It is common for hybrid buses to use electric or diesel-powered heaters to supplement cabin heating during engine-off driving, but these devices will ultimately reduce EV range and increase fuel consumption and harmful emissions.
Vantage Power has recently completed a development project, in collaboration with Sunamp, in which a ‘heat battery’ was installed into one of VP’s retro-fitted hybrid buses and used to store waste engine heat. The heat battery, developed by Sunamp, uses a novel phase-change material (PCM), with a high latent heat of fusion, to store large amounts of heat. The stored heat can then be used to provide cabin heating when the engine is turned off or rapidly heat the engine and/or HVAC system at the start of the following day, thus reducing the amount of time the vehicle will be left idling in the depot whilst the engine and cabin come up to temperature.
The project culminated in several days of testing at Millbrook’s Variable Temperature Emissions Chamber (VTEC) facility, during which the heat battery’s performance was assessed for both engine and cabin warm-up (from cold-start) and maintaining cabin heating during engine-off driving. The heat battery enabled engine and cabin temperatures to be maintained during 20 minutes of engine-off driving, and from a cold-start the heat battery was able to reduce cabin warm-up time by 27% and fuel consumption by 45%, because the engine was rapidly heated above its stop-start threshold.
This project was part-funded by the Niche Vehicle Network (NVN).