When PowerGenius is used to control a hwc (hot water cylinder), the controller checks to see if the hot water has been sterilised within the sterilisation period. If the hot water has not been sterilised after the sterilisation period has elapsed the controller will turn the hwc on at full power to sterilise the water. The water is considered sterilised if all of the water in the hwc is heated to the sterilisation temperature continually for the sterilisation time. The controller is not dependent on communication with any other devices or the internet to work for the purpose of managing sterilisation. Once sterilisation is complete the sterilisation period will be reset.
The sterilisation process also uses a 'boost process' to minimise imported energy for sterilisation. The sterilisation boost feature is there to save unnecessary energy from being purchased from the grid by automatically initiating sterilisation at the ideal time when the tank is "nearly" at the sterilisation temperature 'naturally'. When the boost time (default 5 days) is reached and the tank temperature reaches the boost temperature (default 58 degrees) then that is an ideal time to start a sterilisation cycle by buying just a little bit more energy from the grid to perform an early sterilisation rather than waiting the full sterilisation period (default 7 days) and then having to buy from the grid, particularly if the tank is a lot cooler and sterilisation happens in the absence of solar energy, such as at night or during a day of low solar gain. This also has the benefit of resetting the sterilisation timer to a time during the "Solar day" so that the following week sterilisation will occur during the solar day if the sterilisation temperature hasn't been reached naturally.
The algorithm for sterilisation is dependent on temperature data. For correct operation, the lower temperature sensor must be positioned within 100 millimetres of the bottom of the inner tank and slightly above the level of the element. The position of the sensor is required to insure that all of the water in the cylinder is heated.
If there is a Temperature Sensor fault then there is a configuration setting that tells the controller to Force the element on permanently. The hwc then relies on the thermostat for temperature control.
The accuracy of the temperature sensor is +-0.5 deg C. If the sensor is not installed correctly it will measure a temperature lower than the actual water temperature. This will result in the temperature of the water being heated above the sterilisation temperature.
The maximum temperature will be limited by the hot water thermostat which will act to switch the power off when the thermostat temperature is reached. The thermostat temperature must be set above the sterilisation temperature. It is recommended to set the thermostat to its maximum for use with PowerGenius.
The appliance controller uses the following configuration parameters to control sterilisation.
| Configuration variable | Description | Default value |
|---|---|---|
| Sterilisation period | Minimum period between sterilisations. If the hwc has not been heated to the sterilisation temperature continually for the sterilisation time after the sterilisation period has elapsed the sterilisation process will start. | 7 days |
| Sterilisation temperature | The temperature the hot water will be heated to during the sterilisation process. The temperature is measured from the bottom temperature probe. | 60 deg C |
| Sterilisation time | The time the minimum temperature will be maintained for sterilisation to be complete. | 1 hour |
| Sterilisation boost time | If sterilisation has not completed with the sterilisation boost time has elapsed and the sterilisation boost temperature has been reached the controller will activate the sterilisation process. | 5 days |
| Sterilisation boost temperature | The minimum temperature measured at the bottom temperature sensor used by the sterilisation boost process. | 58 deg C |
| Ignore temperature fault | How the controller should respond in the event of a failure of either temperature sensor. | Force On |
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