5.0 Mechanical Ventilation & Air Conditional System 5.1 Literature Review
Air-conditioning system has become a requirement for most of the building in the past few decades. Many of our homes and most offices and commercial facilities wuld not be comfortable without year-round control of the indoor environment. Along with rapid development in improving human comfort came the realization that goods could be prodeced better, faster, and more economically in a properly controlled environment. In fact, many goods today could not be produced if the temperature, humidity, and air quality were not controlled within very narrow limits. Present practitioners of the arts and sciences of heating, ventilating, and air-conditioning (HVAC) system design and simulation are challenged as never before. Developments in electronics, controls and computers have furnished the tools allowing HVAC to become a high-technology industry. Good preparation for a study of HVAC system design most certainly includes courses in thermodynamics, fluid mechanics, heat transfer, and system dynamics. The principles of fluid mechanics, especially those dealing with the behaviour of liquirds and gases flowing in pipes and ducts, furnish important tools. The economic tradeoff in the relaionship between flow rate and pressure loss will be intertwined with the thermodynamic and heat transfer concept. HVAC system generally share common basic elements even though they may differ greatly in physical appearance and arrangement. These systems may also differ greatly in the manner in which they are controlled and operated. HVAC systems are categorized according to the manner by which they distributd energy and ventilation air, by how they are controlled, and by their special equipment arangements.
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In the all-air heating and cooling systems, both energy and ventilating air are carried by ductwork between the furnace or air handler and the conditioned space. The all-air system may be applied in buildings requiring individual control of conditions and having a multiplicity of zones, such as office buildings, scools and universities, laboratories, hospitals, stores, hotels, and ships. All-air systems are also used for any special applications where aneed exists for close control of temperature and humidity, including clean rooms, computer rooms, hospital operating rooms, and factories. Heating may be accomplished by the same duct system used for cooling, by a seperate perimeter air system, or by a seperate perimeter baseboard, reheat, or radiant system using hot water, steam, or electric-resistance heat. Many commercial buildings need no heating in interior spaces, but only a perimeter heating system to offset the heat losses at the interior envelopes of the buildings. During those times when heat is required only in perimeter zones served by baseboard systems, the air system provides the necessary ventilation and tempering of outdoor air. The ideal temperature to achieve thermal comfort is is between 23째C to 27째C (MS 1525, 2007) and air conditioning system is one of the easiest way to achieve. Mechanical Ventilation & Air Conditional System is a control system that applies regulation to a heating and/or air conditioning system.It is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. This system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamic, fluid mechanics, and heat transfer. Refrigeration is sometimes added to the field's abbreviation as HVAC&R or HVACR, or ventilating is dropped as in HACR (such as the designation of HACR-rate circuit breaker).It is important in the design of medium to large industrial and office buildings such as skyscape rand in marine environments such as aquariums, where safe and healthy building, conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.
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5.2 Introduction The main purpose of a HVAC (Heating, Ventilation, and Air-Conditioning) system is to maintain indoor air quality with filtration to provide human comfort for the users. In a commercial building, HVAC is the system which consumes most energy. In First Subang, there’s air handling unit room, chiller, cooling tower and fan-con unit. Though thermal comfort can be achieved through passive design by bringing the outside air into the building, but filters can’t filter all the air contaminates as they can still bypass it sometimes, therefore HVAC is being popular used in commercial building, including First Subang. Besides, HVAC is not just a system to provide thermal comfort, it can be a part to help on fire protection system, like fan room, which will further explain in details in 5.2.5.
Figure 5.2.1 Diagram of the Flow of Active Ventilation
The figure above shows the overall system of HVAC in First Subang, showing how the air flows in within the building throughout the system. The details will be explain further later in 5.3 Case Study.
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Diagram 5.2.2 Diagrammatic Summary of HVAC system in First Subang
The diagram above shows an overall summary of the HVAC system in First Subang. Before the AHU room supplies the cool air into each particular area, the cool air has to be processed in chiller room. Chiller room will compress the warm air into warm water by using compressor and send it to cooling tower. Cooling tower will cool the warm water and transfer back to chiller room. Chiller room will the supply the cool air to AHU. AHU will take the cool air and distribute it to the building. FCU will also take part in the HVAC system in First Subang. The further details for each individual component will be explain later.
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5.3 Case Study 5.3.1 Air Handling Unit Room
Figure 5.3.1 Air Handling Unit Room
Air handling units (AHU) are used to re-condition and circulate air around a building as part of a heating, ventilating and air-conditioning (HVAC) system. The main function of AHU is to take in outside air, re-condition it and supply it as fresh air to a building. All exhaust air is removed, which creates an acceptable indoor air quality. Depending on the required temperature of the re-conditioned air, the fresh air is either heated by a recovery unit or heating coil, or cooled by a cooling coil. Some of the air from the rooms can be re-circulated via an air mixing chamber because the hygienic requirements for air quality are lower, and this can result in significant energy savings. A mixing chamber has dampers for controlling the ratio between the return, outside and exhaust air. AHU room is the first room that we visit in the building. From our observation, the AHU is a large metal box containing separate ventilators for supply and exhaust, heating coil, cooling coil, heating/cooling recovery system, air filter racks or chambers, sound attenuators, mixing chamber, and dampers.
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5.3.1.1 Air Handling Unit System
Diagram 5.3.1.1 Section of Air Handling Unit System
From figure 5.2.2.2 , it showed the new coming air from outside and the recycled air from the room are mixed together, the volume of new air needed is determined by the pressure loop control. If the pressure in the room is too low, more outside air will be used. The mixed air will go through two filters to remove dust and particles. Once the air is pure, it is cooled down to extract water. Indeed the cold air is not carrying as much vapour as the hot one, so when the air is refrigerated in the cooling coil, the water condensates on cold surfaces and is drained. The last step is to reheat the dried air to the temperature needed for supply air to the building.
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Diagram 5.3.1.1 Ground Floor Plan
Few AHU rooms are located at different area as shown in diagram 5.3.1, so the HVAC system does not just count on one particular AHU room but few, if any problems occurred then the other AHU are still running.
Diagram 5.3.1.2 Lower Ground Plan
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5.3.2 Fan Coil Unit
Figure 5.3.2 Fan Coil Unit
Figure 5.3.4 is the fan coil unit in First Subang. The fan coil units are smaller and self contained than the air handling units. The major difference between air handling unit and fan coil unit lies in the fact that in fan coil unit itself has no ducting involved for the movement of air. In the fan coil unit, the fan in the internal section of the fan coil unit carries out the function of moving the air over a heated or cooled coil and then directly moving out the air into the surrounding air without the use of any ducts. Thought fan coil units can connect to air handling units as well depending on the decision making by the architects. The section of fan coil unit has shown in diagram 5.3.2 below.
Diagram 5.3.2 Components of a Fan Coil Unit
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5.3.3 Chiller Room
Figure 5.3.3 Chiller Room
Before the AHU room supply the cool air into each particular area, the cool air has to be processed in chiller room first. Chiller room will compress the warm air into warm water by using compressor and send it to cooling tower. It is also change the state of cool water into coll air by using expansion valve before supplying them to AHU room or FCU. The supply air which is approximately 20 degrees, leaves the cooling coil and goes through heating coil (which is off), through the supply air fan, down the duct and into the conditioned space. The cool supply air picks up heat in the conditioned space. The warmed air makes its way into the return air inlets, then into the return air duct and back to the air handling unit (AHU). The return air goes through the return air fan into the mixed air chamber and mixes with the outside air. The mixed air goes through the filters and into the cooling coil. The mixed air flows through the cooling coil where it gives up its heat into the chilled water tubes in the coil. This coil also has fins attached to the tubes to facilitate heat transfer. The cooled supply air leaves the cooling coil and the air cycle repeats. Refer to Diagram 5.3.3.
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Figure 5.3.3.1 Chiller Machine
Diagram 5.3.3 Internal Components of a Chiller
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Diagram 5.3.3.1 3rd Level Floor Plan
Chiller room is located on the left side of the plan which is same the cooling tower, but chiller is at level 3 while cooling tower is located at level 7 roof top. The reason chiller room is located at the same side with cooling tower is to reduce the usage of pipe, in order to save cost and reduce the internal time of cool and hot air exchange due to shorter distance.
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5.3.4 Cooling Tower
Figure 5.3.4 Cooling Tower
Cooling towers are used in central air conditioning systems. It has to cooperate with other components like chiller plant room, AHU room or FCU to achieve thermal comfort in the exterior of the building. For our site which is First Subang, the cooling tower is located at level 6 and it's the only one cooling tower for the whole building. The function of the cooling tower is to cool the warm water from the chiller condenser. Following the central air conditioning system cycle, the heat from the rooms in a building is transferred to chilled water, which is then transferred into the refrigerant, and finally to the cooling water. The cooling tower is at the final point of the heat transfer. The heat from the hot water is withdrawn by contact between the water and the air. The heat transfer between the air and water occurs though the evaporation of a small part of the water that needs to be cooled. The heat is transferred to the atmosphere and the cooled water is then pumped back to the condenser or process equipment where it absorbs heat.
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Figure 5.3.4.1 Diagram of a Induced Draft Counter Flow Tower Fill
According to our interview, this is the cooling tower system that used in First Subang. It is the common in HVAC&R application. Vertical air movement is induced in opposition to the water flow across the fill. Coldest water will contact the driest air for maximum performance but it can be difficulties with access for maintainance. It has flexible air inlet location and the inlets on all sides will reduce height and pump head. It better suited to sub zero operation and good option with small packaged towers using centrifugal fans.
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Diagram 5.3.4.1 Elevation
Cooling tower is situated at roof top, cause it required a large empty spot due to its’ size and it requires an extra boundary for the leak water, cold water. And placing at roof top would have a very good ventilation, which allows the cool air enters and released off the hot air there.
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5.3.5 Fan Room
Figure 5.3.5.1 Fan Room
Fan room in this building is to access fresh air and discharge return air and exhaust hair from the interior to the openings at fan room. There is a minimum distance of 25’ of fresh air inlet away from contaminant source.
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Figure 5.3.5.2 Fan Sprinter
Fan room is located to adjacent area served, and if fire occurs, the fans will be operated to discharge fire smoke to the openings at the top of fan room. This is to prevent the situation from getting more hazy and minimizes the situation from getting more worse. This room is used as an active fire protection system.
Figure 5.3.5.3 Air Well
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Diagram 5.3.5.1 Basement Plan
As shown in diagram 5.2.4, few fan rooms are situated in the basement carpark level, as it function as part of an active fire protection system. More fan rooms are in this particular level, as a prevention of fire occur by the explosion of car accidents or the explosion of transformer room if it happens to be over heated.
Diagram 5.3.5.2 Elevation
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5.3.6 Smoke and heat exhaust ventilation system
Figure 5.3.6 Window for SHEVS
Smoke will normally form when there's fire in a building. Surprisingly, fire isn't the main cause of people's death but smoke is. Hence, smoke ventilation system is introduced since it's a life saving system that make people's life more secure and firefighters easier to rescue trapped people when there's fire. Smoke and heat exhaust ventilation systems, also known as “SHEVS� is to keep the escape routes clear, especially low level escape routes by removing the smoke from a building and reduce the impact to the a building. It has three main components, which are the exhaust ventilators, smoke barriers and the inlet ventilators. Sometimes, dampers and ductwork work with the components as well.
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Diagram 5.3.6.1 Simple Sectional Drawing
There's two type of SHEVS can be applied to a building, which is natural ventilation system or powered ventilation system. Natural smoke ventilation drive the smoke to the ventilators by using the natural buoyancy of the hot gases. However, powered smoke ventilation only relies on mechanical extraction through fans. For the escape stairs and fire-fighting stairs, well ventilation should be provided with certain rules: 1, a ventilate of at least 1m2 at the top of the stair and 2, an ventilator should included at each storey external wall at least 0.5m2 . Height of the clear layer below the smoke is one of the considerations that need to be noticed. It must be high enough to ensure that the smoke barrier won't effect building usage. Another thing that we need to consider is the supply of replacement air. Sufficient fresh air needs to be sucked into the space as the smoke and gases are extracted out. Otherwise the building will become depressurized and the smoke ventilation system will become ineffective.
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First Subang uses Stand Alone System for this component at emergency staircase, which is shown at diagram 5.3.6.2 below.
Diagram 5.3.6.2 Stand Alone System
Diagram 5.3.6.3 Level 1 Floor Plan
This system is located nearby the fire escape staircase as it’s part of fire protection system as well through ventilation system.
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5.4 Uniform Building By Law ď Ź
Section 40
1)
Where permanent mechanical ventilation or air-conditioning is intended, the relevant building by-laws relating to natural ventilation, natural lighting and heights of room may be waived at the waived at the discretion of the local authority.
2)
Any application for the waiver of the relevant by-laws shall only be considered if in addition to the permanent air-conditioning system there is provided alternative approved means of ventilating the air-conditioned enclosure, such that within half an hour of the air-conditioning system failing, not less than the stipulated volume of fresh air specified hereinafter shall be introduced into the enclosure during the period when the air-conditioning system is not functioning.
3)
The provisions of the Third Schedule to these By-laws shall apply to buildings which are mechanically ventilated or air-conditioned.
4)
Where permanent mechanical ventilation in respect of lavatories, water-closets, bathrooms or corridors is provided for and maintained in accordance with the requirements of the Third Schedule to these By-laws, the provisions of these By-laws relating to natural ventilation and natural lighting shall not apply to such lavatories, water-closets, bathrooms or corridors.
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5.5 Analysis & Conclusion
The picture above is one of the AHU room which we visited, as it has shown clearly, the workers simply put cleaning tools or unwanted stuff inside, blocking the space in the room, which we think this is not a good way of maintainance, as it will be troublesome if air handling unit happens to have any problem. The room itself is mostly to be much more dusty and dirty due to the worker treat it as a store room. We strongly suggest that all the stuffs should be put into a proper store room, as the space in every individual service room is designed for its own purpose, including air handling unit which provides fresh air and thermal comfort in the mall.
According to our observation, we found that the cooling tower is located at level 6, which is uncommon since it usually located at the rooftop structure. Although, it’s reasonable for cooling towers should be located as near as possible to the refrigeration systems they serve according to its principle, but should never be located below them so as to allow the condenser water to drain out of the system through the tower basin when the system is shut down.
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On the other hand, There is a louver fence installed surround the cooling tower in order to protect the cooling tower from being destroyed because cooling tower is one of the main HVAC system. It is also built for the aesthetic purpose of the surrounding area. As for the safety of the building, the fences around the rooftop where the water tanks are located seem like degenerating and tend to fall down from the rooftop. It's quite dangerous since it maybe will hurt the pedestrians which walking through the lower ground when it falls. Hence, comprehensive and regular maintenance should be applied to every single corner of a building since safety must come to first. According to UBBL, First Subang has already covered fully by the mechanical ventilation system so natural ventilation, natural lightning and heights of rooms can be waived. Besides that, it has sufficient space for fresh air to be introduced to enclosure during air-conditioning system falling. Hence, it fulfilled Uniform Building By Law's requirement for mechanical ventilation system.
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6.0 Conclusion We had chosen First Subang as our building for this case study project in order to explore various services systems, which includes electrical supply system, fire protection systems, mechanical transportation system and mechanical ventilation system, through experiential learning in this real life project. Throughout this project, we have learned and identified the basic principles, process and equipment of all these systems and understand their functions and connections. Literature reviews are made after studied several sources, thereby obtaining the knowledge of the basics elements before entering the field of building service, meaning the initial reason of the need of building services in a building. Other than reviewing the knowledge we have gained throughout this real life experience project, we have abstracted our personal view and opinions about the studied systems, with the help and discussion with our tutor, Mr.Adib. This makes us change our previous mindset towards an ordinary building. A building is not just about the structure and skin, but should be functional as well, in terms of precautions for safety and to please the occupants by providing a convenient and comfortable indoor environment. We can totally understand the effort of engineers and architects who had put in depth thinking in the building services system. Diagrams and drawings are prepared for all systems according to buildings standards and conventions. As this is a 5 person grouping project, we did not simply assign a particular topic to the individuals, but working out every task together so each of us would be able to learn all of the building services, instead of just one particular system. Lastly, a thousand thanks to Mr.Mohd Adib for his meticulous guidance throughout the project.
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7.0 References Abbott Consulting. (2014). Dry and Wet Riser Hydraulic Testing. Retrieved from http://www.apexfire.ie/dry-and-wet-riser-hydraulic-testing/ APTA Standards Development Program. (2011). Heavy-Duty Transportation System Escalator Design Guidelines. Retrieved from http://www.apta.com/resources/standards/Documents/APTA-RT-EE-RP-001-02.pdf Benjamin.S, (1997). Technology Mechanical And Electrical System. United States of America. John Wiley & Sons. Billy.C, (2000). Fundamentals Of Air Conditioning Systems. Second Edition. United States of America. The Fairmont Press, Inc. Building Authority. (2011). Code of Practice for Building Works for Lifts and Escalators. Retrieved from http://www.bd.gov.hk/english/documents/code/BWLE2011e.pdf Cooling Tower. (n.d.). Retrieved from http://www.iklimnet.com/expert_hvac/cooling_tower.html CO2 Extinguishing Systems. (n.d.). Retrieved from http://www.iklimnet.com/expert_hvac/cooling_tower.html Difference Between AHU and FCU, (2009). Retrieved from http://www.differencebetween.net/object/difference-between-ahu-and-fcu/ Edvard. (25, November 2013). General Principles of Electricity Supply Systems. Retrieved from http://electrical-engineering-portal.com/general-principles-of-electricity-supply-syste ms Electric Meter. (n.d.). Retrieved from http://science.howstuffworks.com/electric-meter-info.htm Fire Protection Engineering. On Elevator Shaft Pressurization System Standards and Codes for Smoke Control in Tall Buildings. (2014). Retrieved from magazine.sfpe.org Fire Safety Advice Centre. (2011). Types, Use and Colours of Portable Fire Extinguishers. Retrieved from http://www.firesafe.org.uk/types-use-and-colours-of-portable-fire-extinguishers/ Francis.D.K.C, (1991). Building Construction Illustrated Second Edition. United States of America. John Wiley & Sons. Fred.H, (1994). Building Services & Equipments Third Edition. England. Addison Wesley Longman Limited. Maurice.J, (2013). Fire Protection Systems. United States of America. Jones & Bartlett Publishers.
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MFS Fire Extinguishers. (n.d). Retrieved from http://www.mfs-fire-extinguishers.co.uk/types.htm National Fire Fighting Manufacturing FZCO, (2000). Active Systems & Passive Fire Protection Division. Retrieved from http://www.naffco.com/products.php?groups_id=225 Robert.B.B, (2000). Mechanical System Architectural Engineering Design. United States of America. McGraw-Hill Companies. Roger.G, (2000). Building Services Technology And Design. United States of America. Pearson Education Limited. S. Miller, R. (2011, April 1). On Elevator Shaft Pressurization System Standards and Codes for Smoke Control in Tall Buildings. Retrieved from http://magazine.sfpe.org/smoke-management/elevator-shaft-pressurization-system-s tandards-and-codes-smoke-control-tall-buildin Callfire Systems Limited. (2013). Smoke Ventilation System(A.O.V). Retrieved from http://www.callfiresystems.co.uk/our-services/smoke-ventilation-systems/ Tom.L, (2011). Structural Fire Engineering. London. ICE Publishing. Understand Construction. Fire Fighting System. (2014). Retrieved from http://www.understandconstruction.com/understand-fire-fighting-systems.html WILD, J. (1998, November 1). Smoke Control by Pressurization. Retrieved from http://www.flaktwoods.com/3e76e6e3-a3d4-402b-956c-f26dc67eb6a1 Zahurul,M. (n.d). Vertical Transportation: Elevators & Escalators. Retrieved from http://teacher.buet.ac.bd/zahurul/ME415/ME415_elevators.pdf
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