A Triple Win: Achieving Improved Comfort, Indoor Air Quality and Lower Energy Consumption

Bernard Clement is among the world’s experts in global HVAC strategy, having lived in, learned and worked on three continents (North America, Europe, Asia) across his 25+ year career at Johnson Controls. Bernard has embraced the IWBI vision and is a WELL AP, Advisor for Air concept and WELL Faculty.

The global uptake of healthy building practices has surged significantly over the past few years, with rapid WELL adoption serving as one of our best barometers. At the same time, we are also seeing the emergence of new codes and above-code standards to address indoor air quality. For example, the U.S. Centers for Disease Control and Prevention (CDC) recently set targeted guidelines for ventilation rates. In 2023, ASHRAE published Standard 241, “Control of Infectious Aerosols,” to establish minimum requirements to reduce the risk of airborne disease transmission in buildings. These codes and regulatory tools, such as ASHRAE standards and guidelines, help raise the floor for all buildings when they are adopted by states and jurisdictions.

One such guideline, albeit often less recognized, is ASHRAE Guideline 36, which has traditionally been associated with helping lower energy consumption, but also promises to help deliver healthier spaces. ASHRAE Guideline 36, titled, “High-Performance Sequences of Operation for HVAC Systems,” has been used to help reduce energy consumption for years. The guideline, which offers an evidence based, verifiable and implementable collection of control solutions for HVAC systems, spurred many of the advancements in HVAC controls used to help end-users save energy and money. However, this same guideline can also be useful to improve thermal comfort and indoor air quality (IAQ) and help comply with the WELL Air and Thermal Comfort Concept. It’s all about the right controls, for the application.

Team Johnson Controls at the WELL Conference. Right to left: Charlie Gans (Portfolio Leader, Healthy Buildings), Bernard Clement (Portfolio Leader, Technical and Engineering, Healthy Buildings) Brigitte Solis Wolffson (Sustainability & Healthy Buildings Manager), Tyler Smith (Vice President, Healthy Buildings)

Thermal Comfort, IAQ and Energy Efficiency: A Delicate Balance
Thermal comfort, which is influenced by factors as varied as air temperature, humidity, air movement, mean radiant temperature of surrounding surfaces, metabolic rate, and clothing insulation, can be a challenge for building operators, especially when it comes to satisfying all building occupants. It’s no surprise that studies recognize this difficulty. One study found that only 11% of office buildings achieve over 80% of occupant satisfaction in the summer season, despite HVAC systems consuming a sizable portion of energy —51% of the total energy spent in commercial buildings, according to the Department of Energy [Commercial Buildings Energy Consumption Survey (CBECS), Table E1. Major fuels consumption by end use, 2018].

It’s also worth noting that the WELL Building Standard emphasizes the importance of indoor air quality and comfort through the Air and Thermal Comfort concepts (2 of the 10 concepts that make up the WELL Building Standard):

• The WELL Air concept aims to achieve high levels of indoor air quality across a building’s lifetime through diverse strategies that include source elimination or reduction, active and passive building design and operation strategies and human behavior interventions.
• The WELL Thermal Comfort concept aims to promote human productivity and provide a maximum level of thermal comfort among all building users through improved HVAC system design and control and by meeting individual thermal preferences.

As an operating tool, ASHRAE Guideline 36 also addresses this challenge by optimizing how variable air volume (VAV)-based HVAC systems respond to changing building loads, while also delivering comfort and improving IAQ. As a core principle, the guideline acknowledges that building energy loads vary based on time of the year and occupancy. In practice, HVAC equipment is sized to deliver comfort at maximum load, which occurs when a building is fully occupied at peak cooling season or at peak heating season. But this is only needed a few days of the year. One study showed buildings are mostly used at minimum load. This same study found a 47% increase in occupant satisfaction when using ASHRAE Guideline 36 during the intermediate season (i.e., days with lower loads), without compromising satisfaction in the cool season. Isn’t this a solution that building operators dream of?

Hybrid Work Presents a Win-Win-Win Opportunity
The post-COVID shift toward hybrid work arrangements further complicates building management. While pre-COVID occupancy fluctuated by about 12% throughout an average week, today’s buildings experience variations as high as 43%, offering significant potential for energy savings.

Figure 1: Average 2023 daily office attendance

When attendance varies, it impacts the building’s energy load. For example, fewer laptops generating heat are in the office, less energy for coffee machines is used, less lighting is required, and less outdoor air is needed to maintain clean indoor air.

ASHRAE Guideline 36 empowers buildings to adapt to these changes simultaneously by integrating smarter control strategies that save energy, improve thermal comfort and IAQ: a win-win-win. Indeed, it recommends using “Dual maximum VAV control” to improve occupant satisfaction and better track building load. The use of this control algorithm allows the HVAC control system to reduce airflow in the space and significantly reduce the reheat required at the VAV box.

Smarter Controls, Healthier Buildings
Control systems can and should deliver both thermal comfort and IAQ. While this is typically where complexity gets in the way, it does not have to. Smarter VAV controls, temperature and CO2 sensors working together can effectively account for thermal comfort, which is addressed by the total airflow circulation (outside air and recirculated air), and also support clean indoor air, which is addressed by the outside air portion of the airflow. Further optimization can be achieved by integrating a CO2 sensor that tracks the level of occupancy, making the appropriate air adjustments when occupancy is high and decreasing them when the space isn’t being used.

For example, in a school with one classroom fully occupied and an adjacent classroom empty, ASHRAE Guideline 36 prescribes optimal settings for air and temperatures, enhancing indoor air and thermal comfort, respectively — all while helping use the least amount of energy. Peer reviewed studies evaluating this optimization approach (which includes a mix of dual maximum VAV control, static pressure reset, and supply air temperature reset) show an average energy savings of 31%.

What next?
As ASHRAE Guideline 36 continues to evolve, it will remain a powerful tool to help building operators improve energy efficiency while optimizing for comfort and indoor air quality.

In parallel, the continued adoption of leadership standards like WELL, coupled with increasing market demand to prioritize occupant health, will help accelerate the adoption of more and more sophisticated technical solutions that enable healthier buildings. Universities and national labs have already embraced the Guideline and supplemented the body of evidence documenting the energy savings.

Ultimately, the message is clear: comfort, IAQ and energy savings are not mutually exclusive. We can help all buildings by arming building operators with the tools they need to deliver spaces that promote well-being, save energy, and contribute to a more sustainable built environment.