Presented By: John Dolan, P.E. - ASHRAE...• Centrifugal Chiller Applications with Minimal...

transcript

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

jdolan@thermohvac.com

www.thermohvac.com

March 14, 2017

• 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

Positive Displacement Compressor

Basic Refrigeration Cycle

LIFT (ΔP)

Water Cooled Flooded Chiller Refrigeration Cycle

Basic Direct Expansion (DX) Refrigeration Cycle

Refrigeration Cycle

Reducing Compressor Lift (𝑃𝑐𝑜𝑛𝑑-𝑃𝑒𝑣𝑎𝑝 = ΔP)

• 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

• 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

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

Motor Efficiencies (AC Induction vs. PMSM)

NEMA Premium EffAC Induction Motor

PMSM (ECM)

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

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

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

Traditional Centrifugal Design (Oil Based)

3600 RPM AC

Induction Motor

Thrust Bearings

Impeller Gear Set

Radial

Bearings

Traditional Centrifugal Compressor

(Geared Impeller & Traditional Oiled Bearings)

Traditional Centrifugal Design (Oil Based)

Magnetic Bearing Centrifugal Compressor

High Speed

Permanent Magnet

Synchronous Motor

Thrust

Bearing

Impeller +

Inlet Vanes Front

Radial

Bearing

Radial

Bearing

Magnetic Bearing Compressor

Magnitude™ WME Compressor Rotating Group

Magnetic Bearings

and Sensors

Permanent Magnet

Synchronous Motor

Suction Gas

Discharge

Inlet Guide

Single Stage

Impeller

VFD in

External Panel

Water Cooled Centrifugal Chiller Efficiencies

0 10 20 30 40 50 60 70 80 90 100 110

Chiller percent load

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

Operating Cost Comparison – Centrifugal Chillers

0 10 20 30 40 50 60 70 80 90 100

Chiller Percent Load

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

CONSTANT SPEED & VOLUME SCREW COMPRESSOR

Over Compression

or Lost Work

Pc’’

Discharge

Condenser P cond

V displacement

VARIABLE SPEED SCREW COMPRESSOR

VFD on Compressor Motor

Varies the Volume of

Refrigerant and Discharge

Pressure is Controlled by

the Slide Valves

Point APoint B

Discharge to

Condenser

variable

Scroll Compressor Technologies

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

Variable Speed vs. Variable Capacity

% Cooling Capacity

Digital Scroll

RebelVariable

Digital scrolls are Off/On for Compression with

Constant Speed AC Motor

Scroll Compressor Staging (Variable and Constant Speed)

NONINV NONNONINVNON7%

System Capacity

Capacity Control2 Condensing Units

4 Compressors

Airside Compressor Cycling Effects

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)

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

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

Questions

Presented By: John Dolan, P.E. - ASHRAE...• Centrifugal Chiller Applications with Minimal...

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