An Optimised Thermal Design and Development Process for

An Optimised Thermal Design and Development Process for Passenger Compartments

Peter Baker, Morgan Jenkins, Flowmaster Ltd., UKStefan Wagner, Michael Ellinger, P+Z Engineering GmbH, Germany

© Flowmaster Group© Flowmaster Group 2009

The Challenge

• Achieving thermal comfort in a vehicle cabin• Often inconsistent with the fuel reduction demands• Means simultaneous modelling of: air conditioning; engine cooling system;

HVAC module including control strategies; ventilation ducts; passenger compartment and climate environment; the occupants themselves

• Tough time and quality targets combined with financial pressures

• Neither a single 1D tool alone, nor a 3D tool alone nor a co-simulation approach alone is adequate

• Virtual Product Development (VPD) has to be optimised individually for each phase of the design

• All simulation methods and software tools have to work together to achieve a best-in-class VPD process

• Large benefit with cost efficiency


Drivers of Enhanced VPD

• Climate-change considerations• Reduction of fuel consumption and lower CO2 emissions

• New technologies• Use of alternative refrigerants after 2011• Alternative powertrain types, heat pumps, new compressor drives, etc.

• Need to guarantee thermal comfort, dependent on:• Temperature; clothing; air quality; humidity; draft risk; noise level; dynamic

system performance; economic, ecological, ergonomic, physiological and safety factors; climatic, regional, legal, financial and cultural background

• Increasing range of different AC system variants• Coming into development and series production

• Competition intensified by the current economic crisis• The passengers are the measure of all things


A well balanced approach

• Starts with a task-optimised selection of the latest simulation software• Tasks and targets are very different in each phase• Essential to use simulation tools and methods adapted to that phase• Using too many tools is costly and inefficient• Tools used must be able to communicate efficiently with each other• Software should be flexible enough for individual customising

• Specifies a schedule-optimised sequence of necessary development steps

• Uses as much synergy and automation during model engineering as possible

• Focuses on a good compromise between accuracy and effort


Development Strategy

• Different at each company, but –• Can be described in principle by five main steps:

1. Pre-development2. Concept Assessment3. AC Application Design4. Optimisation and Redesign5. Validation

• At the beginning, very quick response times and system level simulations are essential • This is the key strength of 1D simulation methods

• Later, CAD models and prototypes are available• These can be improved in all respects by 3D simulations

• Ultimately, both methods have to come together


Simulation versus Test

Simulation Test

1D

3D CAD

1D+3D

Componentlevel

Systemlevel

Vehiclelevel

Pre-design

Conceptassessment

System-design

Re-designOptimisation

Validationphase


1. Pre-development

• Objective: To specify and fix all targets• Methods: Analytical simulation using either 1D or

simple parametric 3D methods• Risks and obstacles:

• Ill-defined targets – risk to future development costs• No CAD models or hardware prototypes – lack of correct input data

• Parametric studies can overcome these uncertainties• Compare use of predecessor models and

components with application of the latest innovations and technologies• The one can save time and money, but the other may have advantages in

the market

• Use of inverse calculation methods to set parameters


S

R

6

= 1000 W/m²= 43 °C= 40 %= 20 min= 0 km/h

Example of Inverse Calculation

BMW X3 - Inverse Calculation – Cool Down IDLE Summer

0

10

20

30

40

50

60

70

0 300 600 900 1200Time [s]

Tem

pera

ture

[°C

]

Given Cabin TemperatureCalculated Ventilation Temperature

0

1

2

3

4

5

Coo

ling

Pow

er [k

W]Required Cooling Power

Pmax


2. Concept Assessment

• Together with pre-design, this phase offers the most cost saving potential versus required development costs and effort• Decisive in working out clearly the main form of the later system

• Needs the correct procedure to find an adequate concept• The V-approach, which breaks down the task from vehicle through system

to component level and starts modelling vice versa

• Tasks include• Detailed component selection and sizing• Sensitivity studies• Refinement of the system specification• Virtual assembly of all selected and evaluated parts into a complete 1D AC

system coupled with a 1D cabin model.


Sensitivity Study Model


3. AC Application Design

• Risk of conflict between fixed styling and AC system space requirement leading to• Faulty design of air ducts, wrongly placed vents, high duct pressure drop,

poorly dimensioned HVAC units, unbalanced heat exchangers, etc.

• Resolved through• Close collaboration and understanding between stylists and engineers

• Design and packaging by CAD tools according to the needs of the concept• Creation of the human interface device and control unit

• Leading to:• Physical component prototyping and/or supplier selection• Real and virtual component tests, which lead to performance maps. This

may be done using a selection or combination of 1D, 3D and CFD tools.• Real assembly of a first prototype of the AC system


Cabin Heater Calibration


4. Optimisation and Redesign

• Only a few local effects and smaller improvements should require optimisation at this level, but• Troubleshooting and even complete component re-design often takes place

here

• Generally includes• Identification of system improvements by 1D and/or 3D CFD simulation

• Air flow balancing using 1D and/or 3D CFD simulation

• System control studies combining 1D with MATLAB/Simulink®

• Redesign, if necessary, and optimisation of the designs from earlier stages

• Troubleshooting by 1D and/or 3D CFD simulation

• Real assembly of all parts as the final system

• Calibration of the various software models against test results

• Checking progress and results against targets


Co-simulation


5. Validation

• Fully coupled 1D+3D analysis of the complete system

• Validation of targets

• Verification of test results

• Cost reduction by virtual testing of variants

• Virtual sign-off of the full system

• Virtual outdoor winter and summer tests under real conditions

• Judging overall performance and thermal comfort


Example of Validation - BCs

Outdoor Test – Death Valley

y

x

Azimuth

Altitude

0

45

90

135

180

225

270

315

360

6 8 10 12 14 16 18

Time of day

[deg

] AltitudeAzimuth

Moving Sun Simulation


Example of Validation - Results

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]

T [°

C]

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]

T [°

C]

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]T

[°C

]

Q15408seat

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]

T [°

C]

Q37223a-pillar

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]

T [°

C]

Q52606steering wheel

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]

T [°

C]

front door

20

40

60

80

100

6 8 10 12 14 16 18

t [hr]

T [°

C]

air temperature

instrument panel

test


510152025303540Face

Chest

Upper arm right

Lower arm right

Hand right

Upper leg right

Lower leg right

Foot rightFoot left

Lower leg left

Upper leg left

Hand left

Lower arm left

Upper arm left

Back ET

Local Comfort Evaluation

Comfort Range


Conclusions

• Development of air-conditioning systems can be evaluated in a fully virtual manner• By a variety of methods and tools in every phase of the process• Able to assess the local comfort targets by active human sensation models

• Energy-optimised air-conditioning systems have to:• Regard the thermodynamic behaviour of whole system• Include the effects of the cabin composition and human occupants• Use preventive measures and well-balanced strategies

• Virtual techniques have become essential given:• Financial pressures to achieve tough time and quality targets• Many load case scenarios and large number of model variants

• Proper use of a limited number of appropriate simulation methods and tools is the key to success

Documents

An Optimised Thermal Design and Development Process for