SOLAR HEATING BASIC INFORMATION AND TUTORIALS

TIPS ON SOLAR HEATING

WHAT IS SOLAR HEATING?

The amount of solar energy (insolation) that comes into a building through the windows (size, orientation, glazing, and shading) depends on time of year, location, and percentage sunshine (clouds and haze).

The solar heating can be estimated from tables of clear-day insolation by latitude and percentage sunshine by month. Average insolation values by month that take into account cloud cover for different angles of surfaces are available on the Internet.

The data for vertical insolation indicate that in most locations vertical windows on the south can be net heat gainers, depending on climate and R value of the windows. Surprisingly, even single-pane windows on the south can be net energy gainers in temperate climates.

Also, during the summer vertical windows let in less solar energy due to the angle of the sun (cosine factor). There is more reflection due to the larger angle of incidence.

Example 5.1
Calculate the amount of solar heat that comes through a south-facing window (single pane) for January (70% sunshine).
Vertical window, 1.2 by 2.5 m, single pane, transmission = 90%
Area = 3 m2, insolation for January is 6 kWh/m2 per clear day
Energy hitting window per day = 3 m2 * 6 kWh/m2 = 18 kWh/day
Energy transmitted = 0.9 * 18 kWh/day = 16 kWh/day = 55,000 Btu/day
Energy for month = 16 kWh/day * 31 days * 0.70 = 350 kWh = 1.2 * 106 Btu
Maps of solar insolation for the United States by month are available from the National Renewable Energy Laboratory (NREL) for different types of collectors and orientation (http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/). The two-axis concentrating collector gives the normal to the sun. The maps also take into account the percentage sunshine, so the average values of energy per day do not have to be adjusted.