TUGraz OPEN Library

Damanik, Marini

Murkovic, Michael

ORIGINAL PAPER
Formation of potentially toxic carbonyls during oxidation
of triolein in the presence of alimentary antioxidants
Marini Damanik1 • Michael Murkovic1
Received: 11 May 2017 / Accepted: 10 July 2017 / Published online: 19 October 2017
 The Author(s) 2017. This article is an open access publication
Abstract A relation between oil uptake and cancer as well
as induction of hepatic inflammation was shown earlier. It
is discussed that the main oil oxidation products—hy-
droperoxides and carbonyls—might be the reason for the
mentioned diseases. In this manuscript quantitative deter-
mination of aldehydes which are formed during oxidation
of triolein—as a model substance—using the Rancimat 679
is described. The oxidation of 11 g of triolein is carried out
at 120 C sparging air with a flow of 20 dm3/h for 10 h. A
series of aliphatic aldehydes starting from hexanal to
decanal as well as decenal was identified by LC–MS/MS
and quantified as DNPH derivatives. In addition, the total
amount of carbonyls was determined. Based on the cali-
bration with hexanal, all other dominant substances were in
the similar concentration range with maximum concentra-
tions of 1.6 lmol/cm3 of hexanal, 2.3 lmol/cm3 of
heptanal, 2.5 lmol/cm3 of octanal, 3.2 lmol/cm3 of non-
anal, 4.0 lmol/cm3 of decanal after 6 h. The total amount
of carbonyls reached a maximum after 6 h being 27 lmol/
cm3 for triolein without antioxidant. The results of this
investigation will be a basis for further toxicological
studies on oxidized oils.
Graphical abstract
Keywords Triolein  Lipid oxidation  Aldehydes 
DNPH  Antioxidants  b-Carotene  a-Tocopherol
Introduction
Prolonged exposure to oxidized lipids can be detrimental to
human health. It has been reported that lipid hydroperox-
ides from processed dietary oils can enhance the growth of
hepatocarcinoma cells [1]. Another issue was published by
Bo¨hm and co-workers [2] who found that oxidized fat
might result in liver inflammation which was shown in
experimental rats. In the latter publication, no relation to a
specific substance or group of substances was established.
Therefore, a quantitative characterization of oxidized oils
is a prerequisite to start further mechanistic investigations
on the toxic principles of oxidized oils.
In earlier manuscripts the formation of different perox-
ides (hydroperoxides, epidioxides) and epoxides was
described in detail [3, 4]. A second group of reactive
products from oil oxidation are the carbonyls which are
formed during further reactions of the primary peroxides.
The formation of carbonyls during oil oxidation was
investigated earlier in rapeseed oil [5] when it was shown
that as a result of the degradation of the intermediate
Hexanal (1.6 μmol/cm3) 
Heptanal (2.3 μmol/cm3) 
Octanal (2.5 μmol/cm3) 
Nonanal (3.2 μmol/cm3) 
Decanal (4.0 μmol/cm3)
& Marini Damanik
marini.damanik@student.tugraz.at
1 Institute of Biochemistry, Graz University of Technology,
Graz, Austria
123
Monatsh Chem (2017) 148:2031–2035
DOI 10.1007/s00706-017-2036-3
hydroperoxides a great variety of aldehydes and ketones
are formed. It is well known that medium and short chain
aldehydes which are formed from higher unsaturated fatty
acids are the key aroma-active components which are
responsible for a rancid aroma. These are C7–C11
monounsaturated aldehydes, or C6–C9 dienals, or C5
branched aldehydes or some C8 ketones which are impor-
tant contributors to the oil aroma having negative attributes
(rancid, winey-vinegary, fusty, muddy sediment, musty)
[6].
These carbonyls and other compounds such as alde-
hydes, terminal alkenes, carboxylic acids, and aliphatics
are formed by a b-cleavage of lipid alkoxyl radicals [7].
The fragmentation reactions of allylic hydroperoxides by
the Hock rearrangement create two different carbonyls
from the same lipid peroxide, i.e. aldehydes or ketones [8].
Mechanistically, this is achieved by the insertion of one
oxygen atom into the lipid carbon backbone and delocal-
ization of a positive charge on a carbon or oxygen atom.
The main aim of this work was to establish an analytical
method for a quantitative determination of the carbonyls in
the lipid (oxidized oil) phase for determination of the ali-
mentary exposure. For the easier identification and
assignment of the reaction products, a defined matrix (tri-
olein) which did not contain any interfering compounds
was used. It was decided to use the derivatization with 2,4-
dinitrophenylhydrazine (DNPH)—a commonly known
derivatization reagent for carbonyls—that would give the
possibility to identify and quantify single components as
well as the total carbonyl content. These derivatives are
stable and can be analysed by HPLC with ESI-MS in the
negative mode or by its absorption at 400 nm [9–11].
With this background, we have started to characterize
the formation of carbonyls during oxidation of triolein in
the oil phase and not the volatile phase in which these
compounds are mostly related to sensory sensation. On
basis of reversed phase chromatography with UV and MS
detection, the non-evaporating carbonyl compounds
formed during oxidation of triolein were identified and
quantified. In this case, triolein was used as model oil. The
results of these experiments will be a basis for future work
on food oil oxidation. In addition, the interaction of
antioxidants (b-carotene, a-tocopherol) with the carbonyl
formation was analysed.
Results and discussion
Secondary oxidation products analysis
The derivatization of carbonyls is commonly used in
chromatographic analysis. The hydrazones formed are
stable enough for MS experiments. In some cases the
carbonyls from fatty acid oxidation are too volatile to be
analysed by LC/MS. Therefore, the DNPH adds molecular
weight to increase sensitivity and selectivity [12]. Negative
ionization using APCI was the most sensitive MS method
which could be used. The hydrazones formed were anal-
ysed using visible light absorption (400 nm) or by MS. The
advantage of detection at 400 nm is that practically all
peaks that appeared in the chromatogram were DNPH
derivatives. In the control chromatograms only the baseline
could be observed at 400 nm (Fig. 1). The semiquantitative
evaluation of the carbonyls was based on a calibration
using hexanal with the peak area relating to the molar
concentration of hexanal. The linear calibration of hexanal
was done in the range of 8–1000 lg/cm3 (0.08–10 mM).
The formation of carbonyls could be explained by a Hock
cleavage which was reviewed by [7]. This might explain
the formation of, e.g. decanal and 2-undecenal which are
produced by homolytic cleavages on either sides of the
8-hydroperoxide and nonanal from either the 9- or 10-hy-
droperoxide. The linearity of the hexanal analysis was
tested in the range of 5–1300 lg/cm3 according to Mandel
[13] with a limit of detection of 4.1 lg/cm3 and a limit of
quantification of 13 lg/cm3.
The formation of carbonyls began after 2 h of oxidation
at 120 C while bubbling air through the oil. A strong
increase of carbonyl formation was observed between 2
and 4 h with a maximum after 6 h and a slight decrease or
constant concentrations afterwards. A series of linear
aldehydes (from 6 carbons to 10 carbons) could be iden-
tified positively by LC–MS. Based on the calibration with
hexanal all other dominant substances were in the similar
concentration range with maximum concentrations of
1.6 lmol/cm3 of hexanal, 2.3 lmol/cm3 of heptanal,
2.5 lmol/cm3 of octanal, 3.2 lmol/cm3 of nonanal,
4.0 lmol/cm3 of decanal after 6 h (Fig. 4). These identified
4 6 8 10 12
0
10
20
30
40
50
60
70
80
90
100
110
H
ex
an
al
H
ep
ta
na
l
O
ct
an
al N
on
an
al
D
et
ec
to
r r
es
po
ns
e 
/ m
A
U
Retention time / min
fresh triolein
4 h oxidation
6 hours oxidation
D
ec
an
al
Fig. 1 Chromatogram of DNPH derivatives of fresh triolein and after
4 h as well as 6 h of oxidation in the Rancimat
2032 M. Damanik, M. Murkovic
123
aldehydes were volatile and undergo further degradation
reactions which may explain the reduced concentration.
The double peaks which could be seen after 4 h of
oxidation were attributed to Z/E isomer formation since no
difference in the mass spectrum and UV absorption could
be observed. After 6 h of oxidation the double peaks dis-
appear resulting in a shift in the relative concentrations
(Fig. 1).
The identification of the peaks was done by LC–MS/MS
as is shown in Fig. 2. The earlier mentioned saturated
aldehydes (hexanal–decanal) including decenal could be
identified. The fragmentation of all of these compounds
was similar with a specific fragment of m/z = 182 origi-
nating from the DNPH moiety.
In this experiment, nonanal and octanal were the main
products. 2-Nonenal and 2,4-decadienal which are the
known degradation products of linoleic acid were not
detected. Additional compounds (heptane, heptanol,
octane, 1-undecene, and 2-undecenal) that were described
earlier are produced by a homolytic fission of the inter-
mediary formed R–O bond [14–19]. However, non-
carbonyls could not be detected with the method described
here.
The total amount of carbonyls formed is shown in
Fig. 3. Similar to the single aldehydes, a maximum con-
centration is reached after 6 h with a decrease afterwards.
The maximum concentration is 27 mM which is based on a
calibration with hexanal.
Influence of lipid-soluble antioxidants on carbonyl
formation
In a second series of experiments, two lipid-soluble
antioxidants were added, namely a-tocopherol and b-car-
otene. The earlier experiments showed that the best
stabilization was obtained by addition of 300 ppm of
ascorbyl palmitate to soybean oil (SO). In addition, a
combination of ascorbyl palmitate (300 ppm) and a-toco-
pherol (1000 ppm) was able to limit hydroperoxide and
hexanal formation in SO at 35 C for 12 weeks [20].
Antioxidants inhibit lipid oxidation by quenching free
radicals and physically stabilizing the micelles at reaction
sites [21]. As described in [22] the oxidation starts after 5 h
in both, the refined and fortified oils (containing b-car-
otene), with the formation of hydroperoxides. In this case,
the addition of b-carotene resulted in a pro-oxidant effect.
b-Carotene was still measurable after 10 h [22]. During the
course of the oxidation in the experiments described here,
the levels of the formed carbonyls were lower in the
samples with added antioxidants (Fig. 4). In addition, the
pattern of the chromatograms did not change significantly
6 7 8 9 10 11 12 13 14
0
200000
400000
600000
800000
1000000
de
ca
na
l (
m
/z
 =
 3
35
)
D
et
ec
to
r r
es
po
ns
e 
/ c
ou
nt
s
Retention time / min
he
xa
na
l (
m
/z
 =
 2
79
)
he
pt
an
al
 (m
/z
 =
 2
93
)
oc
ta
na
l (
m
/z
 =
 3
07
)
no
na
na
l (
m
/z
 =
 3
21
)
de
ce
na
l (
m
/z
 =
 3
33
)
Fig. 2 Selected ion traces of the DNPH conjugates of the saturated
and unsaturated aldehydes found in oxidized triolein
0,00,1 2 4 6 8 10
0
2
19
20
21
22
23
24
25
26
27
28
to
ta
l c
on
ce
nt
ra
tio
n 
of
 c
ar
bo
ny
ls
 / 
m
M
Oxidation time / h
Fig. 3 Formation of the total amount of carbonyls during oxidation
of triolein at 120 C with constant air sparging
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
C
on
ce
nt
ra
tio
n 
of
 a
ld
eh
yd
es
 / 
m
M
Oxidation time / h
triolein -carotene -tocopherol
Fig. 4 Formation kinetics of single compounds during oxidation of
triolein in presence of lipid-soluble antioxidants at 120 C with
constant air sparging for 10 h (filled circle hexanal; filled square
heptanal; filled upward triangle octanal; filled downward triangle
nonanal; filled diamond decanal)
Formation of potentially toxic carbonyls during oxidation of triolein in presence of… 2033
123
indicating the same carbonyls are formed but at lower
amounts. The sample containing a-tocopherol showed a
higher formation of octanal after 10 h (Fig. 5).
For this, b-carotene and a-tocopherol were dissolved in
acetone and added to the triolein. The concentrations of the
antioxidants were 300 lg/g ± 0.5 lg. The fortified triolein
was stirred for 15 min and then flushed with nitrogen for
30 min to remove the acetone before sealing airtight in
glass bottles. For the oxidation in the Rancimat 20 g of
triolein was used. The concentrations which were applied
were in the same range as it can be expected in natural oils.
The a-tocopherol concentration was 300 lg/g and the level
of b-carotene was 500 lg/g. The concentrations were
selected according to the concentrations normally occur-
ring in red palm oil which are in the range of 600–1000 lg/
g for vitamin E and 400–3500 lg/g for a- and b-carotene
[23].
Conclusion
The formation of carbonyls was quantified during oxidation
of triolein by derivatization of the formed products with
DNPH which is a selective reagent for aldehydes and
ketones. Some of the oxidized fragments of triolein were
identified by LC–MS/MS—using APCI in negative
mode—being hexanal (m/z = 279), heptanal (m/z = 293),
octanal (m/z = 307), nonanal (m/z = 321), decenal (m/
z = 333), decanal (m/z = 335), and undecenal (m/
z = 347). Using a Rancimat for reproducible oxidation
experiments with a constant air flow at defined tempera-
tures (120 C) the production of carbonyls showed a good
repeatability. The formation of carbonyls from triolein
showed a maximum after 6 h with a slight or no decrease
during prolonged oxidation.
Experimental
2,4-Dinitrophenylhydrazine (2,4-DNPH) was purchased
from Sigma-Aldrich (St. Louis, USA), hydrochloric acid
(HCl, 37%) was purchased from Merck (Darmstadt, Ger-
many), all solvents (e.g. methanol, ACN, acetone) used
were of HPLC grade and were purchased from Merck
(Darmstadt, Germany), acetic acid was purchased from
Roth (Karlsruhe, Germany), triolein was purchased from
FLUKA (Buchs, Switzerland), b-carotene and a-toco-
pherol were from Sigma-Aldrich (St. Louis, USA).
Analysis of secondary oxidation products in oil
Oxidation of triolein with Rancimat
The triolein oil samples were subjected to oxidation in a
Rancimat (679, Metrohm, Herisau, Switzerland). Eleven
grammes of sample was used for the oxidation experi-
ments. The temperature was set to 120 C and the air flow
to 20 dm3/h. Triolein was treated for up to 10 h. The
oxidized samples were cooled immediately after the oxi-
dation and stored under nitrogen below -18 C.
Derivatization with 2,4-dinitrophenylhydrazine (DNPH)
To 1 cm3 of the oxidized oil samples 4 cm3 of acetonitrile
was added and mixed with 3 cm3 of the reagent 2,4-DNPH
(3.48 mg/cm3). The reaction mixture was kept in the dark
for 1 h. After completion of the reaction, 2 cm3 ethyl
acetate was added for extraction and 1 g KCl for better
phase separation. This mixture was thoroughly shaken for
30 s and centrifuged for phase separation. The organic
layer was analysed without further treatment by HPLC.
Liquid chromatography–mass spectrometry condition
for aldehydes identification
The analyses of the DNPH derivatives of the carbonyls
formed during oxidation were done by HPLC (Agilent
1100, Waldbronn, Germany) using a reversed phase col-
umn (Kinetex, EVO C18, 150 9 3 mm, 5 lm,
Phenomenex, Aschaffenburg, Switzerland). For elution a
gradient was used starting with methanol (45%), water
(30%), and acetonitrile (25%) changing to methanol (6%),
water (4%), and acetonitrile (90%) linearly within 15 min.
The absorption of the eluent was measured at 400 nm for
the presence of the DNPH derivatives.
For mass selective detection, a QTRAP 2000 (AB Sciex,
Framingham, MA, USA) was used. Ionization was done
using the APCI mode with a gas drying temperature of
250 C, capillary voltage of 4000 V, and a fragmentor
potential of 150 V.
4 5 6 7 8 9 10 11 12 13
control
-tocopherol
Retention time / min
-carotene
Fig. 5 Comparison of the carbonyl formation in presence of lipid-
soluble antioxidants (a-tocopherol, b-carotene) after 10 h of oxida-
tion at 120 C. The carbonyls are measured as DNPH derivatives
detected at 400 nm
2034 M. Damanik, M. Murkovic
123
Analyses of a-tocopherol and b-carotene
For the analyses of a-tocopherol and b-carotene 25 mg of
the oil (triolein, triolein with b-carotene and triolein with
a-tocopherol) was extracted with 1 cm3 of methanol in
2-cm3 reactions vials (Eppendorf, Wien, Austria). The
samples were shaken for 2 min vigorously and centrifuged.
Under these conditions, both a-tocopherol and b-carotene
were extracted quantitatively. The methanolic extract was
used directly for HPLC analysis on a reversed phase col-
umn (Kinetex, EVO C18, 150 9 3 mm, 5 lm,
Phenomenex, Aschaffenburg, Switzerland) using a flow of
0.6 cm3/min. a-Tocopherol was separated isocratically
using 5% water in methanol detecting it at 292 nm. b-
Carotene was chromatographed with 100% acetonitrile
with detection at 450 nm.
Acknowledgements Open access funding provided by Graz
University of Technology. This work was supported by Ministry of
Research, Technology and Higher Education of the Republic of
Indonesia.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
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Formation of potentially toxic carbonyls during oxidation of triolein in presence of… 2035
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Formation of potentially toxic carbonyls during oxidation of triolein in the presence of alimentary antioxidants

Ulz, Thomas

Schwarz, Michael

Felfernig, Alexander

Haas, Sarah

Shehadeh, Amal

Reiterer, Stefan

Stettinger, Martin

Human computation for constraint-based recommenders

Schabauer, Martin

Karoshi, Paul

Ager, Markus

Lex, Cornelia

Fahrverhalten für automatisierte Fahrfunktionen - Müssen sich Algorithmen wie Fahrer anpassen?

Steiner, Alois

Mladek, Alexander

2017 Twelfth International Conference on Ecological Vehicles and Renewable Energies (EVER) 
 
“Reducing the energy consumption for comfort and 
thermal conditioning in EVs” 
 
Alois Steiner 
Virtual Vehicle Research Center 
Inffeldgasse 21a 
Graz, Austria  
Email: alois.steiner@v2c2.at  
 
Alexander Mladek 
Virtual Vehicle Research Center 
Inffeldgasse 21a 
Graz, Austria  
Email: alexander.mladek@v2c2.at 
 
Abstract— One of the biggest barriers towards large 
scale adoption of electric and plug-in hybrid cars is still 
range limitation due to limited storage capacity of electric 
batteries. The air conditioning system for passenger 
comfort and the thermal conditioning system (battery and 
powertrain) are main auxiliary consumers in EVs with 
respect to energy consumption. Therefore, the Horizon 
2020 project “OPTEMUS” proposes to tackle this 
bottleneck by leveraging low energy consumption and 
energy harvesting through a holistic vehicle-occupant-
centred approach. This manuscript presents the approach 
of the project and first simulation results of the air 
conditioning system including a heat pump. This system is 
capable of using the ambient air or a preconditioned 
battery as heat source. 
Keywords—electric vehicle, passenger comfort, 
thermal conditioning, heat pump system, battery as 
heat source. 
I.  INTRODUCTION 
Currently electric vehicles are expected to be the most 
promising solution for (locally) emission-free future 
mobility. One of the biggest barriers towards large scale 
adoption of electric and plug-in hybrid cars is still range 
limitation due to limited storage capacity of electric 
batteries. Therefore, the energy efficiency of the 
powertrain and auxiliary consumers in EVs is crucial to 
reach a high driving range. The air conditioning system for 
passenger comfort and the thermal conditioning system are 
main auxiliary consumers in EVs with respect to energy 
consumption. Thus, increasing the efficiency of these 
systems can significantly increase the driving range of the 
vehicle. 
The expected impact of the Horizon 2020 project 
“OPTEMUS” is the reduction of energy consumption 
under extreme ambient conditions for passenger comfort 
by at least 50 % and for component cooling or heating by 
at least 30 %. This will be accomplished by combining 
low energy consumption and energy harvesting via 
photovoltaic cells and regenerative shock absorbers. A 
comprehensive approach for the thermal- and energy 
management system shall be one of the major outputs of 
the project. A schematic overview of this approach, which 
shows the main technologies and their dependencies is 
shown in Fig. 1. 
 
 
 
 
 
 
 
 
 
 
 
Fig. 1: Schematic overview of the main technologies and 
dependencies in the OPTEMUS project 
The compact refrigeration unit (CRU), which basically 
“produces” warm and cold water in the vehicle, is 
supposed to redirect the heat flows in the vehicle 
according to the demands of the different 
systems/components (cabin, electric motor, inverter and 
battery). The use of the waste heat from components of the 
powertrain (e-Motor, inverter) or the battery for cabin 
heating could help to decrease the energy consumption in 
the vehicle [1]. Additionally, the use of a preconditioned 
battery as heat source could further improve the efficiency 
of the heat pump system [2]. The paper discusses 
simulation results, where the CRU operates in heat pump 
mode and uses the ambient air or a preconditioned battery 
as heat source in order to heat up the cabin of an A-
segment vehicle.  
II. SIMULATION MODELS AND BOUNDARY CONDITIONS 
In heat pump mode the CRU, which uses a natural 
refrigerant, transfers heat from a heat source to the 
passenger cabin, that is the heat sink. In the present paper 
the simulation results of the following two use cases are 
shown: 
1) The ambient air as heat source 
2) A preconditioned battery as heat source 
These two cases have been modeled using the Software 
Dymola and the “AirConditioning Library” (Version 1.9) 
[3]. Figure 2 shows the simulation model of the first case, 
where the “cold coolant circuit” of the CRU is connected 
with the ambient heat exchanger (AHX) and the “warm 
coolant circuit” with the cabin. The CRU model itself 
consists of a compressor, two plate heat exchangers 
(refrigerant-coolant) and an expansion valve. Known 
geometries of heat exchangers for an A-segment vehicle 
and the performance curves of pumps were used for the 
parameterization of the component models. As coolant a 
50 % glycol/water mixture was assumed. Also the simple 
cabin model was parameterized with known values for an 
A-segment vehicle. Via a PID-controller the compressor 
speed of the CRU was controlled to reach an air 
temperature entering the cabin of 50 °C. 
 
 
 
 
 
 
 
 
 
 
 
 
 
For the second use case the model of the ambient heat 
exchanger was replaced by a (thermal) battery model, 
that represents the thermal mass of the battery as well as 
the coolant side pressure drop. A battery weight of 
175 kg with an average heat capacity of 0.7 kJ/kgK was 
assumed. The boundary conditions for the two use cases 
for the simulated heat up (fresh air mode) of the cabin at 
-10 °C ambient temperature are shown in Table 1. 
 
TABLE 1: BOUNDARY CONDITIONS FOR THE CONDUCTED 
SIMULATIONS 
Ambient Temperature [°C] -10 
Relative Humidity [%] 90 
Air Flow Heater [kg/h] 250 
Air Flow AHX [kg/h] 2000 
Volume Flow Heater @+70 °C [l/min] 10 
Volume Flow AHX @-20 °C [l/min] 4 
Volume Flow Battery @+20 °C [l/min] 7 
 
The COP for the heat pump has been calculated 
according to Eq. 1, where the heating capacity was 
determined by Eq. 2. 
 
Eq-1 
 
Eq-2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2: Simulation model of the compact refrigeration unit and the connected coolant circuits, using the 
ambient air as heat source 
The electric energy of the compressor was calculated 
by the integration of the compressor power (Eq. 3). 
 
Eq-3 
III. SIMULATION RESULTS 
Fig. 3 shows a comparison of the air temperature 
entering the cabin and the average cabin temperature for 
the two simulated cases with the ambient air and the 
battery as heat source. It can be seen that an almost 
similar heat up behavior could be achieved, which 
enables a fair comparison of both cases. The cabin 
temperature reaches almost 20 °C at the end of the 
simulated 20 min. 
 
Fig. 3: Comparison of air temperatures entering the cabin and 
average cabin temperature for the two simulated cases 
Fig. 4 shows a comparison of the suction and 
discharge pressures for both cases. 
 
Fig. 4: Comparison of suction and discharge pressures for the 
two simulated cases 
It can be seen that the suction pressure is significantly 
higher when the (warm) battery is used as heat source 
compared to the case with ambient air (8.4 compared to 
2.8 bar after 200 s). This leads to a much lower (average) 
compressor speed (Fig. 5) where the battery is used as 
heat source (approximately 2600 rpm), compared to the 
case where the ambient air is used as heat source 
(approximately 7000 rpm in average and for the heat up 
at the beginning the max. speed of 8580 is needed). 
 
Fig. 5: Comparison of compressor speed for the two 
simulated cases 
Further, also due to the lower (advantageous) pressure 
ratio the compressor power in the case where the battery 
is used as heat source is significantly lower and the 
resulting COP higher (Fig. 6). An average COP of 2.1 
can be reached with the battery as heat source (average 
compressor power 2.0 kW) compared to 1.1 with the 
ambient air as heat source (average compressor power 
3.8 kW). 
 
Fig. 6: Comparison of compressor power and resulting COP 
for the two simulated cases 
When the battery is used as heat source, the COP 
decreases with the battery temperature. Fig. 7 shows the 
decrease of the battery temperature, starting at 35 °C 
(preconditioned). During the 20 min heat pump operation 
the temperature decreases to roughly 13 °C. 
 
Fig. 7: Decrease of battery temperature during heat pump 
operation 
A comparison of the used energy for the heat up of 
the cabin to 20 °C (Fig. 8) shows a decrease from 
1.26 kWh using the ambient air as heat source to 
0.66 kWh (-48 %) using the (preconditioned) battery as 
heat source. 
 
Fig. 8: Comparison of used electric energy for reaching a 
cabin temperature of 20 °C for the two simulated cases 
IV. CONCLUSION 
The paper was aimed at comparing two different heat 
pump operation modes using a compact refrigeration 
unit, which redirects the heat flows in the electric vehicle. 
In the first simulated use case the ambient air was used as 
heat source via an ambient heat exchanger. In the second 
use case a preconditioned battery acted as heat source. 
The simulation results for a cabin heat up to 20 °C in 
roughly 20 min showed relevant advantages in terms of 
energy consumption for the second use case (battery as 
heat source). The higher suction pressure (8.3 compared 
to 2.7 bar after 200 s) compared to the case with the 
ambient air as heat source enables the use of lower 
compressor speeds (2600 compared to 7000 rpm). 
Additionally, also due to a lower pressure ratio of the 
electric compressor the operation point of the heat pump 
system is much more efficient. This leads to a 
significantly lower average compressor power 
(approximately 2.0 instead of 3.8 kW) and a decrease of 
energy consumption from 1.26 to 0.66 kWh (-48 %). The 
battery temperature decreases during these 20 min from 
35 °C (preconditioned) to 13 °C, which is still acceptable 
in terms of battery thermal management. 
ACKNOWLEDGMENT  
The work reported in this paper was partially funded 
by the European Union’s Horizon 2020 research and 
innovation programme under grant agreement 
No. 653288, by the COMET K2 - Competence Centres 
for Excellent Technologies Programme of the Austrian 
Federal Ministry for Transport, Innovation and 
Technology (bmvit), the Austrian Federal Ministry of 
Science, Research and Economy (bmwfw), the Austrian 
Research Promotion Agency (FFG), the Province of 
Styria and the Styrian Business Promotion Agency 
(SFG). 
 
The simulation model of the CRU and the data about 
the other thermal system components have been provided 
by DENSO AUTOMOTIVE Deutschland GmbH and 
DENSO THERMAL SYSTEMS S.p.A., respectively. 
REFERENCES 
[1] H. Ayartuerk, E. Doruk, Ismail Durgun, Kemal Ekbic, New 
heating system development working with waste heat for 
electric vehicles, Transportation Research Procedia 14, 2016, 
pp. 1080-1086 
[2] B. Rabl, M. Waltenberger, A. Steiner, M. Huetter, Traction 
battery as heat storage in the heat pump cycle of an electric 
vehicle, ATZ 01/2017 
[3] Modelon AB (2015): AirConditioning Library - Users Guide 
(Version 1.9) 
 
 
 
 
DOI: 10.1109/EVER.2017.7935949 
 
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