Uniform definition of ESP
Uniform definition of ESP
(OP)
What is the definition of External static pressure?
I was asked this because of a problem my PM encountered and I am having a hard time finding the actual definition in ASHRAE. I find the term everywhere and I thought it was easy to know and understand, but I can't find the definition.
I found thread403-164474: esp to be useful but did not get my final answer I was looking for.
The problem site has a AHU (CRAC specifically) with draw through fan with supply duct, diffusers, return grilles and return duct. All other particulars should be irrelevant to the conversation.
Is the ESP measured on supply side only or does it include all supply side losses and return duct right up to the unit?
I assumed it would include all external losses, but cannot find confirmation anywhere.
I was asked this because of a problem my PM encountered and I am having a hard time finding the actual definition in ASHRAE. I find the term everywhere and I thought it was easy to know and understand, but I can't find the definition.
I found thread403-164474: esp to be useful but did not get my final answer I was looking for.
The problem site has a AHU (CRAC specifically) with draw through fan with supply duct, diffusers, return grilles and return duct. All other particulars should be irrelevant to the conversation.
Is the ESP measured on supply side only or does it include all supply side losses and return duct right up to the unit?
I assumed it would include all external losses, but cannot find confirmation anywhere.





RE: Uniform definition of ESP
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A green thought..."We don't inherit the earth from our ancestors, we borrow it from our children." (unknown)
RE: Uniform definition of ESP
If you don't have a return fan, then your supply fan must work against the return duct, return grille, etc.
RE: Uniform definition of ESP
Total pressure is what the fan has to over come, the sum of static and velocity losses.
You will have less problems with purveyor substitutions if you calculate total pressure and use that in the specifications. Let the purveyor worry about his equipment's pressure drop and whether it will meet the operating criteria.
RE: Uniform definition of ESP
Chris,
That is exactly the definition I thought it was, is it defined in any ASHRAE or TABB publications?
I scoured all the ASHRAE publications, but I did not find the definition of external static pressure. The Engineering Toolbox has a HVAC terms section but the definition of ESP is lacking in my opinion. Maybe the term is so obvious it is never explicitly defined.
RE: Uniform definition of ESP
RE: Uniform definition of ESP
I've seen the terms total static pressure, external static pressure, and total external static pressure used interchangeability. Look at it this way Total Static Pressure is what you calculate, EPS is what the manufacturer says it should be once the unit is connected to external ductwork.