Summary
In most commercial and residential buildings, air flow is typically produced mechanically through heating, ventilation, and air conditioning systems, more commonly referred to as HVAC. Beyond personal comfort, HVAC plays a considerable role in the health of building occupants. If a space is poorly ventilated there is a higher likelihood of sick building syndrome (SBS), lowered productivity, and increased transmission rates, especially among airborne diseases such as tuberculosis and chickenpox.
Increasing air flow rates and adjusting air flow direction can help minimize transmission by diluting the density of infectious particles or forcing them away from human occupants. Using mathematical models from the Wells-Riley equation, higher ventilation rates are correlated with decreased transmission. While this idea is often reflected in indoor air quality practices, research substantiating this theory is still insufficient.
Targets
Optimizing ventilation is most effective at preventing airborne transmission, but evidence suggests air flow may have a minor impact on droplet-spread disease.
Ventilation Rates
There is no national building ventilation standard so states and local governments are responsible for providing these requirements. Ventilation standards are typically crafted by technical organizations that consider building occupancy, function, location, and size. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) provides a comprehensive list of ventilation guidelines in Standard 62.1.
The chart below lists a brief summary of the 2019 Standard 62.1 minimum guidelines, but many research organizations and companies will recommend much higher ventilation rates to optimize occupant comfort, performance, and health.
| Building Type |
ft³ / Minute / Person |
Occupant Density / 1000ft² |
ft³ / Minute / ft² |
| Classrooms (age 9+) |
10 |
35 |
.12 |
| Lecture Halls |
7.5 |
150 |
.06 |
| Dining Rooms |
7.5 |
70 |
.18 |
| Kitchens |
7.5 |
20 |
.12 |
| Office Spaces |
5 |
5 |
.06 |
| Public Libraries |
5 |
10 |
.12 |
| Worship Spaces |
5 |
120 |
.06 |
| General Retail |
7.5 |
15 |
.12 |
| Supermarkets |
7.5 |
8 |
.06 |
| Weight Rooms |
20 |
10 |
.06 |
Sustainability
Increasing or maintaining air flow rates does not necessarily require any building modifications since HVAC systems are already installed in most commercial spaces; however, increasing air flow rates also increases energy consumption which comes at a monetary and environmental cost. The general rule of thumb is $1.00/ft² for electricty--ventilation tends to represent 20-50% of that energy consumption. Here are some ways to reduce environmental impact and save electricity:
Reduce ventilation during non-occupancy hours when contamination and transmission is at its lowest.
Consider using natural ventilation, ASHRAE provides guidance for implementing natural air flow properly.
Look into eco-friendly technology such as energy analysis software, HVAC zoning, on-grid solar energy, and scheduled air changes.
Rethinking Ventilation: A benefit-cost analysis of carbon-offset increased outdoor air provision
J.J. McArthur
"
A benefit-cost analysis considered energy costs and carbon emission offsets to achieve net-zero carbon operation for large office buildings across international climate zones with ventilation rates ranging from 125% to 1000% ASHRAE 62.1 minimums. Key findings:
1) The productivity benefit was substantially larger than the incremental energy costs
2) Carbon offset costs were relatively low compared with energy costs and had a negligible effect on results
3) Increasing outdoor air resulted in consistently increasing net benefits on an area basis
4) The benefit-cost ratio was inversely proportional to the severity of the climate, with the most moderate climates actually showing a net energy decrease with elevated outdoor air
This paper frames the question of ventilation rates in sustainable buildings not as an energy issue, but as a health and productivity issue and provides an alternative framework for this evaluation within a carbon-neutral context.
"
Learn More »
Optimizing Ventilation
Only use air filters that are designed for your HVAC system. Filters that are more effective tend to decrease airflow so you might need to adjust your ventilation to compensate.
Routinely inspect HVAC filters, exhaust fans, and outdoor air intake. Excessive moisture, leaky supply ducts, and filter bypasses may be associated with increased airborne transmission.
Air supply and exhuast vents should be placed in a way that blows contaminants away from the breathing zone or cleaner rooms. Downward ventilation places supply vents on the ceiling in order to push air down towards exhaust vents near the floor on multiple sides of the room. Displacement ventilation places supply vents near the ceiling in order to push forceful air across the room then down towards floor near exhuast vents on the opposite side.
Maintain a negative pressure in rooms that are higher in contaminants compared to general spaces. For example, a bathroom should be a negative pressure compared to an adjacent office (2.5 Pa difference). If this is unachievable, attempt to direct air flow from a clean space to a less clean space.