Re: [TRNSYS-users] Types 68 and 34 (shading)

[Enertech <sidler@club-internet.fr>]

This is a part of the TYPE34 code :
...
2000  CONTINUE
      
      GB=XIN(5)
      GD=XIN(4)
      GR=XIN(3)
      RHO=XIN(6)
      IF(VERSNUM.EQ.16) IncAng = XIN(7)


      OUT(2) = GB*FI
      OUT(3) = GD*VFSky
      OUT(4) = RHO*GR*VFGround
        IF (OUT(2).LT.0.d0) OUT(2)=0.d0
        IF (OUT(3).LT.0.d0) OUT(3)=0.d0
        IF (OUT(4).LT.0.d0) OUT(4)=0.d0
      OUT(1) = OUT(2)+OUT(3)+OUT(4)
      OUT(5) = FI
        OUT(6) = RepVFSky
        OUT(7) = RepVFGround
         GTOT=(GB+GD*0.5d0+RHO*GR)
        OUT(11) = 1
      IF (GTOT.GT.0.d0) OUT(11) = 1-OUT(1)/GTOT
         IF(VERSNUM.EQ.16) OUT(12) = IncAng
      
      RETURN 1

...


So, you see that GD = XIN(4) and that OUT(3) = GD * VFSky
VFSky is the sky view factor of the receiver and OUT(3) supposes to be
the sky diffuse solar radiation on receiver.
Look at equation (5.7.4.1) in TRNSYS Manual p. 5-226, you see that the
diffuse part of the total solar radiation incident on the receiver is
composed by the diffuse component of solar radiation incident on the
receiver surface (and not the horizontal diffuse radiation) * the sky
view factor of the receiver. 
You meet again equation (5.7.4.1) in the _expression_ :
OUT(1) = OUT(2)+OUT(3)+OUT(4)
where :

        OUT(2) = GB*FI
      OUT(3) = GD*VFSky
      OUT(4) = RHO*GR*VFGround

That's why I'm almost sure that Xin(4) supposes to be diffuse
radiation on the receiver surface.

Regards,
Christophe.


Christophe, Fernando et al,

> In both cases (a) and (b) I
> suppose that the sky diffuse radiation input
> is always the input number 4 of type34. The label in the proforma is
> somewhat error prone (it says ?sky diffuse on the horizontal?).
>  
> I think you?re right !! There?s an error in the TYPE 34 proforma :
> input(4) has to be the diffuse radiation on surface and not the
> horizontal diffuse radiation. You can check it in the TYPE34 source
> code.

This is NOT an error in the Type34 proforma. Type34 takes the diffuse
radiation on the horizontal surface and the beam radiation on the
shaded opening. 

If you could please point out the spot in the Type34 code that leads you
to believe that the model expects diffuse radiation on the shaded
surface, I would be happy to clarify further.

Regards,
  David

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