Every indoor space is different. Each one is in a different city, town, or rural area. Each one is used for different purposes: sleeping, working, eating, or maybe just sitting and resting. Every indoor space also has its very own microclimate with a unique temperature, humidity, and airborne contaminants. Some spaces have people, but the occupants of almost all indoor spaces are a rich combination of animals, insects, bacteria, plants, and fungi. Most importantly, all of these things are constantly interacting with the outside world and changing in a multitude of different ways.
When considering the best air purifier for your home, the engineers at Molekule have extensively analyzed all of these different attributes to come up with a solution that cleans the air of the widest possible spectrum of pollutants compared to traditional filtration systems. Our purifiers have always had variable speeds so our users can turn them up to a fast speed if air quality gets worse, or turn them down to a practically silent level when the air quality is good. The interplay between efficacy, air quality, and sound has always been an engineering question for our team. Cleaning the air requires moving it around the room, and moving air is the very definition of noise.
In our never-ending quest to clean indoor air Molekule has recently developed Auto Protect mode, which is designed to be a “set it and forget it” option, automatically balancing noise and cleaning efficiency. Molekule Air Mini+ and Molekule Air Pro both come equipped with sensors that inform the device on how much fan speed is necessary. The Auto Protect modes on these devices are designed to keep the air clean without being too loud. Not only did the team have to consider all the ins and outs of indoor air quality, they also had to figure out exactly what “too loud” means to different users.
Auto Protect mode starts with the sensors
Air quality sensors are a relatively new consumer product. Until just a few years ago, air quality sensors were unreliable or so expensive that only research labs with huge budgets could afford one. But with the evolution of manufacturing processes, cheap sensors are now available to the average consumer. These consumer sensors are certainly not as good as laboratory-grade sensors, but they can still provide a snapshot of what is in the air.
Molekule Mini+ and Molekule Air Pro both have sensors to detect particles floating in the air, but slightly different technology is present in the two devices. Even though the two devices were designed from the ground up just a few years apart, available sensors got better between the release of Mini+ and Air Pro. Regardless, both are capable of detecting large particles like pollen and dust and tiny particles of smoke that are invisible to the human eye.
The major difference is that the sensor in Air Pro has different sized bins to detect different ranges of particle sizes while Mini+ just detects the whole size range of particles. The sensor in Mini+ can pick up particles in the air as small as 0.5 microns, which is about 200 times smaller than the width of a human hair.
The sensor in Air Pro can sort different sized particles to tell us a little more about what is in the room. It has three bins: one for particles smaller than 10 microns, one for particles smaller than 2.5 microns, and one for particles smaller than 1 micron. These sizes are respectively correlated with the levels of pollen, dust, and smoke in the air.
Both sensors then report what they’re finding to the user and to the other components of the unit. Mini+ reports the air quality as one of four colors on the top of the device and on the app, and will change the fan speed depending on 1 minute of sampling the air.
Air Pro displays the particles detected in the three size ranges. Air Pro also changes its fan speed faster than Mini+, as quickly as every second to track particle levels changes.
As the purifiers use the sensors to see what is in the air, they can change the fan speed in response to changing conditions.
Predicting pollution when you are not there
It is not as simple as just turning up the fan speed if there are particles in the air. The engineering team had to consider all of the possible polluting events that may occur in an indoor space. They had to design an algorithm that takes the snapshot of air quality provided by the sensor and translate it into a meaningful change in the device’s behavior.
Sources of indoor particle pollution vary quite a bit. They could be continuous low levels of pollution or quick bursts of high levels. Continuous sources might be car exhaust from a roadway or slow emission of gaseous chemicals from building materials, to cite two examples. Burning bread in the toaster, on the other hand, might quickly produce a very high level of particle pollution.
All Molekule air purifiers, even at their quietest speeds, clean the air to keep particles at a lower level. However, if there is a spike in pollution, such as when toast is left too long in the toaster, Auto Protect mode can ramp up the speed of the fan in the unit to more quickly handle the sudden increase in particles. This increase in fan speed also comes along with noise, so as particle levels drop the fan speed will taper off to the original low level.
The algorithm that the units use to decide on precisely how high to increase the fan speed was carefully designed. The team considered that at higher levels of pollutants more particles are inhaled per breath. So these higher levels are a bigger concern than moderate levels of pollutants and should be reacted to faster. When the device detects a high level of pollutants it increases the fan speed by a lot right away.
Along the same lines, if the device detects a medium level of pollutants it increases the fan speed to a medium level. But there is more nuance in the algorithm than this and it will react differently in response to a continuous source of particles. If the device has been increased to a moderate level to deal with a moderate level of particles but the particle levels haven’t gone down, it will ramp up the fan speed to a higher level in recognition that the medium speed wasn’t enough.
The team tried many different algorithm options during beta testing and solicited feedback from real users on how the noisiness of the moving air was balanced by the air quality improvement. They wanted to ensure that the device did not ramp up too high too fast. This was particularly important with Air Pro as its higher speeds can be as loud as someone speaking in a normal tone of voice. Some users will not find this intrusive but someone sleeping or trying to have their own conversation might find it too loud. For moderate particle levels that present only a moderate concern, too much noise is not acceptable.
As a result the team developed two different Auto Protect modes for Air Pro, Standard and Quiet. Standard mode will ramp up the speed to the maximum level if the sensor is picking up a sustained high level of particles. Quiet mode is capped at around 30% of the full speed. It’s designed for people who want the unit to turn up if some invisible particles are floating around, but not so much that it could ever be disruptive.
The limitations of particle detection
Even though our team spent a lot of time perfecting Auto Protect mode, it was just not possible to account for all possible situations. As a result, there are a few conditions where it might be best to manually set the fan speed on your device.
For example, during a wildfire, outdoor air quality can be bad for days or even weeks. In the case of pervasive smoke from wildfire, large amounts of particles can continually seep around windows and doors. This is a time when it is best to manually control your Molekule purifier and to put it on the highest speed you are comfortable with. In this unusual situation, the device might need to maintain a high speed for long periods of time to keep the air at a better quality. In Auto Protect mode the device might see improvement in air quality, assume that the particles are gone, and decrease the speed only to increase it a few minutes later as wildfire smoke seeps back in.
Another shortcoming of Auto Protect mode has to do with the limitations of sensor technology. The sensor works by pulling in a sample of air and illuminating it with a source of light. If there are particles in the sample reflecting light, it can see them and measure their concentration depending on how much light. However, not everything in the air that can be seen by the sensor is pollution. Water vapor from a shower, for example, can be seen by the sensor and might cause a unit in Auto Protect mode to increase the fan speed when levels of particles have not actually increased.
You can read about the performance of Mini and Air Pro on our papers page, and how the technology works to destroy chemicals and infectious microbes on our technology page. And always stay tuned to this blog to learn more about air pollution, air purification, and air quality in general.