July 22, 2020
Reopening Schools - HVAC & Air Purification
by Matt Kunkel & Jeff Alban
Beyond 21st Century Design has released a 100-plus page guide titled "A Clearinghouse of Resources to Aid in Reopening Schools", which includes analyses of design and space requirements to safely educate students in the midst of a global pandemic. There is a powerful desire among teachers, parents, and even students to return children to classrooms. This guide provides insight from industry experts on how to safely educate students of all ages in the midst of a pandemic.
Our President, Jeff Alban was the only MEP contributor in the guide. Jeff provides valuable insight on refining K-12 design to accommodate emergency situations. Jeff is the lead contributor to Topic 5 - "HVAC & Air Purification" and also contributes to Topic 6 - "Sanitizing Schools". Jeff is the only contributor to Topic 5, and this topic is what we will be summarizing.
In Topic 5 ; "HVAC & Air Purification", there are 3 main takeaways. These takeaways are to control airborne infection, upgrade health/nurses' station, and to utilize outdoor air to flush the indoor environment.
Integral to determining rational engineering interventions is having a clear understanding of how effectively the virus is transmitted through the air by infected people and understanding the types of controls utilized by hospitals and other high-risk facilities to reduce the spread. Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can help reduce the airborne concentration of SARS-CoV2-like and thus the risk of transmission through the air.
1) Control Airborne Infection
- Apply the highest efficient MERV filter possible. MERV 12 us the minimum and MERV 14 is recommended.
- Utilize portable HEPA filter units in classrooms.
- The use of UV-C lamps kill microorganisms and can be used in spaces when not occupied, in occupied spaces near the ceiling, and in air handling equipment.
Use of UV-C energy to kill microorganisms used in conjunction with high efficiency filters to capture particles is an effective combination method to kill and capture viruses. ASHRAE recommends consideration of using UV-C in healthcare suites and in high density spaces in non-healthcare buildings.
The use of higher efficiency filters to capture particles used in conjunction with UV-C provides an effective capture and kill approach for cleaning and disinfecting the air. ASHRAE recommends consideration of using the highest efficiency MERV filter achievable and portable HEPA filter room air-cleaners with due consideration to the clean air delivery rate. For high risk healthcare suites local HEPA filtration should be considered. Appropriate PPE is recommended when changing filters.
2) Upgrade Health/Nurse's Station
- Upgrade health/nurses' suites and treat as isolation rooms using:
- 100% exhaust/100% outside air
- Maintain proper pressure relationships and follow ASHRAE Standard 170 design guidelines for "isolation mode."
Increasing outdoor air per person can occur by reducing the number of occupants in the space. Adjusting control sequences can provide extra outdoor air for dilution of contaminates in the space. Exhaust systems are recommended for higher risk areas of concern. Dilution utilizing higher outdoor air rates per person (dilution) should be used in conjunction with upgrades to mechanical air filtration (capture) and disinfection systems (kill).
3) Utilize Outdoor Air to Flush the Indoor Environment
- Utilize outdoor air to flush the building. Maximize/increase outdoor air flow rates to dilute contaminates.
- Maintain indoor temperature and humidity design criteria
Maintaining a clean and sanitized environment will depend not only on the training of the staff to follow defined protocols, but also on the effectiveness of the mechanical system to introduce outdoor air, provide ample air changes, and filtrate the air before it enters spaces. For suggestions on the upgrading and maintenance of the mechanical system, see the HVAC and COVID 19 section.