UNDERSTANDING REFRIGERANT TABLES - RSES.org

1 INTRODUCTIONAM ollier diagramis a graphical representation of theproperties of a REFRIGERANT , generally in terms ofenthalpy and entropy. A familiarity with these dia-grams will make this chapter easier. An understand-ing of the pressure-temperature relationship ofrefrigerants as they pass through the refrigerationcompression cycle also will help you as you studythis chapter on REFRIGERANT of this chapter deals with a REFRIGERANT (R-22)that will soon be phased out of production. However,as a service technician you may continue to comeacross it for years to come.

2 Be prepared rememberthat good troubleshooting requires a thorough under-standing of the 1, on pages 4 and 5, shows the properties ofR-22 at will be used in the examples thatfollow. R-22 will soon be phased out, so you will notsee it as much as you do other refrigerants in thefuture. However, all other REFRIGERANT TABLES workessentially the same way as the R-22 chapter will review the older REFRIGERANT (R-22)first, and then refer to one of the newer replacementrefrigerants (R-410A). As you study their characteris-tics, known problems, limitations, etc.

3 , remember thatthis is a field of rapid change. It is yourresponsibilityto keep current. This can be done only by constantreview ofthelatest technical TABLES TO DETERMINE PROPERTIES AT SATURATIONR efrigerant TABLES have many practical uses for thecompetent service gauges, testinstruments, and thermometers, they are valuabletools. Some of the things that you can determine byusing REFRIGERANT TABLES include: setting of controls checking temperature according to pressure computing correct head pressure for a specificset of operating conditions setting expansion valve superheat noting pressure drop evaluating REFRIGERANT capacities of cylinders andreceivers estimating compressor capacity estimating normal discharge temperature, table at the end of this chapter shows the prop-erties at saturation of R-410A.

4 (Trade names are notused.) The data contained in these TABLES are takenfrom the best available sources, and are as accurateas possible. Note that temperature steps are in smallincrements. Thus, you can use them with a closedegree of accuracy. The values listed in table 1 for R-22 are used for the example calculations. The fig-ures are arranged in columns, each with an appro-priate heading. Each column is discussed in thefollowing 1: TEMPERATUREThe saturation temperatures start with the lowesttemperature at which the subject REFRIGERANT might continue in small increments through theranges in which accuracy is most essential.

5 They goup to the highest temperature for which properties atsaturation are known and saturation properties are based on saturation tem-peratures. Therefore, the temperatures that you see1 Refrigeration ServiceEngineers Society1666 Rand RoadDes Plaines, Illinois 60016 UNDERSTANDING REFRIGERANT TABLES 2005 by the Refrigeration Service Engineers Society, Des Plaines, ILSupplement to the Refrigeration Service Engineers 3 plisted in Column 1 are the reference points in mostuses of REFRIGERANT to the con-dition of a liquid at its boiling temperature, and of avapor at its condensing 2 AND 3.

6 PRESSUREC olumn 2 lists the absolute pressures (psia) and Column 3 lists the gauge pressures (psig) of the sat-urated REFRIGERANT at the corresponding Fahrenheittemperature. An asterisk (*) indicates inches of mer-cury (in. Hg) vacuum. This unit of measurement isused up to atmospheric pressure, or zero pounds ofgauge pressure. Pressures above 0 psig are shownin convert gauge pressures above0 psig to absolutepressures (psia), simply add convert pres-sures below0 psig (that is, those values preceded byan asterisk) to absolute pressures, youmust subtractthe (in.)

7 Hg) vacuum from Then multiply theresult by , or roughly 50%. The vacuum andpressure values in Columns 2 and 3 are those at saturation that correspond to the temperatures inColumn example, assume that the temperature of boilingR-22 in an evaporator is 50 F. Then the evaporatorpressure is vacuum, or psia( = = ). This isalso thelow-side pressure, assuming there is nopressure drop. If there is a 2-psig pressure drop(about in. Hg), thesuction pressurewill be about14 in. Hg, or can also use Column 3 to find thesaturationtemperaturethat corresponds to a gauge example, a compound gauge at the evaporatormay read psig.

8 Then the temperature of the boil-ing REFRIGERANT is 40 F. This is usually considered theevaporator :If the gauge islocated at the compressor, make an allowance forpressure drop in the suction can also check condenserpressure-temperaturevalues by using Column 3. A discharge pressure of226 psig with R-22, for example, means that the normal condensing temperature is 110 F. Note, how-ever, that the condensing temperature should notbeconfused with: entering and leaving air temperatures of an air-cooled condenser inlet and outlet water temperatures of a water-cooled condenser the temperature of the liquid REFRIGERANT leavingthe temperatures and corresponding pres-sures are always the same for a particular refriger-ant.

9 Thus, data in Columns 1 and 3 can be used toset low-pressure controls, high-pressure cut-outs,thermostats, and similar control devices. You can usea thermometer to determine pressure. You can use apressure gauge to determine temperature. Butremember this only works if the REFRIGERANT is at will nothold true if the liquid is sub-cooled below the saturation temperature shown inthe appropriate same thing applies to avapor superheated above the saturation temperatureshown in the same 4: LIQUID DENSITYL iquids vary in their density (weight per cubic foot).

10 Most refrigerants in liquid form have higher densitiesthan water (that is, they have specific gravities ).The densities of refrigerants also vary with theirtemperatures. As a rule, liquids expand as theybecome warmer. Thus, liquid densities at higher temperatures are less than at lower you know the internal volume of a REFRIGERANT con-tainer, such as a cylinder or receiver, you can easilyfind how much liquid REFRIGERANT it will hold. Simplymultiply the internal volume of the container in cubicfeet (ft3) by the density of the liquid REFRIGERANT at aselected temperature.