[BLDG-SIM] Static Pressure Reset modeling in DOE 2

Steve Gates stvgates at pacbell.net
Wed Oct 9 16:44:08 PDT 2002

Currently there is no "optimized static pressure control" for fans/ducts in DOE-2.  However, J. Hirsch & Associates has funding to implement such a mechanism in DOE-2.2 within the next few months.  The funding is provided by Southern California Edison as part of their "Energy Design Resources" program (http://www.energydesignresources.com/).  These enhancement will be incorporated into both DOE-2.2 and eQUEST (not PowerDOE), and will be made available to the user community at no charge.

This control mechanism will be similar to the head reset controls already implemented for variable-flow pumping systems in DOE-2.2, where the pump head setpoint can be reset based on the hourly head demand of the worst-case valve. The actual pump head is then a function of the worst-case valve head, plus the additional variable-flow head losses of the loop piping and the central plant equipment.  This control sequence maximizes the potential savings of variable-speed pumps, as the required speed of a pump is dependent on both the flow as well as the head requirement; with the head requirement usually being the dominant factor. (The maximum head of a pump varies roughly as the square of the impeller speed; if the head requirement does not decrease as the flow drops off, then the speed cannot decrease significantly).

For fans/ducts, the simple curve-fit that varies fan power as a function of flow will become obsolete. Instead, DOE-2.2 will keep track of the static requirement of the worst-case VAV box, as well as ducting, coils, filters, etc.  Each component must be accounted for separately, as the head of all of these devices varies differently for a given flow.  (Some components, such as ducts and sound traps, experience turbulent flow, and their head varies as the 1.85 power of flow.  Other components, such as coils and filters, are more laminar, and their head typically varies in the range of the 1.1-1.6 power of flow.  Still others, such as a VAV box without an intelligent DDC system to monitor damper position, will have a constant head requirement; i.e. a constant head setpoint out toward the end of the ducting.)  These changes will require DOE-2.2 to know about the flow through each component in the system, the component's head characteristic, as well as the fan map for a given type of fan (forward-curved, airfoil, etc.)  Based on flow and static requirement, DOE-2.2 will then be able to determine the fan speed and power consumption.  

In the meantime, you can approximate "optimized static pressure control" by generating a new curve that causes power to fall off more rapidly with flow than the default curves.  However, this is not a straightforward task, as you would have to calculate by hand all of the algorithms we have designed for DOE-2, and repeat the calculations for a series of flows.  Perhaps someone has already done this exercise, and can share their curves with you.

Steve Gates
  ----- Original Message ----- 
  From: babetsk at jbb.com 
  Sent: Wednesday, October 09, 2002 2:41 PM
  Subject: [BLDG-SIM] Static Pressure Reset modeling in DOE 2

  To Doe 2 Users:


  Does anybody know if there is a way to model (in DOE-2) an "optimized static pressure control", that is a control method where the controller dynamically adjusts the static pressure set point based on the position of the modulating devices in the VAV terminal units? 

  Thank you

  Konstantin E. Babets, Ph.D.
  CFD/Energy Modeling Engineer
  Jaros Baum and Bolles
  Consulting Engineers
  80 Pine Street
  New York NY 1005
  Tel:   212.530.9455
  Fax: 212.269.5894

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