Ensuring efficient mechanical and electrical (M&E) services within a mega mall can be a challenge at the best of times. The task is even more testing when sustainability is brought into the equation as is the case for WSP Middle East with the Midrif City Centre.

The UAE-based design, engineering and management consultancy is responsible for the full design and supervision services for the MEP (mechanical, electrical and plumbing) systems, fire and life safety design, acoustic consultancy, specialist lighting and Leed consultancy services.

The nerve centre for the M&E services within the complex is the energy centre, “Due to the substantial size of the project there was a requirement to design and locate on site a dedicated energy centre that includes chillers, cooling towers, pumps, tanks and electrical substation and switchgear,” explains Rob Gregory, building services operations director for WSP Middle East.

The energy centre is located at the southeast edge of the development, adjacent to one of the car-park structures. The cooling towers are hidden from view by an acoustically-treated parapet, which will ensure that resultant noise levels experienced in neighbouring areas are no higher than previously experienced from the local road infrastructure, Rob points out.

He continues: “As the project is targeting a Gold Leed rating, sustainability was always a critical item on the agenda and pursuing this meant efficient HVAC (heating, ventilation and air-conditioning) systems were a must. Essentially, the brief required the designer to provide a central cooling plant with a high degree of efficiency and flexibility. Due to the nature of shopping malls, flexibility is critical as tenant loads can vary significantly depending on the type of use. For example, electrical goods stores and jewellers have very high-density heat gains compared to high-end boutique clothes stores that have relatively low density loads – and at the time of design, the actual tenant is often unknown and in future may change.

“As a result, the final load required can vary significantly at the shop unit level as well as at the plant level where the peak load varies greatly over the year due to climatic variations. Therefore, ensuring a high degree of control and good efficiency at part loads as well as limiting possible tenant interference with systems were key requirements. In addition, it was necessary to provide a design that could be commissioned quickly and would be flexible in nature as well as open to future expansion.”

In order to serve this huge mall with the requisite power, the total connected electrical load is 110 MW, distributed through nine substations with 77 transformers. The total cooling plant capacity is 53.4 MW, which is expandable by up to 62.3 MW with the possible addition of a chiller in the future. Currently, six 11 kV high-efficiency chillers that use the safe refrigerant – HFC-134a – have been installed.

According to Rob, this project sets a benchmark in terms of district cooling and sustainability for shopping malls: The Mirdif City Centre plant utilises the latest systems, by using HV chillers, contra flow cooling towers with condenser water flow, variable primary distribution systems, and can be considered on par with the latest plants.

“One of the major advantages of this ‘district cooling plant’ (DCP) is that we also had control over the design of the secondary systems (or building systems). The extensive measures we have been able to incorporate into the design of the HVAC building systems will, therefore, greatly contribute to realising the actual efficiencies of the DCP, which is something that the large DCP companies are most often deprived of because of poor building HVAC system design or operation from third-party developers/operators,” he says. “The building systems connected to by the DCP companies often provide poor system delta Ts (that is, low return temperatures) and therefore result in poor overall efficiencies for the DCP.

“As we also designed the secondary systems for the Mirdif City Centre, a number of strategies were employed to ensure maximum flexibility in use, efficiency in operation and care in ensuring delta Ts will be maintained for the whole system.

These strategies include:
• Use of pressure-independent control valves on all cooling coils;
• Use of intelligent control strategies such as differential pressure reset control on all secondary (building) chilled water systems;
• Valve position limitation based on chilled water return temperature for all air-handling unit (AHU) coils;
• Night-time set-back operation for AHUs;
• Use of enthalpy control on air-handling systems;
• Utilisation of high delta T cooling coils;
• The use of variable speed drives on all chilled water (primary and secondary) pumps and on condenser water pumps;
• Contra flow-induced draft low flow cooling towers with VFD (variable frequency drive) control of fans;
• Variable air volume (VAV) supply AHUs to all main mall areas;
• Demand-controlled ventilation systems for minimisation of outdoor air cooling based on indoor air-quality sensors;
• Use of heat recovery wheels and heat pipes;
• Use of automatic condenser tube brush cleaning systems; and
• Extensive energy metering provided on the chilled water system.

The lead mechanical designer for WSP Middle East of this highly-efficient and innovative HVAC design was technical director Peter Cummings, who is one of the UAE’s leading mechanical designers according to Rob. “His in-depth knowledge of large district cooling schemes and potential delta T issues is, in our view, second to none in the UAE,” he says.

Turning to the lighting, another critical item for Leed certification, Rob says: “Energy efficiency is a high priority in MEP design and as such the lighting design within the mall areas comprises high-efficiency lamps sources, which are controlled automatically so that elements are switched off when the natural daylight entering the mall space provides adequate light and are also switched in stages to minimise the energy consumption.”

A main driver in the design of Majid Al Futtaim shopping malls is to provide the maximum amount of retail space whilst also not detracting from the functionality of the project or the shoppers’ experience. Due to building code restrictions, a code-compliant building design was not the most suitable design option. Accordingly, a fully fire-engineered solution has been developed by WSP’s Fire & Life Safety designers in conjunction with DCD (Dubai Civil Defence) and comprises fully-sprinklered mall areas and shop units in accordance with the requirements of NFPA fire standards. The fire strategy includes a basic staged fire evacuation sequence but if a fire is confirmed all areas of the mall will evacuate.

WSP Group is one of the world’s fastest-growing design, engineering and management consultancies, specialising in property, transport and environmental projects. The company says it offers clients a quality, well-managed multi-disciplinary service, making use of its shared knowledge, global reach and local relationships.

Employing 550 people in the Middle East, the practice has offices in Dubai, Abu Dhabi, Sharjah, Damascus (Syria) and Qatar, and currently has live projects in the UAE, Syria, Egypt, Oman, Qatar, Saudi Arabia, Pakistan and Kuwait, and has been working on the Mirdif City Centre since November 2006.

“Local knowledge, and the need for a prompt response, was clearly a core part of successfully delivering this exciting project. Our team was acutely aware of the pressing timescales and budget constraints on projects and our priority was always to complete on time and within budget. To augment our core team, we called on a number of specialist teams, such as environmental, sustainability, fire and life safety and lighting specialists. Such niche input allows us to deliver the integrated, modern buildings new developments demand,” Rob says.

WSP, he says, has a reputation for excellence, innovative designs and attention to detail and provides creative, sustainable and cost-effective architectural and engineering solutions through innovative thinking. “To maintain our position at the forefront of UAE’s competitive market, we have developed a flexible approach,” he says.

WSP says it prides itself on being the leading retail consultancy both in the Middle East and the UK offering integrated expertise, which embraces the full cycle of retail projects, from planning support through design to completion and handover.

With a portfolio of current retail appointments across Scandinavia, the Middle East, Far East and South Africa, WSP assimilates retail best practice and lessons learnt from global experiences, and applies them to local markets.

“Creativity and innovation are seldom put to the test more than when engineering buildings. Our approach to all of our commissions has the same underlying philosophy – to work closely with the client, the architect and other team members to develop the most creative engineering solution of the highest quality; on time, and within the specified economic framework.

“We believe this approach has enabled us to deliver sustainable cost-effective solutions, as ably demonstrated on many notable projects, the latest one being Mirdif City Centre,” Rob says

Other MAF projects that WSP Middle East has been involved with include Mall of the Emirates, Deira City Centre, Sharjah City Centre, Ajman City Centre, Deira City Centre Sofitel Hotel, Sabboura Damascus and Mall of Egypt.