return duct entry to plenum

[moideen]

please see a look on image, the return duct enter to plenum through one side. does this create any uneven air distribution across the cooling coil?? i was assigned by my office to check a project where the construction is in progress.almost i see the fcu installations are in that way. what you think......

 

[willard3]

Of course it creates uneven distribution across the cooling coil. The more important question is: is there re there room to fix it?

 

[emalsyd]

If the duct and plenum are sized correctly, I don't think it's going to affect the performance of the cooling coil.

We just installed 4 fan coils on a small job. 3 of the 4, the returns were installed similar. Airflow and supply air temps all came in at design so the ducting didn't affect our units.

 

[moideen]

willard: the system as yet not commissioned.it is an ongoing project.

emalsyd: since the system is not commissioned, i cannot take any parameters. while taking the readings at the full load condition, if the unit shall make low delta T, then can be assured uneven air distribution.

 

[GT-EGR]

Your photo doesn’t really have a scale too it, so it’s hard to say if it matters or not. Even with dimensions it would be hard to say for certain.

Unless this is a critical space application the installation could end up being just fine. Fan coils typically have manufacture return inlets on one side fairly close to the coil - but they are designed and tested and proven to perform that way.

More info we would need would be

Is there supply ducting or does it directly discharge to the space?

What kindof coil is it, more importantly what temperatures does it operate at?

Is dehumidification an expectation of this unit.

In the end what you really need is the performance data once it’s operating. In the meantime you can basically let the contractor know you are suspicious but waiting for testing.

 

[willard3]

Does the ducting of the fan coil units comply with the contract documents?

 

[moideen]

GT-EGR :
I am traying to take the actual dimension, the design delta T is 16F, so obviously the indoor heat exchange area should be wide so as to match with high delta T design. At the look on unit, the length of the unit above one meter and installed with constrained position. Verily, there is no space for maintenance!!
The return is not directly connected to fcu, it is connected to plenum box. Therefore, manufacture has no any role in this case, because plenum box designed by contractor as per the site condition.
It has supply duct, it is not free discharge. Design data is not available, sensible/latent load is proportional since it is for hotel apartment. More pics I will update here………..

 

[moideen]

willard3

i will update. i have requested for all related documents...

 

[moideen]

see a live pic, what you think. still, I am waiting to get the drawings

 

[Drazen]

willard already gave you the answer, air distribution will certainly be uneven.

the question is whether there will be any sensible consequences or not.

commissioning may show some performance issues, but besides that there can be uneven supply temperature if FCU blows into long supply grille.

what can you do in this phase? you can only monitor the result and provide possible explanations for non-conformance.

 

[moideen]

Drazen: there are a consultant and contractor, so they have to provide the explanations. already it raised to their attention.

 

[dbill74]

Where is air being filtered?
If the filters are in the unit, they will be upstream of the coils. These will act as a permeable barrier and you will get more or less even air distribution to the coils.

Assuming this is a draw-thru unit (typical for this type of unit). The driving force for moving the air is the fan, so the air is under a negative pressure. So the typical air distribution / velocity profiles for air off fans do not apply.

Finally, the coils themselves will act as a permeable barrier forcing the air to distribute itself across the face of the coil.

Is the setup ideal? No. But it is nothing to get concerned with.

In short, you are making a mountain out of a molehill.

 

[willard3]

There are many ways that the low-pressure fans in fan-coil units can be compromised.

I would be more concerned with this unit having too much pressure drop reducing the cfm/cooling and, depending upon the fan type (likekly FC) the fan may operate in unstable regions.

You will know the answer to this and all your questions when you have a balance report.

 

[moideen]

dbill74

Thanks for your observation, Filter will become as permeable barrier and then lead to even air distribution. at present I don’t have any comment on your thought. I have already raised my concern before the consultant, still they have not responded. at the commissioning time, I will check the chilled water delta T at the full load. The design delta T is 16F. if shall not maintain the design range, then will see the next step. What you think sir..

 

[dbill74]

16F delta CHW temp? Wow.
That's an unusual delta T, I normally see 10-12F delta. Is the rest of the CHW equipment designed/capable of working with that delta T?

 

[moideen]

This is a big project; the first face capacity 10,000-ton centrifugal chilled water plant and the design was based on the concept of district cooling system. The indoor units were selected based on that criteria. This is the case mainly the indoor unit’s selection got lengthy size so as to match the high delta T design. And the unit’s installation became in confined space due to the bigger size, also it might be a reason of limiting the duct routing and I think the contractor compelled to connect the duct in side way of plenum.

 

[lucaspenalva]

"does this create any uneven air distribution across the cooling coil"

yes. but it will compromise your system performance so little that you wont notice it

 

[moideen]

lucaspenalva :the project is waiting for commissioning.as dbill said, it might be a 'mountain out of a molehill'. if shall maintain the Delat T at full load, then it is not a matter.