[Bldg-sim] eQuest - Model verification

[James V Dirkes II, PE]

Weighing in late on this..

If I get >80% R-squared correlation, I think I'm doing well!  

There are so many unknowns, including the normal situation that the client
doesn't know their own operating schedules, occupancy patterns, or
maintenance / calibration procedures..

 

The Building Performance Team
James V. Dirkes II, P.E., LEED AP, BEMP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Karen Walkerman
Sent: Thursday, April 28, 2011 3:31 PM
To: Carol Gardner
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] eQuest - Model verification

 

Also, a model that is calibrated to actual building use and weather can help
to highlight building operation issues.  I have had models which were off
from actual operating energy use that I was able to determine how the
building was operating inefficiently.

 

In one case, I created a model of an existing building.  For this model, I
made an actual count of lighting fixtures and computers.  For most of the
year, there were few other electrical loads.  I based on their occupancy and
use schedules, I was not quite able to calibrate the electrical energy use.
When I met with the client, I informed him that my model showed somewhat
lower electrical use, equivalent to 1/3 of the computers remaining on
24-hours per day.  As it turned out, about 1/3 of the employees DID leave
their computers on at all times so that they could log in remotely.

 

... I guess what I'm saying is that maybe the goal is not to get the model
within 1% of the building energy use, but get the building within 1% of the
model.

 

--

Karen

 

On Thu, Apr 28, 2011 at 3:20 PM, Carol Gardner <cmg750 at gmail.com> wrote:

Bill summed it up really well, Katherine. Sometimes a client will think a
calibrated model must match the real building by an unrealistically high
number, like 1%. I really can't imagine an instance when that would be
desirable. It certainly would be costly to achieve. 

 

Usually the plan is to use the calibrated model as a tool to examine various
energy saving measures/opportunities that the client may be interested in
implementing. It is important to remember, in this case that you are looking
at the usage between the calibrated model and the ECM model, so the 1%
deviation is consistent in both and not a worry.

 

Carol

On Thu, Apr 28, 2011 at 12:03 PM, Bishop, Bill <wbishop at pathfinder-ea.com>
wrote:

Katherine,

 

The questions I would have for you (or your client) are:

.         Is this an existing building, or something in the design phase?

.         What is the model going to be used for?

.         Is there something magical about the 1% number?

.         1% of what? Annual electrical consumption? Annual gas consumption?
Both? Monthly electric/gas consumption? Monthly/annual electrical demand?

.         Why remove the plug loads? Even if everything else is modeled
perfectly, plug loads are typically 10% or more of annual electrical
consumption but can be all over the place.

.         "Easily adjusted" by whom? Does your client want you to hand them
a model and let them make all subsequent adjustments?

 

Even if you are an expert energy modeler, and there is monitored energy data
available for the building down to the individual electrical panels or
broken out by end use (lighting, plug loads, individual HVAC units etc.) you
will be hard-pressed to get to within 1% on a month-by-month basis. Even 5%
month-by-month is difficult. Sure, you can tweak to your heart's content to
get a model to match annual electric consumption within 1% based on prior
year's utility bills but to maintain a calibrated model to that tolerance
after that would require a lot of work.

 

I suggest searching the bldg-sim and equest-users archives for information
about weather files.

 

Oh, one more question - how much money does your client have?

 

Regards,

Bill

 

William Bishop, PE, BEMP, LEEDR AP | Pathfinder Engineers & Architects LLP

Mechanical Engineer

 

Error! Filename not specified.134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 <tel:%28585%29%20325-6004>  Ext. 114            F: (585)
325-6005 <tel:%28585%29%20325-6005> 

wbishop at pathfinder-ea.com           www.pathfinder-ea.com
<http://www.pathfinder-ea.com/> 

P   Sustainability - the forest AND the trees. P    

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Katherine
Louman-Gardiner
Sent: Thursday, April 28, 2011 1:49 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] eQuest - Model verification

 

Hi All,

Our client would like us to produce an eQuest model that

a)      Can be easily adjusted to include current and recently recorded
weather data

b)      Can be easily adjusted to reflect space occupancies and lighting
loads

c)       Will reflect the actual building energy usage to within 1%

Do any of you have experience trying to validate models like this?  

My concern is that models are approximations, and will not account for small
changes in occupancy, outdoor weather, etc.  

I guess my questions are these:

1)      Even if I manage to put in daily occupant and fan schedules based on
actual use, will the model be accurate enough to take me within 1%?

2)      We have been asked to remove plug loads (both for consumption
purposes and cooling loads).  Will this be too big of an assumption to get
any accuracy out of the model in the future?

3)      How do I modify the weather input file?

4)      Are there any other ideas I'm missing that will help us validate a
model as an absolute measure of actual building energy consumption?

Thank you for your help,
Katherine

 

Katherine Louman-Gardiner, EIT

Mechanical Engineer

 

 

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-- 
Carol Gardner PE


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