Monday, December 20, 2010

Smarter Heating - Some Results

Previously I stated that for an older property, there was the heat required to warm the house up, plus the heat to maintain a given set point temperature. Over this weekend which has been bitterly cold I have had the opportunity to do some datalogging and put some figures on to this.

First, here's the warmup from nominal 17C to nominal 19C on Sunday morning. This took 4 hours and used 50kWh of gas. In each of the following plots the x-axis is the time in minutes.

At the same time the outside temperature was rising from about -4 to about -1C - but more importantly to the controller, was the difference between inside and outside temperature - the Delta temp. As you can see the delta temp was between 20 and 21.5 C for all of the warm up period.

By 10am the room had come up to temperature and the controller enters the second phase - main room temperature at a comfortable 19C +/_ 0.2C.

The next set of 3 plots shows the detail from 10am Sunday to 10am Monday. This was the coldest night so far with temperatures down to -9.3C! Note how the delta reaches a maximum of 29. In real terms this means that the heating has to work about 50% harder, than if delta is about 20 - and thus use a lot more gas.

Below is the plot of the room temperature, once the system had stabilised, holding the room at 19C +/- 0.2C. Each little sawtooth is the effect of the boiler coming on at 18.8C and heating the room up to 19.2C - this maintaining an average temperature of 19C.


Andrew said...

Hi Ken, great blog.

I am really interested to know how you record your temperatures and then go on to display them as I would love to do the same thing myself?



Ken Boak said...


I use an Arduino with 5 thermistors attached and these measure various room temperatures, outside temperature and hot water temperature.

The Arduino reads these sensors once per second and then averages these readings out over a minute, where it then prints them out is comma separated format to a terminal programme "Termite". This logs the readings to a file, and then I can export this CSV format into excel to produce the plots.

There is another open source programme called KST, which will print out readings directly from a file or serial terminal window, so gives a real time graph. I've still got to get around to to using it - but my friends at have used it very effectively for real time graphing of electricity consumption data - see here for how to use KST

Hope this helps,