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 COOLING

  Refrigerant cooled motor-compressors are dependent on return suction gas for motor cooling, and to a considerable extent, on both air and refrigerant cooled motor-compressors, the discharge gas temperature is directly related to the temperature of the return suction gas. Discharge temperature above 325° F. to 350° F. contribute to oil breakdown and valve plate damage, and to avoid compressor damage,  operating temperatures must be kept below this level.

  Peak temperature occur at the discharge valves and normally the temperature of discharge line will be from 50° F. to 100° F. below the temperature at the valve plate. therefore the maximum allowable discharge line temperature are from 225° F. to 250° F

  Suction gas entering the compressor should be no higher than 65° F. under low temperature load conditions, or 90° F. under high temperature load conditions, and must never exceed 100° F. On some abnormally critical low temperature applications it may be desirable to insulate the suction lines and return the suction gas to the compressor at lower than normal temperature to prevent the discharge temperatures from exceeding safe limits, but this is not normally necessary on commercial applications where the saturated evaporating temperature is -40° F. or above. The low discharge temperature characteristics of R-502 have made possible much more trouble free operation in single stage low temperature applications.

  Air cooled motor-compressors must have a sufficient quantity of air impinging directly on the compressor body for motor cooling. Refrigerant cooled motor compressors are cooled adequately by the refrigerant vapor at evaporating temperatures above 0° F. but at evaporating temperature 0° F. additional motor cooling by means of air flow is necessary.

On air cooled condensing units, adequate cooling can normally be accomplished by locating the compressor in the discharge air blast from the condenser fan. For proper cooling, the fan must discharge air directly against the compressor, since the compressor usually cannot be adequately cooled by air pulled through a compartment in which the compressor is located. if the compressor is not located in the condenser discharge air stream,cooling must be provided by means of auxiliary fan discharging air directly against the compressor body. On compressor with multiple heads such as the Copeland 4R and 6R models, auxiliary horizontal air flow may not provide satisfactory cooling, and vertical cooling fan are required

  Water cooled compressors are provided with a water jacket or are wrapped with a copper water coil, and water must be circulate through the compressor cooling circuit before entering the condenser.

  Two-stage compressors are equipped with a desuperheating expansion valve for interstage cooling, and no auxiliary.  cooling is required.
  If compressors or condensing units are located in a machine room, adequate ventilation air must be provided to avoid an excessive temperature rise in the room. To allow for peak summer temperatures a 10° F. temperature rise is recommended, although a 15° F. rise in cooler ambients  might be acceptable.

  The most accurate calculation is to determine the total heat to be rejected by adding the compressor refrigerating capacity at the compressor refrigerating capacity at the design operating input. The CFM can then be calculated by the formula...  CMF= BTU/HR
                                                                           ° T D

  For example, determine the machine room ventilation for an air cooled  condensing unit operating at -25° F. evaporator, 120° F. condensing  with a net refrigeration capacity of 23,000 BTU/HR, 6,400 watts input to the compressor motor, and a 1 H.P. condenser fan motor.

Compressor capacity                                                         23,000 BTU/HR
Heat equivalent 6,400 watts x 3.413                                 21,843 BTU/HR
Heat equivalent 1 H.P. fan motor                                        3,700 BTU/HR
   Total Heat to be Rejected                                               48,543 BTU/HR

                                           48,543 BTU/HR  =    48,543 CFM
                                                  10°  TD

  With remote condensers, approximately 10% of the rejected is given the compressor casting and the discharge tubing, and the ventilation can be calculated accordingly.
   For convenience, table 20A gives a quick estimate of the ventilation air requirement if only the compressor capacity is known.

TABLE 20A
Ventilation Air Requirements For Machine Rooms CFM/1000/ BTU/HR at 10° F. Air Temperature Rise

When a gas is compressed, its temperature increases. Conversely, when it is expanded, its temperature decreases. This is one of the ramifications of the First Law of Thermodynamics.

The temperature of a pure liquid remains constant as it boils or condenses. We have all witnessed this phenomenon in our kitchens. If you measure the temperature of water as it boils, the temperature remains constant at 212°F or 100°C as long as liquid water is present. Also, when gases are condensed, the system temperature remains constant until all the gas converts to a liquid.

REFRIGERANT

  Copeland compressor are primarily designed for operation wit refrigerants R-12,R-22,and R-502.
Operation wit other refrigerants in cascade systems may be satisfactory if the proper motor and displacement combination is selected, adequate lubrication can be maintained, and if adequate compressor protection is provided.
  All applications with refrigerants other than R-12, R-22 and
R-502 must be approved by the Copeland Application Engineering department.

  R-502 is highly recommended for all single stage low temperature applications, and particularly where evaporating temperature of -20° F. and below may be encountered.
Because of the undesirable high discharge temperatures of R-22 should not be used in single stage low temperature compressors 5 HP and larger.

  Different expansion valves are required for each refrigerant, so the refrigerants are not interchangeable in a given system, and should never be mixed. If for some reason it is desirable to change from one refrigerant to another in an existing system, it is usually possible to convert the system by changing expansion valves and control settings providing the existing piping sizes and component working pressures are compatible.

  In some cases the existing motor-compressor may be satisfactory for example, in converting from R-22 to R-502. If the conversion will result in higher power requirements as is the case in changing from R-12 to R-502, then it may also be necessary to change the motor-compressor.

  The refrigerant charge should be held to the minimum required for satisfactory operation, since an abnormally high charge will create potential problems of refrigerant control.


R-410A Refrigerant

In 1987 the Montreal Protocol, an International environmental agreement, established requirements that began the worldwide phase out of ozone-depleting CFCs (chlorofluorocarbons).

In 1992 it was amended to establish a schedule for the phase out of HCFCs (hydrochlorofluorocarbons). HCFCs are less damaging to the ozone layer than CFCs, but still contain ozone-destroying chlorine.

The Montreal Protocol is carried out in the U.S. through Title VI of the Clean Air Act, which is implemented by EPA.

SYSTEM BALANCE

  If the compressor or condensing unit selected for a given application is to satisfactorily handle the refrigeration load, it must have sufficient capacity. However, over capacity can be equality as unsatisfactory as under capacity, and care must be taken to see that the compressor and evaporator balance at the desired operating conditions. Checking the proposed system operation by means of a compressor-evaporator-condenser balance chart as described in Selection 16 is recommended.

  If fluctuation in the refrigeration load are to be expected, which could result in compressor operation at excessively low suction pressures, then some means of capacity control must be provided to maintain acceptable evaporating temperatures. If compressor with unloaders are not available or suitable, and if the load cannot be adequately handled by cycling the compressor, a hot gas bypass circuit may be required.

The job of the refrigeration cycle is to remove unwanted heat from one place and discharge it into another. To accomplish this, the refrigerant is pumped through a closed refrigeration system. If the system was not closed, it would be using up the refrigerant by dissipating it into the surrounding media; because it is closed, the same refrigerant is used over and over again, as it passes through the cycle removing some heat and discharging it. The closed cycle serves other purposes as well; it keeps the refrigerant from becoming contaminated and controls its flow, for it is a liquid in some parts of the cycle and a gas or vapor in other phases.

Let's look at what happens in a simple refrigeration cycle, and to the major components involved. Two different pressures exist in the cycle - the evaporating or low pressure in the "low side," and the condensing, or high pressure, in the "high side." These pressure areas are separated by two dividing points: one is the metering device where the refrigerant flow is controlled, and the other is at the compressor, where vapor is compressed.

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.

Extra

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.

FUNDAMENTAL DESIGN PRINCIPLES REFRIGERATION

If you are like most of us in the HVAC industry, you are a hands-on person - you don‘t want to mess with a lot of theory, but just get in and get the job done. But a refrigeration system is different from most of our work. Unless you understand the basic principles covered in this article, you will never understand refrigeration. The refrigeration process operates on scientific principles that are applied to practical mechanical processes.
There are certain fundamental refrigeration design principles which are vital to the proper functioning of any system.

1. The system must be clean, dry, and free from all contaminants and other.

2. The compressor must be operated within safe temperature, pressure, and electrical limits for safe also.

3. The system  must be designed and operated so that proper lubrication is maintained in the compressor at all times.

4. The system  must be designed and operated so that excessive liquid refrigerant does not enter the compressor. Refrigeration compressor are designed to pump refrigerant vapor, and will tolerate only a limited quantity of liquid refrigerant.

5. Proper refrigerant feed to the evaporator must be maintained, and excessive pressure drop in the refrigerant piping must be avoided.

If these five steps are accomplished, then operation of the system is reasonably certain to be trouble free. If any one is neglected, then eventual operating problems are almost certain to occur. These basic fundamentals are closely inter-related, and must always be kept component, or whenever any change in system operation is contemplated.