P-traps are often installed on air conditioner condensate drains to prevent air leaks. P-traps are designed to allow condensate to flow from the equipment while simultaneously preventing air leakage into or out of the unit. To prevent air leakage, the height of the water “h” (left figure above) in the trap must exceed the pressure created by the air handler with respect to the ambient environment, otherwise the water will be displaced and air will leak out of the trap. Condensate to fill the trap is only generated when the air conditioning is operating and the evaporator coil temperature is below the return air dew point. Therefore, unless the traps are sufficiently tall to hold condensate for months at a time, the trap will likely dry out and leak air during winter and spring/fall seasons, a problem that is exacerbated in dry climates. In these instances, heated and cooled air is lost to the outdoors, wasting energy.
The HVAC Air-trap from Des Champs Technologies is designed to eliminate air leakage from condensate drainpipes and reduce the space required for the trap. An example version of a trap is shown in the figure to the right (above). While there are designs that operate in negative and positive pressure orientations, the example in the above figure is for an air handler that operates at negative pressure with respect to the environment. When no condensate is present, the negative air pressure pulls the lightweight ball against a seal to reduce leakage. When condensate is present, the water pressure moves the ball so that the water can drain.
Laboratory Testing and Analytical Model
WCEC researchers conducted laboratory testing of the Des Champs Technologies HVAC Air-Trap technology to measure its air leakage performance and assess its suitability as a replacement for standard p-traps. Additionally, an analytical model was developed to estimate the air leakage through an open condensate drainpipe.
First, researchers conducted lab testing to measure air leakage in a dry PVC pipe to validate the analytical model. The lab testing for the open pipe was conducted with the following parameters:
- Pipe length of 1 ft, 2 ft, 5 ft and 10 ft
- Pipe diameters of 0.75 in, 1.0 in, 1.25 in, and 1.5 in.
- External static differential pressures of ±0.5 inches of water column ( in W.C.), ±1 in W.C., ±2 in W.C., and ±3 in W.C., where a positive differential pressure means that the fan blows through the chamber in which the drain pan is located. Pipe lengths of 5ft and 10ft were only tested at positive pressure due to limitations of the test setup.
An additional test was conducted for the 1.0 in diameter, 2 ft long pipe with a p-trap at the positive pressure conditions.
Researchers compared laboratory testing results for the open condensate drainpipe to the analytical model for the same parameters tested.
Comparison of results from the analytical model and the lab tests for leakage rates. This is for all pipe lengths and diameters for each static pressure.
Researchers also conducted laboratory testing to measure the performance of the following Des Champs HVAC Air Traps at the listed pressures fitted onto the 1 ft length pipe:
- P-Series, positive pressure trap, diameters 0.75 in, 1.0 in, 1.25 in, and 1.5 in tested at differential pressures of +0.5 in W.C, +1 in W.C., +2 in W.C., and + 3 in W.C.
- N-Series, negative pressure trap, diameters 0.75 in, 1.0 in, 1.25 in, and 1.5 in tested at differential pressures of -0.5 in W.C, -1 in W.C., -2 in W.C., and -3 in W.C.
- RLC-Series, positive and negative pressure trap, diameter 0.75 in tested at differential pressures of ±0.5 in W.C, ±1 in W.C., ±2 in W.C., and ±3 in W.C.
- FCN-Series, positive and negative pressure trap, diameter 0.75 in tested at differential pressures of ±0.5 in W.C, ±1 in W.C., ±2 in W.C., and ±3 in W.C.
The Des Champs HVAC Air Traps were tested to measure the air leakage in comparison to the open pipe laboratory test results. Depending on the model, the air-traps were tested in positive and/or negative pressure orientations for pipe diameters corresponding to the trap size.
All four models of the HVAC Air-Traps showed a significant decrease in leakage compared to the open pipe tests. For all models tested at all pressures and pipe diameters, measured air leakage rates were less than 1 standard cubic feet per minute (SCFM), and 90% of the tests had leakage rates less than 0.5 SCFM. The results demonstrate the HVAC Air Trap is an excellent alternative to a p-trap that will reduce air leakage in a dry condensate drain line to a negligible amount.
HVAC Air Trap test results demonstrating that all traps tested at all pressures and pipe diameters had a leakage rate of 1 SCFM or less.
Sponsor: Des Champs Technologies