Apologies in advance if this belongs in a general forum... seemed more appropriate here
Just some food for thought. Reducing LPD's is obviously a good strategy for lighting energy efficiency, but in some recent demo projects by our local utility, high efficiency gains have been achieved using HIGHER connected loads than allowed by baseline code... The demo project also had more advantages for demand response situations.
http://asset.sce.com/Documents/Case%20Studies/BrookfieldCaseStudy.pdf
Codes give you some credit for controls, but this seems to shake the model up a bit...
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
January 6, 2012 - 10:31 am
The higher the connected load the greater the savings. This is simply a higher baseline which will always generate more "savings" than a lower baseline.
In this case it appears they retrofitted or replaced the existing lighting system which I would assume was a T12 system. For some reason they chose to install more wattage. Perhaps the old system did not provide enough light. But if you take a T12 system at 1 W/sf to a T8 system with 1.38 W/sf you will get significantly higher light levels.
By installing a higher baseline of course they are able to show more savings related to controls. In my opinion mixing up these variables inflates the "savings" associated with the controls. With a lower installed LPD, say good office design at 0.6 W/sf, the adjusted LPD would have been even better than they achieved but the "savings" would be less related to the controls. So if you are trying to show the maximum savings for controls then over-inflate the baseline.
The point of the case study was not to show that higher LPDs are better. The point was to show the impact of lighting controls.
Brenden McEneaney
Director, Northern CaliforniaCity of Santa Monica
47 thumbs up
January 6, 2012 - 12:06 pm
Marcus - thanks for your thoughts. Totally agreed that the point is not to promote higher LPDs but rather to emphasize controls. And I hear what you are saying about gaming the baseline - but that's not the focus here. Forget about percentage savings against a baseline - look at the Actual lighting power. The new system had 0.26 W/sf, which is very low - in fact far lower than a good office design at 0.6 W/sf.
Unfortunately there's not much detail in the link I posted, but if I remember from the presentation, the only way they were able to achieve the high level of control that they got with a task-ambient strategy was to add more fixtures so that they could put light only where and when it was needed.
I was hoping to point out that sometimes there's friction between innovative green strategies and the way that the codes are set up. Obviously, the codes have to be written for the 99% of designers who won't pay attention to green unless they have to, but a super-efficient design like this at 0.26 W/sf wouldn't have been allowed per the letter of the code. Maybe it suggests that as energy codes get tighter, there may have to be a shift towards outcome-based verification in addition to design-based verification?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
January 6, 2012 - 1:28 pm
Yep not quite enough information to evaluate how they got to such a lower number. Typically a task-ambient approach will reduce LPD not raise it.
The code LPD values are maximums, not minimums. The code would not prohibit such a low value as it relates to LEED projects. Sufficient justification would need to be provided which may have to be based on outcome-based results to be convincing enough to count.
The shift from relative comparisons to more absolute comparisons is already happening within LEED so I totally agree with your last statement.
Bill Swanson
Sr. Electrical EngineerIntegrated Design Solutions
LEEDuser Expert
731 thumbs up
January 6, 2012 - 1:58 pm
I do love the web for being able to dig and find more info.
http://www.etcc-ca.com/images/stories/et_09.22_otf_landmark_square_final...
They had an instant 30% "savings" because they dimmed all of the lighting to 70% initial. Then using either programs or sensors will slowly increase over time to compensate for light loss factor. 5 years or so they will be operating at 100% and the "savings" no longer available.
The measured "actual" lpd of 0.24W/sf was based on a 24-hour day average. A peak of 0.61W/sf was measured. No mention of what the average or peak measured baseline was even thought they mention it was recorded between April and May.
They were only allowed to have such a high connected load of 1.33W/sf because of the additional controls allowance that gave an extra 0.26W/sf. No mention if the controls actually reduced the peak or average demand by 0.26W/sf.
Plug load has actually gone up in the office after the lighting revision. My guess is the new task lights were left on.
I don't like these controls allowances in the latest energy Codes. I think they will create an artificial "savings".
Bill Swanson
Sr. Electrical EngineerIntegrated Design Solutions
LEEDuser Expert
731 thumbs up
January 6, 2012 - 2:11 pm
Just to stress my point. In 5 years the measured peak lighting load will be about 0.87W/sf after automatic LLF adjustment.
Designing to ASHRAE 90.1 max connected load of 1.0W/sf for an office building with occupancy sensors will have a very similar peak measured load as this office.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
January 6, 2012 - 2:38 pm
Nice digging Bill.
I have been at this 30 years and I have never seen a complicated lighting control system work in the long term, not even for 5 years. Most of our work is small to medium commercial so I can't comment on the big buildings with professional engineers maintaining them (maybe different in those). So I agree that credit for them is somewhat dubious.
Codes and the BD+C versions of LEED only enable the potential for a facility to be energy efficient. How it is actually operated has as much if not more affect on actual energy use. For lasting savings a smart building is one that is simple to operate, not filled with complex controls in my experience.