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