The effect of air purifiers and curtains on aerosol dispersion and removal in multi-patient hospital rooms

Airborne transmission of disease is of concern in many indoor spaces. Here, aerosol dispersion and removal in an unoccupied 4-bed hospital room were characterized using a transient aerosol tracer experiment for 38 experiments covering 4 configurations of air purifiers and 3 configurations of curtains. NaCl particle (mass mean aerodynamic diameter ~3 μm) concentrations were measured around the room following an aerosol release. Particle transport across the room was 1.5-4 min which overlaps with the characteristic times for significant viral deactivation and gravitational settling of larger particles. Concentrations were close to spatially uniform except very near the source. Curtains resulted in a modest increase in delay and decay times, less so when combined with purifiers. The aerosol decay rate was in most cases higher than expected from the clean air delivery rate, but the reduction in steady-state concentrations resulting from air purifiers was less than suggested by the decay rates. Apparently, a substantial (and configuration-dependent) fraction of the aerosol is removed immediately, and this effect is not captured by the decay rate. Overall, the combination of curtains and purifiers is likely to reduce disease transmission in multi-patient hospital rooms.

A fresh (air) look at ventilation for COVID-19: Estimating the global energy savings potential of coupling natural ventilation with novel radiant cooling strategies

Radiant cooling-assisted natural ventilation is an innovative technical approach that combines new radiant cooling technology with natural ventilation to increase fresh air delivery into buildings year-round with minimal energy cost and improvment of air quality. Currently, the standard paradigm for HVAC (heating, ventilation and air conditioning) is based on central air systems that tie the delivery of heating and cooling to the delivery of fresh air. To prevent heat loss, the delivery of fresh air must be tightly controlled and is often limited through recirculation of already heated or cooled air. Buildings are designed with airtight envelopes, which do not allow for natural ventilation, and depend on energy-intensive central-air systems. As closed environments, buildings have become sites of rapid COVID-19 transmission. In this research, we demonstrate the energy cost of increasing outdoor air supply with standard systems per COVID-19 recommendations and introduce an alternative HVAC paradigm that maximizes the decoupling of ventilation and thermal control. We first consider a novel analysis of the energy costs of increasing the amount of conditioned fresh air using standard HVAC systems to address COVID-19 concerns. We then present an alternative that includes a novel membrane-assisted radiant system we have studied for cooling in humid climates, in place of an air conditioning system. The proposed system can work in conjunction with natural ventilation and thus decreases the risk of indoor spread of infectious diseases and significantly lowers energy consumption in buildings. Our results for modeling HVAC energy in different climates show that increasing outdoor air in standard systems can double cooling costs, while increasing natural ventilation with radiant systems can halve costs. More specifically, it is possible to add up to 100 days' worth of natural ventilation while saving energy when coupling natural ventilation and radiant systems. This combination decreases energy costs by 10-45% in 60 major cities globally, while increasing fresh air intake.