Written by: Christian Lobo
The AEE Canada East chapter was pleased to host an event on the topic of Air Sampling for Ventilation Management on November 26, 2021. As part of our mission to provide our regional energy management and sustainability community with a platform to grow, we are grateful to Effi Frohwein of Siemens for the informative webinar and the engaging technical discussions that followed.
Below are a few (okay, more than a few) of the key takeaways from this presentation that our chapter found particularly interesting:
- The intent of this presentation was to demonstrate the importance of following research-backed approaches to maximizing building ventilation, while mitigating the related energy implications.
- Building owners and employers should be aware of research which correlates poor indoor air quality (IAQ) with impacts on occupant health and productivity, resulting in direct and indirect costs. In other words, research suggests that improving IAQ will reduce absenteeism and increase productivity of workers and students, potentially resulting in significant savings.
- On the other hand, many buildings are overventilated without properly measuring space CO2 levels, which results in significant additional energy usage, costs and GHG emissions.
- A 400 ppm increase in indoor CO2 levels has been linked to a 21% decrease in productivity.
- The presentation included graphs demonstrating increased levels of CO2 (up to 2,000 ppm and consistently above 1,000 ppm) within specific elementary school classrooms. After mitigating measures were taken to properly monitor CO2 and increase ventilation rates, the CO2 levels dropped significantly.
- The presenter said that the primary reason that traditional monitoring doesn’t work since someone has to be paid to regularly calibrate the sensors, which is often not done in practice. This translates to lower accuracies and therefore higher operational costs.
- A study from the Lawrence Berkley National Laboratory, which reviewed the accuracy of CO2 sensors installed in the field, demonstrated that on average 10% of the sensors were dead, 81% read too high (average of 39% too high), and 9% read too low.
- The solution proposed by the presenter is to implement a packaged building controls system that employs multiparameter Demand Controlled Ventilation (DCV). He mentioned that the savings are achieved by modulating ventilation rates based on CO2 , TVOCs and a large set of parameters. This is as opposed to traditional DCV (which only measures CO2 ), as this allows for a more accurate picture of the IAQ.
- Instead of using discrete sensors, a typical system of this kind operates using probes and air sampling ports in the supply air duct (for reference), in the general exhaust duct terminals, and directly from certain rooms. This is tied back to the sensor suite which communicates using BACnet protocol and is tied to the building automation system. It then identifies the IAQ of the entire building on a space-by-space basis and modulates the delivered ventilation rates accordingly. In an office context, this can include measurements in open offices, conference rooms and other critical zones with one sampling location every ~2,500 – 3,500 square feet.
- The presenter mentioned that the sensors should be calibrated on a 6-month cycle to ensure accuracy, and the period between calibrations should never exceed 2 years. He added that this is aligned with research published by ASHRAE.
- The IAQ rating of each space can be shown to end users on a mobile application which provides live IAQ data to reassure them.
- This technology is particularly useful in areas with high ventilation rates, such as laboratories, healthcare facilities, classrooms, casinos, and performance theatres. It can significantly reduce ventilation rates through real time sensing of contaminants and avoid overventilation, which can result in up to a 40 to 60% energy reduction. Several case studies were presented and are available for review in the presentation slides.
- The presenter noted that there is no widely adopted certification body for holding the manufacturer responsible for accuracy of their sensors. The issue with traditional DCV is that the discrete CO2 sensors are often not calibrated for 20+ years after being installed.
- The system presented can work with existing BAS systems that communicate over BACnet IP, although there are also other analog options available to ensure compatibility.
- The measured CO2 levels may be used as indicative “people counters”, however this would be useful for general estimation purposes only.
- The signals can also be harvested and used for other purposes (e.g., monitoring/trending specific points which is especially helpful for applications such as operating rooms where certain parameters must be measured and closely monitored.
If you’d like to watch or re-watch the webinar, you can access it through our events page.
Christian Lobo, P.Eng. is a Mechanical Engineer at Stantec Consulting with 7 years experience in the energy efficiency industry. He is also a long standing chapter board member.