Sizing condensate drain lines 1

[cme]

I've got a dormitory project with 2 dorm buildings and 3 floors each building and the HVAC system is 4 pipe fan coils with air handling unit for ventilation make-up air. Where can I find info on sizing condensate drain lines? Are they discharged into the sanitary system or rainwater system or into a drywell outside the biulding? I am an HVAC engineer but have minimal plumbing system experience and am learning as I go. The International Plumbing Code applies to the project. I am planning on using PVC pipe and does the pipe need to be insulated?

 

[kico]

Hi CME,
My standard condensate drain detail has the following table, but I don't remember how I got these sizes:
0-20 tons 3/4"
21-40 tons 1"
41-90 tons 1-1/4"

Also, you should be able to calculate the amount of moisture being condensed and then size the pipe based on sanitary pipe sizing per code.

Per code, condensate drain lines must be tied into the sanitary drain system by means of an indirect waste connection. Where cities allow drywells, they work fine.

It is good practice to insulate condensate drain lines inside the building. Depending on where the building is located, pipe surface temperature may condense moisture out of the air.

 

[imok2]

The most recent code is the International Mechanical Code (IMC). There was considerable discussion of the condensate disposal requirements. As far as trap requirements, the IMC leaves them in the hands of the manufacturer. If the manufacturer requires a trap, then a trap is required. If the manufacturer does not require a trap, then a trap is not required.

I have found that the majority of residential air handlers do not require a trap, while the majority of commercial air handlers recommend a trap. When asked the reason for the trap, the engineers for the manufacturers respond that the trap allows the drain pan to work properly. Without a trap, the pressure within the drain pan and coil area is not isolated, and the condensate will not drain.

As for the corrosive nature of condensate, for some of the high-efficiency equipment, the manufacturers have pointed out that the condensate is highly corrosive. They state that the trap and drain should be ABS or PVC and not cast iron or copper.

 

[wilg]

Minimum condensate drain size:
0-20 tons.... 1"
21-40 tons.... 1-1/4"
41-60 tons.... 1-1/2"
61-100 tons... 2"
101-250 tons... 3"
251 & larger... 4"

AC condensate flow...
Range: 0.02-0.08 GPM/ton
Average: 0.04 GPM/ton
Unitary Packaged AC equipment: 0.006 Gpm/ton
Air Handling Units (100% outside air): 0.100/gpm/1,000 cfm
Air Handling Units (50% outside air): 0.065/gpm/1,000 cfm
Air Handling Units (25% outside air): 0.048/gpm/1,000 cfm
Air Handling Units (15% outside air): 0.041/gpm/1,000 cfm

Pipe size shall not be smaller than drain pan outlet.
Minimum size below grade and below ground floor shall
be 2-1/2". Drain shall have a minimum slope of 1/8"/ft

Verify pipe sizing and discharge requirements with
local authorities and codes.

Depth of trap must exceed by one pipe diameter the
total static pressure of fan.