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Thu 14 Feb 2008 04:00 AM

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Integrated design

How can you achieve good indoor air quality and energy efficient operations? Reem Emirates Aluminium demonstrates an integrated approach at its new headquarters.

How can you achieve good indoor air quality and energy efficient operations? Reem Emirates Aluminium demonstrates an integrated approach at its new headquarters.

Gaining maximum energy efficiency and a good indoor environmental quality simultaneously is a primary goal of any new building, particularly if it is to meet the green building standards being applied worldwide today.

Achieving this goal is not always an easy task, but Reem Emirates Aluminium believes it can be met by use of its integrated approach to heating, ventilating and air conditioning (hvac). The firm is currently putting its proposed solution into action on its own new headquarters building in Abu Dhabi.

Based in the industrial Musaffah area of the city, the firm's four-storey headquarters is scheduled for completion in March 2008. The crescent-shaped building is being built directly onto the firm's existing warehouse facility and will have a fully-glazed facade that will form a central part of its energy efficient operation.

And Reem is not just purely speculating about the success of its solution. Across the car park from its new headquarters sits an unassuming looking building. From the outside it could be a caretaker's house or storeroom, but step inside and you will come face-to-face with an advanced integrated hvac solution.

The building is in fact a full-scale mock-up that was constructed to test and fine-tune the integrated system. Measuring around 6x6m, it is equivalent to the standard area for four office desk spaces.

Reem describes its solution as a fully integrated, intelligent and energy saving mechanically ventilated double-skin green wall. The overall system includes an active facade, chilled beams, underfloor cooling, light emitting diode (LED) lighting and motorised blinds - all controlled by a complex building management system (bms).

The firm's motivation was to form a true green hvac building solution and launch active facades into the Middle East market reports Reem Emirates Aluminium r&d engineer Imthias Mohamed.

"The company's main focus was to be a next generation curtain wall designer," explains Mohamed. It established an r&d division in September 2006 with a focus of developing a curtain wall that integrates with other building hvac systems. With its headquarters underway, the firm decided to construct the mock-up building to ensure that the proposed solution would work in practice.

"The main concept is to conserve energy consumption," stresses Mohamed. "The system addresses the two major categories of [US Green Building Council's Leadership in Energy and Environmental Design rating system] LEED: energy and atmosphere, plus indoor environmental quality (IEQ). These give a total of 32 points under LEED, which is about 46% of the points straightaway," he adds.

The concept involves creating a constant temperature throughout the room to increase occupant comfort, hence productivity; and achieving this temperature through the minimal use of mechanical energy. The technology and products used in the system was existing; what is new is the use of some components in the Middle East's environmental conditions, plus the integration of the individual products to make a single operating system.

MEP consultant Deerns Middle East carried out a series of cfd modelling and calculations to ensure that the systems could be effectively integrated. "In integrated solutions the design is very important as each part has to be balanced with one another," stresses Deerns Middle East director Hans Hamer.

Creating the desired temperature while eliminating the build-up of condensation on the chilled beams and underfloor cooling system was one of the biggest challenges for the design team.

This was overcome by a series of tests that determined the precise mix of chilled water flow rates and air flow rates that were needed through the various equipment to meet the desired setpoints. From the results of these tests and experiments a series of formulas were created that are used to operate the bms.

Installation of the system is simple and needs no specialist training, assures Mohamed and the payback time is less than three years due to the reduction in energy use that would be achieved.
A building with standard hvac systems would cost around 1250 dirhams/m2 (US $340), [installing this system] would be about 15% more but this can be easily overcome in about two to three years by the energy bills," states Mohamed. "Investment, operational and maintenance costs are very negligible because you will save up to 50% energy," he adds.

The application of the active façade will provide energy savings of around 30% reports Reem, with the combination of the floor cooling and chilled beams adding another 20%. The use of daylighting is maximised and should reduce the artificial lighting load by around 25%.

The integrated system applied to the mock-up room has been tested by an independent third party and achieved Category A under ISO 7,730. It also meets the ASHRAE 55: 2004 standard for comfort.

Around 60% of the firm's new headquarters will be served by the integrated solution; the remainder will have conventional hvac systems installed. This, Mohamed explains, is due to the orientation of the existing building to which it will be attached, but it will also enable the firm to provide long-term energy and cost comparisons.

The system can potentially be applied to all buildings, but Mohamed warns: "This type of concept should be considered at the initial stages, not after the contracts are awarded - it should be at the first stage on the drawing board. The green building concept is difficult to introduce at a later stage," he stresses.

Lighting for lower energy loads

The concept of the integrated system includes maximising the use of daylighting, hence minimising the amount of artificial light used. Photocells located on the ceiling measure the lux level in the room and the automated blinds in the active façade adjust to allow as in much daylight as is needed to maintain the setpoint.

Artificial lighting is provided by light emitting diodes (LED). A series of LED strips are connected with a standard electronic ballast in a specially designed luminaire; these will illuminate and dim as needed to maintain the setpoint lux level. The lamps were chosen for their long lifespan, low maintenance and low energy use.

Their relatively low heat build-up was also a consideration as lighting in buildings can account for up to 40% of the cooling load needs, reports Mohamed.

Reem Emirates manufactured the luminaire casing for the lamps and will be offering the system on a commercial basis in future in conjunction with the LED manufacturer. The firm estimates that lighting energy costs will be 75% lower compared to incandescent bulbs and around 40% lower than if fluorescent lighting was installed.

Chilled beams

Cooling for the building is divided into two distinct systems that operate simultaneously under bms control. The first of these is active chilled beams, which are installed in a false ceiling. An air/water system, this operates using dry cooling principles.

The primary fresh air supply is fed into the chilled beam plenum, from here it is distributed into the room through nozzles located around the base of the beam. The room supply air is directed across the ceiling surface from where it falls gradually, preventing cool spots and draughts.

This system is served by the same chiller as the underfloor cooling, so has a similar water inlet temperatre of 16°C. The cooling capacity is controlled by regulating the water flow rate in conjunction with the building management system (bms): temperature sensors around the room provide the readings needed to ensure the temperature setpoint is maintained.

Active facade with integrated blinds

One of the principal features of Reem's integrated system is an active ventilated double-skin facade. This comprises of a double-glazed outer skin and a single-glazed inner skin, with an air cavity separating the two.

The outer glass has a low-emissivity (low-e) coating, which reduces the solar heat gain while maximising the daylight entering the building. The purpose of the cavity is to remove as much heat as possible before it penetrates the building, so reducing the overall cooling load.
Air is circulated through the cavity space at low flow rate, entering through a profiled air inlet at the base that pushes the flow across the glass surface. It is extracted through a funnel-type chimney at the top of each curtain wall panel, from where it can be recirculated in the hvac system or extracted to the outside.

"The air velocity is very slow; it is about 0.1m/s," reports Mohamed, "Even when [the system] was smoke tested it was very difficult to see [the movement] as the flow was minimal." The overall U-value of the facade is 1.04 and the ventilation system is designed to maintain a laminar airflow with a Reynolds number of less than 2,000.

"During tests we've found that when the surface temperature [of the outer glazing] is about 61°C, the inside temperature was 24°C, so [the active façade] is effectively able to remove heat before it comes inside the building," stresses Mohamed.

A fully-computerised, motorised blind system is installed inside the facade cavity; this controls the amount of daylight entering. The blinds are linked to the building management system and automatically adjust to maintain the setpoint lux level in the building. Light sensors on the ceiling measure the levels in real time for immediate adjustment.

The full length of each concave blind slat is perforated along one half and solid on their other half. This removes problems of glare, while enabling light into the rooms and maintaining an outdoor view for occupants. The perforations also allow the air flow to filter through the cavity regardless of whether the blinds are fully open or closed, explains Mohamed.

The high luminance of the blind surface reflects the sunlight towards the building's ceilings. Blinds are also connected to the fire alarm system and will fully open in the event that an alarm sounds to aid with occupant safety while leaving the building.

In addition to the daylight penetration and solar heat gain control, the facade has been proven to increase sound insulation by up to 20%.

Underfloor cooling

The second cooling system is underfloor cooling. This was provided in a turnkey package by consultant Voland Technologie. In this system chilled water is run through a network of PEX-A pipes over which a concrete screed is poured. The concept of the system is to use the thermal mass of the floor slab as a cooling coil, therefore reducing the mechanical cooling energy needs.

The constant closed-loop operating system is designed to be low maintenance and was tested prior to laying the floor. The inlet water temperature from the chiller is around 16°C, with an outlet temperature of around 18°C. Cooling of the air is by convection, so occupant comfort is increased as there are no draughts.

The pipes are run throughout the room, with the spacing varying according to their distance from the facade and system manifolds. Spacing ranges from around 5cm at the manifolds to 8cm along the facade and 10cm in the main floor area.

Although similar in design to the underfloor heating systems commonly used in Europe, some products have been adapted to meet the demands of the tropical climate experienced locally: the pipes, for example are thinner.

The flow rate through the system is around 2l/s and it's operational reliability has been fully tested in the mock-up room.

Mohamed explains: "The medium for this floor cooling system has been especially adapted for the climate in this region - even if you have a [power] blackout for the whole day you can work as a normal office as [the underfloor cooling] works on a thermal mass. You have the coolth there and it will retain this for about eight to ten hours," he assures.

Building management system

The building management system (bms) is central to the operation of the integrated system. Provided with information from a network of sensors in the building as well as data from the separate hvac systems such as the chilled beams, the bms is ultimately responsible for the efficient running of the systems and for maintaining the indoor environmental quality.

The bms can calculate the preset needs of the building and control the flow rates to the various systems to maintain the temperature that is needed within the building.

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