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Sat 27 Oct 2007 04:00 AM

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Air control

Variable refrigerant flow air conditioning systems are beginning to make their mark in the Middle East.

In an environment that uses air conditioning to such an extent, it is little surprise that technical innovation is constantly strived for. The system chosen to provide cool air to a building can have a significant effect on the overall energy consumption and the sector's manufacturers are continuously developing and improving products in the quest to meet greater demands for energy efficiency.

One technology that is beginning to gain in popularity due to its relatively low energy use is variable refrigerant flow (vrf) air conditioning systems. Recent research from the UK-based Building Services Research and Information Association (BSRIA) found that vrf systems are the fastest growing product type in the air conditioning sector. Its World Air Conditioning Market Review 2007 reports that the vrf market value is growing at double-figure percentage rates in all major countries worldwide and this trend is expected to continue. In the UK alone the market rose 40% in volume and 42% in value during 2006 and their use in the Middle East is beginning to rise. "They provide space saving and energy benefits - two factors which are being taken very seriously in this market, so they are an attractive option," explains Doug Hahn, general manager of the LG Electronics training academy.

By using a vrf system you can save up to 30% energy compared with traditional air conditioning.

Introduced in Japan over 20 years ago and already popular in European markets, the systems' outdoor units were previously unsuitable for use in the region due to the climatic conditions. However, product developments mean that is no longer the case and a number of manufacturers are now offering vrf systems specifically intended for use in such climates, with more set to be introduced later in 2007. But what is a vrf system?

System design

VRF systems typically comprise of an outdoor unit with multiple compressors that serves a number of individual indoor units to provide air conditioning for different zones in a building. The indoor units can simultaneously condition each area to establish individual setpoints.

The systems are ductless and transfer heat to or from a space by circulating refrigerant to evaporators located near or within the individual zones. In contrast, conventional systems transfer heat from the space to the refrigerant by circulating air or water throughout the building. An inbuilt controller regulates the amount of refrigerant flowing to the indoor units to enable temperatures to be met. "Every zone within a building requires a precise amount of cooling," explains Saidja Geirnaert general manager, Daikin Middle East. "This individual cooling capacity is achieved by matching the requirement with the exact amount of refrigerant volume needed to transport the required energy."

A direct digital control (DCC) system provides a network link between the controller and outdoor compressor unit to operate the entire system. This means that fan speeds can be operated to maintain heat, while the evaporator fans can be controlled to maintain precise temperature setpoints.

"An electronic expansion valve continually adjusts the flow of refrigerant to respond to the load requirements of the indoor units," adds Geirnaert. "This enables the system to maintain temperatures at a virtually constant and comfortable level without the fluctuations typical of conventional on/off control systems, meaning that less energy is wasted." Local, individual control of the indoor units is usually also possible.

The technology boasts a number of benefits over other types of air conditioning systems. VRF units are modular and lightweight making installation fast, simple and suitable for phased projects. "The small-bore piping system used can be installed quickly on a floor-by-floor basis so that sections of a building can be put into use quickly," explains Geirnaert. "This means that the air conditioning system can be commissioned and operated in stages rather than on final completion." The primary components of vrf systems also make them suitable for retrofitting into existing buildings as no structural changes are needed.

"The units are small and because [the main unit] is placed outside you have space saving, allowing for more rentable space," explains Basil Al Khayat, air conditioning divisional manager of United Electronics Company, the distributor of Mitsubishi VRF systems. "There is also flexibility over where you install the room units. Mitsubishi Electric's City Multi brand comes in exposed and concealed floor-mounted, ceiling suspended and wall-mounted versions, which can be positioned virtually anywhere within a room.

Variable refrigerant flow systems: the technology

Variable refrigerant flow (vrf) systems are an ‘intelligent', energy efficient means of providing air conditioning to buildings that include several zoned areas.

The systems typically comprise of an outdoor unit with multiple compressors and different types of indoor units to serve the individual zones. Each zone has an independent refrigerant loop, but all loops are controlled by a common system. The inbuilt electronic controls enable simultaneous control of the temperature in each of the zones.

This individual looping and control enables the use of evaporators of differing capacities and configurations within the same system.

"By using a vrf system you can also save up to 30% of the energy needed compared with traditional air conditioning units," adds Khayat. The use of vrf eliminates the losses associated with ducts, which can be around 10% to 20% of the total airflow. There is also the option of heat transfer, with the energy removed from an overheated area transported to a cooler area. In rooms that do not require cooling or heating the system can be completely switched off, increasing overall savings.

Maintenance for the systems requires mainly filter changes and coil cleaning. This compares favourably with water-cooled chillers that require water treatment, which can be costly. Also, because of the system's modularity, electricity sub-metering can be done on a room-by-room basis by simply attaching an electric meter to a condensing unit.

"The initial costs of purchasing a vrf system can be seen as one of the disadvantages," explains Khayat. This can however be recovered through energy savings during operation. A case study undertaken by Daikin showed that the Al Jad Hotel in Saudi Arabia saved around US $19,000 (AED69,800) in a single year by using the firm's VRVII system compared with a similar sized hotel using a traditional chiller system.

VRF systems are most suited to buildings that have several different zones and may require individual temperature control, such as high-rise offices, hotels or schools. Middle East applications of vrf technology include Qatar Navy offices and the Indian Embassy in Oman; Daikin's VRV system will also be applied in the Sharjah Airport expansion.

New developments

Several air conditioning manufacturers have launched updated versions of their vrf systems. Daikin has introduced a water-cooled version designed for use in new build commercial projects where no roof or external space is available for outdoor condensing units or where stringent noise restrictions apply. The system can also be fitted to an existing chilled water/cooling tower circuit during refurbishments. The condenser cooling is achieved by a plate heat exchanger located within the condensing unit casing and supplied with water at temperatures of 10-45°C.

LG Electronics and India-based Blue Star have both introduced models specifically aimed at conditions in the Middle East market. Blue Star's vrf systems are powered by Copeland digital scroll compressors, which can exactly match cooling requirements by delivering capacities of 10-100%. Its systems are offered with "tropicalised" outdoor units that can operate in ambient temperatures of up to 52°C. Compact outdoor units that can be positioned on balconies or terraces removes the need for a separate plantroom.

LG meanwhile is planning to launch the Multi V Tropical in September. An addition to its Multi V series that is already popular in Europe, the model is intended for high outdoor temperature use and can operate in temperatures of up to 54°C. A total of 14 outdoor unit choices will be offered, plus 16 types of indoor units, with a total of 61 model choices. The product has a cooling operation range of -5°C to 54°C and the outdoor unit includes a built-in controller, automatic refrigerant leakage detection and a high efficiency scroll compressor.

"The product will be suitable for the many high-rise buildings under construction in this region," explains Hahn. "It will be launched in September in selected Middle East countries initially. The installation of these systems needs capable, qualified contractors to ensure the correct operation," he explains.

To tackle this issue, LG Electronics offers courses in the installation and maintenance of vrf systems at its Dubai-based air conditioning academy. These range from one-day courses for sales engineers and consultants to three-day courses intended for engineers and supervisors. "VRF systems involve complex controls and special care is needed when installing the pipework, so there should be some experts on hand to deal with any problems," stresses Hahn. "We will train contractors and consultants, but will also provide support for the pipework specifications and selection of units," he adds. "Once contractors see the benefits of the systems the market will grow sharply," Hahn predicts.

System benefits

• Energy efficient operation
• Individual controllers on indoor units enable greater user comfort
• Compact, modular and lightweight design of units means a system is fast and easy to install
• No structural reinforcement or building alterations are needed for its installation
• No large pipes and air ducts required
• Low impact on net lettable space
• Refurbishment of the system is possible while the building remains in use
• Quiet operation.

Air conditioning and refrigeration will be located in Hall 1 at this year's Big 5.

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