Energy Efficiency for Windows

Posted on: January 6, 2014
Tags: Home Improvement, Hunter Douglas, Energy Efficient

Energy Efficiency 

Operating Tips for your Windows

Windows Are Energy Holes

Windows were once called “wind holes.” Fortunately, today’s modern windows do a good job of preventing unwanted air flow. However, closed windows still offer very little resistance to the flow of energy. Windows are, in fact, “energy holes.”

Compared to the well-insulated walls and roofs of today’s homes, standard double- pane windows allow up to 10 to 15 times more heat energy to flow through them. So, even though windows make up only about 10% of a home’s insulated shell, up to half a home’s heating and cooling energy can be lost through them.

How Window Coverings Help

Window coverings are like valves — but unlike most valves that control the flow of liquid or gas, window coverings control the flow of energy. Open the valve and more energy comes in (or goes out) through the window. Close the valve and more energy stays out (or stays in).

Wintertime Energy Flow

In wintertime, energy flow through windows is a two-way street: solar energy enters and heat energy exits. The general rule in winter is to open the window covering when the amount of solar energy entering through the uncovered window is greater than the

amount of heat energy being saved by the lowered shade. This usually means opening the “valve” whenever bright, direct sunlight shines on the window.

It follows from this that, in winter, window coverings should always be closed at night and on cloudy days.

Summertime Energy Flow

In summertime, energy through windows typically flows in one direction only: into the home. Both solar energy and heat energy flow from the outside in, raising the temperature and increasing the load on the cooling system.

For optimal energy efficiency in summer, window coverings should actually be closed all the time. However, that sacrifices the reasons to have windows in the first place: light, view and ventilation. A reasonable compromise is to close the “valve” when direct sunlight shines on the window — just the opposite of what you want to do in winter.

Energy Efficiency Timetables

To help you control energy flow at the window, we have developed Energy Efficiency Timetables. The timetables are guidelines on when to open and close your energy valves. Basically, they show the hours to open window coverings to allow solar heat into the home in cold months, and the hours to close window coverings to block solar heat in warm months.

The times shown on all the timetables are meant to be guidelines only. Modify them as needed for specific climate and weather conditions. For example, January days in Denver vary from cold and frigid to warm and balmy. Window covering operation needs to be adjusted appropriately — let solar energy in if it’s a cold day, keep solar energy out if it’s a warm one.

Swing Months

Some months on the timetable are called “swing months.” These are months that typically vary between cool and warm, with not much need for either heating or cooling. Adapt the hours of window covering operation to the closest cooler month should heating be needed, and to the closest warmer month should cooling be needed.

Solar Time vs. Clock Time

The timetables do not account for Daylight Savings Time. In fact, the hours on the timetables are solar time, rather than clock time. With solar time, noon is the hour when the sun is highest in the sky, not necessarily when the clock reads 12:00 p.m.

Templates on the last page of this document can be used to make your own timetable if you want to convert solar time to clock time. Over the course of a year, note each month the clock time when the sun is highest in the sky (high noon), and adjust the hours on your latitude’s timetable accordingly.

You can roughly approximate solar time by subtracting one hour from the times listed whenever Daylight Savings Time is in effect.

Window Direction

The timetable below is for windows that face north, south, east and west, as shown in the illustration. If your windows do not happen to face these directions, you can again use the template to customize a timetable for your home. On a sunny day near the middle of each month, note the hours direct sunlight falls upon the windows on each side of the house. Then make your timetable for that month, basing the hours of operation on whether it’s a heating, cooling or “swing” month.

What About UV Protection?

In heating-dominated months, the timetables are designed to allow as much sunlight into the home as possible to help heat it. But ultraviolet light is part of that sunlight, and we know that prolonged exposure to UV rays can damage home furnishings. How do we balance wintertime energy efficiency with the need for the UV protection provided by most window coverings when closed?

Carpets, upholstery and wood floor coatings are available with UV protection — plan your home furnishing purchases with that in mind. In addition, spray treatments are offered that claim to protect furnishings from UV rays. 

Lower-tech solutions are also available, such as covering furnishings to block the light. But sometimes you’ll just have to forego the free heat from the sun and close certain shades to help protect against UV.

Exciting Windows! by Apollo
Date: on December 7, 2016

Pete, That's a great question. The best solution for you to have complete control of your windows treatments in your cabin in Wisconsin, is a motorized energy efficient shade. The most efficient shade is the Hunter Douglas Duette® Architella™ honeycomb shade with Powerview™ motorization operation. Powerview™ motorization allows you to have a remote connection to be able to operate your shades from anywhere in the world, by using your smartphone or tablet, as long as you have internet connection. You can set schedules for your shades to open and close and you would not have to think about it. You can read more about the Powerview™ operation on our product information page here - I hope this information helps you, Ashley

Date: on December 7, 2016

What if you need to choose open or closed in Wisconsin - un-occupied cabin in the winter.

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