Variable- Variable ---Speed CompressorsSpeed Compressors · Variable-Variable ---Speed...

1

VariableVariableVariableVariable----Speed CompressorsSpeed CompressorsSpeed CompressorsSpeed Compressors

centrifugal

scrollreciprocating

helical-rotary

Methods of Compressor Unloading

� Reciprocating

� Scroll

� Helical-Rotary

� Centrifugal

Cylinder Unloaders

Cycle On and Off

Slide Valve

Inlet Vanes

VARIABLE SPEED DRIVES

2

Basic Refrigeration System

compressor

condenser

evaporator

expansion device

dischargeline

suctionline

liquidline

A

B

C

D

Split DX SystemSplit DX System

cooling coil(evaporator)cooling coil(evaporator)

supply fansupply fan

air-cooled condenserair-cooled condenser

compressorscompressorsrefrigerant pipingrefrigerant piping

2-stage centrifugal chiller

Refrigeration Cycle

condenserevaporator

expansion devices

economizer

2-stagecompressor

3

Affinity Laws2012 ASHRAE Handbook HVAC Systems and Equipment

1. “Flow (capacity) varies with rotating speed”

2. “Head varies as the square of the rotating speed”

3. “Brake horsepower varies as the cube of the rotating

speed”

“The (third) affinity law assumes that the system curve is

known and that head varies as the square of the flow.”

Many systems don’t follow this assumption

VSDs and Their Effect on System Components

• Cooling tower fans –

Load/power curve nearly cubic

sumpsump

outdoorair

louvers

fill

propeller fan

0%

20%

40%

60%

80%

100%

0% 50% 100%

% Load

Speed^3

85°F Setpoint

Perc

ent

pow

er

4

Chilled and Condenser Water Pumps

• Head/flow curve not “squared”

− Control setpoint

− Minimum Flow requirements

− Cooling tower static “lift”

water flow, %

100

20 40 60 80 1000

80

60

40

20

0

pum

p h

ead dynamic

pressure

fixed pressure/lift

Chilled and Condenser Water Pumps

• Power/flow curve not “cubic”

−DP curve not squared

−Minimum flow rates

water flow, %

100

20 40 60 80 1000

80

60

40

20

0

pum

p p

ow

er

VSDs and Their Effect on System Components

Variable speed chillers:

Load/power curve not cubic

• Lift depends on system

operating conditions

• Power is dependent on

load and lift

• The relationship of power

changes for different compressor

types

coolingtower

water-cooledchiller

coolingload

P

P

44°F

condenser

evaporator

88.2°F

Lift

5

Centrifugal Compressor

volute

diffuserpassages

radial impeller passages

blades impeller

Impeller Dynamics

diameter

Vr ∝ refrigerant flow rate

Vt ∝ rotational speed × diameter

rotational

speed

VrR

Vt

refrigerant flow rate

Compressor Unloading

VrR

Vt

Vr

Vt

full

loadpart load

R

6

Vr

Vt

Surge

Vr < static pressureR

pre

ssure

ris

e

flow rate – capacity (cfm-tons)

best

efficiency

decreasing

efficiency

Fixed-Speed Compressor Map

inlet guide vanes

fully open

minimum

guide vane position

surge

boundary

pre

ssu

re r

ise

design

selection

flow rate - capacity (cfm - tons)

Fixed-Speed Compressor Map

chiller capacity (%)

ch

ille

r p

erf

orm

an

ce (

kW

/to

n) 1.0

0.0

0 50 100

85°F

75°F

65°F

55°F

7

pre

ssu

re r

ise

inlet guide vanes

fully open

minimum

guide vane position

surge

boundarybest efficiency

a best efficiency zone is

created through the

operating map

60 Hz

50 Hz

min.

Variable-Speed Compressor Map

40 Hz


pre

ssu

re r

ise

inlet guide vanes

fully open

surge



speed modulation;

ride wide-open

vane curve

speed and

guide vane

modulation


pre

ssu

re r

ise fully

open

surge


flow rate - capacity (cfm - tons)chiller capacity (%)

ch

ille

r p

erf

orm

an

ce (

kW

/to

n)

1.0

0.0

0 50 100

85°F

75°F

65°F

55°F


8


ch

ille

r p

erf

orm

an

ce (

kw

/to

n)

900-ton chiller selections at 44°/85°F

Design Point Performance

VS @ 0.585 kW/ton

FS @ 0.513 kW/ton (-12.4%)

85°F75°F

65°F

55°F

variable-speed

fixed-speed

1.0

0.0

0 100

Centrifugal Performance Comparison (Equivalent Price)

Fixed Speed versus Variable Speed

40

50

60

70

80

90

100

Fixed Speed / Variable Speed Comparison

leav

ing

co

nd

en

ser

wate

r te

mp

era

ture

(F

)

chiller load (% of design)

0%

+10% VS+20% VS

+30% VS

+40% VS

10% FS

0 100

Positive Displacement Compressors

ScrollScroll Rotary ScrewRotary Screw

• 10-40 tons

• Few moving parts

• 35-450 tons

• Few moving parts

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Centrifugal capacity vs lift

60% 140%

lift

Rotary screw capacity vs lift

60% 140%

lift


Flow versus Pressure Differential


Rotary Screw Compressor

meshing

pointdischarge port


ch

ille

r p

erf

orm

an

ce (

kw

/to

n)

0.0

0

1.0

0.0

100

85°F

75°F

65°F

55°F

Part Load Efficiency with Slide Valve

10


ch

ille

r p

erf

orm

an

ce (

kw

/to

n)

0.0

0

1.0

0.0

100

85°F

75°F

65°F

55°F

Part Load Efficiency with Variable Speed


ch

ille

r p

erf

orm

an

ce (

kw

/to

n)

0.0

0

1.0

0.0

100

85°F

75°F

65°F

55°F

Slide Valve versus Variable Speed

@ equivalent price

variable-speed

slide valve


leav

ing

co

nd

en

ser

wate

r te

mp

. (º

F)

40

0

100

100

+10% VS+20% VS

+30% VS

+40% VS

0%10% SV

Slide Valve versus Variable Speed

11


ch

ille

r p

erf

orm

an

ce (

kW

/to

n)

1.0

0.0

0 100

85°F

75°F

65°F

55°F

CentrifugalCentrifugal Rotary ScrewRotary Screw


0.0

0

1.0

100

Variable Speed Centrifugal vs. Rotary

Summary of performance differences

The Physics of Operation are Different

• Centrifugal impellers operate on the principle

of dynamic compression

• Rotary compressors operate on the principle

of positive displacement

• Unloading Performance may varies greatly for

different modulation technologies

• VSDs on centrifugal chillers benefit from reduced lift

• VSDs on screw chillers benefit from reduced load or lift

• Analysis needs to account for

• Chiller comparison

• Same-price VSD or premium efficiency chillers

• Actual chiller performance

• Actual utility rates

Summary

12

Chiller Chiller Chiller Chiller

Table 6.8.1C Table 6.8.1C Table 6.8.1C Table 6.8.1C ---- ExcerptExcerptExcerptExcerpt

0.639 kW/ton0.450 IPLV


Centrifugals < 300 tons



600+ tons


0.576 kW/ton0.549 IPLV300 – less than 600 tons

0.639 kW/ton0.490IPLV


300+ tons 0.718 kW/ton0.540 IPLV


150 - less than 300 tons


0.775 kW/ton0.615 IPLV75 - less than 150 tons


0.780 kW/ton0.630 IPLVWater cool. pos. displ. >75 tons

9.562 EER12.75 IPLVAir cooled 150+ tons

9.562 EER12.5 IPLV

Air cooled < 150 tons

Path BPath A

90.1-2007 Addendum M

stationaryscroll

drivenscroll

dischargeport

intake

discharge

intakemotorshaft

Scroll Compressor Fundamentals

13

Single On/Off CompressorOperation Evaluation

Cap

acit

y

Mo

du

lati

on

Co

ilT

em

p

Sy

s A

pp

Co

ntr

ol

Co

mp

lexit

y

Co

st

On/OffOn/OffOn/OffOn/Off PoorPoorPoorPoor WideWideWideWide LowLowLowLow LowLowLowLow

Single On/Off CompressorUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On/Off

evaporator

condenser

compressor

hot gas bypass valve

expansion valve

distributor

suction line

liquid line

oil return line

Hot Gas By-Pass

ModulationOperation Evaluation

Hot Gas By-Pass Unloading

Cap

acit

y

Mo

du

lati

on

Co

ilT

em

p

Sy

s A

pp

Co

ntr

ol

Co

mp

lexit

y

Co

st

BestBestBestBest BestBestBestBest BestBestBestBest MediumMediumMediumMedium MediumMediumMediumMedium

14

Hot Gas By-Pass ModulationUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On/Off

HGBP

Higher

▲

Or

Lower ▼

Hot Gas By-Pass ModulationUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On/Off

HGBP

Ported / 2-Stage ScrollCompressor Evaluation

Cap

acit

y

Mo

du

lati

on

Co

ilT

em

p

Sy

s A

pp

Co

ntr

ol

Co

mp

lexit

y

Co

st

GoodGoodGoodGood GoodGoodGoodGood WideWideWideWide LowLowLowLow MediumMediumMediumMedium

15

Ported / 2 Stage ScrollUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On./Off

HGBP

Two Stage

Higher ▲

Or

Lower ▼

Ported / 2 Stage CompressorUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On./Off

HGBP

Two Stage

Digital ScrollCompressor Evaluation

Cap

acit

y

Mo

du

lati

on

Co

ilT

em

p

Sy

s A

pp

Co

ntr

ol

Co

mp

lexit

y

Co

st

BestBestBestBest BestBestBestBest MediumMediumMediumMedium HighHighHighHigh MediumMediumMediumMedium

Suction / Compression /

Discharge

HotGas

Release

RotationWith

No Work

16

Digital ScrollUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On./Off

HGBP

Dual Stage

Digital

Higher ▲

Or

Lower ▼

Digital ScrollUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On./Off

HGBP

Dual Stage

Digital

VSD ScrollCompressor Evaluation

Cap

acit

y

Mo

du

lati

on

Co

ilT

em

p

Sy

s A

pp

Co

ntr

ol

Co

mp

lexit

y

Co

st

GoodGoodGoodGood GoodGoodGoodGood WideWideWideWide HighHighHighHigh HighHighHighHigh

17

VSD ScrollUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On./Off

HGBP

Dual Stage

Digital

VSD

Higher ▲

Or

Lower ▼

VSD ScrollUnit EER

5

10

15

20

25

30

100% 75% 50% 25%

On./Off

HGBP

Dual Stage

Digital

VSD

Hz 20 40 60 80 100 120 140

RPM 1200 2400 3600 4800 6000 7200 8400

Inverter/Compressor Operating Range

cooling

heatin

g

18

Variable Refrigerant Flow System

Source: AHRI1230 Directory

October 20, 2014

19

Size EER SEER

3 Ton 13.0 20.7

4 Ton 14.1 20.2

5 Ton 13.0 20.0

Size EER IEER

12.5 Ton 12.5 20.0

15 Ton 12.7 20.1

17.5 Ton 12.3 19.3

IEE

R/E

ER

What is the value of VSD vs Std

Efficiency (IPAK1 and 2)?

IEE

R/E

ER

8

9

10

11

12

13

14

15

16

17

18

20 25 30 40 50 55 60 70 75 90 105 120 130 150

eFlex/Dig

Scroll IEER

Std Eff.

IEER

eFlex/Dig

Scroll EER

Std Eff.

EER

BLACK BLACK BLACK BLACK ▲▲▲▲ –––– Digital Scroll

SIZE (tons)

Variable Speed WSHPCompressor Technology

20

Model LoadRated

Airflow

(CFM)

WLHP

Cooling

Capacity

(BTUH)

WLHP

EER

WLHP

Heating

Capacity

(BTUH)

WLHP

COP

GWHP

Cooling

Capacity

(BTUH)

GWHP

EER

GWHP

Heating

Capacity

(BTUH)

GWHP

COP

GLHP

Cooling

Capacity

(BTUH)

GLHP

EER

GLHP

Heating

Capacity

(BTUH)

GLHP

COP

VSVE

024

Full 930 24,600 18.4 30,300 6.1 27,800 33.2 24,400 5.2 25,900 22.3 18,400 4.2

Part 625 13,100 22.6 15,900 7.6 15,000 48.5 12,100 6.1 14,300 35.3 9,900 4.8

VSVE

033

Full 1,200 32,900 15.5 40,400 5.5 36,600 24.7 32,400 4.8 34,300 18.1 24,500 3.9

Part 720 17,100 20.8 21,500 7.0 19,400 40.8 16,800 5.6 18,500 31.6 14,100 4.6

VSVE

042

Full 1,650 44,100 18.3 54,700 6.0 50,100 32.5 43,600 5.1 46,200 22.0 31,900 4.0

Part 1,200 25,500 24.2 29,400 7.5 28,700 51.3 22,700 5.8 26,900 40.5 17,800 4.6

VSVE

050

Full 1,890 51,200 15.7 68,800 5.3 57,800 26.2 54,600 4.6 54,100 18.8 41,400 3.8

Part 1,200 29,900 22.1 36,800 6.9 33,500 42.5 28,500 5.5 32,800 34.0 23,400 4.6

VSVE

060

Full 2100 61,800 15.6 81,200 5.5 70,400 25.4 65,400 4.8 64,600 18.3 50,000 4.0

Part 1323 35,900 21.3 46,300 7.3 41,300 41.4 36,200 5.9 39,600 32.9 30,400 5.3

Variable Speed WSHP Unit Efficiency

• ASHRAE 90.1 minimum requirement

• Water Loop (13 EER / 4.3 COP)

• Ground Water (18 EER / 3.7 COP)

• Ground Loop (14.1 EER / 3.2 COP)

• Part Load Efficiency

• AHRI allows additional points for

part load in lieu of IEER or IPLV

What is the Next Refrigerant?

600 GWP

150 GWP

Considering GWP

Variable- Variable ---Speed CompressorsSpeed Compressors · Variable-Variable ---Speed...

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