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ibpsa / modelica-ibpsa

Modelica library for building and district energy systems developed within IBPSA Project 1
https://ibpsa.github.io/project1
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definition of solar azimuth #785

Open mwetter opened 7 years ago

mwetter commented 7 years ago

In the IBPSA library, the solar azimuth is 0 if the sun is in the south. Various conventions exist for how to define the solar azimuth (https://en.wikipedia.org/wiki/Solar_azimuth_angle) but the most common seems to be

clockwise from due north, so east is 90°, south is 180° and west is 270°.

This definition of 0=north, 90=east is also used by EnergyPlus (https://www.energyplus.net/sites/default/files/docs/site_v8.3.0/EngineeringReference/05-Climate/index.html#solar-position) and by the tools from TU Dresden and also by TEASER.

I suggest we change this in the library, which may have implications in other libraries that use this value. Models that use the solar azimuth will need to be updated and hence this is not backward compatible. However, regression tests should catch this change. Do other library developers agree to change this?

Mathadon commented 7 years ago

So the convention changes by 180 degrees? For me that's ok. We'll need to make sure that we catch any changes, but these should indeed show up in unit tests.

mlauster commented 7 years ago

It took us quite some tests to figure out that the definition of the solar azimuth in IBPSA library is shifted about 180° and counterwise than we have it in TEASER and our AixLib models. So I vote for changing that, we could then remove our introduced converters in TEASER. As soon as we merge this changes into all libraries, we will update our subsequent tools.

Mathadon commented 7 years ago

@damienpicard @GlennReynders for me this is ok. Do you have objections?

damienpicard commented 7 years ago

Fine for me, but let's include a note in the release issue.

thorade commented 7 years ago

UdK is currently using the old convention everywhere. The main advantage of the new convention would be that it is the one used in ErnergyPlus, correct? What about other tools like IDA-ICE, Polysun, and so on? Does IFC or similar have a convention? Is the same convention used to describe the azimuth of a wall? If everybody else prefers the new convention we are fine with switching, too.