Static Pressure in AirFRAME® and LEDiffuser™

Static Pressure in AirFRAME® and LEDiffuser™

All information contained in this Knowledge Base is provided for reference only.  SLD products are engineered to order so the detailed requirements of any particular installation will be coordinated according to the codes, requirements, and specifications of that project.  Project-specific information in all cases supersedes information provided here.

Introduction

AirFRAME® and LEDiffuserâ„¢ products both act as the terminal point in HVAC systems.  As such, their inherent static pressure should be taken into consideration as part of overall HVAC system design.

In general terms, our products generate minimal static pressure.  And, because our systems are often customized per job, it is not possible to provide an exact number that is accurate in all cases.  As such, this article provides an estimated static pressure value for a variety of conditions and selected options.  The information presented here is based on a combination of laboratory testing results, published performance data, and estimates based on SLDs many years of experience in HVAC and Diffuser design.
All values shown below are at 30 feet-per-minute outlet velocity which is the center of our 25-35fpm target range (per ASHRAE 170).  Higher velocities than that will generate slightly higher static pressure, and vise versa.

The primary factors that impact static pressure in our products include:
  1. Damper Setting (AirFRAME and LEDiffuser): All values provided are assuming the trim dampers integral to our "damper-diffuser" assembly are fully open.  Closing dampers after installation to trim and equalize air balance can create slightly more static pressure
  2. HEPA Filters (AirFRAME and LEDiffuser): Adding HEPA filters to the system adds additional pressure drop both initially and increasingly as the filters load over time.
  3. Supply Air Inlet Path (AirFRAME): If a system includes internal mount plates (IBs) or other internal features that air has to flow around, it can cause static pressure to rise slightly versus a fully open system (like an AF33).  The more "torturous" the path from supply air inlet to the most isolated diffuser, the more likely there is to be both pressure rise due to air path and some trimming required via damper adjustments.
  4. System Overall Height (AirFRAME): Our standard AirFRAME system height of 18 inches is designed to offer the best balance between internal air flow and minimal system volume requirement.  In some cases, due to space limitations, we are asked to design systems with shorter heights down to and including 13" overall height.  These "shorter" systems will inherently generate a little bit more static pressure due to air having less room to flow internally.  They are also more likely to require some trim damper adjustment to equalize flow across the face of the system which can increase static pressure further.

Static Pressure Table:

Product Line
ConditionApprox. Static Pressure (inches H2O)
LEDiffuser
Standard - no HEPA
0.15 - 0.2

With HEPA
0.2 - 0.4
AirFRAME
Standard, No Inboard Mounts - no HEPA
0.15 - 0.25

Reduced Height or With Internal Mounts - no HEPA
0.3 - 0.7

Standard, No Inboard Mounts - with HEPA*
0.2 - 0.4

Reduced Height or With Internal Mounts - with HEPA*
0.4 - 0.8

Extreme Internal Flow Restrictions
0.4 - 1.0
* Values listed are for clean HEPA filters.  The rate and degree to which HEPA filters will load is beyond SLD's scope and depends on a number of external factors such as upstream filtering, duct cleanliness/configuration, etc.  Concerns about time-based filter loading should be addressed by the mechanical engineer and/or static pressure monitoring with a differential pressure gauge (by others).
In the event that more accurate, system-specific static pressure values are required, SLD can - in most cases - provide Computational Fluid Dynamics (CFD) analysis at additional cost that will provide the best pre-construction value available.  Please ask your Sales Representative for information on this service.
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