Story by Tony Albers
As a former technical support representative, I have heard many amazing stories over the years and have been on some unusual job site visits. The following article details one of those unusual visits.
A contractor phoned in to the technical support department to report his company was unable to locate a water leak coming from the rooftop area, where a new 20-ton, down-discharge, packaged rooftop unit had been installed last summer. The contractor explained that the water leak seems to only appear when it is raining. A roofing company had been called out several times to fix this leak, but they were unable to locate it. The contractor also tried to resolve the problem but the leak seemed to only get worse. Now when it rained, water leaked onto the workers directly below the unit. The contractor was convinced the unit was at fault and the building owner was understandably agitated. Unable to resolve the problem over the phone, I arranged to meet the contractor at his job site.
First, we inspected the occupied space that was getting wet. After removing the wet ceiling tiles, we observed that the water stains seemed to be coming from inside the return air plenum. Leaving his helper downstairs with a two-way radio, the contractor led the building owner and myself to the roof where there was a garden hose placed to simulate rain. Before taking apart the package unit, we inspected the surrounding rooftop area for clues. The only unusual item was the unit’s roof curb – it was heavily coated with mastic from the roofing company, trying desperately to make it waterproof.
We inspected the PVC condensate trap located outside the unit; it was accurate at 4 inches deep and unobstructed. The contractor removed several panels and gained access to the return air section of the unit. The condensate pan was clean and empty. I noticed numerous hard water deposits in the return air section from past water leaks, but found no evidence of their starting point.
Convinced that the water was not being produced inside the unit, I had him reinstalled the panels and turned the thermostat to the “fan on position.” He then flooded the roof area around the base of the unit with the garden hose – no water leaks were found. Next, he carefully flooded the area only around the power exhaust and then the economizer. Still, no leaks were found. The final test was to apply water to the package unit’s top and sides. Not wanting to flood the whole unit at once, we applied the water systematically, first at the base and then at each panel. As soon as water was introduced at the base of the unit, the contractor’s helper was yelling over the radio to turn off the garden hose.
As the mystery was closer to being solved, the panels were quickly removed and flashlights were drawn. We inspected the inside of the unit around the base but didn’t find it wet. The area that was wet was the underside of the package unit’s top panel. I was glad we were able to duplicate the building owner’s water leak but both the contractor and building owner were puzzled on how water, when applied around the base of a unit, could travel uphill 45 inches to the underside of the top panel and produce a water leak. I answered that excessive return air static pressure could cause water to be drawn up the unit’s corner posts and flung into the return air cabinet.
The contractor did not have a static pressure gauge (known as a manometer) to prove this theory, but we inspected the corner posts and they were also wet. As we walked back downstairs to inspect the return air ductwork, I asked the contractor if he had checked the static pressures when he originally installed the unit, to which he answered that he had not.
As we arrived downstairs, I found the key to their water leak problem – the 20-ton package unit that was installed last summer had a single 18 inch return air duct (that was over 40 feet in length). This equated to a heavily restricted return for the quantity of airflow required by the 20-ton unit. This caused such a dramatic negative pressure that rain water was being sucked into the unit. The contractor, in the face of the building owner, learned two valuable lessons the hard way. First, too appropriately size the ductwork. And second, always perform a thorough start-up and unit check which should include adjusting CFM and static pressures whenever possible.
This is a lesson for contractors and installers in the field. The HVAC industry is constantly changing and following the instructions sent with the equipment can save time, money, and possibly embarrassment. There are many classes offered by manufacturers, distributors, trade schools, and trade organizations that cover the latest in servicing and installing equipment.
About the Author: Tony Albers is a highly successful trainer who has taught heating and air conditioning classes designed specifically to meet the needs of today’s busy technicians and engineers. For the past 33 years he has worked to advance the field of heating and air conditioning by teaching classes for IHACI, RSES, Southern California Gas Company, and San Diego Gas & Electric. In the last 23 years he has traveled extensively throughout North America for US Air Conditioning Distributors and Venstar, giving workshops and seminars for large HVAC distributors and manufacturers. Albers has been on the Continuing Education Committee for the Institute of Heating and Air Conditioning Industries and has written articles for Indoor Comfort News, HVAC Insider, and the Southern California Chapter of ASHRAE.