FIGURES FOR CHAPTER 7: Solar Energy for Buildings (1)

Figure 7.1 The sun’s position can be described in terms of its altitude angle and its azimuth angle.

Figure 7.2 We can use the altitude angle of the sun at noon to design overhangs that allow sunlight to hit south-facing windows in the winter, while blocking unwanted sun in the summer.

Figure 7.3 Locating the shadow line at solar noon for a south-facing window.

Solution Box 7.1 Design an Overhang

Figure 7.4 A sun-path diagram showing obstructions that shade the site in the morning and late afternoon from November through January.

Figure 7.5 A solar site survey can be made using a simple compass, protractor and plumb bob. The example shows the compass correction for San Francisco, with magnetic declination of 17oE.

Figure 7.6 Solar gains through south-facing windows are easy to control using overhangs, but east and west-facing windows can cause overheating in the summer.

Figure 7.7 South-facing windows provide solar gains in the winter, when you want it; east and west windows provide when you don’t. Horizontal skyights are the worst for air conditioning loads.

Figure 7.8 A building with its long axis along the east-west direction helps maximize solar gains in the winter, while minimizing morning and afternoon solar exposure in the summer. Vegetation along the east and west sides can help control summer overheating without affecting winter solar gains.

Figure 7.9 East-west street orientation increases the potential for passive solar and decreases cooling loads.

Figure 7.10 Example of a National Fenestration Rating Council (NFRC) window label

Solution Box 7.2 Net Gain for a Solar Window in Boulder, CO

Figure 7.11 A computer simulation of a small, lightweight house showing the impact of having too much south-facing solar gain area and not enough mass. With enough mass, 14% of the floor area in south-facing glass remains comfortable with no external heat source.

Figure 7.12 Three “generic” types of passive solar systems.

Figure 7.13 Identifying the solar aperture area, Ap.

Figure 7.14 Measured specific heating energy for 40 passive solar homes showing most requiring less than 2 Btu/ft2 per degree-day of auxiliary heating required. (Swisher, 1985)

Figure 7.15 Cooling loads are trickier to analyze.

Figure 7.16 Designing for good cross ventilation.

Figure 7.17 Heat gain can be greatly increased due to the elevated temperature of roofing materials.

Figure 7.18 Cool roofing reflects as much IR as possible and enough visible to provide color. The cool roofing tile samples shown increase reflectance by about 0.3.

Figure 7.19 A combination of construction techniques can dramatically reduce the need for cooling

Table 7.5 Daily clear sky insolation on vertical surfaces (e.g. windows)

Figure 7.20 The solar spectrum and the spectrum for objects near room temperature (the near-IR). Low-e windows reflect the far-IR, while spectrally selective, low-e coatings try to block both the near and far IR.

Figure 7.21 Spectrally selective, low-e windows coupled with automatically-dimming interior lighting systems take advantage of available natural daylight to reduce both lighting and cooling loads.