So when calculating the Allowable Exterior Lighting Power for your Baseline energy model, there are Tradable Surfaces and Non-tradable surfaces. My question is concerned with how LEED handles lighting on Non-tradable surfaces.
It's my understanding that allowances for tradable surfaces are such that if you over-light a parking lot, you can make up for it by under-lighting a canopy. You also get to take credit for good lighting design if the sum of your installed lighting on tradable surfaces is less than the sum of allowable lighting per 90.1 table 9.4.5. For example, if you have designed 10 kW of lighting, and the allowable lighting power is 12 kW, you can show 2 kW of savings in your energy model.
For non-tradable surfaces, ASHRAE 90.1 says that you cannot compensate for overlighting a building facade by underlighting a loading dock for ambulances. I have no problem with this. What I have a problem with is the LEED Credit Form saying "Values [for Non-Tradable Surface Exterior Lighting Power] should be identical in the Baseline and Proposed Case." In other words, if a project uses super-energy-effienct lights to illuminate a building facade with 10 kW, and the allowable lighting power per Table 9.4.5 is 12 kW, I CANNOT take credit for this 2 kW savings in my energy model! Instead I have to put only 10 kW of lighting in the baseline case energy model.
This does not seem fair, nor does it seem to agree with the intent of ASHRAE 90.1. Does anyone know the USGBC's reasoning for this?
Bill Swanson
Sr. Electrical EngineerIntegrated Design Solutions
LEEDuser Expert
734 thumbs up
April 6, 2010 - 9:51 am
Sounds like you understand it very well. The ASHRAE 90.1 Handbook describes the non-tradeable allowances as "use it or lose it".
I understand your frustration. Everyone finds things they don't understand about this energy model. I can only guess why they made this as a use it or lose it allowance. Most buildings don't have much facade lighting even without ASHRAE 90.1. So why reward them with an "energy savings" for doing what they were doing anyways.
And some may try to game the system. If I add 1 wall pack with some uplight over a door on a side of the building. What's to stop me from claiming the allowance for the entire wall area on that side of the building, even if the building is 100'Wide x 200'Tall. A 4000 W allowance with a single 50W MH lamp installed. Look at that. A 98.3% energy savings, I am uber green!
While it's frustrating and seemingly arbitrary it won't have much affect on your overall calculations. The difference in wattage in these areas is usually pretty small in comparison to the whole buildings' lighting wattage. I doubt the difference would be noticable.
The interior building allowances also have some "use it or lose it" values. Look at 9.6.2. Art exibits and retail get additional non-tradeable wattage. And the 2004 and earlier versions gave us extra wattage in rooms with computers.
Mark Benson
72 thumbs up
April 6, 2010 - 12:08 pm
Bill, I've reviewed the ASHRAE 90.1 User's Manual and found, like you indicated, that additional interior lighting per 9.6.2 is considered "use-it-or-lose-it." However, nowhere in 90.1 or the User's Manual does it indicate that exterior lighting power on non-tradable surfaces is "use-it-or-lose-it" or has to be the same in the baseline and proposed. On the contrary, the User's Manual states in Chapter 'G', "If the proposed building does not have an exterior lighting application (for instance a parking lot that is not lighted), the baseline building shall not have the exterior lighting application either. If the lighting application exists, however, then the proposed building can take credit for a more efficient system."
I agree that gaming the system is unethical and should not be allowed, but if lighting for non-tradable surfaces should be identical to prevent gaming, why not do the same for lighting on tradable surfaces? I could have one pole-mounted light in a huge parking lot and consider the entire parking lot to be lit in the baseline, showing a large amount of savings. But if it is not the intent of the lighting designer to illuminate the entire parking lot with that one light, the baseline approach would be unethical. The same goes for your hypothetical scenario with the wall-pack. If the intent is to just illuminate the door or the area just above the door, the baseline should not include the entire wall in its allowable lighting power.
Finally, I agree that exterior lighting is usually not a huge component of a building's overall energy consumption. I just want to take credit where credit is due, and I believe the quote from the User's Manual above indicates that this can be done: "If the lighting application exists, however, then the proposed building can take credit for a more efficient system." Thanks for your input.