AirGradient Forum

Integration of wet bulb temperature in dashboards?

#1

Hi there! Most of you are familiar with calculated indices such as “heat index” or “felt temperature”. However, there is one measure that is actually indicative of the danger zone concerning the combination of temperature and humidity, especially during heat waves: the wet bulb temperature (WBT).

Why I think this is relevant: The cooling mechanism of the human body relies on evaporation of water (sweat) into ambient air. That works well as long as the surrounding air can accept further water molecules and the wet bulb temperature measures exactly that effect: what is the lowest possible temperature that can be achieved by evaporative cooling of a thermometer in ambient air? In other words: what is the maximum cooling effect that a human body can produce using sweat (or by splashing oneself with water, wearing wet clothes, etc.)? This WBT is important, as starting from 28°C WBT people will start feeling unwell and once 35°C WBT is reached, prolonged exposure means severe risk of fatal heat stroke because the human body overheats and is unable to cool itself anymore.

That is why I propose implementing the wet bulb temperature as an indicator for AirGradient dashboards.

Further reading:

Nice explainer as a video:

Calculator:
https://wetbulb.1209k.com

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#2

Hi @Baelor, thanks for sharing this. I’ve added it to our feature request list!

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#3

Nice post! Thanks for the video. It helps clarify how I should interpret the temperature data from my wet bulb sensor. After checking the data from the sensor I find that there have already been 9 days since mid-June locally with a wet bulb temperature above 32 C (90 F). One of those days had a wet bulb temperature of 34.2 C (93.6 F). The data clearly shows that the wet bulb temperature has been at or above 28 C (82.4 F) locally almost every day since the first week of May and twice in April, reaching that temperature by 10 am local time and staying above it until around 7 pm local time. I have found it to be a useful tool to determine when I should consider being outside working to avoid the worst heat of the day.

I do find the information in the video to be very useful about finding an air-conditioned area to allow a cool-down and feel very fortunate to have that available to me. I had noticed in the past that using a fan outdoors to facilitate cooling down did not always work and now I know why. Very useful information that I can pass on to others.

Since the sensor depends on an accurate humidity determination to calculate the wet bulb temperature then it is likely that Air Gradient will need to make this a separate sensor package because the current outdoor package that I use, an O-1PST, is not able to calculate an accurate air temperature or humidity reading because their readings are compromised by the warm air flow past the particulate sensors. There is no way to correct to an actual air temperature with the O-1PST since it is a non-linear problem.

With that in mind, I am sure that they can produce an accurate package with appropriate shielding for detecting normal dry air temperature, barometric pressure, and humidity. That package, if it is produced, can be used to calculate wet bulb temperature.

If I remember right, and anyone can correct me here, wet bulb temperature uses actual air temperature (dry bulb shaded), and relative humidity in the calculation.

Good luck guys.

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#4

@Flatspot, I find the video really helpful, too. And thank you for sharing your thoughts and feedback on the Open Air!

We will consider improving the temperature reading accuracy of the Open Air when we have a chance to revise the hardware.

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#5

Tai, I appreciate the reply and would like to clarify about the O-1PST.

I personally do not have any issues with the temperature and humidity data from the unit even though they are not actual dry, shaded air temperatures or humidity numbers. I have other sensors around my place that give that data and, most importantly I think, I understand why the numbers are not correctable to actual values.

Anyone needing information about temp and humidity can check the forums for posts on that subject and it should become obvious to them why there are corrections applied and why those corrections may still not get you to an air temperature that closely matches a different sensor package placed beside the O-1PST. Since the on-board sensors are used in the particulate calculations and are physically inside the Plantronics module they will inevitably be affected by the measurement process and they are in the air stream passing by that module subject to heat accumulation which will affect both the temperature reported and the humidity reported in ways that are probably not correctable. That’s just the way it is.

I understand that the original plan did not include reporting temperature data since it was known to be affected by the process and potentially inaccurate as weather quality sensor data. I saw the footnotes and guidelines about temp and humidity before I purchased my unit. I did not expect to be able to use it as a weather tool. I did and still do download that data for comparison to similar data from other sensors on my property and have so far not found a correction algorithm that allows a tight fit with other sensors that were purpose-built for weather station quality data.

I’m not disappointed at all in the O-1PST. I’m actually impressed that with a signal level consistently in the -82 dB level that I can see it at all from my location. I was gonna upgrade all that wifi stuff and still have the components to do it but so far I only lose contact with the unit when a power outage occurs and that is not because it is no longer available, it is because my router loses power. The O-1PST is powered by batteries on a solar set-up and it just runs whether anyone cares or not.

I think that if y’all are considering wet bulb temperature sensor designs then you should be thinking about a new sensor package line to accompany your outdoor product line of air quality sensors. Weather data, especially wind speed and direction information can be very valuable in understanding air quality issues. Just be sure to use high quality sensors in the units that you build. With a single air quality sensor package deployed such as I have here, I am able to see information about air quality at that sample location but there is no information about where it could be coming from. To understand whether a facility or a situation locally is affecting your sensor data you need to have information from other sensors including wind velocity and direction sensors. That information would also enable you to understand data from other air quality sensors since you could correlate it with wind information and perhaps narrow to a source.

Good luck in your endeavors. I will be watching to see how all this works out.

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#6

@Flatspot, thank you so much again for your comprehensive feedback and for supporting us. We have a lot of cool projects ahead that we are eager to share. Please stay tuned!

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