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Hello All,
I'm new to the forum, but glad to see the technical expertise that exists here.
With that said, I have a fairly technical question about IAQ.
I am the facility manager for a museum in Chicago. The building has VERY tight parameters that mus be met, e.g. 46-50%RH and 68-72degrees.
The main problem I'm having is the building static pressure sensor controls the Outdoor Air Dampers. The sensor is all over the place with it's readings, and most days the readings indicate that the building is in a negative pressure, although I don't believe this to be the case.
I've seen quite a few things about how to measure the building static pressure, but it seems that one end of the manometer tubing tests outside, while simultaneously checking the inside of the facility with the other end. I've done "before coil, after coil" tests to see the condition of the coil, but this is the first time that I've been in the position of being responsible for building static pressure, and how it's supposed to be read.
I have about 8 years of in the field HVAC experience, mostly commercial.
With all that said, here are my problems:
- Building Static Pressure = (-).25 most of the time
- OAD = 100% open most of the time
- RAD = vary with operation, but (OAD + RAD = value not always 100+%). The OAD and RAD(or mixed air damper) are separate entities.
- Condensation collecting inside OAD duct work, right near register on outside of building. (rain isn't possible)
What I think:
- What I think is happening is that the static sensor is causing the building to become over-pressurized, and the over-pressurized air in the building is leaking outward(somewhat) through the OAD ductwork...at 68-70 degrees and 45-47%RH. Because my return air is 68, with this humidity, and it's 30 degrees outside...(insert psychometric chart)I feel that i'm hitting saturation point within the OAD duct work and my 45RH% is increasing to 100% with the temperature drop...leaving the condensation in the duct work right outside the OAD register.
Any threads already made on this, or does anyone have any ideas for me?
Cheers,
Effort
Professional Member
Your building static pressure sensor is wrong. If you had a building pressure of -0.25 inches the doors would be hard to open and a lot of outside air would be drawn in with them open. The doors would also be whistling when closed. Start by measure the building static pressure with the building unoccupied.
No man can be both ignorant and free.
Thomas Jefferson
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Wayne,
Yeah I was under the assumption that the sensor was wrong, as mentioned. The doors aren't difficult to open or close, and they don't whistle either. The real problem is the condensation caused on the third floor.
What I was getting at is does this seem like I'm on the right track? I'm hoping a master of economizing/IAQ systems can help out, as I feel that I merely a solid Professional.
Sponsor & Professional Member*
Wind is most powerful cause of pressure across the surface of structure. Wind usually cause negative. A 20 mph wind is like a blower door test.
Stack effect when cold outside also significant.
Measure pressure on all sides and elevations during different conditions.
I have this during construction with plastic covering the window opening. It is unbelievable. Also add the random location of the structures air leaks.
The last problem is the lack of accuracy and sensitivity of pressure sensors.
Keep us posted.
Regards Teddy Bear
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
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Originally Posted by teddy bear
Minus my bldg static pressure sensor being inaccurate,
Here’s what I’ve gathered so far:
- VFCU-308
o Fan Speed = 100%
o Static Pressure
Actual = (-).80 WC”
Setpoint = (-).20WC”
o Return Air Damper = 100%
o Outdoor Air Damper = 100%
Outdoor Air Fraction = 0.066421 = 6.64% outdoor air introduced to air circulation;
• Being 100% open and the unit being so low under it’s WC” setpoint, this seems low.
o Duct Humidity = ~85%
These are the values of my VFCU at the moment. I'm almost certain there is a blockage of air flow in the unit. More to come.
Professional Member
How is the outside air quantity controlled? How is building static pressure controlled? You need to start with accurate readings. I had to trouble shoot a building that was running similar to the way yours appears to be operating. The controls were measuring all airflows and determining outside air quantity based on the measurements. That simply doesn't work except in theory. Building static pressure control should be done directly from the measured building static pressure. I have seen it tried the other way several times and not once did it work. Get the building static pressure under control and then address the RH control.
No man can be both ignorant and free.
Thomas Jefferson
Professional Member
I would have second thoughts about trying to fix this static problem on my own. Reason being is millions of $$$ of art work and their tight temp and humidity requirements. Started up the addition at the saint louis art museum and after start up the building sat empty except for them building exhibits without the art for 60 days. Get a engineering firm involved with deep pockets in case something goes wrong.
Professional Member
The screw ups I have seen like this were design errors. A control tech that knows his stuff is the best bet. A good balance contractor and engineer should also be involved. He doesn't need an engineer to correct the bogus building pressure measurement. That is a maintenance sue.
No man can be both ignorant and free.
Thomas Jefferson
Professional Member*
Positive or negative building static is one of the easiest things in the world to check. You already own the instrument. Let me find the photo . . . I know right where it is . . .
All you need is this highly developed instrument, and an outside door.
I do a triple evac with nitro to remove non condensables.
Professional Member*
I do a triple evac with nitro to remove non condensables.
New Guest
Professional Member*
Welcome aboard. Please chime in when you have something to contribute.
I do a triple evac with nitro to remove non condensables.
Professional Member
It might be a maintenance issue if the building was commissioned, equipment wasn't added or removed, if someone played with fan speed or dampers. Something changed and if they didn't and was having this problem from day one the mechanical engineer should of been brought in.
Professional Member
Whats OAD and RAD ? Building static sensors need to be in a area by the main doors. Your running -.8" static doors would be like a wind tunnel and hard to open if they pull to open.
Professional Member*
I guess you did not see the photo that I posted.
I do a triple evac with nitro to remove non condensables.
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For what it is worth, I have seen multi-story buildings where the only access to the outdoors was the lobby, and Floors above that we're causing pressure issues on the first.
I do a triple evac with nitro to remove non condensables.
Professional Member
Just wonder how old the building is because i started up a new addition to the St. Louis art museum and the Chicago general contractor was starting another museum in your town. Commissioning was brutal but their was going to be irreplaceable art. Sat empty 60 days just to make sure everything worked while they cleaned the building and built displays. There is no way that i would make a change by myself because if something screws up and something got ruin you would be gone.
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