Hi, Everyone: I'm confused with the value choosing for the equipment & miscellaneous power densities like the illustrate below. The table G 3.1 no.12 said it should be based on the building and space type, but there isn't other information. So do we need to add this load part when we make a baseline model? Maybe this isn't very important , but I want to make sure about it. I know we can choosing the lighting power densities in Section 9, but I can't find the table for other equipment. So what should you do? By the way , about the occupancy density and ventilation inputs shown below, I found the reference information from ASHRAE 62.1, is that a common way when we make a baseline? Thank you for your kindly help.
Generally, the "correct" baseline model values for these entries
(misc/plug loads and occupancy/ventilation) are to match whatever is in
the proposed model.
There is more than one "correct" approach regarding misc load quantities
for the proposed model. In any case you should be prepared to reproduce
what decision you made and back it up for baseline/proposed
documentation:
- Reference tables in the 90.1 users manual (also found in
certain state energy codes) with representative W/SF figures for various
'whole building' types and assign that figure to each space. I've found
this approach to be time-efficient and so far totally accepted by the
USGBC/LEED reviewers.
- Stick with the eQuest defaults per occupancy. I'm unsure of
where they're all derived from exactly (Title 24? Some other
standard/reference?), but they will vary as you change space activity
types and appear sensible from what I've observed. These values,
default or otherwise, are rolled into a weighted average for each zone
group based on the % distribution in the zone group screen - which is
why the resulting W/SF coming out of the wizards can appear somewhat
random at first glance.
- Flex your spreadsheet muscles and do a space-by-space plug
load takeoff to come up with an "actual" number. I have never pursued
this degree of detail myself, but I understand others have specifically
to account for gains from providing efficient plug load equipment with
the project over "standard" equipment... resulting in a deliberate
divergence between the baseline/proposed models.
I've found eQuest default values for occupant density/ventilation/loads
are pretty much on the mark as to what I'd define from ASHRAE
references, so I leave the defaults alone in wizards and only focus on
tweaking the calculated zone occupant quantities in detailed mode as
necessary for model QC and matching loads. I do make a point to assign
the appropriate "space type percentages" for each zone in the following
wizard screens however.
~Nick
NICK CATON, P.E.
Hi Joey,
I thought to write about the 25% topic but thought it best to not bring it up?? Perhaps a quick recap is in order for your situation and others?? benefit!
There has been much discussion regarding that ??25% rule?? between myself and others on these lists ([bldg-rate], [bldg-sim], [equest-users]). Re: archives.
I started out with the same conclusion you??re stating: the baseline consumption is supposed to be 25% plug/process loads. The LEED 2.2 handbook is unfortunately worded under EAc1 to suggest this as a prescriptive default in the absence of substantial documentation, but that ??documentation?? can be as simple as a one-line reference as I described. Note the LEED v3 handbook (under EAp2 I think) re-words those lines on process loads to emphasize the expectation is to simply match between the models ?C no mention of 25%.
I have since that time done an about face on that viewpoint and believe that figure to be entirely arbitrary. ??Forcing?? 25% plug load consumption in the baseline is in many cases arbitrarily detrimental to the overall performance rating, is rarely realistic, and the resulting internal gains can cause irresolvable unmet hours for proposed equipment of a specified capacity (remembering the baseline and proposed should normally have matching process loads). I came to the lists seeking to share and learn better approaches to ??fairly?? mitigate these artificial internal loads, and in doing so learned I was far off the path from others.
I could re-iterate my perception of the history and intent behind the 25% figure, but you??re probably best advised to seek out those discussions in the archives to come to a fuller understanding. I would presently advise referencing and using something reasonable for your proposed building in both models, and not treating the 25% figure as a mandate, but do inform yourself by reading those archived discussions so that you can defend your position against any argumentative v2.2 reviewer.
~Nick
NICK CATON, P.E.