This pre prese senta ntation tion is be b eing brough b roughtt to you by: ASHRA A SHRAE E Ind In d i a Chap Ch aptt er an and d Xy Xyll em em,, Inc In c .
Large Chilled Water System Design Seminar
Presented by: Larry Konopacz, Manager of Training & Education Bell & Gossett Little Red Schoolhouse Saturday, Satur day, Sept emb ember er 21, 2013
Large Chilled Water System Design Seminar The Production Loop
Chilled Water Sources • Chillers • Cooling towers • Free-Cooling & Waterside Economizer • Thermal Storage • Water Source Heat Pumps
What’s a Ton?
I Ton Ton Ice = 2000 2000 LB; LB ; 1LB Ice = 144 14 4 Btu ; 1 Ton Ton ic ice e= 288,000 Btu
Rule of 24 12,000 Btu/h = 500 x gpm x t°F = 1 ton gpm/ton = 12,000/(500 x t°F) = 24/t°F
What Types of Chillers are Available? Compressor
• Centrifugal • Rotary screw
Condenser
• Reciprocating • Absorption Evaporator
Refrigeration Cycle Expansion Device
Hot Water C o n d e n s e r
Cooling Tower
Cool Water
Liquid FlowL H i g h P r e s s u r e Z o n e
o w P r e s s u r e Z o n e
E v a p o r a t o r
Vapor Flow
Condenser Water Pump
Compressor Motor
Supply Water L o a d
Return Water Chilled Water Pump
Where is What Used? • Large chilled water plants - centrifugal • Mid-range size - rotary screw • Smaller chilled water applications reciprocating • Inexpensive source of steam or other energy source - absorption • Combinations of the above
Chiller Piping - Evaporator Side R E L L I H C
Chiller 2
Chiller 1
Return
Common Pipe
Supply
Typical Piping Method Chiller 3
Chiller 2
Triple Duty
Chiller 1
Supply
Triple Duty Common Pipe
Return
Adding Pump Redundancy Chiller 2
Triple Duty
Chiller 1 Supply
Triple Duty Common Pipe
Return
Headered Primary Pumps Actuated Control Valve Chiller 3
Chiller 2
Piped for Standby Pumps
Supply Triple Duty
Chiller 1
Common Pipe Triple Duty
Return
Chiller Piping - Condenser Side Cooling
SRS
Towers
SRS
SRS
Pumps Triple Duty Condenser
Condenser Condenser
Multi-celled Cooling Tower Condenser
Condenser
Condenser
Multi-cell Cooling Tower Triple Duty
SRS
Standby Pump
Tower Equalization Cooling Cooli ng Towers Towers
Equalization Line
Condenser
Condenser
SRS
Triple Duty Condenser
Cooling Tower Piping Practices • Fill Fill all all sec secti tion ons s of of pip pipe e to to pur purge ge air. air. • Size Size pipi piping ng at a min minim imum um of 2 fps fps to move free air bubbles to tower. • All All pipi piping ng ins insta talllled ed bel below ow sys syste tem m purg purge e level.
Condenser Water Piping Above Grade System Purge Level
SRS
Overhead Piping Concerns • Pi Pipi ping ng manif manifol olds ds can can resul resultt in in low low veloci velociti ties es.. • Low Low velo veloci city ty will will allow allow air air to to be relea released sed.. • Ai Airr trap trappe ped d in in pip pipin ing g incr increas eases es head head req requir uired ed.. • Pipi Piping ng inst instal alled led above above purg purge e leve levell com compou pounds nds problem. • Unpu Unpurg rged ed are areas as are are pot poten enti tial al sou sourc rces es of of problems when pumps are turned on.
Elevated Suction Piping Concerns • Conde Condense nserr wate waterr pump pump diff diffic icult ult to purge purge.. • At star startt-up up a manu manual al air vent vent may may be requi require red. d. • Duri During ng opera operati tion on air air wil willl aga again in accum accumul ulat ate. e. • Auto Automa mati tic c air air vent vent may may not not work work.. • If above above the the basi basin n fil filll leve level, l, the the res result ult is cavitation.
Improper Piping Above Basin Level System Purge Level
Basin Fill Level
Multi-tower System, Properly Piped System Purge Level
SRS
Tower Piping Observations • At part load reduced velocities in headers may allow air to be released. • Idle pumps will accumulate air that should be released prior to starting the pump. • Tower basins should be elevated to ensure positive pressure under all flow conditions. • Pump casings should be fitted with automatic air vents.
Condenser Head Pressure Control With centrifugal chillers a minimum supply water temperature is needed to: • Maintain optimum efficiency • Maintain a minimum pressure differential between condenser and evaporator • Prevent pressure imbalance
Hermetic Compressor Guidelines • Condenser water temperature > 75 °F. • Establish 75 °F within 15 minutes. • N/O condenser water throttling valve. • Three-way bypass valve can be used. • Constant condenser water flow. • Water temperature control through fan modulation, or other methods.
Open Compressor Guidelines • Condenser water temperature > 55 °F. • Three-way bypass valve can be used. • Constant condenser water flow. • Water temperature control through fan modulation, or other methods.
Cooling Towers
Air in
Air out
Water In
Water out
Induced Draft, Counter-flow Tower Air Out
Water in
Air in
Water out
Air in
Forced Draft, Cross-flow Tower Air Out
Air in
Air in
Water out Water in
Dynamic Relationship of Load, Approach, and Range Temperature
“L” lb/min of water
Hot water °F ) e F g ° n ” a R R “ (
Cold water °F
Wet bulb °F
Water Flow
h c a o r p ) p F A ° (
Heat Load = L x R
“L” lb/min of water
d a o L
Tower Size Relationships Variables: • Heat Load (Varies Directly) • Range (Varies Inversely) • Approach (Varies Inversely) • Wet-bulb Temperature (Varies Inversely) Varying any of these variables will affect the size of the tower.
Types of Free-Cooling (Waterside Economizer) Air Out
Water in Air in
Air in
Water out
Earth Contact
Evaporative
Earth Contact Characteristics • Usually indirect. • Cooling medium and load separated by heat exchanger. • Stable temperatures. • Water temperature limitations. • Water treatment and pumping costs. • Environmental concerns.
Heat Exchangers
How do they work? •
Thin plates are stamped with a unique chevron pattern and assembled in a frame
•
Four holes punched in the plate corners form a continuous tunnel which acts as a distribution manifold for the inlet and outlet of each fluid
How do they work? •
Each plate has a gasket that confines the fluid to the port or to the heat transfer area of the plate
•
Units are built to order with a standard 150 psi ASME Code stamped design or to custom designs
Earth Contact - Summer Cycle
C O N D
TOWER
E V A P
GPX
H E A T
E X C H
LOAD
Triple Duty Sediment Removal Separator
Triple Duty
Earth Contact - Winter Cycle
C O N D
TOWER
E V A P
GPX
H E A T
E X C H
LOAD
Triple Duty Sediment Removal Separator
Triple Duty
Evaporative Characteristics • Heat rejection device (tower) exists. • As temperature declines, opportunity arises. • Higher sensible vs. latent loads • Leaving water temperature approaches 42 F. • Freeze protection may be required.
Freeze Protection • Sump heaters. • Close temperature control. • Accurate water level control. • Prevention of moist air recirculation. • External piping freeze protection.
Evaporative Cooling - Direct
C O N D
TOWER
E V A P
LOAD
Triple Duty Sediment Removal Separator
Single Tower, Summer Cycle
Triple Duty
Evaporative Cooling - Direct
NOT RECOMMENDED C O N D
TOWER
E V A P
Triple Duty Sediment Removal Separator
* Alternate location of SRS, depending on system conditions
Single Tower, Winter Cycle
LOAD
Triple Duty
Evaporative Cooling - Indirect
C O N D
TOWER
E V A P
GPX
H E A T
E X C H
LOAD
Triple Duty Sediment Removal Separator
Single Tower/GPX, Summer Cycle
Triple Duty
Evaporative Cooling - Indirect
C O N D
TOWER
E V A P
GPX
H E A T
E X C H
LOAD
Triple Duty Sediment Removal Separator
Single Tower/GPX, Winter Cycle
Triple Duty
Temperature Cross and Approach TEMP. DEG. F
57= T1
CH. WATER 52=
t2
7°F TEMPERATURE CROSS
45= T2 3°F COOLING APPROACH
COND. WATER 42=
EXCHANGER LENGTH
t1
Heat Transfer Area vs Approach COND. WATER
CH. WATER
LMTD
AREA
EXCH.
COST
EWT LWT FLOW
EWT LWT FLOW
DEG F
SQ.FT.
MODEL
INDEX
42
52
1000
57
45
834
3.92
1390
GPX807
1.00
42
52
1000
58
46
834
4.93
1135
GPX807
0.85
42
52
1000
59
47
834
5.94
975
GPX807
0.76
Temperatures are in F
Flow is in USGPM
Heat exchanger selection based on max pressure drop of 7 psi 10/3.92=2.55
Approach = 3F
10/4.93=2.03
Approach = 4F
10/5.94=1.69
Approach = 5F
Production Source - Thermal Storage • Application Criteria • Economics • Storage Media • Storage Technologies • System Configurations
Application Criteria • High maximum load. • Significant premium for peak demand. • Incentives. • Limited space available. • Limited electrical capacity. • Back-up or redundancy required.
Storage Media • Chilled Water • Ice Harvesting • External/Internal Ice Melt
Stratified Chilled Water System T Load Variable volume distribution pump
Warm
Vent
Storage
Pressure sustaining and check valve
Cool Constant volume primary pump
Chiller
Temperature Stratification Top 0 D e p t h o f t a n k , f t
-5 -10
Thermocline
-15
Bottom -20 30
40
50
60
Temperature, °F
70
Use of Pressure Sustaining Valves Load
Distribution pump
Primary pump
Chiller
Transfer
Pump
Direction control valves
Vent Warm
Pressure sustaining and check valve
Storage
Cool Constant volume primary pump
Incorporating Heat Exchangers Load
T
Variable volume secondary pump
T
Heat Exchanger
Variable volume primary pump Warm
Vent Storage
Cool Constant volume primary pump
Pressure sustaining and check valve
Chiller
Ice Harvesting System Section Section Section Section 1 3 4 2 Ice harvester chiller
Load
Ice water Chilled water pump
recirculation
pump
External Melt Ice Storage
Discharging Mode Charging Mode
Encapsulated Ice Storage Charge and Discharge Modes Charging Mode
Discharging Mode Ice
Cold glycol
Ice
Warm glycol
Water
Full Storage Strategy Chiller on
Charging Storage
Charging Storage T o n s
Chiller off
Cooling load (met by storage) Chiller meets load directly
Time of Day
Partial Storage - Load Leveling Charging Storage T o n s
Cooling load (met by storage)
Chiller runs continuously Cooling load (met by chiller)
Time of Day
Charging Storage
Partial Storage - Demand Limiting Reduced on-peak demand Charging Storage T o n s
(met by storage) Cooling load
(met by chiller) Time of Day
Charging Storage
Production Source - Water Source Heatpumps • Growing market segment • System temperature range 40 - 90 °F • Energy added below 40 °F (heat) • Heat removed above 90 °F (cooling tower)
Heat Pump Cycles - Water Source Supply
System Water
Return Water Coil
Air Coil
(Condenser)
(Evaporator)
Cool Air
Warm Air
Compressor
Reversing
Valve
Capillary
Air Conditioner Cooling
Water Coil
Air Coil
(Evaporator)
(Condenser)
Refrigerant Loop
Compressor
Reversing
Valve
Capillary
Air Conditioner Heating
Design Considerations • Use slow closing two-way valves for each zone • Good system balance required • Use staged c/s or v/s pumps • Use with cooling towers and GPX • Use with closed circuit cooling towers
Heat Pump-Water Source Schematic Compression Tank Cooling Tower
Water Source Heat Pump
Buffer Tank ( Optional )
Gasketed Plate Heat Exchanger
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Heat Pump-Water Source Schematic Closed Circuit Cooler Heat Rejecter
Water Source Heat Pump
Buffer Tank ( Optional )
Compression Tank
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Water Source Heat Pump
Comments? Questions? Observations?
Large Chilled Water System Design Seminar Variable Volume Distribution
Variable flow through coil Constant flow through system
Variable flow through coil Variable flow through system
Three Way Valve
Two Way Valve
Three-Way Valve Systems • Low return temperatures • Balance problems • Increased flow at part load • Extra chillers to provide flow at low t • Chillers operate at high kW/ton
A
C H I L L E R
Two-Way Valve System with Chiller Bypass
C H I L L E R
A Problem We want: a. variable volume, to save pumping costs at part load, b. constant flow through the chiller to protect it.
A Solution a. constant flow primary system for the chillers b. variable flow secondary system for the load
Primary-Secondary Terms Supply Primary Loop Production
Secondary Loop Distribution C
C
C
H
H
H
I
I
I
L
L
L
L
L
L
E
E
E
R
R
R
Primary-Secondary Common Pipe Return
Fundamental Idea
Secondary Pump
Primary Pump
Tee “ A”
Tee “ B”
Low pressure drop in the “common pipe”
Primary-Secondary Pumping The idea is based on: – Conservation of Mass – Conservation of Energy
Law of the Tee: Diversion 50 GPM
100 GPM
50 GPM
Law of the Tee: Mixing 100 GPM
60 GPM
40 GPM
No Secondary Flow
Secondary Pump Off
A 100 GPM @ 45°F Primary Pump
B
100 GPM @ 45°F
100 GPM @ 45°F
Primary = Secondary
100 GPM @ 45°F
100 GPM @ 55°F
Pump On
A 100 GPM @ 45°F
B 0 GPM
100 GPM @ 55°F
Primary > Secondary
50 GPM @ 45°F
50 GPM @ 55°F
Pump On
Mixing at Tee B
A
B
100 GPM @ 45°F
100 GPM @ 50°F 50 GPM @ 45°F
Primary < Secondary
200 GPM @ 55°F
200 GPM @ 50°F
Pump
On
A
B
100 GPM @ 45°F Mixing at Tee A
100 GPM @ 55°F 100 GPM @55F
Control Valve in Secondary
Two-way Valve
Primary-Secondary Pumping Supply Primary Loop Production
Secondary Loop Distribution C
C
C
H
H
H
I
I
I
L
L
L
L
L
L
E
E
E
R
R
R
Primary-Secondary Common Return
Common Pipe Design Criteria • Use the flow of the largest chiller – Chiller staging at half of this flow is common
• Head loss in common <1 1/2 ft – Distribution pipe size is often used where reductions would be inconvenient
• Three pipe diameters between tees – Excessive length increases total head loss
• Low velocities in system piping
Design of the Common Pipe Secondary Constant Speed Pumps
C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
Supply
Pump Controller Common
Return
10 dia.
Common Pipe Configurations
A
C
B
D
Secondary System Curve Control Valves Closing H1 H2
Control Valves Opening
H3
Head
Flow
F1
F2
F3
Typical System Distribution Production
45F To Loads
C h i l l e r 2 , o f f
C h i l l e r 1 , o n
Secondary Pumps 1500 gpm each
Common 1500 gpm each From Loads
Production = Distribution CHWS Temp 45oF
1500
1500
Secondary Pumps
C h i l l e r 1 , o n
C h i l l e r 2 , o f f
1500
Common -- No Flow 0
1500
1500 ECW Temp 55oF
CHWR Temp 55oF
Distribution > Production CHWS Temp 47.5oF
2000 1500
Secondary Pumps
C h i l l e r 1 , o n
C h i l l e r 2 , o f f
2000 Mixing (1500 @ 45) + (500 @ 55)
0
Common -- 500 1500
2000
ECW Temp 55oF
CHWR Temp 55oF
Check Valve in Common? Supply >1500 GPM
C h i l l e r 2 , o f f
C h i l l e r 1 , o n
0 GPM
>1500 GPM @ 47.5oF
Be Careful!
Common Return >1500 GPM
>1500 GPM @ 55oF
What can we do? Supply
Step Function
C h i l l e r 3
C h i l l e r 2
Linear Function
C h i l l e r 1
Primary/Secondary Common Distribution Production
Return
Typical Load Profile 30 25 20
e m i 15 T % 10 5 0 0-10
30-40
60-70
% Load
90-100
Multiple Chillers Chiller 1 Chiller 2
C h i l l e r 2 , 6 0 %
100
1
80
% Load
60 40 20
2
1 25
50
2 75
% Time
100
C h i l l e r 1 , 4 0 %
What else can we do? Reset Supply Temperature • Lower chiller set point when mixing occurs to maintain a constant temperature to the system. – Allows us to mix colder water and maintain supply temperature to secondary. (coils)
• Expect increases in cost of chiller operation at lower set point: 1-3% per degree of reset. • Adds to control complexity. • Delays start of the next chiller.
Production > Distribution P/S Chiller Bridge - Front Loaded Common (Flow in GPM)
C h i l l e r 2 , o n
CHWS Temp 45oF
3000
C h i l l e r 1 , o n
Secondary Pumps 2100
Common -- 900 1500
Mixing (2100 @ 55) + (900 @ 45) 1500
2100
ECW Temp 52oF
CHWR Temp 55oF
“Loading” a Chiller • A chiller is a heat transfer device. Like most equipment, it is most efficient at full load. • To “load” a chiller means: – Supply it with its rated flow of water – Insure that water is warm enough to permit removal of rated Btu without freezing the water
Chiller Performance Curve 1.1 1.0 K 0.9 W p e r 0.8 T o n 0.7
0.6 0.5 10 20
30
40
50 60 70 Percent Load
80 90 100
Typical Load Profile 30 25 20
e m i 15 T % 10 5 0 0-10
30-40
60-70
% Load
90-100
60/40 Chiller Split to Help Minimize Low Part Load Operation Chiller 1 Chiller 2
C h i l l e r 2 , 6 0 %
100
1
80
% Load
60 40 20
2
1 25
50
2 75
% Time
100
C h i l l e r 1 , 4 0 %
Three Unequally Sized Chillers Chiller 1 or Chiller 2 and
Chiller 3 100
C h i l l e r 3 , 6 0 %
Chiller 1 and
Chiller 2
80 60
% Load 40 Chiller 3 20
Chiller 1 or
Chiller 2
25
50
75
100
% Time
C h i l l e r 2 , 4 0 %
C h i l l e r 1 , 4 0 %
Approaching Flow = Load
% Load
Time
Applying a Variable Speed Chiller 100
Ch 1
75
% Flow
Ch 1
Ch 2
50 Ch 3
Ch 2
Ch 1
25 Ch 2
Ch 3
Ch 4
Ch 1
25
50
75
% Load
100
Back Loaded Common To Loads
C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
Common
From loads
Production = Distribution CHWS Temp 45oF
1500
1500
Common 0 Flow
C h i l l e r 2 , o f f
Secondary Pumps
C h i l l e r 1 , o n
1500
1500
1500
CHWR Temp 55oF
Distribution > Production CHWS Temp 47.5oF
Mixing (1500 @ 45) + (500 @ 55)
500 C h i l l e r 1 , o n
C h i l l e r 2 , o f f
Common 500 gpm
0
Secondary Pumps
1500
2000
1500
2000
500 CHWR Temp 55oF
Production > Distribution CHWS Temp 45oF 900
C h i l l e r 2 , o n
Common 900
600
1500
C h i l l e r 1 , o n
1500 GPM @ 49oF
900 GPM @ 45oF
Secondary Pumps
1500
2100
1500 GPM @ 55oF
600 GPM @ 55oF
Mixing (900 @ 45) + (600 @ 55)
2100 CHWR Temp 55oF
Maximize Free Cooling Secondary Pumps PrimarySecondary Common
C h i l l e r 3
C h i l l e r 2
F r e e C o o l i n g
Supply
Pump Controller
Return
Primary-Secondary System
Secondary Pumps
C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
Supply
Pump Controller PrimarySecondary Common
Return
Pump Horsepower Comparison 150
Constant Flow Primary Pumps, only 125
BHP
100
75
Secondary Pumps + 50
Primary Pumps = V/V 25
25
50
75
Design Coil Flow %
100
2012 ASHRAE Handbook - HVAC Systems and Equipment, p 44.11
Constant vs Variable Volume 150 140
Constant Flow, C/S Pump
C/S Pump (2 Way Valve)
130 120
Base Design HP %
Pump Over-headed by 150%
(3 Way Valve)
110 100
Constant Flow, C/S Pump (3 Way Valve)
90
Pump Head Matc hed to System @ Design Flow
80 70 60
% Full Load 50 (Design) HP 40 30 20 10 0
10 20 30 40 50 60 70 80 90 100
% Flow
Impact of Piping Length and Overheading 350
300
250 c/s @ 1.0 Y e a r l y O p e r a t i n g C o s t x $ 1 0 0 0
c/s @ 1.25
200
c/s @ 1.50 c/s @ 2.0 150
100
50
0 0
1000
2000
3000
4000
5000
Pipe Length , Feet
6000
7000
8000
9000
Always Size the Pump to the System! But... • Uncertainties – Coils – Control valves – Primary data
• Lead times
Dealing With an Overheaded Pump • Throttle at the discharge valve – Limits on the valve
• Flow balance & trim pump impeller – Required by ASHRAE/IES 90.1
Additional Concerns • Pump Protection at minimum flow • Chiller Staging and De-staging instrumentation.
Pump Protection
Minimum recommended flow from ESP Plus = 900 gpm
Bypass Options 1. Establish a minimum flow equal to or greater than the minimum required to protect the pump. 2. Install a bypass at the end of the mains with a balance valve to set minimum flow. 3. Install a bypass at ends of zones. 4. In retrofits, leave a three way valve at the end of the system. 5. Use P or flow sensing to open pump bypass only when needed. 6. V/S pumps are not as big a problem because of lower head at reduced flow.
System Bypass Options 3
Secondary Constant Speed Pumps
C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
Supply
2 Pump Controller
6 Primary Secondary Common
Return
5
Chiller Staging Instrumentation Production C h i l l e r 2 , o f f
TS-S
TP-S
FS
FP
To Loads
C h i l l e r 1 , o n
Secondary/Pumps
Distribution Common
TP-R
TS-R From Loads
Common Pipe Flow Indication Distribution Production To Loads C h i l l e r 2
C h i l l e r 1
Secondary/Pumps F l o w S w i t c h e s
Common
From Loads
Comments? Questions? Observations?
Large Chilled Water Design Seminar Variable Speed Pumping
Why variable speed? 1. When should I use it? 2. How does it work? 3. What about variable primary flow?
Typical operating load profile 30%
20% 15%
5% 2%
3%
15%
5%
3%
2%
Bell & Gossett 70V 1970s
Adjustable Frequency Drives • Rectifier section – converts AC to DC – several varieties available
• Inverter section – forms a synthetic sine wave – several varieties available – maintains a controlled frequency/voltage ratio
• Requires an automatic control system • Adds to the initial cost of the system
Affinity Laws 1. Capacity varies as the RPM change ratio: FLOW 2 = FLOW 1 ( SPEED2 / SPEED 1) 2. Head varies as the square of the RPM change ratio: HEAD 2 = HEAD 1 (SPEED 2 / SPEED 1)
2
3. Brake horsepower varies as the cube of the RPM change ratio: BHP 2 = BHP
1
(SPEED 2 / SPEED 1)
3
Affinity Law s for Centrifugal Pumps 100 90 80
Flow
70
Head
t n 60 e c 50 r e 40 P
Horsepower
30 20 10 0 0
10
20
30
40
50
60
70
Flow /Speed, Percent
80
90
100
Theoretical Savings
120 110
Pump Curves
100
90%
100% Speed
110 100
Design
90
90 80
80% 70%
50
60 50
60%
40
HP Draw 50%
30
40%
0 10 20
40 30
Head 20 BHP
10 30% 0
80
Head
70
d 70 a e 60 H %
20
120
Flow 30 40
50
60
70
% Design Flow
80
10 0 90 100
P H B %
Required Differential Pressure
P
Sensor/Transmitter 25 Ft. Head
System Curve & V/S Control System 110 100
25 FT Differential Head Maintained Across Load (Set Point)
80 d
a e H 60
Overall system curve
40
Distribution piping head loss curve
20 0
0
200
400
600
800
1000
Flow
1200 1400
Set Point P u m p T D H
1600
Effect of Constant* Set Point 110
As the valve closes, the pump slows down
100 H e a d
Set point, 25 FT
Control curve
80
P u m p T D H
60 Overall system curve 40 Distribution piping head loss curve
20 0 0
200
400
600
800
1000
1200
1400
1600
Flow
*What’s Constant?
Pump Initial Speed
Control Curve B
A
Head, H (feet) Pipe, Fitting Friction Loss
Flow, Q (gpm)
Q2 Q1
Decrease in Heat Load Results in T room < T set point Causes Two Way Valves to Throttle Flow
Pump Curve
Speed 1 B Speed 2
Control Curve A
C
Head, H (feet)
Pipe, Fitting Friction Loss
Flow, Q (gpm)
Q3 Q2
Q1
Decrease in Pump Speed Reduces Flow, Reduces Error
Control Curve
Speed 1
B
A
Head (ft) Final Speed
Pipe, Fitting Friction Loss
C
Flow, Q (gpm)
Q4
Q1
System Operation on Control Curve at Lower Speed
Variable vs Constant Head Loss Constant Head Loss Variable Head Loss Supply C H I L L E R
C H I L L E R
C H I L L E R
Pump Controller
Adjustable Freqy. Drives
Return
Variable Head Loss Ratio C/S, Constant Flow System
Base 100
Pump Head Matched to System at Design Flow
90
P e r c e n t D e s i g n B H P
80
C/S, Variable Flow
V/S, 0% Variable Hd Loss, 100% Constant
Hd
70 V/S, 25% Variable Hd Loss, 75% Constant
60 50
V/S, 50% Variable Hd Loss, 50% Constant
40
V/S, 75% Variable Hd Loss, 25% Constant
Hd
Hd
Hd
30 V/S, 100% Variable Hd Loss, 0% Constant Hd
20 10 0
10
20
30 40
50 60
70 80 90
% Flow
100
Variable Head Ratio w/ Overheading Constant Flow, C/S Pump
150 140
C/S Pump (2 Way Valve)
130 120
Base Design HP %
Pump O’Headed by 150%
(3 Way Valve)
110
Constant Flow, C/S Pump
100
(3 Way Valve)
90
Pump HD Matched to System @ Design Flow
80 70 60
% Full Load (Design) HP
50 * 25/75 Means: 25 % Variable HD Loss 75 % Constant HD Loss
40 30 20 10 0
10
20
30 40
50 60
70 80 90
100
V/S Curves 120
50 %
60 %
110
70 % 80 % % Efficiency 85 % 85 % 80 %
100
100 %
90 80
90 %
t e70 e F , d60 a e H
% Speed Curves 80 %
50
Constant Efficiency Curve
70 %
40
60 % 30
50% 20
40 % 10
30 %
GPM
0 0
100
200
300
400
500
600
700
800
900
1000
Efficiency Changes 50 %
120
60 %
110
70 % 80 % % Efficiency 85 % 85 % 80 %
100
100 %
90
90 %
80 t e70 e F , d60 a e H 50
% Speed Curves 80 % Constant Efficiency Curve
70 %
40
60 %
30
50% 20
40 %
10
30 %
GPM
0 0
100
200
300
400
500
600
700
800
900
1000
Minimum Drive Speed 50 %
120
60 %
110
70 % 80 % % Efficiency 85 % 85 % 80 %
100
100 %
90
90 %
80 t e70 e F , d60 a e H 50
% Speed Curves 80 % Constant Efficiency Curve
70 %
40
60 %
30
50% 20
40 %
10
30 %
GPM
0 0
100
200
300
400
500
600
700
800
900
1000
Multiple Pump System Staging Constant Differential Head Loss
Variable Head Loss Supply C H I L L E R
C H I L L E R
C H I L L E R
Pump Controller
Adjustable Freqy. Drives
Return
Parallel V/S Operation
Pump 1
Pumps 1 & 2
Control Curve
1770 RPM 1450 RPM
1150 RPM 600 RPM
900 RPM
Pumps 1, 2 & 3
Variable Speed Pumping Equipment 3f , 60 Hz Power (Control Agent)
Set Point (Input Signal)
Technologic™ Pump Controller
Feedback Signal
Sensor/ Transmitter
Set Point +/- error
Adjustable Frequency Drive (Controlled Device)
3f, Variable Frequency Variable Voltage
Controlled Variable
System
The Controlled Variable Determines the Type of Sensor
Pressure Differential Pressure 4-20 ma signal Temperature Differential Temperature Flow
Pump Controller ••••• •••••
3f , 60 Hz Power (Control Agent)
Set Point (Input Signal)
Technologic™ Pump Controller
Feedback Signal
Sensor/ Transmitter
Set Point +/- error
Adjustable Frequency Drive (Controlled Device)
3f, Variable Frequency Variable Voltage
Controlled Variable
System
Technologic™ Pump Controller • Controls pumps and drives – Accept set point, analyze sensor input – PID function – Pump staging – Pump alternation • Recognize and react to component failure • Provide message display • Central management system link • Safeguard system
PID Control • Eliminates offset from set point • Allows for timely speed change • Handles large, sudden disturbances • Prevents oscillation and over-damping
3f , 60 Hz Power (Control Agent)
Set Point (Input Signal)
Technologic™ Pump Controller
Set Point +/- error
Adjustable Frequency Drive (Controlled Device)
Feedback Signal
Sensor/ Transmitter
3f, Variable Frequency Variable Voltage
Controlled Variable
System
Adjustable Frequency Drive Constant Voltage & Frequency Power
Rectifier Section
Direct Current
Inverter Section
Some important issues: Rectifier and Inverter Design Drive Efficiency RFI and EMI Noise Audible Noise Size and Cost Manual drive bypass
Variable Voltage & Frequency Power
Pump Motor
Typical Efficiency Range Variable Speed Drives 120 100 Currentl y Available AFDs
% 80 , y c n 60 e i c i f f 40 E
Typical Older AFDs Other Types
20 0 0
20
40
60
Design Speed, %
80
100
Pump and Motor
The Pump • Minimum Flow • Minimum Speed • “Inverter Duty” Motors • Motor Couplers
Maintaining Minimum Flow 120
100 % Speed
110 100 90 80 70
d a 60 e H50
30% Speed
40 30 20 10 0
0
10
20
30
40
50
% Flow
60
70
80
90
100
EPDM couplers on variable-speed pumps
Failed Hytrel Coupler from a Variable Speed Pump
Variable Flow Through The Evaporator
Primary-Secondary System Constant Differential Head Loss
Variable Head Loss Supply C H I L L E R
C H I L L E R
C H I L L E R
Pump Controller
Adjustable Freqy. Drives
Return
Primary-Secondary • Common Practice. • Why? – Protection. • Nuisance shutdowns. • Freezing. • Costly downtime.
Variable Primary Flow Flow Meter, option
Two-position Control Valves
r o s n e S P D
r o s n e S P D
C H I L L E R
C H I L L E R
C H I L L E R
D P S e n s o r
D P S e n s o r
Modulating Valve
AFD
AFD
AFD
Controller
What’s different? • Primary pumps only • Flow meters or p sensors at each chiller. • Two-position isolation valves at each chiller • Minimum flow bypass with a modulating control valve. • “Smarter” controller.
Alternative #1
• Minimum Flow Bypass at Chillers –Minimum Chiller Flow –Minimum Pump flow
• Ganged Pumps
T
F
F
FLOW METER
SUPPLY
F SIGNAL TO TECH
DP SENSOR DP SENSOR
DP SENSOR
CHILLER
DP SENSOR
CHILLER
DP SENSOR
CHILLER
SIGNAL TO TECH SIGNALS TO TECH
SIGNAL TO TECH
SIGNALS TO TECH
SIGNALS TO TECH
TDV
TDV
TDV
T NOTE: ALL SENSOR SIGNALS WIRED TO TECHNOLOGIC 5500
RETURN
AFD
AFD
AFD ISOLATION VALVE CHECK VALVE F FLOWM ETER/TRANSMITTER T TEMPERATURE SENSOR
BYPASS: FOR SYSTEMS WITH EXTENDED LIGHT LOADS/WEEKEND SHUTDOWNS. SET BALANCE VALVE FOR LOW FLOW TO REDUCE THERMAL STRATIFICATION AND ALLOW QUICK START UP AFTER SHUT DOWN.
Monitoring Chiller Flow P
sensors - Technologic controller ensures the chiller is in proper working condition by monitoring each working chiller’s differential pressure. Flow through the chiller is calculated using the values defined in the user setup. OR Flow sensors - Technologic controller ensures the chiller is in proper working condition by monitoring each working chiller’s flow rate.
Technologic 5500 • Initial programming is crucial. • Must use accurate data from the chiller manufacturer. • Start-up coordination should include the BMS too.
Technologic 5500 Control Variables 1. Monitor zone differential pressure sensors, compare actual values to the required set points. • Pump speed is modulated to maintain set point. • Pump staging will occur as required to meet set point.
Control sequence is exactly as described earlier.
Technologic 5500 Control Variables 2. Determine if the minimum flow requirements are being met for all working chillers. Prevents freeze-up or chiller low-flow trips If chiller flow is too low, controller opens minimum flow bypass valve in programmed increments. Size the valve for system p. “Requests” de-staging action from the chiller control system or BMS. Allows for operator intervention, decision making. Required by code in some areas.
Ganged pumps allow operation of two chillers with one pump.
Technologic 5500 Control Variables 3. Monitors chiller flow rate to prevent operation above the maximum flow for the chillers and the pumps. Excess chiller flow generates a request to stage on an additional chiller. Minimum flow bypass valve is closed. Operator or BMS intervention required. Ganged pumps allow operation of one chiller, two pumps. Optional system flow meter provides end-of-curve protection for the pumps
Alternative #2 • Bypass at End of System • Minimum chiller flow • Minimum pump flow • Ganged Pumps
T
F
F
FLOW METER
SUPPLY
F SIGNAL TO TECH
DP SENSOR
DP SENSOR
CHILLER
DP SENSOR
CHILLER
SIGNALS TO TECH
CHILLER
DP SENSOR
SIGNAL TO TECH
SIGNALS TO TECH
DP SENSOR
SIGNAL TO TECH
SIGNALS TO TECH
TDV
TDV
TDV
T NOTE: ALL SENSOR SIGNALS WIRED TO TECHNOLOGIC 5500
RETURN AFD
AFD
AFD ISOLATION VALVE CHECK VALVE F FLOWM ETER/TRANSMITTER T TEMPERATURE SENSOR
Alternative #2 • Minimum flow bypass valve is controlled to protect both the pumps and the chillers. – Pump requires >25% BEP flow – Minimum flow of largest chiller
• Size the bypass valve using the zone p. • Best for systems with extended light loads or weekend shut-down.
Alternative #3
• Primary pumps piped directly to chillers. • More common in retrofit systems. • Easier for applying un-equally sized chillers in parallel.
T
F
F
FLOW METER
SUPPLY
F SIGNAL TO TECH
DP SENSOR DP SENSOR
CHILLER
DP SENSOR
DP SENSOR
CHILLER
DP SENSOR
CHILLER
SIGNAL TO TECH
SIGNALS TO TECH
SIGNALS TO TECH
TDV
SIGNAL TO TECH
SIGNALS TO TECH
TDV
TDV
T NOTE: ALL SENSOR SIGNALS WIRED TO TECHNOLOGIC 5500
RETURN
AFD
AFD
AFD ISOLATION VALVE CHECK VALVE F FLOWM ETER/TRANSMITTER T TEMPERATURE SENSOR
BYPASS: FOR SYSTEMS WITH EXTENDED LIGHT LOADS/WEEKEND SHUTDOWNS. SET BALANCE VALVE FOR LOW FLOW TO REDUCE THERMAL STRATIFICATION AND ALLOW QUICK START UP AFTER SHUT DOWN.
Pump Selection
• Equal size pumps. – Redundancy. – Parts. – Maintenance.
• Unequal size pumps. – Control issues. – Flow issues. – Premature failure, large pump at low flow.
Chiller Selection • Equal size chillers. – Redundancy. – Parts. – Maintenance.
• Unequal size chillers. – Control issues. – Flow issues – Additional equipment.
Design Considerations • Size bypass for minimum flow of largest chiller. – Minimum building load?
• Size bypass modulating valve – for system p, if it’s installed near the chillers – for zone p, if it’s out in the system.
• Program the controller with the chiller p set points for minimum and maximum chiller flow. – Verify with chiller manufacturer.
Design Considerations • Sequence chillers based on p or temperature sensors. • Use accurate, calibrated flow meter or p sensors at each evaporator • Allow for operator training. – Initial – On-going
Consider this design if: • System flow can be reduced by 30%. • System can tolerate modest changes in water temperature. • Operators are well trained. • Demonstrates a greater cost savings. • High proportion of operating hours at: – Part load. – Full load with low entering condenser water.
Turn-down Ratio • Chiller manufacturers publish 3 - 11 fps evaporator velocity range (typically). • You may have to increase your “acceptable head loss” targets, use more pump head. • Nominal base of 7 fps desirable. • Variation of
1
to 2 fps.
• Work with the manufacturer.
Rate of Change* Maximum rate of flow change, % design flow per minute Source
Vapor Compression
Absorption
#1
4-12
**
#2
20-30
2-5
#3
**
30
#4
2
**
#5
**
1.67
*Table 2-2 ARTI-21CR/611-20070-01, 2004, Bahnfleth & Peyer ** Information not provided
Do not use if: • Supply temperature is critical. • Three-way valves are used throughout. • Existing controls are old, inaccurate. • Operators are unlikely to operate the system as designed.
Supply Water Temperature • Dependant on : – System volume. – Rate of flow change.
• Application specific. • Consider thermal storage
Operator Ability • Within operator’s ability?. – Commercial buildings may not have well qualified operators.
• Training is mandatory. – Initial – Periodic, in view of operator turnover.
Start-Up & Shut-down • In systems that start-up and shut-down, it may be advisable to anticipate, and avoid, rapid changes in flow as control valves all tend to act together. • Control system, BMS, manual procedures. • Use slow opening/closing valves at the chiller, 60-90 seconds.(?)
Controls Complexity • Additional controls for the chillers • Additional controls the pumps. • Pumps operate on flow, temperature, and P. • Chiller P.
Sensor Calibration • Multiple sensors control: – Flow. – Temperature. – Delta p
• Maintenance. • Calibration.
Summary • Evaluate all the options. • Read some articles: – Variable Primary Flow CHW: Potential Benefits and Application Issues by Bahnfleth and Peyer. Pennsylvania State University, ARTI21CR/611-20070-01 – Chilled Water System for University Campus by Stephen W. Duda, PE, ASHRAE Journal May, 2006
• Another tool for the toolbox.
Comments? Questions? Observations?
Large Chilled Water System Design Seminar Primary-Secondary-Tertiary Pumping Systems
Primary-Secondary-Tertiary Zone C
Zone A Zone B
C H I L L E R
C H I L L E R
Variable Speed Pump
Direct Pumped Zones Zone A
Zone B
WRONG !
C
C
H
H
I
I
L
L
L
L
E
E
R
R
DP Controller
Zone C
Constant Demand Zones Zone A
Zone B
T
WRONG !
C
C
H
H
I
I
L
L
L
L
E
E
R
R
Zone C
Hard set valve
Automatic Flow Control Valve
Primary-Secondary-Tertiary Zone C
Zone A
RIGHT !
C H I L L E R
Zone B
C H I L L E R
Variable Speed Pump
Three Different Buildings • “A” has coils selected for 44°F. • “B” has coils selected for 45°F. • “C” has coils selected for 46°F. • Therefore, the supply water temperature must be at least 44°F for “A”. • But what about “B” and “C”?
Primary-Secondary-Tertiary can be even more useful Zone C
Zone A Zone B
C H I L L E R
C H I L L E R
? Optional Variable Speed Pump
Temperature Sensor Locations Load
Load
Load
T1 Tertiary Zone Pump
MV
MV
MV
T4 T1
Common
T2
T2
T3 Pumped Chilled Water Supply
½” Circuit Setter
Chilled Water Return
T3
T4
Tertiary Bridge Load
Load
Load
MV
MV
MV
T1 Tertiary Zone Pump
T4
Common
T2 T3
Pumped Chilled Water Supply
Tertiary Bridge Chilled Water Return
Temperature Sensor Locations Load
Load
Load
T1 Tertiary Zone Pump
MV
MV
MV
T4 T1
Common
T2
T2
T3 Pumped Chilled Water Supply
Chilled Water Return
T3
T4
ADVANTAGES 1. Permits operating at highest allowable zone temperature 2. Maximizes coil flow rate, good film coefficients 3. Maximizes flow rate through each control valve 4. Ensures good humidity control 5. Minimizes the amount of coil reheat
DISADVANTAGES 1. Temperature of return water is unknown 2. Temperature of return water to chiller may be too high 3. Will not recognize increased supply water temperature
T2 Operation Load
Load
T1 Tertiary Zone Pump
Load
MV
MV MV
T4
Common
T1
T2 T3
T2
T3 Pumped Chilled Water Supply Chilled Water Return
T4
ADVANTAGES 1. Maintains chilled water return temperature at setpoint 2. Will not overload the chiller
DISADVANTAGES 1. No control of zone supply water temperature 2. Could lose humidity control 3. Will not recognize increased supply water temperature
T3 Operation Load
Load
Load
T1 Tertiary Zone Pump
MV
MV
MV
T4
Common
T1
T2
T2
T3 Pumped Chilled Water Supply
Chilled Water Return
T3 T4
ADVANTAGES 1. There are no perceived advantages at this location
DISADVANTAGES 1. Little, if any, valve modulation unless it is set to close on sensing supply temperature lower than permissible in the zone
T4 Operation Load
Load
Load
T1 Tertiary Zone Pump
MV
MV
MV
T4 T1
Common
T2
T2
T3 Pumped Chilled Water Supply
Chilled Water Return
T3
T4
ADVANTAGES 1. Maximizes coil flow rate 2. Ensures good humidity control
DISADVANTAGES 1. Temperature of return water is unknown 2. Temperature of return water to chiller may be too high 3. Will not recognize increased supply water temperature temperature
No single sensor location satisfies all design criteria SO........
Applying Zone Zone Valve Controller Controller Load
Load
Load
MV
MV
MV
T1
T2
T1 Tertiary Zone Pump
Common
T2
T3 Pumped Chilled Water Supply
Chilled Water Return
T3
Control Algorithm 1. Temperature control to the zone (T1 (T1 sensing) sensing). 2. If T1 is satisfied, return water temperature to the chiller plant (T2 (T2 sensing) sensing). 3. Monitor secondary chilled water supply temperature sensing) for temperature increase due to secondary (T3 sensing) return water recirculation or temperature decrease due to chiller leaving water temperature reset. 4. Reference point for automatic reset and T (T2 - T3) control T3 sensin .
So what…? • Sati Satisf sfy y zone zone coo cooliling ng req requi uire reme ment nt at at the the maximum possible supply temperature • Mini Minimi mize ze seco second ndar ary y flo flow w rat rate e • Opti Optimi mize ze retu return rn wate waterr tem tempe pera ratu ture re
3-way Valve Application
Tertiary Pump
C h i l l e r P l a n t
Secondary Pumps
Tertiary Pump
Tertiary Pump
Problems • Bypass returns cold water to chillers, reduces system t. • Linear valve characteristics can cause increased flow at part load. • Balancing required in bypass pipe and coil-to-coil. • High cost per ton at the chiller.
3-way Valve System Load
MV
Load
MV
MV
Load
T1
T1
Common Flow Meter
T3
Small By-Pass
Secondary Supply Secondary Return
T2
T2
T3
Multi-zone Application Zone 1
Zone 2
Zone 3
Terminal Unit Balance Valve
Terminal Unit Control Valve
Zone 4 Zone (Tertiary) Pump
Zone Supply Temperature T1
T1 Chiller Supply Temperature
T3
Common
GPX
Flow Meter
C h i l l e r
Common T3
]e
C Distribution o (Secondary) m Pumps m o Rolairtrol n
Return Water Temperature
Zone Bias Control Valve
T2 C h i l l e r
T1 Common
T3
T3
3D Valves C h i l l e r
T1
T2
T2
T2
District Cooling Application • Individual building temperature control • Static pressure isolation • Return water temperature control • Btu/hr totalization • Outdoor temperature reset • Independent operation
District Cooling Application with GPX • Independent pressure control • HVAC fluid isolation
VPF Application Zone 1
Zone 2
Zone 3
Terminal Unit Balance Valve
Terminal Unit Control Valve
Zone 4 Zone (Tertiary) Pump
Zone Supply Temperature T1
T1 Chiller Supply Temperature
T3
GPX
Flow Meter
Common
C h i l l e r
Common T3
Zone Balance Valve
Rolairtrol
Return Water Temperature
Zone Bias Control Valve
T2 C h i l l e r
T1 Common
T3
T3
3D Valves C h i l l e r
T1
T2
T2
T2
Comments? Questions? Observations?
Large Chilled Water System Design Seminar Primary-Secondary Zone Pumping Systems
Primary-Secondary Zone Pumping
Zone A
C H I L L E R
C H I L L E R
Zone B
Supply
Return
Zone C
Shared Piping
Zone A
C H I L L E R
C H I L L E R
Zone B
Supply
Shared Pipe Return
Zone C
Shared Piping
Zone A
C H I L L E R
C H I L L E R
Zone B
Supply
Shared Pipe Return
Zone C
Present and Future Piping 1500 gpm
Flow : Current = 3000 Future = 4500
C H I L L E R
C H I L L E R
Zone A
1500 gpm
Zone B
(1500 gpm)
Zone C
Supply Current = 1500 Future = 3000
Current = 0 Future = 1500 Return
Future Zone C
Zone A Requirements (1500 gpm)
1500 gpm @ 80’ (1500 gpm)
Zone A
Zone B
Zone C
4500 gpm* A1 Supply
A2 A Zone A Pressure drop:A to A1+B to B1 Present = 20.8’ *Future = 45.2’ B1 Return B 4500 gpm*
A3
B2
B3
Zone A Calculations Table 9-1 Zone A calculations Zone A A to A1 + B to B1 Pi e Size Pressure Dro - ft / 100 ft E uivalent Len th su l & return Pressure dro Zone ressure dro Total ressure dro
Future Flow 14” 2.26
1000 ft x 2 = 2000 ft 45.2 ft 80 ft 125.2 ft
1000 ft x 2 = 2000 ft 20.8 ft 80 ft 100.8 ft
Pum Selection
1510-6G
1510-6G
1500
m
4500
m
56.4 h = 75 h *
Present Flow 14” 1.04
Note: 15 h additional for future re uirements * Nominal horsepower motor for NOL pump
3000
m
45.8 h = 60 h *
Zone B Requirements (1500 gpm)
1500 gpm @ 80’ 1500 gpm @ 80’
Zone B
Zone A
4500 gpm* A
3000 gpm*
A1 Supply
Pressure drop: Zone B AtoA1+ BtoB1 + A1toA2 + B1toB2 Present =20.8’ 9.0’ *Future = 45.2’ 33.4’
B1
B 4500 gpm*
Zone C
A2
Return 3000 gpm*
A3
B2
B3
Zone B Calculations Table 9-2 Zone B calculations Zone B A1to A2+B1 to B2 Pi e Size Pressure Dro - ft / 100 ft E uivalent Len th su l & return Pressure dro Previous ressure dro Zone ressure dro Total ressure dro
Future Flow 12” 1.67
Pum Selection
1510-6G
1500
m
3000
m
1000 ft x 2 = 2000 ft 33.4 ft 45.2 ft 80 ft 158.6 ft
Present Flow 12” 0.45
m
1000 ft x 2 = 2000 ft 9.0 ft 20.8 ft 80 ft 109.8 ft
71.4 h = 100 h * 1510-6G
Note: 40 additional h re uired for future re uirements * Nominal horsepower motor for NOL pump
1500
49.6 h = 60 h *
Zone C Requirements 1500 gpm @ 80’ 1500 gpm @ 80’
Zone B
Zone A
4500 gpm A
A1 Supply
Zone C
1500 gpm
3000 gpm
A3
A2
Pressure drop: Zone C AtoA1+ BtoB1 + A1toA2 + B1toB2 + A2toA3+ B2toB3 Present = 45.2’ + 33.4’ + 21.4’ Future = Present
B1
B 4500 gpm
1500 gpm @ 80’
Return
3000 gpm
B2
B3 1500 gpm
Zone C Calculations Zone C (A2 to A3 + B2 to B3) Future Flow @ 1500 gpm Present Flow @ 0 gpm Pipe Size 10” Pressure Drop - ft / 100 ft 1.07 Equivalent Length (supply & return) 1000 ft x 2 = 2000 ft Pressure drop 21.4 ft Previous pressure drop 78.6 ft (A to A2, B to B2) Zone pressure drop 80 ft Total pressure drop 180.0 ft Pump Selection @ 1500 gpm 1510-6G @ 82.7 hp = 125 hp*; Note: 50 hp more than Zone A
Zone Pumping Summary Summary Zone A Zone B Zone C Total
Present Requirement Future Requirement Duty Pump Standby Pump Duty Pump Standby Pump 1 @ 75 hp 1 @ 75 hp 1 @ 75 hp 1 @ 75 hp 1 @ 100 hp 1 @ 100 hp 1 @ 100 hp 1 @ 100 hp 1 @ 125 hp 1 @ 125 hp 2 @ 175 hp 2 @ 175 hp 3 @ 300 hp 3 @ 300 hp 4 @ 350 hp 6 @ 600 hp
* Nominal horsepower motor for NOL pump
Pressure Diagram - Zone Pumped System Zone Pump A
Zone Pump B
Zone Pump C
Load Friction Loss 0
0
Friction Loss Supply Header Friction Loss Return Header
Primary-Secondary Equivalent 1500 GPM
1500 GPM
3000 GPM A1 1500 GPM A2
(1500 GPM)
A3
Supply C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
A
Pump Controller
AFDs
B 3000 GPM
B1
Return B2 1500 GPM
B3
P-S Calculations Primary-Secondary pressure drop calculation: Pi e Se ment A to A1 + B to B1 A1 to A2 + B1 to B2 A2 to A3 + B2 to B3 Zone B Total
Pressure Dro Present, feet 20.8 9.0 DNA 80.0 109.8
Pi e Se ment A to A1 + B to B1 A1 to A2 + B1 to B2 A2 to A3 + B2 to B3 Zone C Total
Pressure Dro Future, feet 45.2 33.4 21.4 80.0 180
P-S Calculations Distribution pump selection: Present = 3000 gpm @ 109.8 feet, increase impeller to 13.5” for future head requirements: 2 @ VSCS 8x10x17L @ 111.0 hp 125 NOL 1 @ VSCS 8x10x17L @ 111.0 hp 125 NOL, standby Total 3 Pumps 375 NOL, Total Future = 4500 gpm @ 180 feet: 3 @ VSCS 8x10x17L @ 114.4 hp 375 NOL 1 @ VSCS 8x10x17L @ 114.4 hp 125 NOL Total 4 Pumps 500 NOL
Comparison • Zone Pumping – Present • 350 hp
– Future • 600 hp
• P/S Pumping – Present • 375 hp
– Future • 500 hp
Primary-Secondary Zone Pumping Cautions • Excessive initial horsepower • Initial equipment investment • Future considerations • Reduced Horsepower
Comments? Questions? Observations?
Large Chilled Water System Design Seminar Variable Speed Sensor Selection and Location
Direct Return Piped System
Supply C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
Pump Controller
AFDs Return
Differential Pressure Sensor
Single Point Pressure Sensor Supply
WRONG! C h i l l e r 3
C h i l l e r 2
Single Point Pressure Sensor
C h i l l e r 1
AFDs
Pump Controller Return
Control Curve Using Single Point Pressure Sensor 90 80
Shut-off head
Design Point
70
Constant Pressure
60
H e a d , F T
50
1750 RPM (Maximum rpm)
40 30
1480 RPM (Minimum rpm)
20 10 0
0
200 400
600 800
1000 1200 1400 1600
Flow, gpm
Single Point Pressure Sensor in a CHW System • A rise in the average water temperature results in a net expansion of the water. • This “net expansion” volume flows into the compression tank, raising the system pressure. • The pump slows down.
What if? Zone A
P
Zone B
Sensor here Supply
C H I L L E R
C H I L L E R
C H I L L E R
AFDs
Pump Controller Return
Zone C
Sensor Across Mains At Pump • What’s the set point? – It’s the greatest branch and distribution piping head loss calculated at design flow. In other words…design head.
• What will the flow be in each zone? – Determined by the zone path CV
Differential Pressure Sensor at the Pump 90 80
Design Point
70 60
H e a d , F T
50
Maximum rpm
40 30 20
Minimum rpm
10 0
0
200 400
600 800
1000 1200 1400 1600
Flow, gpm
Variable Head Loss Ratio C/S, Constant Flow System
Base 100
Pump Head Matched to System at Design Flow
90 P e r c e n t D e s i g n B H P
80
C/S, Variable Flow
V/S, 0% Variable Hd Loss, 100% Constant
Hd
70 V/S, 25% Variable Hd Loss, 75% Constant
60 50
V/S, 50% Variable Hd Loss, 50% Constant
40
Hd
Hd
V/S, 75% Variable Hd Loss, 25% Constant
Hd
V/S, 100% Variable Hd Loss, 0% Constant
Hd
30 20 10 0
10
20
30 40
50 60
70 80 90
% Flow
100
Coil or Valve?
P
25’ Head
Maximizing Variable Head Loss Constant Head Loss Variable Head Loss Supply C h i l l e r 3
C h i l l e r 2
C h i l l e r 1
Pump Controller
AFDs Return
Differential Pressure Sensor
Control Area Zone 2 20 ft
Zone 1 20 ft
A
B
C
DP Sensor C H I L L E R
C H I L L E R
C H I L L E R
Pump Controller
AFDs
F
E
D
Pressure Drops in Piping (Table 11-1)
P
AB+EF 20FT
TDH =
P
Zone 1 20FT
P
BC+DE 20FT
P
Zone 2 20FT
P AB + EF + BC + DE + P ZONE 2 = 60 FT
Control Area Calculation Table 11-2 Control Area Calculation Flow Zone 1
Friction Friction TDH Friction Friction P P Loss Zone 2 Loss Loss Zone 1 Loss BC+DE Zone 2 AB+EF Zone 1
Flow Zone 2
0 gpm 600 gpm 300 gpm 300 gpm 600 gpm 0 gpm 0 gpm 0 gpm 600 gpm 600 gpm
5 5 5 0 20
0 5 20 0 20
40 25 20 20 40
20 5 0 0 20
20 20 0 0 20
What pump head is required at: zero flow? full flow? less than full flow?
20 20 20 20 20
45 30 25 20 60
Control Area 60 50
H e a d , F T
40 30 20
Lower Limit Upper Limit
10
Single Point 0 0
100
300
500 600 900 1100 1200 Flow, gpm
So What...? • Staging pumps in a closed loop HVAC system by flow alone may not work because of different head requirements for a given flow. • “Wire to water” pump efficiency calculations at part load depend heavily on the assumptions made about the nature and shape of the control curve.
Single Sensor, Including Balance Valve Pressure Drop Zone 2 20 ft
Zone 1 25 ft
B (50)
C
A
E (10) F
D
What do you mean...? • The head loss across the coil and the wide open valve in zone 1 is 25 feet at full flow. • If that’s true, then we need to add an extra 15 feet of head loss in the balance valve to insure adequate flow out to Zone 2 when the Zone 1 valve is wide open.
Set Point, Zone 1, 40 ft Flow Zone 1
Flow Zone 2
Friction Loss
Friction Loss
Head Required
Setpoint -
AB+EF
BC+DE
Zone 2
Friction Loss
0 gpm
600 gpm
5
20
20
0
300 gpm
300 gpm
5
5
5
30
600 gpm
0 gpm
5
0
0
40
Excess head means wasted energy
Sensor Location Zone 2
Zone 1
A
B
C
DP Sensor C H I L L E R
C H I L L E R
C H I L L E R
Pump Controller
AFDs
F
E
D
Single Sensor in Zone 2 Zone 1 requires 600 gpm at 25 ft Zone 2 requires 600 gpm at 20 ft
Flow Zone 1 0 m 300 m 600 m
Flow Zone 2 600 m 300 m 0 m
Friction Loss
Friction Loss
Friction Loss
AB+EF
Zone 1
BC+DE
5 5 5
0 6.25 25
20 5 0
P
P
Zone1, Available 40 25 20
Inadequate head for Zone 1
Avail Friction Loss Zone 1 40 13.75 -5
Sensor in Zone 1 Zone 1 requires 600 gpm at 25 ft Zone 2 requires 600 gpm at 20 ft
Flow Zone 1 0 m 300 gpm 600 m
Flow Zone 2 600 m 300 gpm 0 m
Friction Loss AB+EF 5 5 5
Friction Loss BC+DE 20 5 0
Head Re uired
Zone 2
Inadequate flow in Zone 2
20 5 0
Setpoint Friction Loss 5 20 25
What can we do...?
In this system:
• Single sensor in Zone 2 at 20 ft fails to provide adequate flow only when – load in Zone 2 < 50% and – load in Zone 1 > 75%
• Is this a predictable, recurring situation? – manual adjustment – programming
• Add a second sensor
Applying Multiple Sensors Zone A
Zone B
Supply
DP Sensors C H I L L E R
C H I L L E R
C H I L L E R
AFDs
Pump Controller Return
Zone C
Use Multiple Sensors? • Load – Similarity – Priority – Diversity
• One building or several • Redundancy • First cost vs operating cost
The “Active Zone” • Zone set points do not have to be the same. • Technologic™ pump controller scans all zones often, comparing process variable to set point in each case. • Pumps are controlled to satisfy the worst case. • What happens to the rest of the zones?
Effect of Sensor Location Zone 1
Zone 2
B
C
A OR
E F
D
Multiple Sensors & Setpoints Multiple sensors, set point across Zone 1, = 25 FT and setpoint across Zone 2 = 20 FT, (Table 11-6) Flow Flow Friction Loss Minimum Friction Loss Minimum P P Zone Zone AB+EF Req’d BC+DE Req’d Zone1 Zone 2 1 2 Available Available P Zone 1, P Zone2 0 600 5 0 40 20 20 20 300 300 5 6.25 25 5 5 20 600 0 5 25 25 0 0 25
Row 1. Sensor 2 is controlling, Zone 1 is over pumped. Row 3. Sensor 1 is controlling, Zone 2 is over pumped. Total pump head required: row 1 45 ft row 2 30 ft row 3 30 ft
Reverse Return Piped System
Supply
C H I L L E R
Return
Reverse Return Systems • If all the circuits are the “same length”, will the pump still change speed? • Suppose a coil with a high p requirement and another with a lower p requirement are served by the same reverse return piping system. OK? • If the coils are serving different sides of the building, could we have a problem?
Tertiary Piped System
Zone A
C H I L L E R
Zone B
Zone C
C H I L L E R
Return
Zone Piped System
Zone A
C H I L L E R
C H I L L E R
Zone B
Supply
Return
Zone C
Summary • Give priority to the needs of the branch. • The rule of sensor location is simple and easy to apply: – If you have to use a single sensor, put it across the critical branch. – What’s the “critical branch”? – It’s the same one that determined the pump head.
• As we’ve seen, the analysis is more important than the “rule”.
Comments? Questions? Observations?
Large Chilled Water System Design Seminar Achieving Hydronic System Balance
Systems Approach Control M
Load
Distribution
Air Management
Verification
Philosophy Source
Systems Approach • All components work together as “team” – Components interact and work as well as we understand them
• A collection of mismatched components will not perform as expected • Owner, engineer, architect, contractor, and operators are part of the system too!
Hydronic Balancing • We worry about balance because: – Load calculations are approximate – Piping circuitry analysis is approximate – Control valve selection is approximate – Approximations will lead to underflow and overflow situations
• Results of overflow or underflow – Design Dt cannot be achieved – Supply temperature controller hunts (?) – Sequence of operation can be upset.
For example: • Published by ASHRAE & Hydraulic Institute • DarcyWeisbach Equation. Add 15%!
What Is Balancing? • It’s test, adjust & balance • Test: The system, now built, is verified in operation to perform to the expected level. – What do we measure? • temperature, flow, pressure drop, energy consumption….
– What do we test with? – Can we test with what is installed? – Can we obtain accurate readings?
Adjust Adjust: tested in operation, the system is found lacking and needs fine tuning. • What level of adjustment, and for what purpose? – Create comfort conditions – Minimize energy consumption – Prevent equipment damage
• How do we adjust?
Balance • Balance is often interpreted to mean ±10% of design flow. • This generalization may or may not yield satisfactory heat transfer required for comfort conditions
Redefining Balance • Evaluate System Operation – If the goal is occupant comfort, then heat transfer becomes the key concern. – We control heat transfer as a sensible temperature control process between controller, control valve and coil – Analysis should account for interaction of all key components, and how they affect the rest of the system
Balanced Hydronic Systems • All terminals receive enough flow to produce satisfactory heat transfer (97.5% - 102.5%) • At design conditions, all terminals receive satisfactory flow with the pump in a specified range of operation • Under temperature control modulation to match load, circuit flow does not exceed design flow accuracy
Chilled Water Coil Flow vs. Heat Transfer 120%
45
Total 40 100% 35
n o80% i s s i m60% E t a e40% H %
Sensible
) 30 F ° ( 25 T
∆
e d i s r 15 e t a 10 W 20
Latent
20%
5 0% 0%
0 20%
40%
60%
80%
100%
120%
140%
% Flow • 30”H X 46”W •10 FPI / 4 Row •30 GPM / 10° ∆T •85° DB/ 71° WB Ent •45° EWT •15 Circuits •3/8” Tube •4000 CFM •Nominal 10 Ton Rating
160%
180%
200%
Chilled Water Coil Flow vs. Emission 100 90 80 70 60 50 40 30 20 10
80%
100%
• 30”H X 46”W •10 FPI / 4 Row •30 GPM / 10° ∆T •85° DB/ 71° WB Ent •45° EWT •15 Circuits •3/8” Tube •4000 CFM •Nominal 10 Ton Rating
97%
Flow Tolerance – 97% Design HT -0 / +10% F ° 260 e r 240 u 220 t a r 200 e 180 p m 160 e T 140 r 120 e t a 100 W 80 16° y 70 l p 60 p u 50 S 40 0
±5%
±10%
±15%
±20%
g n i t a e H g n i l o o C
6°
2
4
6
8
10
12
14
16
18
20
22
Suggested Flow Tolerance (%)
24
Balancing, The Obvious Answer • Maximum branch flows need to be controlled • Balancing valves are one solution • Pressure independent flow control is another method • “Systems” perspective needs to be maintained; pipe, valves, calculations.
Pressure Dependent Balancing Valve
Pressure Dependent Balancing Valve 140 120 100 ) t e e 80 F ( d a 60 e H 40 20 0 0
50
100
150
Flow (USGPM)
200
250
Pressure Independent Flow Limiting Valve Orifice is sized for the design flow
Cartridge
Cartridge Operation Flow
Flow
P1
P2
P1 is low Cartridge Opens P1 - P2 = Constant
P1
P2
P1 is high Cartridge Closes P1 - P2 = Constant
Pressure Independent Flow Limiting Valve Fixed Orifice
Control Range M P G n i
Design Flow
w o l F
Differential Pressure in PSI
Accuracy Range
Pressure Independent Flow Limiting Valve ½” – 2” sizes available .18 to 45.46 GPM
Externally adjustable flow limiting balance valves
Pressure Independent Control Valves ½” – 2” sizes available .13 to 37 GPM
Externally adjustable flow limiting balance valve and a modulating control valve
It’s more than just “balancing valves” • Piping system decisions: – Usually have a choice between two size pipes – Varied methods of pipe head loss calculation
• Have to account for safety factors, aging • Control valve selection: may not get the exact flow coefficient you need. • Have to have a way to validate (test) and make adjustments (branch & system) • It takes some judgment and experience.
Design Criteria For Piping ASHRAE recommends: • Velocity
Consider:
• Branch to riser pressure drops should be 2:1 or – General 4 -10 fps greater – Mechanical rm. 6 -15 fps • Direct return circuits in • Maximum velocity variable speed / variable – 1500 hr/yr 15 fps flow hydronic circuits – 3000 hr/yr 13 fps require much more – 6000 hr/yr 10 fps attention to detail and • Pressure drop control sequence – 1.0 to 4.0 ft / 100 ft.
ASHRAE 90.1-2010 CHAPTER 6
HEATING, VENTILATING, AND AIR CONDITIONING SECTION 6.5 Prescriptive Path TABLE 6.5.4.5 Piping Syst em Design Maximum Flow Rate in GPM Operating Hours/Year
<2000 Ho urs /Year
<2000 and <4400 Hours/Year
>4400 Hours/Year
Nominal Pipe Size, in.
Other
Variable Flow / Variable Speed
Other
Variable Flow / Variable Speed
Other
Variable Flow / Variable Speed
2½
120
180
85
130
68
110
3
180
270
140
210
110
170
4
350
530
260
400
210
320
5
410
620
310
470
250
370
6
740
1100
570
860
440
680
8
1200
1800
900
1400
700
1100
10
1800
2700
1300
2000
1000
1600
12 Maximum Velocity for Pipes over 12 in. Size
2500
3800
1900
2900
1500
2300
8.5 fps
13.0 fps
6.5 fps
9.5 fps
5.0 fps
7.5 fps
Piping System Design Maximum Flow Rate – Friction Loss Rate Comparison Friction Loss Rate Operating Hours/Year
<2000 and <4400 Hours/Year
<2000 Hours /Year
Nominal Pipe Friction Size, in. Other Loss Rate (GPM) (Ft/100 Ft) 2 1/2 120 10.01
>4400 Hou rs/Year
Variable Friction Friction Variable Friction Friction Variable Friction Speed Loss Rate Other Loss Rate Speed Loss Rate Other Loss Rate Speed Loss Rate (GPM) (Ft / 100 Ft) (GPM) (Ft / 100 Ft) (GPM) (Ft / 100 Ft) (GPM) (Ft / 100 Ft) (GPM) (Ft / 100 Ft) 180
21.78
85
5.2
130
11.66
68
3.42
110
8.48
3
180
7.26
270
15.78
140
4.5
210
9.74
110
2.86
170
6.51
4
350
6.55
530
14.56
260
3.72
400
8.46
210
2.48
320
5.52
5
410
2.84
620
6.25
310
1.67
470
3.68
250
1.12
370
2.34
6
740
3.47
1100
7.44
570
2.11
860
4.63
440
1.3
680
2.96
8
1200
2.2
1800
4.79
900
1.27
1400
2.95
700
0.79
1100
1.86
10
1800
1.52
2700
3.3
1300
0.82
2000
1.86
1000
0.5
1600
1.21
12
2500
1.18
3800
2.63
1900
0.7
2900
1.57
1500
0.45
2300
1.01
Velocity Operating Hours/Year Nominal Pipe Size, in. Other (GPM) 120 2 1/2 3 180 350 4 410 5 6 740 8 1200 10 1800 2500 12
<2000 and <4400 Hours/Year
<2000 Hours /Year
Velocity (ft/sec)
Variable Speed (GPM)
Velocity (ft/sec)
8.04
180
7.81
270
8.82
>4400 Hours/Year
Other (GPM)
Velocity (ft/sec)
Variable Speed (GPM)
Velocity (ft/sec)
Other (GPM)
Velocity (ft/sec)
Variable Speed (GPM)
Velocity (ft/sec)
12.06
85
5.69
130
11.72
140
6.08
210
8.71
68
4.56
110
7.37
9.12
110
4.78
170
530
13.36
260
6.55
7.38
400
10.08
210
5.29
320
6.57
620
9.94
310
4.97
8.07
470
7.53
250
4.01
370
5.93
8.22
1100
12.22
570
7.7
1800
11.55
900
6.33
860
9.55
440
4.89
680
7.55
5.78
1400
8.98
700
4.49
1100
7.32
2700
10.98
7.06
1300
5.29
2000
8.13
1000
4.07
1600
7.17
3800
10.89
6.51
1900
5.45
2900
8.31
1500
4.3
2300
6.59
SYSTEM SYZER – Flow/Pressure Drop
ASHRAE 90.1 max pipe size information
Estimated annual energy cost based on pipe size Note that cost is based on a constant load – it is independent of the info in ASHRAE frame
Branch to Riser Pressure Drop Ratio
Ratio, Branch To Distribution 4 2 1
% Design Flow In End Circuit 95 90 80
• And it falls off much more below 1:1
Branch:Riser Pressure Drop Ratio 100%
Pump head constant Improved β
d a e H
0
Distance From Pump
Branch:Riser Pressure Drop Ratio 100%
β constant Reduced pump head
d a e H
0
Distance From Pump
Issue: System Curve • When we have many path’s, we have many system curves depending upon which valves are open. • In VS/VF systems, the pump flow changes as the control valves modulate. The pump speed adjusts to those changes.
A much larger system Flow (USGPM)
Pipe Size
5000
12 14 16 18 20 24
5500
6000
Friction Velocity Loss (FPS) (Feet) 4.48 14.34 2.77 11.86 1.41 9.08 0.78 7.17 0.45 5.77 0.18 3.99
14 16 18 20 24
3.33 1.7 0.94 0.54 0.22
13.04 9.99 7.89 6.35 4.39
14 16 18 20 24
3.94 2.01 1.11 0.64 0.26
14.23 10.89 8.61 6.92 4.79
Reynolds Friction Flow Type Number Factor 1172764 1066660 933291 829403 743901 618839
Transition Transition
1173326 1026626 912343 818292 680723
Transition
1279992 1119949 995283 892682 742607
Transition Transition Transition Transition
Transition Transition Transition Transition Transition Transition
Transition Transition Transition
0.014 0.0139 0.0138 0.0138 0.0138 0.0138
0.0138 0.0137 0.0136 0.0136 0.0137
0.0137 0.0136 0.0135 0.0135 0.0136
Balanced Flow Coefficient Available CV ∆P Branch
Set Point = 20 Ft
10
1
340
20
1000
2
287
28
1000
4
3
253
36
1000
4
4
229
44
1000
5
211
52
1000
6
196
60
1000
0
10 CV
G
g
1
4
CV
F
f
2
4
CV
E
e CV
d CV
Total
c CV
B
4
32
5
4
4
24
4
4 C
16
3
4 D
8
4
4
a
6000@68’
4
40 b
6
A
Branch Flow
Branch = 20’ Risers = 48’ Ratio = 0.4
70.0
60.0
50.0
40.0
) t e e F ( d 30.0 a e H
20.0
Inner Valves Close Head Outer Valves CLose System Curve 10.0
0.0 0.0
1000.0
2000.0
3000.0
4000.0
5000.0
600
Flow (USGPM)
2
Q2 Min Control Head h2 h1 Q1
2:1 BRPDR 70.0
10
10
0
CV
G
60.0
1
g
.83 F
CV
2
) t e e F ( d a30.0 e H 40.0
CV
.83 C
CV
Out Valves Close Head
B
Inner Valves Close
.83 e
5.1
.83
4
d CV
6.8
5
.83
20.0
3.4
3
.83 D
.83 f
50.0
.83 E
1.7
.83 c
CV
6
8.5
.83 b
System Curve
.83
10.0
0.0 0.0
1000.0
2000.0
3000.0
4000.0
5000.0
6000.
.83 A a 6000 @ 30
Flow (USGPM)
Plot of Valve & Head Combinations 6000 GPM @ 30’ 2:1 Branch Riser Pressure Drop Ratio (BRPDR)
Variable Primary Flow System F
4’
VFD
6
4’
4’
E
10’
5
10’
4’
D
4
10’
C
4’
3
4’
B
10’
2
A
10’
1
10’
6000 GPM @88 Ft Hd 10’
1 2 2’
3
40’
2’
32’ F’
4’
10’
10’ 24’ E’
4’
16’ D’
4’
8’ C’
4’
20’
These Must Be Balanced!
10’
10’
10’
0’ B’
4’
A’
Contro l Area for Variable Flow -Variable Speed Primary Distribu tion Sys tem 120.0
Valve 6 Closed
Valve 6 & 5 Closed
100.0
Valve 6,5,4,3 Closed
80.0
Valve 6,5,4 Closed
All Open
Valve 6,5,4,3,2 Closed ) t e e F ( d a e H
60.0
40.0 Valve 1 Closed All Closed
Valve 1,2 Closed
20.0
System Curve Inboard Outboard
Valve 1,2,3 Closed Valve 1,2,3,4 Closed Valve 1,2,3,4,5 Closed
0.0 0
1000
2000
3000 4000 Flow (GPM)
5000
6000
7000
Thoughts On Selection • Coil pressure drop dominates system controllability. • Control valve selection with β = 0.5 • Balancing valves: provide trim… – Use as much PD as possible in control valves – Absorb the rest at the balancing valve.
• Use independent flow measurement – Triple Duty Valve – Pump – Circuit Setters
Summary: Why Test & Balance? • Load calculations can be inaccurate causing excess flow • Pipe and fitting predicted losses will vary from actual performance – Aging factors / fouling will actually occur many years in the future – Safety factors result in pump over-heading, improper pump selection and over flow.
• Control valve sizing is not exact. • Systems are not built as designed.