This article will answer the questions to the following :
1) The amount of cooling load added to a home when a window is facing North, West, South,& East direction.
2) When 4' x 4' window is upsized to 5' x 5', how much cooling load is added to the home?
A building with high glazing percentage will have high cooling load due to increased solar heat gain especially in the month of June/July. During these conditions, HVAC system works longer to cool to maintain comfortable indoor temperatures, which can lead to higher energy consumption and operating costs. To figure out how much energy is required to cool the home, this study assumes the following parameters.
Area of Bedroom: 100 square foot
Ceiling: R-38 (U-0.026)
Ceiling Height: 10 feet
Floor: U-0.9
Windows: Size and Orientation Varies
Window U Value / SHGC value: 0.4 & 0.25
Duct Load: None
Weather: Phoenix, Arizona
Summer Outdoor Dry Bulb Temperature: 115 degrees Fahrenheit
Winter Outdoor Dry Bulb Temperature: 34 degrees Fahrenheit
Summer Indoor Temperature: 75 F & 45% RH
Winter Indoor Temperature: 70 F & 30%RH
Energy Calculation for 4' x 4' & 5' x 5' windows
WINDOWS SIZES | 4' x 4' | 4' x 4' | 5' x 5' | 5' x 5' |
ORIENTATION | COOLING | HEATING | COOLING | HEATING |
NORTH | 1435 | 2642 | 1606 | 2755 |
WEST | 1919 | 2642 | 2363 | 2755 |
SOUTH | 1486 | 2642 | 1687 | 2755 |
EAST | 1745 | 2642 | 2090 | 2755 |
Cooling Load Comparison of 4' x 4' Window Relative to North Orientation
​ | 4 ' x 4' Window | ​ |
|---|---|---|
Respective of North value | Value Difference | Relative Percentage Difference |
West _ref_North | 1919-1435 = 484 | 33.72% |
South_ref_North | 1485-1435 = 50 | 3.48% |
East_ref_North | 1745-1435 = 310 | 21.6% |
North window has the lowest gain or cooling load. If there is no room to install window facing north, best to choose South as second preference, and East as the third preference.
Cooling Load Comparison of 5' x 5' Window Relative to North Orientation
​ | 5' x 5' Window | ​ |
|---|---|---|
Respective of North value | Value Difference | Relative Percentage Difference |
West _ref_North | 2363 - 1606 = 757 | 47.14% |
South_ref_North | 1687 - 1606 = 81 | 5.04% |
East_ref_North | 2090 - 1606 = 484 | 30.14% |
North window has the lowest gain or cooling load. If there is no room to install window facing north, best to choose South as second preference, and East as the third preference.
How Much Cooling Load is added to the home when the 4' x 4' window is upsized to 5' x 5' window?
The percentage area difference by upsizing from 4' x 4' window (16 sq.ft.) to 5' x 5' window (25 sq.ft.) is 56.25% . Following table shows the percentage difference of adding 9 sq.ft. glazing to the window .
ORIENTATION | Difference = 5'x5 Gain - 4' x 4' Gain | Relative Percentage Increment |
NORTH | 1606 - 1435= 171 | 11.92% |
WEST | 2363-1919 = 444 | 23.14% |
SOUTH | 1687-1486 = 201 | 13.53% |
EAST | 2090-1745 = 345 | 19.77% |
Energy Calculation is performed as per Software ACCA Manual J Method. The purpose of the calculation is not to size the Equipment. It is merely to show the energy difference if homeowner decides to install window from North to any other orientation. True U-values and SHGC values are used. Calculation does not consider total assembly value.