
 Constant
 Variable
water flow
return-water temperature
 Enhanced
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dehumidification capability with “wild” coils
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Chiller Evaporator Flow

Constant flow is most
common

Variable flow is
possible
 Can
reduce energy
consumption
 Use
only with
advanced chiller and
system controls
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evaporator
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Single-Chiller System
air-cooled
chiller
pump
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coil
three-way valve
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Multiple-Chiller Systems

Redundancy

Part-load efficiency
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chillers piped in parallel
Single Pump
54°F
off
[12.2°C]
on
42°F
48°F
[5.6°C]
[8.9°C]
54°F
[12.2°C]
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Air Conditioning Clinic TRG-TRC016-EN
chillers piped in parallel
Dedicated Pumps
off
42°F
on
[5.6°C]
54°F
60% to 70%
of system flow
[12.2°C]
coil starved for flow
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chillers piped in parallel
Dedicated Pumps
head pressure
2 pumps
1 pump
system
curve
65%
100%
percent flow
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Chillers Piped in Series
electric
chiller
absorption
chiller
three-way valve
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chillers piped in series
Equal Set Points
set point = 42°F [5.6°C]
set point = 42°F [5.6°C]
42°F
48°F
[5.6°C]
[8.9°C]
54°F
[12.2°C]
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chillers piped in series
Staggered Set Points
set point = 42°F [5.6°C]
set point = 48°F [8.9°C]
42°F
48°F
[5.6°C]
[8.9°C]
52°F
[11.1°C]
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Primary-Secondary Configuration
production
pumps
distribution
pump
production
loop
distribution
loop
two-way valve
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Primary-Secondary System Rules

The bypass pipe should be free of restrictions
 Sized
for minimal pressure drop
 Avoid
random mixing of supply- and return-water
streams
 No
© American Standard Inc. 2001
check valve
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Production Loop
production
pumps
supply
tee
return
tee
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Manifolded Production Pumps
production
pumps
isolation
valves
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Distribution Loop
supply
tee
distribution
pump
return
tee
two-way valve
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Primary-Secondary System Rules

The bypass pipe should be free of restrictions

Load terminals should use two-way
modulating control valves
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Varying Distribution Flow
head pressure
B
pressure
difference
variable-speed control
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pump
curve
A
0
50
percent flow
100
riding the pump curve
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Multiple Distribution Pumps
distribution
pumps
return
from loads
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supply
to loads
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Multiple Distribution Pumps
distribution
pumps
return
from loads
C
B
A
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A
C
B
supply
to loads
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Tertiary Pumping
distribution
pump
tertiary
pump
two-way
valve
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bleed line
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Distribution Loop Characteristics

Reduced pump
energy use

Distribution loop
sized for system
diversity

Higher return-water
temperatures
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
Primary-Secondary System Rules

The bypass pipe should be free of restrictions

Load terminals should use two-way
modulating control valves

All chillers should be selected for the same
leaving chilled-water temperature and T
© American Standard Inc. 2001
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System Operation
production
loop
return
tee
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supply
tee
distribution
loop
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Deficit Flow
1,000 gpm at 42°F
[63 L/s at 5.6°C]
1,000 gpm at 56°F
1,200 gpm at 44.3°F
[63 L/s at 13.3°C]
[76 L/s at 6.8°C]
1,200 gpm at 56°F
© American Standard Inc. 2001
[76 L/s at 13.3°C]
Air Conditioning Clinic TRG-TRC016-EN
Excess Flow
2,000 gpm at 42°F
[126 L/s at 5.6°C]
2,000 gpm at 54.6°F
1,800 gpm at 42°F
[126 L/s at 12.6°C]
[114 L/s at 5.6°C]
1,800 gpm at 56°F
© American Standard Inc. 2001
[114 L/s at 13.3°C]
Air Conditioning Clinic TRG-TRC016-EN
Control of Primary-Secondary System
condition
response
deficit flow for
specified period of
time
start another
chiller and pump
excess flow greater
than 110% to 115% of
next pump to turn off
turn off next chiller
and pump
neither
do nothing
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
Types of Fluid Flow Meters

Pressure-based
 Pitot
tube
 Venturi
 Orifice
plate
 Differential
pressure

Turbine and impeller

Vortex

Magnetic

Ultrasonic
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Temperature-Based Calculations
supply
tee
return
tee
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system-level
controller
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Chilled-Water Systems
period three
System Variations
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price of electricity, $/kWh
Electric Utility Deregulation
0.30
0.20
0.10
San Diego, CA
2000
© American Standard Inc. 2001
May
June
July
August September
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Fuel Choice Options
absorption
thermal storage
power
control interface
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indirectly-coupled,
gas-engine
chillers
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Chiller Efficiency Improvements
8.0
COP
0.8
7.0
0.7
6.0
0.6
5.0
kW/ton
0.5
1970
1980
1990
4.0
chiller efficiency (COP)
chiller efficiency (kW/ton)
0.9
2000
year
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Greater Focus on System Efficiency
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Trend Toward Lower Flow Rates
electric-driven chiller
yesterday
today
evaporator
flow rate
2.4 gpm/ton
[0.043 L/s/kW]
1.5 gpm/ton
[0.027 L/s/kW]
leaving
chilled-water
temperature
44°F
[6.7°C]
41°F
[5°C]
condenser
flow rate
3.0 gpm/ton
[0.054 L/s/kW]
2.0 gpm/ton
[0.036 L/s/kW]
entering
condenser-water
temperature
85°F
[29.4°C]
85°F
[29.4°C]
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
annual energy consumption, kWh
Low-Flow Systems
750,000
600,000
chiller
450,000
300,000
pumps
150,000
© American Standard Inc. 2001
0
cooling tower fans
base case
low flow
Air Conditioning Clinic TRG-TRC016-EN
Variable-Primary-Flow Systems
variable-flow
pumps
check
valves
control
valve
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two-way
valve
optional bypass
with three-way valve
Air Conditioning Clinic TRG-TRC016-EN
Critical VPF System Requirements

Chillers must handle variable evaporator flow

System must include a bypass

System-level controls must limit the rate-offlow change

Adequate time to design and commission
controls

Operator must understand the system
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
Preferential Chiller Loading
distribution
pump
equally
loaded
preferentially
loaded
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absorption
chiller
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Sidestream Configuration
distribution
pump
heat-recovery
chiller
© American Standard Inc. 2001
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Heat-Recovery Chiller
heat-recovery
condenser
standard
condenser
evaporator
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Heat-Recovery Chiller Options
heat-recovery
(dual) condenser
auxiliary
condenser
heat pump
 Second,
 Second,
 Large
 Preheating
fullsize condenser
heating
loads
 High
hot-water
temperatures
smaller-  No extra
size condenser
condenser
loads
 Moderate
hot-water
temperatures
 Controlled
 Uncontrolled
 Degrades
 Improves
chiller efficiency
© American Standard Inc. 2001
efficiency
chiller
 Large
base-heating
loads or continuous
operation
 High
hot-water
temperatures
 Controlled
 Good
heating
efficiency
Air Conditioning Clinic TRG-TRC016-EN
Heat-Recovery Chiller Efficiency
cooling
mode
heat-recovery
mode
cooling-only
centrifugal chiller
0.57 kW/ton
[6.2 COP]
not
applicable
heat-recovery
centrifugal chiller
0.60 kW/ton
0.69 kW/ton
[5.9 COP]
[5.1 COP]
chiller type
cooling mode conditions:
• evaporator T = 44°F to 54°F [6.7°C to 12.2°C]
• condenser T = 85°F to 95°F [29.4°C to 35.0°C]
heat-recovery mode conditions:
• evaporator T = 44°F to 54°F [6.7°C to 12.2°C]
• condenser T = 85°F to 105°F [29.4°C to 40.6°C]
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
percent maximum pressure differential
Control of a Heat-Recovery Chiller
120
100
A
B
80
C
60
0
© American Standard Inc. 2001
unloading with
constant entering hotwater temperature
50
percent load
unloading with
constant leaving hotwater temperature
100
Air Conditioning Clinic TRG-TRC016-EN
Asymmetric Design

Different chiller
capacities
Different chiller
efficiencies
10,000
annual operating hours

8,000
4,000
lead
chiller
2,000
0
© American Standard Inc. 2001
lag
chiller
6,000
60% / 40%
50% / 50%
chiller split
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Swing Chiller
equal-capacity
large chillers
small-capacity
“swing” chiller
© American Standard Inc. 2001
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Swing Chiller
100
percent cooling load
swing chiller
80
60
swing chiller
chiller 2
40
20
swing chiller
0
chiller 1
chiller sequence
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
“Free” Cooling

Airside economizer

Waterside economizer
 Strainer
cycle
 Plate-and-frame
 Refrigerant
© American Standard Inc. 2001
heat exchanger
migration
Air Conditioning Clinic TRG-TRC016-EN
waterside economizer
Plate-and-Frame Heat Exchanger
distribution
pump
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plate-and-frame
heat exchanger
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waterside economizer
Refrigerant Migration
from
compressor
condenser
to
compressor
liquid
flow
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shutoff
valve
vapor
migration
shutoff
valve
evaporator
Air Conditioning Clinic TRG-TRC016-EN
Application Outside Range of Chiller
air-cooled
chiller
240 gpm at 45°F
[15 L/s at 7.2°C]
240 gpm at 56.7°F
[15 L/s at 13.7°C]
80 gpm at 45°F
[5 L/s at 7.2°C]
80 gpm at 80°F
[5 L/s at 26.7°C]
process load
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN
Chilled-Water Systems
Types of Chillers & System Design
© American Standard Inc. 2001
Air Conditioning Clinic TRG-TRC016-EN