How to calculate fan setpoint based on CO2 in HA script?

[Tigerstrenght]

Hi all,

Comming from Domoticz and used to Python and Dzvents I find myself struggling a lot with the HA script styles.

After trying for hours I would like to get some advise on how to script this very simple thing. I have a CO2 meter en want a, more or less, stepless calculation to send to my ventilation unit.

In domoticz it was just:

Setpoint = ((CO2 - MinPPM) / Range) * 100 
domoticz.devices('MV box zolder').dimTo(Setpoint)

In HA I try to do the same thing by using this script portion (with fixed numbers for testing, later I need the numbers to be variables who depent on others sensors):

         sequence:
           - service: light.turn_on
             metadata: {}
             data:
               brightness_pct: 
                 value_template: >-
                 {{ ((sensor.esp_woonkamer_co2_woonkamer - 610)/(610-1350)) * 100 | float }}
             target:
               entity_id: light.mv_box_zolder

All I get is an error message “Kan service script/co2_sturing_mv_box_zolder niet aanroepen. Error rendering data template: UndefinedError: ‘sensor’ is undefined”

So I tried this:
{{ ((states("sensor.esp_woonkamer_co2_woonkamer") | float - 610)/(610-1350)) * 100 | float }}

But that errors in:
"Kan service script/co2_sturing_mv_box_zolder niet aanroepen. expected float for dictionary value @ data['brightness_pct']"

These things where so easy in Domoticz, but it can’t be that hard in HA can it? What am I doing wrong here ?

[tom_l]

         sequence:
           - service: light.turn_on
             metadata: {}
             data:
               brightness_pct: >
                 {{ (( states('sensor.esp_woonkamer_co2_woonkamer')|float(0) - 610) / (610 - 1350)) * 100 }}
             target:
               entity_id: light.mv_box_zolder

Templating

[Tigerstrenght]

Thanks @tom_l ! I tried your code but got:

Kan service script/co2_sturing_mv_box_zolder niet aanroepen. value must be at least 0 for dictionary value @ data['brightness_pct']

I did copy the code multiple times to make sure it was correctly copied, but it doenst seems to be working.

[tom_l]

@Tigerstrenght

value must be at least 0

Sounds like you need to adjust your equation.

What value does this return in the developer tools → template editor:

{{ (( states('sensor.esp_woonkamer_co2_woonkamer')|float(0) - 610) / (610 - 1350)) * 100 }}

I tested it with my CO₂ sensor, the template is valid.

If you need to, you can set bounds to your equation output (e.g. 0 to 100%) like this:

             data:
               brightness_pct: >
                 {{ ([0, (( states('sensor.esp_woonkamer_co2_woonkamer')|float(0) - 610) / (610 - 1350)) * 100, 100]|sort)[1] }}

This sorts the list of [0,{{value}},100] by increasing value then pics the middle one [1] (the list element index starts counting at 0).

[Tigerstrenght]

Yes, that was the reason. When running the template editor I saw a < 0 value. Turns out that the equation was wrong indeed (610 - 1350 → 1350 - 610).

Thanks for you assistance! Helped me out a lot. Bottemline was that I should not have used the value_template: key but instead use the brightness_pct: key for the equation to take place.

[Tigerstrenght]

One more thing that I encountered is that it seems impossible to show the brightness_pct value on my dashboard. The device does not have that attribute when I look up the states in developertools. I does have de brightness attribute, but that is from 0-255 instead of 0-100 percent.

Is there a way to convert this when showing on the dashboard?

I tried:

type: entity
entity: light.mv_box_zolder
attribute: brightness
unit: '%'
value_template: {{ (states('light.mv_box_zolder.brightness')|float() / 2.55)}}

But seems like the attribute brightness can’t be found in the value_template part. (when removed the sensor works, but shows 0-255 output). When trying it with:

value_template: {{ (states('light.mv_box_zolder')|float() / 2.55)}} it show that the state ‘on’ was received and the calculation can’t be done, which makes sense as the number value is in the brightness attribute.

@tom_l , do you see where I need to go to get the correct 0-100% output? Learning a lot these days

Edit: I saw the compensation integration, but that would be overengineering such an easy problem I guess.

Edit2: Ah, I fixed the missing attribute issue by finding this formatting:
{{ (state_attr('light.mv_box_zolder','brightness')|float() / 2.55)}}
But how to get this now correct formula to show this value on the dashboard?