Now that I have sensors on all the radiators I can sit back, relax and watch everything happen. I needed some help of the rest of the family to keep the doors upstairs closed, cause that seems to be very hard for some, but after a few days they all knew that when the doors were closed, daddy was doing one of his experiments again.. yep, this house is one big laboratory 😉
However, doing nothing is not really my style, so I went on reading about radiators, calculations etcetera and found some calculation tools for my RADSON Compact and Jaga Tempo radiators. And although it doesn’t add new data, I thought it would be fun to see if I could use the formulas used in these ‘Installer tools’ (in fact Excel sheets) for myself.
And I was right; based on radiator model, dimensions and specific properties it should be possible to calculate the actual heat output performance of the radiators in other circumstances (temperatures) . If you know the heat output conform the European standard EN442 (dutch) for a specific combination of model & dimensions, the so called n-factor (aka the emission line slope) and the air-temperature, you can calculate the heat output for any combination of flow- and return temperature!
So that’s what I did last evening – preparing my system for these semi-realtime heat output calculations.
First I had to add some more flexibility to the database; creating fields for this purpose only didn’t feel right, so I added a free text field in which I could ‘dump’ anything I want – device specific properties. As an example, here are the properties of one of the radiator devices in my system (it feels like ‘Domotica system’ doesn’t quite cover the capabilities anymore):
TYPE=RC QN=1407 N=1.3404 TAIR=BATHROOM.TEMP
This means this device:
- is of type RC (as in Radson Compact),
- has a heat output of 1407 Watt, based on its dimensions and EN442 at 75/65/20 °C (that’s flow, return and air temperature);
- has an n-factor of 1.3403;
- and that the air temperature can be taken from the device value called BATHROOM.TEMP (a foreign key, so to speak)
So every line defines a device specific property, which are dynamically added to the base device class at run-time.
And I had to write 2 Delphi functions to do the math, primarily based on these formulas:
Q is the variable that needs to be calculated, the rest is all known – piece of cake!
Just make sure you take care of unexpected results, like divisions by zero or raising negative values to a power- working with live data can produce strange results, where a radiator can suddenly start cooling instead of heating 🙂
I added the calculated heat output (the “W” column) in the table with all the other sensor data as can be seen below:
Cool! Although these heat output numbers are based on pretty accurate formulas and properties provided by the manufacturer, the real-life numbers will probably be lower. Dust, bad airflow caused by windowsills and such will always result in deviations. How much? Dunno…