<p>O&M for major energy systems and equipment </p><p>Ventilation ductwork</p><p>Topics: Introduction Symptoms of ductwork leaks Common ductwork problems Flexible ductwork Value of minimizing ductwork problems </p><p>Introduction</p><p>Duct leaks, poor installation and inadequate duct insulation will not only fail to deliver necessary conditioned air efficiently, it may even excessively condition spaces which will then require additional heating or cooling to compensate for excessive conditioning from the ductwork. Consider the following:</p><p>Symptoms of ductwork leaks  Go into the spaces through which ductwork passes and see if the air temperature is different than expected. This suggests leaks and/or inadequate insulation.  Leaks will make noise.  During an air balance, the airflow leaving the fan will be greater than the total airflow measured coming out of the diffusers.  When a fan is sped up to increase airflow to a space, the airflow does not significantly increase in the desired space. This is a symptom of pressure dependent leaks (the leaks get bigger as duct pressure is increased).</p><p>Common ductwork problems  Some ductwork systems were not well installed and some of the problems may be nearly impossible to repair. Many 1970’s systems now leak 30% or more due to the standard practices at the time of installation. In general, your best practice may be to repair what you can in the areas you can access and do everything you can to reduce the necessary system pressure. It may be cost effective to increase the size of problem terminal boxes, increase the size of problem duct branches and do the best you can to eliminate flexible ductwork.  Exposed rooftop ductwork deserves regular attention. It is not uncommon to find places where people walk over ductwork damaging insulation and allowing water inside large sections of insulation which reduces insulation effectiveness and rusts the ductwork. Seams in ductwork can open due to the flexing/denting of the ductwork. Note: These problems also apply to insulated pipes. </p><p>Flexible ductwork  Flexible ductwork can be a significant problem in that pinched or twisted ductwork will require excessive fan pressure to push the air through. This wastes fan energy and may cause excessive air noise throughout the system. Always try to minimize the length of flexible ductwork (3’ may be a practical maximum length) and use hard duct for making sharp turns. Flexible ductwork can also spring leaks where it attaches to hard duct and terminal boxes.  Flexible ductwork has been known to ooze air just like a “soaker hose” for watering your yard.  Please note that long specific lengths of “flex duct” may be found coiled up above an exhaust grill. This may be a method of exhaust fan sound attenuation and may be acceptable as long as it is carefully laid out and maintained so there are no kinks.</p><p>Value of minimizing ductwork problems</p><p> Some leaks will be obvious and easy to fix but they may be ignored for years. One medical center had ignored ductwork problems until they ran out of air. They had already sped up the fan and the motor was running hot. Instead of buying a new fan, they went on a “seek and repair” mission. They plugged test ports, repaired flex connections and found a bad seam. Most of these leaks were fairly obvious and easy to repair. Once ductwork was repaired, they found and installed the original smaller motor sheave which slowed down the fan and they no longer had ventilation problems.</p><p> A medical library was complaining about high temperature in a large west facing room. This room had always been a problem on sunny days. Maintenance staff had already increased the supply fan speed and reduced the supply air temperature to try and make the problem go away but now that the new computers were in, that irritating librarian was complaining again.</p><p> o One solution would be to increase fan speed and motor HP. This would increase energy consumption and ventilation system noise throughout the building. The heating system would also end up working year around because too much air that is too cold would be supplied to the rest of the building. o Another solution would be to install a dedicated AC system for the problem room. o The implemented solution was to improve the ventilation system by replacing long runs of twisted flexible duct with hard duct. The size of one terminal box, the diffuser and its ductwork were increased. Heat-reflecting film was applied to the west facing windows. (Surprisingly, the window film was not very noticeable from the outside.) Fan speed was reduced, the supply air temperature was increased and the rest of library is quieter. Energy savings paid for the retrofit in less than 2 months.</p>