exhaust fan not sucking the air from garbage room 1

[moideen]

Hi guys,
I am facing a problem on garbage room, there is not proper air exhausted and smell is coming to outside. I checked the garbage extract fan, found it is working and air is also discharging. But in garbage room, air is not drawing through duct and air is return to garbage box. So the positive pressure in garbage room. So I have doubt on the capacity and static pressure. The details are below
Building =g+71 floor.
garbage room Area =1194.7 ft2
Height = 12 ft.
Volume = 14,336 ft3
Duct effective length(EL)=950 FT.
EXISTING UNIT DETAILS
Duct = 31 inch.
CFM =2884 CFM.
STATIC =1.7WC.
What will be the problem? Any answer would be appreciated.

thanks
moideen-dubai

 

[RandomUserName]

If I am understanding your scenario correctly, sounds like your room is positively pressurized and smell is getting getting to unwanted spaces via exfiltration.

I am assuming you are supplying air, and exhausting air. No return in a garbage room; that would be silly.

Sounds like you have 12 ACH of exhaust which seems OK.

Have you confirmed you are supplying less than 2884 CFM into the room (confirming negative room pressure)?

Can you confirm rooms adjacent to the garbage room are positively pressurized in relation to the garbage room?

I am assuming the exhaust system duct work is entirely negatively pressurized (the fan is the last piece of the exhaust system)?

But in garbage room, air is not drawing through duct and air is return to garbage box.

Could you clarify this statement?

Sounds like you need to get a Test and Balance contractor in the room to perform some measurements.

 

[moideen]

Thanks your reply. Garbage room on ground floor and there is no any fresh air supply, it’s just doors of garbage room are open.it is 12 air change. Garbage doors are open to parking area. Garbage room to be negatively pressurized if 2884 cfm air extracted from room. Yes the fan installed on roof. I can upload it drawing on next working day.

 

[RandomUserName]

If you have confirmed 2884 through the exhaust on the ground floor and you are not supplying makeup air, then we are narrowing it down.

Is is windy at all? Even with 12 ACH ... gusts of air through garage doors is going to play a big role.

Might be reverse stack effect, especially if the tall building (71 stories) is in a hot climate. Air in the building will tend to fall down and pressurize the floors below it. Air tightness between 1st and second floors should be checked, especially in the garbage room.

Is this building in Dubai? Chapter 4 "Tall Buildings" in the 2015 ASHRAE Guideline - HVAC Applications book has a section specifically for Dubai and its stack effect challenges.

 

[moideen]

For checking I closed all garbage chute door from each floor, so I think there is no chance of stack effect on chute. But reversing the air. What you think if I increase the high static fan size with same cfm.

 

[RandomUserName]

I think a quick diagram might help us better help you.

Could you sketch something or take some photos and upload them?

 

[moideen]

ican upload on next working day

 

[dbill74]

Can you clarify where exactly you are experiencing unwanted odors.
You say the garbage room is on ground floor adjacent to or in a parking garage? How is the garage being vented?
You mention a chute with doors going up through the building; do the chute doors open to an indoor space or are they exterior to the building envelope?
Is the garbage chute being ventilated?

 

[moideen]

Chute doors open to indoor space, each floor tenants can deposit their waste easily. Garbage door open to building exterior. Extract fan installed on roof, top of chute. Fan is discharging air, but reversing air on garbage room. Odor spreading around the building.

 

[lukaiENG]

perhaps the exhaust air duct is leaky? if the fan is at the roof, the duct is under negative pressure and could be drawing air from the shaft. This would explain why you have an exhaust air flow rate but no apparent air flow at the room.

 

[dbill74]

So you're pulling garbage exhaust up through the chute to the roof (with the chute being the path of the exhaust air?) and you have access doors on the chute so people can dump their garbage.
Check the seal and closing mechanism on the chute doors. If the seals around the doors are bad (or do not exist), then I am not surprised you have problems. Also if the chute doors are getting stuck open, you are pulling garbage odors right past them. This would also explain why when the fan is running you are not getting air flow in the garbage room. At 71 floors, if a chute door near the top looses its seal of gets stuck open, the fan is going to pull air from the indoor corridor before it pulls from the garbage room.

I'd recommend adding a ground floor exhaust fan for the garbage room. Additional fan(s) to serve the middle and lower portions of the garbage chute. Add or increase the amount of outside air in the corridors.

 

[moideen]

Thanks your responses. I have to check two relevant points. Leakage of duct and whether the chute doors are properly closed. It is not possible to provide exhaust fan for ground floor. Since very near have closed buildings and restaurants. How to fix additional fan middle portion, dumbed waste comes down through the chute.

 

[dynamo78]

+1000 on Random. I assume that the chute for dumping the garbage is in no way connected to the Exhaust duct.As lukaieng said, its a leaky ductworks. what's the classification of the duct(Seal and construction). My experience as a contractor, Its a hotel 22 floors. The engineer set up is "Blow-thru". Fan is in the basement and almost all floors ar complaining with the odor. so we relocated the fan to the roof and reseal the ductworks.

 

[MintJulep]

2884/71=40

Tiny leak at each floor's garbage door = all your air.

If all of those leaks are cool, conditioned (dense) air then the leaky air will fall to the garbage room and out the open door, thus "air is return to garbage box".

 

[willard3]

Has anyone bumped the fan and checked rotation?

 

[1gibson]

I'm not in HVAC, but it seems if you could use an isolated portion of the chute to exhaust and the rest to dropping garbage, problem solved? Basically a sealed exhaust pipe with no openings other than fan at the bottom and vent at the top. Fit that inside the existing chute. Am I missing some reason that this won't work, other than possibly not being able to work it out per code?

 

[317069]

what was the situation before? I mean did you face this problem recently or it is there for a long time or forever?
is this an existing building or newly constructed and occupied building.?

 

[berkshire]

Moideen
A large number of the Garbage chutes installed in high rise buildings are built of short sections of tapered metal tube slip jointed together. There are no fasteners inside the chute and the sections are merely held in place from the outside by the support brackets at the time of installation.
I have worked on these chutes where the sections have slipped allowing air to leak into the duct from the joints. The cure has been to get into the duct on a bosuns chair. secure brackets to the duct, pull it back to its correct position then use truss head pull fasteners from inside the duct to secure it. Not an easy task .
B.E.

You are judged not by what you know, but by what you can do.

 

[moideen]

Sorry for late response and updating. Yesterday I recheck the system. Primarily I went to 71st floor and opened the chute door. Place a tissue paper to see the capacity of air drawing.no effect. There is only maximum 12 ft distance from the fan. I doubt the rotation. Rechecked the flow feels air discharging. But I switched off the fane and checked the blade direction. It is wrong!! Spinning was wrong. It was spinning wrongly from beginning. Technician says, it is single phase, so he thought there is no chance to change the wrong direction! I open the terminal and changed the rotation. Again checked the air flow found drawing from 71st floor down to 38th floor drawing but air drawing capacity comes down.no any effect in ground floor (garbage room).a 12 inch, 12 ft. lengthy flexible duct connected to 30 inch garbage chute on 71st floor. Removed this flexible duct checked the velocity it is 2800 fpm. Then CFM will be 2190. As per the manufacture catalog design fan CFM is 2884.
There is no any compactor inside the chute, but has a cleaning system which do not make any blockage. There is no any fan control as per the door openings.
If we consider the total effective length accounting door opening effect, maximum required static is .5”wc. As per catalog available 1.7’WC.

 

[berkshire]

Moideen,
How was this flex duct connected ? was it through the garbage door , or was it tapped into the chute through a branch of some sort.
Does your trash chute look like this?

You are judged not by what you know, but by what you can do.