Presented By: John Dolan, P.E. - ASHRAE...• Centrifugal Chiller Applications with Minimal...
Transcript of Presented By: John Dolan, P.E. - ASHRAE...• Centrifugal Chiller Applications with Minimal...
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Variable Speed Compressor Technologies
Presented By:
John Dolan, P.E.President - Thermosystems, Inc.
BS in Mechanical Engineering from UIUC
29 years HVAC Equipment Application Experience
www.thermohvac.com
March 14, 2017
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Variable Speed Compressor Technologies
• Why to Apply
― Energy Savings
― Capacity Control
• Available Technologies & Application
― Motors and Bearings
― Centrifugal Compressors
― Screw Compressor – Positive Displacement
― Scroll Compressor – Positive Displacement
• When to Apply
• When Not to Apply
• Questions
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Positive Displacement Compressor
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Basic Refrigeration Cycle
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LIFT (ΔP)
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Water Cooled Flooded Chiller Refrigeration Cycle
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Basic Direct Expansion (DX) Refrigeration Cycle
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Refrigeration Cycle
12
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Reducing Compressor Lift (𝑃𝑐𝑜𝑛𝑑-𝑃𝑒𝑣𝑎𝑝 = ΔP)
8
EXV
EXV
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Variable Speed Compressor Technologies
• Why to Apply?
• Energy Savings (Reduce Lift)
• Lower Compressor RPM = Less Work = Less Energy $
• Fan/Pump Laws - RPM ≈ Energy³
• Take Advantage of Lower than Design Condenser Temps
• How Often is Outside Ambient at Design Temp (DB or WB)?
• O'Hare Weather Bin Data – 6 hours/yr ≥ 95°F
• Match Compressor Operation to Actual Condenser Conditions
(Lower Temperatures ≈ Lower Pressures)
• Capacity Control
• How Often is Building or Space at Full Load? (<1%)
• Proportional Control with VFD vs. Staged Control (On/Off)
• Modulate Flow of Refrigerant to Match Load (Screw and Scroll)
• Chiller - More Stable Control of Leaving Water Temperature
• No Return Water Control or LWT Set Point Reset
• DX Air Handler - More Stable Control of Discharge Air
Temperature (DB & WB)9
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Variable Speed Compressor Technologies
• Why to Apply?
• Higher Efficiency Motors with Variable Speed Operation
• AC Induction Motor with Variable Frequency Drive
• Permanent Magnet Synchronous Motor (PMSM)
• Motor Speed Operating Range with PMSM
• No longer limited to 1800 & 3600 RPM (AC Induction
Motor Speeds)
• Direct Drive Operation
• Gears to Increase Impeller Speed no Longer Required
• No Transmission Losses (Gears)
• Magnetic Bearing Technology
• Eliminate Oil and Oil Components (Oil Sump, Oil
Pump, Oil Heaters, Oil Separators, Safeties)
• Improve Heat Transfer & Reduce Compressor Wear
• Sustainable Efficiencies for Life of Chiller
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Quick Electric Motor Review
• AC Induction Motor
― Most Common Motor in HVAC
― Fixed Speeds Based on 60Hz (1800 & 3600 RPM)
― Max Motor Speed 3600 RPM
― Slip
• Permanent Magnet Synchronous Motor (PMSM, ECM)
― More Efficient than AC Induction Motor - Especially at Part-Load
― Electronically Commutated (ECM)
― Synchronous Motor – Zero Slip
― VFD for Starting Required (Even in Constant Speed Applications)
• VFD Integral to Motor in Some Sizes
― Smaller Size than Comparable Hp AC Induction Motor
― Higher Speeds Allow for Matching Speed to Application
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Motor Efficiencies (AC Induction vs. PMSM)
NEMA Premium EffAC Induction Motor
PMSM (ECM)
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Oil Effects on Heat Transfer
Conclusions and Recommendations:
The heat transfer ratio drops steadily with oil
concentration and reaches a value of 0.65
[from 1.0 normalized] at an oil concentration of
10%.
From ASHRAE Research Project 751-RP,
“Experimental Determination of the Effect of Oil on Heat Transfer
with Refrigerants HCFC-123 and HFC-134a”,
35% heat transfer reduction with 10%
oil concentration in refrigerant
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Oil Effects on Chiller Efficiency
Source: The News, 04/15/04, by Jack Sine
Direct Drive PMSM Oil-Free Compressor Design Eliminates
the Performance Degradation Due to Oil Contamination of the
Refrigerant
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Traditional Centrifugal Design (Oil Based)
3600 RPM AC
Induction Motor
Thrust Bearings
(Oil)
Impeller Gear Set
(Oil)
Radial
Bearings
(Oil)
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Traditional Centrifugal Compressor
(Geared Impeller & Traditional Oiled Bearings)
Traditional Centrifugal Design (Oil Based)
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Magnetic Bearing Centrifugal Compressor
High Speed
Permanent Magnet
Synchronous Motor
Axial
Thrust
Bearing
Impeller +
Inlet Vanes Front
Radial
Bearing
Rear
Radial
Bearing
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Magnetic Bearing Compressor
Magnitude™ WME Compressor Rotating Group
Magnetic Bearings
and Sensors
Permanent Magnet
Synchronous Motor
Suction Gas
Discharge
Inlet Guide
Vanes
Single Stage
Impeller
VFD in
External Panel
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Water Cooled Centrifugal Chiller Efficiencies
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50 60 70 80 90 100 110
Chiller percent load
kW
/ t
on
10% energy
reduction
Fixed Speed Motor
AC Induction w/ VFD
High Speed VFD w/
Magnetic Bearings
30% energy
reduction
Note: Based on 500 ton Chiller with Same Condenser and Evaporator
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Operating Cost Comparison – Centrifugal Chillers
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60 70 80 90 100
Chiller Percent Load
Op
erat
ing
Ho
urs
0
0.2
0.4
0.6
0.8
1
1.2
kW /
to
n
Fixed Speed ~ $243,287/year
Traditional VFD ~ $164,934/year
High Speed VFD w/ Mag Bearing ~ $131,709/year
Cooling Load Profile
10% energy
reduction
Note: Based on 500 ton Chiller with Same Condenser and Evaporator and $0.10/ per kWh
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©2016 Daikin Applied
CONSTANT SPEED & VOLUME SCREW COMPRESSOR
Pd
Ps
Over Compression
or Lost Work
Pc’’
• P
fixed
fixe
d
Discharge
to
Condenser P cond
V displacement
A
B
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©2016 Daikin Applied
VARIABLE SPEED SCREW COMPRESSOR
VFD on Compressor Motor
Varies the Volume of
Refrigerant and Discharge
Pressure is Controlled by
the Slide Valves
Vd
PcA
•
Point APoint B
Discharge to
Condenser
variable
vari
able
B
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Scroll Compressor Technologies
23
Digital ScrollConstant Speed
Variable Capacity
Load/unload 20sec time step
Variable Speed PMSM or
AC Induction Motor w/VFDVariable Speed Compression
and Capacity Control
Fixed Speed ScrollOn/Off
Staged Control
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Variable Speed vs. Variable Capacity
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
25
%
35
%
45
%
55
%
65
%
75
%
85
%
95
%
% C
om
pre
sso
r Po
wer
% Cooling Capacity
Digital Scroll
RebelVariable
Speed
24
Digital scrolls are Off/On for Compression with
Constant Speed AC Motor
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Scroll Compressor Staging (Variable and Constant Speed)
25
NONINV NONNONINVNON7%
100%
System Capacity
Capacity Control2 Condensing Units
4 Compressors
Co
mp
ress
or
Op
erat
ion
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Airside Compressor Cycling Effects
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When to Apply
• Significant Hours with Lower than Design Condenser Temperatures
― Take Advantage of Lower ECWT or Ambients
― Reduce Lift Wherever Possible
• Lower Condenser Temps (Water)
• Higher Evaporator Temps (Chilled Water Temp or Discharge Air)
• Significant Hours with Lower than Design Load
― Watch Minimum Loading with Constant Speed Machines
• Excessive Cycling on Large Hp Compressors
• Generator Back-Up
― VFD Compressors will have Lower Inrush at Start-up
• Variable Chilled Water Flow Applications
― Better Control of LWT
― Less Cycling of Compressors (Air Cooled Chillers)
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When to Apply
• Meeting or Exceeding ASHRAE 90.1 & IECC Efficiencies
― Water Cooled Compliance (Full Load kW/ton and IPLV)
― Air Cooled Compliance (EER and IEER)
― Path A (Constant Speed) vs. Path B (Variable Speed)
― Must Meet Both Full Load kW/ton and IPLV
• Utility Rebates for Higher Efficiency Equipment
― More Rebate $ for Better IPLV or IEER
― Rebate May Offset or Pay for VFD
• Humid Areas
― Stable Leaving Water Control or Leaving Air Control
― More Latent Cooling & Stable Coil Discharge Temperatures
― Minimize or Eliminate Condensate Re-Evaporation when
Compressor Shuts Off
• Sound Sensitive Applications
― Variable Speed Equipment is Quieter than Constant Speed
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When Not to Apply
• Centrifugal Chiller Applications with Minimal Condenser Relief
― Humid Areas with Constant Loads (High WB)
• Very Large Tonnage Plants
― 60,000 ton Plant with 20+ Chillers
• Large Airside Applications with Multiple Scroll Compressors
― 100+ tons with 6 or 8 stages
― Compressor that is Off is Always More Efficient than Operating Compressor
• Airside DX Applications in Dry Climates (Low Latent Loads)
― Sensible Load Applications
― Discharge Air Reset or Leaving Water Reset
• Heat Recovery Chiller Applications – Fixed Lift
• Any Others? Page 29
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Page 30
Questions