Hot tub automation using the UniPi 1.1

References

Thanks to their flexibility and software openness, UniPi controllers can be utilized also in less ordinary applications - such as hot tub automation

The project’s author purchased a hot tub a few years ago. Original controls were, however, rather impractical. To save energy, the owner kept the water temperature lower when the hot tub was not used; but to heat the water, the hot tub had to be manually turned on 4 hours in advance. Hot tub controls also lacked flexibility and were not overly intuitive. The user thus decided to replace the original control unit with a new custom-built system which would allow all hot tub components to be controlled remotely using a smartphone.

Hardware

The system is based on the UniPi 1.1 controller, featuring eight changeover relays. Five of them are switching external 230V relays used for switching following hot tub components

water jets pump
blower
heater
ozonator
circulation pump

Two digital inputs are also used, receiving data from a flow sensor and a magnetic sensor on the hot tub cover. A single 1-Wire temperature sensor is then connected to the controller’s 1-Wire bus, replacing the original resistance temperature sensor.

The original distribution box installation (upper picture), replaced by a custom installation with the UniPi 1.1 (lower picture)

Software

From the software point of view, the project uses the Nymea platform - a software developed specifically for IoT usage, which is compatible with the Raspberry Pi computer. The BerryLan open-source tool is also used for easy connection of Raspberry Pi to the internet via wi-fi, using only a smartphone.

Two operating modes were created in Nymea for the hot tub - summer mode (the water heater is permanently switched off during summer months) and ready mode (switching between “standby” and “ready” water temperatures). The controller behaviour is then set by the Magic tool designed for creating automation rulesets. The controller thus uses the following routines

the ready mode is active, summer mode is disabled, water temperature is below 37°C -> activate the water heater and the circulation pump
both summer mode and ready mode are disabled -> circulation pump and water heater activate when the water temperature is below 29°C
the circulation pump is active and flow sensor is not active -> the system sends a notification
the system sends notification if the water temperature decreases below 3°C
if the cover’s magnetic contact is not switched, the system sends “Hot tub is open” notification
water jets pump activates automatically between 09:00-10:00 AM.

Result

The resulting system allows the user to switch the hot tub heating online by using a smartphone (ie. when returning from work). The hot tub will then automatically send a notification when the water temperature reaches the setpoint. During the bath itself, the user can use a smartphone for switching water jets pump, regulate water temperature or switch both summer and ready modes.