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  • Which IAQ Monitor should I buy? (Part 2)

Which IAQ Monitor should I buy? (Part 2)

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  • By Pan Chaoyang
  • Date December 2nd, 2015 14:52
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  • This is the second part of a simplified post on indoor air quality (IAQ) monitors.

    Rather than go through the long list of now defunct monitors we’ve tested, I’ll simply focus on the best we’ve found within each class. For now, we’ll also only focus on PM2.5, which is less than ideal (more on that below) but will simplify the subject.

    Grade C: Normally, we advise people to avoid this class of monitors. However, there is one Grade C unit that stands above the rest: The Laser Egg.
    The Laser Egg is a PM2.5 monitor that has been getting a lot of attention as of late and rightly so. Not only is it surprisingly accurate - it is also able to measure particulates over an impressive range. The best way to describe it would be a Grade B sensor in a Grade C casing.
    Despite the accuracy, the Laser Egg suffers from the same limitations as other consumer monitors: there is no way to physically re-calibrate it. Although it is possible to adjust or ‘calibrate’ the readings for Shanghai or Beijing and the makers will soon allow users to customize the calibration via software, there is no way to clean or replace the particulate sensor once it gets dirty. Seeing as the function of the monitor is to measure ‘dirt’, the odds of it eventually getting dirty are practically absolute. Buyers should be wary of the fact that although it performs like a Grade B, it’s fate is that of a Grade C. A simple way to understand this is to imagine having an Audi engine in car that has no hood: you'd have no way to maintain it and the engine would eventually die. However, if you are committed to buying a consumer unit, this is the one to get.

    The image above shows two units after several months of intensive use. Although they started with identical measurements, one of the units has drifted by ~30%, most likely because the internal lens is dirty.

    Grade B: This class of monitors provides the long-term reliability and accuracy required by offices, schools, gyms, hotels, serious home users, etc., without the cost of Grade A. Over the course of the next 18 months we will see a significant increase in the number of brands that meet Building Grade standards. Until then options will remain slim. As of yet, the only unit having qualified is the TSI Air Assure. This unit performs almost as well as a Grade A at a fraction of the cost and sees little drift over time. Moreover, it is designed to be re-calibrated: sensors can be cleaned with a jet of pure air or replaced. That is an absolutely critical detail.
    We are currently testing two other units which seem quite promising. Look for updates in this class within the next couple of weeks / months.

    Grade A: This is the kingdom of the Particle Plus, Lighthouse and TSI Dust-trak. If you are a lab, clean-room or factory, these are the units for you. They are also the units most commonly used to benchmark the performance of Grade B and Grade C units on a regular basis. The internal sensors, pumps, fans, electronics, etc., are designed to provide greater accuracy, maximize measuring range, minimize drift, allow for re-calibration and last longer. In short, you typically get what you pay for.

    The image above shows typical readings from all three Grades after several months of purchase and several rounds of exposure tests. The Grade A reference unit displays PM2.5 at 144.38. The Grade B unit is 3.7% different with a reading of 139. The Grade C unit is 37% different with a reading of 91. The Grade B was re-calibrated mid-way through but unfortunately the Grade C unit couldn’t be. All of them started with the same reading and trends.

    The great news is that the IAQ Monitor market is maturing and now includes options for all budgets and needs. That wasn’t the case as little as 18 months ago. The caveat is that most buyers are not educated enough to tell the difference. Hopefully this post helps change that.

    However, ‘the elephant in the room’ regarding this post is that looking at PM2.5 alone can be very dangerous to human health. In fact, PM2.5 should never be looked at without also considering CO2 and ideally TVOCs (chemical gasses) as well. The ideal monitor is a Grade B that tracks PM2.5, CO2 and TVOC. From what we’re seeing and testing in the market, we’re just weeks away from seeing them appear. Stay posted.
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