Indoor Air Quality Versus Energy: A False Choice

by Marcy Marro | December 1, 2021 12:00 am

Early in the 20th century, public health concerns (e.g., tuberculosis, the 1918 flu pandemic) influenced building ventilation design; however changing priorities from the mid-1940s through 1989 led to much lower ventilation standards in the U.S. I remember regularly drifting off in a particular lecture hall in a 1960s building at my alma mater, despite engaging professors, and I now suspect that this was due to poor ventilation.

The Harvard T.H. Chan School of Public Health just released its third Cognitive Function (CogFx) study[1], a global, longitudinal study of the effects of poor IAQ on the speed and precision of cognitive function in office workers (less than 300 participants in 6 countries). This study found that participant’s cognitive test response times and accuracy declined with increasing concentrations of particulate matter (PM_2.5 ≥ 12 µg/m³) and carbon dioxide (CO₂), with measurable difference observed between concentrations as low as 400 to 800ppm.

For reference, the WELL Building Standard[2] sets a PM_2.5 threshold of 15 µg/m³ (based on World Health Organization guidelines) and recommends a CO₂ concentration of 900ppm (or 500ppm above ambient outdoor levels) for enhanced ventilation design. This suggests that even buildings designed to modern standards are not optimized for human performance. In schools and universities, this means that many classroom environments are not supporting learning. In businesses, considering that people make up more than 85% of a typical organization’s budget, the cost of performance impacts from poor IAQ in workplaces can be significant.

In the past, reducing outside air ventilation was used as an easy way to save energy, without awareness of its impact on IAQ. During the pandemic, some building engineers significantly increased outside air to reduce COVID-19 transmission risks, which, in some cases, increased their energy bills. We don’t have to settle on one or the other; there are strategies for improving and controlling ventilation and filtration without sacrificing energy efficiency. Let’s review a few:

Smart Controls

Demand control ventilation is a common strategy in assembly spaces, using CO₂ sensors to control ventilation rates and reduce air flow when spaces are sparsely occupied. The quality of air monitoring devices has increased while their cost has come down, making it feasible to deploy sensors more broadly to measure CO₂, PM, and total volatile organic compounds (TVOC). These can be linked to HVAC controls to modulate ventilation rates based on occupant density and pollutant concentrations. This innovation allows HVAC systems to actively address IAQ issues while saving energy by reducing ventilation rates when interior conditions allow.

Ventilation and Energy Recovery Systems

One of the challenges in balancing IAQ and energy is inherent in building systems that tie ventilation to thermal conditioning. This challenge led to the adoption of dedicated outside air systems (DOAS) supplied by energy recovery ventilators (ERV) that optimize ventilation for occupant health, independent of heating and cooling demands in the space. While DOAS are optimally designed and installed as part of an integrated HVAC system in new construction and major renovation projects, it could be practical in some existing buildings to retrofit DOAS and ERVs as a cost-effective way to increase fresh air ventilation without a significant energy penalty.

High-efficiency Filtration

Low-efficiency MERV 8 filters are commonly used in many commercial HVAC systems and do little to remove small particles that are detrimental to human health; however, there is a common misconception that high-efficiency filters (e.g., the MERV 13 filters promoted by LEED and WELL) are incompatible with many older HVAC systems and can increase the energy used by air handlers. Through careful design, high efficiency filters can be used in the design of new HVAC systems and retrofitted in many existing systems without a significant increase in energy or operational costs. In the review of some applications, the life cycle cost of high-efficiency filters may provide cost savings to the facility.

Energy-efficiency Upgrades

Many existing buildings suffer from poor energy performance due to lower efficiency equipment, deferred maintenance, outdated controls, and other factors. Energy audits and retro-commissioning (RCx) address both energy performance and IAQ, seeking low-cost/no-cost energy efficiency improvements to implement concurrent with ventilation enhancements. These measures offset potential energy penalties associated with increased ventilation.

For example, in many cases economizer dampers in air handling units have been manually closed. By reenabling economizer function, fresh air ventilation increases while also saving energy through free cooling. Additionally, low-cost energy saving measures can be found in most buildings, including lighting retrofits, motor upgrades, and rooftop HVAC unit replacements that provide a rapid return on investment, often with costs offset by utility incentives.

Enhancing human health and comfort while increasing energy efficiency and reducing carbon emissions are vital goals for existing buildings and design of new facilities. The good news is that we do not need to choose between these goals, as there are many available strategies and technologies to support both outcomes. A thoughtful approach to identifying and implementing effective measures is a sound investment in human performance enhancement and operational cost reduction.

---

Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 30 years of experience in sustainable building design. He is a senior consultant with Intertek Building Science Solutions in Portland, Ore. Jim Bagrowski, PE, LEED AP, is an engineer and commissioning agent with over 28 years of experience, and a Project Manager with EEI in Golden, Colo. To learn more, follow Scott on Twitter @alanscott_faia[3].

Source URL: https://www.metalarchitecture.com/articles/indoor-air-quality-versus-energy-a-false-choice/

---