The temperature control system of the fresh air unit consists of a proportional integral temperature controller, a temperature sensor installed in the air supply duct, and an electric regulating valve. The function of the controller is to transmit the supply air temperature detected by the temperature sensor placed in the supply air duct to the temperature controller for comparison with the temperature set by the controller. Based on the PI calculation result, the temperature controller sends an on/off valve signal to the electric regulating valve, thereby maintaining the supply air temperature within the required range.
2. The electric control valve is interlocked with the fan to ensure that the air valve is also closed when the fan power is cut off. The electric control valve can also be linked with the fan (as shown in the dashed box in the figure), and the electric control valve is closed when the fan cuts off the power. The two types of chain connection methods shown in the above figure are respectively used for power-off reset devices and power-off devices. Users can choose according to their specific situations. In situations where antifreeze is required, the hot water valve position can be maintained at the required opening through a travel limiter.
When cooling is required, the thermostat is placed in cooling mode. When the temperature measured by the sensor reaches or falls below the set temperature, the thermostat sends a closing signal to the electric valve, and the closing contact of the electric valve is connected to close the valve. If the measured temperature does not reach the set temperature, the thermostat sends an open signal to the electric valve, and the electric valve opens the valve by connecting the valve opening contact. When heating is required, the thermostat is placed in heating mode. When the temperature measured by the sensor reaches or exceeds the set temperature, the thermostat sends a closing signal to the electric valve, and the closing contact of the electric valve is connected to close the valve. If the measured temperature does not reach the set temperature, the thermostat sends an open signal to the electric valve, and the electric valve opens the valve by connecting the valve opening contact.
When the filter screen is clogged or exceeds the specified value, the differential pressure switch provides a switch signal.
When the temperature of the coil is too low, the low-temperature antifreeze switch gives a switch signal, and the fan stops running to prevent the coil from freezing and cracking.
Functional segment
The fresh air unit has multiple functional sections, roughly including the following:,
Filtering section: Choose coarse efficiency filters, medium efficiency filters, high-efficiency filters, etc. as needed, mainly used to effectively capture dust particles with different diameters.
Surface cooling section: Use a surface cooler to cool and dehumidify the fresh air, and control the supply air temperature and humidity.
Humidification section: using electrode humidification, steam humidification, etc., can ensure strict relative humidity requirements
Fan section: Centrifugal fans and axial fans can be selected according to needs, and centrifugal fans are generally used.
Sterilization section: such as ultraviolet lamp sterilization.
The above are conventional air treatment stages that can meet the requirements of temperature, humidity, and air cleanliness for the human body in air-conditioned rooms. In addition, considering the need for energy conservation, in addition to the above functional sections, the fresh air unit may also be equipped with a heat recovery section. The heat recovery section uses a heat recovery device to recover the cold and heat from the exhaust air to pre cool or preheat the fresh air, thereby achieving energy recovery and utilization.
Selection Guide
The selection steps for fresh air fan equipment are as follows
1. Select the form of the fresh air fan according to the installation settings;
2. The principle of selecting equipment air volume and pressure should not be less than the design value;
3. Determine the design conditions for cooling capacity and heating capacity;
4. In principle, one fresh air unit is only responsible for the fresh air volume required for one floor.