Let your windows help your home save energy
Photos courtesy of Lindal Cedar Homes
Windows play a major role in passive solar design and ventilation strategies that can make a home more comfortable, and contribute to heating and cooling that doesn't cost a dime.
Passive Solar Heating
If you've watched a dogs or cat bask in the warmth of a sunbeam, you've seen passive solar heating in action.
For centuries people have taken advantage of the sun’s radiant heat. Homes constructed of stone were built to capture the sun’s rays, retaining it for the evening hours. Stone and tile floors exposed to southern sunlight perform in a similar manner.
Passive solar design and heating differs from active solar heating systems. Passive solar efforts utilize windows, walls, flooring and other non-mechanical or non-electrical devices to gather and distribute solar energy in the form of heat in the winter, and to reject heat in the summer. Heat rejection in the summer is accomplished through planned landscaping, large eaves and window treatments.
The effectiveness of passive solar design is dependent upon the proper incorporation of the efforts, with the climate in mind. During the design phase window placement, window size, and the type of glazing utilized are critical, as are thermal insulation and thermal mass. Heat is not the only benefit in passive solar design; lighting can be greatly enhanced through proper planning, resulting in lower electricity use.
For instance, Lindal Cedar Homes are carefully sited to take advantage of the sun's energy. Michael Harris, an independent Lindal Cedar Homes consultant in Seattle, said he starts every projectby analyzing the site to find the best orientation for the home.
"We spend a tremendous amount of time designing houses that fit into the site with a minimum amount of disturbance that work well at grabbing the sun in the winter and protecting the house from the sun in the summer and that capture prevailing winds to help ventilate the house," he said. :So I spend a lot of time with people properly siting their houses so they can be energy efficient during the summer and the winter and can ventilate naturally and work properly with topography and minimize impact on the building site itself by being properly sited."
As the seasons change, so does the angle and amount of exposure to the sun. In the heating season, direct rays from the sun should enter buildings at lower angles. During this period, the duration of intense solar gain is limited, lasting only five to six hours a day. Thermal mass captures this heat and absorbs what would otherwise have been excess heat. Throughout this process, the thermal mass prevents the space from overheating and creates a comfortable environment.
When the daily period of solar heat gain ends, the thermal mass will radiate the heat when the temperature drops. With adequate thermal insulation the space can remain comfortable during this time period, but if the temperature falls below the comfort level, supplemental heat will be required.
Emerging materials have been introduced into the industry that allows solar heat to be stored and used at night or on cloudy days. These designs can include passive ventilation strategies that take advantage of convective airflow for heating and cooling purposes.
Many homeowners lower their thermostats overnight, to decrease their use of supplemental heating systems. The load put on the system can be minimized further through the implementation of extensive thermal insulation measures. Over night the stored passive heat will be used and will then begin recharging with the intense mid- morning sunlight. The solar gain provides free, passive solar energy for another day. It is important to have your home well insulated to capitalize on all the benefits of passive solar energy.
We all watch our local news meteorologist prognosticate the weather with the high and low pressure systems on the colorful weather screen. The natural winds we see on the screen are convective currents of air caused by uneven heating of the earth’s surface. Larger differences in air temperatures create stronger winds.
Today, we have the ability to apply these principles to ventilation to exhaust accumulating hot air while drawing in natural cool air for reduced energy consumption and improving air quality.
Operable windows, doors, skylights, and vents can be integrated in a convective method to address the heat buildup in a home or business either manually or by automation. For example, fresh, cooler air can be drawn in from the outside, lower north side or even from an underground heat exchange system. While the cooler air arrives in the home, an automated, multi- stage thermostat system opens a planned series of motorized windows, vents, or skylights.
Both the positioning of these operable systems and the distance between them must be carefully considered in order to maximize their effectiveness. These ventilation strategies also increase fresh air exchanges to improve interior air quality. These convective forces will be determined by the volume of the structure’s space and the rate of ventilation. Such systems can include multiple types of screen solutions to prevent insects from entering during the air exchange process.
Another advantage of such a natural, automated ventilation system is its ability to “think” on its own. Its controller can be programmed to adjust the levels of ventilation in multiple stages, depending upon the interior temperature. If the natural ventilation cannot handle a pre- determined temperature setting, the system will automatically close all the motorized ventilation units and engage the mechanical cooling system.
The ventilation options integrated in to such a system are dependent upon many factors. The square footage, number of levels, locations, terrain and geographic position are some of the variables that need to be studied in order to design an efficient system. Larger spaces need larger areas of ventilation. An expansive, south-facing wall of glass will need a different approach than a north wall. A proper review and installation of such natural ventilation measures will translate in to considerable operational and energy savings.
Energy codes across the country are requiring natural ventilation and reduced energy consumption. For example, the 2013 California Building Energy Efficiency Standards have significantly increased requirements for high performance windows, doors, and skylights. New California standards require large rooms to have additional ventilation, ensuring proper air exchange and air quality is maintained inside commercial and residential buildings. In addition to California, the New York City Department of Buildings began enforcing the “2014 NYC Construction Codes” effective October 1, 2014.
Consider LEED-certified products with a proven track record. Skylights, such as ones manufactured by Solar Innovations, Inc., are excellent solutions for the new requirements. Each skylight is custom engineered to meet the specific design and performance needs required for that location.
Folding glass walls can also be custom- manufactured to meet the design and energy codes for any region. Motorized sliding glass doors are well- suited for residential and commercial applications, especially those in need of automated, natural ventilation. These units can be included in new construction plans or retrofitted to match existing units. Many features are available such as a “crawl mode” that slows the doors before closing to avoid harsh impacts, wall-mounted switches, exterior security keypads and remote controls.
Acoustical sliding glass doors are another product consideration when noise levels need to be addressed.
Read more about energy efficient windows.