Natural resources are renewable energy and available in abundance on the mother earth. After facing a lot of environmental issues, mankind has understood the importance of harnessing or using natural resources instead of fossil fuels which be finished sooner or later as well as creating a harmful impact on the environment. Looking to this phenomena SSC has started an initiative with a new series of articles on “Harnessing Natural Resources in Industrial Steel Building (PEB)” and we are pleased to present our first article on the usage of Wind Energy in designing of Industrial Steel Buildings.
Mankind wanted to harness natural forces since creation. They wanted either to divert the energy to avert its disastrous force or to utilize the energy for the wellness of human beings. Wind energy is one of the abundant energy and available at every location. Checkout the utilization of wind force in modern large Pre-Engineered Building for natural ventilation.
The wind has a natural tendency to rush from cold air region to hot air region. Its second property is hot air move up-ward. These two principles are used to maintain ventilation of modern steel buildings. And that too, in a natural way, using natural wind energy.
In all modern steel buildings, there are two factors related to the wind that is considered, while designing a Steel (PEB) Building. One is Maximum wind speed in the location of the building for the last 50 years. Secondly, how many air changes are necessary for that area of the building. Normally wind volume is calculated as (L x B x H) x No. of air changes required per minute in the building. The number of air changes requirements is determined by the type of product and heat/fumes generated in the production process. If the building is for Rolling Mill of a steel plant, then obviously heat generated by the system is huge and special arrangements must be made to increase the number of air changes inside the building per hour.
There are two ways, air circulation is made inside the building. One is Forced Draught, where the air is forced out with the help of Exhaust fan. The other method is through Induced Draught, where the natural property of air is utilized to ventilate the building. This is done through the building components. We will be focusing on the second method of air circulation.
The induced draught application is made by following building components: Louvers, Turbo vent, Roof Monitor, Gable end openings, Air Chute, Trap Doors / Windows, Smoke Ventilators. All these units are indicated in the diagram referred below:
Louvers:
This is basically the window of the building but the speciality is the baffles, which are curved in shape so that it allows air only and no rain along with it. A typical representation of how wind flows inside the building and the design of baffles is given below
Turbo Ventilators:
These are specially designed rooftop mountings, which operates naturally, without any energy source. The hot air inside the building flows naturally out of the building through this device. Ventilators may be fixed curved vane and fixed straight vane.
For Natural ventilation, the inlet area and exhaust outlet area of Ventilators are calculated as per the following formula:
Legend:
Fj = Exhaust hole area (m²)
Fp = Ventilator Inlet hole area (m²)
Gp = Gross ventilation Quantity in the Exhaust side (kg/sec)
Gj = Gross ventilation Quantity in Inlet side (kg / sec)
g = Gravitational acceleration
hp = Height from top to Exhaust hole (m)
hj = Height from top to ventilator inlet hole (m)
Air density outside (kg/m3)
Air density of average temperature inside (kg/m3)
= Partial resistance co-efficient of the air inlet
= Partial resistance co-efficient of the air inlet
= Partial resistance co-efficient of the exhaust outlet
These calculations are necessary to figure out the inlet dia of the turbo vent to be installed. The nearest higher available size (dia in mm) is chosen from the standard size of availability.
Turbovents are made up of various materials: GI sheet, Aluminium (AL), Stainless Steel (SS), PolyCarbonate (PC) sheet. MOC is chosen depending on the application and area of installation. In the seaside area, where atmospheric corrosion is high, Stainless Steel or Polycarbonate is preferred. It is industry-driven too. If the plant where it is being installed is handling chemical or corrosive material, there SS or PC is preferred. Where both high heat and chemical fumes are to handle, SS is the only recommendation.
For a fixed number of air changes, it is very important to calculate exactly, how many turbo vents are required for a building. It is calculated as per the formula:
Legend:
Vol = Indoor Volume of Building (m3)
N = no. of air changes per hour
Lp = Standard wind speed according to the local weather record ( m/sec)
n = No of ventilators required for the building
Turbo ventilators are not necessarily placed in sequence intervals or symmetrically. These are placed specifically where the ventilation requirement is more. For example, if there is a heavy-duty gas cutting machine is installed in a building, and not much fume generation in other areas, then there will be more concentration of turbo vents in the gas cutting area.
It modern PEB buildings, the base of turbo vent is made out of the same roofing sheet for aesthetical uniformity. On the other hand, Transparent Polycarbonate sheets are used as the base material to allow daylight coming in the building.
Although Number of air changes are non-specific, however, a table of industry-wise building and corresponding desired air changes is depicted in the following table:
| Building Type | Air Changes/Minute | Building Type | Air Changes/Minute |
|---|---|---|---|
| Top Floor | 2-4 | Forging Shop | 1-2 |
| Boiler Room | 1-4 | Foundry Shop | 1-3 |
| Bowling Alley | 2-8 | Glass Factory | 1-2 |
| Machine Room | 1-2 | Theatre | 3-8 |
| School Building | 4-15 | Metal Workshop | 3-6 |
| Light Workshop | 5-10 | Electrical Engine Shop | 2-6 |
| Heavy Workshop | 1-6 | Warehouse | 10-15 |
In this way, we can use wind energy in a natural way which reduces the usage of electricity for ventilation purposes. We will this series on a continuous basis and in the next article, we will bring insights on Forced Air Ventilation, Roof Monitors, and Smoke Wents. It’s on-going series and we can accommodate your feedback for improvement of the same. Do let us know in case of any specific need in the comments section.