With MEP services to be installed simultaneously in 11 under-construction buildings, logistics are playing a key role in the success of the Executive Towers project. Alison Luke finds out how ETA Mechanical & Electrical Division is tackling the task.
Dubai Properties' Executive Towers is located at the heart of Dubai's Business Bay development. Adjacent to the Dubai Creek extension behind Sheikh Zayed Road, the project occupies a prime location within the city - it is also one of the busiest sites. This added to the complexity of the project and the importance of logistics on the tight site.
The project comprises of a luxury hotel and 11 residential towers whose heights vary from 29-52 storeys. The towers are linked by a podium that includes shops, a health centre and villa-style homes, they also have a common basement area. Emirates Trading Agency (ETA) Mechanical & Electrical Division is carrying out the full MEP works on the residential towers and podium.
The firm began work on site in September 2005 when the basement raft was being cast. "We have some drainage systems and electrical works in the basement, so our early presence was required," explains ETA project manager Pradeep Kumar. "The MEP installation started from the basement itself and is following the civil works up to the roof," adds B Satish Kumar, ETA construction manager, plumbing.
With all 11 towers scheduled for completion and handover at the same time, carefully planned and implemented logistics have been essential. The first step taken was to divide the project into two zones, basically encompassing the work on groups of five and six towers as independent jobs. "There are two MEP project managers and we each have a zone [to manage]," explains Kumar. Below the project managers there are separate construction managers for the plumbing, electrical, plus heating, ventilation and air conditioning (hvac) systems in each tower.
Most of the buildings will be serviced as individual entities, although for certain systems the smaller towers have been grouped. There is also a centralised building management system (bms) that loops between all of the towers and connects to a single control room.
Air conditioning for the towers is supplied by a district cooling system. An 18,000TR district cooling plant is currently under construction adjacent to the site; this will serve several other projects within the Business Bay development also. The chilled water is circulated to individual energy transfer rooms adjacent to each tower. Here is it passed through plate heat exchangers, the secondary flow being pumped via a central riser to two further plantrooms at higher floors within the towers for local distribution; the 52-storey tower, for example, has plantrooms at floors 17 and 37. There are tap-off points at each intermediary floor to distribute the chilled water to fan coil units within the individual apartments for cooling.
The lower floors of the towers are served directly from the supply in the basement, the upper plantrooms will then serve floors either side of them. Flow and return temperatures are 5.5°C and 14.5°C respectively, with a supply temperature of 6.5°C at the fan coil units due to 1°C transmission losses in the system. Each apartment has three to four fan coil units depending on the number of rooms; these operate on a recirculation basis.
Air handling units (ahu) of 6,000l/s capacity provide fresh air to the buildings via ceiling diffusers within the apartments and circulation areas. The number of ahu in each tower varies according to the number and scale of floors. They all include heat recovery systems to ensure maximum energy efficiency. "The exhaust air will be passed through a heat wheel and the energy will be recovered from this and transferred to the supply air," explains Kumar. "Even the exhaust air from the kitchens and toilets is passed through a heat recovery wheel, so that all the energy is completely saved," he adds.
Much of the ductwork for the project was prefabricated offsite by ETA. "This meant that [on site] time would be reduced to one-third; we have made savings of 65% of the [on-site installation] time," stresses Kumar.
Electrically the project will be served by a new Dubai Electricity and Water Authority (DEWA) substation that is currently under construction. Power will be distributed underground from the substation to electrical plantrooms the basement of each tower that comprise step-down transformers and the main distribution boards. It is then distributed via 100kVA busbars to local distribution boards on each floor of the buildings; each busbar serves ten floors within a tower. Again, the smaller towers are served by a common set of transformers.
Water supply for the project is also provided in independent circuits to each of the towers. Separate tanks within the tower basements provide fire-fighting and domestic water supplies; water is pumped from here to further tanks at roof level and a lower level plantroom (at floor 37 in the case of the tallest tower). Water is supplied to the mechanical systems within the apartments by gravity feed, a system that has necessitated the inclusion of pressure reducing valves at every third floor.
The maximum allowable water pressure for supply to equipment in the apartments is 2bar. "As the water is coming from the top of the building we provide on every third floor a pressure reducing system," reports Kumar.
With onsite space a premium, products were delivered to site on a just-in-time basis. "We rented an area in Al Quos to store the main equipment [until it was required]," explains Kumar. Delivery of bulk items was primarily carried out after 7pm to meet traffic restrictions on Sheikh Zayed Road and once on site the process of delivery to the workface was carefully planned and controlled.
At peak time each tower had four hoists: "The hoists were used to move people and small materials," reports Kumar, "the bigger, heavier items were lifted in by crane." Al Habtoor is in overall charge of logistics on the project and assigned hoist and crane time as required for the progress of the job. ETA had an additional logistics team to ensure its installations met the construction programme.
The materials were generally moved at night to the specific workface where they were required to ensure that the hoists were free to move manpower during the daytime. "In the daytime if we are shifting materials [using the hoists] it means that shifting manpower may become a big problem, so we set up a special team to transfer the materials at night-time," Kumar explains. Now that the project is in its latter stages two of the hoists have been removed. The remaining hoists will be dedicated to transporting materials, while the main lifts within the buildings will be used for the movement of operatives.
Ensuring that materials were available when needed meant early ordering. "Due to demands on the manufacturers, sometimes it would take two months for materials to reach us, other products had to be ordered a year ahead. You've got to order early," stresses Kumar. The initial orders for products were made immediately after the firm won the contract and received approvals for materials. "We placed the order in Q1 of 2006 so that we would receive all of the equipment and materials in time to finish the job," confirms Kumar.
Over 80% of the MEP installation works are now complete and commissioning of the systems is underway. The firm is due to hand over the project in February 2008.