Battery Electric Vehicles (BEVs) use energy differently, conditioning the cabin accounts for a large portion of energy consumption. A baseline BEV may use half of its energy consumption to condition the cabin for city driving in cold ambient temperature reducing range by 50%, as shown below.
In practice, improving BEV cabin heating holds more opportunities than cooling for two reasons. First, conventional HVAC system designs have been optimized for large quantities of internal combustion engine waste heat, and therefore vehicle cabins are relatively inefficient for heating. For example, over half of the heated air is exhausted. Second, this inefficiency leads to many pathways to improve vehicle heating. Vehicle A/C refrigerant systems, on the other hand, are efficient and mature having been optimized over decades to minimize energy consumption and cost.
A simple baseline for BEV passenger comfort is electric heating of the cabin in conjunction with vapor-compression air conditioning (A/C). This baseline is low-cost and requires short development time since it leverages decades of conventional vehicle experience. The problem with pure electric heating is that the high energy consumption significantly reduces vehicle range in cold ambient conditions.
Source: Valeo and The ITB Group
Automakers are Developing More Efficient Cabin Comfort Solutions
A range of techniques are being deployed to make cabin conditioning more efficient and extend vehicle range. Basic solutions include increasing air recirculation to minimize heat losses from ventilation or reducing interior thermal mass. These solutions complement the vapor refrigerant cycle which is unparalleled for drying air and bulk cabin air cooling. There is considerable investment being made to commercialize localized heating surfaces for more efficient comfort pathways. Likewise, heated windshields are more effective and energy-efficient than using heated air for defrosting and demisting. Waste heat recovery from the EV drive system or ambient air is more efficient than pure electric heating. Waste heat can be captured and delivered through a glycol coolant system and/or conveyed to the cabin through a vapor compression heat pump system for increased air heating efficiency.
A primary challenge for BEVs is to efficiently heat the cabin in cost-effective ways. A heat pump is an excellent step toward higher value cabin conditioning but is costly. It is possible to achieve high performance at a relatively low cost, as Tesla has shown, with an integrated multiple source heat pump design. The key issue is how to keep passengers comfortable at lower cost and limit range impact.
Rethinking Cabin Comfort Priorities to Improve Performance and Cost
ITB suggests that making cabins more efficient requires rethinking the principles of comfort. Traditional cabin architectures are air temperature centric and the HVAC system is designed to accommodate all driving conditions for cabin heating, cooling, defrosting, and demisting. To further improve BEV cabin comfort and energy consumption we predict a shift toward passenger-centric cabin conditioning architectures, as shown below. A key factor is controlling occupant comfort rather than focusing on regulating cabin air temperature. Fundamental changes in BEV cabin thermal architecture offer the potential to shift functions, optimize time to comfort, and downsize the system for maximum value.
In conjunction with an occupant-centric approach, the industry must rethink cabin architectural priorities for making passengers comfortable and safe. A high priority is to complement the refrigerant system with localized electric or thermoelectric devices in seats, steering wheels, and other surfaces. Another priority is heating the cabin, capturing and reusing waste heat from the drive system and/or battery to supplement localized comfort measures. Waste heat is typically captured and redistributed through a glycol coolant system. A heat pump can maximize the efficiency of waste heat delivery from the drivetrain or ambient air. Electric heaters may still have a place for some time when localized heating, waste heat, or heat pumps are insufficient. In contrast, the cabin air ventilation system has a lower priority and can be downsized as the thermal architecture changes.
In summary, there is great latitude to improve cabin comfort value. ITB’s customers are developing solution sets that will be applied to electric vehicles as their volume increases. Contact The ITB Group to gain insights and construct strategies for solution development and commercialization.
Source: The ITB Group
