Using Fhem for Heating Control

Having discussed in previous posts my hardware approach to heating control I’ll now talk about the software.

The key to the whole system is FHEM which is a real discovery. As I’ve found before with the hardware, the Germans seem to have really got to grips with home automation. This system is open source and very mature, having been around for quite a long time and now being up to version 5.7. The problem is that at least initially it doesn’t appear particularly accessible or easy to use, but this is rather misleading. With a bit of effort invested you can get the system working well and it is incredibly flexible.

There is a good community supporting it, although it is predominately German speaking. Most of the documentation is too, but Google Translate has proved very helpful in navigating the forums and the wiki .

I won’t go into the basic setup, but you will need some kind of server (I am using a fairly old but extremely useful HP Proliant Microserver) and a suitable operating system. There are various ways to install Fhem which are detailed on the website and elsewhere.

So once you have a working Fhem system you can access it via a local URL and then the fun begins!

The basics are to get the interface installed and working. Fhem does have automatic mechanism for detecting and installing devices, which is based around a set of configuration files, they key one being fhem.cfg. In my case I am using a CUL device (as in previous posts) but there are various other ways of doing it. Some people have used the official MAX controller although it’s not much cheaper than the CUL and some difficulties have been reported. There are some other ways of getting CUL firmware onto cheaper devices but I haven’t explored these as yet.

What I really like about Fhem is that its basic structure supports a whole range of different devices (see the documentation for details) but it has a common approach to dealing with them. Also, whilst it is mostly based on configuration files the standard front end UI whilst basic is very effective.

So once you have a basic Fhem system up and running and your CUL or equivalent device has been detected – what next?

First thing to do is register all the MAX devices and pair them with your system. You will need to do this using the ‘learn’ mode on the devices and also by setting the CUL device to listen out for new devices.

You can do this by selecting ‘pairmode’ on the Fhem screen for the CUL device:

pairmode

This then sets it to listen for a short period of time, and you then need to set the devices to pair. What exactly you do depends on which device you have, and you’ll need to check the instructions. However, for most of the thermostats I think you have to hold down the ‘boost’ button for a few seconds and then it begins a countdown, which stops again once the pairing is complete.

You will then see the MAX devices appearing in your Fhem screens. The screen for each looks something like this:

maxscreen1maxscreen2maxscreen3

This screen demonstrates the strengths and weaknesses of Fhem, depending on who you are. For me this is great – lots of details, loads of options to play with etc. On the other hand you might think it looks overcomplicated and intimidating… in which case this probably isn’t for you.

All Fhem devices have settings (via the ‘set’ button at the top) and the pick list shows you what variables you can set. The ‘readings’ section shows the enormous amount of data you can extract from what is in reality quite a simple device. This includes the weekly ‘profile’ for each device – ie the combination of settings and times throughout the week. This is different for each individual thermostat which is good from a flexibility point of view, but not so good for consistency and ease of programming. There are solutions to this which I will come to in future.

So you should now be able to pair up all your thermostats, and the Fhem screens will allow you to see the measured temperature and make some changes. However, this isn’t much of a control system on its own and I’ll come to what I’ve done to tie it all together in future posts.

I know I’ve kept this quite general but please post comments or questions and I’ll try my best to answer them. There is a lot of info on the Fhem forums / wiki which are a good place to start if you are stuck.

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