# Alternative Refrigerant AC6 

# Performance Evaluation and Optimization Potential

Sept 28, 2011

By Xinzhong Li Manager of Engineering Creative Thermal Solutions, Inc2



# Presentation Objectives

• 

### CTS introduction

• 

### System and facility used for the evaluation

• 

### Performance of new refrigerant

– AC6 as a drop in replacement for R134a

• 

### Different from R134a:

• High glide zeotropic refrigerant blend

• 

## Analysis of results

• 

### Focus on evaporator distribution

• 

## Discussion of possible improvements??3 

# CTS

- Creative Thermal Solutions, Inc.

Located in Urbana, Illinois near the Univ. of Illinois

 Thermal lab covering 6,000 m 2

 50+ Engineers and technicians

 100+ publications in the thermal
area

 17 environmental chambers for test of Mobile Air Conditioning Systems

 18 environmental chambers for test of Stationary Systems

 MAC leak test facilities following EU and SAE standards

 Various specialized MAC facilities

 In

- house support for fabrication and instrument calibration

 Involved in four previous SAE CRP development activities4



## MAC system hardware

Mid

- size Sedan system Features Core size W*H*D [mm] Overall size

W*H*D [mm] Face Area

[m2]

Evaporators Plate

- fin two slab 4 passes 258*211*58 263*250*58 0.054

Condenser Micro

- channel

condenser with IRD 630*385*16 668*397*16 0.243

IHX Extruded tube type

Compressor ext controlled var disp Control based on average nozzle temperature out of evaporator 163 cc [3

- 100%]5



## Evaluation framework: single evaporator TXV system in environmental chambers

All tests per SAE J27656 

## Three energy balances within ± 3%7 9/28/2011 

# AC6 performance equal to R134a at T amb 

## 35 ° C (high Load) Performance8 9/28/2011 

## AC6 efficiency equal to R134a at 

# T amb 

# 35 ° C (high load)9 

# Performance

- 25 ° C x 80% (low load)

Capacity controlled to be equal10 

## Efficiency

- 25 ° C x 80% (low load)

AC6 efficiency lower than R134a11



# Performance summary

 At high loads (high ambient temperatures):

 Compressor run full stroke

 Capacity equal to R134a

 COP equal to R134a

 At low loads (low ambient temperatures):

 Compressor run at reduced stroke to match the target temp setting

 Capacity controlled to be equal to R134a

 COP lower than R134a

 Difficulties in achieving good distribution with AC6 clearly identified as the main reason

 We have seen similar distribution issues in almost every new refrigerant when used as a drop

- in alternate12 

## What is happening at low loads with



# the evaporator !?

Use modeling for analysis13 

# Good agreement @ high load H35

R134a and AC6 show very good agreement Model (dashed) vs. experiment (solid) lines

Good agreement for different fluids show that refrigerant and circuiting effects are predicted well14 

# Model agrees well with test data
Since evaporator models capture the effects of glides and pressure drops but not mal

- distribution, excellent agreement in previous high load conditions indicates good distribution for both R134a and AC6.

Let’s look at low load15 

## Worse model 

# prediction for AC6 than for R134a 

# at low load L25

R134a model shows small over

- prediction

Mal

- distribution with AC6 is left as the only suspect for the difference (2 o C) between the model and the experiment16 

# Can we see effects of distribution

in the test data?17 

# Look at the refrigerant circuit

first Understanding evaporator

• Four passes

• Two slabs18 

# TC grid (5X4) at the air outlet Understanding evaporator

15 14 11 12 13

25 24 2 1

22 23

35 34 31

32 33

45 44 41

42 43 Differences due to GLIDE

Difference from mal

- distribution19 

## Actual T eao 

## at high load indicate good



# distribution20 

## Temperature distribution at low load indicates mal

- distribution forAC6

Is there any effect of glide in variation ?21 Actual vs. predicted exit air temperature: mal

- distribution @ 25 o C (low load) is more

pronounced for AC6

Top Bottom22



# So, what we learned

• 

### Experiments show very good agreements with CTS 

### model for R134a at high loads where distribution is good

• 

### The same model provides the same good 

### agreement with experiments for AC6 at high loads (good distribution for AC6)

• 

### Measured data agree with the model with R134a at low load (acceptable distribution)

• 

### Model over

- predicts experiments with AC6 at low load

– mal

- distribution is a reasonable explanation23 

# Assessment of potential improvement: COP increase 6.6%

At equal capacity the system model shows that with 2 ° C increase in average evaporating temperature:

COP will increase 6.6%

A new design for the evaporator has a big potential24



# Conclusions

9/28/2011  At high loads (high ambient temperatures):

 Capacity equal to R134a

 COP equal to R134a

 At low loads (low ambient temperatures):

 Controlled to be equal capacity to R134a

 COP lower than R134a

 Refrigerant mal

- distribution identified as a main reason for lower efficiency with AC6 at low loads

 Improving refrigerant distribution in evaporator could improve efficiency for 6.6% at low loads25 

## Other opportunities to make AC6 equal to or better than R

- 1234yf at

low load

• 

### Cycle optimization

• SH control

• Charge optimization (SC control)

• 

### Condenser optimization

• The condenser model indicated potentials for improvement of system efficiency and reduction of high discharge pressure for AC6

• Will test new condensers with different pass configurations in the next steps