Analysis of heat losses from the cabin of a battery electric vehicle
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Examensarbete för masterexamen
Master's Thesis
Master's Thesis
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Model builders
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Abstract
Thermal comfort and air quality are crucial for the efficient operation of Battery
Electric Vehicles (BEVs). Unlike Internal Combustion Engine (ICE) vehicles, which
use the engine waste heat energy in their heating and cooling systems, BEVs rely
solely on electrical energy stored in traction batteries, making thermal management
essential for their driving range. Achieving suitable thermal comfort and air quality
in a BEV cabin has therefore a greater impact on driving range compared to ICE
vehicles. This study aimed to understand heat transfer effects in a car cabin and
their impact in energy-efficient climate control in BEVs.
Computer Fluid Dynamics (CFD) simulations were conducted to investigate heat
transfer within a BEV cabin during a cool-down scenario. The study focused on a
simplified geometry resembling the boundaries of an actual car cabin, considering
factors such as the value of total air mass flow rate, conduction, convection, solar
loads, air mass flow distribution, and driver presence.
Results showed that during a summer night drive (no solar loads) at 32 km/h and
43ºC ambient temperature, cooling the cabin with a total air mass flow rate of
68.5 g/s and 7ºC inlet air temperature lead to average air temperature variations
of ±2ºC inside the cabin, considering different levels of insulation. On a summer
day, considering moderate and intense solar loads, variations of ±5ºC on the average
air temperature were observed. Applying the total air mass flow rate only at the
top air inlets increased the average temperature by 1ºC but improved passengers’
local temperature distribution. In order to achieve thermal comfort inside the car
cabin, at least 120 g/s total air mass flow rate was required in an intense solar load
scenario, whereas only 95 g/s was required in a moderate solar load scenario. At
least 15 g/s total air mass flow was required to achieve proper ventilation of carbon
dioxide in the presence of the driver. A time-step of 1 s was sufficient to capture
the overall time evolution of temperature at probe points of interest.
The study concluded that achieving thermal comfort and proper air quality inside
a simplified car cabin required careful consideration of the total air mass flow rate.
The analysis of heat fluxes at cabin boundaries and the energy consumption of the
HVAC unit further contributed to understanding the system. By gaining insights
into heat transfer mechanisms and improving thermal management strategies, BEV
manufacturers can enhance cabin comfort, air quality, and overall energy efficiency,
ultimately maximizing the driving range of these vehicles.
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Keywords
cabin, BEV, HVAC, CFD, airflow, heat transfer, solar loads