Application of frequency converters in HVAC systems

I. Application Scenarios and Technical Implementation

1. Freezing Water Circulation System

• Principle: The frequency converter regulates the speed of the chilled pump based on the return water temperature to adjust the flow rate and achieve indoor temperature stability.
• Technical Details:
  • Flow Rate and Speed Relationship: The flow rate (Q) is proportional to the first power of the speed (n), and the shaft power (P) is proportional to the third power of the speed. For example, when the flow rate is reduced to 80%, the shaft power is reduced to 51.2%.
  • Control Strategy: PID control is adopted, combined with return water temperature feedback, to dynamically adjust the pump speed and avoid freezing of the evaporator, ensuring system safety.
• Case: A certain type of frequency converter is applied in the HVAC water circulation system to achieve stable outlet temperature of chilled water, with an energy - saving effect of 20% - 40%.

2. Cooling Water Circulation System

• Principle: Taking the temperature difference between inlet and outlet water as the control basis, the speed of the cooling pump is adjusted to optimize the cooling efficiency.
• Technical Details:
  • Temperature Difference Control: When the temperature difference is large, the pump speed is increased; when the temperature difference is small, the pump speed is decreased to keep the condenser working efficiently.
  • Protection Requirements: The cooling tower environment is humid and dusty, so the frequency converter needs to have an IP55 protection level to prevent the entry of water vapor and dust.
• Case: A certain industry - leading product drives the cooling tower fan in a commercial building, achieving 30% energy savings through constant temperature difference control and integrating intelligent modules for remote monitoring.

3. Cooling Tower Fan Control

• Principle: Adjust the fan speed according to seasonal changes and cooperate with the cooling pump to achieve the best energy - saving effect.
• Technical Details:
  • Smooth Start - Stop: The frequency converter reduces mechanical shock and extends the fan life. For example, a certain type of frequency converter is applied in the cooling tower fan, and a lower - limit frequency is set to avoid damage to the gearbox.
  • Energy - saving Effect: When the fan runs at a low speed, the amount of drift water is reduced, the water source is saved, and the noise is reduced.
• Case: The frequency converter controls the cooling tower fan in the building of a certain transmission company, achieving 50% energy savings and realizing automatic management through the BMS system.

4. Ventilation System

• Principle: In scenes such as subways and industrial plants, the frequency converter drives the fan system to adapt to complex environments (such as high temperature, high humidity, and high dust).
• Technical Details:
  • Protection Level: The subway ventilation system needs an IP55 or higher protection level to ensure stable operation of the equipment in harsh environments.
  • Intelligent Control: Integrated PLC monitoring is used to adjust the air volume in real - time. For example, a certain type of frequency converter supports multi - pump variable frequency start in the subway project, reducing the pressure impact on the pipe network.
• Case: A certain city subway project adopts a frequency converter, and through the functions of condensation and frost protection, the reliability of the ventilation system is ensured.

II. Energy - saving Effect and Data Support

1. Significant Energy Savings

• Theoretical Basis: The shaft power is inversely proportional to the third power of the speed. When the flow rate is reduced by 20%, the shaft power is reduced by 51.2%.
• Actual Cases:
  • A Certain Transmission Company Building: After using the frequency converter, the HVAC system saves about 50% of energy, and the annual electricity cost savings are significant.
  • A University Hospital: The frequency converter saves 800,000 kilowatt - hours of energy annually, reduces 750 tons of carbon dioxide emissions, and the COP is increased to 3.6 (heat pump) and 5 (cooling machine).
  • A Certain Type of Frequency Converter: It saves 20% - 40% of energy in the HVAC system and avoids the energy consumption of full - speed operation through dynamic speed regulation.

2. Extended Equipment Life

• Soft Start: The frequency converter reduces the starting current impact of the motor and extends the life of pumps and fans. For example, the maintenance cost of equipment in a certain project is reduced by 30% due to smooth starting.
• Mechanical Protection: The cooling tower fan sets a lower - limit frequency through the frequency converter to avoid damage to the gearbox due to low - speed operation.

3. Environmental Adaptability

• IP55 Protection Level: In HVAC environments with a lot of dust and moisture (such as food processing plants and coal mines), the frequency converter needs to reach an IP55 level to prevent the entry of dust and water vapor and ensure stable operation.
• Case: A certain type of IP55 frequency converter is applied in high - requirement occasions such as military units and weapon manufacturing, adapting to harsh industrial environments.

III. Intelligent Integration and System Integration

1. Integration with Building Automation System (BAS)

• Communication Protocols: The frequency converter supports protocols such as Modbus and Profibus, and can be seamlessly connected with BAS to realize remote monitoring and parameter adjustment.
• Case: A certain type of frequency converter uses an intelligent connection module, and mobile devices can be used for quick commissioning and monitoring, improving the intelligence level of the system.

2. Data Monitoring and Analysis

• Real - time Data: The PLC monitoring system records equipment efficiency, such as the number of cooling machine operations and automatic load adjustment, to ensure the optimal state.
• Fault Warning: The frequency converter stores fault information, such as flexible handling when signals are missing, reducing downtime.

3. Energy Management

• Dynamic Adjustment: Automatically switch the operating mode according to the season and time period. For example, switch to the energy - saving state at night and on weekends, and keep running at a low speed to maintain temperature and humidity.
• Case: The BMS system of a certain building automatically adjusts the frequency converter parameters in winter and summer to meet the demand and save energy at the same time.
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  Conclusion

  The frequency converter realizes the following core advantages in the HVAC system through precise speed regulation, intelligent control, and efficient energy management:

  1. 1. Significant Energy Savings: The shaft power decreases according to the third power of the speed, and the case shows that the energy - saving effect is 20% - 50%.
     2. Extended Equipment Life: Soft start and mechanical protection reduce maintenance costs.
     3. Intelligent Integration: It is seamlessly connected with the BAS system to realize remote monitoring and automatic management.
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