Card 6s - Diffuse Sky View Factor Request

This optional card computes the diffuse incident solar spectrum flux from the sky as well as that reflected from the ground.

Parameters: L, N1, N2, THETA, PHI, BETA, DIFFSKY, REFLG, PSUN, TIME

L

L is the code SKY (or 36)

N1

N1 is the element number or group name of the elements whose front surface will receive diffuse radiation from the sky.

N2

N2 is the element number or group name of the elements whose reverse surface will receive diffuse radiation from the sky. Reverse sides can be created with Card 9 REVNODE.

THETA

THETA is the angle in degrees the vector pointing towards zenith makes with the global Z axis.

PHI

PHI is the angle in degrees the projection onto the global XY plane of the vector pointing towards zenith makes with the global X axis. The counterclockwise direction is positive.

BETA

BETA is the solar altitude angle in degrees, the angle from the horizontal to the sun vector.

DIFFSKY

DIFFSKY is the diffuse sky factor ratio, i.e. the diffuse sky flux on a horizontal plate divided by the direct normal solar flux.

REFLG

REFLG is the ground reflectance.

PSUN

PSUN is the value of the solar flux attenuated by the atmosphere incident upon a surface.

If PSUN is 0, the card 2a PSUN value will be used.

If PSUN is Tn or -n, where n is a table number (e.g. T10 or -10), and n is a table whose dependent variable is QNODE, and TIME is CONSTANT, then the PSUN value will be interpolated from the table n by the Analyzer during run time.

TIME

TIME is the TIME value when the solar heat flux occurs.

Notes

This card computes the diffuse incident solar spectrum flux from the sky as well as that reflected from the ground. The equation used is:

where:

  • Id is the sky diffuse radiation.
  • Ir is the ground reflected radiation.

where VFsky is view factor between the surface and the sky. In case of explicit sky modeling using EXSKY parameter in Card 9 - PARAM, the view factor is computed from the sky model. Otherwise:

where:

  • ItH is the total horizontal irradiation.
  • VFg is a view factor between the surface and the ground.

In case of explicit earth modeling using EXEARTH parameter in Card 9 - PARAM, the view factor is computed from the earth model. Otherwise:

where Ω is the surface elevation angle, for example, the angle between the element surface normal and zenith.

The reference for the equation is found in: ASHRAE Handbook, HVAC Applications 1995, SI edition, p. 30.1 to 30.5.

This card generates equivalent ALB Cards on the VUFF file. When the explicit sky option is activated the shadowing effects is computed. Otherwise, shadowing calculations are not performed. Incident solar fluxes are not computed with this card, they need to be computed separately using the Card 6b - Solar View Factor Request.

You can flag elements that cannot receive fluxes computed with this card using the NOSOLAR option in Card 9 - PARAM.