Additonal Interior Lighting Power

The display area. The whole sales area is covered by the initial allowance.

Hi, I have a further question concerning the modelling of Additonal Interior Lighting Power for a LEED v4 ID+C: Retail.

The main activity of the building is retail, only one room is used for this purpose, while the other rooms are used for auxiliary functions (storage, restrooms etc..).

In the shop area the design lighting power is higher than the baseline, at first sight I understand that it is possible to increase the baseline lighting power up to the design lighting power, within the limits of the Additional Lighting Power according to to section 9.6.2 of ASHRAE 90.1 2010, in order to level the baseline lighting power to the design one.

However, it is also said that "The additional allowance gets modeled in the baseline identical to the proposed", which is also what happens in the Minimum Performance Energy Calculator: as the Additional Lighting Power is declared, it is added to both the baseline and the design. Therefore the gap between the design and baseline lighting power is not mitigated...so, what is the rationale behind the Additional Lighting Power, if not levelling the baseline to the design?

Furthermore, being the Additional Lighting Power in my case 1000 W + 15 W/m2 * shop window area, in the Minimum Performance Energy Calculator, only the 15 W/m2 are actually added to the maximum allowance at the end of the sheet, why not the 1000 W?

Best regards, thanks in advance

The reason that the additional allowance is modeled identically is that display lighting is considered a process load, not a regulated lighting load. If the proposed general lighting design is higher than the baseline then you should be paying a penalty for that. So the purpose of the additional allowance is not to increase the baseline up to the proposed. Not sure about what is happening in the MEPC. All of the additional allowance should be process and modeled identically.