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LATEST TRENDS INAIR-CONDITIONING FOR GREEN

BUILDINGS

Mr. Krishna V JogManaging Director

Kirloskar McQuay Ltd

ABSTRACTAir-conditioning systems for Hotels/Multistoried office buildings, Nuclear PowerEstablishements and almost all other commercial buildings used to be made with halocarbonrefrigerants about 30 to 40 years ago. The halocarbons mainly used to comprise of CFC’s.These refrigerants most commonly known as “FREONS” were treated as magic refrigerants,which were considered to be having only excellent properties and no negative factors. Therewere no restrictions on spillage of refrigerants into the atmosphere. No one ever thoughtthat they have to be handled carefully, and not be let off in the air. The theory of ozonedepletion potential was put forward about 25 years ago and was presumed to be linked withemission of substances containing chlorine. Over a period of time, it was established that theCFCs are related to depletion of ozone and there by risk to human life by way of skin cancer.

Montreal Protocol was formulated and many countries of the world started becomingsignatories to this protocol. Few years ago, India also became the signatory. Manymanufacturing industries were encouraged to join by giving monetary aids. Many industriestook advantage of financial gains, but have hardly done anything to update their technology.Today, Kirloskar McQuay Limited, is the only company in India, who manufactures largecapacity chillers working with HFC R134a containing no chlorine and having no phase outdate. Many leading users such as BARC, TIFR, NPCIL, IGCAR etc have fully implementedthe concepts of maintaining the environment and remaining ‘e-conscious’. It is time that allusers realise this fact and switch over to refrigerants such as HFCs containing no chlorine.Many industrial units in the world are slowly accepting these facts but still there is somereluctance due to advantages of lower price for R123 machines. We must contribute to asafer environment and cannot afford to delay this process.

1.0 INTRODUCTION

Any air-conditioning system whether a unitary product or an engineered machinery item isto be judged by the efficiency of the system. The definition for efficiency for ACR is different

than the definition for efficiency for mechanical engineers. Here for ACR applications, theefficiency exceeds 100% and therefore is normally termed as COP. There are 3 different waysin which energy efficiency is defined. These are explained in ANNEXURE I (EFFECTIVENESSOF REFRIGERATION SYSTEMS).

The efficiency or the COP has improved substantially for various systems over the last twodecades. A machine which has highest COP, will consume lowest power, and should beencouraged to use to qualify for a green business centre.

2.0 TYPES OF SYSTEMSThe entire world of air-conditioning can be divided in small tonnage and high tonnageequipments. The small tonnage upto about 25 to 30 TR falls in the unitary products group,whereas tonnages from 50 to about 12000 TR in a single system will fall into the category ofengineered machinery systems. There are various types of equipment with various refrigerantsboth water-cooled and air-cooled and are explained briefly in ANNEXURE II (TYPES OFREFRIGERATION EQUIPMENT IN HVAC).

3.0 TYPES OF CHILLERSThe Vapour Compression Systems (VCS) are more commonly used than Vapour AbsorptionSystems (VAS). This is due to the fact that co-efficient of performance (COP) of VapourCompression System are in the range of 5 to 7, whereas COP of Vapour Absorption variesfrom about 0.6 to 1.15. The absorption machines run on the heat energy as the source,whereas vapour compression systems usually require electrical energy as input. Electricalenergy is a costlier form of energy, as 100% conversion of heat into energy is not possible bythe second law of thermodynamics. A simple comparison of COP and Heat Rejection Ratio(HRR) is as shown in ANNEXURE III (VCM’s Vs VAM’s)

3.1 RECIP CHILLERSThe recip systems have been introduced since the inception of ACR Industry. These willcontinue to be used till the end of this world as they have outstanding merits in them. Thesesystems have built in capability for adjusting the compression ratios depending on theconstantly changing ambient conditions. In a single stage, they can easily go to about 8 to 9compression ratios. For lower temperatures, where higher compression ratios are required,one can easily have multi-staging which will save power.

These types of systems will typically have COP in the range of 3.5 to 4.5. Although, recipsystems are presumed to be consuming more power than screw, it may not remain so,depending on the type of refrigerant and other technical parameters. Typically for ammoniaas refrigerant and for low evaporating temperatures, recips consume less power than

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the screws. These systems are very economical and generally have minimum costs. Thesesystems should be considered seriously typically for Airconditioning applications whereusage is for 8 to 10 hours a day and work 5 to 6 days a week.

The recip systems, either air-conditioning or refrigeration, are more efficient with R134arefrigerant as compared to R22. Although the capacity for the same compressor displacementwith R134a will drop, the specific power consumption also invariably drops. The advantagesof using R134a over R22 are with R134a, as an HFC, having no phase out date and can beused permanently. It has much lower operating and standard pressures as compared to R22.It is readily available since most of the new applications such as refrigerators, transportrefrigeration and air-conditioning etc all use R134a as the undisputed refrigerant. The fall incapacity, as compared to R22, can be compensated by increasing the speed. The reductionin power consumption is quite attractive and justifies a fast pay back period. Many MNCsdo not encourage use of R22 and prefer R134a even in India today.

The power consumption for a typical recip system has further come down in the recent yearsdue to advancement in the tube geometry used for evaporator and condenser. In the olderdays, smooth bore tubes typically of ¾” OD were used for DX Chiller applications andintegral finned tubes of ¾” OD having 19 FPI from outside with smooth bore from insidewere standard. As power became more costly, it was realised that it is more efficient to usesmaller diameter tubes with internal grooving for DX chillers and using 26 FPI instead of19 FPI from outside with internal grooves inside of smooth bore for condenser tubes. Theseimprovements have resulted in achieving higher evaporating temperatures and lowercondensing temperatures for the same chilled water outlet temperature and same condenserwater inlet temperatures. In addition to the improvements in geometry, the improvementsin quality of the compressor as well as switch over to the semi-hermetic from the open hasresulted in overall improvements in efficiency, power consumption, compact sizes, lowernoise and less vibrations. The semi-hermetic packaged chillers of today are becomingincreasingly common for both chilled water and brine chilling applications as standard unitswhich are run and performance tested from factory prior to despatch. The recip chillers arevery economical in price and have outstanding flexibility for varying ambient conditions.The recip systems should therefore be considered very carefully particularly for tonnagesupto or around 100 TR capacity.

The slide on recip chiller (ANNEXURE IV) whether water-cooled or air-cooled will emphasisethat the power costs upto about 10% could be lowered, if environmentally friendly HFC134ais used, instead of phasing out HCFC 22.

3.2 SCREW CHILLERSScrews have been in use for over 20 years in the International Market. These have penetratedin our Indian Market only recently. Screw type of compressors have outstanding merits forhigh compression ratios where either low temperatures on evaporator or high condensingtemperatures such as Air-cooled applications are involved. For air-conditioning type ofapplications, compression ratios are low. Screws may not necessarily be the attractiveproposals. Screw chillers are rotary machines, but these compressors are usually imported.This technology of manufacturing the screw compressors for ACR applications is yet notdeveloped in our country. Some of the overseas manufacturers are still carrying out R & Dactivities and there can be many problems in the field once something goes wrong. Thereare 2 types of Screw machines available in the market, they are Mono Screw or Dual Screw.Usually for air-conditioning applications, mono screws are preferred, whereas for lowtemperature refrigeration duty, dual screw may be preferred. Screw chillers usually costmore than recips, and the advantage in power both at full load and part load may notbe significant. Screws are usually considered as an option to recip if the capacities are in therange of 150 to 250 TR.

Many times it is misconceived that the screw compressors consume less power than recipmachines. This may not be true in many cases. The typical performance data for dual screwopen compressor is as shown in ANNEXURE V (YORK ROTARY SCREW COMPRESSORUNITS ENGINEERING DATA). The power consumption at typical 35°F/115°F is 1.2 BHP/TR. This power consumption is very high even as compared to the recip compressors. Onemust note that this is BHP and not IkW. There is a difference of about 10 to 15% betweenBHP and IkW. When comparing the two figures for open vs. hermetic, one must take careto see that fair comparison is made between IkW to IkW and not IkW to BHP. In many cases,for low temperatures in particular, the difference in power consumption between screw andrecip may be much higher and recip may be a clear winner.

3.2.1 FULL LOAD AND PART LOAD PERFORMANCEVarious manufacturers claim different performances, and authentic published information isgenerally not available. Many a times, the exact refrigerant is not known, whether theperformance is with ARI Relief or without is not known and also the figures are indicative andnot guaranteed. It becomes extremely difficult for a proper judgement as to which data is to bebelieved. Various performance characteristics at part-load capacities for R22/R134a with orwithout ARI Relief for mono and dual screw compressors are as depicted in FIGURE NO. 1.

As discussed before, under recip chillers, the performance with R134a with screw compressorsis invariably better than with R22. Here again the same considerations will apply for theselection of HFC 134a Vs HCFC 22 to be phased out.

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3.3 CENTRIFUGAL CHILLERS

Centrifugal Machines are fully balanced rotary machines having the lowest power consumptionboth at full load and part load. The centrifugal is ideal for capacities about 250 TR and upto2500 TR or more. For air-conditioning or chilled water applications, always hermetic machinesare preferred, because of compactness and low noise and vibration. Generally open typecentrifugals are considered for very low temperature applications having 6 to 8 stages.

Due to toxicity, unavailability and many other negative factors such as negative operatingpressures, R123 is not considered as a good option. R123 was born as a temporary substituteto R11, since no other permanent refrigerant without chlorine has still been found withsimilar temperature-pressure characteristics. R123 is classified in B1 category and has verylow AEL and TLV limits.

By considering the phase-out of CFC refrigerants and fast approaching deadlines for HCFCrefrigerants, the only strong candidate for centrifugals, which is a pure HFC and has nophase out date is R134a. There are many countries who have banned R123. Considering allfactors including the global warming and the total TEWI, R134a is found to be one of the bestrefrigerants known today. The centrifugals of hermetic type with R134a can typically give0.6 IKW per TR or lower for standard operating conditions prevailing in India. These are thebest types of machines both from full load and part load efficiency point of view.

3.3.1 POWER CONSUMPTIONA substantial improvement in COP has taken place during the last 20 years. This has happenedbecause the cost of energy has been rising. One of the main factors responsible for thisimprovement in COP is the tube geometry. As discussed earlier in this paper, the finningof the tubes both internally and externally, both for evaporator and condenser has given riseto increase in evaporating temperatures and reduction in condensing temperatures. Thelatest TURBO-B II and TURBO-C II tubes have given rise to IkW’s in the range of 0.5 to 0.6,for standard applications, with prevailing fouling factors for Indian conditions. A typical p-h Diagram is as shown in FIGURE NO. 2.

3.3.2 ENERGY COST OF REFRIGERANTWhen refrigeration capacity of 250 TR and above are required, usually the clear winner is acentrifugal chiller. Typically energy cost of refrigeration as published in ISHRAE Journal ofJuly 1998 written by a leading consultant in Mumbai are as shown in FIGURE NO. 3. Fromthis diagram, one can see that it costs minimum to run a centrifugal chiller. This is becauseof the fact that COP for these chillers is the highest and the power consumption minimum.The figure also shows average power consumption figures in IkW per TR. This is a good

guideline mostly for air-conditioning range. The higher cost of centrifugal is more thanjustified by a faster pay back period because of savings in power consumption.

3.3.3 R134a Vs R123The old centrifugal machines used to operate on R11 as a refrigerant. This is a low pressurerefrigerant having high vacuum on suction and moderate positive pressure on discharge sidewhile in operation. The standing pressure is only slightly above the atmospheric pressure.Since the operating pressures were negative, a lot of air and water vapour used to get suckedinto the machine from the atomosphere necessitating continuous operation of the purge unit.Inspite of inclusion of a purge unit, there would be heavy rust and corrosion due to watervapour inside the shell. The system used to get rusted and refrigerant contaminated withcorrosion. It was impossible to clean such systems and the performance would get affectedover a period of time. As the ban on CFC refrigerant has come into effect, an alternative toR11 was searched. Interim solution was the birth of R123. This is a refrigerant having similarcharacteristics to R11 but which is an HCFC. This is very toxic and the AEL and TLV’s arestringently low. Should any leak occur, the monitoring system must give an alarm and mustput the ventilation system ON. This is mandatory in view of the toxic nature of the refrigerant.The R123 refrigerant is not a long term solution and since no permanent solution havingcharacteristics of R11 is found, R123 is strictly used as an interim solution. This refrigerantis not readily available and has to be imported against a special import license. The negativepressure refrigerants are ones which have operating pressures in the vacuum range. Asagainst these refrigerants, R134a is a positive pressure refrigerant, which has positive operatingpressures. A comparison of positive pressure technology vs. negative pressure is as shownin ANNEXURE VI.

There are many countries in the world who have totally banned use of R123. R134a, is anHFC, having no phase out requirement, and a permanent refrigerant. It is the most preferredone for all applications, be it recips, screws or centrifugals. This has become a universalrefrigerant for most of the applications which believe in ‘e-consciousness’.

4.0 CONCLUSIONSAlthough many MNCs, Government and BARC applications have almost switched over toa safer chlorine-free refrigerant R134a, it is time that each large capacity air-conditioninginstallation must use only R134a or R407c or R404a or other similar HFCs and not promotethe use of toxic refrigerants such as R123, which are only an intermittent substitute, andmuch worse than other HCFCs such as R22. All green buildings must essentially ban theHCFCs, and particularly the toxic R123 refrigerant.

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Capacity in Tons of Refrigeration

Types of Refrigeration Equipment in HVAC

Typ

e o

f E

qu

ipm

ent

VaporCompression

VaporAbsorption

0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

3500

3750

Unitary products

Available Reciprocating chiller range 15 ~ 500 TR; W/c & A/c applications

McQuay W/c Reciprocating chiller range 25 ~ 385 TR; HCFC 22 or HFC 134a

McQuay A/c Reciprocating chiller range 20 ~ 420 TR; HCFC 22 or HFC 134a

Available Screw chiller range 40 ~ 1,400 TR; W/c & A/c applications

McQuay W/c Screw chiller range 75 ~ 540TR; HCFC22, HFC410A or HFC 134a

McQuay A/c Screw chiller range 65 ~ 555TR; HCFC22, HFC407C or HFC 134a

Available Centrifugal chiller range150 ~ 13,000 TR; W/c & Air cooled applications; Single & multi stage

McQuay W/c Centrifugal chiller range 150 ~ 2,500 TR; HFC 134a.

Available Vapor Absorption chiller range 25 ~ 6,600TR, Direct fired, Steam orHot water, Single & Two stage; Refrigerant H2O (R-718) & Absorbent: Lithium Bromide

Available Scroll chiller range 2~60 TR; W/c & A/c applications

McQuay A/c Scroll chiller range 2 ~ 5 & 30 ~ 45 TR; (HCFC 22, HFC 407C or HFC 134a)

Sanyo Hot water fired Absorption chiller range 30 ~ 525 TR

Sanyo Double effect Direct or Steam or Hot water fired Absorption chiller range 100 ~ 6,600 TR

KVJ-TKN/02/0301/01

ANNEXURE I

ANNEXURE II

ANNEXURE III

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Model shown here:KAR 165.2 OS

Use Kirloskar –McQuay Reciprocatingchillers with Chlorine-free “HFC-134a”.

Water cooled range 50 ~ 384 TRAir cooled range 045 ~ 420 TR

Model shown here:KWR 225.3 OS

KVJ-TKN/02/0301/04

Be Environment Friendly! save upto 10% onPOWER costs !!!

75 85 95 105 115 125132.2 155.7 181.8 210.8 242.7 277.9

- 40 TR 293.4 287.6 281.5 275.0 268.0 260.5 .5 BHP 612.7 676.0 745.0 822.1 906.2 1007.6 - 35 TR 331.2 325.1 318.6 311.7 304.5 296.6 2.6 BHP 638.9 704.9 775.2 852.5 934.8 1031.4 - 30 TR 371.9 365.4 358.5 351.3 343.6 335.5 4.9 BHP 663.9 734.2 807.2 885.5 967.7 1062.5 - 25 TR 415.7 408.7 401.4 393.8 385.7 377.2 7.4 BHP 685.4 762.5 840.0 920.5 1007.8 1098.6 - 20 TR 461.9 454.8 447.0 439.0 430.5 421.5 10.2 BHP 703.9 789.0 872.0 956.9 1046.3 1138.5 - 15 TR 510.5 503.1 495.2 486.5 477.7 468.3 13.2 BHP 718.7 811.2 903.4 992.6 1086.2 1180.3 - 10 TR 562.1 554.1 545.9 537.0 527.6 517.9 16.5 BHP 730.5 829.1 929.7 1028.7 1126.1 1228.5 - 5 TR 615.5 607.1 598.4 589.3 579.5 569.2 20.1 BHP 739.0 844.3 951.8 1060.4 1166.2 1272.3 0 TR 672.4 663.6 654.4 645.0 634.9 624.1 24.0 BHP 744.5 854.9 970.2 1087.6 1203.9 1318.0 5 TR 724.1 714.3 704.3 694.0 682.8 28.2 BHP 862.9 982.7 1107.9 1237.5 1361.7 10 TR 777.3 766.7 755.8 744.5 32.8 BHP 993.1 1125.2 1260.8 1399.5 15 TR 842.7 831.7 820.3 808.5 37.7 BHP 999.8 1138.1 1282.4 1430.0 20 TR 900.9 888.8 876.4 43.0 BHP 1147.8 1298.2 1456.2 25 TR 973.3 960.9 947.9 48.8 BHP CONSULT 1153.1 1310.9 1474.1 30 TR FACTORY 1037.3 1023.8 54.9 BHP 1319.2 1490.0 1.2 BHP/TR 1103.2 1501.7

40 TR 1186.2 68.5 BHP 1508.5

NOTE : Capacities based on Economiser, 10 Deg Suction Superheat with Superheat not contributing to the refrigeration effect. kvj/0392

SA

TU

RA

TE

D S

UC

TIO

N T

EM

PE

RA

TU

RE

, 0F

/CO

RR

ES

PO

ND

ING

PR

ES

SU

RE

, PS

IG

YORK ROTARY SCREW COMPRESSOR UNITS ENGINEERING DATA

HIGH STAGE-CAPACITY and BHP @ 3550 RPM w/ECONOMIZER (60Hz) IS 2350E

R-22SATURATED CONDENSING TEMPERATURE, 0 F/CORRESPONDING PRESSURE, PSIG

1117.61325.2

35 TR61.5 BHP

115

ANNEXURE IV

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Electricity from utility - Rs.per kW.hr (Overall)

0

1

2

3

4

5

6

16 14 12 10 8 6 4

Oil / per Lit

Rs.

/ T

R.h

r

Energy cost of Refrigeration b) Vapor Absorption systemsa) Vapor compression systems

Courtesy: Write up on “Refrigeration Equipment” by Mr. S.K.Murthy, Eskayem Consultants Pvt. Ltd, Mumbaiin ISHRAE Journal, July 1998 issue.

Rs.

/ T

R.h

r

Screw chillers

0

1

2

3

4

5

6

7 6 5 4 3 2

Reciprocating chillers

Centrifugal chillers

Different type of vapor compression equipmentavailable in Industry and its ikW/TR

Range Median

� Reciprocating chillers 0.75 ~ 0.85 0.81

� Screw chillers 0.67 ~ 0.75 0.70

� Centrifugal chillers 0.60 ~ 0.68 0.65

Different type of vapor absorption equipment availablein Industry and its efficiency

Range Median

� Steam fired 4.5 kg of steam / TR.hr 0.35 lit LDO

� Direct fired - 0.35 lit LDO

� Natural gas fired - 0.30 Nm3

Screw chillers

Oil fired absorptionchillers

Gas firedabsorption chillers

KVJ-TKN/02/0301/02

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

%, P

ow

er in

put

Reciprocating I-Mono Screw Centrifugal M-Mono ScrewT-Dual Screw K-Dual Screw Trend Line

M-Mono Screw W/o Relief HCFC22

K-Dual Screw W/o Rel ief

I-Mono Screw with Rel ie f, HFC 134a

Reciprocating

T-Dual Screw with Relief, HCFC 22

Centrifugal wi th Relief, HFC134a

In accordance with ARI Standard 550/590 - 1998

Part load performance:

%, Capacity

KVJ-TKN/02/0301/03