Building Services In Tall Buildings: Mechanical, HVAC, Fire Safety, And Electrical Systems

Your line manager gives you the opportunity to demonstrate further the knowledge you have gained from task one, to really showcase your understandings of the critical and key concepts associated with the construction of tall buildings. You are to work collaboratively and efficiently so as to pull together your collective knowledge to the following requirement.

• Knowledge of building services design and installation in tall buildings

Added to this, after the final conclusion and recommendations within the individual reports, you are required to produce a written statement, describing your critical reflection, you can use Lawrence-Wilkes & Ashmore (2014) model of Relective Rational Enquiry or similar to assist you.

Building services in Tall Buildings: Mechanical Systems

The rural-urban migration causes a higher population in the urban centers demanding more housing. Modern tall buildings are developed to meet the unending demand for residential and commercial space. A number of specialists and architects define tall buildings based on an individual or community circumstance and perception. It is considered that a building that towers above 200 m is a tall building while that which goes above 300m is a super-tall building.  It is important to analyze the building services in tall building which comply with the BIM standards of construction. There are a number of sections of building services that are considered crucial in the design and construction of a tall building such as the fire services, hydraulic services, mechanical services, electrical services, and building management. Some of the tall buildings that demonstrate architectural prowess and design ingenuity are Shanghai towers, Burj Khalifa,  One World Trade Center, and the Empire State Building in New York.

Mechanical systems are broadly implemented in tall buildings. The areas considered are vertical transportation, water and plumbing systems, as well as the air conditioning. It is crucial to analyze the design and implementation of the building services during the design phase. One of the key building services is the means of transportation. Buildings that tower above 200m require the use of escalators, lifts and stairs to facilitate movement from one floor to the other. In the super-tall buildings, the lifts or escalators are designed for evacuation during high risk moments such as fire or a security breach. It facilitates efficient vertical mobility. The building services implemented in the modern construction tend to consider the ‘Go Green’ agenda which focuses on energy saving. One of the greatest advancement in the escalator technology is the Machine-Room-Less technology that redesigns the gear-less motors used in escalators by eliminating the use of a machine room. Further, most buildings use the elevator ropes which are key in traction elevators as they connect the elevator engine with the cab, sheaves, and counterweight. The lift is able to travel a distance of 500 m holding a 27-ton capacity.

The maintenance of this type of lift takes a very short period of time compared to other models. For instance, the lift is used in Burj Khalifa, where it transports people and goods up to 504 meters above the ground. Similarly, Shangai Tower, has a height of 632 meters and uses about 106 elevators known as the bullet elevators that travel from the second basement level to the observation deck on the 119^th floor.

HVAC Systems

The energy consumption due to lighting, heating, and air conditioning of a tall building accounts for up to 35 percent of the entire energy consumption. Many of the developed countries experience the four seasons of weather. During the winter season, the rooms require a level of heating while during summer, the air conditioner is turned on. The building occupants need to adust the temperatures as needed. There are HVAC systems that are implemented to ensures automated heating, ventilation, and air-conditioning processes. Ventilation is key and it is designed at an architectural point. The designer must perform a wind analysis of the building to determine if the building can withstand huge wind power and if the building can take advantage of natural occurrences to conserve energy. The building needs to make use of natural lighting during the day as well as get ventilation from wind. Further, during design, the site is managed such that there are well-established channels for waste removal, storage locations of portable cold and hot water supply, water recovery and treatment systems, fuel gas piping, rainwater, surface and subsurface water drainage.  The systems are installed as large multi-split section systems, rooftop units, heat pump units, ducted packaged units, and the variable refrigerant flow systems.

The plumbing is carried out such that the pipes, valves, plumbing fixtures, tanks, and other apparatus are made using sustainable material and there are recycling channels especially for lavatory sanitation. Key factors to consider on the design and implementation of HVAC systems is the environmental conservation techniques employed, energy consumption, occupancy, and structural or material considerations.

• Absorption chillers are heat-operated devices that produce chilled water via an absorption cycle. These are not very common in commercial buildings and are used in industrial applications where heat source is available. Absorption chillers can be direct -fired, using natural gas or fuel oil, or indirect-fired. Indirect -fired units may use different sources for heat: hot water or steam from a boiler, steam from district heating, or waste heat in the form of water, air, or other gas. Absorption chillers can be single-effect or double-effect, where one or two vapor generators are used. Double-effect chillers use two generators sequentially to increase efficiency. Several manufacturers offer absorption chiller/heater units, which use the heat produced by firing to provide space heating and service hot water.

Buildings are designed to ensure that they can minimize the risks from heat and smoke.  The fire detection systems need to detect fire using sensors in terms of excessive heat or the presence of smoke. The system incorporated should alert the occupants to evacuate the building. Each building has a guideline followed during evacuation. It is preferred that the occupants use the fire exit points which are usually stairways. In the very tall buildings, there are specific lifts designed for evacuation purposes.  With the advent of modern technology, the sensors can be computerized to perform certain actions. For instance, if smoke is detected in a kitchen compartment on the 91^st floor of a building, a sprinkler may be initiated to stop the fire. When the magnitude of fire is considered greater, the system considers evacuating occupants in the entire building. The fire detection systems are such as the optical smoke alarms, heat alarms, ionization smoke alarms, and multi-sensor alarms. These alarms detect the carbon monoxide component in the air. Tall building require extended evacuation time due to height, has pronounced stack effect, height beyond available resources of fire department ladders, and water supply limitations. During design, the fire prevention and alarm systems follows a set of building codes and standards. These codes determine what is implemented in given circumstances to provide optimum protection. For instance,

• NFPA 30 for flammable liquids
• NFPA 54 for the National fuel gas code
• NFPA 70 for the National electrical code
• NFPA 101 life safety code
• IBC is the international building code.

Fire Safety, Detection, and Mitigation Systems

The standards implement the codes based on a particular building service:

• It caters for the portal fire extinguishers for each floor
• It caters for smoke sprinkler systems in different building or floor rooms
• The NFPA 72 has a list of the steps followed when installing the fire alarm systems in tall buildings as well as other buildings.

The codes and standards include mandatory requirements as well as the recommendations.

Besides the design considerations factored in, the systems are installed based on the standards recommended by structural engineers and other key stakeholders. For the installation of the fire detection and alarm systems, a detector is installed in all rooms and connected to the electrical power system. One of the best design and implementation strategies revolves around risk assessment and anticipation at the design stage. Using the fault tree analysis.

The fire event tree evaluates the occurrence of a fire based on the systems implemented in the building. The building service implemented in this regard makes fire safety decisions based on the following tree,

The latest method implemented in the fire exit lighting system is the smooth and efficient egress strategy. During power failure, the system provides photo-luminescent markings as illustrated in the figure below,

The tall buildings have a lot of electrical systems and other mechanical and hydraulic systems that run on electrical power. The electrical power systems obtain power from a voltage distribution center, in such tall buildings, there is an inverter room that obtains power from the national grid and converts it to voltages that can be consumed by users. The standards used for construction purposes are AS3000:2007, AS3439 and AS3008 for cable selection. The AS3000 guideline uses load specific factors and does not amount to the sum of switchboard circuit breaker ratings. During the installation of electrical systems, the architectural design illustrates the pipe works for wiring and the outlets for sockets and other power uses.

The design considers the distribution boards, main switchboard, and the mains connection. The electrical systems are crucial as they power all the other building services that require automation. The electrical systems must take into consideration the intended use so that the distribution boards can be structured to suit the needs of the building occupants. Some systems such as the kitchen systems, laundry systems, and pumping systems require higher electrical power compared to building lighting systems. Every tall building needs to have lightning arresters as well as ways to mitigate EMF errors and cable malfunctions. The building standards have regulated the user interface to very low voltages with are safe for residential use. The building design makes provision for clients who would want to use voltage ratings above the set standard for residential implementation.  The building management systems are computer based and they are used in monitoring and controlling the building services.  The systems can be used to develop data and generate relevant reports that illustrate risks and information that alerts the stakeholders of causes of action. The installation takes into consideration:

1. Service rooms, spaces, and risers
2. Structural constraints
3. installation of lightning arresters in tall buildings
4. installation of aircraft warning lights
5. extra low voltage systems

Electrical Systems

It is very important to involve the key stakeholders in the design and implementation stages of the construction project. The aim is to have the stakeholders involved in all the processes of the construction so as to make the necessary contributions at early stages in the project especially at the design level. The involvement ensures that when the implementation commences, there are fewer or no adjustments. Stakeholders discuss all matters pertaining the construction on a wider scope such that any decision made can be financed, accommodated within the set time and budget frames, as well as improve either the aesthetics or the structural design of the building.

In design some of the considerations in building design and installation of services for tall buildings, one must compute the area to perimeter ratio, volume to surface ratio, floor efficiency ratio, net to gross floor ratio, as geometric and building efficiency factors respectively.  The architects design the HVAC systems defining the routes and pipework channels. The energy consumed by these systems constitutes 40 percent of the total energy consumed by the entire building facilities.

Investors procure a site and decide to develop a tall building on the site. The investors forms a team of experts from different disciplines such as structural engineering, wind engineering, water engineering, quantity survey, electrical engineering, and interior design. The steering committee is mandated to determine the best techniques to use to design and construct a tall building with regards to the budget allocated by the investors. The foundation is key in the design of tall structures. The quantity surveyor evaluates the site location vis-a-vis the type of structure.

Other considerations are ground conditions of the site, the magnitude and distribution of loading on the building, availability of construction materials, economic considerations, and the local construction practices in a given region. For instance, in very hilly regions, the foundation is not so firm hence tall structures are not recommended.

Tall buildings have a large number of occupants which increases the population of a region. The region needs to have utilities to support the large number. Further, the designers need to consider the environmental conservation while building to ensure that the natural resources are well utilized and recycled. For instance, the stairways and the open spaces should have proper ventilation from wind and natural lighting from the sun and moon.

Conclusion

In a nutshell, the building services comprise all the other systems designed and implemented during a tall building construction. They support the functions of the building and are implemented alongside the stone and beam construction. They are mechanical, electrical, HVAC, and hydraulic in nature. They provide the building occupants with the utilities such as lighting, water systems, transportation systems, and risk management options especially in the case of fire.

References

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