Enjoying the chilled-beam experience
Since their introduction to the UK in the 1970s, fan-coil units (FCUs) have provided air conditioning to thousands of commercial buildings. However, there is another option to consider, which delivers energy efficiency and, importantly, flexibility — namely the chilled beam. Yan Evans of Fläkt Woods explains why it’s time to move on from the FCU.
Chilled beams can provide energy efficient air conditioning, ventilation and high indoor air quality in commercial buildings such as offices, hotels, healthcare facilities and educational institutions. Their market has been increasing at a significant rate and, according to a recent report*, is expected to continue to do so between now and 2020 (globally at an 11.14 % compound annual growth rate). The market growth is mainly at the expense of traditional FCUs, and it’s easy to see why.
The most important factor is energy efficiency. Although in recent years FCUs have become more efficient due to the legislatively driven introduction of electronically commutated (EC) motors, they still can’t compete against chilled beams.
Chilled beams are significantly more energy efficient, with around 75% of cooling handled by water, rather than by having the full load handled by air. They offer savings of up to 40% over traditional air-conditioning systems.
Chilled-water temperatures in chilled beams are higher than in fan-coil systems — for example 14°C flow compared to 6°C. This higher flow temperature means the chiller used to create the chilled water will perform more efficiently for a chilled beam than for a fan coil — with energy savings of around 35%.
Free cooling is also available when the outside ambient air is sufficiently dry and cooler than the return-water temperature, and energy can be saved in the chiller and primary-air supply by using this free cooling.
Installation and maintenance costs are also higher with an FCU. Fan coils obviously have a fan, which involves electrical wiring, resulting in additional costs. Also, because the water temperature is so low in an FCU system, condensation will form on the pipework and the coil. This results in the need for anti-condensation protection, for example drip trays, at additional cost. As condensation will form on the coil and makes it wet, FCUs usually need a filter to prevent the coil becoming clogged with dirt.
In contrast, the installation and maintenance requirements for chilled beams are much lower. In a chilled-beam system there is no need for condensation protection, because the chilled water temperature is above a room’s ‘dew’ point (i.e. where condensation is formed). Since a chilled beam coil is dry, it doesn’t require a filter.
Although chilled beams offer many benefits, there is still a general lack of awareness about them. As market research indicates, the chilled-beam market is set to increase, but there are some misconceptions and stigmas that need to be addressed to further accelerate growth.
A major misconception is flexibility. In modern buildings, particularly offices, being able to adapt to change quickly has become a necessity. When a building is restructured, walls, people and furniture move around, and room functions and occupancy levels change. Therefore, air-conditioning and ventilation systems must be flexible to minimise effort and lead times involved in moving and adapting them. Often, the ability to adapt the room comfort system to new layouts is equally as important as investing in the latest energy-saving solution.
FCUs were sometimes favoured over chilled beams because they were considered more flexible.
Often when consultants and specifiers think about a chilled beam they picture a large, 3 m-long, rectangular beam that’s largely immovable and inflexible — not particularly helpful if walls need to be moved to change the layout of a building.
Today’s chilled beams are much more flexible. An example is Fläkt Woods’ Wega II chilled beam, an active system for ventilation, cooling and heating developed for the high demands of the modern, dynamic office.
With Wega II it is possible to change an office layout without having to move or install new chilled beams; only simple adjustment and reconfiguration of the vanes that control the airflow pattern and the variable-position nozzles is required. Even the Pi functionality (the Pi function is pressure independent and makes the product suitable for many types of ductwork system) is designed for change; it can be easily moved with the high-occupancy rooms by disconnecting, reconnecting and resetting the values.
The enhanced design includes variable-geometry nozzles to offer the widest choice of airflow settings. Nozzle change can be actuated to automatically adjust ventilation flow rates to occupancy levels, regardless of pressure changes in the ductwork system.
Today, chilled beams not only deliver a comfortable environment, high indoor air quality, minimum energy consumption and ease of installation and maintenance — they are also highly flexible and can be easily adapted to suit any future modifications of a building’s layout.
Yan Evans is vice president of the UK sales unit at Fläkt Woods