Soft-optimization test of R-410A alternative refrigerant R-32 in a split condensing unit - Phase II

Stephen Li

Daikin / Goodman Manufacturing

Jan. 2016

1

See the impact of R-32 on air conditioning

system;

Extend to extreme conditions in cooling mode

and observe the degradation of different

refrigerants;

Check impact of compressor lubrication oil on

system performance;

2

Test objectives

Test combinations & steps

3

• Tests performed

– Test unit:SSX140361 + ARPT36D14;

– Rating w/ original compressor ZP29K5E-PFV: 34,000 btu/hr, EERA 12, SEER 14.5;

– ANSI/AHRI 210/240 cooling conditions A/ B/ C/ D & (115oF/ 84, 66oF)/ (125oF/ 84,

66oF), required by AHRI;

– Tested with compressor ZP31K6E-PFV;

– Test 1 (baseline) - R410A, POE oil, 4T TXV, charge determination;

– Test 2 - R-32, POE oil, 3T TXV, charge determination;

– Test 3 – R-32, prototype R-32 POE oil, 3T TXV, charge determination;

• Test / optimization steps

– ID TXV was adjusted based on superheat (SH) out of evaporator (E/O) = 3 oF;

– Charge was adjusted based on subcool (SC) at liquid service valve (LSV)=

8 oF;

– ID fan @ low speed w/ static pressure 0.23” H2O;

Lubrication oil comparison

4

Copeland POE Copeland Prototype R32 oil

Supplier Emkarate RL 32-3MAF Chemtura

density g/cm3 at 20 degC 0.981

viscosity cst@40degC 31.2 46

cst@100degC 5.61

Flash point 240 473

Pour point -40

Water content ppm 40 slightly soluble

Polyol ester % >99

Additives % <1

Color clear yellow clear

Form liquid liquid

Odor No data typical ester-like

Stability Stable avoid heater, strong acids and

strong bases, hazardous

decomposition products:

carbon oxides

Test setup & instrumentation

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comp

OD

coil

dryer

TXV

Sight

glass

ID

coil

OD ROOM ID ROOM

P, T

#1

T

#5

T

#14

P, T

#11

P, T

#13

P, T

#17

Flow

meter

cooling

m

P, T

#19

T#7

P, T

#24

Pressure & temperature measurement locations

6

data locations in refrigeration system P T

Comp discharge (#1) x1 x1

OD coil common in (#5) x1

OD coil out (#7) x1

OD Liquid @ SV (#11) x1 x1

Before ID TXV (#13) x1 x1

ID coil in (#14) x1

ID coil common out @ TXV bulb (#17) x1 x1

OD vapor @ SV (#19) x1 x1

Comp suction (#24) x1 x1

Total x6 x9

Compressor was tripped when testing R-32 (test 2) at 125 oFOD ambient by compressor overload protector and maybe by HPS as well, therefore, no test of 125 oF in test 2;

Another compressor of same model was used in test 3 with prototype R-32 POE oil, therefore, an unknown compressor-to-compressor variation was introduced;

Difference of heat balance is larger than the improvement of EER of R-32, therefore, refrigerant side capacity and efficiency are calculated for comparison;

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What happened during test

test # compressor oil refrigerant TXV test conditions optimization

1 ZP31K6E-PFV

#1

POE R410A 4T A/B/C/D/

(115, 84/66) /

(125, 84/66)

E/O SH = 3 F,

LSV SC = 8 F

@ 95 F

2 ZP31K6E-PFV

#1

POE R32 3T A/B/C/D/

(115, 84/66) /

(125, 84/66)

E/O SH = 3 F,

LSV SC = 8 F

@ 95 F

3 ZP31K6E-PFV

#2

prototype POE R32 3T A/B/C/D/

(115, 84/66) /

(125, 84/66)

E/O SH = 3 F,

LSV SC = 8 F

@ 95 F

System capacity – air side

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• For each combination of ref. and oil, capacity decreases as OD ambient temp increases;

• R-32 has better capacity than R410A at rating conditions +4% w/ POE and 7% w/ the prototype

R-32 oil;

• At high ambient conditions, R-32 shows even better capacity (up to +14%);

• R-32 has less HAT degradation than R410A;

System efficiency – air side

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• For each combination of ref. and oil, system eff. decreases as OD ambient temp increases;

• Due to heat balance, R-32 shows same EERA, EERB, and SEER, but better efficiency (+0.5) w/

prototype R-32 oil;

System capacity – refrigerant side

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• For each combination of ref. and oil, capacity decreases as OD ambient temp increases;

• By eliminating the impact of heat balance, R-32 has better capacity than R410A at rating conditions +6% w/ POE and ~ 8% w/ prototype R-32 oil;

• At high ambient, R-32 capacity is even higher (+13%);

• R-32 has lower high ambient temperature conditions (HAT) degradation than R410A;

System efficiency – refrigerant side

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• For each combination of ref. and oil, system eff. decreases as OD ambient temp increases;

• R-32 shows better EERA, EERB, and SEER (+0.1 ~ 0.5) by eliminating the impact of heat

balance;

• At high ambient conditions, R-32 efficiency is even higher than R410A (+0.7);

Charge & cyclic degradation coefficient

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• Charge reduction is about 12-14% in this air conditioning unit;

• Cd of R-32 w/ prototype R-32 oil is within test accuracy;

R410A + POE oil R32 + POE oil R32 + prototype oil

M (oz) 101 87 89

Cd 0.11 0.109 0.081

Refrigerant flow rate

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• R-32 flow rate is consistently ~30% lower than R410A;

Outdoor coil pressure drop

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• ∆pOD = discharge pressure – LSV pressure

• Due to lower flow rate, R-32 has 2 ~ 4 psi lower pressure drop across the OD coil;

• 5mm HP may be possible with R-32 application;

Indoor coil pressure drop

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• ∆pID = after expansion pressure – suction pressure

• Due to lower flow rate, R-32 has 2 ~ 4 psi lower pressure drop across the ID coil;

• Smaller tube size may be possible for R-32 application;

Compressor discharge pressure

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• R-32 discharge pressure is approximately 10 psi higher than R410A at rating conditions;

• At high ambient conditions, R-32 discharge pressure is 15 ~ 18 psi higher than R410A;

Compressor discharge temperature

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• R-32 discharge temperature is approximately 20+ oF higher than R410A;

• At high ambient conditions, R-32 discharge temperature is over 30 oF higher than R410A which

could be the reason that R-32 test trips at 125 oF;

• Further optimization of oil, compressor, & system may be needed to reduce discharge temperature;

Compressor isentropic efficiency

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• ɳs = (hout,s - hin) / (hout - hin)

• R-32 shows higher compressor isentropic efficiency that R410A;

Compressor volumetric efficiency

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• ɳv = mref / (ρ V RPM)

• Overall, R-32 shows lower compressor volumetric efficiency w/ POE oil than R410A at rating

condition, but better w/ prototype R-32 oil;

• At HAT, R-32 has better compressor volumetric efficiency than R410A;

Conclusions R-32 works in existing R410A system, including extreme conditions;

Due to R-32 high discharge temperature, there is risk of compressor tripping at 125 oF

ambient, the compressor needs to be modified to adapt to high ambient operation;

Heat balance has big impact on the comparison of air side capacity and efficiency,

therefore refrigerant side capacity and efficiency need to be considered;

R-32 has higher capacity by 4 ~ 8% and efficiency by +0.1 ~ 0.4 at rating conditions;

R-32 shows higher capacity (up to +14%) and efficiency (up to +0.8) at HAT conditions. The

HAT degradation of R-32 is less than R410A;

R-32 has higher discharge pressure (+10 psi) and discharge temperature (+25 oF) than

R410A at rating conditions;

At HAT, R-32 discharge pressure and temperature is even higher, +20 psi and +50 oF,

respectively;

Cd of R-32 is within test accuracy;

Charge of R-32 is 13% lower than R410A for this condensing unit;

R-32 flow rate is 30% lower than R410A, therefore, pressure drop of OD and ID unit is 2 ~ 4

psi lower;

R-32 shows higher compressor isentropic efficiency and lower volumetric efficiency w/

POE oil than R410A at rating conditions, but better in both w/ prototype R-32 oil;

R-32 has better compressor isentropic efficiency and volumetric efficiency than R410A at

HAT;

Although there is compressor-to-compressor variation, the prototype R-32 oil from

Copeland shows positive impact on system performance with R-32 refrigerant;

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