Measuring Static Pressure

[FrostGiant]

35-Ton Vertical Packaged unit. Has a factory supplied plenum with 8 equal sized grills for outlets. Return is wide open to the filter rack, no ductwork.
Can I simply place my manometer in front of the filters then drill a hole in the side of the plenum to take an ESP reading? Does it matter the location
in the plenum (it's 9 feet long) ?

[jman2794]

Static pressure would build on the supply side any where on the supply side. So think about it this way in the RTU you would still be on the supply side. Drill a tap into RTU cabinet and your still on the supply side just make sure it's after the blower wheel cabinet. Return side yes you can take measurement before filters same thing drill Into cabinet just mark where to not hit anything you shouldn't. These are good place to use for your delta t and static pressure.

[Ray Esquivel]

Static pressure would build on the supply side any where on the supply side. So think about it this way in the RTU you would still be on the supply side. Drill a tap into RTU cabinet and your still on the supply side just make sure it's after the blower wheel cabinet. Return side yes you can take measurement before filters same thing drill Into cabinet just mark where to not hit anything you shouldn't. These are good place to use for your delta t and static pressure.

External statics should be taken outside of the RTU...such as in ductwork where possible. Delta T's should be taken before & after coil which may require more holes being drilled in unit.

[jman2794]

External statics should be taken outside of the RTU...such as in ductwork where possible. Delta T's should be taken before & after coil which may require more holes being drilled in unit.

Good catch Ray. I'm missed ESP; I don't use that or have in the past. Now it be nice to see how the original question is answered since it seems you may use this formula and apply it more than most of us. If not at least you helped defined the difference

[slctech]

I am not a TAB or NEBB certified guy and if someone needs or an engineer requires such exhaustive reporting, then they can obtain the services from such entities or we can sub-contract one for them.

However, if I am troubleshooting or performing a BASIC commissioning of a particular piece of equipment, and I am searching for a relatively close/approximate ESP of a unit/system I am sometimes limited to where I can take such readings. A residential furnace/air-handler is really not to complicated with the exposed SA and RA duct work, along with rooftop units that utilize horizontal duct. But when it comes to rooftop equipment that sets on a curb with vertically installed and usually unaccessible duct locations, I will utilize the compartment most closely associated with the RA and SA duct.
If one needs more exact measurements then one will need to access the main trunk lines about 5 feet aft of any turning elbows and prior to any take-offs. If we are talking about concentric kits, these can become a bit tough since you may need a very deep pitot/static tube to reach through into the inner RA duct.

To become even more exact, one would need to utilize duct tranversing methods.

So on a rooftop unit setting on a curb I will remove the filters and utilize the engineering manual to verify that their blower performance charts include the evap coil, heat exchangers, steam coils, electric heat strips, or whatever is in there. If the charts do not include some or all of these possible points of static drop, then I am utilizing the engineering to find their listed static drops to add to my over-all calculations.

It is important to also know exactly which blower package and drive package was either factory or field installed. You have low, normal, and high static options with a myriad of drive kits to achieve specific cfm needs based on the calculated static across the over-all system. By knowing which blower chart to reference will assist dramatically.

There are a few basic links that I guess are appropriate for the OPEN forums:
http://contractingbusiness.com/comme...atic-pressures
http://contractingbusiness.com/enews...s/cb_imp_69579
http://contractingbusiness.com/archi...ressure-part-2

[WAYNE3298]

The system you described is not really conducive for measuring static pressures. The air balance certification agents consider field measured static pressures as approximate. There are several reasons for this which include access to the best place to measure, fan blast area and airflow is dynamic. I'm not saying to not take them but don't bet your entire pile of chips on static pressures alone. Temperature measurements have similar problems with almost all including stratification.