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

Jim Dirkes jim at buildingperformanceteam.com
Thu Jun 28 11:48:41 PDT 2012

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 Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at 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

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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