Increasing Cognitive Function by Decreasing Indoor CO2 Levels

Another example of engineering design that proved harmful to the human condition is the use of asbestos insulation for boiler piping throughout the first half of the 20^th Century. Asbestos insulation was the state-of-the-art at the time, but little did engineers know then that someday asbestos would be related to respiratory conditions such as mesothelioma.

Studies are just now finding that CO₂ might be the most critical CoC in tightly-constructed buildings. As more research is completed and engineers someday look back at this current period of HVAC engineering design, CO₂ might be considered equally as harmful to the human condition as chloramines or asbestos.

Studies Prove Negative Effects of CO₂

The CO₂ study that stands out is Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments developed by the Harvard T.H. Chan School of Public Health, Boston, in its Department of Environmental Health’s Exposure, Epidemiology and Risk Program.  

The 2015 study posed participants in a conventional building test environment versus a “green” environment with few variables other than controlled CO₂ concentrations. Nine different functional domains were assessed: 

1. Basic Activity Level;
2. Applied Activity Level;
3. Focused Activity Level;
4. Task Orientation;
5. Crisis Response;
6. Information Seeking;
7. Information Usage;
8. Breadth of Approach; and
9. Strategy.

The three domains that stood out in the study were Crisis Response, Strategy and Information Usage (97, 172, 131-percent higher in green v. conventional test environments, respectively), which are related to higher cognitive function and decision making.  

The green environment produced cognitive scores that were 61-percent and 101-percent higher on day 1 and day 2, respectively, versus conventional environments created by the study where CO₂ levels were 600 to 1,000 and 2,500-ppm.

Another study, Is CO2  an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance by the Lawrence Berkeley National Laboratory (LBNL) in 2012 confirmed many of the Harvard study’s cognitive function findings. The LBNL and Harvard studies used human cognitive test criteria developed by Dr. Usha Satish in the Upstate Medical University department of the State University of New York (SUNY).

Aside from cognitive function, high CO₂    levels have also been correlated with lower test scores in schools.

Furthermore, NASA is also concerned with CO₂  in the International Space Station (ISS) and is expected to find methods to reduce the levels in the near future.

There is enough study evidence for engineers and contractors to educate building owners on CO₂ effects and specify equipment that minimizes airborne contaminants. However, ideal indoor CO₂ levels should are still open for debate. Outdoor CO₂ levels have steadily risen to just over 400-ppm due to climate change. Indoor levels can run anywhere from 600 to 3,000-ppm, the latter which is commonly found in high occupant density areas, such as crowded classrooms. Ironically, the National Institute for Occupational Safety and Health (NIOSH) calls for 1,000-ppm or less of CO_2., which surpasses cognitive level safe zones revealed by most studies. Most study facilitators saw a noticeable change in cognitive function where the test spaces’ CO₂ were purposely raised 400-ppm or more above their base levels. Since outdoor CO₂  levels average slightly more than 400-ppm, they can be used to lower average indoor CO₂  levels by incorporating more outdoor air via ventilation.              

How To Minimize CO₂

Oversizing new RTUs or calibrating existing units to surpass the current ASHRAE Standard 62.1 recommendations for outdoor air is one solution, but that strategy carries a significant energy penalty for dehumidifying, heating or cooling the additional air. The oversized new equipment’s additional energy usage may also fall short of ASHRAE Standard 90.1 compliancy for energy efficiency. Thus the engineer must walk a tightrope of providing additional outdoor air for IAQ, but also complying with energy efficiency requirements, which eventually will be future law under the U.S. Department of Energy (DOE) requirements.

The answer is energy recovery ventilators (ERV) or dedicated outdoor air dehumidifiers (DOAS) equipment for outdoor air consideration in new construction and retrofit projects. Specifying ERV or DOAS is beneficial in new construction, but also in retrofit situations, because odds are high that the original space may change in terms of occupant density, occupant use or sensible load throughout its lifecycle. An office space designed for a few desk workers that is later converted to an area generating more heat and respiration, such as a fitness gym with 50 occupants, will certainly need more outdoor air capacity than the original intent.

Specifying ERV or DOAS: That is the Question

DOAS and ERV each have individual benefits for different HVAC formats. For example, DOAS is ideal for VRF/VFV systems, radiant panels and chilled beam applications that have little capacity for latent loads and outdoor air compliances. DOAS can handle the latent load of outdoor air and allow VRF/VRV systems, radiant panels and chilled beams to cool or heat the space. For RTU systems, DOAS can provide outdoor air with optimum relative humidity more energy-efficiently before the RTU conditions it for the space. It can be ducted into the space, combined with indoor air handlers, function independently of other equipment, or just simply provide air into a space without ducting.

While DOAS are typically used in conjunction with some type of HVAC system, they can also function as 100-percent outdoor air units. Ideal 100-percent outdoor air applications are gyms, battery storage rooms, animal hospitals, operating rooms, laboratories and other areas where recirculating indoor air with excessive VOCs, particulates or biological contaminants can harm occupants. Of course, CO₂ levels would also decrease to outdoor air levels during the process.

ERV technology, on the other hand, is ideal for applications where exhaust air has thermal attributes that can be extracted to pre-condition outdoor air. 

On-demand ventilation can also be part of the solution. Instead of increasing outdoor air at a constant percentage, sensors detect whether CO₂ levels have surpassed a predetermined set point and then activate the DOAS system when needed to dilute CO₂ independently of the temperature/humidity control. The unit can turn off after acceptable levels are reached, or via occupancy sensors for energy-efficiency during off-peak hours. In most cases, diluting CO₂ levels will most likely bring other CoCs down to acceptable levels.

Recent studies prove that minimizing indoor CO₂   and maintaining recommended levels will enhance human cognitive function and worker productivity, while also increasing test scores in school environments. Engineers and contractors should use DOAS and ERV in both new construction and retrofit applications to ensure minimum CO₂ and CoC levels until it is known what long-term effects these air pollutants have on IAQ and the human condition.                             

A 37-year veteran of the HVAC industry, Agopian holds an engineering degree from Vanier College and an MBA from Duke University. He is a member of ASHRAE TC 2.3 “Gaseous Air Contaminants and Gas Contaminant Removal Equipment” and ASHRAE SPC 62.1 “Ventilation for Acceptable Indoor Air Quality” committees. Now Vice President of Sales and Marketing at RenewAire, he can be reached at [email protected].