HVAC

How to prepare a facility to be IAQ centric

Indoor air quality is key in buildings, and there are several ways to measure and improve upon it

By Raj Setty September 15, 2021
Courtesy: CFE Media

Learning Objectives

  • Understand the different engineering sensor reading to improve indoor air quality.
  • Know the thresholds of different variables for IAQ.
  • Grasp the fundamentals of creating and air quality index.

The air quality in classrooms and our schools was not as an important topic of discussion before COVID-19 hit. School lunches, class sizes, test scores, daylighting, water quality and other items were what administrators, teachers and parents thought were the most important and budgets were deployed accordingly. Once COVID-19, an airborne virus, shut down schools, air quality and filtration elevated to the top of everyone’s list of priorities.

We are in a new paradigm where air quality can be spoken in the same breath as life safety. We have to move to a more active indoor air quality monitoring and adjusting in real time. When IAQ becomes the front line of protection for students and teachers, the engineering community has a much smaller margin of error.

An important step for school districts and buildings should to return children to in-person learning has been to address ventilation and MERV 13 filtration upgrades to central air handling stations. Following ASHRAE epidemic task force guidance, the industry standard for technical air quality guidance during the pandemic, thousands of heating, ventilation and air conditioning systems across the country have been addressed with filter and ventilation modifications.

In the HVAC engineering community, there has been a tug of war between the advocates of energy efficiency and improved IAQ. With the introduction of more ventilation (fresh air), during most outside conditions there will be increased energy usage to heat and cool the ventilation air. The optimal way to balance IAQ and energy efficiency is to deploy a suite of IAQ sensors to provide a data driven approach to proper HVAC operations.

While energy efficiency strategies must be maintained, in the new paradigm of advanced IAQ, precedence must be given to increased ventilation during the occupied hours. Building engineer operators must have the ability to both increase ventilation during occupied times as well as reduce energy consumption by reducing the ventilation air during unoccupied times.

A pragmatic approach to effective ventilation reduction to code-minimum levels can only be done with the inclusion of air quality sensors. Upgrading to MERV 13 filters can also increase the pressure drop of the air handler and will also increase motor power usage. Filters can be selected with the same pressure drop as a MERV 8 or MERV 11 that was previously installed.

Minimizing the risk of COVID-19 and other airborne viruses isn’t the only reason to focus on air quality in school. In fact, significant IAQ problems can arise from a combination of common minor problems.

As examples, a school might not get enough outdoor air because a fan belt is broken or a damper motor is not engaging. I have encountered a seldom-used drain trap drying out, resulting in sewer gases being drawn into the mechanical room. In some areas of the country, like the West, during fire season, we should have the ability to close our outdoor dampers to avoid entraining fire particulate (PM 2.5) into the building’s air. PM 2.5 when breathed in can have detrimental health impacts to respiratory systems.

IAQ sensors distributed throughout a school building will provide a baseline IAQ profile of the entire building. There will never be a singular tactic to HVAC operations and ventilation due to the varied nature of the outside environment and the state of the HVAC’s unique system in each school. But we have to give building engineers the option of multiple ventilation and HVAC air supply approaches.

From our work across millions of square feet of buildings, we have found that an IAQ sensor every 4,000 square feet or one per HVAC zone provides a very comprehensive IAQ profile of the building. Ideally, one IAQ sensor per classroom and corridor could be provided but this leads to excessive costs and a tremendous amount of unfiltered data to process. At the minimum, schools and education buildings should have IAQ sensors deployed in rooms served by all HVAC main central air handling stations.

Courtesy: CFE Media and Technology

Courtesy: CFE Media and Technology

These sensors should read carbon dioxide (CO2) levels, particulate matter (PM 2.5, PM 1.0) and total volatile organic compounds (TVOC) at a minimum. If the budget allows, we are also recommended adding ozone to the list of sensor readings.

CO2 is our benchmark of ventilation effectiveness in the space. As the CO2 is expelled from occupants, the levels increase. As the HVAC supplies air with the introduction of ventilation air, the level of CO2 will decrease as the overall air becomes diluted. When the indoor level reaches within 10% of the outdoor level (generally averaging 415 ppm), we know that our HVAC did its job and has ventilated the building.

PM 2.5 positive readings demonstrate that our filters are properly filtering and provides us with an indication of when filters should be changed out or to modulate our ventilation dampers to mitigate the particulate matter introduction into the building. In a majority of instances, the particulate matter levels are associated with the outdoor air conditions such as pollen, dust and fires.

Finally, the monitoring that will provide the significant impact for IAQ will be the measurement of volatile organic compounds. VOCs are carbon-based organic compounds that originate from many sources such as cleaning, chemical reactions, building materials, paints, people, furniture and other products/packaging.

Pollutants and IAQ

We can also see outdoor pollutants become a source of indoor VOCs via the HVAC system. Formaldehyde and benzene for example, have been shown to cause cancer in animals at high concentrations. By monitoring the IAQ for COVID transmission reduction efforts, we also gain the added benefit of identifying indoor/outdoor pollutants and improving our school’s air quality.

As we begin to unravel the onion of IAQ, a great resource for information is the Berkeley Lab, which has aggregated many studies of VOCs from across the world. Some of the key findings of the various studies indicated that VOC concentrations indoors is much higher than outdoors. This must be addressed with our HVAC systems and how we think about air in our schools. The basis of this analysis and HVAC adjustments will be based on our IAQ sensor readings and locations.

Collecting and analyzing the readings daily is imperative; but, if you have the resources to be dedicated, I highly recommend uploading all the data into an aggregation platform. Real-time analysis is the best way to closely monitor IAQ. This platform will be set up with critical alarm thresholds and a real time alert system for building operators to adjust the HVAC systems.

At the most simplistic level, we have two main levers to improve the IAQ in real time, increased ventilation and longer HVAC run times. We don’t want to overthink the solution when our sensors cross the established thresholds.

To be effective in real time, use one or both of the simple solutions. Then do a deeper dive of why the thresholds were crossed so we can formulate a longer lasting IAQ solution. If sensor threshold alarms can be directly linked to the HVAC building management system, then efficiencies can be gained. In some cases, we are finding the cleaning staff has not followed the dilution rates of the cleaning solutions. There are also off gassing events with new furniture or even painting causing a degradation in the air quality. The good news is the HVAC systems can operate and ventilate until the air quality gets below our thresholds. Our sensors can direct the HVAC unit operational protocols.

The sample protocol that I developed is our first step in our direction from the sensors to real time HVAC adjustments. The establishment of the thresholds should be completed locally at each school site and in most cases will be very similar based on the geographical area.

After four months of data is collected and overlaid with occupancy profiles, we intend to create a ventilation performance score or an IAQ index. This index will be based on a weighted average of the sensor readings to create a single score by sensor zone. From here we will aggregate the sensor scores to a building level IAQ score or ventilation performance index. This index should be normalized by time factors and decay rates of the various sensor readings.

For example, TVOC’s levels may spike after cleaning but the HVAC system must be afforded the time to dilute and bring the levels down. If they do not come down within 120 minutes, then the index would register that zone as red or poor. We will also use this data to inform the HVAC modifications and operational run times that will need to be made. In our case study school system, we found that based on the unique air change rate of the building HVAC system, the decay rate of the TVOC’s varied greatly. We then decided that the most effective localized approach to improve our filtration and TVOC mitigation was to deploy classroom air cleaners.

As engineers and school facility managers finalize IAQ sensor planning, there are two levels of recommendations: base minimum and advanced IAQ.

Here’s a quick overview of the recommendations for both levels:

Base minimum

  • IAQ sensors deployed at all rooms served by HVAC main central air handling stations.
  • Readings should be taken daily and trending data shared with a building management system.
  • Monitor PM 2.5, CO2 , temperature, TVOC and humidity.
  • Sensor alarms are monitored manually at each sensor and HVAC systems adjustments done accordingly to clear alarms.

Advanced IAQ

  • IAQ sensors deployed throughout the building at no less than one sensor per 4,000 square feet or one per classroom.
  • Readings should be taken every five minutes and trending data shared with a BMS.
  • Data aggregation and analysis software to create a IAQ daily profile .
  • Monitor PM 2.5, CO2 , temperature, TVOC, humidity and ozone.
  • Create baseline algorithms that take IAQ alarms and adjust HVAC equipment sequences for flushing, higher ventilation or air flow changes to improve the IAQ in real time.

This originally appeared on CxEnergy. ACG is a CFE Media content partner.


Raj Setty
Author Bio: Raj Setty is president of Setty. He is also on the ASHRAE epidemic task force for schools.