Masonry Magazine January 1980 Page.16
ENVIRONMENTAL DATA AND REQUIREMENTS
Many environmental factors must be considered to fully utilize the concepts of passive solar heating systems. The environmental data is given in Tables 1 and 2 of this Technical Notes, and is for use with the design methodologies detailed in Technical Notes 43A.
Temperature
Exterior design temperatures are necessary considerations in developing passive solar heating systems. The size of the system will depend upon daily, monthly, and annual temperature fluctuations. In mild, sunny climates, the required glazing and thermal storage areas may be relatively small. In mild temperature, cloudy climates, the required glazing area may be small, but the required thermal storage will be greater. In colder climates, the amount of glazing and thermal storage is usually large.
The average monthly heating degree days are related to exterior temperature conditions. These values are necessary to determine the total monthly thermal load of the building. The average monthly heating degree days and exterior temperatures are given in Table 1.
Latitude
Latitude is important to determine the amount of solar radiation and the appropriate summertime shading, provided by overhangs and other devices. The further north the building is to be located, the less winter solar radiation it will receive. This is because the sun is above the horizon for a shorter period of time and the solar radiation must penetrate more of the atmosphere. Values of solar radiation at various latitudes are given in Table 2.
At higher latitudes, the sun appears lower in the sky. At these latitudes, where the position (altitude) of the sun in the sky is low, larger overhangs are required to shade the south-facing wall from the summer sunlight. Figure 3 shows how the altitude of the sun changes from winter to summer, showing how the south-facing wall may be shaded from summer solar radiation and still be exposed to winter solar radiation by using an overhang. The length of projection required to shade a south-facing wall from the summer sun is given in Table 3.
Solar Radiation Data
Solar radiation data is required to determine the amount of radiation transmitted through the south-facing glazing. Actual average solar radiation data for various geographical locations is given in Table 1. The amount of solar radiation is dependent on climate, elevation and latitude. Clear day solar radiation for various latitudes is given in Table 2.
Orientation
Orientation is extremely important in the design of passive solar buildings. The best performance will usually result with the passive solar system facing true south. True south may be obtained by referencing isogonic (magnetic variation) charts developed by the United States Department of Commerce, Coast and Geodetic Survey, or by consulting a local land surveyor.
When the passive solar system faces true south, the system will be exposed to the maximum amount of winter solar radiation. Deviations of more than 22.5° east or west of true south are not recommended, especially where maximum performance is desired.
Site Topography
The topography of the site is of major concern. If the south-facing wall of the building is shaded by natural or man-made elements, it will probably not be feasible to consider passive solar systems. The ideal siting for a passive solar building is to be bermed into a south-facing slope. This provides a south wall exposed to the sun, and a north wall protected from environmental changes by the earth berm. Berming the north wall of the building should be done cautiously to avoid problems caused by ground water.
BUILDING TYPE AND USE
In addition to the environmental considerations and concepts, the building type and use are very important in developing and applying passive solar systems to buildings. Building type and use are flexible requirements which allow the designer to make appropriate adaptations to the structure to provide the desired energy performance.
Thermal Load Requirements
The thermal load requirement is important to the selection and sizing of passive solar heating systems.