Book - School of Science and Technology

Solar heat gains 711280.0Heat gain / cooling load (k.Watts) August1024.0768.0512.0256.0Cooling loadInstant. gain0.00.00 4.00 8.00 12.00 16.00 20.00 24.00Time (hours)Figure 3.4 Computer plot of building heat gain and cooling loadTo make a preliminary assessment of the maximum solar heat gain for the buildingas a whole, a schedule of the various rooms and spaces may be constructed and, usingvalues of intensity as described later for various sun altitudes, notes taken of thecoincident load each hour on each face. In addition, the peak load for each face orany other combination may be established. While this exercise is fairly straightforwardin the case of a square or rectangular building it becomes more complex in instanceswhere the plan has re-entrant angles or internal courts where other parts of the buildingconsidered cast moving shadows on adjacent faces. While a model can be helpful,extensive analyses of this nature are tedious if attempted manually and use of a suitablecomputer program is the obvious approach. Figure 3.4 shows a plot of the heat gainand cooling load for a whole building having a load of about 750 kW, drawn asprogram output by such means.A second use for a sun-path diagram is in the design of shading devices taking the formof external sun-breaks. Their shape and angle of incidence may be set up on the plan andseparate diagrams made for the various aspects; both vertical and horizontal devices maybe so examined. This subject will be discussed in more detail later.As may have been appreciated, sun-path diagrams provide a valuable aid in assistingvisualisation of sun position vis aÁ vis a building but, in terms of calculation, have beensuperseded by the development and presentation of data which allow heat gain to beread directly for orientation and time of day without the intervention of a search forincident angles and basic intensities. In turn, computer use, which has opened upfacilities for exploring coincident loads and more rigorous examination of time lag,etc., is well on the way to superseding the refined tabular data. In consequence, thereference here has been abridged and is included to indicate the process rather than thedetail.