A boiler that heats the water
An in -home controller/thermostat that tells the boiler when to switch on or
off (this may be a separate thermostat and programmer, or just one
device).
A gateway that provides a low power connection to the controller and
bridge out to the internet
A cloud service that stores user account information and remote access to
the system
Smartphone and web apps that connect to the cloud service.
Figure 9.14: system diagram of a heating system (Thermostat by Iconathon,
boiler by Axeny Virtinsky, radiator by Jose Hernandez from the Noun Project)
Both the Tado and British Gas Hive systems work in this way, but user-facing
functionality is distributed differently. The Tado thermostat/heating controller
has almost no UI (see figure 9.15). User can view the current temperature and
set or alter the setpoint, but most interactions are handled on the smartphone^10.
This may keep manufacturing costs down. Smartphone interfaces are much
cheaper to develop than physical interfaces, as components like screens and
buttons are relatively expensive. It’s an elegant choice for a small household
occupied mainly by smartphone owners but there are trade-offs. If you don’t
have your phone to hand, or the battery is dead, or you’re a guest in the house
without access to the phone UI, you have limited control.
(^10) The first generation Tado controller had no onboard controls at all: all interactions
were via the smartphone.