HVAC Technologies Library

Corrosion Issues? Solve Them Using Six Proven Steps

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by PJ Sikorsky

If you wanted to create a single laboratory device to study multiple types of corrosion you might start by designing an air conditioning machine - a mechanical device

  • made from a variety of dissimilar metals,
  • subject to changing moisture and temperature conditions,
  • frequently located in hostile environments and
  • often subject to minimal maintenance, cleaning or inspection.

In my 30 years of materials engineering experience in the HVAC industry I've seen

  • general corrosion,
  • pitting corrosion,
  • galvanic corrosion,
  • fretting corrosion,
  • crevice corrosion,
  • corrosive wear,
  • erosion/corrosion,
  • stress corrosion,
  • thermal oxidation and
  • biological corrosion in HVAC equipment.

We'll discuss in more detail how to go about solving corrosion problems specific to the HVAC industry.  

Is It Time to Update Your Compressor Driveline Technology?

HansWallin.jpgby Hans Wallin

The traditional driveline for air conditioning centrifugal compressors comprises of an air cooled induction motor, which is connected to the compressor low speed gear shaft  through a coupling. A mechanical shaft seal separates the refrigerant and the pressure in the compressor from the outside air. The high speed impeller shaft is driven by the gear shaft through a pinion. Both the impeller and the gear shafts are supported on hydrodynamic bearings, two radial and one axial for each shaft. The motor has separate bearings.

 

Understanding Oil Return in Refrigeration Systems

by Ed Keuper & Dick Cawley

Part 1:  Flooded Evaporators Ed Keuperby Ed Keuper

With few exceptions, all compressors that are lubricated with oil will discharge oil into the gas stream.  The rate of discharge can be as small as parts of oil per million parts of refrigerant for direct drive hermetic centrifugal compressors and as much as several percent for screw compressors.  Oil discharge rates are usually expressed in terms of lbm of oil discharged per lbm of refrigerant compressed or in mass percent of oil in the discharge gas.

Part 2:  Use of Eductors for Oil Return by Ed Keuper

On screw chillers using eductors for oil return, when operating at low load conditions, it appears that the eductor does not operate efficiently enough to return a sufficient amount of oil to the oil separator or sump to maintain its oil level, which then causes the chiller to shut down on low oil.

Part 3: Liquid In The Compressor Suction by Ed Keuper

Ideally, any liquid entering the compressor suction will be rich enough in oil and lean enough in refrigerant that lubrication will be satisfactory.  Yet, if any liquid ingested into a compressor has too low a concentration of oil, lubrication may be compromised and wear leading to compressor failure can ensue.  All compressors are vulnerable to lack-of-lubrication failure, either from lack of oil or from too much refrigerant in the oil.

Part 4: Lubricant Issues with Unitary Systems by Dick Cawley

This sequence deals with direct expansion unitary systems that are designed to moveDick Cawley lubricant around the system and back to the compressor sump by momentum, in the case of refrigerant gas transport (suction and discharge), and solubility where refrigerant is in liquid form. Three areas discussed include: 

  • Equilibrium and Minimum Run Time
  • Maintaining an Adequate Lubricant Level  
  • Minimum Velocities in Suction and Discharge Gas Risers

 

Reliability of R-410A Heat Pumps by Dick Cawley

Hermetic motors, seals, elastomers,compressors, thermal expansion devices,distributors, capillary tubes, short tube orifices, line valves, service valves, switch over valves, check valves, filters / driers, accumulators, heat
transfer surfaces and connectingtubing could cause a refrigerant related failure.

 

Benefits of Air Source Heat Pumps by Larry Butz

(PPT file - 1.2 MB) Slide presentation at Dairyland Power Annual Conference 3/24/10 by Larry Butz . Includes discussion of reasons for increased use in colder northern climates.

 
The Smart Grid and You  by Duane LomDuane Lom

The Smart Grid Consumer Mantra
"Ask not what the grid can do for you. Ask what you can do for the grid – and prepare to get paid for it.

Imagine it’s a hot, humid day and the temperature is rising. The local electric company is reaching it maximum generating capacity, so it sends a signal to your home automation system to reduce the electrical consumption in your house. Your home automation system responds by raising the set point of your thermostat and only energizing the water heater when absolutely necessary. For your ability to shed some load, you get a discount on your energy bill. Welcome to the "Smart Grid".