NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Integrated Vehicle Thermal 

Management – Combining Fluid 

Loops in Electric Drive Vehicles

John P. Rugh

National Renewable Energy Laboratory

Vehicle Technologies Program Annual Merit Review

Arlington, Virginia

May 15, 2013

NREL/PR-5400-58161 Project ID: APE052

This presentation does not contain any proprietary, confidential, or otherwise restricted information.
2

Overview 

Project Start Date: FY11

Project End Date: FY14

Percent Complete: 50% 

• Cost – cooling loop components 

• Life – thermal effects on energy 

storage system (ESS) and advanced 

power electronics and electric 

motors (APEEM)

• Weight – additional cooling loops in 

electric drive vehicles (EDVs)

Total Project Funding (to date): $ 1225 K *

Funding received prior to FY13: $ 750 K *

Funding for FY13: $ 475 K *

Partner In-Kind Cost Share: $ 300 K **

Timeline

Budget

Barriers (to EDVs)

• Interactions/ collaborations

– Delphi

– Halla Visteon Climate Control

– Magna Powertrain - Engineering 

Center Steyr

– Ford

• Project Lead

– National Renewable Energy 

Laboratory

Partners

* Shared funding between VTO programs: VSST, APEEM, ESS

** Not included in total
3

Relevance - The PHEV/EV Thermal Challenge

• Plug-in hybrid electric vehicles (PHEVs) and 

electric vehicles (EVs) have increased vehicle 

thermal management complexity

o Separate coolant loop for advanced power electronics 

and electric motors (APEEM)

o Thermal requirements for energy storage systems 

(ESS)

• Additional thermal components result in higher 

costs

• Multiple cooling loops lead to reduced range 

due to 

o Increased weight 

o Energy required to meet thermal 

 requirements 

1 

2 
4

Relevance 

• Support broad VTO efforts

o DOE VTO MYPP 

– “.....development of advanced vehicles and components to maximize vehicle 

efficiency .....”

– This projects seeks to maximize vehicle efficiency by developing combined 

cooling loop solutions to reduce parasitic power, improved battery 

temperature, and increase range. 

o President’s EV-Everywhere Grand Challenge

– A goal of EV Everywhere is to have automobile manufacturers produce a car 

with sufficient range that meets consumer’s daily transportation needs. 

– This project is researching techniques to reduce vehicle thermal management 

power and improve range.

• Task Objective

o Collaborate with industry partners to research the synergistic benefits 

of combining thermal management systems in vehicles with electric 

powertrains

o Solve vehicle-level heat transfer problems, which will enable 

acceptance of electric drive vehicles 
5

Approach/Strategy 

• Research benefits of combining EV 

thermal management systems 

• Develop solutions to combine 

vehicle-level cooling systems

• Improve vehicle performance (fuel 

use or EV range) and reduce cost 

• Reduce APEEM coolant loop 

temperature (to less than 105°C) 

without requiring a dedicated 

system

3 

4 

5 
6

Overall Approach

• Build a 1-D thermal model 

(using KULI software) 

• Conduct bench tests to verify 

performance and identify 

viable hardware solutions

• Collaborate with automotive 

manufacturers and suppliers 

on a vehicle-level project 6 
7

Vehicle Systems

Lee Slezak 

David Anderson

Energy Storage

Tien Duong 

Brian Cunningham 

Peter Faguy

Power Electronics 

& Electric Motors

Susan Rogers 

Steven Boyd 

Approach/Strategy - Integration Between Vehicle 

Technology Programs

Hybrid Electric Systems

Dave Howell – Team Lead

Electric range and fuel consumption

APEEM temperatures

Battery temperature and life

7 
8

Approach - Milestones 

Month 

/ Year

Description

Sept/12 Milestone

• Identified advantages of combining fluid loops and strategies for 

bench testing

Go/No-Go

• Based on the successful outcome of analysis of the thermal 

management system concepts, build a bench test facility to 

evaluate combined cooling loop strategies

Sept/13 Milestone

• Evaluate combined cooling loop system performance during 

cooling mode using bench testing

Go/No-Go

• Based on bench test results, design a vehicle-level test that can 

demonstrate vehicle system level performance using a combined 

cooling loop system
9

• Improved air conditioning (A/C) compressor control

– Blower speed

– Compressor rpm

– The control state is determined by the ambient environment, target 

temperatures, and the component temperatures. 

– Developed control logic with anti-windup 

• Added inverter model (based on feedback from Electrical

and Electronics Technical Team)

• Updated battery thermal model based on review with the NREL ESS 

group (battery properties and thermal performance)

• Added ability to heat battery coolant to improve warmup

• Created component models for cabin heater core and electrical fluid 

heater for cabin heating

• Built a cabin heating loop

• Added controls for battery temperature

– Pump speed

– Valve position

– Developed control logic with anti-windup proportional integrator controllers 

Accomplishments

Improvements to Baseline Models (March/12 – March/13)
10

EV Baseline Thermal Management System Air Air Air Air

Bypass

ESS Heat Exchanger

Vehicle Cabin

PEEM Heat Exchanger

Liquid to Refrigerant

Heat Exchanger

Battery Case

Cells

Evaporator

Power 

Electronics 

and Motor

Condenser

Heater

Electric 

Heater

Heater Core

Comp

• Multiple operating modes
11

EV Baseline Thermal Management System

• Hot Cooldown

Air

Air

Air

Bypass

ESS Heat Exchanger PEEM Heat Exchanger

Liquid to Refrigerant

Heat Exchanger

Battery Case

Cells

Evaporator

Power 

Electronics 

and Motor

Condenser

Heater

Electric 

Heater

Heater Core

Comp

Vehicle Cabin

• Battery or ESS cooled with 

chiller

• Cabin cooling provided with 

conventional A/C system
12

EV Baseline Thermal Management System

• Mild Cooldown

Air

Air

Air

Bypass

ESS Heat Exchanger PEEM Heat Exchanger

Liquid to Refrigerant

Heat Exchanger

Battery Case

Cells

Evaporator

Power 

Electronics 

and Motor

Condenser

Heater

Electric 

Heater

Heater Core

Comp

Vehicle Cabin

• Battery or ESS cooled with 

radiator
13

EV Baseline Thermal Management System Air Air Air Air

Bypass

ESS Heat Exchanger PEEM Heat Exchanger

Liquid to Refrigerant

Heat Exchanger

Battery Case

Cells

Evaporator

Power 

Electronics 

and Motor

Condenser

Heater

Electric 

Heater

Heater Core

Comp

• Cold Warmup

Vehicle Cabin

• Electric heater for cabin heating 

(5-7 kW for small vehicle)

• Electric heater for battery or 

ESS heating (1 kW)
14

• 24-kWh EV

• Environment 

– 43oC, 35oC, 30oC, 25oC 

– 25% relative humidity 

– 850 W/m2 

• 0% recirculation

• US06 drive cycle

• Cooldown simulation 

from a hot soak

• ESS – cooling loop 

with chiller and low 

temperature radiator

• Waste heat load from 

FASTSim simulations

Baseline EV Thermal Management System 

EV Test Case at Four Ambient Temperatures

8 
15

Baseline System 

Total Vehicle Thermal Management Power Including Compressor, Fans, Blowers, Pumps

Power drops off when battery cell 

temperature reaches control level

Hotter ambient temperatures 

require more power

Less power required with radiator cooling of the battery

A/C evaporator antifreeze control 

limits A/C compressor power
16

Combined System

Combining APEEM and ESS Cooling Loops

Electric Drive WEG 

Cooling System

Air

Air

Vehicle Cabin

Cabin 

Cooler

Power 

Electronics and 

Motor

Radiator

Liquid

Refrigerant

Condenser

Refrigerant

Liquid Evaporator 

Comp

WEG Coolant Loop Distribution System

Battery

Cells

Cabin 

Heater

Electric Heater

WEG = Water/Ethylene Glycol
17

Combined System – Configuration 1

Combining APEEM and ESS Cooling Loops

Electric Drive WEG 

Cooling System

Air

Air

Vehicle Cabin

Cabin 

Cooler

Power 

Electronics and 

Motor

Radiator

Liquid

Refrigerant

Condenser

Refrigerant

Liquid Evaporator 

Comp

WEG Coolant Loop Distribution System

Battery

Cells

Cabin 

Heater

Electric Heater

• Enables use of APEEM 

waste heat for ESS 

heating

WEG = Water/Ethylene Glycol
18

Combined System – Configuration 2

Combining APEEM and Cabin Heating Loops

Electric Drive WEG 

Cooling System

Air

Air

Vehicle Cabin

Cabin 

Cooler

Power 

Electronics and 

Motor

Radiator

Liquid

Refrigerant

Condenser

Refrigerant

Liquid Evaporator 

Comp

WEG Coolant Loop Distribution System

Battery

Cells

Cabin 

Heater

Electric Heater

• Enables use of APEEM 

waste heat for ESS 

heating or cabin heating

WEG = Water/Ethylene Glycol
19

Warmup: Auxiliary Load Power

VTM Power Reduced by Using APEEM Waste Heat

Baseline:

• 7-kW cabin heater

• 1-kW ESS auxiliary electric heater

APEEM and ESS:

• 7-kW cabin heater

• 1-kW ESS auxiliary electric heater off

• ESS warmup supplemented by APEEM waste heat

Configuration 1 (APEEM and ESS)
20

Warmup: Auxiliary Load Power

VTM Power Reduced by Using APEEM Waste Heat

Baseline:

• 7-kW cabin heater

• 1-kW ESS auxiliary electric heater

APEEM and Cabin:

• 5.8-kW cabin heater

• 1-kW ESS auxiliary electric heater

• Cabin warmup supplemented by APEEM waste heat

APEEM and ESS:

• 7-kW cabin heater

• 1-kW ESS auxiliary electric heater off

• ESS warmup supplemented by APEEM waste heat

Configuration 1 (APEEM and ESS) and Configuration 2 (APEEM and Cabin Heating)
21

Warmup: Cabin Heater Fluid Temperature

Cabin Heater Fluid Temperatures Are Very Similar

Configuration 1 (APEEM and ESS) and Configuration 2 (APEEM and Cabin Heating)
22

Warmup: Average Cabin Air Temperature

Cabin Air Temperatures Are the Same While Using Less Electrical Power

Passenger comfort was not degraded

Configuration 1 (APEEM and ESS) and Configuration 2 (APEEM and Cabin Heating)
23

Warmup: Battery Temperature

Battery Is Warmer with APEEM Waste Heat

Better battery performance

Configuration 1 (APEEM and ESS) and Configuration 2 (APEEM and Cabin Heating)
24

Warmup: APEEM Coolant Temperature

APEEM Coolant Temperature Is Under The Limit (<70°C )*

* “Electrical and Electronics Technical Team Roadmap.” [Online]. Available: 

http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/ 

eett_roadmap_12-7-10.pdf. [Accessed: 11-Oct-2011].

Configuration 1 (APEEM and ESS) and Configuration 2 (APEEM and Cabin Heating)
25

Combined System – Configuration 3

Liquid Cooled Condenser 

Electric Drive WEG 

Cooling System

Air

Air

Vehicle Cabin

Cabin 

Cooler

Power 

Electronics and 

Motor

Radiator

Liquid

Refrigerant

Condenser

Refrigerant

Liquid Evaporator 

Comp

WEG Coolant Loop Distribution System

Battery

Cells

Cabin 

Heater

Electric Heater

• Enables use of APEEM 

waste heat for ESS 

heating or cabin heating

• Reduces front heat 

exchangers from 3 to 1 

using shared lowtemperature radiator

WEG = Water/Ethylene Glycol
26

Combined System – Configuration 4

Refrigerant to Liquid Evaporator (Secondary Loop)

Electric Drive WEG 

Cooling System

Air

Air

Vehicle Cabin

Cabin 

Cooler

Power 

Electronics and 

Motor

Radiator

Liquid

Refrigerant

Condenser

Refrigerant

Liquid Evaporator 

Comp

WEG Coolant Loop Distribution System

Battery

Cells

Cabin 

Heater

Electric Heater

• Enables use of APEEM 

waste heat for ESS 

heating or cabin heating

• Reduces front heat 

exchangers from 3 to 1 

using shared lowtemperature radiator

• Single chilled-liquid loop

• Compatible with heat 

pump operation

• Compact refrigerant loop

WEG = Water/Ethylene Glycol
27

Cooldown: Cabin Air Temperature

Slightly Warmer Cabin Air (A/C Performance Not Significantly Impacted)

Configurations 3 & 4 (Liquid-Cooled Condenser and Refrigerant to Liquid Evaporator – Secondary Loop)
28

Cooldown: Battery Temperature

Slightly Warmer Battery (But Still a Reasonable Cooldown)

A reasonably sized front 

heat exchanger can handle 

the APEEM, cabin, and ESS 

heat loads

Configurations 3 & 4 (Liquid-Cooled Condenser and Refrigerant to Liquid Evaporator – Secondary Loop)

Battery cooling performance 

is adequate with heat 

exchanger located 

downstream of the cabin 

cooling heat exchanger
29

Cooldown: APEEM Coolant Temperature

Lower APEEM Coolant Because Refrigerant to Air Condenser Is Eliminated

Configurations 3 & 4 (Liquid-Cooled Condenser and Refrigerant to Liquid Evaporator – Secondary Loop)

Lower coolant temperature 

enables higher electric drive 

power
30

• Developed preliminary combined cooling loop concept for testing

– Maximizes operating configurations and total system energy efficiency 

while minimizing valves, pumps, and heat exchangers

– Thermally conditions vehicle cabin, PE, EM, and ESS

– Recovers PE, EM, and ESS waste heat when advantageous

– Enables heat pump operation to reduce electrical resistance load

Accomplishments – Bench Test

• Significance 

– Unique vehicle thermal 

system configuration that 

focuses on maximizing 

vehicle range, occupant 

comfort, and component 

lifetime
31

• Inventoried current testing capabilities to determine what can be achieved

– Maximized use of existing equipment and infrastructure

• Designed preliminary bench test facility

– Simulation of vehicle cabin response via a mathematical model, which controls 

inlet air conditions to cabin heat exchangers

– Replication of PE, EM, and ESS responses via mathematical models, which control 

component outlet coolant temperatures

Accomplishments – Bench Test

• Significance

– Initiated bench-testing phase of 

task while minimizing test 

facility upgrade cost
32

• Delphi

• Halla Visteon Climate Control

– Data 

– Engineering support

• Magna Powertrain – Engineering Center Steyr

– KULI software

– Engineering support

• Ford

– Electric Focus (loaned to NREL for the Electric Drive Vehicle 

Climate Control Load Reduction Task)

• VTO Tasks

– Advanced Power Electronics and Electric Motors

– Vehicle Systems

– Energy Storage

Collaboration and Coordination with Other Institutions
33

• Remainder of FY13

– Finalize combined cooling loop design in conjunction with industry

o Coordinate with Delphi and Visteon on configuration and components

– Construct bench testing facility

– Conduct bench testing to evaluate combined cooling loop system 

performance during cooling mode

– Validate previously built KULI models of combined cooling loop

• FY14

– Utilize existing bench testing facility and experimental system to 

conduct heating mode testing

– Work with industry partners to design a vehicle-level test that can 

demonstrate vehicle system level performance when using a 

combined cooling loop system

– Install experimental system and measurement equipment in a test 

EDV

– Experimentally evaluate EDV performance to demonstrate the 

effect that the combined cooling loop has on electric vehicle 

range

Proposed Future Work
34

• DOE Mission Support

– Combining cooling systems in EDVs may reduce costs and improve 

performance, which would accelerate consumer acceptance, 

increase EDV usage, and reduce petroleum consumption. 

• Overall Approach

– Build a thermal 1-D model (using KULI software) 

o APEEM, energy storage, engine, transmission, and passenger 

compartment thermal management systems

o Identify the synergistic benefits from combining the systems 

– Select the most promising combined thermal management 

system concepts and perform a detailed performance assessment 

and bench top tests

– Collaborate with automotive manufacturers and suppliers on a 

vehicle-level project

– Solve vehicle-level heat transfer problems, which will enable 

acceptance of vehicles with electric powertrains

Summary 
35

• Technical Accomplishments

– Completed baseline EV thermal systems model

– Investigated combined cooling loop strategies

– Identified advantages of combining fluid loops

– Identified strategies for bench testing

• Collaborations

– Collaborating closely with Delphi, Halla Visteon Climate Control, Magna 

Powertrain - Engineering Center Steyr, and Ford

– Leveraging previous DOE research

o Battery life/thermal model

o Vehicle cost/performance model

o Lumped parameter motor thermal model

– Co-funding by three VTO tasks demonstrates cross-cutting 

Summary (cont.)
For more information, contact:

Principal Investigator

John Rugh

john.rugh@nrel.gov

Phone: (303)-275-4413 

APEEM Task Leader:

Sreekant Narumanchi

Sreekant.Narumanchi@nrel.gov 

Phone: (303)-275-4062

Acknowledgments: 

David Anderson

Steven Boyd

Brian Cunningham

David Howell

Susan Rogers

Lee Slezak

Vehicle Technologies Office

U.S. Department of Energy

Team Members:

Kevin Bennion

Daniel Leighton

Jeff Tomerlin
37

Photo Credits

1. Matt Jeffers, NREL 

2. John Rugh, NREL 

3. Matt Jeffers, NREL 

4. John Rugh, NREL 

5. Michelle Rugh, Amateur Photographer

6. Charlie King, NREL

7. John Rugh, NREL

8. John Rugh, NREL
Reviewer-Only Slides

(Note: please include this “separator” slide 

between those to be presented and the 

“Reviewer-Only” slides. These slides will be 

removed from the presentation file and the 

DVD and Web PDF files.)
39

Feedback: The reviewer said that continuing to refine and incorporate more data as you go forward is a must.

Response: In FY12 and FY13, the baseline model of an EV thermal management was refined (components added, 

controls improved). The model was then modified to assess combined cooling loop strategies.

Feedback: Overall, the reviewer asserted that the project seems to have a reasonable approach, but that it would be 

good to know whether it has been vetted and received positively by industry.

Response: A project overview and results of the modeling was presented at the 2012 SAE Thermal Management 

Systems Symposium

Feedback: Another reviewer indicated that the model seems okay but so far seems to be looking at limits and tradeoffs 

one at a time.

Response: The liquid cooled condenser and refrigerant-to-liquid evaporator were assessed in a single simulation. In all 

combined concept cases, the critical parameters were assessed (cabin, ESS, motor, and APEEM fluid 

temperatures as well as total VTM power.)

Feedback: While the presentation provides a reference for a thermal model of a permanent magnet motor, the reviewer 

did not have a chance to read it, and said that it was not clear what level of detail is included in the electric 

motor model. According to the reviewer, it is critical to limit the peak temperature of the motor, and using a 

lumped model representation may not provide adequate resolution to capture the peak temperature.

Response: While the motor thermal model is a 3-node representation, careful review of literature and selection of the 

lumped-node parameters provided confidence that the motor temperatures were representative.

Feedback: A different reviewer pointed out the project needs more direct contributions and involvement from major 

subsystem suppliers and an OEM.

Response: We have added Delphi and Ford as partners. 

FY12 AMR Reviewer Comments & Response
40

Rugh, J. P. and Bennion, K.; (2012) “Electric Vehicle Thermal Modeling 

to Assess Combined Cooling Loop Concepts ,” Proceedings of the SAE 

Thermal Management Systems Symposium, October 31-November 1, 

2012, Scottsdale, AZ.

Rugh, J. P., (2012) “Integrated Vehicle Thermal Management – 

Combining Fluid Loops in Electric Drive Vehicles,” FY2012 Advanced 

Power Electronics and Electric Motors Annual Report.

Publications 
41

• Assumption: Maintaining cabin and battery cooling performance with a 

series configuration

– Analysis results indicate the battery can be cooled in a reasonable time while maintaining 

cabin comfort. This will be verified with tests.

• Assumption: Year-round benefits of a combined cooling loop configuration 

will outweigh the secondary loop disadvantages experienced in hot 

environments 

– Delphi research showed the performance of a similar system. They reported the reduction in 

heating power offset the increase in cooling power. Performance of the proposed system will 

be verified through testing.

• Assumption: In a bench setting, simulation of the APEEM, ESS, and cabin 

performance is equivalent to an actual vehicle in a real environment

– Testing will verify numerical models accurately represent the APEEM components, ESS, and 

cabin. 

• Issue: Potential for excessive control complexity

– The system must operate in all environments. With multiple valves , temperature 

requirements, and fluid loops, the control logic will likely be complex. Research will investigate 

ways to reduce complexity.

Critical Assumptions and Issues