Climate Control Load Reduction Strategies for Electric Drive Vehicles in Cold Weather

Abstract

When operated, the cabin climate control system is the largest auxiliary load on a vehicle. This load has significant impact on fuel economy for conventional and hybrid vehicles, and it drastically reduces the driving range of all-electric vehicles (EVs). Heating is even more detrimental to EV range than cooling because no engine waste heat is available. Reducing the thermal loads on the vehicle climate control system will extend driving range and increase the market penetration of EVs. Researchers at the National Renewable Energy Laboratory have evaluated strategies for vehicle climate control load reduction with special attention toward grid-connected electric vehicles. Outdoor vehicle thermal testing and computational modeling were used to assess potential strategies for improved thermal management and to evaluate the effectiveness of thermal load reduction technologies. A human physiology model was also used to evaluate the impact on occupant thermal comfort. Experimental evaluations of zonal heating strategies demonstrated a 5.5% to 28.5% reduction in cabin heating energy over a 20-minute warm-up. Vehicle simulations over various drive cycles show a 6.9% to 18.7% improvement in EV range over baseline heating using the most promising zonal heating strategy investigated. A national-level analysis was conducted to determine the overall national impact. If all vehicles used the best zonal strategy, the range would be improved by 7.1% over the baseline heating range. This is a 33% reduction in the range penalty for heating.

Ford AZTECS Vehicle - Thermal Testing (CRADA CRD-09-340 Final Report)

“…Energy savings from HVAC load reduction solutions translate directly into increased energy for vehicle propulsion, which improves driving range for EVs and can lead to wider EV adoption. Cold weather, heating evaluation summary, work is documented in detail in an SAE journal paper [11]: Outdoor vehicle tests and thermal modeling were used to assess strategies for reducing vehicle cabin heating loads through zonal control and advanced seating for and comfort optimization. Testing showed that using only existing HVAC vents and focusing the conditioned air on the driver, a 5.5% reduction in heating energy can be realized.…”

Review of Cabin Thermal Management for Electrified Passenger Vehicles

“…These models often include some type of CFD model for the cabin that is verified by experimental measurements. Jeffers et al developed a human physiology model for evaluating the influence on occupant thermal comfort [48]. The model included a virtual manikin, which enabled human thermal comfort analysis using the human physiology model.…”

“…According to Kambly and Bradley, the cabin heating is considered as a technical bottleneck for electric vehicles in the cold regions [37]. The maximum driving range of today's midsize EV is about 250 to 300 km and many studies demonstrate that the range decreases about 40-50% by the operation of the cabin electric heating [9], [48]. The challenge is to improve the heating system efficiency and minimize the energy consumption, having only limited amount of heat available.…”

Optimal Control Strategy for Series Hybrid Electric Vehicles in the Warm-Up Process

“…References [12,13] found that application model predictive control shortens the after-treatment device warm-up time of an HEV. References [14,15] considered the heating requirements of cabins and improved the load control strategy of hybrid vehicles. Reference [16,17] considered the low-temperature characteristics of power batteries in energy management strategies.…”