Heat Calculation significantly above same calculation from other sensors

[Flatspot]

I am watching the sensor package and comparing the values that I see in the AG with the same values reported by other sensors that are nearby and I see a consistent difference that appears way out of range.

My AG Outdoor is located on a post within a few centimeters of max recommended height (203 cm). The location is on the shady side of the post in a garden that is shaded by large trees.

I have a weather station temp/humidity sensor installed about 8m away on a post in a location that is shaded all day long by large trees.

I have an additional sensor package inside a small greenhouse/shed a little less than 5m from the AG.

The weather station reports Temp / Humidity / Heat Index (Feels Like) / Dew Point / VPD

The sensor inside the greenhouse reports Temp / Humidity / Barometric Pressure / Dew Point / VPD

The AG Outdoor reports Temp / Humidity / Heat Index (Feels Like)

Letting Temp = A ; Humidity = B ; Heat Index = C ; Dew Point = D ; VPD = E ; Barometric Pressure = F

Weather station is WS ; AG is AG ; and Greenhouse is SP

For WS we have A = 81.5 ; B = 72 ; C = 85.6 ; D = 71.4 ; E = 0.30 inHg

For AG we have A = 86.2 ; B = 72 ; C = 96

For SP we have A = 88.2 ; B = 61 ; F = 30.16 inHg ; D = 73 ; E = 1.76 kPa (o.52 inHg)

The calculated Heat Index for the AG, though it calculates correctly if you use the documented equation, always is way above the reported Heat Index from the weather station. The weather station closely matches the values reported by wunderground.com for the local area during the day.

I have seen the Heat value regularly reported above 123F at the same time the weather station is reporting a value 15F or more under that.

What part of the calibration am I missing in correlating these values between closely spaced sensor packages?

I do have an anemometer/wind vane installed and it has a solar energy/UV exposure meter. I do not know whether those parameters are considered in the WS correction of Feels Like temp.

The weather station is an assemblage of Ecowitt components with individual sensors placed according to guidelines in locations that are favorable for their accuracy. The exception is the wind vane/anemometer which is not on a tall pole or tower but is closer to the ground than recommended so wind values may be compromised.

The greenhouse sensor is a SensorPush HTP.xw.

I’m trying to understand how to compensate for the differences between these packages.

[Ethan_AirGradient]

Hi @Flatspot,

From what I can tell, in the given example, both the Ecowitt and AirGradient devices are providing the correct heat index based on the given temperature and humidity values (as you’ve mentioned). However, the AirGradient device is giving a significantly higher heat index since it is also recording a higher temperature. From what I’ve been able to find online, Ecowitt doesn’t include any other parameters except wind data when the temperature is quite low - in this case, I believe it is only considering temperature and RH.

My suggestion would be to apply the standard Open Air Calibration to your dashboard and see if this brings the values more in line. You can apply this at Admin → Advanced Settings → Temperature/Relative Humidity. Please see the screenshots below for further information:

With this correction applied, do you notice much of a difference?

[Flatspot]

Thanks for the quick reply Ethan.

I have changed the calibrations for temperature and humidity so that they both use the Standard AirGradient Open Air Calibration.

Right now I see AG reporting A = 87.6F ; B = 73% ; C = 101F

Checking the Ecowitt I find A = 82.8F ; B = 71% ; C = 88.2F

That’s still a large difference that I feel makes no sense because it absolutely does not feel like anywhere close to 101F outside right now. The Heat Index calculated is way off.

I cross-checked the temperatures just now using a BBQ thermometer at each sensor and found the temps reported by the BBQ thermometer to be within 0.1F of the temp reported by each sensor (AG. Ecowitt, SP) so I am confident they are reporting what they see.

I do find that the AG on the post is catching partial sun while the other two are in permanent shaded locations.

That suggests that a shield to block direct sunlight may improve some of this. I did have the AG shielded a few weeks ago but removed all that because the shields I used were aluminum and were blocking the WiFi to the point where the signal level prevented the unit staying online. It has now improved to the point where I regularly see signals in the -78 to -82 dBm range instead of constant -85 dBm or worse that I had originally seen.

I will look into fabbing a plastic or wood shade cover for the AG and update this post to note any improvements or degradation I see.

[Flatspot]

After making the calibration change this morning, over the last 8-9 hours I still see a significant difference between the Heat Index reported by the AG versus the Ecowitt. The actual temperature difference is as high a 18F with the Ecowitt reporting 99F at the same time that the AG is reporting 117F.

I will see about fabbing a heat shield. At the time where the temperature difference was greatest this afternoon, both sensors packages were in shade.