Ductwork and Condensation 1

[friartuck]

Does anyone have any experience in utilising bare ductwork (i.e. uninsulated) when supplying conditioned air. I have seen systems installed without it, but I am concerned that condensation will occur.

Are there any simple guidelines or any documentation that indicates what the limitations are.

My scenario is a large glazed car show room (10m high glass by 60m long) and I will be supplying about 6m3/sec of air at about 13 to 14C.

The room will typically be at 22 to 23C (no specific humidity control,(i.e. only heating or only cooling)).

I know that I can estimate (from the room conditions) that the dew point for the air in the space will be 11C for 22C/50% and the supply air will be 13C so theoretically the risk of condensation at these conditions is zilch, but if the room temp rises to 24 and the % hum is 60% then the dew point is 15.7C and so theoretically condensation will occur.

I suppose I have answered the theory side, but what about the practical side. i.e. would it really cause a problem? How often would it happen?, are there any simple mods to the controls I could make to reduce the risk? (possibly raise the supply temp if the hum level goes too high etc etc?

Any comments

Cheers



Friar Tuck of Sherwood

 

[HVAC68]

Is this open ducting ? or above a false ceiling which itself acts as return air plenum ?

I have done and seen many installations where supply air duct is a bare uninsulated one and the return air is collected freely and returned back to the AHU room without ducting.



HVAC68

 

[rogzog]

We have done many projects where there was no insulation required on the ductwork exposed in the conditioned space. Some examples are Gymnasiums, auditoriums, theaters and even telephone switching equipment buildings.

TOK

 

[friartuck]

The ducting would be at high level and exposed to view in the show room. Other ductwork (i.e. in plant rooms etc) would be insulated.

If I insulate the exposed ductwork, I think it would look yucky, unless there is a nice insulated finish anyone can recommend..or perhaps I could paint the insulation.

It would be better if the ductwork is left bare as it would look better and be more cost effective.



Friar Tuck of Sherwood

 

[imok2]

Tuck, These are quite common in California and they are usually painted in bright colors and look quite attractive.
I have never seen any with condensate problems and many newer restaurants are going this route with open ceilings.

 

[imok2]

Tuck this may be of some help;

http://207.21.201.151/design1.htm

 

[HVAC68]

You could also think of painted circular spiral ducting which is aesthetically pleasing as compared to the conventional rectangular ducting.



HVAC68

 

[quark]

I have seen many installations where supply ducting is not insulated, when run in controlled space, and running without problems(however, I didn't observe 24x7x365).

There shouldn't be any problem unless there is some stratification and this is negligible if you have low return. The reason for painting the duct in bright colors may be to increase the emittance of the ducting and thus minimizing condensation.

Regards,

 

[vannic]

Exposed spiral ductwork does not need to be insulated. However, you can specify dual-walled spiral ductwork if you feel the need.

 

[atilashorse]

You can use uninsulated ductwork when air temperature, or moisture inside and outside the ductwork are very similar.
For instance, you can run uninsulated supply AC ductwork through conditioned spaces, not close to radiant surfaces like hot roofs, where warm air will gather. Do not run uninsualted ductwork though spaces where the difference in temperature between inside adn outside dcutwork air is quite diffrent, for instance AC ductwork through unconditioned spaces like attics.

 

[vannic]

If you use a Psychrometric program (PMTherm), you can see that the dewpoint of the plenum air (assuming you're maintaining 22-23C) should be slightly above the supply air dewpoint temperature for most applications.