Building Systems and Services - Research Paper Example

Running head: VENTILATION Research Paper on Ventilation May 7, This research is a collection ofconcepts and principles related to ventilation of building. It begins by defining ventilation and the reasons that it is used in building design. It is followed by a section on building designs for improved natural ventilation. The next two sections discusses artificial ventilation in terms of cooling loads and factors that affect cooling loads, while the paper ends by differentiating two fire protection systems that involve building ventilation design. Ventilation Ventilation is the process of supplying and removing air by natural or mechanical means to and from any space (Adler, 1999, p. 38-23). Because it is concerned with air movement, it has significant impact on human comfort and safety. Human comfort while inside a building can be objectively defined using the concept of thermal comfort. It is achieved when the amount of heat produced in the human body balances with the heat it loses through various activities. Basic metabolic process, human activity, indoor thermal conditions are some of the factors that produce heat in the human body. As such heat is released; its interaction with the environment determines the rate of the heat loss. As the human body loses heat, the ventilation of its environment can take away the heat, e.g. supplying cold air during summer, or preserve the heat, say minimal ventilation or supplying hot air during winter. The other essential reason for applying ventilation in buildings is to ensure environment safety in terms of good indoor air quality. Poor air quality means that the air surrounding the human contains noxious gases and particles that are not safe for the human respiratory system (Air Pollution, 2009, p. 944). Since the human body needs oxygen to survive, an indoor environment that is lacking sufficient supply of oxygen will harm the human. Thus, the building needs to be ventilated with better quality air in order to bring more oxygen in and extract the polluted air away from the human’s environment. Improved Performance of Natural Ventilation Natural ventilation is achieved by considering air movement and air pressure. Cross- ventilation considers that pressure difference as wind passes through a building (Adler, 1999, p. 38-23). The wind movement causes the air entering the building to push out the lighter, negative pressure air inside the building. Apart from speed of the wind, the orientation of the building and location of its openings determine the best design to achieve cross-ventilation. Warmer air is more buoyant than cooler air therefore, when mixed together in a space where the warmer air rise on top of cooler air. This is known as the stack effect (Adler, 1999, p. 38-22). When applied to buildings where the inside air is warmer, letting the cooler outside air in pushes the warmer air up and out to an exhaust opening, naturally. To apply the two principles of natural ventilation in building design, below are possible strategies: 1. Orient the building and its openings perpendicular to the movement of the wind. This will ensure that the building will intercept the wind movement at its peak, thus maximizing the pressure difference of air entering and leaving the building. A useful reference on wind behavior is the Bureau of Meteorology website featuring maps of Australia’s wind roses at http://www.bom.gov.au/climate/averages/wind/index.shtml (2005). 2. Keep building width to a maximum of 45 ft (Walker, 2010) to maximize effectiveness of the stack effect. An example of this is recommended by Hurburgh, was used on a building with long and narrow floor plate with air entering from the North and operable vents allow for air with negative pressure to exit at the South (2005). 3. Introduce openings at the highest building elements to maximize the stack effect. Using the ridge roof for example, provide for provide for an unobstructed opening on the entire ridge to draw hot air up and out of the building. If skylights are included in the design, install it while considering allowance for air flow within the structure. 4. On areas with cold nights and warm days like in the New South Wales, consider a closed-building design to keep warm air from entering the building. At nights where the temperature is colder, outside air is allowed to enter and cool the mass of the building. During the day, the whole building is closed to shut out the warmer outside air while allowing occupants to exchange radiant heat with the already-cooled mass of the building. 5. For buildings with multiple floors, include an atrium in the whole building design which will serve as a large chimney where warm air can rise and be exhausted. Ensure that the position of the building as well as the openings will allow for maximum change in wind pressure in both the cross-ventilation principle and the stack principle. Cooling Load The term cooling load is defined as the energy required in maintaining a comfortable level inside a building. The normal body temperature is 37 °C. In order to maintain comfort, the environment surrounding the body should ideally keep the body in the same temperature level at all times. Thus, the air surrounding the body should be conditioned to remove whatever heat is given off by the body and its activities as well as the heat contributed by the environment. Thus, cooling load is a determining factor in designing the air conditioning system of a building in order to maintain human comfort. Factors Required for Space Design Cooling Load Calculation 1. Building Composition The materials used in constructing the building are a major factor of consideration in cooling load calculation. The quality of the material—composition, density and construction, will dictate the capability of the building to retain or give off heat, or its thermal capacity (Adler, 1999, p. 38-3). A building made of steel and wood for example will easily absorb heat from the sun and conduct such heat to the inside of the building. As such, the air conditioning design or cooling load capacity of the building will need to consider the heat conducted by the walls of the building. On the other hand, a building made of concrete, which has a higher thermal capacity than wood, is thicker and denser, and thus can resist the outside heat more than wood. Thus, the inside of a building made of concrete may need less cooling load than a building made of light materials such as wood. 2. Infiltration Infiltration or air leakage is defined as an “uncontrolled movement of air in to and out of a building which is not for the specific and planned purpose of exhausting stale air or bringing in fresh air” (Building Sciences, 2004). Loosely constructed walls with small cracks, gaps in between walls and window panels, ceilings and attic hatches or exhaust pipes are some examples of installations with possible air leakage. Buildings can be tested for air leakage using methods applying fluid dynamics to understand how much air movement and heat loss is contributed by the leaks. When the air infiltration level is measured in terms of cubic meter per hour per square meter of building, the information will be considered in the cooling load requirement. 3. People Heat generated by the occupants of the building and the activities performed by the occupants also contribute to the cooling load calculation. The human body has basic metabolic functions that give off heat in order to maintain its normal body temperature. In addition, the activities that people conduct in a given space will also generate heat. An office worker for example, who spends his day on his desk doing light office work, generates significantly less heat than a worker on a metal fabrication shop. Such activities generate heat that needs to be considered when designing the cooling requirements of their respective workplaces. 4. Equipment Equipment inside the building is a factor in calculating cooling loads. A personal computer generates heat as it operates. If it operates an entire day, the heat given off by the computer will linger in the workspace. Multiply that say by ten or 100 more computers in a call center office space for example and that is the amount of heat that needs to be cooled during office hours so that the computer users will not feel the heat generated by all the machines. In the same manner, cooling a data center where bigger computing machines operate at extended periods of time will be cooled differently than a normal office workspace. Zone Pressurization System A zone pressurization system follows the building regulations mandated by National Fire Protection Association code 92 on the basic design guide for pressure differential system (Elovitz, 2006). The intent of the code is to prevent fire from crossing a zone that is classified as smoke free. As an example, building stairwells are designed to be smoke-free in case of a fire to allow for safe evacuation of occupants as well as easy access for fire fighters. Thus, stairwells are installed with a pressurization system that activates in the event of a fire. Recalling the discussion on the stack effect wherein warm air rises above cold air, the same principles hold true during a fire inside a stairwell which essentially is a stacked structure. Without pressurization, a fire occurring on the ground floor will emit smoke and fire to the upper floors since ambient air is colder than the on-going fire. This will prevent occupants from the higher floors to safely evacuate to the ground. A pressurization system then will activate fans to introduce positive pressure in the stairwell and push warmer (heated) air onto areas of less pressure, i.e. to the floors where the fire is on-going or to designated exhausts vents that will clear the path of the stairs. In designing the pressurization system, the number of doors open during the fire evacuation must be considered to ensure correct pressurization design. As per the code, the target pressure difference should be more than 0.15in(+37Pa) and not less than 0.35in(+87Pa) (Miller and Beasley, 2008, p.4). Air Purge System An air purge system is also a fire protection mechanism designed for buildings. Unlike the zone pressurization system that uses differential pressure to prevent the spread of smoke and fire, an air purge system uses buoyancy principles of air to create a clear space amidst the on-going fire. With an understanding that warm air rises, fire protection professionals have figured that as the air rises, especially in tall buildings, the air cools (Wild, 2008, p.6). As such, the cooled air remains buoyant and lingers at the high levels preventing the warmer air below from being exhausted. With an air purge system, the flow of warm air will be matched to create a pulling pressure at the higher floors to pull the buoyant air out of the building faster than the fire can create. Doing so creates a cleared air space where occupants of the building can escape without inhaling smoke or being burned References Adler, D. (Ed.). (1999). Metric handbook planning and design data, 2nd edition. Oxford, UK: Elsevier Ltd. Air Pollution. (2009). In The Columbia Encyclopedia (6th ed.). New York: Columbia University Press. Australian Government Bureau of Meteorology. (2005, May 6). The wind across Australia. Retrieved May 4, 2008, from http://www.bom.gov.au/climate/averages/wind/index.shtml. Building Sciences. (2004). Air leakage resource center. Retrieved on May 5, 2010 from http://www.airleakage.co.uk/what.htm#impact. Cooling load. (n.d.). McGraw-Hill Dictionary of Architecture and Construction. Retrieved May 03, 2010, from Answers.com Web site: http://www.answers.com/topic/cooling-load. Elovitz, K. M. (2006). Commissioning Smoke Control Systems. Fire Protection Engineering. Retrieved on May 6, 2010 at http://www.fpemag.com/archives/article.asp?issue_id=38&i=248. Hurburgh, T. (2005, June). Natural ventilation and lighting, ESD design guide - Video and transcript. Australian Government Department of the Environment and Heritage, June 2005. Retrieved on May 5, 2010 from http://www.environment.gov.au/settlements/publications/government/esd-design/natural.html Miller, R. S. & Beasley, D. (2008, August 8). Smoke control by pressurization in stairwells and elevator shaft. Retrieved on May 6, 2010, from http://afscc.org/Papers/Smoke_Control_by_Pressurization_in_Stairwells_and_Elevator_Shafts_080808.pdf. Walker, A. (2010). Natural Ventilation. Whole Building Design Guide. Retrieved on May 4, 2010 from http://www.wbdg.org/resources/naturalventilation.php. Wild, J. A. (2008, October). Fan applications in fire smoke control systems. Retrieved on May 6, 2010 from http://www.flaktwoods.com/a6446a99-1da8-40bb-b47a-a9394cd79f87 Read More