Thinking Inside the Box - Volume 2
More Stuff for the Five Pound Bag
by Moses D. F. Ling, PE, RA
When I was assigned my university office sometime ago, the previous occupant advised me to remind M&O to clean the air-handler condensate pan overhead each summer. Spring pollens would block the drainage path and cause water to drip onto the contents of the room. A more serious problem, I discovered was mold growth, as the tiles turned gradually darker one year.
In the recent editions of the International Mechanical Code (307.2.3), preventive measures have been added to mandate perceived answers with the intention of eliminating this risk. As with other code requirements, it is prudent to examine the offending problem as well as the cure.
Condensate is the moisture removed by cooling coils and collected by the drain pans in HVAC units. Proper disposal of this liquid is necessary. Window air-conditioners merely spit the moisture to the outside. Most other HVAC equipment have engineered systems which collect and dispose of this liquid. The destination of the condensate depends on the local regulations.
This type of issues is what architects pay engineering consultants to worry about, right? Implicit in this IMC mandate is the potential need to increase floor-to-floor heights and the predictable cost increase for Division 15. IMC offers three alternatives for the prevention of this potential problem.
- Add an auxiliary drain pan under every cooling unit and provide a separate drain line, which discharges to a conspicuous point of disposal. By this means, the occupants is alerted of the problem. The pan must be 3” wider in length and width than the unit and at least 1½” deep.
- Install a separate overflow drain line located higher on the equipment primary drain pan. Such overflow drains shall discharge to a conspicuous point and alert the occupants.
- Provide a drain pan similar to Option 1, but no drainage piping. Install a water level detection device in the pan to shut off the equipment if water is detected.
Most manufacturers do not yet provide a secondary overflow drain as outlined in option 2, leaving the external auxiliary drain pan the only choice. In above-ceiling applications, it adds height to the space needed to accommodate the mechanical equipment. The drain line, required by Option 1, needs additional ceiling space below the bottom of the secondary drain pan for the piping to slope properly. Depending on the travel distance, this may lower the ceiling another 4” or 5”. Further more, drain pans hanging below the units may limit accessibility to the units.
Trying to comply with “conspicuous point of disposal alerting the occupants” is not a simple task. I am not aware of available devices for this purpose. What conspicuous solution is acceptable to the architect, the owner, and the engineer? Would simply letting the carpet get wet qualify?
If one analyzes the basic rationale for this provision, it would become apparent that the perceived problem is a result of poor housekeeping. If maintenance practices of HVAC systems were diligently followed, the designs might be spared some of these belt and suspender solutions. If we extend this line of thinking, pretty soon we will be adding secondary drain pans and alarms below everything that holds liquid. My coffee cup is the next candidate.