E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

intelligent systems architectures and smart management software important ways to reduce its impact, along with efficient components and subsystems. One HVAC control hardware developer notes that systems designed for EVs now typically feature multiple blowers instead of a less efficient single unit. The total blower power in an EV is typically between 200 and 600 W, much lower than the 500-1000 W typically seen in IC-engined vehicles, says the company. There are also gains to be had from the use of more efficient heaters, an HVAC systems builder emphasises. In the absence of the abundant waste heat from an engine, most EVs now rely on electric air heaters and coolant heaters, which have a coefficient of performance (COP) of 0.8-0.9, meaning 1 kW of power consumed by the heater results in 0.8 to 0.9 kW of heat output. As a more efficient alternative, the company offers heat pump systems. Essentially, instead of using energy to generate heat, these devices absorb existing heat from the ambient air and put it somewhere else. Natural thermodynamic flow transfers heat from warm places to cooler ones, which tends to even out temperatures. As with refrigerators and air conditioning systems, heat pumps reverse this flow by using energy applied to a working fluid to move heat from cooler places to warmer ones. The working fluid, a refrigerant, runs in a loop around the heat pump system. Upon activation, a compressor draws in refrigerant vapour and increases its pressure and consequently its temperature to above ambient as it pumps it into a condenser (a heat exchanger) where it gives up heat to its surroundings, causing it to transform from a vapour into a liquid. From the condenser, it passes into an evaporator (another heat exchanger), where it absorbs heat from its surroundings and changes state once more from liquid to vapour. As well as drawing heat from the ambient air, heat pumps can also be used to harvest waste heat from the battery and vehicle electronics to heat the cabin. Potentially, they can achieve COP figures of 2 or 3, meaning that 2 or 3 kW of heat can be moved to where it is needed for every 1 kW of power used in the process. System architecture and control logic In the past, our engineering simulation expert notes, the engine cooling and cabin heating constituted one system, while the air conditioning was an entirely separate loop, a situation reflected in vehicle OEMs’ separate because it is probably only the propulsion system that needs cooling, and the low power demand combined with the high efficiency of electric machines keeps energy demand small, they add. In contrast, the largest energy demands are made at extremes of ambient temperatures in the first few minutes of the journey, as the thermal management system works hard to achieve the target temperature ranges for the cabin and the battery. High-performance driving at high ambient temperatures (around 40 C) also creates a high cooling demand, the experts say. In this case, the HVAC system is called upon to cool both the battery and the cabin, and with a high additional solar load, around 50% of the energy drawn from the battery could be needed to cool components and the cabin. Depending on the HVAC system’s configuration and the vehicle’s speed profile, temperatures at the other extreme (around -20 C) can see about one-third of the energy demand being allocated to heating. A further complicating factor is that even at temperatures of 5-20 C, dehumidification can be needed, so the heating and cooling systems must operate at the same time. Although the vehicles and their operating profiles are very different, the story with vehicles such as electric buses is similar. One HVAC, battery and charging systems supplier has carried out tests on a small bus driving at a constant speed for 40 km with an outside air temperature of 0 C, and reports that 35% of the energy consumption went to HVAC, which included bringing the interior back up to temperature after passengers boarded and alighted. The company also studied a typical last-mile parcel delivery service, noting that the system’s share of electrical energy consumption reached 50%. Numbers like this show that HVAC can be an energy hog, which makes As they are more efficient than Positive Temperature Coefficient heaters, heat pump systems such as this bus installation can reduce electric power demand in cold conditions by 50% (Courtesy of Konvekta) Running coolant heaters (and other components such as compressors) at high voltages eliminates conversion losses and improves efficiency (Courtesy of BorgWarner) Autumn 2022 | E-Mobility Engineering 65 Focus | HVAC systems