basics1 - liquid injection ref

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Form ApprovedREPORTDOCUMENTATIONPAGE MB No 0704018Pubic reporting burden forthis collection of information Is estimated to average 1 hour per response, including the time for reviewing instructions, searchingexisting data sources, gathering and maintaiing the data needed, and completing and reviewing the collection of information. Send comments regarding thisburden estimate or any other aspect of this collection information, including suggestions for reducng this burden, to Washington Headquarters Services,Directorate for Information and Reports, 121 5Jeffemon Davis Highway, Suite 1204, Arlington, VA 22202-4302, and tothe Office of Management and Budget.Paperwork Reduction Project (0704-O1SM),Washington, DC 20503.

1. AGENCY USE ONLY aLeave blank 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

IJune 1994

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

LIQUID PRESSURE AMPLIFICATION AND LIQUID INJECTIONIN AIR CONDITIONINGAND REFRIGERATIONSYSTEMS

6. AUTHOR S)

Bradley Yee

7. PERFORMING ORGANIZATION NAMEIS) AND ADDRESSE S) 8. PERFORMING ORGANIZATION REPORTNUMBER

Naval FacilitiesEngineering Service Center TDS 2005 ENGPort Hueneme, CA 930434328

0 o~~o..o .o. o..o - o .o o ,o o.o..,.oS SPONSORING MONITORING AGENCY t ANI W*ESSES 10. SPONSORINGIMONITORING AGENCY REPORT

NUMBER

11. SUPPLEMENTARY NOTESVV

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approvedfor publicrelease; distribution is unlimited.

13. ABSTRACT Maximum 2 words

Liquidpressure amplificationand liquidinjection are two patented methodsof decreasingcompressorenergy comsumptionand increasing condensercapacityin an existingreciprocatingvapor compression refrigera-tion system. Althoughthis 6-year-oldtechnology has been installed on thousandsof existingsystems, it continuesto generate controversy in engineeringand utility circles.

995O 2 014. SUBJECT TERMS 15. NUMBER OF PAGES

Liquid pressureamplification, liquidinjection, air condition, refrigerationsystems, thermo- 4static expansionvalve, 16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OFOF REPORT OF THIS PAGE OF ABSTRACT ABSTRACT

Unclassified Unclassified Unclassified UL

NSN 7540401-20-5500 Standard Form 298 (Rev. 2-89)Prescribed byANSI Std. 239-18


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Tech data

heet TS2 NJune 994NAVAL FACLTE EGNEIGSRIECNEPOT H NMCA 93 4342

Liquid Pressure Ampulication

and Liquid Injection in ir Conditioning

and Refrigeration Systems

INTRODUCTION The evaporator absorbs the heat from the sur-rounding air which causes the low-pressure liquid refrig-

Liquid pressureamplificationand liquid erant to change phase and become a low-pressurevapor.-~injection are two patented methods of de-

creasing compressorenergy consumptionand The compressor raises the pressure and tempera-increasing condenser capacity in anexisting ture of the vapor. The refrigerant leaves the compressorreciprocating vapor compression refrigera- s a superheated vapor so it then can be condensed by

tion system. Although this 6-year-old tech- relatively warm water or air.nology has been installed on thousands ofexisting systems, it continues to generate The condenser rejectsheat from the superheatedcontroversy in engineering and utility circles, vapor and the refrigerant condenses into a high-pressure

liquid.CONVENTION L REFRIGERATION _______________CYCLE ~ R E F R I G E R A N T FL13W

CONDENSER-

As shown in Figure 1, the basic vaporsuehadvpocompression refrigeration system is com- Subcooted Liquidprised of an evaporator, a compressor, a HI HPRSU MRSOcondenser, a liquid receiver, and a thermo- ICMRSOstatic expansion valve (TEV). The cycle isa closed-loopsystem. Refrigerant, the work- LOWJ RESSURE t-auae vaoing fluid, flows through each part of the EXPANSIONjsystem in sequence, changing phase from VALVE -.- EVAPORATORliquid to vapor and back again at specific LOWTEPEATUE


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The liquid receiver stores the erant in the liquid line that cannot be used to absorb heat inhigh-pressure liquid, maintaining a con- the evaporator. The LPA pump also ensures that a minimumstant supply for the TEV. pressure drop across the TEV is maintained whileallowing *

the condensing pressure to remain low. If the minimum The TEV separates the high-pres- pressure drop specific to a particular TEVis not maintained,

sure part of the system from the low- the valve operation will become unstable and causeexces-pressure part. The TEV lowers the pres- sive superheat at the evaporator discharge. Excessive super-sure and temperature of the liquid re- heat at the evaporator discharge may cause the compressorfrigerant so it can be evaporated again, to overheatand fail. By maintaining correct TEV operation,

the evaporator capacity is also maintained while the com-A conventional refrigeration system pressor head pressure canbe reduced.

maintains a fixed refrigerant pressure asit leaves the compressor. This discharge LIQUID INJECTIONpressure or head pressure is designed toallow condensation at highambient con- Liquid injectionis an additional modification to a vaporditions. Unfortunately, energy is wasted compression system. A small amount of subcooled liquidduring mild and cool ambient conditions createdby the LPA pump is injected into the compressor

because the condenser temperature and discharge (see Figure 2). The subcooled liquid immediatelypressure are unnecessarily high. flashes as it enters the compressor discharge and reduces theWith floating headpressure control, temperature of the superheatedvapor.

the compressor discharge pressure canbe lowered according to the ambient con- CONDENSER LIQUID INJECTION -. REFRIGERANT FLOWditions. Unfortunately, the amount the N ,compressor discharge pressure can be LPA superheated vapor

lowered is limited to the minimum pres- tequd \sure difference required across the ex- HIGH PRESSUE COMPRESSORpansion valve to maintain a liquid sealat the valve inlet and ensure stable valve ..........

operation without excessive evaporator W PESSURE saturatedsuperheat. Excessive liquid line pres- EXPANSIONJ ,sure drop or a large difference in height VALVEbetween the condenser and the evapora- saturated 1;quid/ - -EVAP-RATORtor would further limit the minimum LOW TEMPERATURE E-.-> HIGH TEMPERATUREcompressordischarge pressure. I

Figure 2LIQUID PRESSURE Vapor compression cyclewith LPA and liquidinjection.AMPLIFICATION

Liquid injectionbasically desuperheats the vapor refrig-Liquid pressure amplification (LPA) erant. This increases the effective efficiency of the con-

requires the installation of a pump be- denser by decreasing the overall condenser desuperheatingtween the liquid receiver and the TEV load.(see Figure 2). Increasing the liquid re-frigerant pressure directly before the CAPITAL COSTTEV serves two purposes. By increas-ing the pressure of the saturated liquid Initial capital costs for LPA pumps are summarized in.from the liquid receiver, the refrigerant Table 1. Additional capital costs may include special con-entering the TEV is less likely to controls to float the compressorhead pressure.tain flash gas. Flash gas is vapor refrig-


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Table 1. Initial Capital Cost for an LPA Pump periods of peak electrical demand, furthersavingmay be possible.

LPA Because of these factors, independent,thirdSystem Size Pump Size Cost party testing of LPA technology proving substan

(nominal tons) (hp) ( ) tial energy savings over a wide range of the abovevariables is not readily available. ASHRAE (Amer

3 - 10 0.13 600 - 800 can Society of Heating, Refrigerationand Air Con10 - 35 0.40 1,400 - 1,500 ditioning Engineers, Inc.) Fundamentals Handbook

60 - 140 0.75 4,400 includes a table of the general effects of condensetemperatureon theoretical compressorhorsepowerBased on this table, a theoretical 1.4 percent aver-

ENERGY SAVINGS age reduction in compressor energy per Fahrenheit degree can be calculated. An LPA pump can

The performance of the LPA is dependent on potentially lower the working condenser temperaa number of factors: ture when the ambient air temperature is low.

However, caution must be used when utilizing theAmbient Temperature theoretical 1.4 percent energy reductionper Fahr-

enheit degree to estimate the potential savings thatA low condensing temperature is requiredwhen can be realized by LPA technology. LPA distribu-decreasing the compressorhead pressure, which is tors have used values between 1.1 and 1.4 toonly possible during cool weather. The exact tem- predict energy savings. This theoretical reductionperature at which savings will occur is site spe- is strictly for the compressor and does not includecific. The ambient temperaturemust be low enough the possibleincreasedcondenser fan and LPA pump

O to not only extract sufficient heat from the con- energy required to achieve the low condensingdenser coils, but also make up for increases in pressures. Most compressor manufacturers do notenergy consumption by the LPA pump and con- provide compressor performance data at such lowdenser fans. condensing pressures. Unless such data is avail-

able, predicting the actual available savings fromSystemDesign large reductions in condensingpressure is impos-

sible.A system with an excessive liquid line pres-

sure drop or a large difference in height between CONCLUSIONthe condenser andevaporator will limit the allow-able reduction in compressorhead pressure. Our experience in evaluating Navy heating,

ventilating, and air conditioningsystems indicatesSystemLoad Profile immediate energy savings are available by simply

performing the required maintenance to operateIf the system load profile is directly related to systems as designed. Therefore, before consider-

the ambient temperature, the total energy con- ing implementing LPA, we recommend focusingsumption by the system will be at a minimum on the maintenance of existing systems.when maximum LPA energy savings are avail- Because of the application-specificnature ofable. A system load profile which is independent this technology, it is difficult to develop generalof ambient temperatures(e.g., computer rooms guidelines for savings resulting from LPA installa-and refrigerationprocesses) would be ideal. tions. Energy savings in the case studies fromthe

manufacturerof this patented technologyrange fromOperatingHours 6 to 60 percent. In these cases, the energy savings

were not documented in detail and measurementIf the above factors can be optimized during were not carried out long enough to determine the


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long-term benefitsof LPA. However, one test per- turer. In our opinion, independent, controlled test-formed by an independent thirdparty shows an ing over a range of applications andconditions isincrease incompressor energy consumption.Other neededto truly evaluate the energy savings poten- 0independentevaluators have performed tests, but tial of LPA and liquid injection. It is Navy policyrefuse to release any documentation of LPA test- that these independenttests be the responsibilityofing. However, they have verballydisclosed to the the manufacturer. We recommend waitinguntilNavy that their tests indicated overall energy sav- such test results are available before consideringings much less than those claimed bythe manufac- investing in LPA technology.

NFESC CONTACTS

Bradley Yee or David Hardisty, Code ESC23HVAC and Controls Division

Naval FacilitiesEngineering Service CenterPort Hueneme, CA 93043-4328

Phone: (805) 982-4259 or 982-6508;DSN 551-4259or 551-6508FAX (805) 982-5388; DSN 551-5388

DEPARTMENT OF THE NAVY Accesion For

COMMANDING OFFICER NTIS CRA&INFESC DTIC TA B560 CENTER DRIVE UnannouonncedPORT

HUENEME CA 93043-4328 J ] s t f i f i ca t ion .

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