[Bldg-sim] Fwd: [Bldg-rate] LEED+90.1 Process/Plug LoadsConundrum
Marcus Sheffer
sheffer at energyopportunities.com
Mon May 3 08:30:28 PDT 2010
Let me see if I can add some clarity to the reasoning behind the 25% process
rule.
First of all and most important – every project should model what has been
designed/built and nothing more.
The 25% value was selected since that is a pretty typical plug load
percentage for an office building (LEED was originally created for an office
building and there are still vestiges of this lineage). This value was
never intended as a hard and fast minimum for all projects. The intention
was to make sure that all energy uses in any building were accounted for in
the model, unfortunately it has been widely misunderstood. This is an
indication that we have a problem in the LEED credit language. LEED 2012 is
likely to drop this “requirement”.
The 25% had nothing to do with raising the level of difficulty. We clearly
understand that facilities with high process energy loads have a harder time
earning points in LEED than those with low loads. This is a problem for
many LEED projects and USGBC is slowly adding baselines for process loads so
energy savings can be claimed against them.
One should NEVER add non-existing loads to get up to 25%. This is
completely counter to the intention of this rule.
If you are under 25% James has it correct, simply document what you have.
Most typically this would include a spreadsheet and perhaps a narrative if
anything would need to be explained so the reviewer can understand the
situation. In the vast majority of cases this information should exist as
it is often needed in order to perform the HVAC load calculations correctly.
So I don’t really understand the perceived difficulty. For many building
types with only plug loads as process one can also use the W/sf values in
the 90.1 Unser’s Manual.
It is the intention of USGBC to make sure that the energy model addresses
all of the energy in and associated with the project. This was the intent
of the 25% rule. This language is in the credit requirement but its
connection to process energy is certainly not clear.
As a company that was one of the original 5 review firms, our reviewers will
question a project whose process energy is exactly 25%. This gives the
appearance that either non-existing loads have been added or even worse that
process loads have not even been included in the models and a value equating
to 25% was added to the modeling results. Again model what you have. If
over 25% do nothing. If under 25% document why.
Always keep in mind that the purpose behind modeling is to guide
design-decisions and to the greatest extent possible accurately project the
actual energy consumption of the facility. Under the USGBC’s Building
Performance Initiative and MPR #6 in LEED 2009, your modeling results will
be compared to the actual building’s energy use (although this comparison
will not be made public on an individual project basis) so every effort to
improve quality and accuracy should be taken.
Marcus Sheffer, Chair USGBC EA TAG
Energy Opportunities, Inc/a 7group Company
1200 E Camping Area Road, Wellsville, PA 17365
717-292-2636, <mailto:sheffer at sevengroup.com> sheffer at sevengroup.com
www.sevengroup.com
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, April 30, 2010 7:31 PM
To: Carol Gardner; bldg-sim at lists.onebuilding.org;
equest-users at lists.onebuilding.org; bldg-rate at lists.onebuilding.org
Subject: Re: [Bldg-sim] Fwd: [Bldg-rate] LEED+90.1 Process/Plug
LoadsConundrum
Firstly, apologies for the cross-posting, but it appears this topic has
grown include many lists so I can’t come up with an alternative!
Secondly, a huge thanks to Carol, James and a large number of others (who
shall remain unnamed until they should decide to join the public discussion)
who have given me direct input on their personal thoughts, outside of the
mailing lists.
I have received a flood of suggestions regarding approaches when the intent
is to follow the 25% rule, and additionally regarding how one might go about
appeasing a USGBC LEED model reviewer when attempting to document a lower
figure. My impression up until this point, based on colleagues’
experience/advice, has been that attempting to substantiate anything less
than 25% process loads would be a futile task and would be flatly rejected.
As a result I never really considered this to be an option available to us
LEED energy modelers. I now understand that for many, documenting something
less than 25% has proven a feasible, if occasionally exhaustive, task.
When the intent is to follow the 25% baseline process load prescriptive
requirement, I have been exposed (again outside of the lists) to a
surprising number of unique viewpoints and seemingly legitimate approaches
which have led to successfully reviewed LEED model submissions for others.
Among the approaches to build the process loads to 25% are:
- Adding a single direct internal/external load to the project
electrical meter in addition to the designed space equipment loads – this
approach avoids additional internal heat gains.
- Adding additional or redefining designed space equipment loads,
adding internal heat sources. If and when these additional loads should
result in too many unmet cooling hours in the proposed model, there are two
basic approaches:
o Specify larger system cooling capacities and/or airflows
o Allow those systems cooling capacities/airflows to auto-size
- Keeping the designed space equipment loads without adding any
further, but modifying their utilization schedules to increase space
equipment usage during non-peak cooling hours – this of course adds heat to
the models, but avoids unmet cooling hours due to clashes with proposed
system cooling capacities.
I sincerely hope Carol and others will not misunderstand… Myself and others
do not wish to “game the system,” but we seem to have a variety of
viewpoints as to what the intent is for the 25% rule.
If it may help and add to the discussion, my personal opinion leading up to
this inquiry has been that the default 25% rule exists simultaneously as a
means of normalizing the “difficulty level” of attaining LEED EAc1 points
for projects with various actual process loads. Perhaps at some point in
time, somebody decided it would be unfair for someone designing a LEED
Platinum toolshed with zero process loads to have an easier time of it than
some poor sucker trying to get some EAc1 credits for an automotive
manufacturing facility with immense process loads?
I will unfortunately be unable to participate in or respond to this topic of
discussion for some time as I will be away from my inbox. I very much look
forward to gaining a better understanding of how we as a group might come to
agree on a “best practice” for this issue. If anyone should currently have
access to a relevant CIR that would probably be very useful.
A humble thanks again to everyone,
~Nick
cid:489575314 at 22072009-0ABB
NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Carol Gardner
Sent: Friday, April 30, 2010 5:12 PM
To: bldg-sim at lists.onebuilding.org; eQUEST Users List
Subject: [Bldg-sim] Fwd: [Bldg-rate] LEED+90.1 Process/Plug Loads Conundrum
---------- Forwarded message ----------
From: Carol Gardner <cmg750 at gmail.com>
Date: Fri, Apr 30, 2010 at 2:40 PM
Subject: Re: [Bldg-rate] LEED+90.1 Process/Plug Loads Conundrum
To: James Hess <JHess at tmecorp.com>, Nick Caton <ncaton at smithboucher.com>,
Karen Walkerman <kwalkerman at gmail.com>
Cc: "bldg-rate at lists.onebuilding.org" <bldg-rate at lists.onebuilding.org>
Hi Nick,
I'm glad you raised this issue.
First, I agree with James, and have heard from other people, that LEED
accepts documentation saying something as basic as "hey, I don't have 25%
plug loads".
Second, when you have to create a baseline to measure up from, you are
forced to say what that baseline is. For instance, in 1985-86, working on
the BPA-funded Energy Edge project, we had to figure out the baseline for a
group of buildings being designed to exceed the current energy codes by 30%.
We didn't have a baseline then. To deal with this we assembled a group of
people that we euphemistically called The Greybeards (so sorry to you all).
The tables now known as G3.1.1A & G3.1.1B in Standard 90 came out of what we
created in that moment of time. We were trying to limit what is called
"gaming the system"
So now it seems it has been deemed important to control the baseline a
little more: by specifying plug loads at 25%. The goal of trying to limit
gaming the system might be the source of the 25%. The danger which Nick has
clearly demonstrated in his email is that what is meant to control gaming
the system, may now actually be creating it.
Further thoughts/comments welcome,
Carol
On Fri, Apr 30, 2010 at 1:42 PM, James Hess <JHess at tmecorp.com> wrote:
This is a good question. On prior projects we have worked on, I have found
that you can have less than 25% plug loads, so long as you have some
documentation to back it up.
For example, we are currently working on a prison project. The plug loads
are very low for obvious reasons; they don’t provide stereos, computers,
ipods, TV’s, etc. to the inmates (typically, all they get is an alarm
clock/radio that uses ~ < 10 watts). There is no way on this project that
we could get the plug loads to come in at 25% unless we artificially jacked
them up to levels that would never exist in reality. We would have a
similar problem in that the Proposed Design equipment would not be able to
cool the spaces. So, we just document the loads we do have and I believe we
are good. The project has been through the 1st review and this has not come
up as an issue.
I believe we have had other projects where we documented the loads we had
and passed the review with no problems. We will typically develop a simple
spreadsheet and document the internal loads that each room has. That is
easy enough to do these days I believe, for most applications. For example,
a typical desktop computer uses about 65 watts on average, monitor = ~ 45
watts (depending on size), clock radio ~ 10 to 15 watts, etc. you get the
point. (get a “Killawatt” power meter from Amazon and have some fun taking
some measurements to see approximately how much power stuff uses, guaranteed
to provide hours of fun).
Just provide some documentation on some good reasonable estimates for the
loads and I think you will be fine.
An alternate method is to use default values from Table G-B from the ASHRAE
90.1-2007 Users Manual.
For example, the Receptacle Power Density for the Office Building Type is
0.75 watts/SF per Table G-5.
If using that value results in the process loads being less than 25%, my
comment to the reviewers would be that the 0.75 watts/SF is the value
determined by ASHRAE to be appropriate for the building type.
I think the most important thing is to use something reasonable and
defendable, and make it the same between the Baseline and Proposed Design
energy models. Our experience indicates that it does not have to be exactly
25%, can be less than 25% or greater than 25%, depending on the building.
One thing that is interesting is that on federal projects, per EPACT
requirements, you do not have to factor in the process/recep loads for the
purpose of determining whether the 30% savings requirement has been met.
That makes it easier to show 30% savings.
Thanks!
Regards,
JAH
James A. Hess, PE, CEM
Senior Energy Engineer
TME, Inc.
Little Rock, AR
Mobile: 501-351-4667
From: bldg-rate-bounces at lists.onebuilding.org
[mailto:bldg-rate-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, April 30, 2010 12:55 PM
To: bldg-rate at lists.onebuilding.org
Subject: [Bldg-rate] LEED+90.1 Process/Plug Loads Conundrum
Something new occurred to me this week and I’d love to hear others’
thoughts!
LEED prescribes baseline/proposed energy models to follow ASHRAE 90.1 with a
caveat: the “process energy costs” must total 25% of the baseline energy
costs. By extension, 90.1 requires the same loads/schedules be applied to
the proposed model as they have to match. As an aside, the LEED EAc1
templates appear to calculate/check this using process energy consumption
(not cost), but that’s not what I’m getting at…
I just had a typical case where I had to inflate the baseline internal
miscellaneous equipment loads to get to 25%. These additional loads were
substantial enough that when applied to the proposed model/design, I ran
into many unmet cooling hours for the equipment capacities entered.
Then I realized: We can define additional equipment electricity loads but
simultaneously apply a multiplier (in eQuest anyway – I expect this is
feasible other programs also) to reduce/negate the corresponding heat load
contributions. This results in the energy consumption/costs showing up
correctly in the final results/reports, but does not artificially inflate
the internal loads that the baseline/proposed systems must handle.
Would this practice (which incidentally can be a time saver) of accounting
for extra process/miscellaneous loads without extra thermal contributions be
in line with the intent of ASHRAE/USGBC? It would still normalize the
otherwise unstandardized process consumption/costs of the baseline/proposed
models between different building types…
On the other hand, if it really is the intent of USGBC to add arbitrary
additional internal heat loads to our models that our actual designs were
not designed and sized for, does it follow that we should allow the proposed
models to autosize cooling equipment/fan capacities and not specify them
(this would seem incongruous with 90.1 to me)?
~Nick
Error! Filename not specified.
NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ <http://www.smithboucher.com>
www.smithboucher.com
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