Basic Refrigeration Cycle Components

Compressor Basics

Compressor  The “Driver” of the System. Draws (Suction) Low Temperature and Pressure Refrigerant Vapor and Discharges this Same Refrigerant Vapor to a Higher Temperature and Pressure  Result(1): The Pressure in the Evaporator is Maintained Low Enough for Liquid Refrigerant to Boil Off at a Temperature Lower than the medium which it is Cooling so that Heat is Absorbed

Compressor  Result (2): The Temperature of the Refrigerant Entering the Condenser is Higher than that of its Surroundings so that Heat can be Rejected

Types of Compressors  Reciprocating: Pistons move Up and Down in a Cylinder, Drawing in and Compressing Refrigerant Vapor  Rotary: Intermeshing Screws or an Eccentric Chamber with Vanes Draw in and Compress Refrigerant Vapor  Centrifugal Compressors: Revolving Impellers Draw in the Refrigerant Vapor and Discharge it at High Velocity by Centrifugal Force

Reciprocating Compressors Open Reciprocating Compressors  The Crankshaft Extends Outside the Crankcase and a Seal is Required to Prevent the Refrigerant from Escaping  Drivers can be Electric Motors, Natural Gas Motors and can be Belt Driven or Direct Drive  Serviceable and Found in Industrial Applications

Reciprocating Compressors Hermetic Reciprocating Compressors  Compressor and Motor are Housed or Sealed in the Same Housing Eliminating Shaft Seal  Driver is Electric Motor and Entire Unit is Welded Shut  Non-Serviceable and Found in Small Commercial Applications

Reciprocating Compressors Semi-Hermetic Reciprocating Compressors  Similar to Hermetic However Cylinder Heads, End Plates and Bottom Plates can be Removed For Servicing of the Internal Mechanisms

Reciprocating Compressors

History

Horizontal Double Acting  Derived from steam engines, it had two suction and two discharge valves and compressed in both directions.  The drive shaft extended through a Stuffing Box that served as a shaft seal- very problematic.  Inertia related foundation failures.

Vertical Double Acting  Solved foundation failures.  Stuffing boxes still leaked.

Vertical Single Acting  Stuffing box became a rotating crank with a shaft seal, much more reliable.  Reliable and efficient.  Large sheaves to reduce speed required, expensive to make.

Modern V or W Style Recips  Smaller size but with more cylinders allow higher rotation speeds and more displacement in a smaller package  Reliable and efficient.  Higher speeds increase wear.

Recip Maintenance  Relatively high maintenance costs compared to screw compressors.  Most manufacturers advise rebuilding each year.  “Top End” a misnomer. Discharge and Suction valve plates and springs, gasket set are top end items. Cylinders and rod journals should be mic’d, rod bearings and cap nuts replaced and piston rings should be replaced along with the shaft seal. Bearings should be inspected for wear or damage.  Older oil separators were inefficient so recips typically pumped lots of oil into the system.  Low/No tolerance for liquid in the suction gas.  Much more efficient at part load and full speed than screw compressors  Change the oil fitler and oil at least once per year. Clean the crankcase and note any debris.  Do compressor alignment twice per year.  Vibration analysis is tough to interpret. The human ear is better.

Rotary Compressors The Compression of Low Pressure Gas is Drawn From the Evaporator by Rotary Motion

Rotary Compressors Rotary Vane Compressor  Features a Rotor Within the Cylindrical Body of the Compressor  The Rotor is Eccentric to the Cylinder so that as the Rotor Moves, One Point on its Circumference is Always in Contact with the Cylinder and the Refrigerant Vapor is Compressed and Pushed Ahead of the Vane

Rotary Vane Relatively compact with a high CFM. Low compression ratio only. Great for vacuum pumps. Can handle some entrained liquid with the vapor.  Very loud.  Oil delivery system is elaborate and require constant maint.  Vanes produce debris as they wear and can clog the slots causing vane breakage    

Screw Compressor  Used on Large Industrial Applications, 150hp to 4,000hp  Advent of Mini-Screw, Enables use Within the Light Industrial Market, 15hp to 250hp  Small size relative to CFM capacity.  Fewer Moving Parts to wear.  High Volumetric Efficiency at Full Load  Capable of High Compression Ratios (19:1)  Can withstand small amounts of entrained liquid, but very bad on the bearings.

Screw Compressor  Features Two Mating Screw (Helically-Grooved) Rotors Contained Within the Body of the Compressor  The Refrigerant Vapor Drawn from the Evaporator is Trapped Between the Rotating Grooves as it Travels from the Suction to the Discharge  Its Volume is Gradually Reduced Causing the Pressure and Temperature to Increase.  Similar Screw Compressors use a single screw rotor and two mating gate rotors.

Screw Compressor Maintenance  Rebuilds for some mfrs at 30,000 hours, other only when vibration readings dictate.  Oil filter changes once per year.  Alignment and vibration analysis 2 per year.  Electrical maintenance 2 per year. Mantenance Schedule Maintenance

Change Oil Oil Analysis Change Filters Clean Oil Strainers Clean Liquid Strainers Change Coalescers Check and Clean Suction Screen Check Alignment (RWB, RDB Only) Check Coupling (a) Check Electrical Connections (b) Check Sensor Calibration (c) Vibration Analysis Replace Shaft Seal

As Directed By Oil Analysis Every 6 Months

Annually Regardless of Operating Hours

Every 6 Months, More Frequently If Levels Increase When Leak Rate Exceeds 7 - 8 Drops Per Minute

95,000

90,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

50,000

45,000

40,000

35,000

30,000

25,000

20,000

15,000

10,000

8000

5000

1000

200

Hours Operation (Maximum)

Screw Compressor Volume Ratio (Vi)  Defined as the volume of the suction gas entering the compressor over the volume of the discharge gas leaving the compressor.  For every compression ratio, there is an ideal Vi.  Vi too high: Over compression, more HP needed.  Vi too low: Blow back at discharge port, lost capacity.

Screw Compressor Slide Valve/VFD  Slide valve capacity control loses efficiency as it uloads  VFD Control keeps the slide valve at 100% and varies the speed.

Keyway

Keyway

Key fell out !!!!

Coupling damage from loss of key

Hammers and Couplings

Crack - Can damage the coupling - Can damage the bearings (both motor and compressor) - Can damage the shaft seal

Assembly Damage Don’t Install coupling hub with a hammer

How Clean was the system when the compressor was started up?

Refrigerants are excellent cleaners, and they will clean anything in the piping out. What they clean out of the piping system, ends up in the strainers and oil. What refrigerant was used and what was its Quality?

0.07 C

0.06

PK Velocity in In/Sec

MCKE - COMPRESOR 3 -MOH HORIZ LADO LIBRE DEL MOTOR

COMP3 C

C

C

C

C

C

C

C

C

C

90 Frequency in kCPM

120

Route Spectrum 07-Jul-06 10:11:00 OVERALL= .0804 V-DG PK = .0802 LOAD = 100.0 RPM = 3590. (59.83 Hz) >FAG 6313 C=BPFO

C

0.05 0.04 0.03 0.02 0.01 0 0

30

60

150

Acceleration in G-s

3

180

Route Waveform 07-Jul-06 10:11:00 RMS = .7998 PK(+/-) = 2.33/2.33 CRESTF= 2.92

2 1 0 -1 -2 -3 0

20

Label: 3071x

40

60 80 Time in mSecs

100

120

140

Freq: 11.03 Ordr: 3.071 Spec: .01588

When to change shaft seal? When the leak rate exceeds 7-8 drops Per minute – or when the drain bottle Fills every 48 hours.

Motor Maintenance Follow the motor manufactures recommendations.

Ram Motors Lubrication Schedule

Customer complaint – motor bearings fail too often and motor / bearings run hot.

Failure to lubricate motors when required will result in a destroyed bearing and motor, and the potential for fire, misalignment, seal failure, coupling failure becomes very high.

How Much Grease is Enough

Centrifugal Compressors  Refrigerant Vapor is Compressed by High Velocity Through a Rapidly Rotating Impeller; there are no Pistons, Vanes etc.  Refrigerant Vapor is Drawn from the Evaporator into the Center of the Impeller  Vapor is Forced Radially Outwards to the Impeller at High Pressure and Temperature

Centrifugal Compressor

The centrifugal compressor adopts the principle of dynamic compression by converting kinetic energy to static energy to increase the pressure and temperature of the refrigerant. A centrifugal compressor comprises rotating impeller the center of which is fitted with blades that draw refrigerant vapor into radial passages that are internal to the impeller body. The rotation of the impeller causes the refrigerant vapor to accelerate within these passages that leaves the impeller and enters the passages. These passages start out small and become larger as the refrigerant travels through them. As the size of the passage increases, the kinetic energy of the refrigerant decreases.

Identifying Good Filters • Filters are proven by testing, not by nominal  rating.  So make sure filters are proven. • Must be tested in oil and refrigerant  combination.  Not all media and glue is  compatible with all refrigerants. • High dirt holding capacity is key to avoid  frequent changes. ( varies widely) • Must have high rupture pressure to prevent  damage on starting and stopping. • NO BY‐PASS ALLOWED.

Incompatible Filter Media - Ruptured, dumping particles into Bearings

Conclusion: Buy Good Full Flow Filters You get what you pay for.

Saving money by eliminating oil filters  .. • They were plugging too often.   • Must be defective filters. • Oil analysis says change oil but they are just  trying to rip me off.

Slide Valve is Too slow moving !

Analytical Tests Metals Analysis: Tests for wear and additive metals. Any metal appearing at a 5 ppm level or lower would be considered normal. This instrument detects dissolved metals as well as particles smaller than 5 microns (assuming they are suspended in the lubricant).

Wear Metals • Wear metals that are normally tested for: – Iron – Titanium – Silver – Lead – Copper

– Tin – Nickel – Aluminum – Vanadium – Chromium

Wear Metals The wear metal analysis will show only soluble metals, it  will not necessarily show metal particles that will remain  suspended in the oil.  Because of this, compressor failures  will not necessarily be detectable by an increase in the  wear metals, especially if  failure is in a short period of  time.  Babbitt type bearing failure may show tin,  aluminum, lead.  Anti‐friction bearing failures only show  iron.  Sometimes an increase in iron results from high water in  the oil thus causing corrosion, (rust). High iron can also  just come from suction pipe rust.

Contaminants ‐ Metals • The contaminants that are normally tested for are: • Zinc • Calcium • Molybdenum • Sodium • Phosphorus • Silicon • Barium • Magnesium

Wear Metal Guidelines • Greater than 10 ppm – Filter Change • Greater than 20 ppm – Filter Change and  sample in 500 hours • Will only condemn if increase trend continues  (level greater than 150 – 200 ppm) – Judgment based on other lubricant parameters

Common Sources of Metals • • • • • •

Silver (Ag): bearing alloys Aluminum (Al): Bearings,  Bushings, Pistons and Pumps Copper (Cu):  HX tubing, Bearing  cages, Bushings Iron (Fe): Corrosion, Rust  Bearings, Cylinders, Gears Barium (Ba): Lubricant additive Calcium (Ca): Lubricant additive  and ground water

• • • • •

Magnesium (Mg): Lubricant  additive Sodium (Na): Water, Coolant  additive Phosphorus (P):  Lubricant  additive Silicon (Si): Sand, Dirt, Lubricant  additive Zinc (Zn): Galvanized parts,  brass/bronze alloy, and Lubricant  additive

Contaminate Metal Guidelines • Greater than 10 ppm – will mention as  marginal. Normal sample frequency • Greater than 20 ppm – will mention as high.   Sample in 1000 hours • Will only condemn if increase trend continues  (level greater than 150 – 200 ppm) – Judgment based on other lubricant parameters

Lubricant Considerations • • • •

Correct base stock for the application. Proper viscosity. Correct temperature. Minimal Additive package proven for years in  the application. 

Correct Base stock for the  Application • NH3 ‐ Paraffinic or Napthenic based  Mineral oil, HT Parafinnic, PAO • R‐22 Napthenic mineral oil, Alkyl Benzene • HFC ‐ Polyol ester, PAG • CO2 – PAO, ester •

This information is representative only,other combinations may be  recommended in some applications.

Lubricant considerations  • Important parameters – viscosity, viscosity index, aromatic content,  lubricity, correct additives, pour point  appropriate,  compatibility with system  chemistry, low foaming tendency, quality base  stock that won’t separate 

Proper Viscosity • Follow manufacturer’s recommendation. • Generally 68 ISO for large refrigeration  compressors. • Different viscosity used for special  applications.

What is the correct* oil temperature?

Oil Viscosity cSt

Oil Viscosity vs. Temp. NH3 System 80 70 60 50 40 30 20 10 0 100

Oil temp range 68 ISO Mineral

120

140

160

Degrees F

180

200

* General guideline for NH3 systems only.

What Oil Should You Use ? • Manufacturer’s recommendations are based on  year’s of experience and testing. • There are many good oils in the market but not all  are equal. • Failures can be caused by unproven additives  breaking down over time.

Frick #3 after 400 hrs accelerated  durability test

Seal Face

Royal Purple after 400 hrs accelerated  durability test Seal Face

Unusual failure mode caused by breakdown of oil additive reaction over time.

Don’t Mix Oils Black deposits formed in oil system, wherever pressure drop occurred. Incompatible transformer oil from rotary vane compressor jacket mixed with ammonia. Resulted in compressor failures.

My Refrigeration oil is just as good as Frick – and cheaper too. Insoluble Amide formation.

Multiple compressors with insoluble Amide formation in the separators. Only solution is cut off heads and clean out the separators.

Oil and Refrigerant additives • Risky to put unproven additives in your  refrigeration system.  • Any claims for large savings from “reducing  friction” should be met with skepticism.  Total  friction in a screw compressor is on the order  of 3‐6 % of total power.   • Horror stories abound.

Deposits on Coalescing Filters from  “Efficiency Improving Additives”

How much testing do you think this additive supplier actually did ?

Using “Magic Oil Additives” that promise great things is risky. Best oil in a refrigeration system is that recommended by the compressor manufacturer.