MACS Monthly Newsletter - 2022 - OCT1

Service Reports
MOBILE AIR CLIMATE SYSTEMS ASSOCIATION ©
By Timothy Craig, Owner & Lead Consultant,
Melrose Technologies LLC
sion thermodynamic cycle, generally referred to as
the Direct Expansion or DX cycle, has provided the
means for thermally managing automotive auxiliary
thermal demands such as vehicle cabin comfort systems.
This focus on the DX cycle owes its longevity
to the relatively high efficiency and well-developed
parts available when compared to possible alternatives.
Over
the decades, the evolution of the main components
- compressor, condenser, evaporator and
expansion device - along with multiple new refrigerants,
has enhanced the DX cycle and enabled a
substantial reduction in the weight along with improvements
in the efficiency and effectiveness of
the system. Further, the introduction of relatively
few (essentially three since the 1940s) refrigerants
has been a path towards enhanced system safety
and environmental friendliness.
More recently,
the architecture of
thermal systems
has evolved and been adapted to the changing
performance demands. One area of evolution in the
architecture takes the form of adding a secondary
fluid or " loop " that is linked to the primary DX system.
This so-called Secondary Loop System (SLS),
while common in other related industries such as
stationary cooling, is now becoming mainstream in
the mobile industry as vehicle electrification grows.
In this article, the goal is to provide a perspective
on the history, basics, application and advantages
of the SLS and as well as a view on the impact
on vehicle service of what are now termed vehicle
Thermal Management Systems (TMS) with Electric
Vehicles (EVs).
October 2022
A Perspective on the Secondary Loop System Thermal Architecture
For most of the past 80 years, the vapor compresBackground
In
an effort
to enhance the efficiency and lower
the carbon footprint of mobile thermal systems and
components in the industry, the SLS was given serious
study in the Society of Automotive Engineers
(SAE) cooperative research work under the IMAC
umbrella in the later 1990's and early 2000's. In that
work, the architecture and performance of the SLS
were demonstrated on multiple vehicles, some having
dual evaporators. Further, work as part of Ward
Atkinson's " Phoenix Forum " , in which new refrigerant
alternatives were investigated to meet Europe's
F-Gas regulation, the SLS technology's performance
was demonstrated on multiple occasions. Included
in these was a vehicle level demonstration completed
as part of a US EPA study in 2007. The SLS history
is documented in an SAE paper of Ref. 1 and a
guide to SLS design and performance is documented
in Ref. 2. Adding to the technology development,
a project sponsored by the EU entitled OPTEMUS
along with a US Department of Energy sponsored
project, UTEMPRA, both investigated the automotive
SLS architecture.
Many of the benefits of the SLS are focused on
the cabin cooling demand and include protecting
vehicle passengers from potential refrigerant hazards
such as toxicity or flammability and, somewhat
unexpectedly, can be operated to improve a vehicle's
fuel efficiency. Further, by isolating the vehicle
cabin from toxic or flammable refrigerants with
the SLS, very efficient refrigerants, such as R-152a,
mildly flammable yet desired due to its properties,
can be used and, in turn, enable a refrigerant charge
reduction of up to 40%. Moreover, the system can
provide cold thermal storage which, when the storage
is available and applied with appropriate control
software logic, can improve an Internal Combustion
MACS Service Reports is the official technical publication of the
Mobile Air Climate Systems Association, P.O. Box 88, Lansdale, PA
19446. The material published in MACS Service Reports expresses
the views of the contributors and not necessarily that of MACS. Every
attempt has been made to ensure
October 2022
1
the accuracy of the content of MACS Service Reports. MACS, however,
will not be responsible for the accuracy of the information published
nor will MACS be liable in any way for injury, labor, parts or
other expenses resulting from the use of information appearing in
MACS Service Reports.
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