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UdK-VPT / BuildingSystems

Modelica BuildingSystems library
http://modelica-buildingsystems.de/
BSD 3-Clause "New" or "Revised" License
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SolarRadiationTransformer models #19

Closed carlesRT closed 7 years ago

carlesRT commented 9 years ago

The models in the SolarRadiationTransformers package can be improved.

proposed changes

Edited 1. Remove Deg and Angle of the name of the cos.. and sin.. variables such as cosAngleDegInc

There are some variables with the name AngleDeg.... So I guess it is not a good idea to change the names.

  1. Change Type BuildingSystems.Types.Angle_deg per Modelica.SIunits.Conversions.NonSIunits.Angle_deg (It could be done per other models too). see 6b3da87
    • SolarRadiationTransformerIsotropic
  2. Add upper limit to the direct irradaition on a tilted surface (In some simulations the value of IrrDirHor*R is higher than the total irradiance on a tilted surface IrrTotTil, thus the diffuse irradiation on the tilted surface radiationPort.IrrDif becomes negative). See f397b20
  3. Some changes in docu. See da1f359
carlesRT commented 7 years ago

Incident direct radiation on tilted surface IrrDir, is equal to R * IrrDirHor. The geometric factor R=cosAngleDegInc/cosAngleZen is wrong (That's why negative diffuse radiation was appear, etc.). I will correct it.

nytschgeusen commented 7 years ago

I think the equation for R is in principle correct, but during extreme situations (during sunrise, sunset) in could calculate not plausible values. You will look for alternative modelling approaches as discussed.

mlauster commented 7 years ago

This might relevant in this context? https://github.com/ibpsa/modelica/pull/625 https://github.com/ibpsa/modelica/issues/608

carlesRT commented 7 years ago

Thanks @mlauster. Yep these are the same problems. @nytschgeusen you are right, equation R is correct. Regarding the irradation on a tilted surface: Direct irradiation increases too much, because of the R-issue you mentioned, even over the solar constant value. The total irradiation is limited to the solar constant which yields negative diffuse irradiation...

In annex60 the normal direct radiation (it corresponds to our IrrDirHor/cosAngleZen) is limited to the solar constant 1367.7 W/m2. Since cosAngleDegInc <= 1 it is hardly to expect neither too high values for the direct irradiaiton nor negative diffuse radiation in the annex60 model. Besides, diffuse radiation is independently calculated.

Anyway we might want to adapt the same approach. @nytschgeusen ?

nytschgeusen commented 7 years ago

This seems to be solved