Development of heat recovery solution for heavy duty truck cabs to improve energy efficiency.

Abstract: The recent climate actions to reduce greenhouse gas (GHG) emissions have set the stage for decarbonizing the transportation sector through electrification, which has led to a surge in the deployment of battery electric vehicles (BEV). Trucks are no exception, which has led automakers to shift their focus toward producing Battery Electric Trucks (BET). While tail-pipe emissions are reduced drastically, certain aspects of BET prevent its widespread deployment, prominent of which is the range anxiety. The range of a BET is heavily impacted in cold weather as energy from traction batteries is also used to warm the battery pack and cabin, where 70% of cabin airflow at minimum is continually expelled through exhaust vents for proper ventilation. In this study, three heat recovery techniques were investigated with the objective of harnessing the waste heat from evacuating cabin air to reduce the heating energy consumption in a BET. One proposed technique employs the use of an air-to-air heat recovery system (AAHRS). Baseline experiments were conducted on a SCANIA test truck for benchmarking and to gather data on the performance of the installed HVAC system, which aided the prototyping stage of basic engineering design to ensure it is operable and safe. The prototype was modelled in CATIA, then fabricated and fitted to the test-truck. Validation experiments were done to evaluate the energy savings from the prototype in a climate chamber at various ambient temperature and fan speed settings. The study found a 20-53% reduction in the heat dissipated by the coolant with the implementation of AAHRS, which is beneficial in reducing the energy that need to be replenished by electric batteries for a BET. In contrast, the electrical power consumption increased 1.7-3.3 times higher than the baseline due to the additional power-consuming components, such as the exhaust blower and heat wheel motor. Moreover, the preheating effect from the heat wheel operation enabled the increase of HVAC air intake temperature by 7-28°C from ambient levels. Overall, the energy savings from integrating the AAHRS prototype was about 19-47% considering the coolant heat was produced from an electric heater as was simulated in the tests, whereas the range was estimated to reduce by17-39% if an automotive heat pump would instead deliver the heat into the cab heater core. Two other presented techniques operate on air-to-liquid heat recovery system (ALHRS), whereby each is envisioned to be coupled separately to a heat pump assisted integrated thermal management system (ITMS). One scheme recovers heat from the evacuating cabin air to raise the chiller coolant inlet temperature, whereas the other scheme proposes to adopt a multi-evaporation process in the concept liquid-cooled heat pump, wherein the evacuating cabin air serves as the direct heat source for the higher temperature-chiller. The two schemes were initially evaluated via vapor compression system performance analysis to have the potential to increase the condensation heat and condenser coolant outlet temperature with simultaneous increase in the coefficient of performance, which is beneficial in terms of available heat that can be dissipated into the downstream battery cold plates and cab heater core. As initial step towards assessment of the energy-saving potential of proposed ALHRS solutions, a simulation model of an adopted baseline ITMS concept was developed in this study using Engineering Equation Solver (EES) software, which then was validated against internal bench test results for a mock-up ITMS model. Results of initial validation test indicated an absolute error between the simulation outputs and bench test results of 8-14% for condensation heat, while it was below 7% for all the other relevant performance parameters.