Wireless home automation

Some people are massively into home automation, with a motor and remote control fitted everywhere they possibly can be. I’ve largely not really seen the point of it. I live in a small house, the light switch is never far away. I’ve also found it baffling that in order to switch on the light I need an internet connection.

However, I did buy a internet connected heating control system opting for Hive by British Gas. The system is easy to install and designed to be a direct replacement for many UK domestic installations. The wireless side of the system uses zigbee and it consists of a boiler control, wireless thermostat and hub that connects to your network. Overall it’s worked well in allowing me to remote control the ancient heating system in my house, but it isn’t really very sophisticated.

The Hive thermostat is a bit…. basic. As far as I can tell it’s old school in that it runs the heating until the temperature measured by the thermostat reaches the target and then stops. The problem is the radiators are then hot, so the temperature in the room keeps rising and will significantly overshoot the target. Before the room temp has dropped to below the target it can start to feel a little cool, because we’ve just acclimatized to that higher temperature. The result is you turn up the heating and end up running the system at a higher temperature than is necessary to be comfortable.

This is how heating control systems have worked for years, but there’s a much better way. Secure (Horstmann) and a few others implement something called Time Proportional Integral (TPI). I don’t pretend to know how this works, but the result is the heating system runs for shorter bursts, switching a predetermined number of times per hour until the temperature is reached and reducing the overshoot that’s common with simple thermostat control.

We have recently got a place in Northern Ireland which we’re using as a base to visit family more frequently. The controls here use TPI but they’re otherwise a standard wired system and I want remote heating control so I can keep an eye on the temperature to make sure it isn’t getting too cold, and also it would be really useful to be able to turn the temperature up before we visit in winter.

Hive is out for the reasons above. Other systems such as Nest that do clever learning of your life patterns are useless in a building that’s not fully occupied all the time. So I’ve gone to rolling my own using Z-Wave controls and Home Assistant with the hass.io distribution on a raspberry pi.

Z-Wave is a really interesting wireless home automation protocol. Like zigbee it employs low bit rate, low energy RF so devices can be battery powered. It is a proprietary protocol though, unlike Zigbee, and whilst I tend to prefer open standards in the real world having a proprietary chipset in every device means it’s easier to get devices from different manufacturers to work together. I have a USB adapter in my raspberry pi so it can act as the Z-Wave controller but a particularly neat feature is devices can be directly paired.

This means I can setup my thermostat to directly control the boiler switch. The state of the two devices is also reported on the Z-Wave network. There’s a really big win with this. If I had a temperature probe in the room and my automation server had to turn on the heating based on a rule what happens if my automation server fails? No heating. Also, adjusting the heating becomes harder. The beauty of using Z-Wave controls, and directly pairing them, is I can have a normal looking thermostat on the wall, and this directly controls the heating. But then I can control the temperature set point of that thermostat remotely using Home Assistant. I can also override the boiler control should the thermostat fail (unlikely) or the batteries run out (more likely).

This gives me the same level of control I have with Hive, but the system isn’t reliant on the hub device being in the middle, I only need my thermostat and my boiler control to make it work. Then you can start getting into the smarter automation functions. Home Assistant can pull in calendar information using caldav and turn that into a switch. So I can automate whether the heating is set above frost protect based on whether there’s a booking in the house booking diary. Which means I don’t have to worry about a visitor using our house turning the heating up and leaving it.

Using Home Assistant with Z-Wave allows for other neat control options such as lighting, blinds, whatever, in order to make an empty home look less empty. But it also allows for those controls to always have a local activation so when a family member who doesn’t own a smartphone wants to use our house, that’s no problem. Essentially I can build up a home automation system to be as simple or sophisticated as I want, but never need to have an internet connection in order to turn on the bathroom light.

But for now, it’s just going to be the heating.

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