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Due to Copeland Scrolls inherent ability to handle liquid refrigerant in flooded start and defrost cycle operation, an accumulator is not required for durability in most systems. However, large volumes of liquid refrigerant repeatedly flooding back to the compressor during normal off cycles, or excessive liquid refrigerant flooding back during defrost or varying loads can dilute the oil, no matter what the system charge is. As a result, bearings and moving parts will be inadequately lubricated and wear may occur.If an accumulator must be used, the oil-return orifice should be from 1 to 1.4 mm in diameter for models ZH12K4E to ZH45K4E and ZH09KVE to ZH18KVE, and 2.0 mm for models ZH56K4E to ZH11M4E and ZH24KVE to ZH48KVE, depending on compressor size and compressor floodback results. To protect this small orifice from plugging with system debris a large-area protective screen no finer than 30 x 30 mesh (0.6 mm openings) is required. Tests have shown that a small screen with a fine mesh can easily become plugged causing oil starvation to the compressor bearings.The size of the accumulator depends upon the operating range of the system and the amount of subcooling and subsequent head pressure allowed by the refrigerant control. System modelling indicates that heat pumps that operate down to and below -18°C will require an accumulator that can hold around 70% to 75% of the system charge.
The EXV valve is to be installed vertically with stepper motor locked into position. See Figure 22 for correct orientation. To ensure the valve has the proper mounting, calibration and control, only the Emerson supplied stepper valve (p/n 998-0340-**) should be used with CoreSense Diagnostics for Copeland Scroll K5 refrigeration compressors.NOTE: When using an EXV stepper valve a liquid line shutoff solenoid will need to be installed on the liquid line. This is in the event of a power loss that will leave the EXV motor in it's current position and potentially allow liquid to enter the compressor while off. A vapor line shut off may be needed in the event of a motor protection trip where the control circuit is not opened. It is recommended to use a current sensing relay to ensure that liquid line solenoid is to be closed when compressor is off.
De nämnde ett annat intressant fenomen som kan leda till allvarliga olyckor; Dieseleffekten. Det innebär att om det skulle komma in luft i köldmediesystemet så finns det en risk att smörjoljan i kompressorn kan antändas som bränslet i en dieselmotor. Detta eftersom det är så extremt höga tryck. I en dieselmotor är det runt 20 bar vid antändningstillfället. I ett kylsystem så ligger ju trycket mellan 20 och 40 bar beroende på köldmedium. Därför föreligger det en explosionsrisk vid drift om det kommer luft in i kompressorn.
Det verkar märkligt. Det är inte trycket i sig som är problemet utan det är kompressionsförhållandet som bestämmer temperaturstegringen. Även om det är 20 till 40 bar på köldmediet efter kompressorn så är trycket i förångaren betydligt högre än atmosfärstrycket. Det går inte att jämföra med en dieselmotor som suger luft som har ett tryck på 1 bar.
Angående PLC/controller så får du et problem med en VP dersom du får "PLC freeze", som av og til forekommer. I industrien anvendes Siemens S7 i kritiske applikasjoner, og det blir vel en smule "overkill" og ha en Siemens S7 i en VP?
Temperaturökningen bestäms av kvoten mellan sluttrycket och starttrycket. Formeln är T2/T1 = (P2/P1)((k-1)/k) där k = 1,4 för luft och runt 1,3 för köldmedier vars molekyler har fler atomer än luftmolekylerna. Det betyder att ett visst tryckförhållande ger lägre temperaturstegring för ett köldmedium än för luft. ...
This diagram shows the economizer circuit parameters:LI is the liquid temperature at the inlet to the heat exchanger and it may be lower than the condensing temperature due to subcooling in the condenser. The maximum condenser subcooling value is limited to 5.5K and if a lower liquid temperature is entered, then the performance of the EVI models is shown for 5.5K VO is the vapour temperature at the outlet of the heat exchanger. This is automatically set for 5K superheat.LO is the liquid temperature at the outlet of the heat exchanger. This is automatically set to 5K above the heat exchanger inlet temperature.LX is the liquid temperature at the inlet to the expansion valve of the evaporator. It is only shown for refrigeration vapour injected compressors, and it can be adjusted by entering a value for EVI Liquid Line Temperature Rise to allow for heat gain in the liquid line between the heat exchanger and the evaporator inlet.EVI Liquid Line Temp Rise: Temperature increase of liquid between the subcooler outlet and the expansion valve inlet. This temperature rise will normally be due to heat pick up in the liquid line from the surroundings. It is only applicable to Vapour Injected scrolls and 2-stage compressors with subcoolers. When this parameter is set the liquid temperature shown in the Performance record will be adjusted upwards by the amount entered, and the Evaporator Capacity will be reduced accordingly
A solenoid valve should be added if the expansion device does not close completely. This will avoid liquid migration to the compressor during the off cycle. In single compressor configuration, the solenoid valve may be in the liquid line or the vapour line. A liquid line position is usually preferred because the valve is smaller. However, if the compressor rotates in reverse direction during the first seconds of the off cycle, the valve should be installed in the vapour line in order to limit the volume of refrigerant between the valve and the compressor. With multiple compressors used in parallel with one economizer it is required to install a solenoid valve in the single injection line of each compressor. This would avoid injection in idle compressor.