Siddharth,

Are you actually changing the weather file with data for those years, or are you changing the "analysis year" in the wizard? The TMY2 or TMY3 weather file uses data averaged from 30 years worth of data. Changing the analysis year will affect how weekends and holidays line up with the weather data for each day of the year.

________________________________
Keith Swartz, P.E., LEED AP

Paul, I believe the TMY3 refers to the file format and minor changes to the
weighting of the various fields and other updates compared to prior TMY file
types. Some of the TYM3 may use 30-year data if it was always available,
and some may use 15-year data if fewer years are available for each site.

As you mention, you wouldn?t want to assume that a TMY2 for a location would
give the same results as a TMY3 due to the updates. I haven?t checked any
of the ?usual suspects? yet for comparison on just how much different the
results might be.

David

*
*

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

*
*

*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Paul Diglio
*Sent:* Tuesday, March 22, 2011 4:58 PM
*To:* Keith Swartz; Siddharth V; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] Internal manipulation of Weather data

Keith:

It is my understanding that TMY2 is based on data from 1961 through 1990.
TMY3 data is based on the data from 1991-2005, not 30 years.

Do you have different information?

If Siddharth is comparing a model using TMY2 v. TMY3, there will be a
noticeable difference.

Paul Diglio

------------------------------

*From:* Keith Swartz *To:* Siddharth V ; "equest-users at lists.onebuilding.org"
*Sent:* Tue, March 22, 2011 5:48:40 PM
*Subject:* Re: [Equest-users] Internal manipulation of Weather data

Siddharth,

Are you actually changing the weather file with data for those years, or are
you changing the ?analysis year? in the wizard? The TMY2 or TMY3 weather
file uses data averaged from 30 years worth of data. Changing the analysis
year will affect how weekends and holidays line up with the weather data for
each day of the year.

________________________________

Keith Swartz, P.E., LEED AP

*From:* Siddharth V [mailto:siddharth.v at tcs.com]
*Sent:* Tuesday, March 22, 2011 5:42 AM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] Internal manipulation of Weather data

Hi All,

I have observed 3% difference in the energy consumption for a given location
while specifying two different years (2010 and 2011). How does eQUEST (or
any energy simulation s/w) internally extrapolates the weather data based on
the specified year?

I feel 3% difference in energy is very significant. Any guidelines on
selection of TMY (typical meteorological year) ?

Thanks in advance!

Regards,
Siddharth Venkataraman