Dew Point with rules

[grovkillen]

I'm helping a curling club with this and that and they wanted to have the dew point monitored. In general they use this to know how to proceed with the ice making. Anyhow, I found out a way to calculate this within ESPeasy. Heres how I did it.

First of I hooked up two BME280. This is possible due to the fact that it is possible to re-address them using a simple resolder+cut (see picture below; red=cut, green=solder).


First I added the two BME280 according to basic settings:


Then I set up a Dummy device according to this set up:


It happened to have this task number:


I then fixed this rule (please observe that my obscure nomenclature leave a lot to desire):

Code: Select all

on TempHumidityPressure_OUTSIDE#%RH do
  TaskValueSet,7,1,[TempHumidityPressure_OUTSIDE#°C]-(100-[TempHumidityPressure_OUTSIDE#%RH])/5
if TempHumidityPressure_OUTSIDE#%RH>49
 Publish %sysname%/DewPoint_OUTSIDE/°C,[Dew_point#°C1]
else
 Publish %sysname%/DewPoint_OUTSIDE/°C,[Dew_point#°C1]*
endif
endon

on TempHumidityPressure_INSIDE#%RH do
  TaskValueSet,7,2,[TempHumidityPressure_INSIDE#°C]-(100-[TempHumidityPressure_INSIDE#%RH])/5
if TempHumidityPressure_INSIDE#%RH>49
 Publish %sysname%/DewPoint_INSIDE/°C,[Dew_point#°C2]
else
 Publish %sysname%/DewPoint_INSIDE/°C,[Dew_point#°C2]*
endif
endon

The extra "*" is added for values below 50%RH since the simplified calculation of Dew Point is not really good below this value. Please see more here.

So there's how you add dew point to your nodes!

[toffel969]

I'm helping a curling club with this and that and they wanted to have the dew point monitored. In general they use this to know how to proceed with the ice making. Anyhow, I found out a way to calculate this within ESPeasy. Heres how I did it.

First of I hooked up two BME280. This is possible due to the fact that it is possible to re-address them using a simple resolder+cut (see picture below; red=cut, green=solder).


First I added the two BME280 according to basic settings:


Then I set up a Dummy device according to this set up:


It happened to have this task number:


I then fixed this rule (please observe that my obscure nomenclature leave a lot to desire):

Code: Select all

on TempHumidityPressure_OUTSIDE#%RH do
  TaskValueSet,7,1,[TempHumidityPressure_OUTSIDE#°C]-(100-[TempHumidityPressure_OUTSIDE#%RH])/5
if TempHumidityPressure_OUTSIDE#%RH>49
 Publish %sysname%/DewPoint_OUTSIDE/°C,[Dew_point#°C1]
else
 Publish %sysname%/DewPoint_OUTSIDE/°C,[Dew_point#°C1]*
endif
endon

on TempHumidityPressure_INSIDE#%RH do
  TaskValueSet,7,2,[TempHumidityPressure_INSIDE#°C]-(100-[TempHumidityPressure_INSIDE#%RH])/5
if TempHumidityPressure_INSIDE#%RH>49
 Publish %sysname%/DewPoint_INSIDE/°C,[Dew_point#°C2]
else
 Publish %sysname%/DewPoint_INSIDE/°C,[Dew_point#°C2]*
endif
endon

The extra "*" is added for values below 50%RH since the simplified calculation of Dew Point is not really good below this value. Please see more here.

So there's how you add dew point to your nodes!

thanks for sharing. maybe you can put it on the wiki for the rh&t sensors. also it would be nice to make it part of the rh&t sensors plugin and calculate as athird sensor value. this might interfere with transmission to domoticz/other controllers, but very handy if you do standalone node (which to me is still the most reliable if outputs are involved)

[grovkillen]

thanks for sharing. maybe you can put it on the wiki for the rh&t sensors.

Will do but I still wait to get approved as editor for the wiki...

[grovkillen]

It's now live on the wiki: Wiki: Dew Point for temp/humidity sensors

[toffel969]

It's now live on the wiki: Wiki: Dew Point for temp/humidity sensors

very good, thanks

[danmero]

Base on http://inspectapedia.com/Energy/Dew_Poi ... lation.php

Lawrence is saying that for moist air, the dewpoint temperature td will decrease about 1°C for every 5% decrease in RH (starting at td = t, where t = the dry bulb temperature when RH = 100%)

From here is just try a schetch to compensate -1C for each 5% below 50%.

Code: Select all

[Temp#T1]-(100-[Temp#RH1])/5-(10-[Temp#RH1]/5)-1

Maybe someone will work from here.

Regards,

[lyndondr]

This Dew Point formula seems pretty accurate over a larger range.
dewpoint = (%rh/100)^(.125) * (112 + 0.9*Temp) + 0.1*Temp - 112
https://www.ajdesigner.com/phphumidity/ ... p#ajscroll

Here are the rules I use.

on DHT22#%RH do
TaskValueSet 2,1,(([DHT22#TempF]-32)*5)/9 //Conversion to Celsius stored in a Dummy device value
endon

on FtoC#TempC do
TaskValueSet 2,2,([DHT22#%RH]/100)^.125*(112+.9*[FtoC#TempC])+.1*[FtoC#TempC]-112 //Dew Point calculated and stored
endon

on FtoC#DewPC do
TaskValueSet 3,1,[FtoC#DewPC]*1.8+32 //Dew Point Celsius converted and stored to a different Dummy device value
endon

[grovkillen]

I will try this and see if that's better. But we really should add this conversion to a formula function within the core.

[grovkillen]

https://github.com/letscontrolit/ESPEasy/issues/1688

I added it to the issue tracker.

[Donnie]

Did somebody test which of the two formulas is more accurate?