COOLING COILS CONDENSATE DRAINAGE AND COLLECTION

Cooling coils produce condensate at a rate approximately as follows:

GPH = 0.53 x CFMOA x (H - 0.0078)

where CFMOA is the outdoor airflow rate and H is the average outdoor humidity ratio (lb of water/lb of dry air) during the summer cooling season (normally May through September). This data should be computed from monthly weather data for the project location available from NOAA.

For most comfort conditioning applications, condensate drain lines can be sized in accordance with the following table:

Gravity Condensate Drain Pipe Sizing
(Flowing full at 1% slope)
Pipe Size (in) / Max Coil Load (tons)
3/4 / 2
1 / 5
1-1/4 / 30
1-1/2 / 50
2 / 160
3 / 300
4 / 430

However, for applications with high ventilation rates (i.e., 40% outdoor air or higher), the drain piping must be sized for the anticipated peak condensate flow rate, computed from the equation above when the value of H is the outdoor humidity ratio at peak cooling load design conditions, and the following table:

Gravity Condensate Drain Pipe Sizing
(Flowing full at 1% slope) /
Pipe Size (in) / Max GPH /
3/4 / 96
1 / 204
1-1/4 / 360
1-1/2 / 582
2 / 1242
3 / 3618
4 / 7680

Where possible, recovery of cooling coil condensate for cooling tower make-up water or other use should be part of the design. However, there are limitations on the use of condensate due to water quality issues. Condensate contamination can occur from two sources: (1) air contaminants that are not removed by filtration and impinge on cooling coil surfaces, ultimately draining into the coil pan, and (2) drain pan biologic contaminants, along with chemical contaminants introduced by anti-biologic water treatment tablets. Thus, the best application for recovered condensate is for cooling tower or evaporative cooler make-up since this equipment is already equipped with water treatment systems to deal with the types of contamination that may introduced. Any other application will typically require the use of a treatment system to remove contaminants.

HVAC Design Guidelines

COOLING COILS CONDENSATE 1