Calculate LENI-number
The LENI number is the rating index for lighting’s specific annual energy usage. The coming standard EN 15193, Energy performance of Buildings - Energy requirements for lighting, describes an harmonised calculation method for how energy usage for interior lighting is to be calculated within different buildings. The lighting’s energy efficiency in the building shall be rated by an index expressed in kWh/m², year (LENI*).
The LENI-number is to be presented for the entire building and can be used to compare the energy consumed for lighting. The comparison can be made between different buildings with the same function, but of a different size and design.
The standard will give example values of the LENI number for a number of common building types. These can be used as the basis for national recommendations.
The calculation of the LENI number for the building is done using the formula:
LENI calculated = W total / A (kWh/m², year)
The quick method
The quick method is used to give an estimate of the building’s annual energy usage. The method can be used for just a number of common building types. The standard includes tables where the annual standard data for different types of buildings can be read to aid calculation according to the quick method.
These are offices, buildings for tuition, hospitals, hotel, restaurants, sports centres, department stores and retail shops and manufacturing industries.
The quick method also includes a standard value for the parasitic energy (Wparasitic) which is stated as 6 kWh /m² and year and which should be used when applicable.
It is distributed over 1 kWh /m² and year for charging emergency lighting and 5 kWh /m² and year for standby energy for the ballast.
LENI = Wlight + Wparasitic/A kWh/m², year
The comprehensive method
The comprehensive method is based on actual values for each room. Unlike the quick method, the comprehensive method can be used for all types of buildings even at different geographical positions. As the comprehensive method is based on actual values it gives a lower LENI number than a calculation with the quick method.
The comprehensive method can be used for all types of buildings irrespective of geographical location. Using the comprehensive method you can calculate for a selected period (not only the whole year) under the condition that you can get an estimation of the presence and availability of daylight. In the examples on the coming pages we have used the comprehensive method.
LENI = Wlight + Wparasitic/A kWh/m², time
| LENI | is calculated on the lighting for the entire building. At the same time the lighting shall conform to current standards and recommendations for indoor lighting (EN 12464-1). |
| Wtotal |
is the total annual energy usage for lighting. |
| A | is the building’s total interior areata (m²). |