Coal, Emissions, Policy & Regulations

The Use of Natural Ventilation for Power Plants

Issue 1 and Volume 119.

Installation of a high efficiency Roof Vent at Power Plant. Photo courtesy: Moffitt Corp.
Installation of a high efficiency Roof Vent at Power Plant. Photo courtesy: Moffitt Corp.

By Chris Sheheane, Caldwell/Sheheane Industrial

In certain parts of the country, working inside of a power plant during summer can be very challenging on both personnel and equipment. Also, the higher you go inside a power plant, the hotter it gets. The closer you get to the roof, you may start thinking, “If we could just cut a big hole in our roof, we could get rid of this heat.” Well, that would be called natural ventilation.

Over the years, many industries have discovered the benefits of natural ventilation. While the steel industry has utilized natural ventilation principles since its inception, industries such as paper production and glass plants to aluminum smelters and gypsum plants have all seen the advantages of natural ventilation as well. Power plants however, have been slow to adopt to this technology mainly due to a lack of exposure and understanding of a “natural ventilation System” and its benefits. Such benefits include a reduction of plant energy consumption, reduced maintenance costs in parts and labor and in some cases is viewed as “going green”.

Oftentimes powered fans and equipment are used out of habit or “common sense.” Natural ventilation was dismissed as unpredictable and the potential savings in the electric bill seemed inconsequential. However, in the past few years, due to many plants looking at ways to reduce their footprint as well as costs, Power Plants have been adopting natural ventilation. Power plants are in the business of producing and selling power and by using a natural ventilation system a plant can sell more power rather than consuming it to run a Mechanical System.

In fact, since 2010, Southern Company has put natural ventilation systems in place at 5 different plant sites. They were installed at various plant sites for various applications but the ultimate goal at each site was to reduce the heat load inside the building and to help keep Plant personnel and equipment cool. In doing so, these plants have seen a reduction of maintenance costs that were associated with previous mechanical systems. Plant personnel do not have to change out moving parts and pieces associated with mechanical systems and now they are able to sell the power that was being used to operate the mechanical systems instead of consuming it. Over the course of a few years, this equals significant savings to the plant.

Installation of labyrinth roof vents on penthouse of a precipitator. Photo courtesy: Moffitt Corp.
Installation of labyrinth roof vents on penthouse of a precipitator. Photo courtesy: Moffitt Corp.

One of the plants located in West Alabama was having issues with the heat inside of the Penthouse of a Precipitator. This power plant would get very hot during the middle of the day making it almost impossible for plant staff to do maintenance work inside of the Penthouse. These penthouses did not have access to electricity so the plant had to bring in generators for lighting and ventilation purposes each time they had to perform maintenance work making it costly to the plant. Temperatures inside the penthouses would get up to around 115 degrees in the late afternoons which only allowed the workers limited time inside to perform their work. By installing weatherproof roof vents and wall louvers, the hot stagnant air was able to more freely move about the facility. Natural ventilation increased internal airflow, leading to a cooler work floor and more comfortable, more productive plant personnel. The Natural ventilation system was able to reduce the temperature inside by more than 20 degrees allowing plant personnel to work continuously instead of on a limited time basis as was the case before the installation. One of the other benefits of adding the natural ventilation system was that it allowed natural light into the Penthouses, therefore the plant no longer needed to bring in generators for lighting and ventilation purposes.

Natural ventilation works on the principles of gravity and natural air flow. Warm air has a natural propensity to rise and placing a natural ventilator on the roof allows this warm air to escape. This process is aided by placing wall louvers at the ground level to push fresh, clean air into the building. This creates an airflow cycle that then pushes out the hot stagnant air at an increased rate. A cycle of air, flowing through the building helps keep the interior environment and plant personnel cool.

Maintaining a consistently cool temperature, and more importantly, adapting to changes in temperature are crucial for keeping a building’s interior comfortable. As the day goes on and the temperature increases, a natural ventilation System is self-compensating with the cycle of air moving through the building increasing as the temperatures rise, keeping the interior space cool.

Of course not every environment is ideal for natural ventilation. There are certain requirements to ensure that the air will flow at the proper rate to make natural ventilation effective. For instance, a building needs to be of a certain height (typically 24 feet and higher) to allow for a proper stack effect for air movement. Additionally, natural ventilation works best in a facility that is already producing its own heat. Of course, power plants often meet these requirements, making them good candidates for natural ventilation.

Advancements in technology, such as computational fluid dynamics (CFD), help better illustrate the effectiveness of natural ventilation. A CFD analysis is an effective tool for determining how to best ventilate a building. By inputting the building dimensions, heat sources, and surrounding areas, a CFD model can stimulate the transfers of energy though the building. Utilizing thermal imaging technology CFD modeling helps determine the best design for a ventilation system and depicts the results as easy to interpret 3D models.

CFD modeling allows for a more effective ventilation solution to be made for a given building. Various factors, such as placement of vents and louvers, temperature changes, and weather conditions throughout the year can all be tested before construction ever takes place. This ability to better determine the necessary vent size and placement allows for natural ventilation systems that are more effective than ever before, greatly reducing hot-spots and dead zones.

Utilizing the natural flow of air and heat means a ventilation system with no fans and in turn, no consumption of electricity. Of course, many plant managers will argue that electricity costs are hardly an issue and that the energy it takes to power fans is insignificant. However, with the push from customers and local governments to go green, reduce their footprint and be more efficient, many facilities are seeing the benefits of implementing green practices.

Energy costs are not the only issue when it comes to a Mechanical Ventilation System. Any fan or powered ventilation system has moving parts and therefore needs maintenance and repair more often. Whereas the failure of a few fans can lead to the work floor quickly becoming unbearable or difficult to operate. We often walk into a plant and find that many roof fans are not in operation due to a lack of maintenance. Changing belts or replacing a motor on a rooftop fan can get expensive and time consuming, especially if the fan (or fans) are not easy to access. Often times, these fans will sit inoperable until a normally scheduled PM takes place, therefore creating higher temperatures inside the building. A Natural ventilation system is continuously operating with no moving parts to break or wear down. Wall louvers, roof vents and other natural ventilation products last for a long time before requiring any attention or replacement.

Of course, for all of its benefits, natural ventilation does not work in all power plants. If the building is not high enough to allow for proper air flow, it would be a bad candidate for natural ventilation. A certain height is needed to ensure that the air will rise through the building at the proper rate. Additionally, a plant where the turbine hall is enclosed would also be unable to utilize natural ventilation. Other issues such as environments with persistent bad weather or plants in certain areas, will make natural ventilation a poor option.

However, due to the advancements in design technology, the increasing need to reduce power consumption, and the long-lasting life of the equipment, more and more power plants are implementing natural ventilation techniques.

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