EAc1 LEED points can't fall entirely on the back of the MEP!

I've probably seen as many LEED files as most LEED reviewers. What blows my mind is that most of the files I have seen save very little in lighting, even though lighting is often 25% of the building energy costs. In my opinion, this is a result of Architects and firms who, let's face it, are too set in their ways to change their designs. (Either that, or it's just plain laziness).  Perhaps, I am being harsh and they simply don’t understand the huge impact lighting has on LEED points. So, I’m going to spell it out mathematically, but first let’s see how a typical conversation goes:

"We have a design that is going to save 30% on energy costs annually. The HVAC has an improvement of 35% over the 90.1-2007 baseline, and we are using such and such.."

…..But then, I look at the lighting and see that it is designed at 1.2 watts/sq ft compared to a baseline building at 1.3 w/sq ft .

Now if you're asking, "what's wrong with this?"-  I want to ask you, "What's wrong with you and why are you reading my blog?" Okay, maybe I'm being harsh again but it's really simple math and I shouldn't need to explain it in depth. The truth is that lights are one of the best ways to earn LEED points.

Here's a rule of thumb for LEED buildings:

 Whatever your intended net savings on LEED is, your lighting design should save that percentage against the whole building method. (for buildings where lights are the typical 15-25% of savings)

Example:  

Target savings: 30%

Whole building method lighting: 1.2 w/sq ft

Designed lighting (after 10% credit for sensors) equal or less than: 1.2 *.7  = .84 w/sq ft 

Now, I see a lot of jaws drop at this, but that's only because they have been designing buildings the same way for 30 years. The message from LEED is that things need to change. The work that will go into this design will save days and maybe weeks of backtracking in the design when you find that it’s mathematically impossible to save 30% on your project without saving more in your lighting. That said, let’s take a look at the TRUE impact of lights on LEED points

What is the true extent of designing highly efficient lighting systems?

Let's assume we are comparing to a baseline building that uses 1.3 w/sq ft on (whole building area method) and let's assume the whole building design averages to .84 w/sq ft. What is the savings on this? Well, most people will say, "that's easy, .46/1.3 or 35%"

However, most people forget about the additional savings that comes from lights, especially in a cooling and in heating when the heat is non-electric. Remember, lights give off heat and therefore increase the amount of cooling energy (compressor, fan, and heat rejection).

So, what's the real saving:

Let's assume a VAV system and that lights save on the compressor, fan, and heat rejection with an overall EER of 13.65 (~COP of 4)

.46 w/sq ft = .46 w/sq ft immediate lighting savings

.46 w/sq ft * 1/4 = .115 w/sq ft compressor/fan savings          

Total: .575 w/sq ft actual savings in cooling mode

So, a 35% savings on the lighting yields an effective savings of nearly 45%.

Yeah, but don't the lights provide "free" heat in heating mode?

Let's assume there is gas heat, electricity costs $ .10 kw-hr, and gas costs $1.00/therm (so we will do this in costs). We will also assume a 90% efficiency in heating equipment and 4000 hours of operation.

Using the energy-modeler's unit converter, we find that 1 therm = 29.3 kw-hr

.46 w/sq ft *$.00010/w-hr*4000hrs = $.184 /sq ft immediate lighting savings

.46 w/sq ft /29300 w/thm*1/.9*4000hrs =  -$.070 /sq ft addtnl heating required  

  Net savings of $.114/sq ft in heating mode

So, yes, there is an offset in heating mode but there is still substantial savings as long as the heating is provided using low cost fossil fuels (relative to electricity) or if heat pumps are used in heating mode. 

Furthermore, most commercial buildings have a significant amount of cooling required. Remember, even in economizer mode, additional cooling means more fan energy.

Several sets of data were simulated in eQUEST to see how various cities saved. As predicted, cities with greater cooling showed the greatest savings per watt of lighting saved. It was surprising that even Fairbanks, Alaska had similar savings to climates like Miami. If additional effects, such as summer demand charges are considered, the savings would further increase!

See the calculated data for yourself: