Moving air

Using home automation as a temporary solution to problems

While waiting to start/finish bigger and interesting projects I have on the table I want to share with you something that might seem minor but indeed was a quick and free solution to a problem I got with the fireplace. In the end home automation is not always about new fancy hardware and sensors to play with, it is a tool for our toolbox and can come in handy in cases like the one I am about to present.

The problem

Main heating system we use at home is a fireplace that is located on one side of the open space at ground floor. It has been there since we bought the house and with some minor fixes over time (this thing has at least 25 years) it is still rocking. The warmth it produces is simply incomparable to any other system, plus seeing embers and fire burning during winter is really nice. We light it up usually in the afternoon and let it run until we go to bed. At some point in the evening we just open the door of the stairs so that warm air goes upstairs and heats first floor as well. The fireplace has a fan that pushes out the hot air from two vents pointing in different directions in the open space in order to split warmth homogeneously. Unfortunately, for some reason well beyond my knowledge on fireplaces, the vent pointing towards the other side of the open space stopped to blow hot air even if the fan works regularly and the other vent is fine. Because of this you can feel that in the half part of the open space far from the fireplace the temperature is lower: in fact I have a temperature sensor (Switchbot Meter Plus) in the middle of ground floor and another one (integrated into a Daikin HVAC split) in the side opposite to the fireplace and readings differ easily by 1-2 degrees Celsius.

The solution

Lucky enough on the side of the open space opposite to the fireplace there is an HVAC split system air source heat pump that we use mainly for cooling/dehumidifying over summer of for quick heating when we get home and fire was not lit up. The cool thing is that it has one mode which is pure ventilation and just blows air within the room without heating/cooling. It moves air and that’s exactly what I need!

Since the split has its own temperature meter (even though tolerance does not seem to be super good) I can compare the two temperatures and use that difference to start the ventilation above a certain threshold value.

In Home Assistant I created then a simple binary sensor using a template helper defined in this way for the moment:

{% set switchbot = states('sensor.meter_plus_e488') | float %}
{% set daikin = states('sensor.ground_floor_inside_temperature') | float %}
{{ (switchbot - daikin) > 1.5 }}

The newly created binary sensor has value on when temperature difference is higher than 1.5 Celsius degrees and off in all the other cases. This is really useful since the status change from off to on can be used as a trigger for a new automation that will actually switch on the HVAC split system in ventilation mode!

First iteration of the automation is pretty basic and I am sure I will improve it over time based on the special cases I’ll experience using this. Trigger for the automation is the helper previously created so when the temperature difference between the two sensors is bigger than 1.5 Celsius the automation will start and execute the following actions:

• set the mode of the split to “Fan only“ (no heating/cooling)

• set the fan mode of the split to “4“

• turn on the split so it starts to blow air

• run for 10 minutes

• turn off the split

So far it looks good as the automation is triggered and moves the air that would otherwise not reach all the open space area. What I’ll do next is:

• try to find the sweet spot about temperature difference threshold and how long the fan should work

• use the same binary sensor to run another automation to stop the fan instead of using a fixed time delay

• compare graphs of the temperature to see how long it takes to have the open space not homogeneously warm

Let me know if you’re interested in reading updates about this project!

Until next time!
Daniel