How to Make Homes More Energy Efficient
Reducing energy use in your home can be achieved by selecting energy efficient heating and air conditioning equipment and by properly insulating your home against heat loss in the winter and heat gain in the summer. According to the California Energy Commission, as much as 40% of your home’s cooling requirements are due to solar energy entering through glass. Even a small amount of glass on the south or west side of a home can result in overheating and increased air conditioning cost.
The best place to stop heat and reduce air conditioning to increase savings is at the window. For existing homes experiencing energy problems from heat, the most expensive option in treatments is to replace existing glass and frames with a new window system designed to block heat and deal with a home’s energy performance needs. A less expensive treatment is keeping existing frames and replacing only the glass. In either case of these treatments, homeowners may be reluctant to replace existing windows in their homes, whose energy saving performance is generally adequate, though not optimum in blocking unwanted heat. For all existing glass and in new construction, applied window film is the least expensive treatment and preferred energy efficient saving solution in homes.
Conventional tinted and reflective window film treatments do block heat, but they also block light. In some cases, highly reflective film treatments block as much as 85% of the visible light outside from entering the inside of homes or office buildings. The result is a property in which natural levels of light are permanently excluded. The consequent darkened interiors require increased lighting which not only adds increased energy cost, but as a generator of heat, often results in more, not less, use of air conditioning, defeating the cost-savings benefit of applied window film in the first place.
Energy Saving Window Treatments
The new breed of energy efficient window film is clear, colorless, heat blocking and spectrally selective. Clear spectrally selective applied window film offers the most efficient ratio of visible light transmission to heat rejection. Spectrally selective refers to the ability of the film to select or let in desirable daylight, while blocking out undesirable heat. Such treatments block heat as well as solar control glass and even in new construction; often the cost of solar control glass exceeds the cost of standard insulating glass to which a spectrally selective film is later applied.
When faced with a choice between tinted or reflective film that blocks more heat and spectrally selective film that blocks less heat but transmits more light, consider the Los Angeles Department of Water and Power’s rebate program for window film. It is based on a film’s luminous efficacy constant, a measurement of its efficient ability to simultaneously block heat and transmit light.
While a very reflective film that blocks more heat than a spectrally selective film earns a 55 cent per s/f rebate from LADWP, a spectrally selective film that blocks less heat but lets in more light receives a higher rebate of 85 cents per s/f. Only spectrally selective films with luminous efficacy constants over 1.0 receive the higher rebate. Less expensive conventional films show quicker savings compared to more expensive spectrally selective films. However, the cost of extra energy used for lighting and air conditioning operation due to a conventional film’s inability to transmit sufficient visible light, makes the payback for the conventional film and spectrally selective film comparable. Given rising cost of electricity, the rate of payback for spectrally selective film is always improving – averaging 4 years. Factor in the issues of occupant morale, building appearance, energy savings and it’s clear that spectrally selective window film is the preferred choice for efficient energy saving window treatments.