Green Building: Louvers in Natural Ventilation

Home » Green Building: Louvers in Natural Ventilation

A Paradigm Shift to Sustainability

 

In recent years, the exposure of the construction industry to green building concepts has led to concepts such as building sustainability. In Malaysia, the percentage of energy consumed by buildings is 48% and this value is expected to increase as we progress further developmentally; transitioning from an agricultural-based economy to a technological and services-based economy (Hassan et al., 2014; Shaikh et al., 2017). Malaysia’s consumption of energy is growing exponentially, from approximately 26,000 kilotons of oil equivalent (ktoe) in 1997 to 62,000 ktoe in 2017 – an increase of more than double the energy consumption within the span of 20 years (Energy Commission Malaysia, 2019).

 

In the US, buildings consume the most percentage of energy at 76% of the total energy produced. Out of which, 35% of the aforementioned value is used for HVAC systems (Department of Energy, 2015). This has led to a particular focus for the reduction of excess energy use in building HVAC systems (U.S. Green Building Council, 2000), which includes the introduction of natural ventilation in buildings. The usage of natural ventilation can be further enhanced by using louvers.

 

Applicability of Louvers

 

A few concepts need to be weighed when considering the implementation of louvers in buildings for airflow. Infiltration of rainwater can lead to a whole host of predicaments inside a building. Thus an important variable is, to determine whether the installation of louvers require high water penetration resistance. Ignoring such variables could lead to quandaries that range from water damage to ceiling tiles and drywall, mould growth, equipment damage and personnel injury due to wet floors (AMCA International, 2016).

 

Subsequently, when considering installing a louver in a building, the direction of the building needs to be considered relative to the wind direction. Other variables such as weather and temperature also play a crucial role in determining the applicability of such technology.

 

Moving on, the energy conservation goal includes the percentage of a certain room or region that desires increased reliance on natural ventilation whilst achieving a reduced reliance on mechanical ventilation. This variable is closely linked to louver air penetration into a room.

 

Louver Pressure Drop

 

Estimating the pressure drop across a set of louvers can be done. Figure 1 shows the nomenclature of the equations required.

 

Figure 1: Louver pressure drop nomenclature.

 

The louver pressure drop can be calculate using the simple Bernouli’s equation:

 

Equation 1: Simplified Bernouli’s Equation

 

The modified volume flow rate for louver can be obtained by multiplying the velocity through the opening, the area of the opening, A and the coefficient of discharge, CD. On top of that when considering different wind angles,  the effectiveness of opening, Cv needs to be included. According to (ASHRAE, 2017, Chapter 16.14) Cv is assumed to be 0.5 to 0.6 for perpendicular winds and 0.25 to 0.35 for diagonal winds. However other researchers have proposed the coefficient Cv to range from about 0.4 for wind hitting an opening at a 45° angle of incidence to 0.8 for wind hitting directly at a 90° angle (Thorpe, 2017; Walker, 2016). A more accurate volume flow rate through the opening can be obtained through CFD simulation.

 

This equation is helpful to engineers to determine an accurate volume flow rate that enters a specific region. Certain building laws or green building accreditation require a minimal volume flow rate that enters a room. This is also useful to determine the velocity of wind passing through the louver.

 

Equation 2: Modified volume flow rate for louver

 

Subsequently, by substituting equation 2 into equation 1, the following equation for the pressure drop across a louver can be obtained:

 

Equation 3: Equation for pressure drop across louver.

 

A typical louver will have a pressure drop around 25 Pa. This depends on the geometry and the other aforementioned variables. This equation is imperative because it guides the engineer on how much pressure drop will be caused by the louver. Knowing this will enable the engineer to be certain that a negative backflow of air does not occur at the site of the installation. Conversely, this equation can also enable the engineer to design a negative backflow of air as required. This phenomenon can be observed in Figure 2 below.

 

Figure 2: Pressure differential as a result of varying wind velocity (Price Industries Limited, 2011).

 

As the incoming air velocity decreases, the static pressure increases. The airspeed on the windward side of the building is reduced as it collides with the building, thus this causes an increase in the static pressure at the windward opening. On the other hand, the airspeed on the top, sides and leeward side of the building increases. This causes a reduction in local static pressure, and thereby a pressure differential is observed throughout the interior and exterior of the building (Price Industries Limited, 2011).

 

In summary, natural ventilation through the integration of louvers in buildings is able to propose a plethora of solutions to uprising concerns at the global frontier for climate change. This is achieved through lower reliance on HVAC systems and a shift to higher reliance on natural ventilation. However as described in this article, the solution is not straightforward because of the inclusion of various variables, thus proper planning needs to be performed to ensure that adequate air supply is provided in compliance with local and international standards.

 

References

  1. AMCA International. (2016). Introduction to Intake and Exhaust Louvers An AMCA International White Paper. June. www.amca.org/whitepapers
  2. ASHRAE. (2017). ASHRAE Handbook Fundamentals.
  3. Department of Energy, U. (2015). AN ASSESSMENT OF ENERGY TECHNOLOGIES AND RESEARCH OPPORTUNITIES Chapter 5: Increasing Efficiency of Building Systems and Technologies.
  4. Energy Commission Malaysia. (2019). Malaysia Energy Statistics Handbook. 44–45. https://meih.st.gov.my/documents/10620/bcce78a2-5d54-49ae-b0dc-549dcacf93ae
  5. Hassan, J. S., Zin, R. M., Majid, M. Z. A., Balubaid, S., & Hainin, M. R. (2014). Building energy consumption in Malaysia: An overview. Jurnal Teknologi, 70(7), 33–38. https://doi.org/10.11113/jt.v70.3574
  6. Price Industries Limited. (2011). Engineering Guide Natural Ventilation.
  7. Shaikh, P. H., Nor, N. B. M., Sahito, A. A., Nallagownden, P., Elamvazuthi, I., & Shaikh, M. S. (2017). Building energy for sustainable development in Malaysia: A review. Renewable and Sustainable Energy Reviews, 75(May 2015). https://doi.org/10.1016/j.rser.2016.11.128
  8. Thorpe, D. (2017). Passive Solar Architecture Pocket Reference.
  9. U.S. Green Building Council. (2000). Optimize energy performance – LEED 2.0 – HVAC | U.S. Green Building Council. https://www.usgbc.org/credits/commercial-interiors/v20/eac13
  10. Walker, A. (2016). Natural Ventilation. National Renewable Energy Laboratory. https://www.wbdg.org/resources/natural-ventilation

 

 

Related Articles

0 Comments

Submit a Comment

Your email address will not be published. Required fields are marked *