# Alternat ives in Co mmer cial Refrigerat ion

Th is is the second instal lment of a two part series lo oking at the testing of new lo w GWP 404A alternative. In the last issue (November) we lo oked at the thermodynam ic properties and perf ormance of the re frigerant. In th is issue of we wil l co ver practical testing of DR-7 and DR-33 in co mmercial fo od storage un its. 

## Reach-in freezer system testing In or der to measur e system perf ormance of DR-7 and DR-33 in a system, a re ach-in fr eezer was selected (F ig. 1), ful ly instrumented and placed in a co nstant temperatur e ro om. The fr eezer is a 1,5 m3 double-door un it designed fo r R-404A with a re frigerant char ge size of 1,15 kg

. It has a re cipr ocat ing co mpr essor wh ich uses a pol yo l ester (POE) 32 cent istok es lu bricant. The test setup was selected to co nf orm as closel

y as possible to AHAM Standar d HRF-1-2008 Ener gy and Internal Vo lu me of Refrigerat ing Appl iances (AHAM 2008). It was not possible to use ANSI/ ASHRAE Standar d 72 because the system was not set up to open and close fr eezer doors during the test. The re ach-in fr eezer is co ntr ol le d with two thermostat ic ex pansion val ves (TXVs). 

# REFRIGERAN TS

The empty freezer (per AHAM HRF-1-2008) was placed in a co nstant temperature ro om and ful ly instrumented with temperatures (T), pressures (P), mass flow rate (M) and energy measurement (W), shown in Fi gure 2. Though hum idity was not re quired to be co ntrol le d in the chamber (per the standard Section 5.3.2) , tests at each co ndition fo r each re frigerant were re peated three ti mes to insure re sults were re produced and any hum idity variation was not impacting re sults Te sts wer e co nducted at thr ee amb ient co ndit ions 32°C re quir ed by the standar d and also 24°C and 21°C. An R-404A basel

ine was tested at the thr ee amb ient co ndit ions fi rst. At each co ndit ion, the evaporator ex it superheat was co ntr ol le d by adjust ing the TXV to 3-4K. The evaporator superheat was calculated fr om the suct ion pr essur e and the temperatur e re ading at the ex it of the evaporator

. The fr eezer internal average co mpartment temperatur e (average of fo ur thermoc ouple re adings, placed thr oughout the fr eezer co mpartment) was co ntr ol le d to -17°C. The co mpr essor was al lo wed to cy cle to ma inta in the cab inet set po int temperatur e. Te mperatur es and pr essur es ar e re ported as averages onl y wh ile the co mpr essor was runn ing. After test ing, R404A was re placed with DR-7, then DR-33. In each test, the system was fl ushed to re move lu bricant and a new char ge of the same type of POE lu bricant was added to the system. No other changes wer e made to the system exc ept to adjust the evaporator superheat with the TXV to match R-404A superheat co ndit ions. Fo r both candidate re frigerants, the TXV s wer e closed one turn. Steady state re sults ar e shown in Ta ble 3.

Table 3: Reach-in Freezer Steady State Test Results Figure 1: R-404A Reach-in freezer used in ex perimental testing Figure 2: Schematic showing instrumentation of reach-in freezer

Ener gy Co nsumption [kWh/da y] Ener gy

Co ns Rel to R404A Evap Exit

Sup Heat [K] Mass

Flow Rate [kg/h] Suction

Pr essur e [kPa] Dischar

ge Pr essur e [kPa] Co mpr

Ratio Co mp

Disch Te mp [°C] Amb ient t = 32°C R404A 33,46 100% 4 4 4 2 11 2027 10 90 DR-7 30,81 92% 3 3 4 1 91 2133 11 105 DR-33 32,16 96% 4 3 0 1 72 1931 11 104 Amb ient t = 24°C R404A 25,11 100% 3 4 6 1 98 1647 8 7 5 DR-7 23,91 95% 4 3 5 1 84 1728 9 9 1 DR-33 25,00 100% 3 3 1 1 72 1551 9 8 8 Amb ient t = 21°C R404A 23,39 100% 3 4 8 1 99 1558 8 7 0 DR-7 22,62 97% 3 3 6 1 79 1600 9 8 5 DR-33 23,41 100% 3 3 3 1 72 1448 8 8 3



## Visit us @ www.acrt oda y.c o.uk December/January 2014 

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# REFRIGERAN TS



# 30 December/January 2014 

## A CR TO DA

Y Experimental re sults in the re ach-in fr eezer show DR-7 and DR-33 ex hi bi t sim ilar perf ormance co mpar ed to R-404A, with both demonstrating impr oved ener

gy effi ciency at hi gher amb ient co nditions. DR-7 co nsumed 8% le ss ener gy at 32°C amb ient temperatur

e and DR-33 4% le ss ener gy
. At lo wer amb ient co nditions, DR-7 still demonstrated 3-5% impr

oved effi ciency, wher

eas DR-33 was equival ent to R-404A. The mass fl ow rate was sl

ightl y lo wer and the dischar

ge temperatur

e was sl ightl y hi gher

. However

, the dischar

ge temperatur

es wer e still lo w enough to not re quir e li quid injection wh ich is usually needed at temperatur es gr eat than 125°C. Evaporator superheats and co mpr ession ratios fo r both refrigerants wer

e also sim ilar to R-404A. 

## Te st ing - Displa y Case with External Co ndensing Un it In order to co mpare system perf ormance of DR-33 in a system with R-404A, a spl it co ndensing un it with a 2,5m open fo od displa y case was selected. Both were ful ly instrumented and placed in two co nstant temperature ro oms, the displa y case in the indoor ro om (F ig. 3) and the co ndensing un it in an outdoor ro om (F ig. 4). The open displa y case was ful ly lo aded with fo od simulators.

Figure 3: Open Display Case in Indoor Room

Figure 4: Co ndensing Unit in Outdoor Room The whole system designed fo r R-404A was charged with 3,8kg, and DR-33 charge adjusted sl ightl y based on li quid density

. The co ndensing un it has a re ciprocating co mpressor wh ich uses a pol yo l ester (POE) 32 centistokes lu bricant. The test setup was selected to co nf orm to ASHRAE Standard 72-2005. Te sts were co nducted at two amb ient temperatures fo r the outdoor ro om, 35°C and 28°C and al ways at 24°C fo r the indoor ro om. An R-404A basel ine was tested at the two amb ient co nditions at lo w and medium temperature co nditions fi rst. After testing, R404A was re placed with DR-33. In each test, the system was fl ushed to re move lu bricant and a new charge of the same type of POE lu bricant was added to the system. No other changes were made to the system exc ept to adjust the evaporator superheat with the TXV to match R-404A superheat co nditions. Fo r DR-33 the TXVs were closed 1,6 turns. Steady state re sults are shown fo r LT

- in Ta ble 4.1 and fo r MT

co nditions in Ta ble 4.2.

Table 4.1: Co ndensing unit/ Display Case LT -T est Results

Table 4.2: Co ndensing unit/ Display Case MT-T est Results Experimental re sults fo r the co ndensing un it with display case show DR-33 ex hi bi ts sim ilar perf ormance co mpared to R-404A in lo w and medium temperature co nditions, with both demonstrating improved energy effi ciency, especial ly at hi gher amb ient co nditions. Te st re sults show DR-33 co nsumed 3-4% le ss energy in lo w temperature and 8-12% in medium temperature. The suction pressure was in both cases sim ilar than R-404A and the discharge pressure fo r both co nditions lo wer
. The mass flow rate was sl ightl y lo wer and the discharge temperature was sl ightl y hi gher

. However, the discharge temperatures of DR-33 were stil l lo w enough to not re quire li quid injection wh ich is usual ly needed at temperatures great than 125°C. Evaporator superheats and co mpression ratios were also sim ilar to R-404A. 

## Co ncl usion Tw o new lo w GWP re frigerants have been developed wh ich can potent ial ly re place R-404A in co mmer cial re frigerat ion. The fi rst, DR-7 has a GWP of about 250 wh ich is 94% lo wer than R-404A. It is mi ld ly fl ammable (2L) and ther ef or e ma y have some li mi tat ions fo r use in lar ger re frigerant char ge systems such as supermark et racks. However, it co uld be suitable fo r single co ndensing un it systems and stand-alone co olers and fr eezers. DR-33 is fo rmulated to be nonfl ammable, with a GWP of about 1400 wh ich is about 65% lo wer than R-404A. It is suitable fo r lar ge rack systems and other re frigerat ion un its wher e use of fl ammable re frigerants is not pr ef

err ed or is re stricted. It is also a potent ial re tr ofi t re frigerant. Pe rf ormance of both re frigerants has been eval uated in a re ach-in fr eezer and DR-33 in a spl it co ndensing un it with displa y case, original ly designed fo r R-404A. The onl y changes made to the system wer e a TXV adjustment to co mpar e at equivalent evaporator superheat. Overal l, ener gy co nsumpt ion fo r both re frigerants is at le ast equivalent to R-404A wh ile other perf ormance parameters ar e sim ilar

. At the re ach-in fr eezer at hi gher amb ient co ndit ions, DR-33 and DR-7 ex hi bi t 4 and 8% lo wer ener gy co nsumpt ion re spect ivel

y. Te st re sults fr om the co ndensing un it with DR-33 showed 3% lo wer ener gy co nsumpt ion at lo w temp and even 8-12% impr ovement vs R-404A at medium temp co ndit ions. Use of these lo w GWP re frigerants can eff ectivel y re duce the en vironmental impact of re frigeration systems by al lo wing transition away from R-404A with mi ni mal system changes. Ener gy Co ns Rel to R404A [%] Mass Flow

Rate [kg/h] Suction

Pr essur e [kPa] Dischar ge

Pr essur e [kPa] Co mp.

Ratio Avg Fo od

Te mp [°C] Co mp

Disch Te mp [°C] Amb ient t = 28°C R404A 100 32 112 1438 12,8 -17 78 DR-33 97 26 104 1407 13,5 -17 83 Amb ient t = 35°C R404A 100 33 127 1722 13,6 -16 87 DR-33 96 26 115 1685 14,6 -15 92

Ener gy Co ns Rel to R404A [%] Mass Flow

Rate [kg/h] Suction

Pr essur e [kPa] Dischar ge

Pr essur e [kPa] Co mp.

Ratio Avg Fo od

Te mp [°C] Co mp

Disch Te mp [°C] Amb ient t = 28°C R404A 100 38 262 1544 5,9 2,2 72 DR-33 92 32 262 1496 5,7 2,2 75 Amb ient t = 35°C R404A 100 41 248 1827 7,4 2,2 82 DR-33 88 34 283 1792 6,3 2,8 84

Barbara Minor DuPont Fl uor opr oducts USA BA RB ARA.H.MINOR@dupont.c om Joach im Gerstel DuPont Fl uor opr oducts German y JO AC HIM.GERSTEL@dupont.c om Please see re fe re nces and discla imer on AC R To day website.

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