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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
5
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;
7
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
8
• 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
9
• 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
10
• 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
11
• 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
12
• 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
13
• R-32 flow rate is consistently ~30% lower than R410A;
Outdoor coil pressure drop
14
• ∆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
15
• ∆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
16
• 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
17
• 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
18
• ɳs = (hout,s - hin) / (hout - hin)
• R-32 shows higher compressor isentropic efficiency that R410A;
Compressor volumetric efficiency
19
• 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;
20