Design Variations-Orientation

Orientation in the Northern Zone (mostly heating)
It is generally accepted that simply orienting the majority of windows to the south in a heating-dominated climate will result in greater solar gain and less heating energy use. The results shown in the figure indicate that, as expected, there is a difference between orientations and south-oriented windows perform best. The difference between orientations is most notable when clear single-glazed windows are used (Window A) but is diminished when higher-performance windows with lower U-factors and higher SHGCs are used.

Window orientation in a house is often dictated by views and factors other than optimal solar gain. By using high-performance windows, any orientation can result in a very energy-efficient house. For example, when the house has triple-glazed low-E windows (Window F), even a north-facing orientation has about the same energy us as a south-facing orientation with clear double-glazed windows (Window C). All of the cases shown have average shading conditions. If there was a greater window area or different shading conditions, the difference in energy costs between less efficient and more efficient windows may be greater.

	Window A	Window B	Window C	Window D	Window E	Window F
Glazing	Single Clear	Double Clear	Double Clear	Double High-Solar-Gain Low-E	Double Low-Solar-Gain Low-E	Triple Mod-Solar-Gain Low-E
Frame	Aluminum	Aluminum with Break	Wood, Wood Clad, Vinyl, Hybrid/Composite	Wood, Wood Clad, Vinyl, Hybrid/Composite	Wood, Wood Clad, Vinyl, Hybrid/Composite	Insulated Vinyl, Fiberglass
U-Factor	1.16	.63	.49	.37	.34	.18
SHGC	.76	.62	.56	.53	.30	.40
VT	.74	.62	.58	.53	.50	.49

Orientation in the Central/North and Central/South Zones (heating and cooling)
In climates where there is both a significant heating and cooling season, orienting windows to the south will result in greater solar gain in winter while overhangs can be designed to reduce summer solar gain. East and west window are difficult to shade and should be avoided. North facing windows perform the best in summer but are worse in providing winter heat gain. The results shown in the figure indicate that, as expected, there is a difference between orientations and south-oriented windows perform best. The difference between orientations is most notable when clear single-glazed windows are used (Window A) but is diminished when higher-performance windows with lower U-factors and SHGCs are used. In this particular climate (Sacramento), the low-solar-gain low-E window (Window E) outperforms the high-solar-gain low-E window (Window D). This may be reversed in a climate where the heating load outweighs the cooling load. The triple-glazed low-solar-gain low-E window (Window F) has the best performance.

Window orientation in a house is often dictated by views and factors other than optimal solar gain. By using high-performance windows, any orientation can result in a very energy-efficient house. For example, when the house has triple-glazed low-E windows (Window F), any window orientation uses less annual energy than a south-facing orientation with clear double-glazed windows (Window C). All of the cases shown have average window area and shading conditions. If there was no shading or greater window area, the difference in energy costs between less efficient and more efficient windows would be greater.

	Window A	Window B	Window C	Window D	Window E	Window F
Glazing	Single Clear	Double Clear	Double Low-Solar-Gain Low-E	Double Clear	Double High-Solar-Gain Low-E	Double Low-Solar-Gain Low-E
Frame	Aluminum	Aluminum	Aluminum with Break	Wood, Wood Clad, Vinyl, Hybrid/Composite	Wood, Wood Clad, Vinyl, Hybrid/Composite	Wood, Wood Clad, Vinyl, Hybrid/Composite
U-Factor	1.16	.76	.47	.49	.37	.34
SHGC	.76	.68	.33	.56	.53	.30
VT	.74	.67	.53	.58	.53	.50

Orientation in the Southern Zone (mostly cooling)
In predominantly cooling climates, the goal is to face most windows north, where there is little direct exposure, or to the south, where they can be designed with overhangs that will keep out most of the hot summer sun. Overhangs are much less effective against the lower angles of the east and west sun. Therefore, simply reducing the size and number of east and west windows can be the best strategy.

The figure illustrates the impact of different window orientations on annual energy costs for a typical house in Phoenix, Arizona. As expected, facing windows in different directions has a significant impact when typical clear single-glazed windows are used (Window A). Note that high-solar-gain low-E (Window E) performs worse than low-solar-gain low-E (Window F) and is not optimal in this climate. When higher-performance windows with low-solar-gain low-E coatings are used, window orientation has a greatly diminished impact on energy use (Windows D and F). In effect, with these more advanced windows, nearly all of the glazing can face east, west or south without a significant energy penalty. These computer simulations are done for a house with average window area and shading conditions. If there were no shading or greater glazing area, the less efficient glazing would perform worse in comparison to the low-solar-gain low-E windows.

	Window A	Window B	Window C	Window D	Window E	Window F
Glazing	Single Clear	Single Tint	Double Clear	Double Low-Solar-Gain Low-E	Double High-Solar-Gain Low-E	Double Low-Solar-Gain Low-E
Frame	Aluminum	Aluminum	Aluminum	Aluminum	Wood, Wood Clad, Vinyl, Hybrid/Composite	Wood, Wood Clad, Vinyl, Hybrid/Composite
U-Factor	1.16	1.16	.76	.59	.37	.34
SHGC	.76	.65	.68	.37	.53	.30
VT	.74	.56	.67	.57	.53	.50

Note: The thermal performance properties of specific glazings and frames can vary depending on product design and materials. The results presented here are averages. Consult specific manufacturers for NFRC rated U-factors and SHGCs for products of interest. The annual energy performance figures shown here were generated using RESFEN for a typical new 2000 sq. ft. house with 300 sq ft of window area (15% of floor area). The windows include typical shading (interior shades, overhangs, trees and neighboring buildings). U-factor, SHGC, and VT are for the total window including frame. Energy use and savings between different window options will typically be higher for homes which are not as well insulated as typical new homes. The costs shown here are annual costs for space heating and space cooling only and thus will not correlate to utility bills. Costs for lights, appliances, hot water, cooking, and other uses are not included in these figures. The mechanical system uses a gas furnace for heating and air conditioning for cooling. These figures are based on typical energy costs for this region. Natural gas prices and electric prices are provided by the Energy Information Administration (www.eia.doe.gov).