Page 176 - AGC_EN_iBook

176
SPeCIFIC PeRFORmaNCe LeVeLS
Certain speci c performance levels are achieved with a view to saving energy or ful lling legal requirements.
the temperature factor
The temperature factor of a construction detail equals the inside surface temperature when the temperature difference inside- outside is equal to 1°C.The temperature factor is a measure
of the risk of surface condensation.
The technical requirements de ned by Belgium’s BBRI (Belgian Building Research Institute) state that, in Belgium, the tempera- ture factor at each point of an indoor surface must be higher than 0.7. It may be less for window frames when there is a system available for evacuating condensation.
the airtightness of the building envelope
The airtightness of a building envelope is a measure of in ltration losses (uncontrolled and unintentional ventilation).The ‘blower- door test’ is used to measure a building’s airtightness in accord- ance with standard NBN EN 13829 (Thermal Performance of Buildings – Determination of air permeability of buildings –
Fan pressurisation method).
Airtightness is expressed as the air change rate n50. This value represents the number of air changes per hour at 50 Pa.
In Belgium there is no legal requirement regarding a build-
ing’s airtightness, though BBRI recommends an n50 air change value between 1 and 2 to ensure optimal operation of the heat exchanger. Ideally an n50 air change value of 0.6 should not be exceeded. Achieving this performance in practice requires great care to be taken in designing and implementing the various build- ing details.
The blower-door measurements conducted for the building (including of ces, meeting rooms, restaurant and gallery) showed a value of 0.77 for the air change rate n50.
the energy use of the fans
Energy use of the fans is determined by the ow rate, the perfor- mance of the motors and the mechanical transmission systems, the air velocity in the air handling unit and in the ducts, the net- work’s geometry (curves, ttings, etc.) and the losses in the differ- ent system components (coils, silencers, lters, grilles, etc.).