W7 Radiation Flashcards
Define ‘Circumsolar Activity’ and significance in modelling solar radiation.
➤ The apparent ring around the sun which highly directional diffuse radiation.
➤ This requires that the true direct be increased b y the circumsolar component.
➤ When subtracted from measured diffuse then the a more accurate background diffuse irradiance is achieved.
Discuss…
➤ Isotropic and
➤ Anisotropic sky conditions
➤ Uniform brightness
➤ non-uniform brightness
raises the complexity of the calculating the diffuse component of solar heat gain.
Explain how solar radiation makes it way into building to become a cooling load
➤ Solar flux strikes the opaque (outter surface) some is absorbed and reflected.
➤ Absorbed componnent then through a time lag (thermal inertia) due to the material is conducted to the inner surface and convected to the room
➤ there is also LWR transmission to the componnents in the room which sees it as a cooling load as heat passes from colder internal to the warmer internal.
➤ Windows also see radiation transmitted absorbed and reflexted. Flux entering strikes surfaces which also absorb reflect and potentially emmit their own radiation
Room surfaces also emit LWR.
How to determin complex geometry View Factors
➤ Divide both surfaces into finite elements
➤ each element perform the following
➤ ➤ unit hemisphere at element centre
➤ ➤ Discrtise hemisphere into patches
➤ ➤ ➤ each patch - extend a ray from base center through patch center
➤ ➤ ➤ determine point of interaction with secont componnent and calc view factor from areas and angles4
➤ sum all patches in element
