Changes to UK Building Regulations
There has recently been a change to Part L of the UK Building Regulations, which gives recognition to the energy efficiency of Active Chilled Beams, in that they use no secondary fan power.
Part L contains limiting SFP (Specific Fan Power) figures for both ‘primary’ Air Handling Units and also secondary terminal units (e.g. Fan Coil Units), but until recently made no differentiation for AHUs serving different secondary system types. Active Chilled Beams don’t use a secondary fan, so consume no secondary fan energy, relying instead on the pressure generated by the primary Air Handling Unit fresh air supply to generate induction of room air through a cooling/heating coil. This additional pressure means that the SFP of the Air Handling Unit delivering the building’s primary fresh air requirement may increase, but as no secondary fan energy is required to recirculate room air through the cooling or heating coil of the room terminal units, the overall system fan energy is lower. Prior to the recent addendum, the maximum SFP within Part L could on occasion prevent designers from using Active Chilled Beams as the additional pressure could raise the primary Air Handling Unit SFP above the regulatory limit, thus forcing the designer to use a system with secondary fans, which gave the counter-productive outcome of a higher system energy use.
Thankfully however, having had this anomaly brought to their attention by the UK CBCA (Chilled Beam and Ceiling Association), the governmental department responsible for Part L (the DCLG) have recognised and addressed this by issuing an addendum to Part L that gives an additional allowance of 0.3w/l/s to the SFP of an Air Handling Unit serving an Active Chilled Beam system, meaning that designers now have more possibility to utilise Active Chilled Beam technology, avoid secondary fans and thus improving efficiencies to reduce overall system energy use.