A recent episode of the ASHRAE podcast titled ‘Ventilation in Theory vs. Ventilation in Practice’, featured ASHRAE members Megan McNulty and Andy Persily, two seasoned professionals in the field of mechanical engineering and ventilation. This is part three of a five-part series.

…continued from part two.

This is part three of a five-part series. Image supplied by rorozoa on Freepik

This is part three of a five-part series. Image supplied by rorozoa on Freepik

Baseline understanding: a crucial starting point

The narrative pivots to the critical concept of baseline understanding in ventilation assessments. Persily and McNulty emphasise the significance of confirming whether a system is operating as intended before delving into discussions about adjusting ventilation rates. They stress the importance of functional ducts, operational dampers and overall system integrity. McNulty underscores the need to prioritise fixing fundamental issues before fine-tuning ventilation rates, reinforcing the idea that a well-functioning system forms the basis for any subsequent adjustments.

As the conversation progresses, the duo addresses the flexibility inherent in ventilation and filtration. McNulty shares experiences of resistance to change, particularly concerning filtration upgrades. Despite initial reluctance, she highlights the potential for positive changes and the need to educate clients on the capabilities of their systems. The discourse extends to the post-pandemic era, where heightened awareness of indoor air quality has prompted a re-evaluation of ventilation practices.

The discussion takes a reflective turn as the two draw from their extensive walkthrough experiences. McNulty notes the importance of recognising that every building is unique and requires a tailored approach. Persily interjects with the wisdom that “everything breaks, can break, and will break”, emphasising the need for ongoing operations and maintenance to ensure optimal system performance. The conversation underscores the symbiotic relationship between proper maintenance, improved ventilation, energy efficiency and occupant comfort.

Insights from the EPA Base Study

McNulty prompts Persily to share insights from the EPA Base Study, a comprehensive evaluation of 100 randomly selected office spaces in the late ’80s. The study aimed to provide insights into indoor air quality in seemingly normal buildings. Persily reveals that half of the buildings assessed couldn’t locate the minimum outdoor air design value, indicative of the challenges in documentation and record-keeping. The conversation touches on findings related to ventilation rates, with some buildings falling below design values and others exceeding them due to economiser cycles.

As the two navigate the intricacies of building assessments and ventilation realities, a nuanced understanding of the challenges and opportunities in maintaining optimal indoor air quality emerges. Their experiences underscore the need for ongoing vigilance, proper documentation, and a holistic approach to ventilation that goes beyond mere compliance with standards. The conversation serves as a valuable resource for professionals and enthusiasts alike, offering a glimpse into the dynamic world of building assessments and ventilation practices.

The duo also explores the ubiquitous use of CO2 sensors in indoor spaces and the potential misinterpretations associated with these readings.

They also acknowledge the seasonal nuances that impact ventilation requirements. Persily emphasises the significance of not solely focusing on minimum ventilation rates, but also considering dynamic conditions throughout the year. The mention of economiser mode takes centre stage, highlighting its effectiveness in optimising temperature control, particularly during shoulder seasons. The duo stresses the importance of systems adapting to conditions dynamically rather than adhering to a static set of parameters.

Continued in part four…


Live webinar on ASHRAE website.