Return Air Fan

A Return Air Fan facilitates the extraction of used or conditioned air from building spaces and directs it back to the system for reprocessing. This fan plays a vital role in maintaining indoor air quality and optimizing energy efficiency by efficiently managing the air circulation and ensuring a balanced return of air to the HVAC system.


Fan Speed Method

Specifying Fan Speed Method determines how fan speed can be adjusted, offering choices between Continuous and Discrete. Continuous allows smooth variation up to the Design Maximum Air Flow Rate, while Discrete confines operation to specific speed settings. Use Discrete with the Number of Speeds set to 1 for constant volume or on-off fans. In contrast, variable air volume fans benefit from Continuous, requiring a fan performance curve input in the Electric Power Function of Flow Fraction Curve Name field. This selection impacts how power is calculated, with Discrete using time-weighted averaging and Continuous using flow-weighted averaging.

Fan Power Minimum Flow Rate Fraction

Specify the Fan Power Minimum Flow Rate Fraction to determine the minimum operating level for a variable-speed fan. This Design Maximum Air Flow Rate fraction calculates fan power at low flow rates during simulation. Note that it doesn't enforce a lower limit on airflow during the simulation. Ensure the value falls between 0 and 1. This field exclusively applies when the Speed Control Method is set to Continuous.

Fan Motor Efficiency

Specify the Fan Motor Efficiency value, calculated as the ratio of shaft power to the electric power consumed by the motor. This parameter characterises the effectiveness of the fan motor. Ensure the entered value accurately reflects the motor's efficiency in converting power.

Fan Motor In Air Stream Fraction

Specify the Fan Motor In Air Stream Fraction, indicating the proportion of motor heat added to the air stream. This value should range between 0 and 1. A value of 0 implies the fan motor is entirely outside the air stream, adding none of its heat to it. On the other hand, a value of 1.0 signifies the motor is entirely inside the air stream, adding all its heat to it.


Fan Design Power Sizing Method

Specify the Fan Design Power Sizing Method:

Power Per Flow: Size Design Electric Power Consumption based on Electric Power Per Unit Flow Rate.

Power Per Flow Per Pressure: Size power using Electric Power Per Unit Flow Rate Per Unit Pressure.

Total Efficiency And Pressure: Size power using input Fan Total Efficiency and Design Pressure Rise. Adjust based on specific system requirements.

Fan Total Efficiency

Specify the Fan Total Efficiency value, representing the motor's efficiency, calculated as the ratio of shaft power to electric power consumed by the motor. Ensure this value accurately characterizes the overall efficiency of the fan system.

Fan Design Pressure Rise

Specify the Fan Design Pressure Rise, indicating the total system pressure rise experienced by the fan in Pascals at full flow rate. This should be at an altitude-adjusted standard density of dry air, considering a 20 degrees Celsius dry bulb temperature. Set this value based on the specific requirements and characteristics of the fan system.

Sizing Method

Specify the Sizing Method:

Autosize: Allow the system to automatically determine the appropriate size based on specified parameters.

Manual: Manually input the sizing parameters according to specific requirements.

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