Table of Contents
- It should have low boiling point.
- Normal boiling point should be less than temp of refrigerant.
- Critical temperature (lowest temperature at which matter can exist in liquid state??) should be high and critical pressure (pressure at which we cannot compress gas into liquid by application of pressure only??) low.
- Inflammability: Hydrocarbons are inflammable and highly explosive, but flurocarbons are not.
- Reaction with water, oil and construction material.
- Solubility: Ifit is wholly soluble or insoluble then OK. It should not be partially soluble.
- Easy to detect leakage.
- Leakage tendency should be minimum.
- Dielectric strength should be high.
- Low viscosity (Higher heat transfer coefficient)
Saturated: Given by the formulae CmHnFpClq, where n + p + q = 2 × m + 2, and is denoted as R(m-1)(n+1)(p) like CFCl3 or R-11.
Unsaturated: Given by the formulae CmHnnFpClq, where n + p + q = 2 × m, and is denoted as R1(m-1)(n+1)(p) like C2H4 or R-115.
Inorganic Compound: It is denoted as R(700+molecular weight weight) like NH33 or R-717.
New Refrigerants: So far R-22 is used, which is an HCFC, but now R-134a and R-407c are there (they are HFC refrigerants) and they can be used to replace R-12 & R-22 respectively. These are polyolester oil (POE) or mineral oil and are hygroscopic.
R -134a: This refrigerant is an alternative to R-12 and R -500 in new & existing medium pressure centrifugal chillers. It is also used as a optional to R-22 in positive displacement (screw & reciprocating) water chillers. Having an ODP of zero, R-134a is the only refrigerant at present for centrifugal chillers without a phaseout. The relevant properties are as below
- NBP: -14.92 °F or -26.1 °C (at 14.696 psia)
- Evaporator pressure at 40 °F: 49.7 psia or 35 psig
- Condenser pressure at 105 °F, 149.6 psia: 134.9 psig
- Refrigeration effect (w/o sub-cooling): 62 Btu/lb
- Theoretical kW/TR ≈ 0.43
- Actual kW/TR ≈ 0.43 (10 °F sub-cooling)
It is a halocarbon refrigerant and can exist in two structures, one symmetrical other asymmetrical (Isomers) and is positive pressure.
Changeover of Refrigerants:
If the system is not leaking and is operating properly, there is no technical reason to replace the HCFC refrigerant; and sometimes compressor warranties may be infringed. However if changeover is decided (by R-407c), following considerations should be given:
- Retrofitting systems that employ compressors manufactured prior to 1973 is not recommended. This is due to the different materials used in motor insulations that may have not been evacuated for compatibility with the new refrigerants and lubricants.
- Suction reeds must be upgraded to the latest hardened reeds.
- Proper lubricant suitable for the refrigerant should be used.
- R-407c should be used only in the systems that currently use R-22. It should not be mixed with R-22 or any other regrigerant.
- Tha capacity of expansion valve will be approximately the same, but superheat settings must be checked and may have to be readjusted after the system is put back into operation.
- Filter driers must be changed at the time of conversion.
- Because of glide, pressure regulators such as EPR valves may have to be reset. Systems with receiver may experience some fractionation of the refrigerant in the eceiver and have somewhat lower capacity.
- R-407c exhibits higher pressures than R-22 at normal condensing temperatures. This may require adjusting the high pressure safety control to operate as intended.
Systems that use a low pressure controller to maintain space temperature may need to have the cut in and cut out point changed. With R-407c, the pressure settings must reflect an average temperature of refrigerant in the evaporator. Because of refrigerant glide, the refrigerant entering the evaporator for a specific suction pressure is approximately 10° F colder than the refrigerant vapour at the outlet of evaporator (not considering the superheat). Therefore the average refrigerant temperature will be at a midpoint pressure/temperature equivalent.
For example a 70 °F AC space usually requires that the refrigerant temperature in the evaporator be approximately 45 °F. Using R-407c, the liquid entering the evaporator may be as cold as 40 °F and the vapour temperature before superheat may be 50 °F. Some pocket P-T charts give a midpoint evaporator temperature versus pressure. This may be used for the initial sensing of the pressure activated room temperature controller. If the midpoint data is not available, subtract five degrees from the desired average evaporator temmperature (in this case 45 – 5 = 40 °F) and set the initial pressure setting for the corresponding bubble point (liquid) pressure shown on the P-T (pressure temperature) chart (in this case 40 °F = 79 psig).
Due to refrigerant glide, it is important that when measuring and/or adjusting TEV superheat, the pressure and saturated vapour (DP) tables are used. The pressure measured at the TEV bulb is 79 psig. The P-T chart shows that the saturated vapor temperalure, at the dew point, of R-407c at 79 psig is ≈ 51°F. If the actual refrigerant temperature is 60 °F, the superheat is 9 °F.
To measure sub-cooling at the condenser outlet or at the TEV inlet to verify that a solid column of liquid is present, measure the pressure and the temperature at the location that the sub-cooling informtion is needed. Compare it to the saturated liquid (bubble point) tables. Foe example if a pressure of 250 psig is measured at the condenser outlet and from the R-407c chart, 250 psig is 108 °F saturated liquid temperature. If the actual refrigerant temperture is 98 °F, the liquid is sub-cooled 10°F.
- Systems using R-407C may have a higher system pressure drop than with R-22. Check with the manufacturer of any pressure regulators and pilot operated solenoid valves used in the system to be sure that they will operate properly.
- Mineral oil lubricant such as 3GS, cannot be used as compressor lubricant. Instead Plolyol Ester (POE) may be used
Before slarting the changeover, it is suggested that at least the following items be ready:
- Safety glasses.
- Refrigerant service gauges.
- Electronic thermometer.
- Vacuum pump capable of pulling 250 microns.
- Thermocouple micron gauge.
- Leak detector.
- Refrigerant recovery unit including refrigerant cylinder.
- Proper container for removed lubricant.
- New liquid control device.
- Replacement liquid line filter/drier(s)
- New (POE) lubricant.
- R-407c pressure temperature chart.
- R-407c refrigerant.
- The system should be thoroughly leak tested with the R-22 still in the system. All leaks should be repaired before the R-407c refrigerant is added.
- It is advisable that the system operating conditions be recorded with the R-22 still in the system. This will provide the base data for comparison when the system is put back into operation with R-407c.
- The system should be electrically shutt off and the refrigerant properly removed from the system. Measure the quantity of refrigerant removed. This will provide a guide for recharging the system with R-407c.
- The mineral oil must be removed from the compressor crankcase. Hermetic compressors will have to be removed from tile piping and the lubricant drained out through the suction stub. It is advisable to do an acid test on the lubricant removed.
Measure the amount of lubricant removed. It should be within 4 to 6 ounces of the compressor's factory oil charge. The lubricant charge is indicated on the nameplate.
Those systems that have oil separators, oil reservoirs, oil floats and suction line accumulators must have the oil drained from them. If the liquid control device is going to be replaced, it is advisable that tile suction line, liquid line, and evaporator coil be blown clean using properly regulated dry nitrogen.
The lubricant should be properly disposed.
- Before the new lubricant is installed into the compressor be sure all leaks are repaired, and any system components are changed if necessary. Install the correct liquid line filter-drier. Driers must be compatible with the refrigerant and lubricant.
- POE’s are very hygroscopic. They will very quickly absorb moisture from the air once the container is opened. Once the lubricant is added to the compressor, the compressor should be quickly installed. Like an open container, an open compressor with POE will absorb moisture. Add the correct amount of lubricant to the compressor. On systems using enhanced surfaces in the heat exchanger, excessive mineral oil can adversely effect the heat transfer due to logging. Therefore it is desirable to have no more than one percent mineral oil in systems employing these types surfaces.
- Once the compressor is installed and tile system is closed, the system must be evacuated to 250 microns or lower.
R-407c is a zeo-tropic mixture. It is important that during initial charging or "topping" off a system that the refrigerant be removed from the charging cylinder in the liquid phase. Many of the cylinders for the newer refrigerants use a dip tube so that in the upright position liquid is drawn from the cylinder. Do not vapor charge out of a cylinder unless the entire cylinder is to be charged into the system. Refer to charging instructions provided by the refrigerant manufacturer.
With the system in a 250 micron or lower cacuum, liquid can be charged into the system "high side." The initial charge should be approximately 80 percent of the amount of refrigerant removed from the system.
Start the system and observe its operation. Additional refrigerant may have to be added to obtain optimum performance. Note: On systems with long liquid lines, tile sigllt glass sllould be installed near the expansion valve to avoid erroneous llasll gas indication caused by pressure drop or ambient temperature.
When adding refrigerant to an operating system, it may be necessary to add the refrigerant through the compressor suction service valve. Because the refrigerant leaving the refrigerant cylinder must be in liquid phase, care must be exercised to avoid damage to the compressor. It is suggested that a sight glass be connected between the charging hose and the compressor suction service valve. This will permit you to adjust the cylinder hand valve so that liquid can leave the cylinder while allowing vapor to enter the compressor.
- Operate the syslem and record the operating conditions. Compare this data to the data taken in item 2 in this seclion. Check and adjust the TEV superheat setting if necessary. Make adjustments to other controls as needed.
- Properly label the components. Tag the compressor with the refrigerant used (R-407c) and the lubricant used. The proper color code for R-407c is Burgundy PMS (Paint Matching System) 471.
- Clean up and properly dispose of the removed lubricant. Check local and state laws regarding the disposal of refrigerant lubricants. Recycle or reclaim the removed refrigerant.
The above guidelines are for use with R-407c only, and not for refrigerants which are similar to R-407c. Other refrigerant may not be compatible with the materials used in our compressors or the libricants recommended in this bulletin resulting in unacceptable reliability and durability of the compressors.
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