This Application Manual (AM), released from the Chartered Institution of Building Services Engineers (CIBSE) is a revision of the original AM Chartered Institution of Building Services Engineers (CIBSE) Applications Manual AM10, March , Natural Ventilation in Nondomestic Buildings on. CIBSE Applications Manual AM Natural ventilation in non-domestic buildings. In Construction Information Service. Search by author or title. Add to My.
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Module 107: Predicting and delivering good building IAQ using natural ventilation
School buildings are often built and operated within tight financial constraints but, at the same time, require applcation standards of indoor air quality IAQ to promote good learning and health. This article will reflect on the application of natural ventilation as a method of maintaining IAQ, and consider the application and control of natural ventilation for school buildings.
As discussed more fully in the December CPD article Hybrid ventilation for schoolsventilation in buildings can be broadly categorised as natural, mechanical or hybrid ventilation. All three ventilation types have appropriate applications; however, determining whether there is an opportunity for natural ventilation would be the normal starting point for a project.
CIBSE Guide A4 and application manual AM10 provide detailed methods and examples for assessing the practical potential for natural ventilation that are based on networks of airflow paths through openings including cracks in the building fabric, and the available driving pressure.
C p is the pressure coefficient, and will applicqtion on the shape of the building and the direction of the wind. Values of C p are typically determined using wind tunnel tests as well as computational methods. Wind pressure will, of course, be variable and is subject to interference at ground level from obstructions.
For stack ventilation, the pressure difference is caused by the difference in mass between the air in the building and that of the air outdoors. Pressure Pa at the base of a column of fluid such as air is simply 9. By including a relationship that determines the value of air density at a specific temperature, the available pressure for driving ventilation between two openings in a building can be determined.
Integrating a ventilation tower to provide top-down natural ventilation Source: As shown in the preceding calculations, the available pressure to drive natural ventilation is likely to appplication relatively small. For comparison, in a mechanical ventilation system a clean panel filter is likely to require a minimum of 40 Pa and a standard louvre will need around 20 Pa to pass a cise airflow. The methods by which spaces are naturally ventilated may be split into four groups.
Typically, windows would provide the openings, and this mode is likely to be effective up to a room depth of approximately twice the room height. For cross ventilation to be successful, a pressure differential is needed between two openings on opposing faces of a room, which would normally mean applifation both sides have to be open to the outside air some have an open side into a building atrium or ventilation chimney.
If the openings are subsequently closed on one side, the ventilation system will revert to a single-sided system. As the air moves across the space, it will pick up heat and pollutant from the internal environment before it leaves the room. This can provide effective ventilation for a room width of up to four-to-five times the room height.
CIBSE – AM Natural Ventilation in Non-Domestic Buildings | Build Up
In simpler applications it may be from a low-level window, or louvre, on one side of the room to a high-level window or louvre on the same side, or on the opposite side of the space.
This can provide air flowrates during hot, still applicatiion — and work in deeper plan spaces. Top-down ventilation as shown in Figure 2 takes advantage of both wind-driven and applicatikn ventilation. However, it is not completely reliant on either. Stack-driven buoyant air rises within the space and, as it leaves through a purpose-made ventilation tower, is replaced with outdoor air that enters the tower through the positively pressured windward side.
The leeward faces of the ventilation tower have a lower pressure that helps to extract the buoyant, stale, warm air from the space below. Air introduced from high level is typically less likely to carry airborne pollutants, and less prone to noise pollution compared with ground-level sources. These systems can ventilate deep plan areas that do not otherwise have direct access to outdoor air, and are not affected by the depth of the room.
The system will only be successful if the supply air not only removes the pollutants and heat, but also provides fresh as opposed to stale or already contaminated air to the occupants. Appljcation is this consideration that will affect the practical effective depth of a naturally ventilated space. The complexities of airflow movement within the space and the building itself mean that computational fluid dynamics is often required to evaluate properly the patterns and resulting effectiveness.
It is challenging to forecast properly natural ventilation because of the multiple variable parameters, including: And, as the wind direction changes, so does the whole pattern of flow paths through the building, as the pressure coefficients alter across the building surfaces.
As a,10 earlier, the practical driving pressures are likely to be small, and so require particularly careful consideration to determine the flow through appropriately low resistance networks of applicatin. However, as reflected in that article, CFD still requires expert input to provide credible output. Manufacturers of natural ventilation systems have joined with simulation software suppliers to produce robust tools that require fewer inputs than normal commercially available simulation tools.
This can provide a useful tool for sizing natural ventilation systems, particularly during the early stages of a project, when full details of a building are not always readily available. Libraries of predefined objects are also increasingly available for dynamic thermal simulation software as shown in Figure 3 that provide both a geometric representation and functional parameters. These are likely to become more common as building information modelling BIM methods further permeate the industry.
This allows the assessment of performance to investigate the capabilities of a potential scheme within a standard modelling environment. Ventilation controls may be used to monitor CO 2temperature and humidity. They can typically be linked into the building management system so that they can be integrated into wider building monitoring and control, with the operational data collected and processed for system management.
Module Predicting and delivering good building IAQ using natural ventilation – CIBSE Journal
The use of accessible linked visual display interfaces can help educate end users about how the systems operate so that they may better maintain a comfortable, productive environment with minimum energy use.
An example of applying a windtower-driven natural sm10 system.
The windtowers pass through the roof of Simone Veil nursery and primary school, aplication Lyon, France Source: A natural ventilation system was used as part of the building system for a French school renovation that subsequently received a Green Building Solutions Award from the Construction 21 Network for Health and Comfort.
Located close to Lyon, south-east France, the ambient temperature is typically 3 to 4K warmer in summer and 2 to 3K cooler in winter than London. The thermally heavyweight, carefully constructed fabric of the two-storey buildings was designed to minimise solar gains. The natural ventilation system consists of external static louvres and internal active louvre arrangements, which vary the opening and free area through the louvre face.
The natural ventilation is driven with 16 windtowers above individual classrooms. Levels of indoor air quality and measured CO 2 levels have readily met design requirements.
New UK guidelines 5 on ventilation, thermal comfort and indoor air quality in schools are soon to be published. An appropriately designed and controlled natural ventilation system should be considered as a potential option to meet these requirements as, in many applications, it is possible to maintain IAQ levels while meeting the comfort requirements with low energy consumption.