How to Avoid the High-Temperature (and Odorous) Exhaust Associated with Diesel Generators

by Matt Gaedtke |

Electricity. Practically everyone uses it. We power everything from a children's toy to hearing aids using some form of electrical power. Electric power makes life productive and comfortable. Sometimes, it even saves lives.

However, what happens when the power is interrupted? For most, it's an irritation. Still, in some situations, it is the difference between life and death. The possibility of power interruption is why some applications rely on backup power. Hospitals, laboratories, data centers, and other mission-critical facilities almost always use backup power sources. These sources often are diesel-powered generators.

Diesel generators are fuel-efficient and run longer—helpful in the event of a long-term power outage. These generators, while providing life-saving electricity, also have a darker side.

The complaint against diesel generators comes from the high temperatures it produces, along with the distinctive smokey odor. This combination of a noxious odor and high temperature causes problems when the generator is operating. Placement of the exhaust stack and changing wind direction can cause the smoke, heat, and odor to re-entrain into the facility or a neighboring building.

One Solution

Most diesel generators are very heavy, often requiring placement on the lowest floor of a building. Generators can range widely in power generation capabilities depending on the use. For example, a 1500kW generator can produce 12,000 cfm of exhaust fumes. The temperature of those fumes can exceed 775°F.

Exhausting those fumes requires ductwork running from the generator to the building roof deck. The ductwork connects to an exhaust stack. The variables of exhausting these fumes often cause air quality issues inside the facility and neighboring buildings.

One solution to prevent re-entrainment uses extended roof stacks. The extended roof stack will place the exhaust higher above the roof deck. However, this solution does have its own set of challenges.

  • Added cost
  • Additional back pressure on the diesel generator
  • Aesthetics

  • The Best Solution

    The previous solution addressed the high-temp, odorous exhaust coming from a diesel generator. However, the additional cost, stress on the generator, and aesthetics make this solution a poor choice. The best solution allows the high-temp exhaust to enter a bypass plenum where it mixes with ambient air. (Figure 1)

    Avoid_the_High-Temperature_and_Odorous_Exhaust Figure 1
     Figure 1

    This mixing cools and dilutes the hot and harmful exhaust. Then, an exhaust fan designed for high temperatures pulls the air through a high-plume dilution nozzle, where the exhaust cools and dilutes more. However, the most important aspect of the dilution nozzle is its ability to create stack height, propelling the exhaust effluent away from the facility roof deck and air intakes. The best part is that this dilution nozzle does so without the expense and impact on aesthetics. (Figure 2)

    Avoid_the_High-Temperature_and_Odorous_Exhaust Figure 2
     Figure 2


    Mission-critical operations such as those in hospitals and laboratories cannot be without power for extended periods. Diesel generators currently provide most backup options for these situations. However, these generators create high-temperature exhaust and diesel odors that can add cost and increase the potential for effluent re-entrainment.

    The best solution addresses all these concerns, reducing the effect of high-temperature exhaust, ensuring no exhaust reenters the building or nearby facilities, and does so without affecting building aesthetics.

    You can learn more about high-plume dilution systems for diesel generators and watch the following video to see the system in action.

    Laboratory Exhaust
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    Matt Gaedtke
    Matt Gaedtke
    Matt Gaedtke
    Matt Gaedtke is the segment manager for Greenheck’s fume exhaust and tubular inline products. He has a BS in Mechanical Engineering from the University of Wisconsin, Madison and an MBA from University of Wisconsin, Oshkosh. Matt has 26 years’ experience in sales, marketing, and applications of commercial and industrial fans and has presented on a variety of HVAC subjects including fan fundamentals, laboratory/hospital exhaust systems, enclosed parking facility exhaust, ammonia exhaust systems, and fan efficiency. Matt is a member of NE Wisconsin ASHRAE and is Chairman of AMCA International’s statistical program.
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