Building Services - Ventilation System PDF 2024-2025

12/4/2024 DUHOK POLYTECHNIC UNIVERSITY DUHOK TECHNICAL INSTITUTE BUILDING CONSTRUCTION TECHNOLOGY DEPT. BUILDING SERVICES VENTILATION SYSTEM ASST. LEC. BAYAN A.TAHA SECOND YEAR FIRST SEMESTER 2024-2025...

12/4/2024 DUHOK POLYTECHNIC UNIVERSITY DUHOK TECHNICAL INSTITUTE BUILDING CONSTRUCTION TECHNOLOGY DEPT. BUILDING SERVICES VENTILATION SYSTEM ASST. LEC. BAYAN A.TAHA SECOND YEAR FIRST SEMESTER 2024-2025 Lecturer Bayan A.Taha 1 Ventilation  Ventilation moves outdoor air into a building or a room, and distributes the air within the building or room.  The general purpose of ventilation in building is to provide healthy air for breathing by both diluting (decrease) the pollutants originating in the building and removing the pollutants from it. 1  12/4/2024 Ventilation is necessary in buildings to remove ‘stale‫ ’الراكد‬air and replace it with ‘fresh’ air: 1. Helping to moderate internal temperatures. 2. Replenishing (‫)تجديد‬oxygen. 3. Reducing the accumulation(‫ )تراكم‬of moisture, odors, bacteria, dust, carbon dioxide, smoke and other contaminants (polluting) that can build up during occupied periods. 4. Creating air movement which improves the comfort of occupants. VENTILATION REQUIREMENTS The factors which determine the difference in ventilation are : 1. Type of buildings 2. Size of the buildings and the floor areas. 3. Type of roof 4. Locally prevalent wind directions 5. Number of persons occupying the room 6. Proximity(near) to commercial or industrial areas 7. Sanitation of the surrounding area 8. Nature of work being carried out inside the buildings (work type). 9. Geographical locations such as closeness to sea, large water badies,hilly areas There are three methods that may be used to ventilate a building: Natural, Mechanical and Hybrid 2  12/4/2024 FACTORS AFFECTING VENTILATION On the basis of such experimental observations the following factors can be isolated which affect the indoor air flow (both patterns and velocities): 1. orientation (‫)التوجيه‬ 2. external features 3. cross‐ventilation 4. position of openings 5. size of openings 6. controls of openings Lecturer Bayan A.Taha 5 What is Natural Ventilation?  Natural forces (e.g. winds and thermal buoyancy force due to indoor and outdoor air density differences) drive outdoor air through purpose built, building envelope openings.  Purpose built openings include windows, doors, solar chimneys, wind towers and ventilators.  This natural ventilation of buildings depends on climate, building design and human behavior. Lecturer Bayan A.Taha 6 3  12/4/2024 Natural ventilation is generally categorized as: 1. Wind-driven (or wind-induced) cross ventilation:, where pressure differences between one side of the building and the other draw air in on the high pressure side and draw it out on the low pressure side. Lecturer Bayan A.Taha 7  Cross ventilation occurs where there are pressure differences between one side of a building and the other. Typically this is a wind-driven effect in which air is drawn into the building on the high pressure windward side and is drawn out of the building on the low pressure leeward side. Wind can also drive single-sided ventilation and vertical ventilation.  Cross ventilation is suitable for buildings up to approximately 12 to 15m in depth (five times the floor to ceiling height, or 2.5 times the floor to ceiling height if openings can only be provided on one side). Lecturer Bayan A.Taha 8 4  12/4/2024  Providing sufficient fresh air creates draughts close to openings, and additional design elements such as internal courtyards are necessary, or the inclusion of elements such as atrium that combine cross ventilation and stack effects.  A disadvantage of cross ventilation is that it tends to be least effective on hot still days, when it is needed most. Lecturer Bayan A.Taha 9 2. Buoyancy-driven stack ventilation (the stack effect):, where cooler air enters the building at low level, is heated by occupants, equipment, heating systems and so on, becomes less dense and so more buoyant and rises through the building to be ventilated to the outside at the top. Lecturer Bayan A.Taha 10 5  12/4/2024  Stack ventilation As air gets warmer it becomes less dense and so more buoyant. This means that warm air has a tendency to rise.  This effect can be used to naturally ventilate buildings. Cooler outside air is drawn into buildings at a lower level, it is warmed by sources of heat within the building (such as people, equipment, heating and solar gain), and then rises through the building to vent out at a higher level. A positive pressure area is created at the top of a building and negative pressure area at the bottom.  This process can take place without mechanical assistance, simply by introducing openings at the bottom and the top of buildings. Lecturer Bayan A.Taha 11  The effectiveness of stack ventilation is influenced by; the effective area of openings, the height of the stack, the temperature difference between the bottom and the top of the stack and ,pressure differences outside the building.  Where ventilation is needed high up in the building, this can require the addition of ventilation stacks that achieve the height necessary to create a pressure difference between the inlets and outlets. Lecturer Bayan A.Taha 12 6  12/4/2024  ADVANTAGES OF NATURAL VENTILATION 1. Does not require any mechanical appliances. 2. Non operational cost. 3. Non maintenance cost for the appliances/ equipment. 4. Silent processes. 4. Combination benefit of ventilation, lighting and esthetical value Lecturer Bayan A.Taha 13  DISADVANTAGES OF NATURAL VENTILATION 1.The system is uncontrolled: …in terms of speed & distribution …high rise building received strong velocity thus windows should be kept closed. …slow wind velocity during rainy season 2. Internal temperature cannot be monitored: …difficult to achieved the required human comfort temperature. 3. Rate of air humidity is uncontrolled : …depends on the existing external humidity Lecturer Bayan A.Taha 14 7  12/4/2024 4. Uneven uniform distribution : …ventilation rate depends on sizes of opening. …distribution is maximum at the area/space nearby the opening. …low ventilation rate for rooms further inside a bldg. 5. Quality of fresh & clean wind cannot be assured …maybe contaminated from the external harmful element such as smoke and dust Lecturer Bayan A.Taha 15 What is Mechanical (Artificial) Ventilation?  A building ventilation system that uses powered fans or blowers to provide fresh air to rooms when the natural forces of air pressure and gravity are not enough to circulate air through a building.  Mechanical ventilation is used to control indoor air quality, excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air.  A mechanical system is capable of meeting the requirements of air quantity and qualities regarding humidity, temperature, etc  This system is costly, but it results in considerable Increase in the efficiency of persons under the command of the system Lecturer Bayan A.Taha 16 8  12/4/2024 Where Mechanical Ventilation is Needed? 1. The building is too deep to ventilate from the perimeter. 2. Local air quality is poor, for example if a building is next to a busy road. 3. Local noise levels mean that windows cannot be opened. 4. The local urban structure is very dense and shelters the building from the wind. 5. Air cooling or air conditioning systems mean that windows cannot be opened. 6. Privacy or security requirements prevent windows being opened. 7. Internal partitions block air paths. Lecturer Bayan A.Taha 17 Advantages of artificial ventilation 1. No need to depend on natural conditions or weather 2. Provide required amount of air exchange and can be easily controlled 3. Air is distributed in places where it is required 4. Natural ventilation often includes opening windows, facades or doors which brings dust or outdoor dirt in situations of strong wind, which is not seen in artificial ventilation 5. Air can be humidify or dehumidify, filtered, cooled or heated according to occupants’ desires or location weather and climate Advantages of artificial ventilation 1. involved initial, operation 2. extra space to allocate equipment's 3. required power supply & backup systems Lecturer Bayan A.Taha 18 9  12/4/2024 Principles of Mechanical Ventilation Air Distribution Air Exchange Air Movement Careful design of the duct Mechanical ventilation The system brings in fresh layout and register systems use fans and ducts outdoor air and exhausts placement ensures even air to actively move air, unlike stale indoor air to maintain distribution throughout the passive natural ventilation. indoor air quality. space. Lecturer Bayan A.Taha 19 What is hybrid or mixed-mode ventilation? A hybrid ventilation system allows the controlled introduction of outdoor air ventilation into a building by both mechanical and passive means. It uses mechanical ventilation when the natural ventilation flow rate is too low. When natural ventilation alone is not suitable, exhaust fans (with adequate pre-testing and planning) can be installed to increase ventilation rates in rooms housing patients with airborne infection. However, this simple type of hybrid (mixed-mode) ventilation needs to be used with care. The fans should be installed where room air can be exhausted directly to the outdoor environment through either a wall or the roof. The size and number of exhaust fans depends on the targeted ventilation rate, and must be measured and tested before use. Lecturer Bayan A.Taha 20 10  12/4/2024 There are two variants of hybrid ventilation: 1. The Changeover Type: spaces are ventilated either mechanically or passively, but not both simultaneously (at the same time). Can switch between mechanical and passive ventilation seasonally. 2. The Concurrent Type: both methods provide ventilation simultaneously (at the same time). Appropriate controls are needed to prevent “fighting” between the two ventilation methods. Lecturer Bayan A.Taha 21 11