Ventilation plays a critical role in mitigating the airborne transmission of exhaled virus-laden aerosol particles in indoor environments, particularly underscored by the recent COVID-19 pandemic. Strategies such as more frequent natural ventilation, higher fresh air ratios in mechanical ventilation systems, or decentralized air purification technologies have proven effective in reducing the indirect risk of infection indoors. However, when maintaining thermal comfort, these strategies also lead to higher energy consumption for heating, cooling, and air circulation. This presents a challenge, as the effort to eliminate potentially infectious airborne particles indoors conflicts with the objective of increasing energy efficiency within buildings.

To address this problem, novel approaches are required that take into account not only air quality based on CO₂ concentration and thermal comfort, but also the risk of indirect infection by virus-laden aerosol particles and energy expenditure, when designing ventilation concepts for occupied spaces. In this context, we present an analytical model that can be used to assess both the spatiotemporal probability of infection based on a Wells-Riley approach and the spatiotemporal air quality based on the analytical CO₂ concentration in indoor spaces. Experiments and flow simulations using a representative test aerosol that mimics infectious exhaled particles inform this model.

By combining different ventilation measures, including natural ventilation, stationary ventilation systems, and mobile filtering air purifiers, we aim to reduce the concentration of airborne pollutants in occupants' breathing zones while partially substituting fresh air with purified recirculated supply air. This approach minimizes ventilation heat transfer and mechanical energy demand while allowing for compliance with thresholds for air quality, thermal comfort, and infection probability. We vary operating conditions of ventilation measures, such as employed filter classes, air purifier locations or volume flow ratios, to assess their impact.

To correlate the impact of operating conditions on energy expenditure, we determine the analytical energy demand in a steady energy balance, assuming optimal operative temperatures for maintaining thermal comfort. By partially substituting fresh air from an HVAC system with filtered recirculated air from a mobile air purifier, significant ...