Additional Features

Open Window (I3)

The I3 digital input is dedicated to connect window contraction, which checks if the window is open or closed. If the input detects the open window status (rising edge on the I3 input), it starts counting down the time defined in the Window_Status_Delay network variable (60 seconds by default). After the time elapses, if the window is still open, the application calls the FCU Off mode (for more information, please see section 4.2.1 OFF mode). If the input detects the closed window, the application resets the counter and continues normal operation. If the input detects the closed window before the time elapses, the application also resets the counter and continues normal operation. If the window is open, only the anti-frost protection can start. By changing the I3_Window_Contact_Invert network variable, the application can be connected to the devices with normal open NO or normal close NC outputs.

Anti-frost Protection

This function is designed to protect room equipment, which can be damaged in low temperatures. If the application detects a temperature drop below 6°C, it starts the fan and activates all actuators of the heating valves (including 2^nd stage, if it is active) with maximum defined value. This action is continued until the room temperature reaches above 8°C. The anti-frost function is always active even if the user switches off the device from BMS or local panel. To prevent unnecessary start after sensor fault, there is a built-in algorithm, which detects a sensor brake. If the temperature value from all available sensors is incorrect (out of the range from -100°C to 100°C), the anti-frost function is disabled.

Return Temperature Sensor Control

The default application can control room temperature based on the air return temperature sensor, SI1. To prevent an incorrect temperature value if the fan is off, the CV temperature is taken from the room sensor. The built-in algorithm checks, which sensor is available (from the room panel, SI1 room sensor, or from the network variable if the FCU is working as slave). After the fan start, the algorithm waits for time defined in the Return_To_Space_Time network variable (by default 30 s) to blow the ducts and switch the CV to the SI1air return sensor. To activate this function, the Return_To_Space_Enable network variable must be set to true.

Supply Air Temperature Limitation

In order to maintain room conditions comfortable for the user, the supply air can have a temperature limitation. This function is available only if the supply air sensor is connected and works correctly. The supply air temperature can have a high limit defined by the Supply Temperature High Limit slot (default value 40°C), and a low limit defined by the Supply Temperature Low Limit slot (default value 10°C). The range between the Supply Temperature Low Limit and Supply Temperature High Limit values is called a comfort range.

Supply Air Temperature limitation in the 1^st stage, binary control

If the supply air temperature value is exceeds the comfort range, the default application disables heating (if the temperature value is above the SupplyTemperatureHighLimit), or cooling (if the temperature value is above the SupplyTemperatureLowLimit). If the supply air temperature value returns to the comfort range, the FCU application resets the delay counter and returns to normal operation.

Supply Air Temperature limitation in the 2^nd stage, binary control

If the supply air temperature value exceeds the comfort range, the default application disables the 2^nd stage and starts counting 30 seconds delay time. After 1 minute, if the supply air temperature value is still out of the comfort range, the FCU application disables heating (if the temperature value is above the SupplyTemperatureHighLimit) or cooling (if the temperature value is above the SupplyTemperatureLowLimit). If the supply air temperature value returns to the comfort range, the FCU application resets the delay counter, enables the 2^nd stage, and returns to normal operation.

Supply Air Temperature limitation in the 1^st stage, analog control

In the analog control, if the supply air temperature approaches 1°C to the comfort range limit, the FCU application starts a built-in algorithm, which reduces the air temperature (if the temperature value is close or above the SupplyTemperatureHighLimit) or increase the air temperature (if the temperature value is close or below the SupplyTemperatureLowLimit). If the supply air temperature value returns to the comfort range ±1°C, the default application resets the delay counter and returns to normal operation.

Supply Air Temperature limitation in the 2^nd (with external heater/cooler), analog control

In the analog control, if the supply air temperature approaches 1°C to the comfort range limit, the FCU application disables 2^nd stage and starts counting 30 seconds delay time. After 1 minute, if the supply air temperature value approaches 1°C to the comfort range limit, the default application starts a built-in algorithm, which reduces the air temperature (if the temperature value is close or above the SupplyTemperatureHighLimit) or increase the air temperature (if the temperature value is close or below the SupplyTemperatureLowLimit). If the supply air temperature value returns to the comfort range ±1°C, the default applications resets delay counter, enables 2^nd stage, and returns to normal operation.

FCU Test Mode

This mode was implemented to conduct a quick heating/cooling test. In this mode, the FCU application starts the fan and heating or cooling actuators with 100% value. Depending on  the FCU_Test_Mode network variable value, the test mode activates heating or cooling function. Network variable values and corresponding test functions are presented in the table below.

FCU Controller Outputs Manual Override

This function allows to override the FCU controller outputs control signals by the user values. Each control signal has 2 network parameters: first–for the output value, and second–for the switch between auto and manual control. The control value depends on the output working mode. In the analog control mode, network parameters are working in the range from 0 to 100%. In the binary control mode, the fan works in the range from 0 to 3 and valve actuators outputs (triacs) work in the range from 0 to 1. During the manual override fan and valve actuators status network parameters show real value. By default, all outputs are working in the auto mode.