Question about External static pressure (ESP) 3

[immsk]

Hey guys, I am doing some pressure loss calculations for a duct run. The duct starts at a roof top heating and cooling unit. I have the spec sheet here

http://i.imgur.com/xXWhI.png

and I am not quite sure which value to use for the ESP, should I use 3.0 in. wg or the 4.7 in. wg as mentioned in the summary. Any help would be really appreciated.

 

[MintJulep]

They are consistent.

 

[immsk]

I am sorry but that doesn't really answer my question

 

[Drazen]

use external static pressure, that is what you have available for duct calculations, means 3 iwg.

 

[MintJulep]

ESP listed on the left equals ESP on the right.

 

[willard3]

ESP = external static pressure, ie, external to the unit.

 

[Wilbur55]

The entire ESP may not be available for moving air down the duct at all times. The stated ESP is probably for clean filters.

The fan's TSP is governed by the fan curve. As the filters become dirty, the fan will be capable of the same TSP at the design flow rate, but the fan will see all the pressure drops listed on the right side of your image *plus* and additional pressure drop due to dirty filters. The fan performance will follow the fan curve to the higher operating pressure and the air flow rate will be reduced.

Unless you design your ductwork to require less than the stated ESP. Then your system will see *more* air flow than stated in the selection as the performance point follows the fan curve to the lower initial operating pressure.

 

[immsk]

Thanks everyone for their input