Condensation in ducts

[avs2600]

Dear Forum Members,

I am working on the ventilation systems for a snack company. We have already installed three kitchen hoods above the production line but unfortunately we detected oil condensation falling down from the ductwork to the snacks.

Could any of you tell me what should I do in order to avoid condensation inside the ductwork?

Ambient temperature: 55 - 75 degrees F.

I am looking for any arrangement that could help me to route the condensation out of the ductwork instead of falling to the snacks.

Any tip, sketch, drawing, plan will be extremely helpful.

I look forward to hearing from you.


Cesar Villavicencio
Ecuador, South America

 

[SAK9]

Your post says the leak is thru the duct work.Kitchen exhaust or for that matter any exhaust that contains vapours should be of welded construction.The duct should be sloped to a covenient drain point with provision for draining any condensate or draining during wash down.Preferred transport velocity is above 10 m/s.Please check if your design meets these basic guidelines.

Check with a hood supplier such as Halton regarding maximum entrainment at the hood ie technologies such as UV disinfection modules break down the oil into gases and water vapour.

 

[avs2600]

Yes, we got transport velocities above 10 m/s, welded ductwork.

The leakage is not outside the ductwork, the oil and vapors condensation is inside the ducts and when this happens we start to have oil drops falling onto the snacks. This is a mess and of course is a nightmare for the client. The problem is worst when the exhaust fan is turned off.

We need to find any ductwork design or any system that could help me to avoid the problem in reference. I am even thinking in using an electric resistance on the ductwork, specially on the first elbow above the hood where the air strikes and condensation starts.

I am also thinking in using a horizontal section above the hood to reduce condensation from falling on the production line.

We look forward to hearing from you.

 

[Compositepro]

Are your hoods above deep fryers? If it is oil that is dripping the problem is not condensation on surfaces. Hot oil vapors condense in contact with cold air to form a fume or mist of oil prticles in air. Most kitchen hoods over cooking areas have mist filters at the hood opening to collect the mist so it dosen't get into the ducting. These screens then have to be cleaned regularly.

You should also take measures to minimize the contact of cold air witrh hot oil. Your ventillation could be creating more mist that you would have with no ventilation.

 

[SAK9]

AVS,

It appears from your second post that the exhaust duct is running vertically up from the hood which in my opinion is not a good design.You need to have a horizontal run sloping away from the hood with a drain point.The vertical run should start after the drainpoint so any condensation falls back to the lowest point in the system.

 

[avs2600]

Yes, we have ducts running vertically up to the roof of the building.

From your point of view we made a bad design but I wonder if the use of filters in the hoods will help us to solve this problem?

The hoods we installed have no filters.

Some hoods are above deep fryers but others are just at the inlet and outlet of the flavoring section, were the snacks are spiced. This section is a rotating tunnel where oil is sprayed over the snacks at the same time that small particles are applied to give the snacks the colour and appeareance the customer wants. Anyway, the problem is the same in both type of applications.

The exhaust system draws a mixture of dust and oil, looks like a whole mess over the duct surfaces. Anyway, it is the condensation that turns our lives in hell.

If you could share a sketch of what could we do to solve the problem we will deeply appreciate your support.

Rgds,


Cesar

 

[AbbyNormal]

Cesar

Your name sounds familiar, like from a tour of greenheck years back and an ASHRAE show.

Maybe consider directing this condensate back to a trough or trap.

Perhaps the exhaust enters in through the branch of a tee. The bottom of the tee is capped. The condensate coming back drips straight into the capped part of the tee, come up with a way to get the pooled oil out of the tee, be it manually to start or automatically



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[marcoh]

My thoughts would be that grease filters are essential similar to a normal (maybe large in your case?) kitchen exhaust hood.

Also should take into account that grease will build up in the exhaust duct and pose a fire hazard, installation filters will reduce build up, though you should still steam clean the duct as part of scheduled maintenance regime.

 

[SAK9]

AVS,

As a first step I would suggest to have baffle type inclined grease filters installed inside the hood.The filters should drain to a grease gutter at the periphery of the hood.Since this is an industrial application the gutter may need to be connected to a drain. As already pointed out greas trapped inside the duct is a fire hazard and there should be regular steam cleaning to get rid of it.

 

[trashcanman]

I agree with SAK9, install grease filters. Exhaust the fumes at 1500 ft/min, straight up with a good grease exhaust fan.

 

[hollandhvac]

AVS260,

From your last information I am getting the impression that this is a factory that is producing snacks?

From the flavoring section where all kinds of stuff is added id goes to a continues fryer from where you want to exhaust the fumes that come from the frying process , with ths you are also taking the flavoring powder with it into the exhaust system?

In this case I would say: a filter will not help, because it gets filled with the power and you should now more look at reducing the speed in order not to take the powder from the snacks..

Just my thoughts and my 2 cents.

Had a simular problem once, but that had to do with condensation and using outside air with an on controled condition. With this teh condensation happened during the process and gave a large mess as well. But your situation is different.