Purpose of a DESIGN-DAY CLIMATE input?

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Hi Nick,

Design day is the day at which design or peak load calculations are done.
It is not a very big deal to have climate as Tropical as it would be
between the Tropic of Cancer to Tropic of Capricorn.
In the midst of which there is equator.
It is mere a margin to show that the Tropical shows that the location is in
the margin of 23.5 degree south of equator to 23.5 degree North of the
equator.

The Mid-latitude can be the location near to the equator as it is the
middle or zero degree latitude of the earth.

The Subarctic region is the space near and hence off the polar to sub polar
region.

The thing that you are missing is the temperate zone which is in between
the 23.5 to 66.5 degree region.

The climate is very hot and warm in tropical region.
The climate is of mild nature in the temperate zone and very cold in the
sub arctic region.
As the solar angle declines away from the equator to the pole.
The solar angle is very less at polar and sub polar region and hence very
cold climate. The solar angle is directly over the head in the equator
region for major part of the year. Hence a sign of mid latitude as it is in
the midst of the globe.

*Thanks,*
Sharad.

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I think the ?transition from doe2.1e? document may be congruous actually with Joe?s original suggestion? It does reinforce that we?re on the right track to consider CLIMATE as associated with determing solar pathing for design days.

I?ve gone digging into Fundamentals 2005 and, googling after citations therein to try and lock in on this ?Climate/Latitude? binning for solar angles. Found nothing direct in the Handbook to clarify but it does appear this (older) ?ASHRAE clear sky model? was in fact limited to the Northern hemisphere (which may lead to why there?s seemingly nothing presently in DESIGN-DAY inputs to directly inform North vs South hemispheres? it seems a distinct possibility eQUEST makes a separate check of weather file latitude or other solar inputs however to account for this).

I?ve come across many papers/names associated with evaluation and improvement of that clear sky model. The ?midlatitude? term particularly pops up in a few such abstracts / summaries for papers I can?t readily access, so I suspect doe2.2 initially was following one such extension to the pre-2006 ASHRAE clear sky model.

~Nick

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Nick Caton, P.E., BEMP
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Schneider Electric

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Nick, others,

Your reading of the HOF is correct. As a member of TC 4.2 (Climatic Information), I
remember quite well the progression of events that led to the development of the new
ASHRAE Clear Sky Model. More than 10 years ago, the TC conducted an exercise to look
through the HOF to find where weather-related issues were being dealt with by other TCs.
This led to the design day formulation in the Loads Calculation section of the HOF and the
realization that the so-called ASHRAE Clear Sky Model was very antiquated, of unknown
provenance, and very North America - specific.

Since we had a very good solar expert in the TC (Chris Gueymard), we eventually contracted
with Chris to work with Didier Thevenard, the contractor for the ASHRAE Design Condition
tables, to create a better Clear Sky Model based on Chris' REST2 model. The REST2 Model
is a physical model that requires some 30 input parameters that can get very arcane
(Aerosol Optical Depth, Precipitable Moisture, etc.) but is very accurate (Chris once
said that NREL has found that REST2 was within 5% of NREL's measurements, which Chris
attributed to measurement errors :-) ).

Anyway, Chris compiled the inputs from satellite data and ran REST2 for the whole world,
which Didier then simplified into a 2-parameter model with a Taub and Taud for each
location and month, 24 numbers in all. So now the new ASHRAE Design Day procedure is to
look up the Taub/Taud for your location, plug those into two exponential equation, and get
the hourly profiles for GHI (global horizontal) and DNI (direct normal) by month (although
you still need to calculate the sun position in order to get the extraterrestrial
radiation, so don't try to do this in a spreadsheet just yet).

However, implementing it into DOE-2.2 would be very easy, since DOE-2 already calculates
the sun position. I just don't know whether anyone has tried to do so.

Joe

Joe Huang
White Box Technologies, Inc.
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