Highly Efficient Year-Round Energy and Comfort Optimization of HVAC Systems in Electric City Buses

TL;DR

This paper introduces a highly efficient simulation method for HVAC systems in electric buses, enabling large-scale analysis of energy performance and comfort, demonstrating significant energy savings with heat pumps and radiant heating.

Contribution

The paper presents a novel, computationally efficient simulation approach for HVAC energy optimization in electric buses, allowing large dataset analysis and comparison of heating strategies.

Findings

Heat pumps reduce annual energy consumption by up to 60%.

Radiant heating elements can cut heating energy use by 10%.

Cooling energy costs are much lower than heating, with less impact from COP improvements.

Abstract

In this paper, we present a novel approach to perform highly efficient numerical simulations of the heating, ventilation, and air-conditioning (HVAC) system of an electric city bus. The models for this simulation are based on the assumption of a steady-state operation. We show two approaches to obtain the minimum energy requirement for a certain thermal comfort criterion under specific ambient conditions. Due to the computationally efficient approach developed, we can evaluate the model on a large dataset of 7500 scenarios in various ambient conditions to estimate the year-round performance of the system subject to different comfort requirements. Compared to a heating strategy based on positive temperature coefficient (PTC) elements, we can thus show that a heat pump (HP) can reduce the annual mean power consumption by up to 60%. Ceiling-mounted radiant heating elements complementing a PTC heating system can reduce the annual mean power consumption by up to 10%, while they cannot improve the energy efficiency when used in conjunction with a HP. Finally, a broad sensitivity study reveals the fact that improving the HP's heating-mode coefficient of performance (COP) manifests the largest leverage in terms of mean annual power consumption. Moreover, the annual energy expenditure for cooling are around eight times smaller than those for heating. The case study considered thus reveals that the advantages of improving the COP of the cooling mode are significantly lower.