Page 45 - ATZ WORLDWIDE

AUTHORS 150
130
Vehicle speed [km/h] 90
110

70

Dipl.-Ing. (FH) Peter Drage 50
30
is Branch Manager at qpunkt in
Graz (Austria). 10
-10
0 200 400 600 800 1000 1200 1400 1600 1800
Time [s]
25

20
Frank Seebald, M. Eng.
is Development Engineer Thermal 15
Management E-Vehicles at qpunkt
T_Cabin [°C] 5
in Stuttgart (Germany). 10

0 T_Cab_Old_Gas
T_Cab_New_Gas
T_Cab_Old_Diesel
-5
T_Cab_New_Diesel
-10
Dipl.-Ing. (FH) Christian Paul 0 200 400 600 800 1000 1200 1400 1600 1800
is Manager Air Conditioning at Time [s]
qpunkt in Ingolstadt (Germany). FIGURE 1 Comparison of the heat-up curve for different generations of vehicles with gasoline and diesel
engines; the thermal properties of the cabin are assumed to be similar (© qpunkt)

amount of refrigerant needed in the sys- conventional engines (“old” gasoline, “old”
tem, he is able to evaluate problems in diesel) is higher than for new generations,
Dipl.-Ing. Markus Hinteregger the refrigerant cycle like inefficient oil hence those vehicles reach the target tem-
is Project Leader R&D Technologies circulation, extensive compressor power, perature faster, FIGURE 1. At steady state
at qpunkt in Graz (Austria).
etc. already in an early stage of condition at -10 °C ambient temperature,
development. the passenger compartment requires
In hybrid and electric vehicles the con- approximately 3 to 4 kW (including con-
ditioning of the battery is often directly vection, radiation and outgoing air) to
or indirectly done via the refrigerant keep +20 °C in the cabin. In a transient
circuit. Accordingly, the complexity heat-up mode over the entire WLTC
driving scenario. The air-side of the con- increases due to additional components considerably more heating power needs
denser implemented in the refrigerant like indirect condensers (iCond), indi- to be supplied [2].
cycle is connected with one outlet of the rect evaporators (Chiller) or additional FIGURE 2 shows the same comparison
A/C system-test bed where a dynamic air valves (thermal expansion valve, TXV; for an electric vehicle, comparing a PTC
mass flow including temperature and electric expansion valve, EXV; fixed ori- heater with a heat pump. The energetic
humidity control can be defined. The fice) which are integrated in the cycle. advantage of the heat pump is obvious,
mass flow corresponding to a certain The development of vehicles in terms but depends on the coefficient of perfor-
driving velocity and fan stage is derived of efficiency and passenger comfort has mance (COP) of the system which is
from a full 3-D Computational Fluid increased the thermal management’s com- strongly influenced by ambient condi-
Dynamics (CFD) simulation. The HVAC plexity (engine cooling, heating and cool- tions such as temperature and humidity.
unit with the evaporator and the heater ing of passenger compartment). Based The cooling power necessary in the sum-
is as well connected with the test bed, on the Worldwide Harmonized Light-Duty mer is in a similar order of magnitude
again the dynamic fresh air mass flow Vehicles Test Cycle (WLTC Class 3) at an than the demand for cabin heating. For
depends on the driving velocity and the ambient temperature of -10 °C, a compari- hybrid and full electric vehicles, the
blower speed which is also simulated in son of different heating powers and their refrigerant cycle is not only utilised for
CFD. In this way, all relevant climatic influence on passenger compartment tem- passenger compartment cooling, but also
scenarios can be fully tested on a rig. perature for a target temperature of +20 °C for cooling of the traction battery and
The engineer then can determine the was done. The available heat rejection of other high voltage components. FIGURE 3
ATZ worldwide 09|2017 43