Alternatives in Commercial Refrigeration

This is the second installment of a two part series looking at the testing of new low GWP 404A

alternative. In the last issue (November) we looked at the thermodynamic properties and

performance of the refrigerant. In this issue of we will cover practical testing of DR-7 and DR-33

in commercial food storage units.

Reach-in freezer system testing

In order to measure system performance of DR-7

and DR-33 in a system, a reach-in freezer was

selected (Fig. 1), fully instrumented and placed

in a constant temperature room. The freezer is

a 1,5 m3 double-door unit designed for R-404A

with a refrigerant charge size of 1,15 kg. It has

a reciprocating compressor which uses a polyol

ester (POE) 32 centistokes lubricant. The test

setup was selected to conform as closely as

possible to AHAM Standard HRF-1-2008 Energy

and Internal Volume of Refrigerating Appliances

(AHAM 2008). It was not possible to use ANSI/

ASHRAE Standard 72 because the system was

not set up to open and close freezer doors during

the test. The reach-in freezer is controlled with

two thermostatic expansion valves (TXVs).

REFRIGERANTS

The empty freezer (per AHAM HRF-1-2008) was placed in a constant temperature room and fully

instrumented with temperatures (T), pressures (P), mass flow rate (M) and energy measurement (W),

shown in Figure 2. Though humidity was not required to be controlled in the chamber (per the standard

Section 5.3.2) , tests at each condition for each refrigerant were repeated three times to insure results were

reproduced and any humidity variation was not impacting results

Tests were conducted at three

ambient conditions 32°C

required by the standard

and also 24°C and 21°C. An

R-404A baseline was tested at

the three ambient conditions

first. At each condition, the

evaporator exit superheat was

controlled by adjusting the

TXV to 3-4K. The evaporator

superheat was calculated from

the suction pressure and the

temperature reading at the exit

of the evaporator. The freezer

internal average compartment

temperature (average of four

thermocouple readings, placed throughout the freezer compartment) was controlled to -17°C. The

compressor was allowed to cycle to maintain the cabinet set point temperature.

Temperatures and pressures are reported as averages only while the compressor was running. After

testing, R404A was replaced with DR-7, then DR-33. In each test, the system was flushed to remove

lubricant and a new charge of the same type of POE lubricant was added to the system. No other

changes were made to the system except to adjust the evaporator superheat with the TXV to match

R-404A superheat conditions. For both candidate refrigerants, the TXVs were closed one turn. Steady

state results are shown in Table 3.

Table 3: Reach-in Freezer Steady State Test Results

Figure 1:

R-404AReach-infreezerusedinexperimentaltesting

Figure 2:

Schematic showing instrumentation

of reach-in freezer

Energy

Consumption

[kWh/day]

Energy

Cons Rel

to R404A

Evap Exit

Sup Heat

[K]

Mass

Flow Rate

[kg/h]

Suction

Pressure

[kPa]

Discharge

Pressure

[kPa]

Compr

Ratio

Comp

Disch

Temp

[°C]

Ambient t = 32°C

R404A 33,46 100% 4 44 211 2027 10 90

DR-7 30,81 92% 3 34 191 2133 11 105

DR-33 32,16 96% 4 30 172 1931 11 104

Ambient t = 24°C

R404A 25,11 100% 3 46 198 1647 8 75

DR-7 23,91 95% 4 35 184 1728 9 91

DR-33 25,00 100% 3 31 172 1551 9 88

Ambient t = 21°C

R404A 23,39 100% 3 48 199 1558 8 70

DR-7 22,62 97% 3 36 179 1600 9 85

DR-33 23,41 100% 3 33 172 1448 8 83

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REFRIGERANTS

30 December/January 2014 ACR TODAY

Experimentalresults in the reach-in freezer show

DR-7 and DR-33 exhibit similar performance

compared to R-404A, with both demonstrating

improved energy efficiency at higher ambient

conditions. DR-7 consumed 8% less energy at 32°C

ambient temperature and DR-33 4% less energy. At

lower ambient conditions, DR-7 still demonstrated

3-5% improved efficiency, whereas DR-33 was

equivalent to R-404A. The mass flow rate was slightly

lower and the discharge temperature was slightly

higher. However, the discharge temperatures were

still low enough to notrequire liquid injection which

is usually needed at temperatures great than 125°C.

Evaporator superheats and compression ratios for

both refrigerants were also similarto R-404A.

Testing - Display Case with

External Condensing Unit

In order to compare system performance of DR-33

in a system with R-404A, a split condensing unit

with a 2,5m open food display case was selected.

Both were fully instrumented and placed in two

constant temperature rooms, the display case in

the indoor room (Fig. 3) and the condensing unit

in an outdoor room (Fig. 4). The open display case

was fully loaded with food simulators.

Figure 3: Open Display Case in Indoor Room

Figure 4: Condensing Unit in Outdoor Room

The whole system designed for R-404A was

charged with 3,8kg, and DR-33 charge adjusted

slightly based on liquid density. The condensing

unit has a reciprocating compressor which uses a

polyol ester (POE) 32 centistokes lubricant. The test

setup was selected to conform to ASHRAE Standard

72-2005. Tests were conducted at two ambient

temperatures for the outdoor room, 35°C and 28°C

and always at 24°C for the indoor room. An R-404A

baseline was tested at the two ambient conditions at low and medium temperature conditions first. After

testing, R404A was replaced with DR-33. In each test, the system was flushed to remove lubricant and a

new charge of the same type of POE lubricant was added to the system. No other changes were made to

the system except to adjust the evaporator superheat with the TXV to match R-404A superheat conditions.

For DR-33 the TXVs were closed 1,6 turns. Steady state results are shown for LT- in Table 4.1 and for MTconditions in Table 4.2.

Table 4.1: Condensing unit/ Display Case LT-Test Results

Table 4.2: Condensing unit/ Display Case MT-Test Results

Experimental results for the condensing unit with display case show DR-33 exhibits similar performance

compared to R-404A in low and medium temperature conditions, with both demonstrating improved energy

efficiency, especially at higher ambient conditions. Test results show DR-33 consumed 3-4% less energy in

low temperature and 8-12% in medium temperature. The suction pressure was in both cases similar than

R-404A and the discharge pressure for both conditions lower. The mass flow rate was slightly lower and the

discharge temperature was slightly higher. However, the discharge temperatures of DR-33 were still low

enough to not require liquid injection which is usually needed at temperatures great than 125°C. Evaporator

superheats and compression ratios were also similar to R-404A.

Conclusion

Two new low GWP refrigerants have been

developed which can potentially replace R-404A

in commercial refrigeration. The first, DR-7 has

a GWP of about 250 which is 94% lower than

R-404A. It is mildly flammable (2L) and therefore

may have some limitations for use in larger

refrigerant charge systems such as supermarket

racks. However, it could be suitable for single

condensing unit systems and stand-alone

coolers and freezers. DR-33 is formulated to be

nonflammable, with a GWP of about 1400 which is

about 65% lower than R-404A.

It is suitable for large rack systems and other

refrigeration units where use of flammable

refrigerants is not preferred or is restricted. It is

also a potential retrofit refrigerant. Performance of

both refrigerants has been evaluated in a reach-in

freezer and DR-33 in a split condensing unit with

display case, originally designed for R-404A.

The only changes made to the system were

a TXV adjustment to compare at equivalent

evaporator superheat. Overall, energy

consumption for both refrigerants is at least

equivalent to R-404A while other performance

parameters are similar. At the reach-in freezer

at higher ambient conditions, DR-33 and DR-7

exhibit 4 and 8% lower energy consumption

respectively. Test results from the condensing unit

with DR-33 showed 3% lower energy consumption

at low temp and even 8-12% improvement vs

R-404A at medium temp conditions.

Use of these low GWP refrigerants can effectively

reduce the environmental impact of refrigeration

systems by allowing transition away from R-404A

with minimal system changes.

Energy Cons

Rel to R404A

[%]

Mass Flow

Rate

[kg/h]

Suction

Pressure

[kPa]

Discharge

Pressure

[kPa]

Comp.

Ratio

Avg Food

Temp

[°C]

Comp

Disch

Temp [°C]

Ambient t = 28°C

R404A 100 32 112 1438 12,8 -17 78

DR-33 97 26 104 1407 13,5 -17 83

Ambient t = 35°C

R404A 100 33 127 1722 13,6 -16 87

DR-33 96 26 115 1685 14,6 -15 92

Energy Cons

Rel to R404A

[%]

Mass Flow

Rate

[kg/h]

Suction

Pressure

[kPa]

Discharge

Pressure

[kPa]

Comp.

Ratio

Avg Food

Temp

[°C]

Comp

Disch

Temp [°C]

Ambient t = 28°C

R404A 100 38 262 1544 5,9 2,2 72

DR-33 92 32 262 1496 5,7 2,2 75

Ambient 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 Fluoroproducts USA

BARBARA.H.MINOR@dupont.com

Joachim Gerstel

DuPont Fluoroproducts Germany

JOACHIM.GERSTEL@dupont.com

Please see references and disclaimer on ACR Today website.

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