A new generation of air quality sensing

By Gord Cooke

Our 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?

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 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.

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 in a bathroom triggering the bathroom fan to turn on or a fully-ducted HRV to go to high speed.

Indeed, this discreet technology already exists. However, a broad-band sensor in the bathroom that measured VOCs could also trigger the ventilation response if someone was applying hair sprays or other personal hygiene products. A sensor in the kitchen for VOCs and CO2, or even CO could respond to troublesome pollutants from a gas range and turn the range hood to high speed.

It could be argued that knowledgeable homeowners have been doing this intuitively and manually for years. However, using sensors does take away some of the guesswork of optimizing air quality versus energy efficiency. Moreover, there may be less obvious circumstances to address. Recall that CO2 is a good indicator of appropriate ventilation levels for occupants. A CO2 sensor in a master bedroom that ensures the whole house fresh air system, the heat-recovery ventilator (HRV) or energy recovery ventilator (ERV), operates appropriately to empower a healthy night’s sleep adds value to the system. I have found that some HVAC contractors still think whole house ventilation systems may not be warranted in older homes. These integrated air quality control systems should help validate the efficacy of a wider range of air quality devices.


The appeal of an integrated system

Ventilation alone couldn’t be expected to resolve or reduce levels, indeed on certain days it could make it worse. Imagine the wood smoke from wildfires, or smoggy days in an inner city. Even activating a furnace fan might be counter-productive if the central filtration system is not optimized for fine dust; it would require at least a MERV 13 filter to remove up to 85 per cent or particles smaller than 2.5 microns.

This is an excellent opportunity for mechanical contractors with this new resource of an integrated air quality sensor/control system. The appropriate technology can be selected and programmed into the control response. For instance, if an ERV system with HEPA filtration of the fresh air is part of the mechanical system for a home, then that device could be selected when one or more air quality sensors in the system calls for a reduction in fine particulate matter.

The ERV could also be included or considered in humidity control responses in a home, knowing that an ERV does a better job of retaining humidity in the winter and minimizing outdoor humidity in the summer. I see great possibilities even if it’s just to finally resolve and integrate the multiple devices currently in homes that affect relative humidity levels. It is well known that indoor humidity levels of 35 to 45 per cent in winter and 50 to 60 per cent in summer are optimal for human health and comfort. We have humidifiers, dehumidifiers, air conditioners, ERVs and HRVs that can impact humidity levels, each with their own controls with widely variable sensor technology. These often show different readings from each other. A whole home air quality monitoring and control system may well be able to resolve this specific critical humidity control objective.

These systems warrant interest by professional contractors, builders and even manufacturers. I envision an expanding network of devices from a variety of manufacturers having communication compatibility to these types of sensors and even new homes with more discreet sensors hard wired into critical rooms such as kitchens, bathrooms and bedrooms.

Achieving desirable air quality has never been possible with one technology or device and contractors should be excited to see that the industry is on the verge of collating a whole solution system to address the ever-increasing expectations of their clients.

Fully-automated fresh air systems use sophisticated sensor technology to monitor IAQ.


The best sensing solution

 At present, the integrated systems mentioned here are offered by ventilation companies. There is a need to engage with humidification and dehumidification equipment manufacturers, central and in-room filtration devices, and ultimately even radon mitigation equipment to complete the overall air quality control solution. The systems I have seen already include smart plugs that can be installed in normal electrical outlets that do accommodate more than ventilation-based solutions.

I see great value in plugging in a portable HEPA filtration system in an asthmatic child’s bedroom that could be triggered by high fine particulate matter levels in that specific room rather than trying to rely on a media filter installed in the central furnace system to control airborne dust. Fine dust particles are a specific area of concern to leading air quality researchers. Specifically, PM2.5 levels, the count of particles that are 2.5 microns in diameter or less, are of concern because those particles can travel deeply into our respiratory tract and affect lung function and worsen medical conditions such as asthma. Sensing PM2.5  levels, specifically in rooms where people spend extended periods of time, is intriguing and useful.