MACS Monthly Newsletter - 2022 - OCT8

dual loop SLS system. It also puts the well-known
secondary fluid in the role of transporting the heating
or cooling to the required component. Therefore,
coolant pumps, valves and reservoirs are front and
center in each coolant loop.
Additionally, the fluid used in the secondary loop of
today's systems is mostly the very common 50/50 mix of
ethylene glycol and water. However, it must be noted that
when operating the system at very low ambient temperatures
(where -40°F (-40°C) is typically the low temperature
design point), this coolant mixture becomes more viscous
and can be difficult to pump. This must be accounted for in
the system design. It is possible to warm the coolant during
charging however, when the vehicle sits without being
plugged-in at cold ambient temperatures, when pumping
the fluid can be challenging and will require more pump
electrical power. In addition, newer heat transfer fluids are
available for the second, indirect loops, yet would represent
a new fluid to the mobile industry and therefore, are
not in use today.
One suggestion to the shop owner is to include the system
diagnostic tools in your shop that are typically provided
by the OEM or the service tool provider. Past experience
with a diagnostic tool developed by the OEM has
shown that many of the key system performance parameters
are monitored and reported to assist the technician
during service. Additionally, since the tools may have been
used in the development of the vehicle system, they report
those key values needed of the many that are available on
the vehicle's software bus.
Summary
As discussed, along with the electrification of the vehicle
market, thermal management of the on-vehicle systems is
more extensive as compared to the historical IC engine
vehicles. And, since a coolant loop is used on essentially
all EVs to help thermally manage the propulsion system,
applying the SLS architecture can result in advantages
when refrigerant options, charge amount and system
functionality are considered. Most EVs contain some version
of the SLS design with the number of coolant loops
and the related size and content of the associated refrigerMACS
Service Reports is published monthly by the Mobile Air Climate
Systems Association. It is distributed to members of MACS and
is intended for the educational use of members of the automotive air
conditioning service and repair industry. Suggestions for articles will
be considered for publication, however, MACS reserves the right to
choose and edit all submissions.
Unless otherwise noted, all photos/art by author.
October 2022
8
ant system matched to the desired functionality.
Moreover, the heating demands of an EV are a substantial
drain on the stored battery energy. Many studies have
documented the reduction in the cold weather driving
range of between 40% and 60%. In response, the thermal
engineers in the mobile industry have implemented
and continue to innovate on applying the heating-efficient
heat pump technology and, as discussed, the SLS provides
effective, high COP heat pump operation with waste
heat recovery adding to the performance benefit.
Finally, in the independent thermal service shop, the
EV thermal system presents both an opportunity for increased
business and a challenge to be knowledgeable
about and have the tools and training to service the more
complex EV thermal system.
And don't forget, MACS is a great resource to assist service
shops with all aspects of servicing systems to keep
your customers happy!
References
1. Andersen, S., Chowdhury, S., Craig, T., Kapoor, S.
et al., " Comparative Manufacturing and Ownership
Cost Estimates for Secondary Loop Mobile Air Conditioning
Systems (SL-MACs), " SAE Technical Paper
2017-01-0173, 2017.
2. Ghodbane, M. et al., " Demonstration of an Energy
Efficient Secondary Loop HFC-152a Mobile Air Conditioning
System " , US EPA Project Final Report, 2007.
3. Lustbader, J., Wood, E., O'keefe, M., Reinicke,
N. et al., " Real-world Evaluation of National Energy
Efficiency Potential of Cold Storage Evaporator
Technology in the Context of Engine Start-Stop
Systems, " SAE Technical Paper 2020-01-1252, 2020,
doi:10.4271/2020-01-1252.
4. Patti, A., Chairman, SAE Cooperative Research
Program on Thermal Management Refrigerants,
2020.
5. Chowdhury, S. et al., " Integrated Thermal System
(ITS) to Increase EV Driving Range " , 19-TMSS-0041,
2019. v
Editor:
Production Designer:
Steve Schaeber
Laina Forcey
Manager of Service Training: Steve Schaeber
Mobile Air Climate Systems Association
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsmobileairclimate.org
Website: www.macsmobileairclimate.org
MACS Service Reports
http://www.macsmobileairclimate.org
MACS Monthly Newsletter - 2022

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