COMPRESSOR SPEED

  Open type compressor operating from a truck engine by means of a power take-off or by a belt driver are subject to extreme speed ranges. A typical truck engine may idle at 500 RPM to 700 RPM, run at 1,800 RPM at 30 MPH, and run at 3,600 RPM over the highway at high speed. Whatever the power take-off or belt ratio, this means the compressor must operate through a speed ratio range of 6 to 1 or greater unless it is disconnected from the power source by some means.

  The compressor speed must be kept within safe limit to avoid loss of lubrication and physical damage. Operation within the physical limitations of the compressor may be possible for example from 400 RPM to 2,400 RPM. It may be possible to use a cut-out switch ta disconnect the compressor from the power source at a given speed. The compressor manufacturer should be contacted for minimum and maximum speeds of specific compressors.

  If the compressor is of  the accessible-hermetic type, there is no problem concerning speed so long as the electrical source is operating at the voltage and frequency for which the motor was designed. If the speed of the generator is varied in order to obtain variable speed operation, the voltage and frequency on the normal alternating current generator will vary proportionally. Since the compressor speed and motor load will vary directly with the frequency, it is often possible to operate over a wide speed range with satisfactory results.

  However, it should be born in mind that increasing the frequency and voltage of the generator above the level for which the compressor motor was designed will increase the load on the compressor, may overload the motor, and can result in bearing or other compressor damage. Operation at speeds too low to provide adequate compressor lubrication must also be avoided, although normally lubrication can be maintained on Copelametic compressors down to 600 RPM and possibly lower speeds.

  Each new application involving operation of the compressor at a voltage and frequency differing from its nameplate rating should be submitted to the Copeland Application Engineering Department for approval.

  One other problem that may arise with operation from a variable speed generator is the operation of electrical contactors, relays, etc. on voltages below or above their nameplate rating. Field tests have shown that the winding design and physical construction of electrical components can cause wide variation in voltage tolerance. The drop-out voltage of various types of commercially available 220 volt contactors may vary from 145 volts to 180 volts depending on construction. If it is planned to operate at variable voltage and frequencies, the electrical  components which are to be used should be extensively tested at the electrical extremes in cooperation with the manufacture to insure proper operation

COMPRESSOR LUBRICATION

  An adequate supply of oil must be maintained in the crankcase at all times to insure continuous lubrication. The normal oil level should be maintained at slightly above the center of the sight glass while operating and possible damage to the compressor valves.

  Compressors leaving the Copeland factory are charged wit Suniso 3G, 150 viscosity refrigeration oil, and the use of any other oil must be specifically cleared with the Copeland Application Engineering Department. The naphthenic base oil has definite advantages over paraffinic base oils occurs at substantially higher temperatures with the same oil-refrigerant concentration When this separation or two phase condition exists the oil floats on top of the refrigerant and the oil pump inlet at the bottom of the sump is fed almost pure refrigerant at start up.The resulting improper lubrication can result in bearing failure. Because of the lower separating temperature of Suniso 3G oil, the possibility of two-phasing is greatly reduced.

  Copelametic compressors are shipped with a generous supply of oil the crankcase. However the system may require more or less oil depending. On field installed systems, after the system stabilizes at its normal operating conditions, it may be necessary to add or remove oil to maintain the desired level.

On compressors with step-up gearboxes, the main oil pump may be driven mechanically from the gearbox, and the auxiliary pump operates during the start-up and run-down phases of the compressor train. Relief valves protect both pumps from the effects of excessively high pressures. Check-valves prevent reverse flow of oil through the stationary pump.

COMPRESSOR SELECTION HVAC

   The compressor must be selected for the capacity required at the desired operating conditions in accordance with the manufactures recommendations for the refrigerant to be used. Standard Copeland single stage compressors are approved for operation with a given refrigerant in one of the following operating ranges.

                                                                ( Evaporating Temperature )
                                                                             
                                                                       
* High Temperature                                                45° F. to 0° F.
                                                                            or 55° F. to 0° F.

* Medium temperature                                           25° F. to - 5° F.

* Low Temperature                                                 0° F. to -40° F.

*Extra   Low Temperature                                    -20° F. to -40° F.

   Operation at evaporating temperature above the approved operating range may overload the compressor motor. Operation at evaporating temperature below the approved operating ranger is normally not a problem if the compressor motor can be adequately cooled, and discharge can be kept within allowable limits. Evaporating temperatures below -40° F. are normally beyond the practical lower limit of single stage operation because of compressor inefficiencies and excessive discharge gas temperatures. Because of problems of motor cooling or overloading, some motor-compressors may have approval for operation at limited condensing or evaporating temperatures within a given range, and if so, these limitations will be shown by limited performance curves on the specification sheet.

   A given compressor may be approved in two different operating ranges with different refrigerants, for example, high temperature R-12 and low temperature R-502. Since the power requirements for a given displacement with both R-22 and R-502 are somewhat similar, in some cases a compressor may be approved in the same operating range for either of these refrigerants.

  Two stage compressors may be approved for evaporating temperatures as low as -80° F., but individual compressor specifications should be consulted for the approved operating range.
Operation at temperatures below -80° F. is normally beyond the practical efficiency range of Copeland two stage compressors, and for lower evaporating temperatures, cascade systems should be employed.

  Copeland motor-compressors should never be operated beyond published operating limits without prior approval of the Copeland Application Engineering Department.

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Danfoss focuses on providing energy efficient, sustainable and smart refrigeration compressors for a varied range of commercial applications such as cold rooms, display windows, ice making machines, glass door merchandisers, process cooling etc. Their qualification with lower GWP refrigerants make them compliant with refrigerant regulations such as F-Gas in Europe.