Understanding Fans

 Flow rate (Flow rate = flow rate of liquid and gas, air volume = flow rate of gas) 

* Type of flow rate (air volume): Mass flow rate (kg/sec), Volume flow rate (㎥/sec), Mass flow rate = density x volume flow rate.


* Type of flow load (Figure 1, Source-https://www.nationalpolyindustries.com.au/2018/06/14/understanding-water-pump-rated-maximum-and-normal-flow-rates/)

    - Maximum flow rate: The maximum flow rate that can be conveyed without connecting a duct system to the fluid machine. 

    - Rated flow rate: Flow rate considered in design for fluid machine selection (design maximum load flow rate) --> Specific altitude, maximum airflow condition (maximum door opening condition in case of fire) 

    - Normal flow rate: The flow rate that the fluid machine is expected to operate for the longest period of time --> Specific altitude, normal flow condition (All doors closed in case of fire?) 


Fans

* Fan = a machine that transports a constant volumetric flow rate under specific duct system application conditions (non airflow control conditions) (Rationale: Principles of smoke management (John H. Klote) Chapter 12, page 176 "Fans are approximately constant volumetric flow rate devices." See wording) 

    - Constant volumetric flow rate regardless of inlet air temperature

    - Fan pressure is inversely proportional to inlet air temperature (see Figure 2) --> Typically, industry only considers the lowest temperature when sizing (firefighting?). 


Performance curve

*  A line connecting the operating points (airflow & pressure) that one specific fan can exert depending on the amount of pressure losses induced in various duct systems.


System resistance curve 

* A line connecting the operating points of different capacity fans at a specific temperature (specific air density) and a defined duct system condition.


Fan laws

* Temperature changes --> cause pressure and power changes 

* RPM changes (inverters, belt pulleys) --> cause airflow, pressure, and power changes 


Stall and Surging

* Definition of Stall: Airflow separation from the blade profile --> causes mild differential pressure hunting 

* Definition of Surging: A phenomenon in which the stall grows significantly, causing a change in airflow direction and oscillation --> causing severe pressure hunting. 

* Definition of Maximum Efficiency: Efficiency of the wing with the least amount of stall. 


Series and parallel operation



 * Parallel connection : One of the measures in case of insufficient air volume with one blower, 2 blowers are connected in parallel --> air volume is not doubled. 

  * Series connection : One of the measures in case of insufficient pressure with one blower, 2 blowers are connected in series --> pressure is not increased by 2 times. 


Fan air volume control method 

* Outlet damper control method: Performance curve is unchanged when controlling air volume, 

* RPM/intake damper/inlet vane/wing angle control method: system resistance curve unchanged when controlling air volume 

* Suitability of control method for annex room : Outlet damper (multiple control differential pressure, non-surging fan) > Inlet vane/intake damper (multiple control differential pressure) > Inverter (multiple control differential pressure) > Outlet damper (single control differential pressure, surging fan) 


Precautions when requesting blower type selection 

* Definition of fan static pressure: Ps(Fan static pressure) = Pt(Fan voltage) - Pv,o(Fan outlet dynamic pressure) 

* Select power considering the lowest operating temperature 




* Back to Main Procedures : General COMTAM Simulation Procedure for Pressure differential system(Mainly High-rise building) (contamsmulationlab.blogspot.com)



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