Automated VIOM Central Heating – Review

Submission by David Pullen – Well it took a long time to get round to it; it was always one of those things on the list. But it’s done now and it even works. So what did I do?

Our central heating system is not typical and is also quite extensive so it looked as if I needed a custom solution. We have 6 separate zones: 4 for the heating and 2 for hot water (see the picture of the pumps).

Each zone is controlled by a separate time clock – Smiths Timeguard timers that are designed for immersion heaters. The fact that there are 6 separate clocks is a pain as they all have to be programmed individually and they are always losing synchronisation. Not the end of the world but somewhat frustrating.

We have room thermostats for each of the heating zones and individual thermostats on each radiator so we were not too bothered about incorporating additional thermostatic control (at the moment!). We were quite keen to introduce more convenient control as all the clocks are in the cellar and it is quite a trek from some parts of the house, particularly my office which is on the second floor at the far end of the house!

Our requirements were fairly straightforward:

Browser control with an option of using a remote – IR or radio
Full flexibility in programming on/off times
Ability to fall back to existing system should the HA server fail – which, of course, is bound to happen whilst I am away and out of contact.

A quick check of the existing wiring indicated that the solution could be fairly simple. Each timer contained a feed from a fused switch. The timer simply switched the live. Neutral is connected straight through.

The thermostats were also wired to the outputs from the timers. All I needed to do was substitute the timer switching with my own switching. I already had a VIOM (the Versatile Input Output Module available from www.phaedrusltd.co.uk) driven by Homeseer (www.homeseer.com) so in principle the solution was simple! In practice, it wasn’t difficult but did take much more time than expected to implement – no surprises there!

I had a relay output module for the VIOM so I decided to use the output relays to drive the 240v relays that would do the switching. I suppose this could be seen as overkill but I wanted to make sure that I had good isolation and I didn’t want to overdrive the VIOM outputs. The VIOM outputs are open collector Darlington drivers that are supposed to be able to sink 100mA. The 240V relays were going to draw just over 100mA so it was better to be safe.

I used Finder plug-in power relays with 12 Volt dc coils. For convenience I purchased DIN rail mount bases. I split the relays into two sets of three and mounted them on DIN rails in two simple FIBOXes. The boxes were then mounted on the wall underneath the timers (see picture below).

Close-up of one relay box (the middle relay is not active at this stage).

The VIOM is local to the HA server in node zero. I needed to drive 6 relays and I wanted to use Cat5. I tested the setup using just a single run of Cat5 and found no problems. I ran one core to each of the outputs on the VIOM relays and used two cores for the 12V power supply. I was just a bit concerned that when three adjacent relays were on I would be running over 300mA through a single core of CAT5. I therefore ran a second cable just in case. For anyone who is remotely interested, the CAT5 connections are shown below.

The fused switch outputs were rewired from the timers to the common terminals of the relays (see relay inputs). The coil is driven from the CAT5 connections.

The outputs from the relays were wired to the inputs and outputs of the timers. When the relays are off, the power is delivered to the timers and they can be activated by simply switching them on. When the relays are powered, the outputs of the timers go live and the system operates as if a timer had switched on.

The wiring for a single zone is shown below. This is repeated 5 more times. I decided to switch live and neutral so that the timers really are switched fully out of circuit when the relays activate. The earth cores were commoned in the FIBOXes and at the timers.

The finished relay boxes are shown here with the CAT5 connection. I have just coiled the excess CAT5 as it is in the cellar. I might clip the excess from the cable ties.

The VIOM is currently controlled by a script running under Homeseer. I have plans to write a plug-in but I have to admit that the script works very well so it is not exactly urgent. The VIOM module is shown below (on the right) with the relay module on the left.

The VIOM connects to the PC through a serial port. I do intend to enclose the VIOM in the future but I am still introducing new inputs and outputs and so I have delayed this bit for now. I have been very pleased with the VIOM. It has worked faultlessly and is IMHO reasonably priced. It really extends the capability of Homeseer allowing it to become much more of a general HA controller. It is worth noting that Homeseer has a huge device capacity as it is not restricted to the X10 housecodes A to P and unit codes 1 to 16. The virtual device codes (q to z and 17 to 64) can be used for many other elements such as relays, non-X10 PIRs, pressure mats, MP3 and CD players, etc. without having any impact on the supply of X10 codes.

Timed events are set up directly in Homeseer. Overrides are performed using browser control. All my browser control is based on the HACT panels found on the Homeseer forum. The code has been significantly modified but I have to thank the originators (Paul Augusto and Aaron Levey) for their work in producing them in the first place. It certainly made my job a lot easier. I run the control panels on my wireless Fujis (thank you Gareth Cook) and all the other PCs around the house. I generally use kiosk mode on the Fujis to maximise screen space. The heating control panel is shown below. It allows each zone to be switched on or off (by clicking on the led icon) or boosted for 30 minutes to 2 hours. I did consider producing a fully flexible boost timer but there has been no call for it! When the boost button is clicked the end time is shown in the “Boost until” column.

And does it all work? Well yes! The system ran in test (not connected to the heating) for over a month. I learnt not to implement new elements of my home automation (without considerable testing) the hard way! It has been running in full operation for another 2 months. We haven’t had to revert to timer operation. I was told that it had failed to work on one occasion when I was away but that turned out to be a false alarm! The server hasn’t failed for more than a year despite being Windows based. I usually reboot once a month just to be on the safe side but it easily runs for much longer than that. We have tested the fallback operation on all zones and there were no problems – but then it is fairly simple.

Is there anything that I would do differently? Well so far no. But you can ask me the question again in six months!

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