I’m finding that the lighting energy requirements of ASHRAE/IESNA Standard 90.1 are less efficient than standard practice in the field. Standard 90.1 is the “Energy Standard for Buildings Except Low Rise Residential Buildings” and is often used by design professionals as the de facto energy code. The 2013 edition of the Standard has just been released and amazingly, the allowed lighting power density (LPD)1 has increased since 2004 for several common space types, such as private offices, and for multiple building types, including offices and parking garages. Yet, since 2004 the energy efficiency of lighting equipment has improved dramatically. Why is the code going the wrong way?
Because lighting technology is increasingly efficient, yet the standard allows higher connected loads for lighting, most design teams are achieving lighting designs that are more efficient than the standard. In a recent code compliance study completed by Cx Associates for New York State, we found that lighting compliance with LPD requirements was consistently high and that in fact the installed LPDs of the buildings surveyed was 10% better than that required by 90.1-2004. The buildings addressed in this study did not participate in any energy efficiency programs.
The failure to increase the restrictiveness of the lighting power density requirements does not necessarily result in new buildings constructed with significantly more lighting or higher connected lighting loads. Since lighting fixtures are expensive, there are budget-driven downward pressures on lighting loads in most projects. However, in many cases, the baseline design for the building lighting is easily achieving 20-30% energy savings relative to the code. The lax lighting requirements enable designers to either use more energy elsewhere while still complying overall, or it generates huge “paper” savings relative to a code compliant building.
With the new focus on trading off lighting allowances for controls in recent editions of the standard, design professionals can generate even higher baseline loads for their building lighting and claim additional savings for installing controls such as daylight dimming. However, since an office can be adequately illuminated with a lighting design that has an LPD less than 1 W/sf, then why would there need to be an allowance to increase the connected load simply because it will be automatically turned off when the sun is shining? Using a 10 x 12 office with two 2-lamp fixtures with HP-T-8 lamps, we can achieve an installed LPD of 0.8 watts per square foot and maintain illuminance levels at the desktop of 30 FC (foot candles). This very typical design saves 28% from the maximum allowed private office LPD. However, if we add daylighting controls and a zoned occupancy sensor control we get a bonus of 9.6 watts in the lighting allowance, increasing the baseline to 1.19 W/sf and upping the “savings” relative to code to 33%.
The art allowance
The standard allows additional interior lighting power “for spaces in which lighting is specified to be installed in addition to the general lighting for the purpose of decorative appearance or for highlighting art … provided that the additional lighting power shall not exceed 1.0 W/sf of such spaces.” The office described above might include two LED spots for illumination of art in executive offices. Including two 15 watt LED spot lights to illuminate art in this office results in an LPD of 1.05 W/sf, while the code provides an allowance of 1.44 W/sf for the space including the controls bonuses outlined above. I’m sure most design teams won’t exploit the additional allowance, but some will and we will see buildings that receive awards and appear to be extremely energy efficient that are using significantly more lighting energy than similar buildings constructed only 5 years ago.
Energy savings undermined
There is another aspect of the controls-based allowances that concerns me. Since most states have minimal enforcement of the energy code, and commissioning practices and skill sets range drastically, it is unlikely that the “additional” savings from controls will be fully realized. In our work doing re-commissioning and measurement and verification, we have found two things that will undermine savings.
- People tend to turn off lights significantly more than might be expected, and people close blinds to control glare and solar gain. This means that the savings associated with daylight dimming may be considerably less than expected.
- Controls often don’t work as expected. This means that the higher installed lighting wattage for a minimally code compliant building may well be on all day, resulting in a long-term energy penalty for the minimally code compliant building.
Buildings and lighting design
Lighting design is important to me. I believe that good lighting makes a significant contribution to the quality of the built environment. I do not support poorly designed, under illuminated “solutions” to code compliance that in rare instances do occur. Lighting should be designed for ambiance, comfort and effectiveness. I’ve been an Illuminating Engineering Society of North America (IESNA) member for the past 10 years and for most of the 10 years during which I practiced as an electrical engineer in San Francisco.
Buildings and carbon emissions
According to the U.S. Energy Information Administration, the buildings we live and work in contributed to just over 40% of the country’s CO2 emissions; more than any sector including transportation. The IESNA needs to recognize that global warming is real and that buildings contribute significantly to carbon emissions. We can create beautiful, artful spaces with less installed lighting wattage and then reduce energy consumption even further with controls. The code should reflect current practice at a minimum instead of lagging behind by a decade or more. Because I care about lighting and the planet, I’m looking for the IESNA to show better leadership relative to energy efficiency.
1 LPD is the maximum power allowance for lighting energy use per building square foot. For example, if a light fixture wattage is 50W and if the limit is 1W/sf, then you could have a maximum of one fixture for every 50 square feet of space.