Development and Testing of a Supercharger Compressor for

Cold Climate Air Source Heat Pumps

Presented by: Travis A. Jonas

Written by: Thomas J. Walter

July 14, 2014 2Mechanical Solutions, Inc.

Compact centrifugal compressor» Single-stage/ high speed pre-compressor

Cold climate operation of heat pumps» Boosts refrigerant pressure

» Oil-free bearings

Air source heat pumps» Extracting heat from coldest ambient air

» No backup heat – maintains full capacity

» No refrigerant type change

» No change in basic positive disp. style primary compressor

*This work is being performed under a Phase II Small Business Innovative Research(SBIR) grant from the US Department of Energy

Breakdown of Concept

Schematic of Supercharger

July 14, 2014 3Mechanical Solutions, Inc.

Pre-Compresses Refrigerant

Foil Journal BearingsFoil Thrust Bearings

Manufacturing Methods (Aero Parts)

Additive Manufacturing Options» 3D printing

» Direct Metal Laser Sintering

– Impeller

» Selective Laser Melting

» Electron Beam Melting

Rapid Investment Casting Options» Stereolithography

» Selective Laser Sintering

– Volute Housing

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Prototype Aero Hardware

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Volute Housing

Impeller

Diffuser

Manufacturing Validation

Material Strength Assessment» Tensile Test Specimens (3)

» Spin Tested to 115,000 rpm (15% over speed)

Impeller Surface Finish» DMLS 130 micro in. as

fabricated– Measured adiabatic

efficiency 0.68 vs. predicted 0.72

» Electro-polishing Option– Localized pitting

Volute Housing Fabrication

» 356 Al rather than 17-4PH (non-uniform flowduring casting process)

» Hydro-tested to 150 psi(150% of workingpressure)

Diffuser

» 304 SS machined usingtraditional methods

July 14, 2014 Mechanical Solutions, Inc. 6

Drivers

Motor» Induction/ Permanent Magnet Designed by MSI

– PM decided for smaller, higher efficiency– 100,000 rpm, 4 pole, 10 kW (13 HP)

Controller» Digital Drive Variable Frequency Drive (VFD)

July 14, 2014 7Mechanical Solutions, Inc.

Gas Foil Bearings | Labyrinth Seals

Designed and fabricated by MSI

Parametric design» Load vs. Length & Diameter

Two radial bearings 13 lbf load capacity

One thrust bearing 55 lbf load capacity

Two principal seals» Impeller inlet

» Shaft behind impeller

Design» Close clearance, non-contacting

» Small amount of “leakage”– Flow is retained within sealed

refrigerant system & recompressed

July 14, 2014 Mechanical Solutions, Inc. 8

Rotordynamics

Gas foil bearings» Lower stiffness than oil journals

» Lower load carrying capability than oil journals

» No liquid lubrication needed

» No rotordynamic instability at high speeds

Critical speeds & Mode shapes» Journal bearing stiffness determined using proprietary code

» Inputs into RotorLab software

» Motor magnet assembly, mass but no stiffness contribution

» Rigid modes predicted well below minimum operating speed

» First bending mode predicted well above max speed

July 14, 2014 9Mechanical Solutions, Inc.

Testing & Results

In-house Vapor-only Test Loop

Flow meters

Accumulators

Heat exchangers

Instrumentation to measure performance & vibration

Eddy current displacement sensors for shaft orbit

National Instruments LabVIEW data acquisition system

Damping Determination

Gas foil bearings have lower damping (and cross-coupling) than oil film bearings» Net damping can be

engineered to be adequate Damping is important at speeds

higher than rigid modes, which otherwise can go unstable

“Ring-down” involves tapping motor housing while running» Lateral displacement response

measured

July 14, 2014 10Mechanical Solutions, Inc.

Confirmation

◦ Rigid modes somewhat lower due to lower bearing stiffness

◦ Bending modes higher due to higher overall built-up shaft stiffness

Rotordynamic Results

July 14, 2014 11Mechanical Solutions, Inc.

Mode Number

Mode Shape

@ 50k rpm

@ 100k rpm

Observed During Test

1 Rigid Body 23,430 24,450 15,0002 Rigid Body 28,800 31,400 18,0003 Bending 143,720 146,970 154,000

000000

Compressor End Shaft Displacement, milsrms @ 100,000 rpm No Runout Compensation

Shaft Orbits

July 14, 2014 12Mechanical Solutions, Inc.

Compressor End Vibrations

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milsrms, During Rundown from 100,000 rpm to 10,000 rpmNo Runout Compensation

“Ring-Down” Test Results

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Compressor End Shaft Displacement, milsrms @ 10,000 rpmNo Runout Compensation

Aero Performance Map

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Compressor Performance Map for First ArticleAnticipated Operating Line

Head & Flow Coefficients

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Coefficients for First Article Compressor

Other Performance Metrics

Vibrations» Motor housing vibration levels 0.02 in/s RMS or less

Acoustics» Not measured but observed as principally a low-level tone

Thermally» Bearing losses were in line with predictions

Windage and Stator losses» Higher than expected

July 14, 2014 17Mechanical Solutions, Inc.

Present Status & Plans

Present configuration» Suited for 45 kW heat pump class

» COPh of 2.32 (@ minus 13 degrees F)

» Solo and simultaneous operation underway with a suitably sized scroll compressor

Planned work» Recently awarded a contract from New York State to configure

the compressors with associated heat exchangers, fans, andcontrols for loop demonstration to interested third parties

» Talk with potential commercializers (OEMs)

» Outreach to suppliers of commercial coolers, chillers, andfreezers as alternative to existing methods, with potential forincreased capacity or lower temperature operation

July 14, 2014 18Mechanical Solutions, Inc.

Conclusions

The work performed concludes that a motor driven supercharger can dramatically improve the cold-day performance of air source heat pumps

The design of the supercharger is mechanically and electrically practical, and small enough to be easily packaged or retrofit

July 14, 2014 19Mechanical Solutions, Inc.