2. Normal Performance
Chilled Water Systems
ASHRAE/IESNA 90.1 (LEED Prerequisite)
System configuration
Design parameters
System control
3. ASHRAE Standard
90.1-2007 Purpose
“… Provide minimum
requirements for the energy-
efficient design of buildings
except low-rise residential
buildings”
4. Purpose of
ANSI/ASHRAE/IESNA
Standard 90.1-2010
To establish minimum energy
efficiency requirements of buildings,
other than low-rise residential
buildings for:
1. design, construction, and a plan for
operation and maintenance, and
2. Utilization of on-site renewable
energy resources.
5. Publication and Final
Savings Estimates
Performed by Pacific Northwest National
Laboratory (PNNL)
Savingsof 90.1-2010 compared to
90.1-2004
Savings shared are modeled as of
January 2011
Includeventilation changes in ASHRAE 62.1
between 1999 and 2007 versions
6. 90.1 Progress Indicator
Including receptacle loads in modeling
Including receptacle load in % savings
calculation
Energy cost savings % Energy savings
%
Ventilation rate changes
between 62.1-1999 24.0 25.5
and 62.1-2007
7. 90.1 Progress Indicator
Excluding receptacle loads in % savings
calculation only
Including receptacle loads in modeling
Excluding receptacle load in % savings
calculation Energy cost savings % Energy savings
%
Ventilation rate changes
between 62.1-1999 30.1 32.6
and 62.1-2007
8. LEED Energy and
Atmosphere
LEED 2009
10% energy cost savings beyond 90.1-2007
LEED 2012
Public Review 2: September 2011
EA Prerequisite: 10% average energy cost and source
energy savings beyond 90.1-2010 (new construction)
EA Credit: Credit for reductions beyond 10%
9. 90.1-2010
Chiller Efficiencies
Paths A & B Before 1/1/2010 As of 1/1/2010c Test
Procedureb
Equipment Type Size CategoryUnits Path A Path Bd
Full Full Full
Load IPLV Load IPLV Load IPLV ARI 550/590
<150 tons EER ≥9.562 ≥10.416 ≥9.562 ≥12.50 NA NA
Air-cooled
≥150 tons EER ≥9.562 ≥10.416 ≥9.562 ≥12.75 NA NA
<75 tons kW/ton ≤0.780 ≤0.630 ≤0.800 ≤0.600
≥75 tons and < ≤0.790 ≤0.676
Water Cooled kW/ton ≤0.775 ≤0.615 ≤0.790 ≤0.586
150 tons
Electrically Operated,
≥150 tons and
Positive Displacement kW/ton ≤0.717 ≤0.627 ≤0.680 ≤0.580 ≤0.718 ≤0.540
< 300 tons
≥300 tons kW/ton ≤0.639 ≤0.571 ≤0.620 ≤0.540 ≤0.639 ≤0.490
<150 tons kW/ton ≤0.703 ≤0.669
≥150 tons and ≤0.634 ≤0.596 ≤0.639 ≤0.450
Water Cooled kW/ton ≤0.634 ≤0.596
< 300 tons
Electrically Operated,
≥300 tons and
Centrifugal kW/ton ≤0.576 ≤0.549 ≤0.600 ≤0.400
< 600 tons ≤0.576 ≤0.549
≥600 tons kW/ton ≤0.570 ≤0.539 ≤0.590 ≤0.400
Must meet both full and part load requirements
10. Heat rejection equipment
Fan speed control 7.5 and
greater
Capability to operate at 2/3
fan speed or less
Exceptions
Climates > 7200 CDD50
(e.g. Miami)
1/3 of fans on multiple fan
application
11. Hydronic system
design and control
Pump isolation
Chilled and hot water reset if >300,000
Btuh
Exception: Variable flow systems that
reduce pumping energy
12. 90.1-2007
Hydronic System
Design & Control
These provisions apply if pump system
power > 10 hp:
Must be variable flow unless …
Pump power ≤ 75 hp
≤ 3 Control valves
Limit demand of individual variable-flow
pumps to 30% of design wattage at 50%
flow (e.g., use VSD)
Pump head > 100 ft
Motor > 50 hp
13. Waterside
Energy Recovery required
Service Water Heating
24 hrs per day and
Heat rejection > 6 MMBtuh and
SWH load 1 MMBtuh
Recover smaller of
60% of heat rejection
Preheat water to 85°F
14. Configuration
Normal Performance
Chilled Water
production
pumps
distribution
pump
production
loop
distribution
loop
two-way valve
15. Design Parameters
Normal Performance
Chilled Water Plant
ARI 550/590 Standard Conditions
44°F chilled water
2.4 gpm/ton chilled water (10°F T)
3.0 gpm/ton condenser water
(10°F [9.3] T)
16. Control
Normal Performance
Chilled Water Plant
Chilled water distribution pump
P at most remote load
Cooling tower fans
55°F (as cold as possible)
Constant speed condenser water pumps
All these “normal” assumptions will be examined
17. High Performance
Chilled Water Plants
Standard high performance
Reduced flow rates, increased ∆Ts
Variable primary flow
Advanced high performance
Equipment capabilities
System configurations
System control
18. a history of
Chiller Performance
8.0 centrifugal
>600 tons
chiller efficiency, COP
screw
6.0 150-300 tons
scroll
<100 tons
4.0
reciprocating
<150 tons
2.0
0.0
ASHRAE Standard 90 NBI “best”
90-75 90-75 90.1-89 90.1-99 available
(1977) (1980)
19. chilled water plant design …
Provocation
Are our “rules of thumb” …
44 F chilled water supply
10 F T for chilled water system
3 gpm/ton condenser water flow
… in need of repair?
20. High Performance
Design Parameters
ASHRAE GreenGuide and CoolTools™
Chilled water T: 12°F to 20 °F
Condenser water T:
12°F to 18 °F (multi-stage)
Kelly and Chan
Chilled water T: 18°F
Condenser water T: 14.2°F
(3.6 - 8.3% energy savings in various
climates)
21. chilled water plant …humid climate
Base Design: 450 Tons
0.5% design Coil, valve and chilled
wet bulb: 78 F water piping pressure
drop: 80 ft
Entering condenser
water temperature Condenser water piping
(ECWT): 85 F pressure drop: 30 ft
Evaporator and Pump efficiency: 75%
condenser Pump motor
temperature efficiency: 93%
differences: 10 F
22. traditional design …humid climate
System Energy
Consumption
350
Energy Consumption, kW
300
250
200
150 Tower
Condenser Water Pump
100 Chilled Water Pump
Chiller (100% Load)
50
0
2.4/3.0
Chilled / Condenser Water Flows, gpm/ton
23. traditional vs. low-flow design …
System Summary At
Full Load
350
Energy Consumption, kW
300
250
200
150 Tower
Condenser Water Pump
100 Chilled Water Pump
Chiller (100% Load)
50
0
2.4/3.0 1.5/2.0
Chilled / Condenser Water Flows, gpm/ton
24. comparison …humid climate
System Summary At
75% Load
350
Energy Consumption, kW
300
250
200
150 Tower
Condenser Water Pump
100 Chilled Water Pump
Chiller (75% Load)
50
0
2.4/3.0 1.5/2.0
Chilled / Condenser Water Flows, gpm/ton
25. comparison …humid climate
System Summary At
50% Load
350
Energy Consumption, kW
300
250
200
150 Tower
Condenser Water Pump
100 Chilled Water Pump
Chiller (50% Load)
50
0
2.4/3.0 1.5/2.0
Chilled / Condenser Water Flows, gpm/ton
26. comparison …humid climate
System Summary At
25% Load
350
Energy Consumption, kW
300
250
200
150 Tower
Condenser Water Pump
100 Chilled Water Pump
Chiller (25% Load)
50
0
2.4/3.0 1.5/2.0
Chilled / Condenser Water Flows, gpm/ton
28. High Performance
Design Parameters
kWh/ton/year
600
Chilled water
400 pump
200 Chiller
0
41/16 42/14 43/12 44/10
Chilled water supply
temperature/DeltaT
29. Pipe Size Example
90.1-2010 Table 6.5.4.5
800 ton system
3,000 hours of operation
Chilled water, variable flow
Condenser water, constant flow
Past Design ASHRAE GreenGuide
Practice
∆T Flow Pipe ∆T Flow Pipe
(°F) (gpm) Size (°F) (gpm) Size
Chilled 10 1920 10 16 1200 8
Water
Condenser 9.4 2400 14 14 1600 12
Water
30. High Performance
Design Options
Either …
Take full energy (operating
cost) savings
Or …
Reduce piping size and cost
Experienced designers use pump,
piping and tower savings to select an
even more efficient chiller
31. Reduced flow works for
all chiller manufacturers
Logan Airport - Boston:
$426,000 Construction cost savings
7.3% operating cost savings
Large Chemical Manufacturer -Greenville
$45,000 Excavation and concrete savings
6.5% Operating cost savings
Computer Manufacturer - San Francisco
Existing tower, pipe savings
2% Operating cost savings (tower not changed)
32. Low flow works for
retrofit applications
Chilled water side
Coil
It’s a simple heat transfer device
Reacts to colder entering water
by returning it warmer
Ideal for system expansion
33. Low flow works for
retrofit applications
Condenser side retrofit opportunity
Chiller needs to be
replaced
Cooling needs have
increased by 50%
Cooling tower was
replaced two years ago
Condenser pump and
pipes are in good shape
34. Condenser side
retrofit opportunity
Existing Retrofit
Capacity (tons) 500 750
Flow rate (gpm) 1500 1500
Condenser Entering Water 85 88
Temperature (F)
Condenser Leaving Water 95 103
Temperature (F)
Design Wet Bulb (F) 78 78
35. Humid climates
Low flow works for
short piping runs too
Condenser Water Side Only - original
350.0
300.0
Energy Consumption (kWh)
250.0
200.0
3.0 gpm/ton
2.0 gpm/ton
150.0
100.0
50.0
0.0
25% 50% 75% 100%
System Load
36. Humid climates
Low flow works for
short piping runs too
Condenser Water Side Only
ZERO piping pressure drop
350.0
300.0
Energy Consumption (kWh)
250.0
200.0
3.0 gpm/ton
2.0 gpm/ton
150.0
100.0
50.0
0.0
25% 50% 75% 100%
System Load
37. High Performance
Design Parameters
Low flow benefits systems - no
matter whose chiller is being
used
Low flow works extremely
well on existing systems
Low flow works on short
piping runs
42. Flow requirements
VPF System
Limits (consult manufacturer)
Absolute flows - Minimum and maximum
Flow rate changes
2% of design flow per minute
not good enough
10% of design flow per minute borderline
30% of design flow per minute
many comfort cooling applications
50% of design flow per minute
best
Always need a way to ensure minimum
flow (bypass)
43. Chiller Control
V a ria b le W a te r F lo w
130 1500
120 1300
110 1100
100 900
Water Temp [degF]
90 700
E vaporator W ater F low
Flow [gpm]
80 500
70 300
60 100
50 E vap E ntering W ater T em p -100
40 -300
E vap Leaving W ater T em p
30 -500
3:50:00 3:55:00 4:00:00 4:05:00 4:10:00
T im e (h o u r:m in :s e c )
44. More information
VPF System
Http:/trane.com/commercial
/library/newsletters.asp (1999 and 2002)
“Primary-Only vs. Primary-Secondary Variable Flow
Systems,” Taylor, ASHRAE Journal, February 2002
“Don’t Ignore Variable Flow,” Waltz, Contracting
Business, July 1997
“Comparative Analysis of Variable and Constant
Primary-Flow Chilled-Water-Plant Performance,”
Bahnfleth and Peyer, HPAC Engineering, April 2001
“Campus Cooling: Retrofitting Systems,”
Kreutzmann, HPAC Engineering, July 2002
45. High Performance
Chilled Water Plants
Standard high performance
Reduced flow rates, increased ∆Ts
Variable primary flow
Advanced
Equipment capabilities
System configurations
System control
46. Equipment Capabilities
High Performance
Chilled Water Plant
Constant speed
0.570 FL / 0.479 IPLV
Higher efficiency “same price” options
Variable speed (spend money on drive)
Constant speed (spend money on copper)
Purchase both a drive and more heat
exchange surface
Down to 0.45 kW/ton FL available (22%
reduction)
49. Example
Office building
Two 400-ton chillers
Comparisons
Base system - constant speed
AFD on both chillers
High efficiency for both chillers
AFD on one chiller
High efficiency for one chiller
50. What is the actual
utility rate?
Utility costs
‘Combined’ utility rates ($0.10 / kWh)
Actual utility rates ($12 / kW and $0.06 /
kWh)
51. Utility rate comparison
Simple paybacks, humid climate
Combined rate Actual rate
on one AFD 6.1 10.8
chiller
High efficiency 6.3 7.7
on both AFD 7.2 12.7
chillers
High efficiency 7.1 8.3
Using incorrect “combined” rate
leads to incorrect decisions
53. Temperate climate
with economizer
Annual operating cost Simple payback
$100,000 30
$80,000 25
20
$60,000
15
$40,000
10
$20,000 5
0
Base case AFD on High efficiency AFD on High efficiency
both chillers both chillers one chiller one chiller
Chiller plant operating cost
Simple payback
54. Temperate climate,
no economizer
Annual operating cost Simple payback
$100,000 12
$80,000 10
8
$60,000
6
$40,000
4
$20,000 2
0
Base case AFD on High efficiency AFD on High efficiency
both chillers both chillers one chiller one chiller
Chiller plant operating cost
Simple payback
55. Humid climate,
no economizer
Annual operating cost Simple payback
$100,000 14
$80,000 12
10
$60,000
8
$40,000
6
$20,000 4
2
Base case AFD on High efficiency AFD on High efficiency
both chillers both chillers one chiller one chiller
Chiller plant operating cost
Simple payback
56. Dry climate with
economizer
Annual operating cost Simple payback
$100,000 18
16
$80,000 14
12
$60,000 10
8
$40,000
6
4
$20,000
2
0
Base case AFD on High efficiency AFD on High efficiency
both chillers both chillers one chiller one chiller
Chiller plant operating cost
Simple payback
58. Guidance:
VSD or High Efficiency?
High efficiency VSD
Significant demand Many hours at low
charges, especially condenser water
ratchet charges temperature – and low
load
Climates where the
wet bulb doesn’t vary Perhaps only on one
substantially chiller
Multiple chillers in the Factor replacement
plant cost of VSD when
performing life cycle
Economizer that assessment
reduces low load/low
lift operating hours
59. High Performance
Chilled Water Plants
Standard high performance
Reduced flow rates, increased ∆Ts
Variable primary flow
Advanced
Equipment capabilities
System configurations
System control
61. What may not be a
good VPF application?
Two packaged chillers
Limited evaporator configurations
Assume minimum flow is about 1.2 gpm/ton
In parallel
Wide ∆T (low flow)
e.g 18°F ∆T is 1.33 gpm/ton
Why isn’t it a good application?
Flow can only be turned down 10%
62. Variable-Volume Pumping System
(series chillers)
48.4°F
Upstream chiller operating at higher
temperature is more efficient
41°F
57°F
Bypass alternatives
64. Series Chiller
Advantages
Simplifies pumping and Simple preferential
sequencing loading of chillers
No flow rate transitions Adjust upstream
chiller’s setpoint
Makes VPF simple
Upward to unload
Downward to load
Upstream chiller
operates at elevated
temperature
Efficiency increases
Capacity increases
10% or more for
absorption
65. High Performance
Chilled Water Plants
Standard high performance
Reduced flow rates, increased ∆Ts
Variable primary flow
Advanced
Equipment capabilities
System configurations
System control
66. Control
Normal Performance
Chilled Water Plant
Chilled water distribution pump
P at most remote sensor
Cooling tower fans
55°F (as cold as possible)
Somewhere else
Constant volume condenser water pumps
67. High Performance
Chilled Water Pump
Control
Communicating
BAS Pump
Pump Speed Valve position
Pressure
Sensor
69. High Performance
Chiller-Tower Control
Plant Power vs CWS
Chillers cannot meet load
1,200.0
Lowest condenser water above this condenser water
temperature available from temperature
tower at this load and wet-bulb
temperature
1,000.0
1,550 tons, 65°F Wet-bulb
T t
800.0
1,160 tons, 59°F Wet-bulb
Power (kW)
T
600.0
730 tons, 54°F Wet-bulb Temperature
400.0 Optimal operation
200.0
0.0
60
62
64
66
68
70
72
74
76
78
80
82
84
86
88
Condenser Water Setpoint (°F)
Hydeman, et. al. Pacific Gas and Electric. Used with permission.
70. Cooling tower basics
Fan energy consumption
% Full load power
100
80
60
40
20
0
0 20 40 60 80 100
% Airflow
72. simple case: constant water flow
Operating Dependencies
Wet bulb Load
Condenser water Condenser water
temperature temperature
Load Chiller design
Tower design
73. condenser water control
“Normal” Setpoint
Hot?
e.g., 85°F, minimizes tower
energy consumption
Cold?
e.g., 55°F, minimizes chiller
energy consumption
Optimized?
74. optimal condenser water control
Chiller–Tower Interaction
400
total
energy consumption, kW
300
chiller
optimal
200 control point
100
tower
0
72 74 76 78 80 82 84
condenser water temperature, °F
76. chiller–tower optimization
An Example …
720,000 ft² hotel
2 chillers, 2 tower cells
Control strategies
Make leaving-tower water cold
as possible (55F)
Optimize system operation
Entering-condenser setpoint
equals design …
85°F for humid climates
80°F for dry climates
77. chiller–tower control strategies
North America
350K
control strategy:
annual operating cost, $ USD
300K 55°F lvg tower
optimal control
250K
design ECWT
200K
150K
100K
50K
0
Mexico City Orlando San Diego Toronto
78. chiller–tower control strategies
Global Locations
500K
control strategy:
annual operating cost, $ USD
55°F lvg tower
optimal control
400K
design ECWT
300K
200K
100K
0
Dubai Paris Sao Paulo Singapore
79. operating cost savings, %
0
2
4
6
8
10
12
Dubai 14
Paris
Sao Paulo
Singapore
Mexico City
location
chiller–tower optimization
Orlando
San Diego
Operating Cost Savings
Toronto
80. chiller–tower optimization
Perspective on Savings
For centrifugal chillers ≥ 300 tons, ASHRAE
90.1 requires …
0.576 kW/ton at full load
0.549 kW/ton at IPLV
… using ARI standard rating conditions
86. VSDs and centrifugal chillers
A Closer Look at IPLV
Load Weighting ECWT kW/Ton
100% 0.01 85°F 0.572
75% 0.42 75°F 0.420
50% 0.45 65°F 0.308
25% 0.12 65°F 0.372
VSDs improve part-lift performance, so running two chillers
with VSDs at part load seems more efficient than one chiller at
double the same load, but …is dependent on condenser water
temperature
87. Chiller power only
45% Plant load
Operate 1 or 2 Chillers?
Chiller kW Only
350
1@90% Load
300
2@45% Load
250
Chiller kW
200
150
100
50
0
55 60 65 70 75 80 85
Available Tower Water Temperature (ºF)
88. Chillers plus pumps
45% Plant load
Operate 1 or 2 Chillers?
Chiller Plus Pump kW
400
1@90% Load
350
Chiller Plus Pump kW
2@45% Load
300
250
200
150
100
50
0
55 60 65 70 75 80 85
Available Tower Water Temperature (ºF)
89. Operate 1 or 2 chillers?
Run 1 or 2 VSD Chillers?
400
1@90% Load
350 2@45% Load
1@80% Load
Operate multiple chillers here,
300 2@40% Load
Total Chiller Plus Pump kW
otherwise single chiller
1@70% Load
250 2@35% Load
1@60% Load
200
2@30% Load
1@50% Load
150
2@25% Load
100
50
0
60 65 70 75 80 85
Available Tower Water Temperature (ºF)
90. Operate 1 or 2 chillers?
45% plant load: One chiller until tower
temperature is < 65°F
40% plant load: One chiller until tower
temperature is < 60°F
35% plant load and below: One chiller
91. High Performance
Condenser Water Pump
Control – Variable?
Pump speed limits
Tower static lift
Tower nozzles (minimum flow)
Condenser minimum flow
Pump speed reductions result in
Increased leaving condenser water
temperature
Decreased cooling tower effectiveness
Possible chiller surge
92. High Performance
Condenser Water Pump
Control – Variable?
The condenser water pump is the hardest
place to properly utilize a variable frequency
drive during operation
There are successful installations
97. variable condenser water flow
Guidance
Can provide savings …
Finding proper operating
points requires more time,
more fine-tuning
Two-step process:
1 Reduce design pump power
2 Is variable condenser-water
flow still warranted?
99. High Performance
Chilled Water Plants
Standard high performance
Reduced flow rates, increased ∆Ts
Variable primary flow
Advanced high performance
Equipment capabilities
System configurations
System control
101. Medical Center
Winchester, Virginia
Five 750-ton chillers VFD’s on
0.571 kW/ton full load Chilled water pumps
Chilled water Cooling tower fans
58 to 42°F
Condenser water
Condenser water pumps
84 to 95°F
(missed opportunity) Sophisticated control
system with lots of
VFD’s
Programming
Variable primary flow
Commissioning
105. Winchester Medical
Center - Mark Baker
“Please use our data,
names, etc. We're
proud of our facility!”
“By the way, we're
now operating @
-0.20 kW/ton. The
power company just
sent us our 1st check.
Ha..Ha…”
106. Remember...
Without controls,
it’s not a system.