Before I start, because I’m a new user I’m only permitted to embed one image. I have replaced some images with links, others I had to remove. See comments below.
I have a Brink Renovent HR/Medium heat recovery unit that has three different fan speeds. After a house renovation I no longer had room for the bulky wired switch that could be used to select the fan speed. The manual showed that instead of the switch (connected to a perilex wall-outlet) the unit could also be switched using three wires that are connected to the unit using a simple RJ11 connector. (See X4-3, X4-5 and X4-6).
I bridged and removed the old switch so the unit was still functioning. I used one Shelly 1 switch to connect X4-3 to X4-5, and one to connect X4-3 to X4-6. See contacts 0 and I in this image. The Shellys are powered with 230V. The SW contact was not used. When both Shellys are off the unit is set to fan speed 1, when X4-3 to X4-5 is closed the unit is set to fan speed 2 and when X4-3 to X4-6 is closed it operates at fan speed 3. I would rather have used a Shelly 2.5 , but since it’s switch contacts are not isolated from the mains, that was not possible.
Because switching them on using the Shelly app, which works quite good, is something I tend to forget I decided to create an Automation for fan speed 2. Fan speed 2 is active from 0700 in the morning to 2300 in the evening.
For fan speed 3 I was looking for something a bit more intelligent. Fan speed 3 is useful e.g. when someone is using the shower or taking a bath. I added a Shelly Humidity and Temperature (H&T) unit with a USB power supply to my setup and spent a few days looking at the humidity readings of the bathroom. It’s very important to set the CoIoT peer as described in https://www.home-assistant.io/integrations/shelly/.
I was looking for foolproof triggers to switch fan speed 3 on and off. I decided that using the humidity value itself as input was not very useful, because humidity tends to vary a lot in a day and over the days. It’s not a very accurate indication of someone using a lot of hot water in the bathroom and it proved difficult to find a reasonable threshold value.
I ended up using the Home Assistant Derivative platform, because it always signals an increase when the bathroom is used.
sensor:
- platform: derivative
source: sensor.sensor_badkamer_humidity
name: Humidity derived
unit_time: min
time_window: "00:05:00"
I created an automation that turns on the fan speed 3 switch when the derivative reached a value higher than 1 (emperically established value). I created another automation to switch it off again when the derivative reached a value lower than -0.2, with a delay of 10 minutes. It turned out that this automation was sometimes triggered just before the automation that turns the switch on, which resulted in a premature switch off. The on automation therefore kills the off automation to prevent triggers from 5 minutes ago from shortening the automation on duration. After a brief delay the off automation is reenabled.
On Automation
alias: Ventilation Bathroom On
description: ''
trigger:
- platform: numeric_state
entity_id: sensor.humidity_derived
above: '1'
condition: []
action:
- type: turn_on
device_id: hidden
entity_id: switch.ventilatie_stand_3
domain: switch
- service: automation.turn_off
target:
entity_id: automation.ventilation_bathroom_off
- delay:
hours: 0
minutes: 0
seconds: 30
milliseconds: 0
- service: automation.turn_on
target:
entity_id: automation.ventilation_bathroom_off
mode: single
Off Automation
alias: Ventilation Bathroom Off
description: ''
trigger:
- platform: numeric_state
entity_id: sensor.humidity_derived
below: '-0.2'
condition: []
action:
- delay:
minutes: 10
- type: turn_off
device_id: 35c16770069531bb893af11feed6f368
entity_id: switch.ventilatie_stand_3
domain: switch
mode: parallel
max: 4
I’ll try to add a picture of how the Shellys are wired. I used their own packing material and a sealable container to protect them from dust. They do not seem to be getting very hot, even when in a closed container.
