Fully charged Fig 2 Lighting in nondomestic buildings
The LENI approach LENI offers a more holistic approach to energy efficiency, encouraging the effective control of lighting in equal measure to the use of energy efficient lamps and fittings; this means the designer is not restricted to specifying lamps and fittings above a set efficacy but through incorporating effective controls has the flexibility to select a range of luminaires, including lower efficacy ones. This flexible approach can be especially beneficial for creative lighting schemes, such as those designed to provide a particular visual effect. However, irrespective of the controls and fittings used the designer must demonstrate that the overall lighting scheme is both energy efficient, and provides the appropriate level of illuminance recommended in BS EN 12464-1: 20115 on the task areas (for example, providing a minimum illuminance of 300 lux on office desks). This is achieved where the calculated LENI value does not exceed the maximum energy Fig 3 Table 44 BSCG (part)
4 BS EN 15193-1: 2007 Energy performance of buildings. Energy requirements for lighting. 5 BS EN 12464-1: 2011 Light and lighting Lighting of work places - Indoor work places. 6 LENI has been written into the Simplified Building Energy Method (SBEM) UK software by the Building Research Establishment (BRE).
limit given in Table 44 of the non-domestic BSCG (see Fig 3). Table 44 of BSCG not only enables the designer to determine a maximum LENI but also gives a breakdown of the day time (Td) and night time (Tn)hours to be used in the relevant part of the calculation. The process is, therefore: • design the lighting system to meet the needs of the client for the space to be lit • look up the lighting energy limit for the number of hours and illuminance from Table 44 of BSCG • calculate the parasitic energy use where some form of lighting control that consumes energy is used - Ep • determine the total power consumed by the luminaires within the space - Pi • determine the occupancy factor – which is used to account for the energy saving created where there is automatic control for the turning off of lighting - Fo • determine the daylight factor – which is used where dimming is available during daylight hours and where sufficient light is available - Fd • determine the constant illuminance factor – takes into account both the maintenance factor used and the possible under-running of the lights. As illuminance falls due to age, power can be increased to account for the reduction in light levels. Where such a system is in place then a factor may be applied - Fc • calculate the day time energy usage Ed = (Pi×Fo×Fd×Fc×Td)/1000 • calculate the night time energy usage En = (Pi×Fo×Fc×Tn)/1000 • calculate the total energy per square metre per year (LENI) - LENI = (Ep×Ed×En)/A To demonstrate compliance the calculated LENI should not exceed the maximum energy limit value given in Table 44 of the non-domestic BSCG. In practice, software packages, such as the Simplified Building Energy Method6 (SBEM), are more likely to be used to perform the calculations. However, even where this is the case a sound knowledge of the method is still required to ensure the correct parameters are entered. Summary The role of the Building Regulations is not merely to set minimum efficiency targets but to encourage improved systems: an efficient lighting installation that is poorly controlled provides no real benefit. The LENI method offers an alternative option for demonstrating compliance that is based on the efficiency of the system, and as such allows the designer the flexibility to balance controls and energy efficient lights in a more holistic way. Connections Spring 2016
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