# Thread: Sampling static pressure

1. Regular Guest
Join Date
Feb 2009
Location
CA
Posts
4
Post Likes

## Sampling static pressure

Does anyone have a good diagram or easy explaination on where to take static pressure readings on an RTU? The question is geared toward the return side....is your TSP referencing before or after the draw through coil?

BDP 588ANW060100

http://www.docs.hvacpartners.com/idc...i588a-18-9.pdf
http://www.docs.hvacpartners.com/idc...588a.18.4b.pdf

2. The blower performance chart is using External Static Pressure (see pg. 41 of your first link).

I would punch wholes in the duct next to the unit if it's a horizontal discharge.

If it's vertical discharge, I'd punch wholes in the horizontal duct connection panels.

If you wanted to use the wet coil pressure drop table on page 44, you'd punch holes in the blower access door and the return panel/duct.

3. Total Static Pressure is fan discharge static-fan suction static.

External Static Pressure is supply static-return static

If the fan discharge static is 2" w.c and the fan suction static is -1", the fan's TSP would be 3" (2"-(-1")

4. Regular Guest
Join Date
Feb 2009
Location
CA
Posts
4
Post Likes
thanks!

5. Originally Posted by BergerMech Rob
Total Static Pressure is fan discharge static-fan suction static.

External Static Pressure is supply static-return static

If the fan discharge static is 2" w.c and the fan suction static is -1", the fan's TSP would be 3" (2"-(-1")

this diagram is one of the best explanations that i have ever seen!

thanks!

6. Glad I could be of assistance.

7. Regular Guest
Join Date
Jun 2009
Posts
147
Post Likes
Originally Posted by BergerMech Rob
Total Static Pressure is fan discharge static-fan suction static.

External Static Pressure is supply static-return static

If the fan discharge static is 2" w.c and the fan suction static is -1", the fan's TSP would be 3" (2"-(-1")

thanks.

8. thanks for the diagram

9. Static Pressure (Sp) This is pressure that is exerted in all directions of a duct. When static pressure = total pressure there would be no flow.

Velocity Pressure (Vp) The difference between total pressure and static pressure.

Total Pressure = Static Pressure + Velocity Pressure.

10. Regular Guest
Join Date
Jul 2009
Posts
30
Post Likes
Good diagram can somone also diagram this for an AHU with a SF and a RF

11. I modified it a bit to show a little more detail and now it has a supply and return fan.
Last edited by Tech Rob; 02-08-2010 at 09:46 PM.

12. Regular Guest
Join Date
Jul 2009
Posts
30
Post Likes

## Ext SP

Thanks for the new diagram with the SF and RF. Thats about what I figured. But the reason I wasn't sure is becuase on the Fan shcedule ( on the plans) it has a design ESP for each fan. ( SF & RF ) while I would expect to see a design TP for each fan I thought I would only see one ESP for the AHU not the way they have it...so i'm still a lil confused...but thank you for confirming what I thought...Noel

13. Originally Posted by Noelcon
Thanks for the new diagram with the SF and RF. Thats about what I figured. But the reason I wasn't sure is becuase on the Fan shcedule ( on the plans) it has a design ESP for each fan. ( SF & RF ) while I would expect to see a design TP for each fan I thought I would only see one ESP for the AHU not the way they have it...so i'm still a lil confused...but thank you for confirming what I thought...Noel
I don't see how you could have more than one ESP for the same piece of equipment. I'd put in a request for information to that engineer, and maybe he can put a good word in for you with his dealer
Last edited by Tech Rob; 02-09-2010 at 08:31 PM.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•

## Related Forums

The place where Electrical professionals meet.