Static pressure loss thru sidewalk type grate.
Static pressure loss thru sidewalk type grate.
(OP)
None of the manufactures that I can find have any data on it. I am designing multiple tall shafts to exhaust large volumes of air from an underground parking garage. The shafts will be between 95' and 150' tall. The owner wants sidewalk type grates installed in multiple levels of this shaft with access to them thru doors on various levels of the building.
If I was doing this ONCE I'd make a conservative estimate and go on down the road. But since there may be 4-7 grates in the shaft in series... I thought I'd see what ya'll thought about it.
The shafts are 60-90 sqft each and will have air velocity between 1000 and 1500 fpm.
Jabba
If I was doing this ONCE I'd make a conservative estimate and go on down the road. But since there may be 4-7 grates in the shaft in series... I thought I'd see what ya'll thought about it.
The shafts are 60-90 sqft each and will have air velocity between 1000 and 1500 fpm.
Jabba





RE: Static pressure loss thru sidewalk type grate.
Easy to do.
Then you'll know.
RE: Static pressure loss thru sidewalk type grate.
I don't access to facilities like that.
Can you turn me on to where I could do something like that?
Jabba
RE: Static pressure loss thru sidewalk type grate.
As for pressure drop, the most it could be is the velocity pressure in the duct. At 1500 fpm, Vp=(1500/4005)^2=0.14"W.G.
You say they are in series. I think you really mean they are operating in parallel, all connecting to a common exhaust shaft. Right?
RE: Static pressure loss thru sidewalk type grate.
Jabba
RE: Static pressure loss thru sidewalk type grate.
ETL-Intertek (or one of their assoicated companies) has the cabaility. http://www.intertek-etlsemko.com/
As does Quest apprently. http://www.qes.com/airflow2.pdf
RE: Static pressure loss thru sidewalk type grate.
Say you have 93,750 cfm (based on 1,250 feet per minute velocity and a 75 ft^2 cross section). It's important to know the free area of the grate. If we assume 70%, plug & chug using the ASHRAE equation:
Q = 2610 A (dP^.5)
(Q is 93,750 cfm)
(A is open area in square feet = 52.5)
(dP is resulting pressure loss in inches w.c.)
You get about 0.5 in. w.c. per grate.
I don't know if this is the best estimation for this job (the result seems a bit high to me) but the method is traceable to a known source...
Good luck,
CB
RE: Static pressure loss thru sidewalk type grate.
RE: Static pressure loss thru sidewalk type grate.
With 4 to 7 grates in series the total resistance will not be negligable, and it follows that the additional fan costs associated with blowing air through this resistance continually will be non-trivial over the life of the facility. Have you thought about a life-cycle cost analysis yet?
Consider hinging the grates at the access door floor level. When you open the door the grate is staring you in the face, blocking access. Fold the grate down only when necessary to access the interior of the shaft.
RE: Static pressure loss thru sidewalk type grate.
RE: Static pressure loss thru sidewalk type grate.
Jabba