Direct Fire MUA Exhaust Fan Opinions
I'm looking to get some opinions on the design of our ventilation systems installed were I work. I am by no means an HVAC expert, but probably know enough to be dangerous !
I work in a facility that sorts small packages and houses between 150-200 delivery vehicles inside, mostly diesel.
Around the beginning of winter, I noticed fumes to be worse in the building, I had found out, that a section of the building's exhaust fans where 1/2 of the vehicles park were disabled. I had brought this to the attention of the plant engineering people, and the next day, ALL of our exhaust fans were shut off (we had the ability to turn on fans in my area as needed if it got smoky). I was informed that these exhaust fans are obsolete because we employ 2 Rapid 4000 AM Direct Fired Heating Unit with CO sensors and when the air gets too bad the sensors will draw in more fresh air, and if it gets real bad, 1 unit goes 100% fresh air, the other 100% Exhaust. I was told if fumes get bad to crack a pedestrian door and the unit will sense pressure loss and push the fumes out of the building.
It seems to me that the system will be pushing the fumes right past everyones breathable air space instead of exhausting the fumes closest to the source.
4 of the sensors used are CO only, 2 are CO / NO2 (used to sense diesel). It is my opinion that they should not rely on said sensors, seeing how diesel fumes contain MANY other contaminents other than CO / NO2, and it is best to have good circulation PRIOR to setting an alarm! The building is a loose building but when they start and move vehicles and the doors are closed, it can be pretty irritating.
I was hoping someone could shed some light on best practices or industrial hygiene protocol.
Thanks in advance for the help!
Rapid 4000's are make air units. They don't have the ability to exhaust air.
Originally Posted by goodwrench1
As far as code for your building, it depends on what code the local jurisdiction has adopted. So it can vary alot.
But with that said, you need to run the exhaust fans. Normally the CO/N2 system controls the exhaust fans. Then the MUA's provide fresh air based on building pressure.
For example, we have 5 building that have anywhere from 100-500 trucks parked in them. We have N2 and CO detectors through out the building. If the trigger, it turns on the exhaust fan in that area. The whole time the building is occupied the Rapid units are running. It will sense the drop in building pressure and modulate fresh air in. we also have all the fans on a time clock. Most of the trucks leave and return at the same time everyday, so we have the time clock all the fans on, during these windows.
I hope that helps.
are the sensors accurate? has the system been properly checked out recently to ensure that it would even work? i would start here...if it does work as installed/programmed and the sensors are accurate AND THEN if the smell/smoke is still noticably present, then speak with said design engineers.
"Mother" is the name for God on the lips and hearts of children....The Crow
Rapid actually offered to come out for free and inspect since they've sold/sell alot to our company.
Originally Posted by jayguy
I did a little test tonight and cracked an overhead door open about a foot and placed a piece of paper in the air stream and it was blowing back into the building as if it were negative. However I tried that same test earlier last week and the paper was blowing out (unscientific but just curious to see what would happen).
I'm going to reiterate to them that they need it checked out PROFESSIONALLY!
[QUOTE=ascj;5780112]Rapid 4000's are make air units. They don't have the ability to exhaust air.
Rapid does make units with "flush" and "exhaust" modes.
Since this is a work environment your system is going to have to meet whatever OSHA proscribes for it. I'd head over to osha.gov and do some searching.
You have any specs or info on that. I have been working on Rapids for awhile and have never seen that. The only time I have seen exhaust and purge functions is with combination of exhaust fans.
Originally Posted by ascj
I have seen that also. An output relay energizing a relay to turn a fan, or set of fans on. 3000 and 4000 series units offer F & E options, for the "310" and "ICSII" Control Systems.
Originally Posted by german 8'er
As I know it...
model #'s, serials #'s don't change (.i.e M- 4073, S- 969412).
Model# = "40" = "4000 series, "73" = size of blower wheel - 73"
Serial # = "969412" = "96" = year manufactured, "9" = represents that it is an Air Handler unit, "412" = sequencial # for unit manufactured in said year
Flush and exhaust modes are an optional feature at a cost. It is basically performed with additional output and input relays commanding additional dampers actuators and dampers to cycle into a different OA/RA damper configuration. Basically an output relay is energized to a dry set of NO contacts, which when close, send voltage back to an input relay, starting a new command sequence for damper/burner operation.
"Flush" mode is nothing more than setting the unit to a "manual damper" mode and "% outdoor air" to 100% OA.
"Exhaust" mode closes an additional set of dampers in front of the blower wheel discharge, opens an additional set of dampers on an opposing side of the discharge side, and closes the OA dampers as it opens the RA dampers
Typical applications: parking garages, docks, transportation maintenace buildings, package handling facilities
So basically is closes a supply air damper to the building and opens a supply air damper to the outside?
Originally Posted by ascj
I would imagine this feature would only be used on CO or N2 alarm or smoke purge. And you would still require exhaust fans.
That's what I'm trying to tell the management. The flush mode doesn't initiate until 35 PPM CO, which is the TWA (Time Weighted Average) threshold for MIOSHA. PLUS can't possibly distinguish ALL diesel contaminant and particulate (PAH or Polycyclic aromatic hydrocarbon) so good ventilation when the building is occupied especially when there is vehicle movement is imperative in my opinion.
Originally Posted by german 8'er
It's hard to deny that continuous air changes are required and I can appreciate your quest for knowledge, but you're not actually going to stick your neck out to fight the good fight are you? I want to know what OSHA has to say about all of this, clearly they are the authority that establishes MINIMUM levels and procedures. Please post the (eventual)outcome.
0 PPM – (.0000%) - Desirable level
9 PPM – (.0009%) - Acceptable level of CO in a living space
50 PPM – (.0050%) - Maximum concentration for continuous exposure in any 8 hour period
100 PPM – (.0100%) - Slight headaches in 2 to 3 hours
400 PPM – (.0400%) - Frontal headaches in 1 to 2 hours, life threatening after 3 hours*
800 PPM – (.0800%) - Nausea and convulsions, death within 2 hours*
1,600 PPM – (.1600%) - Nausea within 20 minutes, death within 1 hour*
12,800 PPM – (1.280%) - Death within 1 to 3 minutes*