Page 54 - GRIHA Manual Volume III - Introduction to National Rating System
P. 54
Building and system design optimization 47
Step7 Calculate the number of luminaires: By the lumen method of calculation, calculate the
number of luminaires. In the example above, the number of luminaires would be 24 in
order to maintain 300 lux (as recommended by NBC-2005). The lamp lumen output in this
case is 2450 lumen.
40W Tube
Light
Figure 32 Software snapshot showing ineficient lighting system
Step 8 Calculate lighting power density: The interior lighting power density (LPD) should not
exceed the value recommended by ECBC-2007 for either the building area method or space
function method. For example, if the total lighting load of an office space is [(40+15) × 21]
2
2
= 1155 watt and area is 84 m , the LPD of that particular space is (1200/84) = 13.75 W/m .
Step 9 Compare with the standards: From the energy efficiency point of view, the lighting
2
power density, which is defined as the ratio of connected load (watt) to floor area (m ),
is mentioned in the ECBC-2007. The lighting power density of a space should not exceed
2
the recommended lighting power density. This exercise gives an LPD of 13.75W/m , which
exceeds the recommended ECBC-2007 criteria. Hence, the lighting system is overdesigned.
Then, the decision would be to redesign the lighting scheme.
Step7 Calculate the number of luminaires: By the lumen method of calculation, calculate the
number of luminaires. In the example above, the number of luminaires would be 24 in
order to maintain 300 lux (as recommended by NBC-2005). The lamp lumen output in this
case is 2450 lumen.
40W Tube
Light
Figure 32 Software snapshot showing ineficient lighting system
Step 8 Calculate lighting power density: The interior lighting power density (LPD) should not
exceed the value recommended by ECBC-2007 for either the building area method or space
function method. For example, if the total lighting load of an office space is [(40+15) × 21]
2
2
= 1155 watt and area is 84 m , the LPD of that particular space is (1200/84) = 13.75 W/m .
Step 9 Compare with the standards: From the energy efficiency point of view, the lighting
2
power density, which is defined as the ratio of connected load (watt) to floor area (m ),
is mentioned in the ECBC-2007. The lighting power density of a space should not exceed
2
the recommended lighting power density. This exercise gives an LPD of 13.75W/m , which
exceeds the recommended ECBC-2007 criteria. Hence, the lighting system is overdesigned.
Then, the decision would be to redesign the lighting scheme.
