[Bldg-sim] Constant air volume systems

[Rathna Shree]

 Thank you Mr. Bill for the clarification. This helps.
    On Tuesday, 22 September, 2020, 06:07:15 pm IST, Bishop, Bill <bbishop at pathfinder-ea.com> wrote:  
 
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Hi Rathnashree,
 
You need to know more about the air handling unit and system (controls, ductwork and zone dampers, if any) to know how to simulate the minimum flow associated with a VFD. An AHU may be designed as a constant volume unit and still use a VFD to balance the system at a fixed flowrate. You don’t automatically get energy savings by using a VFD, and you actually incur a small energy penalty associated with drive losses. If the system does not have any adjustable zone dampers that are automatically controlled, it may be designed to operate at constant volume, and you would use a minimum flow ratio of 1. If the unit only handles a small number of zones, it may be designed to run at constant volume. I suggest you ask the design engineer how the unit will be controlled. You can also look for a controls drawing or talk to a factory rep for that unit.
 
Regards,
 
~Bill
 
  
 
William Bishop, PE, BEMP, BEAP, CEM, LEED AP
 
Senior Energy Engineer
 
  
 
T: (585) 698-1956                        F: (585) 325-6005
 
bbishop at pathfinder-ea.com        www.pathfinder-ea.com
 
134 South Fitzhugh Street
 
Rochester, NY 14608                     Ask me why Carbon Fee & Dividend may be right for you.
 
  
 
From: Bldg-sim <bldg-sim-bounces at lists.onebuilding.org>On Behalf Of Rathna Shree via Bldg-sim
Sent: Tuesday, September 22, 2020 7:39 AM
To: bldg <bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Constant air volume systems
 
  
 
Dear All,
 
  
 
In many of our projects, we have Air handling units with VFD and no VAV system. When simulated with minimum flow ratio as 1 and AHU with VFD, there is no difference in energy consumption. The impact of with and without VFD is negligible. Since there will be a small amount of variation in Airflow in zones due to VFD in AHU, can we reduce the minimum flow ratio from 1 to about 0.8 or 0.7?
 
  
 
Regards,
 
Rathnashree
   
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