Understanding Role of HVAC in the Spread of Viral Particles in Indoor Environments and Finding Ways to Inhibit Their Dissemination
1Rheem Manufacturing Company, USA; 2School of Mechanical Engineering, Purdue University, West Lafayette, USA; 3School of Energy and Environment, Southeast University, Nanjing, China
With the emergence of COVID-19, the airborne spread of the virus became evident. Several studies have been conducted to understand the spread and dissipation of this viral transmission but a tangible strategy for mitigation is still elusive. A numerical study by computational-fluid-dynamics (CFD) is presented here focusing on the role of the HVAC system and its contribution in the spread of the COVID virus in an indoor environment. Airflow simulations have been conducted for a common office space to understand the role that flow patterns and register exit velocities associate with the risk of how such systems can contribute to the spread. The CFD method was validated against detailed experimental data of air velocity, temperature, tracer-gas, and particle distributions. Release of sneeze droplets with a diameter of 5 micron have been modeled and the investigation reveals that such size of droplets remains suspended in the air while being carried for considerable distances well beyond the 6 feet social distancing recommendation. This study evaluates various distribution system scenarios and makes recommendations for design changes to the HVAC system to reduce the droplet and aerosol distance dispersion and assist in viral particle removal from the human breathing zone, thus reducing the probability of human exposure to viral particles. In conclusion, with HVAC system modifications and the addition of a newly developed novel design of a UV-C air purification system introduced to the indoor space, infectious viral aerosol removal through dilution and control of dispersion is realized resulting in a safer indoor environment.
Real-Time Occupancy Detection in Hospital Patient Rooms Using Sensor Fusion
1RWTH Aachen, Germany; 2Turku University of Applied Science, Finland
The presence of occupants has a profound influence on the climatization of buildings. In the healthcare sector, occupants can also be considered as sources of pathogens, which applies further requirements to the ventilation system beyond the regular comfort criteria. The German standard DIN 1946-4 defines a minimum required fresh air volume flow rate depending on the number of occupants. Such minimum flow rates are defined for room types like examination and treatment, intensive care, isolation care, and supporting facilities related to operating theatres. The ASHRAE 170-2021 allows for unoccupied turndown. Hence, the occupancy is required to allow for energy-saving methods like demand-controlled ventilation. This study proposes a sensor fusion occupancy detection approach and analyses its practicability for the use in hospitals. To increase the robustness of CO2-based occupancy detection, it is combined with an activity-based approach. The fused sensor readings are the CO2-concentration of the room and corridor air, the motion via passive infrared sensors (PIR), and the door opening state via magnetic contact switches. We conducted the occupancy detection in 64 patient rooms of a German hospital. The simulated occupancy is validated with the occupancy gathered by on-site observations in 4 rooms over 8 hours. The influence of uncertainties in the data and information basis is analyzed and discussed. The methodology is evaluated towards its practicability for occupancy-based demand-controlled ventilation. The occupancy detection obtained an average mean absolute error of 2.2 persons or an occupancy number match of 44% for the validation period. The higher the air change rates, the more sensitive is the occupancy detection towards inaccuracies in the CO2 readings.
Today's Indoor Air Quality Solutions and Digital Air Quality Monitoring in the Built Environment
AtmosAir Solutions, United States of America
The built environment today is being challenged more than ever to offer solutions which provide for a healthy and energy efficient space for occupants with the ability to monitor and track successful outcomes.
Electronic and reactive air cleaning technologies can provide for an energy efficient means to improve air and surface disinfection at an occupant level. There has been a conflation of confusing data about these technologies, some new and some studied though time.
This presentation will focus on the science of these technologies, the methods of micro-organism deactivation that electronic and reactive technologies can offer and modes of operation and application. This presentation will educate on what these technologies can and cannot do. What studies and information have been complied and how these technologies can be incorporated into a layered approach to provide answers to the health and safety of occupied spaces in today’s built environment.
Also, this paper will study methods of continuous monitoring of indoor air quality and how this data can be used to improve indoor conditions.