September 22, 2011 - Dallas ASHRAE · 2016. 9. 7. · Chiller Energy Fundamentals A chiller’s...
Transcript of September 22, 2011 - Dallas ASHRAE · 2016. 9. 7. · Chiller Energy Fundamentals A chiller’s...
September 22, 2011
Roy Hubbard – HVAC Systems Technology
Lesson Objectives (YC-3)
At the end of this session, you will understand:
� Understanding Chiller Energy Fundamentals
� Impact of VSDs (maintenance and energy)
� chillers
� pumps
� towers
2
Chiller Energy Fundamentals
� A chiller’s energy(kW) use is dependent on both cooling load & compressor head.
(lift/press diff)
Chiller Energy Fundamentals
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
5
6
Load
(weight of
rock)
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
Lift
(height of mountain)
7
Load
(weight of
rock)
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
100%
EN
ER
GY
0%
8
Lift
(height of mountain)
Load
(weight of
rock)
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
De
sig
n L
ift
9
Load
(weight of
rock)
Lift
(height of mountain)
100%
EN
ER
GY
0%
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
10
Evaporator Temp.
Condenser Temp.100%
EN
ER
GY
0%
De
sig
n L
ift
Load
(weight of
rock)
Lift
(height of mountain)
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
11
100%
EN
ER
GY
0%
De
sig
n L
ift
Evaporator Temp.
Condenser Temp.
Load
(weight of
rock)
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
55°F (12.8°C) ECWT
70%
EN
ER
GY
0%
12
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
Evaporator Temp.
Condenser Temp.
Off
-D
es
ign
Lif
t
Load
(weight of
rock)
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy – Cold Condenser Water
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Load
% K
W
85
75
65
55
Off-Design Energy Performance Curves – Poor!
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Load
% K
W
85
75
65
55
Off-Design Energy Performance Curves – Great!
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Load
% K
W
85
75
65
55
Off-Design Energy Performance Curves – Poor!
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Load
% K
W
85
75
65
55
Off-Design Energy Performance Curves – Great!
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Load
% K
W
85
75
65
55
Off-Design Energy Performance Curves - Average
� A chiller’s energy(kW) use is dependent on both cooling load & compressor head.(lift/press diff)
� A chiller’s efficiency (kW/ton) varies little with load, but much with compressor head
Chiller Energy Fundamentals
How does chiller efficiency
change as load and head vary?
Chiller Efficiency
20
kW/ton vs Load/Head
Design
21
kW/ton vs Load/Head
Design
Chiller Efficiency (Constant Speed)
Chiller Efficiency (Constant Speed)
Chiller Efficiency (Constant Speed)
Variable Speed Chillers
26
100%
EN
ER
GY
0%
De
sig
n L
ift
Evaporator Temp.
Condenser Temp.
Load
(weight of
rock)
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy
27
70%
EN
ER
GY
0% Evaporator Temp.
Condenser Temp.
Off
-D
es
ign
Lif
t
Load
(weight of
rock)
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
55°F (12.8°C) ECWT
Energy Usage - Constant Speed Driven Chillers
Chiller Energy Analogy – Cold Condenser Water
50%
0%
28
EN
ER
GY
Evaporator Temp.
Condenser Temp.
Off
-D
es
ign
Lif
t
Load
(weight of
rock)
55°F (12.8°C) ECWT
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
Energy Usage - Variable Speed Driven Chillers
Cold Entering Condenser Water
29
Evaporator Temp.
Condenser Temp.
Off
-D
es
ign
Lif
t
70%
EN
ER
GY
0%
Load
(weight of
rock)
55°F (12.8°C) ECWT
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
Energy Usage - Constant Speed Driven Chillers
Cold Entering Condenser Water
50%
0%
30
EN
ER
GY
Evaporator Temp.
Condenser Temp.
Off
-D
es
ign
Lif
t
Load
(weight of
rock)
55°F (12.8°C) ECWT
44°F (6.7°C) LCHWT
85°F (29.5°C) ECWT
Energy Usage - Variable Speed Driven Chillers
Cold Entering Condenser Water
Energy vs. Load & ECWT (CSD)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Design Load
% D
esig
n K
W
Energy vs. Load & ECWT (VSD)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Design Load
% D
esig
n K
W
Energy vs. Load & ECWT (CSD)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Design Load
% D
esig
n K
W
Energy vs. Load & ECWT (VSD)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Design Load
% D
esig
n K
W
25-30% Savings
Variable Speed Chillers
Chiller Energy Fundamentals
� A chiller’s energy draw is dependent on both load and compressor head (lift/press diff)
� A chiller’s efficiency (kW/ton) varies little with load, but much with compressor head
� Variable Speed on Chillers saves from both compressor head change and load
change
1/2 of Savings Head Change 1/2 of Savings Load Change
25-30% Savings
Variable Speed Chillers
� Load Savings depends on Head Reduction
� Head Savings does not depend on Load Reduction
Variable Speed Chillers
Chiller Energy Fundamentals
� A chiller’s energy draw is dependent on both load and compressor head (lift/press diff)
� A chiller’s efficiency (kW/ton) varies little with load, but much with compressor head
� Variable Speed on Chillers saves from both compressor head change and load change
� Variable Speed saves energy on Multiple Chiller Plants and Single Chiller Plants
Variable Speed Chillers
Load-based Sequencing
� Difference - Single vs Multiple?
� Load? - Heavier Chiller Loading (less variation), if using old load-based sequencing
Variable Speed CHW Pumps
Variable Speed CHW Pumps
� Good Savings on Pump Energy
RPM ~ Flow (GPM, CFM, etc.)
RPM 2 ~ Head (ft, SP)
RPM 3 ~ Ideal Power (hp)
Apply only to Water hp = Flow X Head / 3960
� note pump/motor/VSD efficiency not included
Apply only to fixed, unchanging piping systems (flow varies, but no valves close)
Variable Flow Affinity Laws (VSD Control)
Des. HP = GPM X Head
3960 X PumpEff
Des. kW = HP X 0.746
MotorEff X VSDEff
Pump Energy
Variable Speed CHW Pumps
� Good Savings on Pump Energy
� Chiller energy Unaffected
� Maintain Tube Water Velocity 1.5 to 12 fps (Flooded 2P – 45’, 3P – 67’ max)
� Set Proper Ramp Function Time for VSD (5% to 30% per min – 10% is typical)
Variable Speed CW Pumps (Variable Flow)
Variable Speed CW Pumps (Variable Flow)
� Good Savings on Pump Energy
� Chiller Energy will be higher
� Chiller Maintenance will be higher
Variable Speed CW Pumps (Variable Flow)
� Good Savings on Pump Energy
� Chiller Energy will be higher
� Chiller Maintenance will be higher
� Tower Maintenance may be higher
Variable Speed CW Pumps (Variable Flow)
Variable Speed CW Pumps (Variable Flow)
� Good Savings on Pump Energy
� Chiller Energy will be higher
� Chiller Maintenance will be higher
� Tower Maintenance may be higher
� Tower Approach may deteriorate
Variable Speed CW Pumps (Variable Flow)
Dry Spots in Cooling Tower Fill destroys Approach
Variable Speed CW Pumps (Variable Flow)
� Good Savings on Pump Energy
� Chiller Energy will be higher
� Chiller Maintenance will be higher
� Tower Maintenance may be higher
� Tower Approach may deteriorate
� Piping System Maintenance will be higher
� Maintain Tube Water Velocity 3.3 to 12 fps
� Use to replace balancing valve
Cooling Towers Fans – Variable Speed
Fan Affinity Laws (VSD Control)
Chiller Plant Component Energy
� CHWP at 160 ft head (10 deg rise) = .10 hp/t
� CWP at 50 ft head (10 deg rise) = .05 hp/t
� Tower Average = .05 hp/t (induced draft, gravity fed average)
� Chiller (at .6 kW/t) = .75 hp/t
September 22, 2011
Roy Hubbard – HVAC Systems Technology