Calculating absolute humidity out of rules

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Wiki
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Calculating absolute humidity out of rules

#1 Post by Wiki » 18 Oct 2019, 19:16

Small project: I wanted to give a ventilation recommendation depending on indoor/outdoor humidity and temperature. As I learned by teacher google et al you need the absolute humidity to be compared.

Calculating the absolute humidity needs a bunch of formulas, but I've found some sources where these formulas were compressed to a useable format - useable in our rules. This is the result:

Code: Select all

  TaskValueSet,7,2,(6.112*(2.71828182845904^((17.67*[AUD#C])/([AUD#C]+253.5)))*[AUD#H]*2.1674)/(273.15+[AUD#C])   //outdoor
  TaskValueSet,7,4,(6.112*(2.71828182845904^((17.67*[AUD#IC])/([AUD#IC]+253.5)))*[AUD#IH]*2.1674)/(273.15+[AUD#IC])   //indoor
AUD#C & AUD#H are outdoor values of temperature and humidity, AUD#IC and AUD#IH the indoor ones. Comparing the results: as long as the indoor result is bigger than the outdoor one it makes sense to open the window (or switch on a blower or whatever), otherwise not.

On my site it raised the WAF concerning my electronic playground by 100%.

Might be helpful for someone else.....

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Re: Calculating absolute humidity out of rules

#2 Post by TD-er » 18 Oct 2019, 20:36

There is already the formula present for this, but it has not (yet) made available as an external variable.
I use it in the BME280 plugin to compensate for temperature offset.

Hmm this function you describe differs from the one I used.
Do you have a source for this one?

Wiki
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Re: Calculating absolute humidity out of rules

#3 Post by Wiki » 18 Oct 2019, 23:05

But nowhere I have found neither in the documentation of espeasy nor in this forum any information of the challenge 'out of rules'. Lack of docs? Or are you talking about dew point?

I don't have a source at once at hand, but you can find this kind of calculation at least in the sources of:

viewtopic.php?f=5&t=3672&p=20040&hilit= ... ity#p20040

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Re: Calculating absolute humidity out of rules

#4 Post by TD-er » 19 Oct 2019, 00:48

In order to compute the correct humidity when applying an offset in the temperature, you also need to compute the absolute humidity, right?
Perhaps you're right in that it is probably the dew point. Well when I start asking myself these questions, it is often a good idea to realize it is time for some sleep :)

Wiki
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Re: Calculating absolute humidity out of rules

#5 Post by Wiki » 19 Oct 2019, 13:16

I did a little research with google and I think, I have found the source of the formula I am using: https://carnotcycle.wordpress.com/2012/ ... -humidity/

The formula itself I had found somewhere else (don't remember where), but if you scroll through the linked blog it seems, that the above linked source is spread all over the world.

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