Ooi,
Although I'm totally in support of using weather data to determine best how buildings will perform in the future, rather than the past, I want to clarify some misstatements and then share some of my perspectives on this issue of extreme or future weather.
1. EPW is just the format of the weather files used by EnergPlus, and does not relate to their contents, which could be typical year, actual year, future year, etc.
Perhaps you're thinking of the typical year weather files such as those on the EnergyPlus Weather web site.
2. Typical year weather files are generally created by extracting the most representative months from a historical period of record; Meteorologists have traditionally
used 30 years as a good sampling, but that was before there was much awareness of climate change. This is something I'm starting to look into, i.e., at what point
does lengthening the period of record actually worsens the predictive ability of the weather file or computed design conditions for the future? Of course I can't see
into the future, so I intend to look into the recent past and see how well we did (or could have done) with different periods of record.
3. Although it is possible to create future year weather files from GCM (Global Circulation Model) projections, I have some concerns:
a) while GCMs generally agree that average global temperatures will rise, the results at the regional level can vary greatly depending on the model,
b) the GCM results have to be downscaled for specific locations, but with all the unknowns is this perhaps just false precision?
c) some GCM outputs, e.g., wind speeds, cloud amounts, are highly conjectural, so the differences might be simply that between real and synthetic data.
4. There are other ways to account for climate change without directly importing GCM outputs:
a) "morphing" a historically-derived "typical year" based on GCM projections of future trends
b) using shorter more recent period of record in generating the "typical year" file (for California, I've recently used just the last 10 years)
c) selecting not the average months but those that correspond to GCM projections.
d) or simply using the hottest year over the past decade.
I've tried a, b, and d in various projects over the past decade. The results, especially if you push things to 2080, can be quite startling, but I always present
them as indications of what "could happen", not what "will happen".
5. Extreme weather is best studied by looking at the historical records, rather than by climate modeling (IMHO). The models show that likelihood of extreme events
will increase, but as for their intensity and duration, it's difficult to say.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx http://weather.whiteboxtechnologies.com for simulation-ready weather data (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
On 8/11/2013 2:47 AM, ooikoonbeng wrote:
Hello,
Excuse me for putting a slight diversion on this subject of weather data.
Correct me if i am wrong, the EPW is typical year data, which is a compilation of typical months' data of the past 20-30 years historical records.
A not-so-far-fetched, apologies if it is overly ambitious, objective of simulation is to predict how much conditioning energy a building needs during the design or planning of retrofitting stage, i.e. before the building is built.
Would it not be fair then to have predicted weather data for the coming year/s? This could be based on some of the 'projections of global warming' by year.....
Just a passing thought
regards, ooi
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Joe Huang <YJHuang@...> wrote:
>
> Hu Jia,
>
> Here's more information on the ASHRAE Research Project that might be of interest to you.
> It's RP-828 "Sequences of Extreme Temperature and Humidity for Design Calculation",
> principal investigator Don Colliver (former ASHRAE president (!)), 1997. The abstract
> follows:
>
> Specific values for the design temperature have long been used as a starting point for
> design and sizing calculations for many applications. Designs using these extreme one-hour
> values are appropriate if the time constant of the system being designed is short; however
> if the system being designed has a significant thermal lag the extreme single-hour value
> can be significantly inadequate. The purpose of this report is to document the development
> of a technique to select sequences of data from long-term weather records and then present
> the results of using this technique on long-term weather data from a number of locations
> in North America. A number of different methods of combining the multiple hours of data
> within a sequence to produce a single value which then could be ranked were tested. The
> method of taking the average of the parameter over the time window was selected as the
> best method. It was found that the non-steady-state heat transfer method could not be used
> as a reliable indicator of the extreme sequences because the specification of the wall
> type to be used introduced a large variation in the selection of the extreme sequences.
> The purpose of this project was to develop a technique to select sets of data from
> long-term weather records which could be used in designs needing weather data longer than
> one hour and then use this technique on long-term weather data from a number of locations
> in North America.
>
> You can get the technical report from the ASHRAE Web site (free for members), but when I
> tried the Web site said it couldn't find the PDF. If so, you could also try to contact
> Don himself colliver@...
>
> Joe (also JH!)
>
> Joe Huang
> White Box Technologies, Inc.
> 346 Rheem Blvd., Suite 108D
> Moraga CA 94556
> yjhuang@...
> http://weather.whiteboxtechnologies.com for simulation-ready weather data
> (o) (925)388-0265
> (c) (510)928-2683
> "building energy simulations at your fingertips"
>
>
> On 8/9/2013 4:12 PM, Joe Huang wrote:
> > Your best bet is the National Solar Radiation Data Base (NSRDB) from NREL that contains
> > the hourly weather data for 1,454 US locations from 1991 through 2010.
> > http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2010/
> > That'll give you plenty of data to work with.
> >
> > What is your definition of extreme weather conditions? Are you looking for individual
> > hourly values, or actual weather sequences? If you're studying this with EnergyPlus (or
> > any simulation program), I would recommend the latter, since the building's response to
> > climatic conditions depends a great deal on the thermal history extending for up to
> > several days. 20% above normal sounds much too lax to me, since ASHRAE design conditions
> > are defined as 0.4%, 1%, and 2% for cooling and 99.6%, 99%, and 98% for heating.
> >
> > If you're working to select extreme temperature sequences, e.g., most extreme 3-day or
> > 5-day sequences, you might look at work done about 20 years ago by Don Colliver for
> > ASHRAE (don't remember the RP number or title), where he produced 5-day design sequences
> > for 230+ US locations based on the highest or lowest average daily temperatures,
> > selected using the same 0.4%, 1% criteria and method as used for the ASHRAE Design
> > Condition tables. I would think that updating that work using the NSRDB would get you
> > what you need, but you might want to modify the selection criteria.
> >
> > Joe
> >
> > Joe Huang
> > White Box Technologies, Inc.
> > 346 Rheem Blvd., Suite 108D
> > Moraga CA 94556
> > yjhuang@...
> > http://weather.whiteboxtechnologies.com for simulation-ready weather data
> > (o) (925)388-0265
> > (c) (510)928-2683
> > "building energy simulations at your fingertips"
> >
> > On 8/9/2013 7:40 AM, Jia Hu wrote:
> >>
> >> Hi all,
> >>
> >>
> >> I am studying the impact of extreme weather conditions using EPlus. I am trying to find
> >> the source years (e.g., 20 year data) to extract the extreme data for each day? Anyone
> >> has suggestion about how to get the extreme weather condition (e.g, 20% above normal)?
> >> Where can I find these source data. The location of my interest is in US.
> >>
> >> Thanks,
> >>
> >> JH
> >>
>
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