Thermostat basics - cflurin/node-red-contrib-ramp-thermostat GitHub Wiki

First let's see how a programmable (mechanical) thermostat works, generally we can set the day/night temperature and the start/end time. There are several types but the basic function is almost similar to all.

The chart shows the target temperature for following settings:

day time: 07:00 until 19:00
day temp: 20°C

night time: 19:00 until 07:00
day temp: 18°C

This means that at 07:00 the target (setpoint) is set to 20°C until 19:00 where the target is set to 18°C.

But the actual temperature is obviously not the same as the target, the actual temperature will increase/decrease until the actual temperature is equal to the target one.

How long it takes, depends mostly on the heating system (radiator, floor heating, etc.), the house construction and on the outdoor temperature. So the chart may look as follow:

How does the ramp-thermostat work?

It works like a programmable thermostat with an additional ramp (gradient), generally used when the heating is turned on.

Let's take a look at these two scenarios for a typical example:

• Scenario A: outdoor temperature = 5°C (temperature difference indoor - outdoor = 15°C)
• Scenario B: outdoor temperature = -10°C (temperature difference indoor - outdoor = 30°C)

Scenario A)

In the morning the heating will start at approx. 06:15 and takes approx. 2 hours to reach 20°C until approx. 08:00.

Scenario B)

When the outdoor temperature is lower the room temperature is also lower in the morning because of the greater temperature difference and therefore the greater thermal loss. So the heating has to start earlier in the morning e.g. at approx. 04:30 and takes approx. 3.5 hours to reach 20°C until approx. 08:00.

Our goal is to reach a room temperature of 20°C at 08:00 independently of the outdoor temperature.

In the evening the target is set to 18°C, that means the actual temperature decreases until 18°C. How long it takes, depends again on the house construction and on the outdoor temperature.

We want also to save energy during the night and not to reach the target temperature of 18°C as soon as possible.