The GO AQS ventilation working group convened on April 4, 2025, to discuss various aspects of ventilation in buildings and recommend the best solutions and practices in order to achieve good indoor air quality.

Prioritizing Indoor Air Quality and Energy Conservation

The session began with a survey of members’ perspectives on the importance of indoor air quality and energy conservation. Encouragingly, all members agreed that indoor air quality in buildings is of maximum importance. When asked about the importance of energy conservation, the majority still considered it very important, but with more flexibility, indicating a willingness to prioritize air quality in certain situations. This trade-off was further explored in different environments:

• Schools: Indoor air quality was deemed the most important factor by everyone.
• Commercial Spaces: A balance (50/50) between indoor air quality and energy was largely favored.
• Retail Spaces: Energy considerations slightly outweighed indoor air quality, though a 50/50 balance was also significant.
• Residences: Indoor air quality was paramount, but managing costs associated with achieving it was also a key consideration.
• Hotels: Indoor air quality and a 50/50 balance with energy were equally highlighted.
• Hospitals: Similar to schools, excellent air quality was considered a substantial priority.
• Restaurants and Cafes: Opinions aligned with commercial spaces, emphasizing a balance between air quality and energy.

These responses highlight the contextual importance of ventilation strategies, varying based on the specific needs and priorities of different building types.

Strategies for Increasing Air Changes and Reducing Energy Impact

The discussion then shifted to common strategies for increasing air changes per hour (ACH) without significantly impacting energy consumption. Several recommendations emerged from industry members:

• Control Ventilating Systems: Implementing controlled ventilation to optimize air intake.
• Energy Recovery Ventilation (ERV): Utilizing ERVs to bring in more outdoor air while conserving heat.
• Dual Path Filters: Employing specialized filters for balanced energy and filtration.
• High Filtration with Strategic MERV Ratings: Using MERV 13 filters when particles are detectable by sensors and lower MERV ratings otherwise.
• Balanced Outdoor Intake with Internal Recirculation: Adjusting ventilation based on sensor data for CO2 and other chemicals.
• UV Lamps for Sterilization: Using UV-C technology to sterilize air, potentially reducing the need for excessive outdoor air intake and heat loss.
• Smart Air Quality Sensors: Adapting ventilation rates based on real-time monitoring of parameters like CO2 levels.
• Central Air Handling Units and Heat Exchangers: Efficiently managing air exchange and heat recovery.
• Indoor Air Purification: Reducing indoor pollutants to lower the requirements for outdoor air or high-level filtration, potentially leading to significant HVAC energy savings.
• Optimizing Existing HVAC Systems: Recognizing that older HVAC units were primarily designed for heating and cooling, members discussed how existing systems could better support indoor air quality by ensuring proper MERV filter use and potentially upgrading motors and filter sections to reduce pressure drop.
• Proper HVAC Maintenance: Emphasizing the importance of well-maintained systems, including correctly tensioned belts in VBET assist motors, to ensure efficient operation and prevent energy waste.

The discussion underscored the importance of considering the pressure drop associated with filtration, as low pressure drop is key to saving energy, and filters themselves do not save energy. Modifying filter sections in HVAC units was also suggested as a way to improve efficiency.

Impact of Gas Contaminants on Air Change Rates

The working group addressed how gas contaminants such as carbon dioxide (CO2) and volatile organic compounds (VOCs) affect the required air change per hour. It was noted that VOCs can significantly impact indoor air quality, especially in public buildings. Accurate measurement of VOCs through chromatography and laboratory analysis is crucial to rule out dangerous concentrations.

Regarding CO2, some comments suggested that CO2 is not a real problem in the absence of other air pollutants as long as concentrations remain within certain limits (up to 5,000 ppm or even 8,000 ppm for humans without other pollutants present). This viewpoint aligns with some ventilation standards that focus on diluting CO2 and other contaminants. However, it was emphasized that the presence of unwanted gases necessitates increasing air exchange rates, although careful consideration is needed to avoid drawing in outdoor pollutants. Notably, some pollutants like VOCs and radon can be found in higher concentrations indoors, making dilution via increased fresh air intake the primary removal strategy. Understanding the sources of pollution is therefore vital.

Advantages of Ventilation Technologies for Optimization

The discussion explored various ventilation technologies that can optimize air exchanges and improve indoor air quality. These included:

• Physical Air Purification Systems: Emphasizing strictly physical, non-chemical purification methods like non-dielectric electrostatic systems for particle trapping and VOC degradation, provided the potential difference remains below the first ionization energy of oxygen to avoid harmful byproducts.
• Air Purifiers: Standalone units were also considered as a means to improve indoor air quality.
• Demand Control Ventilation (DCV): Controlling ventilation based on real-time needs indicated by sensors and air quality monitors was highlighted as an effective solution for optimizing air exchange.
• Soft Ionization: This was suggested as a potentially good option that doesn’t produce harmful byproducts. However, it was clarified that the terms “soft” and “hard” ionization are commercial terms, not scientific classifications.
• Combined High-Efficiency and Low-Pressure Drop Filters: Utilizing filters that offer good filtration without significantly increasing energy consumption.
• Heat Recovery Ventilation with Enthalpic Cores: This terminology was new to some members, indicating ongoing advancements in the field.
• Carbon Filters: Using carbon filters dynamically or with sensor-based switching to remove gaseous pollutants.
• HEPA and Activated Carbon Filters in CMV and Recovery Units: Integrating high-efficiency filtration into centralized ventilation systems.

Concerns were raised about marketing claims surrounding air purification technologies, particularly regarding the production of harmful byproducts like hydroxyl radicals and ozone. It was emphasized that any technology claiming “no byproducts” should provide certification detailing which byproducts are not created, as various oxygen radicals, many of which are potentially carcinogenic, are a concern. The importance of understanding the underlying physics and chemistry of these technologies was stressed.

Photocatalytic oxidation (PCO) was discussed, noting that while it can produce hydroxyl radicals, the energy used and potential byproducts need careful consideration. The US EPA’s perspective on the challenges and marketing overstatements associated with some air cleaning technologies was also acknowledged. A call for a standardized classification of air purification technologies based on their physical and chemical principles was made to ensure regulatory compliance and informed consumer choices.

Air Exchange Rates in Schools

The discussion touched upon specific air exchange rates in schools, with the majority of members agreeing on a range of 6 to 8 ACH, although the average among all responses was around ten ACH. It was emphasized that the optimal ACH for any building, including schools, depends on specific factors such as volume, occupancy, and the types of pollutants present. Therefore, the exact required amount should be calculated based on accepted occupancy and pollutant levels to achieve the desired indoor air quality.

Smart Buildings and Ventilation Adjustment

Regarding the prevalence of smart buildings capable of adjusting air change based on occupancy levels, the majority of participants estimated that 10 to 20% of new buildings have such systems in place.

Ventilation Standards Followed

The survey revealed that ASHRAE standards were the most predominantly followed ventilation standards among the working group members. European standards for residential and non-residential buildings, along with ASHRAE standards 62.1 and 62.2, were also frequently mentioned. The newer ASHRAE Standard 241, which provides for even more air in buildings, was noted. Other standards mentioned included local Spanish regulations (RITE, CTE, UNE-EN 16798) and passive house standards. It was highlighted that for older buildings, design specifications for ventilation may not exist.

Conclusion

The Ventilation Working Group session provided a comprehensive overview of key considerations for achieving optimal indoor air quality through effective ventilation strategies. The discussion underscored the necessity of balancing air quality with energy efficiency, the importance of understanding and mitigating the impact of various indoor air pollutants, and the potential of diverse ventilation technologies when properly understood and implemented. The shared knowledge and perspectives laid the groundwork for a deeper understanding of the complexities and advancements in the field of ventilation. The ongoing efforts to standardize the evaluation and labeling of air purification technologies, as highlighted by the Belgian initiative, and the development of comprehensive databases, such as the one being compiled under the European COST Action Net4CleanAir, represent crucial steps towards ensuring healthier and more sustainable indoor environments.

• Recording: Ventilation WG – 2025 April 04