Passive Ventilation - Essay Example

Passive Ventilation Introduction Passive ventilation can be defined as a building design approach that aims at heat dissipation and heat gain control in a building. The main aim of this design is improving the indoor thermal comfort with nil or low energy consumption. The approach works by either inhibiting heat to enter the interior or through eliminating heat from the building. The natural cooling uses the on-site energy present from the natural environment in conjunction with the building components’ architectural design rather than the mechanical systems of heat dissipation. Natural cooling, therefore, depends on both the building’s architectural design and how it makes use of the local sites’ natural resources such as heat sinks. Examples of the on-site sinks include the outdoor air, the upper atmosphere and the soil/earth (Bodart and Evrard 2011, p.4). The passive cooling entails the entire natural techniques and processes of heat modulation and dissipation without using energy. Passive ventilation can be integrated together with simple mechanical systems such as economizers and pumps in passive cooling provided they will enhance the natural cooling process effectiveness. These applications are termed as the hybrid cooling systems. The passive ventilation/cooling can be broadly classified into heat dissipation or modulation techniques and preventive techniques. The preventive techniques focus on providing prevention and/or protection of internal and external heat gains. The heat dissipation and modulation techniques allow the building to dissipate heat gain and store through the heat transfer from the heat sinks to the climate. This technique may result in either natural cooling or thermal mass (Carey & Carey 2013, p.12). For passive ventilation to be successful in a building, there are some considerations that need to be incorporated as the document analyzes. Discussion Passive ventilation systems make use of a series of vents in the exterior walls or at the exterior windows to enhance the outdoor air to enter the building in a controlled manner. Wind, natural airflow and temperature differences in outdoor and indoor air help in drawing in fresh air and circulating it through the home. The fresh air forces the humid, polluted and warmer air into vertical ducts or thermal chimneys leading to the attic. This air is eventually exhausted outside. The fresh-air vents are designed specially to slow down the incoming air and dispersing it indoors. An adjustable precision damper available within the vent gives room for airflow regulation while the vents are equipped typically with a filter for screening out insects and dust (Bodart and Evrard 2010, p.24). Some of the fresh-air vents possess acoustical features used in masking the outdoor noises from the sources like trains, airplanes, and traffic. Passive ventilation has advantages over other modes of ventilation such as mechanical processes in that they allow improved air quality inside the home. The system is also silent and offers a home with improved ventilation. The system is economical and has low running cost. The passive ventilation system is maintenance free and consequently economical thus another advantage over methods of ventilation. Passive ventilation is not only energy saving but also environmentally friendly. These aspects make it a preferable mode of passive cooling in the building. The fact that the system is environmentally friendly it is hence suitable for installation in busy towns (Johansson et al. 2012, p.78). The passive ventilation principle is also applicable to open commercial building the same way it is in homes. There are some aspects; however, that need to be incorporated into the system to be effective in an open commercial building. An open commercial building tends to accommodate a relatively large group of people. This is an indication that the system needs to be well structured since the rate of heat dissipation from the building’s occupants is relatively high. For the passive ventilation principle to be effective in an open commercial building, the windows, roofs and walls of this building should be shaded from direct solar radiation (Steemers et al. 2000, p.37). This will help the building not acquire much heat from the sun and hence the building will not be extremely hot. Another strategy essential for the effectiveness of the passive ventilation principle in an open commercial building is using lighter colored roofs. These types of roofs reflect heat falling on the building rather than absorbing it. This aspect is crucial in that no heat is being added to the building. This will help the building’s interior to remain cool. The other strategy is using the buffer zones and insulation. Since there is much heat being radiated and conducted in this building as a result of economic activities going on in the building, this strategy will greatly help in minimizing heat gains. There should be limited or selective use of thermal mass (Treloar 2010, p.77). This will help in avoiding storage of daytime heat gains. The architectural design of this building should concentrate on maximizing the heat loss. There should, therefore, adequate mechanisms that will give room for a sustainable air movement in the building, entry of cooling breeze in the building, earth coupling, as well as a reflection of the radiations. These strategies will make the passive ventilation a success in an open commercial building. There are a number of requirements that need to be put into consideration when installing the passive ventilation. For one to achieve thermal comfort in the cooling applications, the building envelops designed in a way that they can minimize heat gain during daytime and maximize heat loss night time. The system should also encourage access to cool breeze whenever it is available. The building that is meant to incorporate the passive ventilation needs to consider the following requirements. One of the requirements needed is that the floor plan of that building and the building itself should be formed so as to respond to the local site and climate (Yao 2013, p.21). Thermal mass in that building is required to be positioned carefully so that it can store coolness rather than unwanted heat. The architecture is also required to choose windows and glazing that are appropriate to the climate around that building. Some glazing and windows will regulate the air in a certain type of environment while others will not work out in that area. The architecture is, therefore, required to be updated to the right quality of windows and glazing in a particular region and those of the other region. The other requirement essential for the realization of passive ventilation is the positioning of openings and windows (Gelfand & Duncan 2012, p.41). The openings and windows should be positioned in such a way that they can ensure cross ventilation and air movement. Well-positioning of the openings and ventilators will help in the maintenance of air circulation thus maintaining coolness in that building. It is also essential for one to shade windows, roofs and solar exposed walls where possible. The other requirement essential for the realization of passive ventilation or cooling is making use of the roof spaces and the outdoor living areas as the buffer zones (Yao 2013, p.22). This aspect plays a vital role in limiting the heat gain. There are various measures that enable passive design in an architectural design. One of the measures is the installation of cooling sources. Sources of passive cooling tend to be more complex and varied as opposed to passive heating that originates from a single and predictable source, the solar radiation. However, all these aspects need to be considered so as to achieve the real ventilation aspect. Air movement in a building is a very crucial aspect or measure that helps in the realization of passive ventilation aspect. Air movement cools people occupying the building through increasing evaporation. It also cools the entire building through carrying the building’s heat out as warmed air and replacing it with external air which is cooler (Reed 2010, p.41). The air movements call for well-designed openings such as doors, vents, and windows as well as unrestricted breeze paths. Air movement is essential in all types of climates. However, it might be less effective in high humidity periods. 0.5 m/s air speed is equivalent to 3 degrees Celsius drop in the temperature with relative humidity. Air movement tends to expose the skin to a more dry air. It is worth noting that air speed that exceeds 1.0 m/s causes discomfort. It is, therefore, crucial for the architecture to provide openings that will allow air to flow at the right speed. The cool breeze is another aspect that is essential when it comes to passive ventilation (Allard & Ghiaus 2005, p.21). Unlike the cool night air, the cool breezes take place in early evening or late afternoon when cooling requirements are at a peak. Cool breeze aspect is effective in open or narrow plan layouts. They usually rely on the air-pressure differentials caused by breezes or wind. They are less effective in small rooms that are independent and deep floor plans. They may also be ineffective in the areas where security is an issue or with high noise, or the quality of external air is poor. Such aspects may force windows to remain closed thereby obstructing the passive ventilation aspect (Brebbia et al. 2014, p.63) The other measure that is usually put into consideration when it comes to passive ventilation is the cool night air. The cool night air is a reliable source of cooling in the inland areas where the diurnal temperature exceeds 6-8 degrees Celsius, and cool breezes are limited (Bainbridge & Haggard 2011, p.45). The hot air being radiated from the building fabric’s thermal mass gets replaced with the cooler night air that tends to be drawn by the internal to external temperature differences rather than the breezes. The full height, double hung windows serves this purpose effectively. The other measure that is essential in creating the passive ventilation aspect is the convective air movement. The convection rule implies that the warm air rises while the cool air falls. The convective air movement tends to rely on the increased buoyancy of the warm air that rises to escape the building through the high-level outlets. This process helps in drawing in the lower level cool night air or the air of the cooler daytime from the shaded external regions or the evaporative cooling ponds as well as fountains (Chiras 2002, p.51). Convection causes warm air to rise thereby drawing in cool air. The convective air movement tends to improve the cross-ventilation and also overcomes numerous limitations of all unreliable cooling breezes. Even at the times when no breeze is available, convection gives room for heat to leave the building through the vented ridges and roof ventilators, clerestory windows, gables and ceilings and eaves. The air movement produced by convection is usually capable of cooling the building in most cases it tends to be insufficient to cool people (Santamouris 2007, p.16). Solar chimneys are also essential in providing the passive ventilation aspect. They do so by providing additional height as well as well-designed air passages hence increasing the air pressure differential. Warmed by the solar radiation, the chimneys tend to heat the rising air and increase the temperature difference the out-flowing and incoming air (Chhetri & Islam 2008, p.34). The increase in the natural convection from these measures supports drawing of air through the building. The solar chimneys enhance ventilation. Evaporative cooling is another aspect that is essential when it comes to passive ventilation. When water is evaporating, it tends to draw massive quantities of heat from the surrounding air. Evaporation is hence another measure that can be incorporated in providing effective passive ventilation. However, this measure works best when the relative humidity is below 70% in hot periods since air has a great capacity for taking water vapor up (Levin & Okubo 2001, p.63). The evaporation rates are increased by the air movement. Ponds, pools and water features adjacent to windows or that are in courtyards can pre-cool the air entering the house. The water features that are carefully located can also create convective breezes. These aspects create a cooling effect in the building and consequently facilitating the passive ventilation. The earth coupling of the thermal mass protected from the external temperature extremes like floor slabs can lower temperatures substantially. This possible through absorption of heat as it is entering the building or as it gets generated by the household activities (Lucangelo 2008, p. 12). Earth coupling utilizes cooler ground temperatures. The passively shaded regions around the earth-coupled slabs usually keep the surface ground temperatures low during the day while allowing the night-time cooling. The poor shaded environments can make the earth temperatures to exceed the internal comfort levels. In such an event, an earth-coupled slab becomes an energy liability. For a passive ventilation to be realized, envelop design can also be utilized. This design entails the building form and floor plan. The envelop design can be defined as an integrated design of building materials and form as a total system to acquire optimum energy savings and comfort. It is evident that heat enters and also leaves a house through the walls, roof, floor and windows collectively denoted as the building envelop (Gelfand & Duncan 2012, p.42). The internal layout the doors, walls and the room arrangements also tend to affect the heat distribution within a building. A good design of internal layout and envelope responds to site and climate conditions to optimize the thermal performance. This effect tends to lower operating costs, improve lifestyle and comfort and minimize the environmental impact. Thermal mass is another crucial factor that is essential for facilitating the passive ventilation aspect. Thermal mass can be termed as the storage system for coolness and warmth. The climate responsive design entails positioning the thermal mass where it is exposed to the appropriate levels of passive summer cooling. If a thermal mass is badly positioned, it tends to heat up and radiate heat at the night when the external temperatures have dropped (Hyde 2008, p.23). The earth-coupled concrete or slabs on the ground tend to provide a heat sink where the deep earth temperatures are favorable. However, they should be avoided in the climates where the deep earth temperatures give rise to heat gain. In such areas, it is good for the architecture to consider making use of open vented floors that have high insulation levels. This will help in avoiding heat gain. For the passive ventilation to be realized in areas where deep earth temperatures are low, it is recommendable to enclose the subfloor areas (Kibert 2012, p.27). This allows the reduction of temperatures as a result of earth coupling consequently gaining heat. Roof spacing is another aspect that plays a very crucial role in facilitating passive ventilation. Well-ventilated roof spaces are very essential when it comes to passive cooling. They usually provide a buffer zone between the internal as well as external spaces in difficult areas to the roof. These ventilators can help in reducing temperature difference across the ceiling insulation eventually increasing the effectiveness by approximately 100%. Correct ventilation are also essential in providing an effective air circulation. It is evident that passive cooling incorporates air circulation more than anything else (Barnhart 2004, p.32). This indicates that the right ventilation is very vital when it comes to passive ventilation. Conclusion From the discussion above, passive ventilation is a very crucial aspect to be incorporated both in homes as well as commercial buildings. The idea is both cost efficient and also environmental friendly. These aspects make it a suitable method of achieving a suitable and comfortable living environment. It is; however, clear that the architecture of the building needs to put into consideration all the aspects will facilitate passive ventilation. The type of environment required inside the house should be the guiding principle of the architecture when designing the aspects that will give rise to passive ventilation. References List Allard, F., & Ghiaus, C. (2005). Natural Ventilation in the Urban Environment: Assessment and Design. London, Earthscan. 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