In my industry, we mostly deal with monitoring and controlling heating, ventilation, and air conditioning (HVAC). For those who have ever wondered if the air they’re breathing is clean, or if enough fresh air is coming into an indoor space, or whether they have too much CO2 in their spaces, we engineer and manufacture the sensors that answer those questions and the controllers that make necessary adjustments when something is out of spec.
Fresh Air Has Always Been Important
Fresh air has always been important, but it’s rarely been taken seriously, and incorporating the necessary tools to monitor and control our built spaces has historically been among the first things to be discarded to cut costs. For example, after the energy crisis in the mid-1970s, national conservation measures were put into place which called for a reduction in ventilation to five cubic feet of air per minute (CFM) per person—a reduction of 66% from previous standards. Unfortunately, many buildings are still set at that level due to cost. However, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommends a “minimum ventilation rate of 15 CFM per person in residential buildings in order to provide indoor air quality (IAQ) that is acceptable to human occupants and that minimizes adverse health effects.”
Ventilation—defined as the rate of indoor air exchanges with fresh, conditioned outside air—has been recognized as the first line of defense for healthy buildings. Further, smart infrastructure and high-performing building guidelines stipulate that the accurate measurement of outdoor airflow rates is a fundamental component of building design.
Why Airflow Matters
One pressing reason airflow matters is, obviously, COVID. However, COVID is not the only illness that impacts wellness, nor is it the only danger that buildings and their occupants face. For a population that spends most of its time in buildings, bringing fresh outside air inside is the most efficient and systematic way to improve the quality of the air people breathe. According to the EPA, Americans, on average, spend approximately 90% of their time indoors, where the concentrations of some pollutants are often two to five times higher than typical outdoor concentrations. Pollutants can be combustion byproducts, allergens, biological agents such as mold, pesticides, lead, asbestos, ozone, or other volatile organic compounds that derive from a variety of sources. However, it is important to note that most pollutants affecting IAQ come from sources inside buildings.
Insufficient Airflow
How can people know if the buildings they occupy are getting the proper amount of outside air? Buildings with insufficient levels of airflow may have occupants who complain of frequent headaches, frequent fatigue, or who feel more irritated than normal. These are all symptoms of building related illness (BRI) or sick building syndrome (SBS).
In the United States, it is estimated that poor air quality results in $150 billion of illness-related costs per year, and $93 billion, or 62% of those costs, represents lost productivity from symptoms associated with SBS. It’s important to note that those numbers are all pre-COVID. The cost of poor ventilation is skyrocketing, and that will not slowdown anytime soon.
In fact, because fresh air has such significant health benefits, ASHRAE, CDC, EPA, WHO, and others have identified ventilation as a cornerstone in any IAQ monitoring and control strategy. That’s because it has been demonstrated that occupant productivity and cognitive function can improve 8-11% by improving IAQ.
Current Practices
Drawing and conditioning outside air for heating, cooling, and ventilation is common for any building, and the need for proper ventilation of buildings is not new. Over the last two years, however, we have heard of many instances where outside air dampers were either disconnected or boarded over, which may not have come to light without the recent focus on IAQ. In this way, the COVID pandemic has shone a spotlight on the implications of poor IAQ.
And until al fresco schools, offices, and storefronts become a widespread movement, it’s safe to expect that the amount of time spent indoors is not likely to change anytime soon. So, outside airflow will remain critical to providing safe, productive, and energy efficient indoor environments.
Challenges
There are numerous challenges to measuring ventilation rates, or airflow measurements. First, most buildings are not designed with outdoor airflow measurement in-mind, making it difficult to accurately determine the amount of air entering a building. Further, traditional technology is heavily affected by the weather. Wind gusts, low air velocities, temperature and humidity variations, airborne particulate matter such as dust, dirt, pollen, waste, and dampers, bends, or restrictions that affect airflow—all common occurrences—will negatively impact airflow measurement in traditional technology.Energy efficiency schemes, such as what we saw in the 70s, can also affect ventilation rates. Demand control ventilation (DCV) schemes seek to regulate airflow as a function of occupants in a given space, often using indoor CO2 levels as a proxy for head counts, which will obviously impact ventilation rate.
Delivering accurate, repeatable measurements in any environmental condition is critical to establishing a proper ventilation strategy, whether that includes DCV, minimum airflow or damper position, or optimizing conditions for occupant comfort.
Traditional Technologies
There are numerous airflow measurement technologies available, but few that can produce repeatable, accurate measurements for all types of equipment. Nearly all measurement devices have extremely restrictive installation parameters, which can limit the equipment that traditional devices may be applied to.
Differential pressure, which uses pitot tube, is an accepted standard for measuring airflow, but it is not recommended for ducted systems that have bends or restrictions or for measuring low velocities.
Thermal dispersion sensors have proven to be accurate in measuring low-velocity airflow, but airstream pollutants like dirt, dust, feathers, cobwebs, or animal waste significantly impact performance. Thermal dispersion sensors are also affected by bends and restrictions in ductwork. Additionally, thermal dispersion sensors require regular maintenance and factory calibration for any repair.
Conditioned orifice plates are effective but may require significant modification to mechanical systems, resulting in the highest installed cost, and they are not guaranteed to be a fit for all equipment. Additionally, when measuring low velocities, a conditioned orifice must artificially amplify the differential pressure across the orifice, which compromises resolution and accuracy.
Solutions
The most recent innovation for measuring outside airflow is a patented technology which uses a characterized damper method. This method is not impacted by the weather, low air velocities, temperature, ductwork bends, turbulent airflow, or any of the other traditional pitfalls in the airflow measurement space.
Given that measurements are based on measured damper performance, this approach can also be applied to nearly any type of equipment or mechanical system, ducted or not. This new method uses a high-precision inclinometer mounted on an outside damper blade to establish a damper characterization curve, as well as several probes to accurately measure outside air (OA), return air (RA), and supply air (SA) temperatures.
Problem-Solving Technology
The cost to install a characterized damper airflow measurement system can be dramatically less than traditional technologies. More buildings, especially schools, need to measure outside airflow, which means solutions to truly address to this problem must be affordable and reliable. Today’s technology, coupled with the characterized damper method of outside airflow measurement, allows this technology to provide real-time performance metrics which can be monitored with a building automation system or a local display for building occupants.
Ongoing maintenance costs are minimal, since there are no probes in the unfiltered airstream to be cleaned or recalibrated, and the supply airflow measurements are taken in filtered air. To ensure long-term accuracy, system diagnostics are regularly performed using automated air-measurement methods. If the system is found to be out of tolerance, the calibration routine can be reinitiated to establish an updated characterization curve to reflect the current mechanical system.
Considering the advantages of utilizing a characterized damper airflow measurement system, it could make proper ventilation achievable for nearly any building. And remember, the solution to pollution is dilution.
