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BSEE CHILLED BEAMS & CEILINGS Adversing: 01622 699116 Editorial: 01354 461430


Andrew Gaskell, Chairman of the Chilled Beam & Ceiling Associaon, dispels some common misconcepons about chilled beams and draws aenon to some of their key benefits that building managers should consider when choosing their cooling system.


THE CASE FOR CHILLED BEAMS Dispelling the misconcepons


D ‘


espite making their first appearance in the UK in the 1960s, chilled beams are, still considered a new concept by some. They have also drawn their own set of criticisms too,


but many of these are borne more out of misunderstanding or lack of knowledge, than actual evidence.


Energy eciency of chilled beams versus other systems


Chilled beams have no integral fans, passive chilled beams (PCBs) utilise natural convection and active chilled beams (ACBs) rely on primary air as the driver to generate induction of secondary air over the heat exchanger coils, which saves fan energy.


Most energy savings are due to the system’s use of elevated chilled water temperatures. The central chiller that supplies the chilled beam circuits should be designed to operate at the chilled beam elevated temperatures; this results in increased chiller COP and allows for the chiller to obtain ‘free cooling’ through certain times of the year (subject to the chiller having a free cooling coil), which all saves substantial energy. The latest chilled beams can improve energy efficiency further as they can provide much higher cooling levels than the previous technology, with no increase in product size or cost. It is becoming much more beneficial to increase the summer design chilled water flow temperature from the industry standard 14°C to higher temperatures such as 18°C to achieve increased energy savings.


Chilled beams


have no moving parts and so, subject to correct water quality, the life expectancy can easily exceed 20 years. Other systems with fans are oen replaced when the fan fails, as it is cheaper to replace the unit than just the fan.


The following graph (based on the findings of an independent energy study conducted by EDSL for FETA) details typical plant energy savings for using a chilled water flow condition above 14°C:


water temperatures to use elevated temperatures this normally results in increased unit sizes, more products and so increased capital expenditure. Chilled beams have, in the past, been deemed to be large, chunky pieces of equipment that can’t be moved, say if the building is undergoing redevelopment. In fact, the latest solutions are extremely flexible, allowing changes to be made to the building’s internal layout without moving or adding beams. Restructuring the chilled beam system can be a straightforward process with slight alterations to the settings without impacting on the air conditioning and its overall performance. Beam aesthetics can also be customised to meet specific client requirements.


Are they dicult to maintain?


One of the main advantages with chilled beams is that they have no moving parts, no filters to replace, no drip trays to biocide and no condensate lines to maintain. Apart from cleaning on the outside with a damp cloth or vacuuming, the coils may only need to be cleaned once every five years or more depending on the installation (hospitals require six monthly checks but offices often never need cleaning). Chilled beams have no moving parts and so, subject to correct water quality, the life expectancy can easily exceed 20 years. Other systems with fans are often replaced when the fan fails, as it is cheaper to replace the unit than just the fan.


Can they provide comfort cooling?


Chilled beam systems can achieve lower air velocities and more uniform temperature gradients within the occupied zone than other forms of cooling; this achieves higher occupant comfort. Active chilled beams (closed back) only induce air from the room and so do not take air


from within the ceiling void, which improves air quality (ceiling voids can have dust/debris, which lowers air quality).


Radiant chilled ceilings and also radiant chilled beams/sails can be used with displacement ventilation to achieve much higher air quality within the occupied zone. Chilled ceilings produce the lowest level of mixing of the room air, with hybrid radiant chilled beams the next best solution. As there is less mixing in the space as cooling is achieved by radiant transfer the extract air at high level will remove most of the contaminants as the warmer air rises because the occupied zone is provided by the cooling displacement ventilation. Also, chilled beams have no fans, therefore noise levels are much lower.


What about actual ‘real’ energy usage?


As chilled beams are a complete terminal unit the performances stated during the design process can easily be determined/investigated. Eurovent Certification for instance spot checks manufacturers’ data by testing random products so, subject to the correct physical parameters, the chilled beam should achieve what is specified. All energy is consumed by the chiller, AHU, pumps and controls which, with a centralised plant, is relatively easy to measure and confirm that the energy use is as expected.


In contrast, other systems with integral fans which are not a complete terminal unit require air discharge grilles and interconnecting ductwork, all of which add resistance and so affect fan energy. In most instances the manufacturer’s fan consumption data is based on a small amount of straight ductwork and a low pressure drop grille. In reality, installations will have varying amounts of ductwork with bends and may have a grille which is untested with the FCU, which all increases fan energy over that of the design.


Acve Chilled Beam Addendum to Part L ’


To further improve energy savings from that shown in the above chart it is most beneficial for the chilled water flow temperature to be controlled based on the outside conditions. The system design level of cooling will only be required for a relatively small proportion of the year and for the majority of the rest of the year higher than normal chilled water temperatures can still achieve the required cooling but offer further increased energy savings due to higher Coefficients of Performance (COPs) and additional free cooling (subject to having a free cooling chiller).


Other technologies try to offer similar energy savings by promoting elevated temperatures, however, as other solutions are designed for lower


18 BUILDING SERVICES & ENVIRONMENTAL ENGINEER DECEMBER 2017


ctive Chilled Beams (ACBs) can provide the major part of system cooling but often require higher Air Handling Unit (AHU) specific fan power (SFP) in order to achieve adequate induction on the terminal units; although the AHU SFP may be increased by use of ACBs as the chosen terminal unit, the overall/total system energy consumption is greatly reduced and as such there is a reduction in carbon emissions in both new and existing non-domestic buildings. To enable designers a greater choice of AHU for systems with ACBs as the terminal units for an overall reduction in energy usage, there has been an addendum to the non-domestic building services compliance guide (2013 edition) to make allowance for ACBs’ overall system efficiency. The addendum incorporates DCLG’s view that when referring to Table 35 the maximum SFP for the central air handling unit, with heating and cooling for an active chilled beam system has an additional 0.3 SFP allowance as follows:


A


The above AHU SFP figures are prior to the inclusion of further SFP allowances for additional components as detailed in Table 36 of the compliance guide.


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