Cooling Coil Condensate Drain Pipe Sizing 2

[ssn61]

Is there a standard or code required condensate drain line sizing procedure or chart? I have charts from different manufacturers that I have used for sizing these pipes but none of them say where they got the information from.
I have looked up IMC and IBC but did not see any information.

 

[CarolinaPE]

An old table I have is as follows: Up to 20 tons use 3/4", 21-40 use 1", 41-90 use 1-1/4", 91-125 use 1-1/2", and 126-250 tons use 2". This is from an older UMC code.

 

[ssn61]

Thanks CarolinaPE. I just found out this information is in IMC 2009 as well. What my actual question is, where these numbers are coming from. My understanding is that it is dependent on type of equipment (because amount of moister rung out of air varies in different coils), also the region where the equipment is installed (more humid area will have more condensation), and then using plumbing design rules will result in these numbers.

 

[chicopee]

ssn61, bear in mind that you will also drain out dust, contaminants and debris which would form clumps and plug the drain lines if drain sizes were too small.

 

[mech5]

I think I have that old chart. That's what I usually use, unless the manufacturer recommends something different. Your best approach would be to use some kind of chart to size up your lines.

 

[trashcanman]

Funny that you should ask this. Just yesterday, I calculated that very problem. Using Manning's equation (open channel flow) for a 1" (standard steel, 1.049" id) line @ 1/8" slope, it will handle 2.67 gpm of flow (full pipe flow). How much condensate is that? Using psychrometrics, assuming 95/80 outside air dehumidified to 55/54, I calculated that it would require about 17000 cfm to produce that flow rate of condensate. That is an outside air load of 132 tons.

I never use less than a 1" pipe for condensate drainage, because as others have said, debris can clog the line if it is too small.

An 1-1/4" line can handle about 33960 cfm of outside air going from 95/80 to 55/54.

 

[DRWeig]

My old reference chart says 0.0224 gpm/latent ton.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[ProcessHVAC]

Unless there are any restriction, we always go with the >1" regardless of the coil size, only because small lines tend to clog easily.

 

[hvacpiper]

Plumbing codes generally govern condensate disposal (U.S. anyway).

CarolinaPE has the sizing right,those are the current values given from the IPC(2009 edition)Section 314.

Btw, do the plumbers a favor and stay away from using 1 1/4",especially if it's PVC,it's increasingly hard to find,and generally costs more then using 1 1/2".

Also keep in mind,that condensate disposal falls under the jurisdiction of the plumbing inspectors,and when combining mulitiple condensate lines to a single source,the condensate system has to be piped in,according to the plumbing code,which means the use use of Wye's and T-Wye fittings,for branch connections.Those fittings are not available in sizes smaller then 1 1/4".

 

[MTES93]

IMC-2009 Section 307.2.2 Table 307.2.2.

CarolinaPE nailed it as it is the same as this table....

agree w/ the clogging thing.... but here is a starting point.

 

[ChasBean1]

It all depends on latent load. It’s common for main AHUs to dehumidify while local FCUs cool sensibly and are not designed to provide any latent cooling. For these, ¾” is not unusual as real condensation could be an occasional drip…

I completely disagree with Chicopee (nothing personal). You wouldn’t size drainage to have a certain velocity to purge dust and contaminants… the bigger the better. Go a little larger if you are unsure.