Node-RED Compare two temperatures

With this flow, you can compare the current state of two temperature sensors.

Node-RED flow You can download this flow here.

Scenario:

Open a window open if, in the summer, the outside temperature is lower than the inside temperature.

Explanation of each node:

[inject node] Every 30 minutes a trigger between 16.00 and 21.00. It’s also possible to use the ‘other temperature’ as trigger for this flow.
- top flow [get node]* Get the current temperature in a room.
- bottom flow [get node]* Get the current outside temperature.
- bottom flow [trigger node] Add a delay of 1 second to force the correct order of input values for the next node.
```
Send       nothing
then       wait for
          1 seconds
then send  the original message
```

[join node] Merge the two temperatures together as one value like “26|18”. The second value is always the outside temperature.

  Mode                              Manual
  Combine each                      msg.payload
  to create                         a String
  joined using                      [a-z] |
  Send the message:
    After a number of message parts  2

[function node] Calculate the difference between the two temperatures.

 var temps = msg.payload.split('|');
 var diff = Math.round(temps[0] - temps[1]);
 node.status({text:diff})
 msg.payload = diff;
 return msg;

[switch node] Only continue if the difference is bigger than X degrees.
```
 Property  msg.payload
 > [0-9] X
```

[template node] Define the text which will be sent to inform you.

  The temperature in room X is \{\{payload\}\} degrees higher than outside

[debug node] This can be replaced with an output node of your choice. Like Telegram/Whatsapp/speaker/etc

* This get node is part of the additional nodes set, named node-red-contrib-zigbee2mqtt. You must install this first to used it. Via the menu > Manage Palette > Palette

Suggestions for related flows:

This flow can also be used for controlling a fan in the bathroom, compare humidity in the bathroom with the humidity from somewhere else in the house. During the year the humidity has different values.

Additions to this flow:

Use the ‘other temperature’ sensor as trigger for this flow;
You can also check if the window is already open, before running this flow. This can be accomplished by adding a contact sensor on the window;
If you use the temperature sensor as trigger then the inject node can be removed. And you need to add a filter to only send messages in a specific timeframe and limit the amount of messages.

Table of Content ^

<< See also my other Node-RED pages

Top | Homepage | Best Buy Tips | Shirts, mugs, stickers with IT quotes

vd Brink Home Automations

Home automations: Home Assistant, ESPHome, Node-RED and more.

Node-RED Compare two temperatures