Add support for cascading PID

README.md

@@ -79,6 +79,28 @@ climate:
     pwm: 0
 ```
 
+```
+climate:
+  - platform: smart_thermostat
+    name: Smart Thermostat Cascading PID Example
+    unique_id: smart_thermostat_outer_pid_example
+    heater: climate.smart_thermostat_single_on_off_heat_example
+    target_sensor: sensor.ambient_temperature2
+    min_temp: 7
+    max_temp: 28
+    ac_mode: False
+    target_temp: 19
+    keep_alive:
+      seconds: 60
+    away_temp: 14
+    kp: 5
+    ki: 0.01
+    kd: 500
+    output_min: 7
+    output_max: 28
+    pwm: 0
+```
+
 ## Usage:
 The target sensor measures the ambient temperature while the heater switch controls an ON/OFF 
 heating system.\
@@ -123,6 +145,15 @@ PID output value is the weighted sum of the control terms:\
 `output = P + I + D`\
 Output is then limited to 0% to 100% range to control the PWM.
 
+#### Cascading PID
+Optionally, 2 (or more) PIDs can be used in a cascading matter, e.g. for underfloor heating define an outer
+PID between the room temperature and the floor temperature, and an inner PID between the floor
+temperature and the PWM. See details [here](
+https://en.wikipedia.org/wiki/Proportional%E2%80%93integral%E2%80%93derivative_controller#Cascade_control).
+
+To enable, create the inner thermostate as detailed above, and then create another thermostate that will
+control the inner one.
+
 #### Outdoor temperature compensation
 Optionally, when an outdoor temperature sensor entity is provided and ke is set, the thermostat can 
 automatically compensate building losses based on the difference between target temperature and 

custom_components/smart_thermostat/climate.py

@@ -48,7 +48,9 @@
 
 from homeassistant.components.climate import PLATFORM_SCHEMA, ClimateEntity, ClimateEntityFeature
 from homeassistant.components.climate import (
+    ATTR_HVAC_MODE,
     ATTR_PRESET_MODE,
+    DOMAIN as CLIMATE_DOMAIN,
     HVACMode,
     HVACAction,
     PRESET_AWAY,
@@ -59,6 +61,8 @@
     PRESET_HOME,
     PRESET_SLEEP,
     PRESET_ACTIVITY,
+    SERVICE_SET_HVAC_MODE,
+    SERVICE_SET_TEMPERATURE,
 )
 
 from . import DOMAIN, PLATFORMS
@@ -750,7 +754,7 @@ async def async_set_hvac_mode(self, hvac_mode: HVACMode) -> None:
                               self.entity_id,
                               self._control_output,
                               hvac_mode)
-                await self._async_set_valve_value(self._control_output)
+                await self._async_set_valve_value(self._control_output, self._hvac_mode)
             # Clear the samples to avoid integrating the off period
             self._previous_temp = None
             self._previous_temp_time = None
@@ -910,7 +914,7 @@ async def _async_control_heating(
                         await self._async_heater_turn_off(force=True)
                     else:
                         self._control_output = self._output_min
-                        await self._async_set_valve_value(self._control_output)
+                        await self._async_set_valve_value(self._control_output, self._hvac_mode)
                 self.async_write_ha_state()
                 return
 
@@ -938,6 +942,8 @@ def _is_device_active(self):
             try:  # do not throw an error if the state is not yet available on startup
                 for heater_or_cooler_entity in self.heater_or_cooler_entity:
                     state = self.hass.states.get(heater_or_cooler_entity).state
+                    if heater_or_cooler_entity[0:8] == 'climate.':
+                        return state != HVACMode.OFF
                     try:
                         value = float(state)
                         if value > 0:
@@ -1008,7 +1014,7 @@ async def _async_heater_turn_off(self, force=False):
                     service = SERVICE_TURN_OFF
                 await self.hass.services.async_call(HA_DOMAIN, service, data)
 
-    async def _async_set_valve_value(self, value: float):
+    async def _async_set_valve_value(self, value: float, hvac_mode: HVACMode):
         _LOGGER.info("%s: Change state of %s to %s", self.entity_id,
                      ", ".join([entity for entity in self.heater_or_cooler_entity]), value)
         for heater_or_cooler_entity in self.heater_or_cooler_entity:
@@ -1024,6 +1030,20 @@ async def _async_set_valve_value(self, value: float):
                     VALVE_DOMAIN,
                     SERVICE_SET_VALVE_POSITION,
                     data)
+            elif heater_or_cooler_entity[0:8] == 'climate.':
+                state = self.hass.states.get(heater_or_cooler_entity).state
+                if hvac_mode != state:
+                    data = {ATTR_ENTITY_ID: heater_or_cooler_entity, ATTR_HVAC_MODE: hvac_mode}
+                    await self.hass.services.async_call(
+                        CLIMATE_DOMAIN,
+                        SERVICE_SET_HVAC_MODE,
+                        data)
+                if hvac_mode != HVACMode.OFF:
+                    data = {ATTR_ENTITY_ID: heater_or_cooler_entity, ATTR_TEMPERATURE: value, ATTR_HVAC_MODE: hvac_mode}
+                    await self.hass.services.async_call(
+                        CLIMATE_DOMAIN,
+                        SERVICE_SET_TEMPERATURE,
+                        data)
             else:
                 data = {ATTR_ENTITY_ID: heater_or_cooler_entity, ATTR_VALUE: value}
                 await self.hass.services.async_call(
@@ -1136,7 +1156,7 @@ async def set_control_value(self):
                     self._time_changed = time.time()
                 await self._async_heater_turn_off()
         else:
-            await self._async_set_valve_value(abs(self._control_output))
+            await self._async_set_valve_value(abs(self._control_output), self._hvac_mode)
 
     async def pwm_switch(self):
         """turn off and on the heater proportionally to control_value."""