My house has a ventilation unit which I can control with a homebrew ESP/C1101 868 MHz module. I wanted to have it automatically switch on when I take a shower.
Sensors:
I am sensing high humidity with a Wemos D1 mini with DHT22 sensor and sensing hot water usage via my Nefit Easy thermostat. The bathroom is the only user of hot water in my house (close-in boiler in kitchen)
Humidity:
Humidity is varying, so how do you baseline the measurement? Humidity data is stored in an InfluxDB database via MQTT. So I’ve made a sensor in HASS that retrieves the lowest absolute humidity value in the past two hours:
- platform: influxdb
host: localhost
username: xxx
password: xxx
queries:
- name: "minhum"
unit_of_measurement: 'mg/m3'
value_template: '{{ value | round(1) }}'
group_function: min
where: '"property" = ''abshumidity'' AND "sublocation" = ''bathroom'' and time > now() - 2h'
measurement: 'sensors'
database: sensors
If I compare this value with the current value, I can easily sense an increase in humidity. Why absolute humidity? Because at higher temperature (happens when shower is on), the increase in relative humidity is less pronounced.
[/details]
- platform: template
sensors:
humdelta:
value_template: '{{ (float(states.sensor.badkamer_abshumidity.state) - float(states.sensor.minhum.state)) | round(1) }}'
unit_of_measurement: 'mg/m3'
Now, define the thresholds, via an automation:
- id: hum_high
alias: high humidity
trigger:
platform: numeric_state
entity_id: sensor.humdelta
above: 4
action:
- service: input_select.select_option
data:
entity_id: input_select.humidity
option: high
This sets an input selector to high. Similar for medium and low
Hot Water:
The smart thermostate script spits out a mqtt status topic few times per minute.
- platform: mqtt
name: "wk_boilerstatus"
state_topic: "/woonkamer/woonkamer/thermostaat/boilerstatus"
Combining the two
If the humidity is high, or if Hot Water is on for more than a minute, or when a selector in the interface is changed to high, the fan is set to high via an mqtt topic, and the input selector is set to high.
- id: fan_01
alias: Fan Speed high
trigger:
- platform: state
entity_id: input_select.humidity
to: high
- platform: state
entity_id: sensor.wk_boilerstatus
to: HW
for:
minutes: 1
- platform: state
entity_id: input_select.fanstate
to: high
action:
- service: mqtt.publish
data:
topic: /hass/itho
payload: high
- service: input_select.select_option
data:
entity_id: input_select.fanstate
option: high
Similar for low humidity. Difference is that I want to turn down the fan with a delay of 15 minutes. The condition makes sure I am not issuing a low topic all day long. I should build a similar condition for high 
- id: fan_05
alias: Fan Speed low
trigger:
- platform: state
entity_id: input_select.humidity
to: low
for:
minutes: 15
- platform: state
entity_id: sensor.wk_boilerstatus
to: 'No'
for:
minutes: 15
- platform: state
entity_id: input_select.fanstate
to: low
condition:
condition: state
entity_id: input_boolean.itho_not_low
state: 'on'
action:
- service: mqtt.publish
data:
topic: /hass/itho
payload: low
- service: input_select.select_option
data:
entity_id: input_select.fanstate
option: low
Lessons learned:
Numeric state doesn’t work with for
- platform: numeric_state
entity_id: sensor.humidity.state
above: 4
for:
minutes: 15
gives an error
Value_template sensor with calculation
At first I made a value_template sensor with if statements to select the required fan state. Although it did work in the template editor http://192.168.0.9:8123/dev-template, it did not work in reality.
- platform: template
sensors:
bkfanhumidity:
friendly_name: Fan status for BK humidity
entity_id:
- sensor.bkfanhumidity
icon_template: mdi:water-percent
value_template: >-
{%- if float(states.sensor.humdelta.state) > 4 -%}
high
{%- elif float(states.sensor.humdelta.state) < 4 and float(states.sensor.humdelta.state) > 1 -%}
medium
{%- else -%}
low
{%- endif -%}
did not work (properly). It was high or undefined (or low, I forgot)
Cleaning up
I need to clean up my code, I realized while writing this post
What is next?
Tie CO2 measurement to the automation