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DEVELOPMENT THERMAL MANAGEMENT

depicts the influence of compressor P_PTC P_Heatpump Veh_Speed
power on the passenger compartment 5990 140
cool down and the corresponding energy 120
demand. The refrigerant cycle with the 4990 100
electrical compressor has a better cool 3990 80
down performance and can be operated P_Electric [W] 2990 60 Vehicle speed [km/h]
at a higher efficiency, provided a smart 1990 40
control concept is implemented [2]. 990 20
0
To reduce the influence of HVAC to the -10 -20
driving range of electric vehicles, two 0 200 400 600 800 1000 1200 1400 1600 1800
basic heat pump concepts can be imple- Time [s]
mented. Taking into account different
heat sources from the vehicle and by T_Cab_PTC T_Cab_Heatpump
exchanging energy with the ambient, the 25
heat pump should perform at a high 20
COP. Concerning the detailed implemen- 15
tation into the holistic thermal manage- 10
ment architecture, various strategies T_Cabin [°C] 5
have been proposed in the automotive 0
industry. -5
-10
0 200 400 600 800 1000 1200 1400 1600 1800
INDIRECT AND DIRECT
HEAT PUMP SYSTEM Time [s]
FIGURE 2 Comparison of the heat-up curve for an EV with a PTC heater (light green) or a heat pump (dark green)
The indirect heat pump consists of a and the required power; thermal properties of the cabin are assumed to be similar (© qpunkt)
refrigerant cycle and different cooling
cycle, which are coupled by means of a
plate heat exchanger. Particularly when
using alternative refrigerants like R744 oration of refrigerant in a plate heat without considering the thermal mass,
(CO 2 ) at high system pressure levels, the exchanger which is part of the battery a huge optimisation potential is present.
refrigerant cycle is mounted in the module. In case of driving uphill, the cooling
engine compartment only and thus, high demand increases rapidly. A completely
pressures at the cabin heater can be IMPLEMENTATION OF heated battery needs to be cooled down
avoided. Here the thermal inertia of the THE HV BATTERY INTO THE to the target temperature against its ther-
secondary coolant cycle may have a neg- THERMAL SYSTEM mal mass. The thermal mass heated up
ative impact on the system dynamics in before the uphill driving needs to be
transient mode. To positively influence The thermal mass of the traction battery cooled down during the uphill driving.
system dynamics, the hose length at the cannot be neglected, but its thermal Would the uphill driving be recognised
secondary circuit needs to be as short as momentum can be reasonably used in before by predictive control algorithms,
possible, therefore mounting the A/C combination with new technologies (for heating and cooling power could be
unit close to the passenger compartment example connected vehicle). Depending saved. The saved energy can either be
is mandatory [3]. FIGURE 4 shows the on ambient temperature and operating used for heating of the passenger com-
build-up of an indirect heat pump sys- conditions, the high battery needs to be partment or converted into a driving
tem prototype, developed at qpunkt. either heated or cooled. The aim is to range benefit.
The direct heat pump utilises refriger- ensure the optimum operating tempera- During cool down, the saved pump
ant at the cabin heater. By means of ture of all battery modules to achieve power in the cooling cycle is a direct effi-
reversing the thermodynamic cycle, the highest battery lifetime. Not only mini- ciency and driving range benefit. The
heat can either be extracted in cooling mum and maximum temperature of each usage of the traction battery as heat stor-
mode or released in heating mode at the individual cell is relevant, but to ensure age needs to take place inside a narrow
cabin heater. The system of the direct homogeneous temperatures of all cells temperature window, within which the
heat pump is more complex and the nec- which leads to uniform battery aging. benefits of driving range extension do
essary control effort is higher. The space At cold start in winter the traction bat- not lead to premature and excessive bat-
requirement of the refrigerant cycle tery first needs to be heated, the same is tery aging.
increases. Considering these facts, the valid for the passenger compartment. The thermal mass of the traction bat-
usage of alternative refrigerants like Since the available heating power is lim- tery can in principle be used for heat-
R744 or R290 (propane), due to higher ited, the battery heating decreases the ing of the passenger compartment. If a
volumetric cooling power and more com- passenger comfort. Keeping in mind that region with lower ambient temperatures
pact space requirements starts to pay off. without the option of a predictive con- is known in advance, and the battery is
In this case the cooling of the traction trol, the traction battery will be con- at operating temperature, the waste heat
battery can be achieved by indirect evap- trolled towards the target temperature can be rerouted to the heating cycle. The
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