Refrigerants and Brines (2)

Chap

9 Refrigerants and Brines

The refrigerant, as discussed earlier, is Lhe medium Lhat absorbs the heat from the substance t cooled and d iscards the heat so absorbed to the atmosphere. In this process the Refrigerant doe~ undergo any chemical change; the change is only physical. IL only alternately vaporizes from the lie state (to absorb Ll1e heal in the evaporator) and condenses to its liquid state (for reuse in evaporator) by rejecting to atmosphere its superheat and latent heat of vaporization through condenser. These processes occur in the vapour compression as well as in the vapour absorp1 sy terns.

The refrigerants hould have cenain chemical, physical and thermodynamic properties tom it safe and energy efficient.

No single refrigerant satisfies all the qualities desired of a refrigerant and that can be used all types of applications. So no ideal refrigerant exists. If a refrigerant has certain advantages, it s1 will have some disadvantages as well. So a refrigerant that has greater advantages than disadvanta is chosen. The selection of a refrigerant for an application is based on characteristics, such as, pressure-temperature characteristics, density, viscosity, flammability, toxicity, miscibility with ' energy efficienl, etc.

DESIRABLE PROPERTIES

The Pressure - Temperature Characteristics

To limit the energy consumption to the minimum, we have seen that compression ratio of the syste should be low. For this, the saturation pre sure of the refrigerant at the evaporating temperatu should be high and condensing pressure (i.e. condensing temperature obtainable with respect to ti maximum ambient conditions) hould be as low as practicable.

Economic Power requirement to produce unit refrigeration (Bhp/ton) should be Im\. Latent he of vaporization, compression ratio, specific heat and density of vapour are the main factors whic influence power requirement.

Critical Pressure If the critical pressure of the refrigerant is low, the power required for con pressing the vapour goes up. Further with very low critical pressure (like C02) it is not possib

oes not e liquid in the

ugh the orption

to make

ed for , it sure antages has, its ,ith oil,

·system rature t to the

nt heat which

•r comossible

Refrigerants and Brines 73

condense the vapour in the condenser at higher ambient tempe1·ature. So the refrigerant H have high critical pressure (see para on 'Critical pressure/temperature' in the chapter on

•nenta/,s').

Critical Pressure/Temperature As condensing temperature approaches the critical pressure the critical temperature) of the refrigerant, COP and refrigeration capacity of the refrigerant reduced significantly. So the refrigerant should have higher critical pressure and critical

rature.

Safety It should be non-toxic, non-explosive, non-inflammable and chemically inert, i.e. should e to use. ASH RAE standard classifies refrigerants according to their toxicity and flammability. lassification uses a capital letter to denote toxicity of the refrigerant and its flammability is

~ated by a numeral, as under:

,ass A-no toxicity identified (not toxic) even at a low concentration of 400 ppm, by volume ,ass B-where evidence of toxicity is identified (i.e. toxic) !ass 1-does not propagate flame in air at 18.3°C(65°F) and atmospheric pressure 'lass 2-lower flammability lass 3-highly flammable.

So there are six groups viz Al, A2, A3, B 1, B2 & B3 in the safety classification. Refrigerants with 1'Cn low/nil toxicity and non-flammable are least hazardous, identified as group Al and those com

, under group B3 are most hazardous. Table 9.3 shows some of the relevant physical properties of commonly used refrigerants along with their safety classification.

LOW FREEZING POINT

lf the refrigerant has high freezing point, it will freeze under operating condition, hindering the continuous operation of the plant. So freezing point should be very much below the expected C'\""aporator temperature.

Stability It should not breakdown or decompose under the operating conditions of the refrigera-1 •n system. Also it should not react with the materials used in the system.

Oieledrlc Strength Should have high dielectric strength. As this is also indicative of the moisture <.untent in the refrigerant. it becomes an important factor, particularly for hermetic svstems-as discu,sed under lubrication also.(see: 'Dielectric strength' in Chapter on 'Lubrication') .

'Solubility of Water in Refrigerants Except for ammonia, the solubility of water in the commonly ed refrigerants is low. Solubility is expressed in ppm by weight of water/moisture present in the refrigerant. The solubility of moisture in the refrigerants varies with refrigerants; also solubility decreases

ubstantially) with temperature of the refrigerant. When moisture or water present in the system r refrigerant) at a particular temperature, exceeds the solubility limit for the refrigerant at that

1 ·mperature, the excess separates out as free water/moisture. It follows, therefore, that as the temperature of the refrigerant falls (for example, as it enters the

low side of the system) the quantity of moisture it can hold too comes down and the excess if any, parates as free water/moisture. If the temperature of the refrigerant falls down below the freezing point (0°C) of water, (as it

n ppens at the throttling device and evaporator in cold store and low temperature applications) the

7 4 Basic Refrigeration and Air Conditioning

excess water/moisture will freeze as ice at the throttling device. This restricts or even totally blocb the refrigerant flow through the throttling device, affecting refrigeration capacity or can even resull in complete cessation ofrefrigeration.

Free water/moisture reacts with the refrigerant at higher temperatures (in the high side of thr system) forming acids, which attacks the system components and causes corrosion.

Where the evaporating temperature is above 0°C(32°F), obviously, the freezing will not take placr at the throttling device. But the acidic reaction does take place, attacking the system. This unfortir nately, will become evident only when the system fails, that is, after the havoc has occurred. In hermeac compressors, excess moisture renders the polyester or paper motor insulation brittle and weak, leading to premature motor failure, high re-operating costs and in many cases, a system that can never be brought back to a really clean condition - an irreparably contaminated system. Therefore the water moisture content in the system has to be kept very low (see: Chapter on 'Evacuation & dehydration"\

Solubility of water in ammonia is so high that free water separating out from the refrigerant never happens.

In the field it is not possible to ascertain the moisture content in the refrigerant system. The moisture left in the system could be the sum of: (l) faulty drying of components/system durin manufacturing; (2) moisture left in the system after evacuation/dehydration during installation' service; (3) moisture content in refrigerant; (4) in oil; and (5) formation of moisture/water due chemical reaction within the system.

Some important precautions for keeping the moisture content in the system at a very low level~ therefore:

~ strict quality control at manufacturing stage, ~ adopting proper deep evacuation procedures at pre-commissioning stage and during service

operations, ~ procuring refrigerant and oil from reliable sources and ensuring a clean system during

erection/service.

( Table 9.1) Solubility (in ppm by weight) of water in liquid refrigerants

Temperature R 11 R 12 R22 R 123 R 134a

37.8°C (100°F) 168 165 1800 1200 1800 4.4°C (40°F) 44 22 690 470 600 -17 .8°C (0°f) 15 8 308 220 250 -40°C(- 40°F) 4 2 120 90 89

MISCIBILITY OF REFRIGERANT WITH LUBRICATING OIL AND OIL RETURN

Gas velocity in equipment and refrigerant lines coupled with miscibility of oil with refrigerant aid in return of oil from the system to the compressor (see: 'Lubricant-refrigerant compatibility' and 'Oil return in Chapter on 'Lubrication').

In flooded evaporators, special oil bleeder line is provided for oil return, as oil entrainment b' gas velocity is not possible (see: Chapter 32-Suction line).

In centrifugal compressor, by construction, the possibility of oil coming in contact with refrigerant being minimal, carry over of oil is very low. In some makes of centrifugal, the small amount of oil

3Ja

()()

()()

50 g


~e~ carried, collects at the bottom of the discharge volute, from where the oil is returned to :hmiber by a venturi arrangement

nia systems, because of its extremely poor/nil miscibility in oil, oil does not return, but the oil legs provided in the evaporator from where it is drained periodically. [see

-refrigerant compatibility' in Chapter on 'Lubrication'; also see details on 'Oil return' in Chap·gerant piping'.]

the refrigerant gases are heavier than air. So gas escaping to the plant room from a gas leak ~ ...ervice operations, drops down, fills up and displaces atmospheric air from the room. c...ise asphyxiation (unconsciousness or even death) by lack of oxygen, to personnel in the

~ Therefore plant rooms should have positive ventilation to limit the concentration level 111 the room much below the 'Acceptable Exposure Level' (AEL) of the refrigerant in use

monitor can be used to detect presence of gas in the plant room. These monitors are «:'!S:::~to detect even very low concentration of 1 to 3 ppm of refrigerant and thus help in alerting

a very minute leak and concentration level in the plant room .

... -=-m-ies of Refrigerants in Common Use

? ~ves the chemical names, chemical symbols, group, 'Ozone Depletion Potential' al Warming Potential' (GWP) and 'Acceptable Exposure Limit' (AEL) of (single sub

::di-i~erants commonly in use.

"U Symbol Group ODP GWP100 AEL

(CCI 3F) CFC 1.00 3800 1000

(CHCIF2) HCFC 0.05 1700 1000

(CHCl2CF3) HCFC 0.02 90 50

(CH2FCF3) HFC 0 1300 1000

(C4H10) hydrocarbon 0 3. 1000

(NH3) inorganic 0 0 50 compound

- Olloro Fluoro Carbons -no hydrogen atom in the molecule- have great stability and so m a;mosphere for many years; ultimately enters into the stratosphere, where they break

~ing chlorine which depletes the ozone - Hvdro Chloro Fluoro Carbons - replacement of one or more of the halogen atoms

-.rith hydrogen atoms in the molecule considerably reduces its life in the atmosphere and

so has less impact on the environment than the CFCs, yet with the chlorine content han ozone.

HFC - Hydro Fluoro Carbons (no chlorine, contain hydrogen and fluorine atoms)-n substance.

AEL - Acceptable Exposure Level in parts per million (ppm). Halon - This is not a refrigerant but is mentioned here because of its impact on the ozone I

the stratosphere. A compound containing bromine, fluorine and carbon is used as a fire exti1 ing agent. On break down, releases bromine, which is more destructive than chlorine.

(Table 9.3 ) Some important properties of the commonly used refrigerants

Ref rigera11t Rll R 12 R22 R 123 R 134a R 600a ---- -Boiling point oc 23.80 -29.80 -40.80 27.87 -26.20 -11.73

OF 74.90 -21.60 -41.40 82.20 -15.20 10.9 Critical- Kglcm2 43.9 40.9 49.7 36.44 40.44 36.2 Pressure psig 625 582 707 518 575 514 Critical oc 198 112 96 184 101 135 Temp. OF 388 234 205 363 214 275 NRE** kcal/kg 37.33 27.86 38.83 34.01 36.02 62.82 2

Btu/lb 67.2 50.15 69.89 61.22 64.83 113.07 4 Comp.displacement per TR** m3/m 1.033 0.165 0.10 1.3 0.17 0.321

:cfm 36.5 5.83 3.55 46.02 6.021 11.36 Discharge gas oc 40 38.3 53.3 34.44 43 45 Temperature** OF 104 IOI 128 94 109.4 113 Bhp/TR (theoretical)** 0.939 0.992 1.011 0.974 1.07 1.07 COP** 5.09 4.69 4.75 4.36 4.42 4.55 Safety@ Al Al Al Bl Al A3 Miscibilty with mineral oil good good fair good nil nil Synthetic oil good good good

.. al -l 5°C (5°F) evaporating and 30°C(86°F) condensing temperatures Note: The discharge temperatu1·e indicated is for open type compresso1: This will be higher in semi-hermetics a higher in hermetics.

@Safety classification (see para on Safety in this chapter).

Toxicity

Class A: no toxicity at concentration of 400 ppm by volume Class B: tocxicity identified

Flammability --- --

Class I: no flame propagation at l 8°C(6. Class 2: practically not inflammable Class 3: highly inflammable

115.5 1642 133 271

263.43 474. 18

0.097 3.44 98.9 210

0.989 4.84 B2

nil nil

(65°F)


S' IMPACT ON ENVIRONMENT

refri~erants in use for the past several decades have impact on the environment, in two ~um a•uf Global wanning (greenhouse effect) .

.& :ariant of oxygen, the ozone molecule having three atoms of oxygen while the oxygen made up of two atoms (03 and 0 2). An ozone layer surrounds the earth's stratosphere,

11 kilometers above the surface of earth at the equator and 5 to 6 kilometers up at the ozone la\ er absorbs sun's ultra-violet (UV) rays substantially, thus acting as a protective

life on earth from the harmful effects of high concentration of UV radiation. If depleozone layer occurs in the stratosphere, UV radiation to the earth will increase. Conse

can be health hazards such as, skin cancer, severe infectious diseases, environmental • -:lobal warming, melting of polar ice caps, rising of sea level, droughts etc.-a matter

---.-<"r .... ,..m for life on earth.

COO' muously being produced and destroyed in a natural cycle, but in this cycle the _______ __. .•• t <if ozone remains essentially stable. However the gases, chlorine and bromine, react

ua. ozone to oxygen and can destroy it much faster than the natural cycle of its creation, ozone depletion in the stratosphere. Chlorine is present in many compounds in regular

".>contain bromine. c:nh l qsos and until a few years ago, most of the refrigerants in use with mechanical

re ion systems were the Chlorofluorocarbons (CFC) and Hydro chloro Ouoro car. These compounds contain the ozone depleting chlorine.

lhe:.e compounds (CFCs & HCFCs) are heavier than air, some eventually migrate to the once they are released to the atmosphere. The time taken to reach the stratosphere may h \ery long (may be a decade or much more). But the fact remains that, being very

===ll~nds (among the most stable compounds developed) they do reach the stratosphere, s rong ultra-violet radiation breaks the compound and converts to chlorine monoxide,

ozone at a very rapid rate. It is estimated that one chlorine atom can destroy 100,000 _Jes. Higher the chlorine content of a compound longer will be its atmospheric life, so

ill be its impact on the ozone layer. CFCs have more chlorine content than HCFCs; so hinher potential for ozone depletion. It is estimated that CFCs contribute nearly 70% of

-~===~ozc ne depleting chemicals in the atmosphere. teed to extinguish fire) are compounds containing bromine, fluorine, and carbon. Like

break down in the stratosphere releasing bromine. Bromine is even more destructive la\er than chlorine.

eia111eDepletion Potential (ODP) The potentials of compounds for ozone depletion, obviously, ing to their chlorine/bromine content and the period of their stability in the atmosphere.

;;:cential known as 'Ozone Depletion Potential'. (ODP) is a factor based on the percentage weight e in a compound and its lifetime (stability) in the atmosphere.

".!the refrigerants, (CFC) R 11, with 3 atoms of chlorine in a molecule, has the maximum and its ODP is fixed at 'one'. ODP of all others are relative to that of R 11. e.g. ODP of

78 Baste Rejrigeralion and Air Con.dttioning

R 22 (a HCFC) is 0.05, so its destruction potential is only 5% that ofR I I.This is because it has l chlorine content( one chlorine atom per molecule) and also the hydrogen in it decreases its stabilt making it difficult to last long enough in the atmosphere to reach the ozone layer, while R 11 with hydrogen content has very high stability and so longer atmospheric lifetime. Hydro Fluoro Car (HFC) have no chlorine content, so ODP is zero. CFCs have the highest ODP, HCFCs have comparr tively less and HFCs (no chlorine content) have zero ODP.

Greenhouse Effect-Global Warming Potential (GWP)

Some of the heat absorbed by the earth from the sun is reflected back to the space thus notallowin the earth temperature to rise above an average level. A film of gases envelops the earth's atmosphere. Certain of these gases trap some of the reflected heat preventing it to reflect back to space, there~ increasing the earth's average temperature leading to 'Global Wanning'. This is known as thegre~ house effect and so the gases that trap the heat are known as greenhouse gases [green house: a room house of glass walls and roof for the cultivation of plants at controlled (high/tropical) temperatu and (high) humidity conditions]. Obviously higher concentration of the greenhouse gases in atmosphere will lead to a warmer earth and consequent harmful ecological changes.

The impact of the emission of the various greenhouse gases on the climate varies according their atmospheric life. The impact of the various gases is compared with that ofC02, which is one the main greenhouse gases in the atmosphere. So an index relative to the impact ofC02 is used is known as the Global Wanning Potential (GWP). The GWPofC02 is fixed as 'one'. GWPs have a ti component, since the atmospheric lifetime of the greenhouse gases varies. So the time compone spreads from 20 to I 00 years and written as GWP20 (for 20 years), GWP100 (I 00 years lifetime) etc.. For example, emission of one kgofR 134a is roughly equivalent to emission of 1300 kgofC02 in I years, so GWP 100 ofR 134a is 1300. Thus the Global Warming Potential (GWP) ofa greenhouse is an index of its ability, relative to that of C02, to trap heat radiated from earth to space.

The main greenhouse gases in the atmosphere are cabondioxide (C02}, methane and nitro oxide. All halogenated refrigerants (CFCs, HCFCs and the chlorine free HFCs too) are found to greenhouse gases. HCFCs (e.g. R 22) and HFCs (such as R l 34a) have shorter atmospheric life th CFCs. They are destroyed in the lower atmosphere itself by chemical reaction and so they have low ODP and GWP values. However, though the GWP values of these are lower than those of the CFU. their emissions do contribute to global warming and their influence is much greater in compariS09 with C02 (their GWP 100 values ranging between 1000 and 3500).

C02 (one of the main greenhouse gases) is generated and emitted to the atmosphere by the fuel m generating energy in power plants. Thus any equipment or gadget using energy (in the generation which C02 is released to the atmosphere) for its operation, contributes to global warming, we caa say, indirectly.

The average C02 release from an electrical power plant (based on fossil fuel) is estimated to be 0.6 kg per unit (kWh) of electrical energy produced (in developed countries). The refrigeration and air conditioning system contributes to global warming in two ways. (1) Thr

direct impact is by the escape of refrigerant gas to the atmosphere from the system, while servicing and also due to leak; (2) Indirectly by way of consumption of energy (in the generation of which C~ is released) for its operation.

Thus the toLal effect on global warming, known as, Total Environmental Wanning Index-TEW!, is

the sum of the direct and indirect effects.

e. nd nitrous

found to be ric life thaa have lower fthe CFCs.

·-TEW!, is


comumption of refrigeration and air conditioning systems is reckoned to be about the total electrical consumption. So a significant greenhouse effect occurs during their e_ Thi- indirect effect on power consumption is found to be comparatively larger than

dfea due to escape of the refrigerants to the atmosphere while servicing and through

(i) to minimize the effect of indirect warming, the refrigeration and air conditioning be enerm efficient (low BhpfrR), i.e. high efficiency compressor and ancillaries. (ii)

<&ea warming, the refrigeration system has to be leak tight and also calls for very careful ~fri .... erants.

:Jemenl of systems' energy efficiency and maintaining it through the life of the system, role m reducing the greenhouse effect

.. _.-:;w and Control Measures on Ozone Depletion-Montreal Protocol, London and •-•cg•n Amendments Since the effect of CFCs, H CFCs etc on the Ozone layer is a global -~--ahas been a live issue in the international forums. In the international conference held in

7, the famous 'Montreal Protocol' (an international treaty) was signed by number of "m:;.=::;.--noolbl} the developed countries-followed by amendments/revisions, agreed to at the

Copenhagen conferences in 1990 and 1992 respectively. treal protocol and the subsequent amendments/revisions call for, as a first step freezing

_..._ ........ ..,n levels of all 'Ozone Depleting Substances' (ODS). This is to be followed by complete their production. Ultimately all these substances are to be completely phased out. A

--~-. Table 9.4 applicable to the developed nations with a different time frame for the develop:==:::=::s.. has also been agreed upon.

••

Developed nations

100% phase out by January 1996

production frozen at 1989 level by Jan 1996 35% cut by 2005,65% cut by 2010 90% cut by 2015,99.5% by 2020 100% phase out by 2030

complete cessation of production by

Developing nations

production frozen at 1996 level by Jan '99;100% phase out by Jan 2010*

additional time limit up to 2040 for 100% phase out

Jan 1994 Indian industry :production of CFCs frozen at mean 1996 level from July 1999, I <>%consumption cue by end

b\ 2005; 85% by 2007; 10~ by end 2009, OEMs (own equipmem manufacturers) to effect 100% phase out

all countries have similar strict comrols no import (and also export) of CFCs or CFC containing equipment possible. Though there are no such controls as yet on HCFCs, better performing/more efficient HFC systems

me competitive. the HCFC, R 22 in new equipment is being completely prohibited (by the respective authorities of each in Germany from Jan 2000, in Sweden since 1998 and in olher European union countries, expected to

effective from Jan 2000. R 141 b(a HCFC)-a substitute for R 11 for foam blowing of thermal insulation-is phased out in USA by 2004 [ODP - 0.1 l and GWP20 - 1800].

80 Basic Refrigeration and Air Conditioning

Production/use of HFCs (R 32, 125, l 34a, l 43a and their blends- R 404A, 407 & 410) is not regulated by the Montreal Protocol, but may be regulated by individual countries.

Control on Greenhouse Effect- KYOTO Agreement Since many of the refrigerants are found to be greenhouse gases also, TEWI (total equivalent warming impact i.e. direct + indirect warming impact), in addition to ODP, has become an important criteria for developing environmentally safe alternate refrigerants. This aspect formed part of the KYOTO summit held in Dec 1997.

The KYOTO summit agreed that by 2010, greenhouse gas emissions from industrialized countries be reduced to a level below that of 1990. The gases covered are: C02, nitrous oxide, methane (CH4), chloro-fluoro-carbon, sulphur-hexa-fluoride and hydro-fluoro-carbons (HCFCs). The agreement envisages developed countries to finance emission reduction projects in developing countries and receive credit for it. As of now, the controls are applicable only to developed countries. Enforcement of the controls and as how to penalize defaulting countries has been postponed till the next meeting.

The Montreal protocol was signed by number ofnations notably developed countries. Some of the developing countries, capable of (and which are) producing CFCs in large quantities, like India, China etc, refrained from signing the protocol, because of their reservations on the economic feasibility and back-up for developing and producing substitute refrigerants and consequent design changes in equipments. Equally important was their concern about the technology transfer from western nations for the manufacture of the substitutes in the developing countries. Subsequently in the London conference, held in June 1990,attended by about 100 nations, India indicated its willingness to sign the Montreal Protocol, since the developed countries agreed to set up a global fund to help the developing countries ease the burden of switching over to environmentally safe alternate refrigerants. An agreement on the important issue of technology transfer for the manufacture of the alternates was reached.

Corrective Steps Steps in correcting the harmful effects of chlorine on the environment obviously are:

- first to reduce the consumption of refrigerants with high chlorine content and to use alternatives of less chlorine content, followed by

- (or concurrently) a cut on the use of refrigerants with less chlorine content also and use chlorine free substitutes

- in the long-term, use only chlorine/halogen free alternates, with minimum of GWP.

The threat of global warming has the chlorine free HFCs also included in the list of gases to be regulated The control on the greenhouse gases (Kyoto protocol) has changed the ACR industry even more fundamentally than the Montreal protocol.

Chlorine free single substitute refrigerants appear to be limited to a few such as, R 134a, R 600a and the oldest refrigerant of all, ammonia. Other alternatives, presently available, are all 'refrigerant blends'.

REFRIGERANT BLENDS

A blend is a mixture of two or more refrigerants in various proportions. Blends were earlier developed to combine the good properties of its constituents. A typical example is R 502 (a blend of R 22 and R 115) -its discharge gas temperature is lower than thatofR 12,so, much less than thatofR 22 and has near about the same cycle values as R 22.

is not regu-

t:;are found let warming ientally safe ; ~countries lane (CH4), agreement ntries and forcement ·tmeeting.

me of the like India, ( 1mic feasient design

sfer from quently in

red its willlobal fund

stryeven

a, R600a ··frigeranl

ier develd ofR 22 t ofR 22

Refrigerant.s and Brines

'.gerant blends now developed are as alternates for refrigerants in existing plants and also ~ ones. They have properties similar to the refrigerants they replace and have zero ODP and (;1,\·P. Most of the first category contain HCFC as the main constituent to replace the CFCs in

., plants (immediate step to minimize ozone depletion). Others are chlorine free long~bstitutes. These blends have been and still undergoing extensive trials and some have been nl commercially. nds are of two types, auolr<>jlic and uolropic. Azeotropic blends behave as single substance

_erants in the evaporating ('liquid to vapour phase' change) and condensing ('vapour to liquid ·change) processes. That is, at a pressure, the evaporating (boiling) and the condensing tem

'\.res are the same.or in other words, the saturation temperatures of liquid and vapour at a ' re are same e.g. these temperatures of the azeotropic blend R 502 at a pressure of 138 psig are a t 70°F.

hotropic Blends

...... zeotropic blends, however, at constant pressure, the phase changes (boiling and condensing) .xcur at different temperatures, that is, the saturation temperatures of liquid and vapour (both at the

pressure) are different. The difference between the two is known as the 'temperature glide' e means 'to pass gradually'). Table 9.5 shows a few excerpts from the saturation pressure-temture charts of'liquid' and 'vapour' of the zeotropic blend R 401A, to high light the different

!:!mperatures at which the phase changes occur, at constant pressure .

• T.ble9.5 )

P· c<>sure (psig) 3.4 7 14 2 1.5 101 145 159 a :idensing. point °F -7.6 0.5 13. l 23.9 88.7 104 116.6

tling point °F -18.4 -10.3 2.3 13. l 79.7 95 107.6

Example 9.1

- At a suction pressure of 14psig,the saturation (boiling) temperature of liquid is 2.3 °F and the reference point for superheating is 13. 1°F [i.e. the saturation temperature of vapour at the end of the liquid to vapour phase change (boiling/evaporating)].

- At a condensing pressure of 145 psig the saturation (condensing) temperature of vapour is 104°F and the reference point for liquid sub-cooling [i.e.the saturation temperature of the liquid at the end of the vapour to liquid phase change (condensing) is 95°F].

Thus vapour and liquid 'temperature-pressure' charts are essential to determine suction gas - ;>erheat and to assess the liquid sub-cooling available at the start of the liquid line.

Some important points to be noted in handling systems with zeotropic blend refrigerants:

,. Possibility of a change in the concentration of the constituents, when leakage occurs in the system, Leakage in the pure liquid or vapour state may not be critical. But in the phase change areas, namely, after the throttling device in the evaporator and the condenser, the shift can be quite significant; so only brazed joints to be used to minimize leakage possibilities.

~ Charge the system only with liquid refrigerant; if charged in the vapour state, shift in the concentration of the constituents in the system can occur.

82 I Basic Refrigeration and Air Conditioning

)> Some blends have one flammable constituent and hence entry of air into the system should be prevented.

)> Blends with wide temperature glide is not suitable for flooded evaporator systems. )> Special charging hoses with nylon core should be used. )> Adopt deep vacuum procedures.

Alternate Refrigerants

Following is an approximate summary of commercially adopted alternates and potentials under active consideration (single substances and blends):

Transitional (first step)-(HCFC)- single : R 123; R 22 Partly chlorinated (all R 22 based) blends : R 402A; R 403 B;R 408A Mediumlermandlongtenn R401A; R401B; R409NB; R413A

(i) Chlorine free : HFC single: R l 34a; R 125 blends : R404A; R507A; R410A; R407C; R508B

(ii) Halogen free : single: R 717, R 600a, R 290, blends : R 290/R 600a

Above data is not exhaustive. Investigations/tests are continuing for new alternatives.

R 123 ( CHCl2CFJ); a HCFC; ODP-0.02; GWP100-93, AEL- 50 ppm Some manufacturers have adopted R 123, a HCFC, as a replacement for the CFC, R 11, for their centrifugal. Like R 11,it is a low-pressure refrigerant. It is compatible with most of the materials and mineral oil used in R 11 machines, except motor winding and gasket materials. Physical-thermodynamic properties are similar to R 11 and has same operating efficiency.

It is classified as carcinogen (long time exposure to which can cause cancer) category 3 and maximum recommended 'Acceptable Exposure Limit' (AEL) is 50ppm. This calls for caution against long term exposure and good plant room ventilation.

Because of this negative aspect, there is international pressure for banning its use immediately. At the same time there is also the strong stand against its immediate phase out or even along with other HCFCs. The arguments in its favour are:

)> it has comparatively a short atmospheric life time of 17 months (against 12 years for R 22, 14.6 years for R l 34a) and so it is not going to make it to the stratosphere;

)> being a low pressure refrigerant and with an efficient purge recovery system, the emissions can be contained at very low levels. Further, with positive plant room ventilation, exposure level in equipment room can be held at a very low level.

)> high refrigeration cycle efficiency combined with very low, or possibly, 0 emission level, the indirect and direct greenhouse effects or TEWI are quite low.

R 123 can be a retrofit refrigerant for R 11 centrifugal system. Since gaskets are to be changed and motor windings too in hermetic/semi-hermetic systems, the retrofit however cannot be just a simple straight change over.

R 22 (CHCIFJ; a HCFC; ODP-0.05; GWP100 -1700,AEL-1000 ppm R22 has been (still is) the widely used HCFC refrigerant. Here it is analyzed as a transitional replacement for CFCs.

tern should be

. ms.

tentials under

BB

es.

facturers have ·keR 11,itisa used in R 11 roperties are

tegory 3 and ution against

mediately. At ng with other

for R 22, 14.6

emissions can sure level in

ion level, the

changed and JUSt a simple

n (still is) the

fFCs.


__ a n be an alternative to R 12 and R 502, but with limitations, such as:

,.. ~ has over 40% more refrigerating capacity than R 12. So the compressor size will have to be er, to match with the system capacity with the R 12 compressor .

,, compressor displacement required per TR with R22 is lower than that of R 12. So the velocity R 22 in refrigerant lines, evaporator, condenser etc of the R 12 system will be lower and this

c:r.a lead to oil return problems. , ause of its higher pressure and discharge gas temperature levels (than R 12), it is not

i•...:.ble for transport refrigeration-such as cars, buses, train, trucks etc. "" the- higher discharge gas temperature also becomes a draw back in low temperature applica

oo~. Due to higher compression ratios associated with these applications, d ischarge gas tempc rature is naturally higher; more so with R 22 and consequent possibilities oflubricating oil .u J refrigerant breakdown, system turning acidic, etc.

"" d- :- •tiling device needs changing.

•usly R 22 is not a straight replacement for R 12.

34o (a HFC); CH2'CF3 ; ODP- O; GWP-1300 , AEL- 1000 ppm R l34a is chlorine free and · ·.'le very few single substance replacement refrigerants. It is mainly a substitute for R 12 and ••ted range for R 22. It is also used as a component for a variety ofblends. Its toxicity is very

eptable Exposure Limit (AEL) is 1000 ppm- same as ofR 12. harge gas temperature [at -l5°C (5°F) evaporating and 30°C (86°F) condensing] for R l34a i-. between the values for R 12 (38.3°C) and R 22.(53.3°C).

Thermodynamic properties are similar to that of R 12; refrigeration capacity, energy requirepressure-temperature characteristics are comparable in air conditioning and medium temre refrigeration applications However, in applications with lower evaporating temperatures it

. .:>wer refrigeration capacity. Compared to R 12 system, the capacity will be about 90% and 82% ~;:>orating temperatures of-20°C(-4°F) and -30°C(-22°F), respectively, while the corresponding

e requirements will be about 89% and 83%, COP being practically the same. Up to evaporator ==perature of -10°C(l4°F) same compressor si1e as for R 12 system is satisfactory and for lower

perature applications larger compressor size is required. R 134a is not miscible with mineral oils. So synthetic oil, Polyolesters (POE) or Polyalkylene glycol

:\G has to be used. PAG oils are used mainly in car air conditioning systems. Both these oils ~ t.1ghly hygroscopic. So special larger sited R 134a drier (molenilar sieve matched to the £:Jal er molecule size of R l 34a) has to be used (see: Lubricant-refrigerant compatibility in Chapter on

,1/ion). ... r ecial refrigerant hoses are required for R l 34a (in Car/transport air conditioning). r r retrofitting (converting) an existing refrigeration system with R 12- mineral oil pair to R 134a

olester oil pair, it is enough to drain the mineral oil and R 12 from the system. The system e\er has to be clean, to avoid reaction of oil, refrigerant and moisture with remnant contamit:. in the system. So before charging R l 34a and polyolester oil into the system, it is always better

ll:l horoughly evacuate the system for removal of remnant traces of chlorine compound and for deep hvdration. As mentioned above special R l 34a drier has to be provided and moisture indicator is

a "":lUSt. .\s R 22 is progressively phased out, R 134a can be a substitute for it, but to a limited range of

applications. A larger compressor is needed for R l 34a as it requires higher compressor displacement


per TR than R 22 [at-15°C (5°F) evaporator & 30°C (86°F) condensing, R 134a needs 0.17 m3 'm (6.02 cfm) and for R 22, it is O. lm3/m(3.55cfm)].

Centrifugal with R l 34a as the refrigerant (its impeller and tip speed different from the R : _ design), gives same or marginally better capacity than the centrifugal with R 12.

R 12 centrifugal system can be retrofitted with R 134a, (with POE oil). There will be 25 to 33<K reduction in capacity.

Some of the important measures to be taken during installation ofR 134a systems are:

}i> thorough cleaning of pipes/components, }i> brazing/soldering only with a nitrogen bias in the pipes, ).. provide good suction filter on compressor, particularly for steel pipe jobs, }i> use of only dry nitrogen for pressure/leak testing, }i> charge/add oil only from originally sealed containers, }i> while servicing, every time the system is opened utmost care is to be taken to prevent ingression

of moisture and carry out evacuation.

R 125; a HFC (CF3CHF,); ODP-O;GWP100 - 3200,AEL- 1000 ppm This is used asacomponem for blends, though it can be, to a limited range, a replacement for R 502 and R 22.0nly ester oils are compatible.

The plus points are: is nonflammable; low isentropic compression exponent (so lower discharge gas temperature); high volumetric efficiency in reciprocating compressors, requires high mass flo"' rate - advantageous for suction gas cooling.

The disadvantages: relatively high GWP; steep pressure curve (so higher compression ratios); lo" critical temperature of 66°C; COP drops, as the condensing temperature approaches the critical temperature. These negative characteristics render it suitable only to a limited range of applications. not suitable for air-cooled applications. In cooler temperate zones, relatively efficient operation in low temperature applications can be achieved, particularly with water-cooled systems.

(Table9.6 ) HCFC- blends R 402A R403B R 408A Only short term

Constituents - R 22/125/290 R 22/218/290 R 22/143a/125 service ODP 0.02 0.03 0.026 replacements GWP100 2570 3680 3050 for R 502 Temp.glide °C 2 2.4 0.6 AEL (ppm) - 1000 1000 IOOO

R 22, though low in proportion, makes these blends, ozone depletion substances and also their GWP are comparatively high. Hence they are only short-term replacements.

The high discharge gas temperature associated with R 22 is reduced by the addition of chlorine free R 125 and 143a and also due to the low isentropiccompression exponent ofR 125, R 143a and R 218. All the blends have great similarity to R 502.and are miscible with mineral oils. Synthetics also can be used, as R 22 is present.

Components of the R 502 system need not be changed on conversion with these blends. However the system should be quite clean, to avoid reaction and consequent poor chemical stability. Liberall'

s 0.17 m3 /m

re:

nt ingression

a component · ester oils are

) slwrt term

service placements or R 502

nd also their

n of chlorine ·, R 143a and

. Synthetics

ds. However lity. Liberally

Refrigerants and Brines I 85

J suction gas filter and liquid line drier should be provided and an oil change after 100 hours ieration.

- le9.7)

HCFC blends HFC blend

R 40JA/B* R 409A!B* R 413A Sero ice

,tituents R 22/l24/ l52a R 22/l24/142b R 218/ l 34a/600a replacement 0.03 0.05 0 for R 12

· P100 1080 1440 1770 .,... .p.glide °C 6.4/6.0 8. l/7.2 6.9

- -ppm 1000 1000 1000

• · IA & 40 I B have same components but only % of constituents varies slightly. Similarly in R 409A & _ also].

me compressors in existing R 12 systems (particularly older models and in systems of doubtful _mess) may not be suitable for straight conversion to R 134a. Also it may not be that easy to drain il from hermetics and carry out repeated oil flushing necessary for the R l 34a conversion. For cases, these are available as straight Service (transitional) replacements, instead ofR 134a.

'.neral oils are compatible with R 40 lA,R 401 B and R 409NB. Alkyl- benzene or POE oils also It! used. Alkyl benzene does not readily absorb moisture and so can be handled in the same way

-neral oils · -l l 3A is compatible with mineral oils. Ester oils also can be used. This is particularly suitable for

cstic refrigerators, car air conditioning, refrigerated transport, cold stores etc ~ all the cases, for conversion, the oil will have to be drained and after 100 hours of running, oil .ng a couple of times is recommended; new liberally sized liquid line drier has to be provided;

C n conversion the expansion valve will need fine adjustment. These being azeotropic blends, temperature glide-so expansion valve adjustment has to be done carefully, using vapour tables. under Refrigerant Blends in this chapter) 22 being the main component in the HCFC blends, the discharge temperature can go high

..cularly in low temperature applications. Therefore the application limit of the compressor er conversion should be checked before carrying out the conversion.

R 404A R 507A

C nstituents R 125/ 143a/134a R 125/143a long term DP 0 0 alternative

C ".\'P 100 3750 3800 for R 502 T .. :np.glide °C 0.7 0 .IL-ppm 1000 1000

:-he component R 143a is of flammable category. However in combination with R 125, the flam~ility is effectively suppressed in both the blends.

861 Basic Refrigeration and __ A_ir_Co_nd_ i_tio_ n_ing __________________ _ _ _

All the components have low 'isentropic compression exponent' . Hence the blends have dischar):' gas temperature, even lower than that ofR 502. Thus these blends are suitable for low temperatu applications, that too in single stage compression.

R 143a and R 125 have same boiling point (-48°C) and the proportion of the third component 134a in R 404 being very low (4%) its temperature glide is less than l °C. Thus R 404 is a 'ne .. azeotrope' and acts practically as a single substance.

With only the firsl two components, obviously, R 507 A has azeotropic characteristic (no temper. ture glide). So this is even better than R 404A as an alternative to R 502.

These blends resemble R 502 in capacity and COP. Both are compatible with the materials, exce~ mineral oil used in R 502 system. POE oil is used.

The relatively high global warming potential (GWP100- 3750 & 3800) is a disadvantage, but bette compared to 5600 of R 502.

In converting existing R 502 systems with these blends, the mineral oil in the system has to bot. flushed out with POE oil. The usual precautions as mentioned earlier in handling POE oils have t be taken, including provision of liberally sized drier.

R407C- Blend of R 32/125/134a; ODP-0; GWP100-1610, Temp. Glide 7.4°CAEL-1000 ppm, Short-term Replacement for R 22 Its properties are very much similar to that ofR 22,in termof pressure, mass flow rate, vapour density and refrigeration capacity- compatible with the material• used in R 22 systems, but not with mineral oils. POE lubricants are used.

I ts wide temperature glide, however, is a big disadvantage. Applications are very much limited tc air-conditioning systems and to a narrow range of mediu m temperature refrigeration. In low temperature applications, capacity and COP drop down significantly; so not suitable. It is not recommended for use with flooded evaporators, as there will be a significant shift in concentration and layer formation in the evaporator. Thus its scope ofapplication is very much limited and so canno1 be considered as alternate replacement.

R 410A-HFC Blend of R 32/125;0DP-0; GWP100-1800, Glide < 0.2 °C; AEL-1000 ppm Alternative for R22 and Potential Substitute for R 13B 1 It is a near azeotropic HFC blend and is compatible with materials used in R 22 systems, except mineral oil. POE oil has to be used. Ir comparison with R 22, it gives about 40% more capacity and about 92% of COP. The temperature glide (less than 0.2°C) is very low- a near azeotropic blend, behaves practically like a single substance refrigerant.

It is also considered as a potential substitute for R 13B 1 in low temperature applications, particularly in cascade systems-shows less capacity below -60°C.

Against these very advantageous characteristics, there are two distinct disadvantages, viz: (i) relatively low critical temperature of73°C(l63°F), limits the scope ofapplication witl1 respect t

condensing temperature and (ii) pressures much higher than that of R 22, necessitating, in many o the applications, design changes in compressors, heat exchangers, piping, flexible hoses etc, to suit the higher operating pressures.

Saturation pressure at R 410A R22

43°C(l09°F) 25.5kg/cm2 (362 psig) 15.7kg/cm2 (223 psig)

37.8°C(l00°F) 23.6 kglcm2(336psig) 13.8 kg/cm2 (196 psig)

Perhaps it may be long b£jore suitable equipments are available. Obviously none of these altematives(R 407C,R 410A,R 134a) can replace R 22 in all respects.

ave discharge temperature

component R 404 is a 'near

no tempera-

terials, except

ge, but better

rem has to be E oils have to

-1000ppm, R 22,in terms he materials

ch limited to . In low tem

not recomntration and ld so cannot

-1000 ppm FCblendand

be used. In

·ons, particu-

, viz: ·ith respect to g,inmanyof

--es etc, to suit

F) 2(336psig) 2 (196 psig)

a ltematives( R

Refrigerants and B rines 87

~e some European countries are for earlier phase out ofR 22,other developed countries like J a?an, Canada etc and many of the developing countries are for the phase out dates stipulated

p rotocols. The scheduled phase out date (for R 22) is still about 30 years away and it may be le for some more years after the phase out dates by way ofreclamation/ recovery. So R 22 can

pected to continue to play a vital role in the ACR industry.

5C8B- HFC Blend of R 23and116- ODP-0, Temp. Glide 0°C, AEL- 1000 ppm This is as a long term substitute for R 13, R 503 and R 23 in very low temperature applications, such de refrigeration, environmental chambers, etc. It is a good match for R 503, delivers higher

t' than R 13. It is a retrofit for R 23-gives better energy efficiency. POE oil has to be used with usual precautions mentioned earlier.

er Applications of CFCs

Cs ere also used for a wide spectrum of other applications, like: as propellant for aerosols, foam i'In"T agents for insulation/packaging boards, solvent for the electronic industry, stabilizers in the uction of medicines, in scientific studies, etc. Environmentally safe substitutes such as butane,

e have been established for these applications.

OGEN FREE REFRIGERANTS

i 7- Ammonia -NH3- inorganic compound - ODP:O; GWP:O; AEL: SOppm A halogen rubstance, with zero ODP and zero GWP. It is not a manmade compound, but of natural

rr-t-.a.,,,nces-nitrogen and hydrogen. Ammonia is the first successfully used refrigerant in USA, pe etc, since the last century ( 1870-1880). Therefore it is not a new or a substitute refrigerant

!has been in use mainly in industrial, food processing and some cold store applications. Ammomcreasingly lost its significance particularly in the air conditioning sector, with the advent of

refrigerants in 1930s, as CFCs have practically no toxicity and flammability, no reaction with and materials used in the machinery, facilitate use of the compact-energy efficient hermetics/

e rmetics and automatic oil return. The increasing environmental concern over ozone deple-a."ld global warming, has revived the importance of ammonia as a refrigerant, in the developed

nes also. Ammonia has very positive features; at the same time has some strong negative aspects as well,

had restricted its much wider use in refrigeration-air conditioning. Bt.t for its negative points (considering only its thermodynamic and thermo-physical properties)

a:most the nearly perfect refrigerant. Incidentally it is the earliest refrigerant to be manufacin India; it is a by-product in fertilizer manufacturing.

antages

, Environment friendly: its atmospheric lifetime is only days to weeks and thus no ozone depletion and direct global warming potentials.

, The compressor displacement required per TR is much less, compared to other CFC, HCFC, HFC and Hydrocarbon refrigerants now in use (refer Table 9.3). Thus for the same capacity, compressor size will be smaller than for other refrigerants.

, BhpfTR is less than that of the other refrigerants (CFC, HCFC, HFC, etc.) in use. , Because of the lower power requirement, the indirect global warming potential is less.


(Table 9.9 ) Alternate Refrigerants

substitute Alternate Chemical Boiling Compatible ODP GWP Temp. AEL for and type composition pomtC lubncants glide c ppm

R 11 R 123 dichloroLrifluoro- 27.84 MO 0.02 93 0 50 CFC HCFC ethane

Rl l/R 12 R 134a tetrafluoro- -26.5 POE 0 1300 0 1000 CFCs HFC ethane

Blends

R 12 R401A R 22/152a/124 -33 AB/POE 0.03 1080 6.4 1000 CFC HCFC 53/13/34%

R 409A R 22/124/142b -34 MO/AB/POE 0.05 1440 8.1 1000 HCFC 60/25/15%

R 413A R 2 l 8/ l 34a/600a -35 MO/AB/POE 0 1770 6.9 1000 HFC

R 22 R407C R 32/125/134a -43.7 POE 0 1610 7.4 1000 HCFC HFC 23/25/52%

R 410A R 321125 -52.7 POE 0 1800 < 0.2 1000 HFC 50150%

R 502 R402A R 22/ 125/290 -47.4 MO/AB 0.02 2570 2 1000 CFC HCFC 38/60/2%

R 4038 R 22/290/218 -50.6 MO/AB 0.03 3680 2.4 1000 HCFC 56/5/39%

R 404A R l 25/l 43a/ l 34a -46.5 POE 0 3750 0.7 1000 HCFC 44/52/4%

R 408A R 22/125/l 43a -44.5 MO/AB/POE 0.026 3050 0.6 1000 HCFC 47/7146%

R 507A R 125/ 143a -46.5 POE 0 3800 0 1000 HFC 50/50%

R 13,503 & R 5088 R 23/l 16 -88 POE 0 n/a 0 1000

R 23-CFC HFC

MO- mineral oil; AB- alkylbenzene POE- polyolesters AEL-'Acceptable Exposure Limit' in ppm •composition of blends

,,. Good heat transfer coefficients (approximately four times that ofR 22) results in smaller (more compact) evaporator, condenser, heat exchangers; so reduction in capital cost of the system. Further the operating temperature differences (of condenser and evaporator) can correspond-ingl} be changed; for the compressor to operate at higher evaporator and lower condensing temperatures, thereby improving COP of the system.

Temp. AEL glukC ppm

0 50

0 1000

6.4 1000

8. l 1000

6.9 1000

7.4 1000

< 0.2 1000

2 1000

2.4 1000

0.7 1000

0.6 1000

0 1000

0 1000

smaller (more of the system.

corresponder condensing


, friction losses are very low. So requires comparatively smaller diameter refrigerant connecting pipe of the refrigeration plant; so lower material and installation costs.

, There is no necessity of double suction/discharge gas risers for oil return during partial load operation, as ammonia is not miscible with oil.

,,.. Thi~ is the cheapest refrigerant- incomparably low in cost and a\'ailable worldwide. ,, :here 'plate heat exchangers are used for condenser and evaporator, the refrigerant charge

ammonia) is substantially reduced, thus chances ofleakage is minimized and initial and maintenance, Costs come down. ~2 1s many times costlier than ammonia. As only about 10% of ammonia produced world

•m.le is used for refrigeration, its price is not likely to rise, while the new refrigerants may ho ·me still costlier, as they are produced only for refrigeration duty.

r dvantages ,,. Th most serious drawback, the importance of which cannot be minimized, is its high toxicity

.and ll is dangerous in excessively high concentrations. However its very unbearable pungent self-alarming smell (ammonia is its own warning agent) will drive away people even at nond.angerous concentrations of about 5 ppm, The bad effects, like, irritation, panic reaction, cot.~hing, cramps, suffocation, etc. are felt only, as its concentration in air exceeds 250 ppm.

,. Ith also classified as oflowe1· flammability. (an.mania-air mixtures are flammable, but only within a relatrvely narrow range of concenlral1on of l~ 25% by volume in air]. However, as it requires high intensity of ignition source of around 6.: ,- C, possibilities of explosion are very remote or non-existent, also it cannot sustain comb..~uon by itself, but need an outside source of fuel. Hence ammonia is not a fire and explosion hazard. It is significant to note that ammonia installations do not require special frame proof ele ·meals.

e" er, it is advisable to bleed nitrogen through the system, when using acetylene flame during t" an ammonia system.

,,.. Be a use of these negative factors, it is generally not used for comfort, pharmaceutical applications, etc. Ammonia plants are usually manned by experienced personnel.

,,. Cc: mparatively high 'isentropic exponent' (NH3-l .3 l ,R 22-1.18,R 12-1 .14), resulting in higher dh:harge gas temperature and consequent increase in valve reeds and oil temperatures. This c;,'.ls for good thermal stability of the lubricant and steps to limit condensing temperature. So range of single stage compression is restricted [generally not for evaporating temperature below(-) 10°C] To limit the condensing (and so the discharge gas temperature), only water cc-c>led systems are adopted - so air cooled application is not favourable at all and reciprocating ccmpressors should have watercooled cylinder heads and oil cooler.

Hm' ever, with screw compressor, it has been possible to have small air cooled system, as efficient cooler is a must with this compressor and discharge gas temperature does not exceed safe limits the ">Crew compressor.

, .\mmonia-oil miscibility being extremely poor, oil does not return automatically to the compressor, but accumulates at the bottom of the evaporator. It has to be drained periodically from

011 legs provided in the evaporator and oil has to be replenished in the compressor. Special hook-up arrangements can be provided for the automatic draining- transport of the oil from the evaporator to the compressor; but manual oil retrieval is generally adopted. Oil separator

90 Basic Refrigeration and.Air Conditioning

is usually provided to minimize oil carry over to the system, thus reducing the frequency of the oil draining/replenishment work. The brighter aspect of the oil immiscibility (as indicated under 'advantages') is the redundancy of double risers; this means, less pressure drop in the refrigerant lines.

)> Reacts with copper and copper alloys and is incompatible with certain plastics. Hence copper and copper based bearing materials cannot be used in the compressor and in the equipment in the system and the refrigerant lines can be only of carbon steel.

)> Totally soluble in water and vice versa - a water presence of even 5% would not even be detectable in a large ammonia refrigeration system by the indications of pressures and temperatures. Ammonia, oxygen, and moisture react forming harmful acids which attacks the materials in the system, causes degradation oflubricant, forming sludge, thus ruining the system. Hence the system has to be evacuated/dehydrated to a deep vacuum before charging the system with refrigerant and the system has to be kept clean.

)> Has high electrical conductivity and presence of moisture increases the conductivity. Because of the high conductivity, incompatibility with materials (copper and insulation materials) and solubility in water, hermetic compressor, with copper (motor) winding and insulation materials, is not possible with ammonia. Oflate, special hermetic has been developed, to be used with ammonia

)> It is not economical to have ammonia centrifugal compressor. Multi-staging required for the temperature lift (compression) makes it expensive for a light gas like ammonia.

Ammonia has the unique distinction of being used as a refrigerant both in vapour compression and vapour absorption systems of refrigeration.

Ammonia leak is detected by the use of burning sulphur stick, which gives a dense white smoke in the presence of ammonia. Litmus paper also can be used. As ammonia is soluble in water, soap sud test cannot be adopted.

The many advantages of ammonia as a refrigerant are evidently very solid. So it should be endeavoured to find ways to minimize the disadvantages. In this context, ASHRAE issued a policy statement on ammonia refrigerant in 1991, which says that the continued use of ammonia is necessary for food preservation and air conditioning with proper risk management. Further, as per the reclassification of refrigerants by 'ASHRAE standard 34 -1997' or British standard BS4434 -1995' (see the fooc notes in Table 9.3) ammonia can be used with a charge up to 500kg in indirect dosed system even for air-conditioning of public places, like, hospitals, theaters, supermarkets, hotels, schools, lecture halls, dwellings etc. Even where the refrigerant charge exceeds 500kg, the only extra stipulation is, that all compressors and equipments should be located at ground level in a separate plant room. A typical recent example of a high capacity air conditioning system with ammonia is, the OSLO air port (1998); capacity 1800 TR, 2500 kg refrigerant charge. Majority oflarge capacity air conditioning systems the world over use the indirect chilled water system, using chilled water packages. So such plants with ammonia are increasing.

Also thermal storage (ice accumulation) system with ammonia is getting popular.

R 744 -Carbon Dloxlde(C021; Inorganic Compound-ODP:O; GWP: 1; AEL:SOOO ppm am monia carbon dioxide too has been in use as refrigerant since the last century. Positive features are:no ODP, negligible direct global warming effect with a GWP of l ,chemically inactive, nonflammable, harmful only on high concentration in the air, low requirement of compressor displacement of0.0206 m~/min( 0. 727 cfm) per TR, quite cheap, no necessity for recovery/disposal, etc.

e frequency of ility (as indicat ssure drop in

d temperatur the materials ·

he system. Hen µg the system wi

~uctivity. Becau on materials) ancl msulation materi-

should be endeaved a policy stateia is necessary for per the reclassifi-1995' (see the foot

system even for . schools, lecture

xtra stipulation is. te plant room. A is, the OSLO air

city air conditionater packages. So

OOOppm Like ~ .. Positive features iilly inactive, nonrnpressor displace!"\" disposal, etc.


strong negative features:

:::itical temperature of 31°C(87 .8°F) which is below the water temperature obtainable ~2°C(90°F)] from an operating cooling tower with an outside wet bulb temperature of r generally prevalent during peak periods in the coastal regions of India and possi-

ttOiPJcal regions; so can be used only in cooler regions. ___ _ e pressure is excessively high (72.7 kg/cm2 (1034psig) at 30°C (86°F) condensing tem-

1 necessitating very strong construction of the equipment, increasing the capital cost.

- -h it has positive points as a refrigerant but because of the severe limitations oflow rature and high operating pressures, it is of very little commercial use.

II can be used as the low stage refrigerant in a cascading refrigeration system for low llmim:111.""':::;:::::::::e applications.

l••--15.obvtane-( C4H 1oJ - Hydrocarbon - ODP: O; GWP: <3; AEL: 1000 ppm Ahydround, with 'O' ODP and very low GWP-has good thermodynamic properties, easily

much less cost than other refrigerants. But its application is limited, because, like other , 1t is flammable and listed as hazardous. ma, hydrocarbons, Propane and Isobutane have been in use as refrigerants for a long

...:=ited only to applications where expertise and facilities in handling flammable fluids are --~~'Och as in petroleum refineries.

countries of European union, however, on the phase out of CFCs, isobutane has been ----~~.as an alternative to R 12 for the domestic refrigerator, by most of the leading refrigerator

rs. The contention is that it requires a concentration of 17 to 39 gm of isobutane in one cf air to form an explosive mixture, while the charge of isobutane required for the

the biggest domestic refrigerators is extremely small. So, even if a big enough leak develrdea.se the full charge of the refrigerator instantly, the risk of an explosion is practically nil

em. The 'Greenfreeze' refrigerators- a popular European manufactured product-are tw,·e a charge of only 30 to 70 gm ofR 600a (i.e. only roughly 33% of the required charge :34a). But other developed countries like USA, Japan etc, have not adopted R 600a as

fi r the refrigerator because ofits flammability.

--~~elv necessary to have full global compliance of the Montreal Protocol and Kyoto agreestop further damage to the environment, that has been happening for the last several fr m the emission of ozone depleting substances and greenhouse gases. To achieve these,

perating refrigeration systems with CFCs, have to be completely converted to or re~ wstems using environment friendly refrigerants. Obviously this is going to take a very

In the meantime, every one ofus in the ACR industry, particularly personnel engaged in ---=-~ring, erection and service should be fully aware of the impact of the CFCs and other ---c-;;m· on the environment and make conscious efforts to stop/minimize their escape to the __ _.,._.e [see: Look detection used chapter 34-special tools]

·on-Service Sector

5rm...ted that only about 30% of the CFCs used as refrigerants, is consumed for charging new n systems; the balance 70% being utilized for service purposes. Obviously quite a lot is


lost through leaks, such as from equipments, defective cylinder valves, poor handling practices, etc. So erection/service sector has a major role in reducing damage to the environment.

Having been accustomed to handling mainly otherwise safer CFC refrigerants(which have noy, been found to be not environment friendly) for the last several decades, there was not that much concern about safety. But now the service personnel have to get fully acquainted with and strict!\ follow the precautionary measures, with a commitment to safety and enforce the programme to conserve, recover and recycle CFCs.

One can easily list out the steps in this direction-to cite a few, such as:

- Maintaining the refrigeration system leak tight. Regular leak check and prompt rectification of the gas leaks in the systems, have been quite important in ACR service and maintenance, so as to have the system properly charged for keeping up the efficiency of the system, for proper oil return, to limit discharge gas temperature, to keep down cost of maintenance (refrigerants being very costly), etc. Now this has acquired much greater significance, than ever before.

- To minimize the chances of gas leaks from the system, have the absolute minimum of mechanical joints; brazed /welded joints are very much less susceptible to gas leaks.

- Open the refrigeration side of the system only when it is absolutely inescapable and if the system has to be opened for repairs, refrigerant reclaim unit should invariably be used for removal of refrigerant from the system.

- No gas should be purged out to the atmosphere from the system. - Replace and tighten all seal caps on service valves and also on refrigerant cylinders; this is one

item many service personnel miss to do. - Do not use CFCs as tracer gas for leak testing systems. - Do not use CFCs for cleaning contaminated systems (R 11 had been in use for cleaning burnt

hermetic systems). - Improve the efficiency of the purge unit in negative pressure chillers (R 11 centrifugal chiller),

to minimize the quantity of refrigerant getting purged along with the non-condensables purged from the chiller system It is said that in an average purge unit, 3 to 8 kg of refrigerant gas gets purged along with every kg of non condensibles purged out from the system (i.e. 3 to 8 times). By improving the purge unit, the refrigerant purged out can be brought down to 0.5 kg per kg of non condensibles purged from the system. It will be advantageous to replace the conventional type of purge with the thermal (refrigerated) type, which works at very much lower purge discharge pressure and thus the loss of refrigerant on purging is substantially reduced (see 'thennal purge' in chapter on 'Centrifugal compressor').

Short Term and Long Term Plans-Options

Around 70% of CFCs consumed as refrigerants, is estimated to be used for service purposes. Obviously, the service requirement will go up as more plants get added every year and many may require more frequent servicing as they age. Thus, with their requirement going up, side by side with the planned progressive curtailment of their production and ultimate total phase out by 2009, the price of CFCs can/will escalate and eventually impossible to obtain.

In this scenario, the options available for users of existing equipments with CFCs are:

(i) Make existing plant nearly leak proof. Jn normaJly leak proof systems, like the domestic refrigerator and medium siLed hermetic systems, which are running satisfactorily, there is no technical reason to replace the CFC and so can be allowed to live its useful life period.

as not that much with and strictly e programme to

aintenance, so as m, for proper oil ce (refrigerants

n ever before. num ofmechani-

nders; this is one

•r cleaning burnt

mrifugal chiller), on-condensables kg of refrigerant e system (i.e. 3 to brought down to geous to replace irks at very much g is substantially

purposes. Obviany may require

e by side with the v 2009, the price

jCsare:

le domestic refrig~ . there is no techkriod.

Refrigerants and Brinetl 9!_

..(JR- Convert (retrofit) the existing plant with medium term alternate (interim) refrigerant, as rtage of CFC refrigerants tends to become acute.

-OR- Plan to replace the existing plant with new equipment using long term alternate refriger.a:nt at the earliest, depending upon the age of the existing plant. This is applicable particularly

industrial applications, where the industrial process is completely dependant on refrigeraoon Evidently it will be prudent to plan complete replacement of the plant long before a major breakdown of the plant due to old age or as CFC refrigerants become scarce.

d Indian context, even with the tapering domestic production ofR 11 and R 12, these CFCs pected to be available for quite sometime, though at escalating prices. So, probably retrofit

existing R 11 or R 12 systems with interim alternates may not be warranted. This line of his because, that many of the interim refrigerants are HCFCs and HCFC based blends, all of

• -e not manufactured in India and so will have to be imported. Further, because of their content, their production too is being progressively reduced and they ultimately will be

out in due course in the countries where they are being manufactured now. eYer, existing systems with CFCs, like, R502, Rl3, Rl J.l, etc. will need retrofitting with .Jternates, as these are not manufactured in the country and imports too will dry up, since

are already phased out in other countries. re it is planned to convert an existing CFC system with an interim or long term alternate

_ rant, thorough discussions should be held with the designer, also manufacturer or supplier equipment and the supplier of the alternate refrigerant, to ensure that the alternate is compat

oith the existing system in every detail and suitable for the application. deciding whether to convert a system with a even a long term alternate refrigerant or complete ement with new non-CFC system, an important aspect is the comparison of costs of replace-

;..nd conversion. Sometimes the cost of conversion (retrofitting) may turn out to be a very high t of the cost for complete replacement with new equipment using long term non CFC re frig

!.. . .\lso on conversion with interim alternate refrigerant, the efficiency of the system can drop, ~~ .. -... to increased power costs, while the efficiency of the new systems with non CFC refrigerant

been found to be much better. Thus the power requirement comparison too becomes a vital m determining the action plan.

(; ..1ally conversion calls for elaborate internal cleaning of the existing system. There are some .He refrigerants, claimed to be straight replacements i.e. nor needing elaborate internal flush

a"!d cleaning. Such claims are on the assumption that the existing system is quite clean and in condition. So, unless one is quite sure about the condition of the system, it is better, as an

dant precaution, to carry out even component wise flushing co clear the system of all traces of o.! and refrigerant. [see 'Lubricant - Refrigerant Compatibilit/ in chapter on 'Lubricatwnl

Further, there are some (interim, as well as, long-term) alternates that are compatible with the oil materials used in the CFC system, except for some specific items, like, gasket materials, electrical

tion material , shaft seal etc. So, before doing a retrofit, detailed discussions with the alternate ·,..erant supplier is necessary to clear all details.

f ;·om the above points, it will be abundantly clear that the refrigerants and lubricants should be ned only from long term well established, reliable and knowledgeable suppliers, who have

..ence in the country. Retrofit instructions are usually given by the refrigerant manufacturer. The relevant instructions the refrigerant selected to be used, should be obtained and followed.


A summary of points collected from the recommendations ofleading manufacturers of refri ants and compressors voicing a cautious approach is given in the lt.ppendix' section, as an exarr

SECONDARY REFRIGERANTS-BRINES

In large capacity refrigeration plants with evaporators located at widely spread out areas/locatio1 application of cooling, it becomes necessary to run long lengths of refrigerant lines to the evap tors, which will raise the refrigerant charge, increase the pressure drop in the refrigerant side also increase the chances ofrefrigerant leakage.

For such applications, a liquid is chilled in a centrally located chiller package and it is circul by pumps between the chiller and the various cooling coils(in AH Us) or heat exchanger jacke industrial processing, located at the cooling application points, for effecting transfer of of heat f the substance to be cooled . Thus the liquid becomes a carrier of refrigeration and so is kn as'Secondary refrigerant'. As is evident the secondary refrigerant does not undergo any change of s

Water is used as the secondary refrigerant for temperature applications above its freezing poi1 0°C and for sub-zero applications brines or glycols are employed.

Brine is a solution formed by dissolving a soluble substance in water. The soluble substance C<

be a salt, like, sodium chloride or calcium chloride or a glycol. On mixing a soluble substanc water, its freezing point is lowered, or in other words, the solution so formed has a lower free point than water.

( Table 9.10 ) Application of Various Brines

Salt brines Glycols

Application Sodium-chloride Calcium-chloride Ethylene glycol propylene gl;

Dairies " " Food processing " " Ice cream " Breweries Meat packing " Special low temp. " Skating ring Ice plants " Chemical plants " "' The weight of the salt or glycol in the solution, expressed as a percent of the total weight of

solution, is known as the 'strength' or 'concentration' of the brine. As the concentration of the solw increases, its freezing point goes down. Thus for a particular concentration of a solution, there definite freezing point. When a solution at a particular concentration is cooled below its freei point, some portion of water in the solution will freeze out as pure ice. With the reduced w: content, the remaining solution attains higher concentration and consequently a lower freei point. Ultimately on further cooling the solution itself freezes and the temperature at which happens is known as its eutectic point.

With the addition ofa soluble substance in water, the density or specific gravity of the resul1 solution will be higher; but its specific heat becomes lower than that of water. Since both spe•

1~fucturers of refrigeron, as an example

utareas/locationsof Imes to the evapora

t -efrigerant side and

e and it is circulated exchanger jackets in ~,sfer of of heat from

n and so is known any change of state. its freezing point of

' le substance could Jubie substance in

•as a lower freezing

propylene glycol

'1 '1 '1 '1

total weight of the uon of the solution

olution, there is a ' below its freezing the reduced water . a lower freezing

:nun~ at which this

·v of the resulting mce both specific


and specific heat of water are one, the specific gravity of a brine I solution will always be than one, while its specific heat will be less than one. Further, the specific gravity of a brine

pnicular concentration decreases as its temperatu re is increased, while its specific heat in-(fable 9. 11 ). T herefore, wh ile calculating the heat removal from a brine, its specific gravity ~cheat values for the particular concentration should be used.

.1 1) Prope rties of Brines and Glycols

Application Concentration Freezing Specific Specific Viscosity temperature % by weight point gravity heat centpoise

- 1.l C 12 -SC 1.093 0.86 2.2 (30F) ( 17 .5F)

-9.4C . 2 1 -17.2C 1.166 0.8 4.2

(15F) ( IF)

- 1.I C 12 -7.2C 1. 109 0.83 2.4 (30F) (19F)

-9.4C 20 - 17.2C 1.199 0.72 4.8 (15F) ( l f)

-20.6C 25 - 29.4C 1.256 0.67 10.3 (-5F) (-21F)

-34.4C 30 -44C 1.316 0.63 27.8 (-30F) (-47F)

- 1.l C 25 - 10.6C 1.037 0.92 3.7 (30F) (12.9F)

-9.4C 35 -17.SC l.058 0.86 6.8 (15F) ( 0 F)

- 20.6C 45 -26.4C 1.08 0.79 17.2 (-5F) (- 15.5 F)

-34.4C 55 -41.7C 1.106 0.73 75 (-30F) (-43F)

Jene -1.IC 30 -10.6C 1.034 0.94 8 I (30F) (13F)

-9.4C 40 -20. l C 1.046 0.89 20 (15F) (-4.2F)

-20.6C 50 -33.9C 1.066 0.83 80 (-5F) (-29F)

-34.4C 60 -48.3C 1.077 0.77 700 (-30F)

I •

, ~mpl~ ·~.2

Ca curate the heat to be removed, to cool 1000 litres of calcium chloride brine at 20% concentran, from O to-10°c.

aj Basic Refrigeration and Air Conditioning

Mean temperature of brine - Y:z ((0 + (-) 1 OJ = (-) s0 c Range of cooling = 10° C

Sp. gravity of brine at 20% concentration at - s0 c = 1.193 Sp. heat of 20% brine at - s0c = o. 73

Heat to be removed [1000 x 1.193x 0.73 x 10] = 8709 kcal (see under Table A.14 in Appendix section for 'Liquid chilling calculation']

Following are the important factors to be considered in selecting the brine.

Freezing point: The brine should have a concentration for which the freezing point has neces to be lower than the brine temperature to be maintained for the application - generally by abou 8°C. This difference is to prevent sudden crystallization of the brine, if the temperature of the 1

falls down accidentally.

Safety: The brine should be non-inflammable and non-toxic.

Suitability: Should be compatible with the materials of the equipment.

pH value: Ideally should be neutral, to minimize corrosion. But neutral or near neucral brin become corrosive with contamination during the operation.

Specific heat: determines the rate of flow of brine required - higher the specific heat, lower v

the rate of flow required.

Density: has no bearing on heat transfer aspects, but is helpful in finding the strength of a brine the help ofa hydrometer and thermometer.

Viscosity: again does not influence the heat transfer aspect; but where the viscosity of a brine ris· as its temperature falls, the pumping head and so the pumping horsepower will go uneconorr high. A typical example is propylene glycol - its viscosity rises very high below a temperature< C (20° F).

The brines in common use are of sodium chloride, calcium chloride and glycols, such as eth glycol, propylene glycol, etc.

Salt Brines (Sodium Chloride and Calcium Chloride Brines) Sodium chloride (commo is cheaper than calcium chloride. But since the freezing point of sodium chloride brine is corr tively high, it can be used only in applications requiring brine temperature not lower than -12° C ( 10° F). Calcium chloride brine is favoured for most applications, because of its lower ing point. Where contact with calcium chloride brine is not permitted, sodium chloride b1 used, such as in fast freezing I glazing of fresh catch of fish in fishing trawlers and other foo

Ideal pH value for sodium and calcium chloride brines is 7.5 to 8.5; a brine slightly alka considered safer than being slightly acidic. To correct acidic condition of these brines, causti• (an alkaly) dissolved in warm water is added, while for correcting an alkaline condition, ac• chromic or hydro-chloric acid is used.

Standard steel pipes can be used for brine piping- copper pipe cannot be used.

Glycols Ethylene and propylene glycols are widely used in cooling as well as heating a pp lie; Ethylene glycol solution is usually preferred, as it has more desirable properties at lower ten tu res, but operation below-50°C(-60°F) is not advisable. However for food and beverage cc

has necessarih \ by about 5 to .re of the brine

tral brine can

·. lower will be

of a brine with

brine rises fust economically rature of - 7°

has ethylene

ommonsalt) e 1s compara·r than about · lower freezride brine is er foods.

·Iv alkaline is causLic sod a on, acetic or

ipplications. er tempera-1ge cooling/

Re.fiigerants and Brines 97

bcations, \'>here there are chances of the g\yco\ so\ution coming in contact with the • only propylene glycol is employed, as propylene glycol is not toxic as ethylene

arculated by centrifugal pumps, with rubber impregnated asbestos or equivalent for ng. However, to prevent/minimize drip losses of glycol solution through the pump

=maru·cal seal is preferable. ck galvanized surfaces, forming sludge, so should be avoided. Standard steel and

-z ran be used for glvcol lines.

:;.r""'.':~7e Effect of Brines and Glycol Solutions The salt brines can become corrosi\ e, due to n, m handling and operation, like, when too much air gets mixed with the brines. So

.arrauon ofbrines is to be avoided - as far as possible, should be kept in closed systems, the ould be kept cO\ered etc These brines attack copper and steel parts, resulting in ces. If preventi\e measures are not adopted, the copper tubes in the chiller can If brine enters the refrigeration system, it will naturally affect the system, calling for

hing. cleaning, dehydrating, etc. So, in addition Lo correcting the pH of the brines, e to be added to combat corrosion. Inhibiters, like sodium chromate or sodium-dichro

to be effective with these brines in overcoming corrosion. The recommended inhibitor -~-....~n1:

m chloride brine- - - - 2 kg per 1000 litres (l.67lb per 100 US gals) of brine m chloride brine - - - - 3.2 kg per 1000 litres(2.67lbi IOOUS gal) of brine

-~·._..., ... te comes in granular form and it dissolves ver> slowly in cold brine. So it should not be th to low temperature brine; dissolve it in warm water and add the solution away from

pump suction take off point in the brine tank, so that only dilute solution reaches the i\ ore! of caution-if the chromate or its solution comes in contact ''ith skin, rashes can

_ _,.-\\~sh skin immediate!} with water. eth' lene and propylene glycols, when pure, are less corrosive than even water, but due to

of water used for preparing the solution the} can turn to be corrosive, particularly when mixed. Soft water or if possible distilled water or condensate water should be used for

~-"TTTl,,T he solution to avoid the effects of bad water quality. In any case, inhibited glycols, which ble, should be used. If inhibited glycol is not available, the glycol manufacturer should be

~--.--hed for recommending the suitable inhibitor. rhromate or chromate should not be wed as inhibitors with glJcols, as oxidation of glJcol can occur,

• solutwn more corrosive. orrf solution is used here to cover both the salt brines and glycol solutions).

itor Maintenance To ensure fair!) non-corrosive solutions for a long period of time, it is portant to monitor the inhibitor concentration and replenish the inhibitor as necessary. For

lhe pH readings should be regularly recorded follo""ed with pe1·iodical analysis of solution le. This systematic approach also will prevent indiscriminate addition of inhibitor. which is e~ harmful.

The rate of depletion of the inhibitor in a solution depends upon the usage of the plant- this may fi Gm job to job.Hence in the initial stages on commissioning the plant, it may be necessary to do

analvsis of the solution frequently to establish a pattern for the maintenance schedule. mce these solutions are generally used in industrial applications as secondary refrigerants, it Id not be difficult to adhere to these simple yet very important maintainence steps. Plant failures


due to corrosion can be attributed to ignorance or callous negligence of these maintenance stepsthe necessisty of these steps has to be overemphasized.

Other Secondary Refrigerants Many of the halocarbon refrigerants have been in use as secondan· refrigerants also, because of their favourable properties such as, low freezing points, good heat transfer coefficients, non-flammability, stability, low viscosities, etc. But because of environmental considerations now these cannot be used.

Chilled special grade oils for heat treatment purposes, chilled kerosene oil as coolant for machining cast iron, etc. are others in this category.

Refrigerants and Brines (2)

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