Significant Fuel Savings and E

Reductions by Improving Vehicle Ai

John Rugh 

National Renewable Energy Laboratory 

Valerie Hovland 

Mesoscopic Devices 

Stephen O. Andersen 

U.S. Environmental Protection Agency

15th Annual Earth Technologies Forum and Mobile Air Co

April 15, 2004 
Outline

• Modeling approach

• Thermal comfort-based AC 

fuel use prediction 

• Model updates 

• Fuel saved for up to 30%

drop in AC power (equal to a43% increase in COP) 

• Per vehicle (cars, light trucks) • By climate • Total savings and CO2 

reductions across California, U.S., EU, and Japan 

(1.8 billion g

26 billion lit

6.9 billion lit
Predicting Fuel Used fo

• 

– 

2) 

– – 

State A 

TMY Month T C 

T 

H 

PPD Time PPD 

VMT 

w/ 

AC 

MPG 

MPG 

Apr 

July 

0 

0 0 

5 

5 

10 

10 

15 

15 

20 

25 

(C) i

f

Model 

0 5 

10 15 20 25 

i i ime 

1500 

( ) 

i ( ) 

i

Use Multiple Models/Inputs/Data Sets 

Environmental Conditions (Temp, RH, W/m

Thermal Comfort Model Vehicle Simulations (Fuel Economy Reduction 

City B 

City X 

City A 

w/ AC 

w/o AC 

12-6am 6-9am 9am-1pm 1-4pm 4-7pm 7-10pm 10pm-12am 

Jan 

Feb 

Mar 

May 

June 

Aug 

Sept 

Oct 

Nov 

Dec 

Temper atur e n Denver, CO 

Month 

Ti me o Day 

Thermal 

Comfort 

12-6am 6-9am 9am-1pm 1-4pm 4-7pm 7-10pm 10pm-12am 

Hour of the Day 

Percentage of Travel Occurr ng dur ng that T 0.0 1.0 

2.0 3.0 4.0 5.0 6.0 

1000 2000 2500 3000 

Compressor Speed rpm

System Power Consumpt on kW Fixed D 

Fixed D Var D sDefrosDefrosDefros
Model Updates

• Updates to U.S. study, Summer 2003 

– Mean Radiant Temperature varies with vehicle 

• Therefore usage PPD varies with type 

– Thermal comfort: use one assumption for cloth– Include demisting – AC power consumption = f(type, compressor s

State A 

TMY Month T C 

T 

H 

PPD Time PPD 

VMT 

w/ 

AC 

MPG 

MPG 

Demist 

City B 

City X 

City A 

w/ AC 

w/o AC 
Environmental Condition

Phoenix, AZ: Temperatu

State A 

TMY TC Month

T 

H 

PPD 

PPD VMT 

MPG MPG 

Jan 

Feb Mar 

Apr 

June 

Aug 

Sept 

Oct Nov 

Dec 10 

10 

15 

15 

15 

15 

20 

20 

25 

25 

30 

35

Month 

City B 

Time 

City X 

City A 

w/AC 

w/AC 

w/o AC 

12-6am 6-9am 9am-1pm 1-4pm 4-7pm 7-10pm10pm-1

May 

July 

Temperature (C) in Phoenix, AZ 

Time of Day 
Mean Radiant Temperatur

• MRT varies with vehicle type (c• Vehicle data used to generate 

• Ford Crown Victoria • Ford Explorer (White) • Ward At• Plymouth Breeze • Ford Explorer (Black) • Bill Hill – • Jeep Grand Cherokee • Lincoln Navigator 

• Dodge Grand Caravan 

Models 

MRT(car, time) = * Radiation(t)/1000

MRT(truck, time) = 24°C 

27°C 

* Radiation(t)/1000
Mean Radiant Temperatur

Jan 

Feb Mar 

Apr 

June 

Aug 

Sept 

Oct Nov 

Dec 10 

10 

20 

20 

20 

30 

30 

40 

50 

60 

Mean Radiant Temperature (C) in Pho

Month 

May 

July 

12-6am 6-9am 9am-1pm 1-4pm 4-7pm 7

Time of Day 
Thermal Comfort Mode

Percent of People Using 

-3 -2 -1 0 1 

0 

10 20 30 40 50 60 70 80 90 

100 

PPD 

Thermal Comfort Model, 

+ 3 + 2 + 1 

0 

Slightly Cool 

-2 l -3 ld 

PMV Thermal Sensation 

State A 

TMY TC Month

T 

H 

PPD 

PPD VMT 

MPG MPG 

Thermal Sensatio

Cool 

PPD from PMV 

Hot 

Warm 

Slightly Warm 

Neutral 

- 1 

CooCo

City B 

Time 

City X 

City A 

w/AC 

w/AC 

w/o AC 
AC Usage for Coolin

Predicted Percent Dissatisfied (%) in Phoen

Clothing: 0.6, Velocity: 0.1, MRT: Ambient+

Dec 10 1

Month 

NovOct

Sept

AugJuly

June

May

Apr

MarFeb

Jan

1 

1 

10 

10 

20 

20 

30 

30 

40 

40 

50 

60 

70 

80 

90 

AC 

100% of People 

Have AC On 

12-6am 6-9am 9am-1pm 1-4pm 4-7pm 7-

Time of Day 
AC Usage for Demist

AC used for demist if: 

Temperature is between 1.7-12.8°C (35-55°F), and Relative 

Month 

Demist Percent Usage in Brussels, BEL 

Dec 

Nov Oct 

Sept 

Aug July 

June 

May 

Apr 

Mar Feb 

Jan 

1 

1 

10 

No Demist Usage 

20 

20 

30 

30 

40 

40 

50 

50 

60 

60 

70 

70 

80 

80 

90 

90 

100% Demist Usage 

12-6am 6-9am 9am-1pm 1-4pm 4-7pm 7-10p

Time of Day 
Vehicle Usage with Time of D

State A 

TMY TC Month

T 

H 

PPD 

PPD VMT 

MPG MPG 

City B 

Time 

City X 

City A 

w/AC 

w/AC 

w/o AC 

10 15 20 25 

70% Daily Travel 

Percentage of Travel Occurring

in that Month

9 8 7 6 5 4 3 2 

M

Averag

Percentage of Travel Occurring

during that Time 

12-6am 6-9am9am-1pm1-4pm 4-7pm 7-10pm10pm-12am 

1 00 2 4 

Hour of the Day Mo

0 5 
15

27

17

25

18

31

26

49

40

23

50

26

42

40

25

21

41

32

23

26

19

38

18

52

33

20

24

28

50

30 33

25 32

23

26

69

41

57

21 29

58 43

43

6

Percent of Time AC is O

Cooling + Demist 

State A 

TMY TC Month

T 

H 

PPD 

PPD VMT 

MPG MPG 

City B 

Time 

City X 

City A 

w/AC 

w/AC 

w/o AC 

10 

14 

19 

15 

27 

17 

25 

18 

31 

26 

49 

40 

23 

50 

26 

42 

40 

25 

21 

41 

32 

23 

26 

19 

38 

18 

52 

33 

20 

24 

28 

50 

30 33 

25 32

23 

26 

69 

41 

57 

28 

2

21 29 

58 43 

43 

6 
23

24

23

21

26

27

27

25 

23

27

24

23

26

25 

24

2

25

27

26

24

27

25 27

25 25

25

27

26

2

24 22

30 27

17

Climate during AC U

Temperature, Humidity 

19 

27 

24 

25 

27 

23 

24 

23 

21 

26 

27 

27 

25 

27

23 

27 

24 

23 

26 

25 

24 

2

25 

27 

26 

24

24 

27 

25 27 

25 25

25 

25

27 

26 

2

24 22 

30 27 

27

17 

U.S. Average: 25°C 
50

58

37

69

74

63

56

69

72

52

42

76

67

47

75

74

71

81

75 69

71 74

37

71

73

47 68

32 72

76

67

Climate during AC U

Temperature, Humidity 

77 

73 

50 

77

58 

37 

69 

74 

63 

56 

69 

72 

52 

42 

76 

67 

47 

75 

74 

73

71 

81 

75 69 

71 74

37 

71 

73 

47 68 

32 72 

76 

67 

U.S. Average: 66
Percent of Time 

AC in Use 

Cooling and 

Demisting 

ingdom 

i

land 

I land 

Fi

ic 

lgaria 

i

United K

Turkey 

Sw tzerland 

Sweden 

Spain 

Romania 

Portugal 

Po

Norway 

Netherlands 

Jap

Italy 

re

Hungary 

Greece 

Germany 

France 

nland 

Denmark 

Czech Republ

Bu

Belg um 

Austria 
Fuel Economy Impact: Vehicle 

State A 

TMY TC Month

T 

H 

PPD 

PPD VMT 

MPG 

MPG 

City B 

Time 

City X 

City A 

w/AC 

w/AC 

w/o AC 

US Car 

Fuel Economy no AC 22.0 

Fuel Economy with AC 18.0 

Fuel Economy defrost 21.1 

US Car 

FE Drop with AC 18% 

FTP drive cycle FE Drop with defrost 4% 

Hot initial 

conditions 

US car and truck based on e
0

1

4

4

1

6

2

15

5

1

3

1

9

3

3

10

12

1

1

7

1

1

1

6

1

2

9

1

4

4

2

9 5

1

3

1

6

12

3 24

3 2

4

0

Vehicle Registration

State A 

City B 

TMY TC Month

T 

H 

PPD Time 

PPD 

City X 

City A 

VMT 

w/AC 

MPG 

w/AC 

MPG 

w/o AC 

10 

14 

19 4 

4 

3 

0 

1 

4 

4 

1 

6 

2 

15 

5 

1 

3 

1 

9 

3 

3 

10 

12 

1 

1 

7 

1 

1 

1 

6 

1 

2 

4

4

9 

1 

4 

5 

4 

3 2 

9 5

1 

3 

1 

6 

12 

1 

3 

3 24 

3 2 

4 

0 

Million V

Registr

0.4 t0.7 t1.0 t1.4 t1.8 t2.8 t3.3 t3.9 t4.4 t6.0 t9.2 t12.5 
Distance Traveled per 

EU and Japan 

Spain 

l

Italy 

Fi

ic 

l

United Kingdom 

Turkey 

Switzerland 

Sweden 

Romania 

Portugal 

Poland 

Norway 

Nether ands 

Japan 

Ireland 

Hungary 

Greece 

Germany

France 

nland 

Denmark 

Czech Republ

Bulgaria 

Belgium 

Austria 

Vehic e KilometeTraveled 

6500 to 99803 to 110738 to 13321 to 14964 to 17537 to 
7

78

64

43

735

17

66

109

61

52

40

12

17

85

144

86

176

75

242 

26

68

68

76 730

216 86

1

National Fuel Used fo

State A 

City B 

TMY TC Month

T 

H 

PPD Time 

PPD 

City X 

City A 

VMT 

w/AC 

MPG 

w/AC 

MPG 

w/o AC 

• 7.0 billion 

gallons used forair conditioningannually 

• 5.5% total fuel 

consumption 

• 62 billion kg CO2 

• 9.5% imported 

crude oil 

7 

78 

64 

43 

735 

17 

66 

109 

61 

52 

40 

12 

17 

85 

144 

86 

176 

75 

242 

26 

68 

68 

76 730 

216 86 

1 
Total Fuel Use for AC for Cooli

Demisting 

i i

Swi

Spain 

Pol

Italy 

I

ic 

lgaria 

Bel

Totals 

Dehumid + 

Cooling 

Billion 

Gallons 

Billion 

Liters 

Billion kg 

CO2 

EU 100% Market 1.8 6.9 16.0 

Japan 100% Market 0.45 1.7 4.0 

Un ted K ngdom 

Turkey 

tzerland 

Sweden 

Romania 

Portugal 

and 

Norway 

Netherlands 

Japan 

reland 

Hungary 

Greece 

Germany 

France 

Finland 

Denmark 

Czech Republ

Bu

gium 

Austria 
-

AC 

-

1 2 3 4 5 6 7 8 

65% 70% 80% 85% 95% 100% 105% 

0 10 20 30 40 50 60 70 

U.S. Fuel Saved & CO2 Reduced 

by Reducing AC Consumption 

0.5 

0.9 

1.3 

1.7 

2.5 

Consumption 

0.1 

2.1 CO2 

Reduced AC Fuel 

Saved 

75% 90% 

AC Power Consumption: Percent of Baseline 

Billion Gallons 
5.4

6.4

5.0

10.1

17.9

14.2

8.3

7.7

14.0

8.7

16.4

12.5

10.0

6.9 7.1

16.6

11.9

7.9

17.8

12.1

9.3 9.9

8.7

28.2

8.3 11.0

22.8 14.7

15.3

0.4

Fuel Saved per Vehicle by 

30% Reduction in AC Pow

7.6 

10.9 

9.4 

14.0 

5.4 

6.4 

5.0 

10.1 

17.9 

14.2 

8.3 

7.7 

14.0 

8.7 

16.4 

12.5 

10.0 

6.9 

7.1 

16.6 

11.9 

7.9 

7.6

17.8 

10.9 12.1 

9.3 9.9

8.7 

9.4

28.2 

14.0

8.3 11.0 

22.8 14.7 

15.3 

0.4 
0 

2 4 6 8 

10 12 14 

65% 70% 75% 85% 90% 

li 

i 

li 

Per Vehicle Fuel Saved by Reducing AC Consumptio

3.9 

5.6 

7.5 

9.4 

11.0 

80% 95% 

AC Power Consumption: Percent of Baselin

Gallons Saved/Year 

Car: Base ne Use 33Truck: Basel ne Use Average: Base ne Us
U.S. Fuel Savings Taking in

New Technology Pene

• Assumptions

– 15% and 30% reductions 6 

3.7 bSave

in AC power 

– Power reductions begin 

5

in 2010 

4

– Fleet grows through time 

(DOE’s Vision model) 

3

• 234 million in 2010 2 • 293 million in 2050 

1 

– Fleet turnover in 16 

years 

02010 2015 2020 2025 2

– VMT increases over time Tim

• 13,500 miles in 2010 • 19,950 miles in 2050 

Billion Gallons per Year Saved 
Per Vehicle Savings from an Imp

$0 

Savings from an Improved HFC-134a A/C System

(2004 $) 

- /

 -

­ One A/

 ­

­-

$50 

$100 $150 $200 $250 $300 $350 $400 $450 

Assumptions:

 30% reduction in A C energy

 11 gallons of fuel per year saved

C service avoided in year 8

 Cost of service charge = $107

 Cost of fuel = 1.75 $/gal

 Costs rise at rate of inflation 

0 2 4 6 8 10 

Vehicle Life (years)
A l

70% 80% 85% 95% 

i li

Billion Gallons 

-2 4 6 8 10 12 14 16 18 

i

l i

Bil

EU Fuel Saved by ReducinAC Power Consumption 

V

0.02 

0.09 

0.19 

0.28 

0.37 

0.46 

0.56 

EU AC 

Consumption 

C Fue Saved 

CO2 Reduced 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 

65% 75% 90% 100% 105% 

AC Power Consumpt on: Percent of Base ne 

Billion kg CO2 

EU AC Consumpt on EU AC Fue Sav ngs 

 kg CO2 Saved 
i

l

65% 70% 75% 80% 85% 90% 95% 100% 105% 

i line 

Billion Gallons 

-

Billi

Japan Fuel Saved by ReduAC Power Consumption 

V

0.005 

0.02 

0.05 

0.07 

0.09 

0.11 

0.14 

Japan AC 

Consumpt on

 AC Fue Saved

 CO2 Reduced 

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 

AC Power Consumpt on: Percent of Base

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

on kg CO2 
Conclusions

• MAC fuel use & CO2 emissions are strong 

– Vehicle design – Vehicle use – Environment 

• Solutions to reduce fuel consumed by MA

– Reduce the thermal load – improve vehicle des– Improve delivery – design for occupant therma– Improve equipment – Educate consumers on impacts of driver behav

use 
Conclusions (cont

• Thermal comfort-based AC fuel use prediction 

US E

AC Fuel Use, Billion Gallons 7.0 1.

AC Fuel Use, Percent of Total 

Consumption 5.5% 3.2

• Reducing AC fuel use has the potential to greatly be

• Reduce imported oil • Reduce CO2 

• Per vehicle savings allow calculation of payback tim

30% Reduction in Power Units US California 

Savings per Vehicle gal/year 11.0 11.0 

Reference Total Consumption gal/year 30.8 30.5 Savings of Total Consumption % 2.0% - 

Fuel Saved Bil Gallons 2.5 0.26 Fuel Saved Bil Liters 9.5 1.0 

Emissions Reduced Bil k G CO2 22.1 2.3 

• Impact of incremental reduction in AC power: states
Fuel Savings across the 

Billion GallonsDrop in AC Pow
CO2 Reduction across th

Billion kg CO2: 

Drop in AC Pow
Thank you

Thank you

• John Rugh 

– Ph: 303-275-4413 – Email: john_rugh@nrel.gov 

• Valerie Hovland 

– Email: vhovland@mesoscopic.

• Stephen Andersen 

– Ph: 202-343-9069 – Email: andersen.stephen@epa
Back Up
Why So Much Fuel fo

150 Watts 

Metabolic Hea

A/C Cooling 

3-6 kWth! 

Generation 
Cities Used from TMY Da
• Plymouth Breeze

• July 12• Golden, CO

• Jeep Grand • July 12

10 • Golden, CO2030405060708090

5:30 7:30 9:30 11:30 13:30 15:30 17:30

Time

Temperature (C)

TrimSeatAirGlazingIPHeadliner AmbientModel

102030405060708090

5:30 7:30 9:30 

Temperature (C)

TrimSeatAirGlazingIPHeadliner AmbientModel

Car & Truck MRT
Vehicle Modeling in ADVISOR 

• 115 kW SI engine, 1300 kg • 144 kW SI, 1924 kg 

icle 

• 91 kW compression 

ignition diesel, 1220 kg 

gasoline equivalent fuel consumption 

2 

from fuel consumption 

• 

2/liter fuel 

1000 2000 3000 

0 

50 

100 150 200 250 300 350 

) 

(

ici

• U.S. Car • U.S. Truck • EU Veh• Fuel economy expressed in • CO emissions determined 

2.33 kg CO

Speed (rpm

Torque Nm) 

Engine Eff ency 

Mercedes 1.7L Diesel Engine 

0.0

0.15 

0.25 

0

0.35 0.4 

0.45 
AC Modeling

• HFC-134a 

• U.S. trucks: 210 cc fixed • U.S. cars: 180 cc fixed • EU vehicle: 125 cc 

variable displacement

• Compressor power 

consumption based onDelphi compressor curves

• Total power = Pcompressor + 

Pblower 

1000 1500 2000 

( 

i ) 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

2500 

Compressor Speed rp

System Power Consumpt on (kW

• Pblower = 120 W Curves based on work 

• Engine speed/compressor • Cooling mod

speed ratio = 0.64 • Demist mod
Conservative Estimat

Fuel Used for AC

• Fanger’s thermal comfort model 

excludes: 

– Sun hitting a driver – Thermal asymmetry – Sitting on a hot seat – High humidity impacts 

• Model excludes AC use due to

– Automatic Temperature Control 

• EU compressor power 
Se

Incremental Reduction in A

1000 1500 2000 3500 

) 

i ) . 

Fi 

Fi 

Fi 

85% of 

70% o

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

2500 3000 

Compressor Speed (rpm

System Power Consumpt on (kW

0.0 0.7 1.3 2.0 2.7 3.4 4.0 4.7 5.4 

Horsepower 
EU/Japan Per Vehicle Fuel S

Reducing AC Consumption 

65% 70% 80% 90% 95% 105% 

i li

Gallons Saved/Year/Vehicle

LitSd/Y/Vhil

li l

li l

0.08 

0.4 

0.8 

1.2 

1.6 

2.1 

2.5 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 

75% 85% 100% 

AC Power Consumpt on: Percent of Base ne 

0.0 2.0 4.0 6.0 8.0 10.0 EU Base ne: 8.0 gal ons 

Japan Base ne: 7.2 gal ons