HIGH-PERFORMANCE HVAC
A NEW GENERATION OF AIR QUALITY SENSING
O
ur industry has excellent sensors and corresponding controls that turn on heating systems when we are likely to feel cold, and turn on cooling systems when we feel hot. But what sensors and controls are available to respond to increasing expectations for better air quality control?
Winter humidity control is just one aspect of air quality optimization.
report on five or six common indoor air quality parameters such as relative humidity, CO2, volatile organic compounds (VOCs), carbon monoxide (CO) and particulate matter. The early versions were sold to HVAC contractors who were encouraged to deploy them temporarily in clients’ homes to help diagnose concerns or create awareness.
When I joined a heat recovery ventilation manufacturer in 1984, the primary objective of ventilation was to control excess indoor humidity during cold Canadian winters. Winter humidity control, of course, is just one aspect of air quality optimization. There are a range of potential indoor air pollutant sources from the occupants and their activities themselves, as well as from building materials, finishes and furnishings. It is definitely time for a more comprehensive approach. Until recently it has been common to identify a specific sensing technology to respond to a specific pollutant source and control a particular device to mitigate or optimize the air quality impact. For instance, in commercial and institutional buildings, sensing carbon dioxide (CO2) levels is a good indicator of the ventilation needs created by the pollutants from the occupants. The latest generation of CO2 sensor technology links to the controls of variable speed fresh air fan motors or dampers to create a demand-controlled ventilation strategy; a very specific sensor to control a specific device. However, I have been encouraged to see in just the last two to three years a move towards a more comprehensive or integrated approach to indoor air quality (IAQ) control. There has been a proliferation of monitors aimed at the residential market that are able to sense and
Gord Cooke
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More recently, table-top versions or even in-duct sensors have become available online that allow homeowners to monitor air quality on their own. There are valid questions around this approach and about the workings of specific devices. The accuracy, repeatability and resiliency of the sensors being used is often difficult to validate. As an example, CO2 sensors have historically required regular calibration, at least once per year. I found calibration information ranged significantly from some of the commonly available air quality monitors that include CO2 sensing. One manufacturer recommended “frequent manual recalibration by putting the monitor outside in fresh air for 15 minutes or more.” Another manufacturer’s literature describes an automatic calibration logic whereby the sensor logic corrects itself by looking for the lowest CO2 readings over a 15-day period and equating those to normal outdoor levels that are typically known to be 400 to 450 parts per million (PPM) and adjusting calibration accordingly. The most significant shortcoming of most of the early broadband air quality monitors, however, is that until now they couldn’t do much other than signal or alarm occupants that one or more of a number of air quality parameters had gone outside of an acceptable range. This left homeowners with questions as to how important or urgent the drift out of an acceptable range was and what they could do to correct the issue. I am sure a number of readers have gotten that call from customers.
Monitoring systems up the ante Very recently, two ventilation companies have introduced IAQ monitoring systems that can be linked directly to compatible ventilation and humidity control devices or to “smart plugs” that could indirectly turn on portable filtration or other air quality improvement devices. Both of these systems include multi-sensor, multiroom capabilities that can be monitored remotely on multiple devices and linked to multiple devices throughout a home or office. The challenging goal is to match the sensing of an air quality parameter that is outside of an acceptable range with the activation of an appropriate air quality control device. There are some rather obvious events such as a humidity increase
Gord is a professional engineer who has spent 35 years helping builders and HVAC contractors implement innovative technologies into high-performance homes. He has particular expertise in IAQ and airflow management in houses, and can be contacted at gordc@buildingknowledge.ca.
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2022-01-27 3:17 PM
