[Bldg-sim] [EnergyPlus_Support] Food for thought....

Joe Huang yjhuang at whiteboxtechnologies.com
Thu Jun 28 15:48:22 PDT 2012


I think it's difficult to "calibrate" using only annual whole building data.  Most of the 
calibration that I've been involved uses monthly billing data and even at that admittedly 
coarse level, using the actual year weather data becomes important, since the degree days 
by month can easily vary by 40% or more year to year.

But there's another thing that puzzles me - when there are so many unknowns in the input 
data, isn't it a relief whenever it's possible to eliminate one of them, like the weather 
data?  Asked another way, if you had the weather data for the right time period, why would 
you not use it?

Perhaps the question gets back to convenience, and this is where I say that building 
modelers should get better acquainted with what's now available in historical weather 
data.  Just remember that every "typical year" weather file is made from many years of 
historical weather data. So, at any time historical year data  should be more plentiful 
than "typical year" weather data.  The only question is how to get it.  Happily, now that 
the ISH is online, there's very little need to search elsewhere, at least for the US.

If you want to see the situation for 2010,  look at
  http://www.whiteboxtechnologies.com/WB-weather/google-select.php
which shows all the ISH stations for which I've already created simulation-ready weather 
files.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 6/28/2012 2:09 PM, R B wrote:
> I have a different take on this. I think a TMY is good enough for doing model 
> calibration that is used for ECM savings analysis on a whole building level and yearly 
> basis - I think this is the type of project Jim is alluding to. In this scheme of 
> things, the most important factors are the scheduling of the various equipment/loads and 
> the control logic and gathering relevant data and making sure that the bills actually 
> represent the building in question properly. If you are going for hourly calibrations 
> etc, or calibrating to the few weeks of trend data that is collected, then may be actual 
> weather data is useful, although not 100% convinced on this - depends on how much data 
> one is able to collect.
> If we go for a retrofit of a typical commercial building which is mostly internal loads 
> dominated (unless the perimeter to sqft is a lot more-I am sure you can find papers 
> related to this), I am not sure if weather related issues are as important. Also, while 
> doing retrofit, you have access to three or more years of utility bill. Averaging out 
> the utility bills (removing obviously outlier data) and calibrating to it is a 
> reasonable way of proceeding to decide the savings due to ECMs. This takes care of the 
> weather issues as well as all the operating/internal load issues that are also changing 
> over time. Now you are no longer dealing with one year.
> It obviously depends on the building type - OA dominated buildings get calibrated better 
> with actual data - even here the more important data is the amount of OA coming into the 
> building and the control logic.
> Residential and small buildings are a different category - they will get calibrated 
> better with actual data.
> I agree with Jim that only recently a easy/non-time consuming way of using actual data 
> has become available. Has anyone tried it (the files from weather analytics or 
> equivalent) - is it as easy as using TMY without having to worry if the results 
> discrepancy is due to issues in the weather file?
> -Rohini
> On Thu, Jun 28, 2012 at 1:48 PM, Jim Dirkes <jim at buildingperformanceteam.com 
> <mailto:jim at buildingperformanceteam.com>> wrote:
>
>     Dear Joe,
>
>     No fair! You  and Dru have been at the forefront energy modeling research for most
>     of my adult life, and have a big head start.
>
>     My guess is that you spent a lot of time preparing the actual weather files for the
>     research, however.  Unless I’m missing something, the ready availability of high
>     quality (e.g., no big hunks of missing data) actual weather data has been pretty
>     limited until recently.  With folk like Weather Analytics getting on board and
>     making it pretty easy to get and inexpensive, it becomes a lot faster and lower cost
>     than trying to clean some of the NOAA / NCDC data, not to mention getting good data
>     for sites not in or near a major city.
>
>     Kudos for being way ahead of the industry curve (at least my own curve)!  It’s
>     getting easier to catch up!
>
>     p.s., Dru sent me that paper and I’ll be reading it with interest very soon.
>
>     *From:*Joe Huang [mailto:yjhuang at whiteboxtechnologies.com
>     <mailto:yjhuang at whiteboxtechnologies.com>]
>     *Sent:* Thursday, June 28, 2012 1:53 PM
>     *To:* EnergyPlus_Support at yahoogroups.com <mailto:EnergyPlus_Support at yahoogroups.com>
>     *Cc:* Jim Dirkes; bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>
>     *Subject:* Re: [EnergyPlus_Support] Food for thought....
>
>     I've always thought it was a "no-brainer" to use actual weather data whenever you're
>     comparing simulation results to actual consumption data.  Even with the earliest
>     degree-day software such as
>     PRISM (Princeton Scorekeeping Method) in the 1980's, it was stressed to use the
>     degree days
>     from the period of record, and not the long-term average, so I'm not sure why this
>     (using actual
>     year weather data) is such a revelation.
>
>     The variation in total energy consumption of course depends a lot on the building
>     characteristics.
>     Back in 1996, Dru Crawley and I wrote a paper on "Does it matter which weather data
>     you use in energy simulations?", for the ACEEE Summer Study on Energy Efficiency in
>     Buildings (it also appeared as two
>     separate ASHRAE papers at around the same time) where we took some prototypical
>     building models (Dru did commercial, I did residential) and ran them with various
>     "typical year" weather files and also 25 years of historical data in 10-12 US
>     locations.
>
>     Joe
>
>     Joe Huang
>
>     White Box Technologies, Inc.
>
>     346 Rheem Blvd., Suite 108D
>
>     Moraga CA 94556
>
>     yjhuang at whiteboxtechnologies.com  <mailto:yjhuang at whiteboxtechnologies.com>     
>
>     www.whiteboxtechnologies.com  <http://www.whiteboxtechnologies.com>     
>
>     (o)(925)388-0265  <tel:%28925%29388-0265>     
>
>     (c)(510)928-2683  <tel:%28510%29928-2683>     
>
>     "building energy simulations at your fingertips"
>
>
>     On 6/28/2012 8:49 AM, Jim Dirkes wrote:
>
>     Dear Forums,
>
>     I am busy preparing a short talk for the Fall ASHRAE Energy Modeling Conference. 
>     The topic is “An Approach for Calibrating Existing Building Energy Models to their
>     Utility Consumption”.
>
>     As part of the preparation, I will address the issue of how much difference might
>     result in energy conservation measure savings predictions if you use actual weather
>     data for the billing period versus TMY data.
>
>     To get a rough idea  how much variation there might be, I looked at Degree Days for
>     a span of years.  What a variation! (for the city I’m studying at least)
>
>     I am not yet sure how that affects total energy consumption – you’ll have to attend
>     my presentation in Atlanta to find out J.
>
>     In the meantime, I am starting to think that existing building energy models should
>     use actual weather, not TMY data.  Have any of you run similar comparisons for
>     existing building models?
>
>
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