Solar Gain

From Swikipedia

Introduction

All buildings absorb heat from the sun through walls, roofs and windows. This results in an increase in the temperature of the building surface, due to solar radiation and is termed as Solar Gain. The amount of solar gain increases with the strength of the sun, and with the ability of any intervening material to transmit or resist the radiation. Therefore, heat transfer via radiation depends on the material properties, the temperature gradient (outside vs. inside) and the area or size of the building surface.

Brief Description

Solar Gain is calculated through the Solar Heat Gain Coeffficient, whose value ranges between 0 and 1. The lesser the value, the lower is the heat gain.

Solar Gain and Building Design:

Building design should usually aim at maximising solar gain within the building in the winter (to reduce space heating demand), and control it in summer (to minimise cooling requirements). Thermal mass may be used to even out the fluctuations during the day, and to some extent between days.

Ways to maximise and minimise solar gain:

 In heating-dominated climates, major glazing areas should generally face south to collect solar heat during the winter when the sun is low in the sky.

 In the summer, when the sun is high overhead, overhangs or other shading devices (e.g., awnings) prevent excessive heat gain.

 To be effective, south-facing windows usually must have a solar heat gain coefficient (SHGC) of greater than 0.6 to maximize solar heat gain during the winter, a U-factor of 0.35 or less to reduce conductive heat transfer, and a high visible transmittance (VT) for good visible light transfer.

 Windows on east-, west-, and north-facing walls are reduced in heating climates, while still allowing for adequate daylight. East- and west-facing windows are limited because it is difficult to effectively control the heat and penetrating rays of the sun when it is low in the sky. These windows should have a low SHGC and/or be shaded. North-facing windows collect little solar heat, so they are used just to provide useful lighting.

 Low-emissivity window glazing can help control solar heat gain and loss in heating climates.

 In cooling climates, particularly effective strategies include preferential use of north-facing windows and generously shaded south-facing windows.

 Windows with low SHGCs are more effective at reducing cooling loads. The following types of glazing help reduce solar heat gain, lowering a window's SHGC: Low-E, Tinted, Reflective, and Spectrally Selective windows.

References:

http://en.wikipedia.org/wiki/Solar_gain

http://hubpages.com/hub/low_solar_gain_windows

http://www.energysavers.gov/your_home/windows_doors_skylights/index.cfm/mytopic=13360