I am wondering how we can go about justifying not using the default process energy cost of 25% in our base and proposed energy models. As somebody has mentioned on an earlier thread, if the default process energy (receptacle power, lifts, cooking etc) is assumed (25% of base case total energy and identical in both models), then you have to achieve a 13.3% energy reduction in other areas of the building model in order to achieve the minimum 10% total building energy reduction, 27% to achieve 20% total building energy reduction, and 40% to achieve 30% total building energy reduction. In short, it is quite a significant and unrealisitc "dead load" that prevents energy savings and subsequently acheiving points under EAp2 and EAc1 credits.
LEED states that....
"The default process energy cost is 25% of the total energy cost for the baseline building. If the buildings process energy cost is less than 25% of the baseline building energy cost, the LEED Submittal must include documentation substantiating the process energy inputs are approprite"
so my question is....
can i simply use the receptacle equipment power densities for different space types listed in the ASHRAE 90.1 users guide book (e.g.. 0.75 W/sqft for offices) along with a realistic hourly weekday/weekend profiles? alternativily, could i just assume the the ASHRAE receptical power densities on continuous 24hr operation? Either way, the total process energy for the year is far less then 25% of the total building energy use. and therefore we will achieve a greater overall energy reduction.
The reason I ask, is that every LEED submittal I have seen always follows the default 25% rule, and the ones that don't seem to always get picked up on it by the assessors. I honeslty cannot imagine a 'normal' building of any classification or any climate zone (other than industrial) having a process energy use this high. So it seems to me that LEED just wants to account for 'phantom energy' in the models or just make it harder to get credits. If this is the case, then why don't they just increase the percentage margins for credits?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5912 thumbs up
August 24, 2010 - 9:15 am
As a GBCI LEED Reviewer and the immediate past chair of the USGBC EA TAG hopefully I can shed some light on the subject. The wording in the credit requirement has always caused confusion. The use of the word "default" connected to a specific number was unfortunate.
What you do is really, really simple - model the entire facilty's energy use/cost as accuarately as you can. So in the case of plug loads the best way to determine them is to ask the owner and try to figure out what they will be putting in each individual space so you can figure out an allowance and schedule for that space. If the plug loads are unknown then the 90.1 User's Manual figures are probably second best. You should never manipulate the plug load schedules to simply increase plug load energy use to 25%. Again model the facility as accuartely as you can.
Once you have modeled the facility as accurately as you can, see where you are. If over 25% do nothing. If under you simply need to document why you are under. If the data/explanation is plausible then it should not be a problem in the LEED review process. The best way to document it is to provide a spreadhseet with a list of equipment energy values per space or space type which documents your modeling assumptions for these loads. I will suggest to USGBC/GBCI that they develop and post such a spreadhseet for use by project teams.
Many normal buildings have process loads as high as 25%. The national average plug load energy use for office buildings, using US DOE data, is right about 25% which is where this figure came from. High process energy facilties can include restaurants, grocery stores, ice rinks, hospitals, labs, data centers, etc.
Your speculation that the intent was to make it harder to earn the credit is not true. The intent is to make sure projects model all energy use in the facility, not just the end uses regulated by 90.1. The next version of LEED will likely abanon this confusing language related to a default process energy cost.
Sundararaj Subburaman
143 thumbs up
February 19, 2011 - 12:52 am
HI ,
Is it possible to take benefit of energy savers installed in the transformers or other electrical areas on the LPD?
For ex: Suppose the LPD of project is 1 W/Sft. Because of the installed enegy savers can the LPD be reduced by 20 to 30%. Can we take this benefit in the LPD calculation?
Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11478 thumbs up
February 25, 2011 - 12:28 am
S, this is theoretically possible, but I would recommend some caution. Magical, "black boxes" that promise dramatic energy savings with no difference in performance may not perform as advertised. I recommend checking carefully into any improvements that are advertised, and thinking through how to document them.