Electrification Of High Rise Buildings

Once the estimated total demand has been arrived at, we have to decide how we are going to distribute the power... - C V Govinda Raju

September 5, 2015

electrification-highrisebuildings-powerdistribution

The requirements of the planning and execution of electrical works of an ordinary building having ground plus one or two floors housing are quite different from those of a multistoried or high rise building. A building is classified as ‘High Rise’, if it has more than Four floors (Ground + 3 Floors) or height more than 15 meters. It can be regarded as a miniature township requiring entire range of civic services such as electric power from the electricity board, stand by / emergency power from diesel generator, water supplies for various applications, fire fighting system, elevator services, sanitation, recreation facilities, swimming pool, lighting for apartments as well as common areas etc.

Details of electrical power requirements

The basic planning of the electrical works in high rise buildings starts with identifying the various requirements of the occupiers of the building, as well as the requirements of the statutory regulations. For this, one need the layout plan of each of the apartment, the activity planned in each room, the furniture layout, location of various electrical gadgets & their individual power requirement, plumbing needs etc. The requirements of apartments also largely vary depending on whether the occupier belong to high or low income group. Generally the high income group owner may prefer a large number of electrical outlets for lights, fans, table lamps, floor lamps, radio, T.Vs, music system, personal computers, fax machine, cordless telephones, air conditioners, washing machines, geysers, microwave oven, refrigerators, grinders, dish washer etc. This will not be the case with lower income group owners who may have one or two light points in each room, one or two sockets, a TV, a few fan points, refrigerator and a few kitchen appliances. Larger the income, higher is the power requirement & consumption. In addition to the individual requirements of the owners, there are also requirements for certain common areas, common facilities of the entire complex, such as common area and road lightings, elevators, water supply pumps, fire water systems, & fire fighting controls, recreation / swimming pool, communication system, security system etc. In the event of power failures, standby diesel generators need to take care of the common area lighting, drinking water pumps, fire water pumps, sewerage & storm water drainage pumps, elevators and a few lights for each apartment. This calls for laying of separate circuits for emergency lighting and change over facility for elevators, pumps etc. Based on these loads, total requirement of normal power as well as the emergency power with a provision for 15 to 20% future load growth & considering a Load factor of 0.6 to 0.8 depending on the type of load and one’s experience in calculating the total demand.

Power distribution and safety devices

When once the estimated total demand has been arrived at, we have to decide how we are going to distribute it. In a simple 2/3 floor building it is fairly simple as there are only a few individual owners and their cumulative demand is also low. This low demand of power can be generally met by the utilities through a single phase supply to each owner and measured through independent energy meters. However, in the case of high rise buildings the requirement could be in terms of 1 to 2 mega watts depending on the number of apartments. Advance interaction with the electricity board with regard to the availability of catering such large power from their existing system is necessary. Otherwise the utility has to plan necessary High Tension (HT) sub stations / feeders exclusively for the high rise complex. Such large power requirements are generally catered through High Tension supply, which could call for installation of a few step down substation inside the high rise complex. Each such substation has its own three phase + neutral, low tension power distribution boards. The electrical designer has to suitably plan the feeders and the out going cables in such a way that the loads or properly balanced on all the three phases and that each consumer gets proper voltage at his premises. Incoming supply to each consumer has to be protected by provision of an Earth Leakage Circuit Breaker (ELCB) to safeguard the persons against electrical shocks from faulty electrical gadgets. Further each circuit within the apartment is to be protected by Miniature Circuit Breakers (MCBs) to safely trip that particular circuit whenever there is an over load or short circuit. All power sockets need to be earthed through an earth conductor and ultimately connected solidly to earthed ground pits for safety of the personnel. With this provision any leakage current from a defective equipment will be directed to the ground and sensed by the ELCB, without harming the person coming in contact with it. Lightning arrestors provided at the top of the high rise buildings are connected to separate Earth pits through metallic conductors to safeguard the building against lightning.

Usually, separately wired emergency light fittings are catered directly from the standby diesel power generators installed at high rise complexes which automatically switch ‘ON’, on the failure of normal power supply. Similarly the common area lighting loads, water pumps, elevators etc., are so engineered with ‘change-over’ switching facility from mormal to diesel power and vice-versa. Separate routes for communication cabling, television antennas, fibre optics internet facility etc., have to be engineered based on the consumer’s requirement not only inside the apartments but also inside each tower of the building and accordingly separate conduiting to be planned. For this, proper interaction with the interior decorators & civil Engineers, in advance, is necessary. Separate fire fighting controls and public address systems with Battery assisted power supplies are also to be planned.

Solar power on high rise buildings

High rise buildings consume a large amount of energy because potable & Non-potable water that have to be pumped to the highest occupied floors, mechanically ventilated design makes elevators generally used instead of stairs and many lights are used during day times also in rooms, corridors etc, located far from windows & windowless spaces. Further the supply of traditional electrical energy by utilities are becoming more and more expensive as well its availability is in short supply due to the ever increasing demand. In view of this, most of the State Govts., are taking all possible steps to promote solar energy generation in their states. They have even come forward to buy the Solar power at a higher rate than the tariff rates thereby giving an incentive to the installer to recover the entire cost of the solar installation over a period of about 7/8 years and the life of the solar installation is expected to be over 25 years. Roof tops of high rise buildings are ideal sites for the solar power installation (Fig. 1). A 60kWp Solar power project at the roof top, costing around ` 58,00,000/= can generate approximately 1,00,000 units a year of clean & green power & pump it to the grid. The shadow free roof area required is about 450 Sq. metres of the high rise building. Evidently planning & design of high rise building need to take care of the solar power generation and accordingly make provision for cabling, routing of cables, installation of Batteries / Inverters etc.

Fig. 2: 500 LPD solar water heaters…

Energy conservation

With the growth of high rise buildings coming up and correspondingly the demand for large power requirement going up, and supply sources being limited, there is absolute necessity to give importance, at all locations, to conserve energy. This exercise need to be done well at the planning stage of the building itself. Energy conservation could be either from saving in direct electrical consumption, or saving in water consumption (50% of water consumption in a house is at the bath room & toilet), or avoiding wastage of heat etc.

Following areas present potential for energy conservation in high rise buildings.

Planning the usage of LED, Compact Fluorescent Lamps (CFLs) & avoid incandescent lamps. Comparative benefits can be seen in Table 1.
Avoid usage of incandescent lamps in display sign boards, which need to be switched on practically the whole day, such as ‘EXIT’ signs, ‘Fire Exit’ signs etc. Instead preferably use ‘LED’ sign boards. For example, instead of a 40watt incandescent lamp used in a display, an LED display unit consume only about 4/5 watts. The latter has a life of about 50,000 hours.
To provide “solar water heaters” for supply of hot water (Fig. 2).
To provide air tight self closing doors in all Air conditioned rooms.
To prevent air leakages in ventilation ducts.
To provide heat insulation around hot water pipes which are concealed in the walls as well as around bath tubs to avoid loss of heat in to the walls (Fig. 3).
To use pressure assisted toilet flushing tanks of lesser water volume (1.6 gallons/flushing) instead of old gravity assisted design (3.5 – 5 gallos/flush). This pressure is created using the pressure of household water supply line itself)
Wherever gas is cheaper than electricity, to plan combustion gas water heaters instead of electrically heated water boilers to save on running costs.
To plan re-cycling of used water from bath rooms, sinks, dish washers, washing machines, water used in kitchen for washing vessels etc. in a water treatment plant and re-use this treated water for gardening purposes, car Washing, toilet flushing etc. However, this calls for appropriate designing & plumbing of such water lines before starting of the building construction. By this planning, saving of water to an extent of 50% to 75% is possible as well as bring down the water bill considerably.
To provide enough natural lighting to apartments by suitably positioning & sizing of the Windows to avoid usage of Electricity during day time (Fig. 4).

Integrated Building Management System (IBMS)

IBMS with respect to high rise buildings is catching up very fast, more so in large commercial complexes, provide “single window” access, for:

Monitoring & control of fire fighting systems.
Security module for access control.
Elevator control.
Module for management of energy in the complex.
Module for preventive maintenance of equipments etc.

Life saving module provide primary monitoring & full control of smoke detection. Fire detection through hundreds of smart smoke detectors installed assist in providing information of the Floor affected by fire as well as for safe evacuation of persons.

Security module allows operators to control and monitor entry of persons through smart card readers, card holder management & ability to acquire & use data from human resource data base. Numerous CCTVs installed at strategic places also provide ‘movement’ information at the central monitoring cell.. software also enable efficient control & optimal usage of elevators. All these devices communicate via the structured cabling system. The security application has comprehensive reporting capabilities with pre-configured reports customised to the individual needs. Building management module integrates & control the HVAC systems, lightings & energy usage. It maintains an extensive historical data of building which can be accessed at required intervals of time. Any abnormal condition in the building, it will alert operators immediately, making it easy to analyse long-term operational patterns to ensure optimal performance.

Maintenance module provides checklist for maintenance of equipments, their periodicity of execution, data on manpower and man-hours requirements, tools & consumables required for each job etc… thereby ensuring efficient maintenance management. In short high-rise buildings present several unique challenges to designers, which are not found in traditional low-rise buildings.