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

R B slv3sat at gmail.com
Thu Jun 28 14:09:30 PDT 2012

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

On Thu, Jun 28, 2012 at 1:48 PM, Jim Dirkes <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]
> *Sent:* Thursday, June 28, 2012 1:53 PM
> *To:* EnergyPlus_Support at yahoogroups.com
> *Cc:* Jim Dirkes; 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****
> www.whiteboxtechnologies.com****
> (o) (925)388-0265****
> (c) (510)928-2683****
> "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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