By Amanda Jaffe-Katz
Smart lighting and cooling can reduce indoor energy consumption
Prof. Rachel Becker with a sample of phase
Prof. Rachel Becker‘s research at the Faculty of Civil and Environmental Engineering and National Building Research Institute leads her into energy-efficient buildings. Here she studies new methods to improve the energy performance of buildings, enhance thermal and visual comfort, and ensure indoor air quality.
change materials (PCM) that function as
energy buffers in building infrastructure
“Optimal energy consumption in buildings is something we have been researching at Technion for more than 30 years,” says Becker. “Lately, we study the behavior of buildings under summer conditions with an emphasis on reducing cooling energy demand. With global warming, even the cool European countries may become concerned with the warmer summers. They could learn from knowledge we develop in Israel.”
Until air-conditioning became so widespread, humankind had become resigned to “suffering quietly” from the summer heat. “Our research premise is that it is necessary to balance between the strategies for improving building performance under heating and cooling conditions, and that we should take a more holistic approach regarding all the seasons. We emphasize an integration of different means for the summer and winter periods,” she says.
In 1995, Becker and colleagues published research pertaining to night ventilation as a low-energy strategy for cooling the thermal mass of buildings in order to improve thermal comfort next morning, conserve cooling energy, and reduce peak cooling loads. The internal thermal mass of office or school buildings heats up considerably during the daytime, due to people and activity that emit heat. The aim is twofold: to lower peak energy demand and to reduce total energy consumption used for cooling by up to 50 percent. The most effective way to do this is to design the buildings with means for natural ventilation at night.
Modern urban buildings – particularly in densely populated countries like Israel – are taller, and for speedy construction, light industrialized components are used. Moreover, to gain architectural flexibility, internal partitions are lightweight, false ceilings hide electromechanic systems, and in some cases raised floors are installed. All these result in very little internal thermal mass. An alternative strategy for reducing cooling energy and peak loads is necessary.
“In the last several years, the industry has developed building materials and products that include phase change materials (PCM) that function as energy buffers according to a simple physical principle. With PCM, heat storage and release are gained through change of phase: during the day it absorbs heat from the internal heat sources and melts, and during the night it releases the heat and changes from liquid back to solid. The latter process can be effective only if extensive night ventilation takes place. The advantage is that, with a sufficient amount of PCM, a constant temperature can be maintained throughout the entire cyclic process,” Becker says. “One can plan buildings that contain PCMs or add them to existing structures behind thin wall coverings. Even furniture can be made using PCMs.“
Regarding the relationship between energy savings and indoor air quality, according to Becker, there is a gross misconception: “Air conditioning systems do provide proper-quality, clean air,” she says. However, the air handling systems are designed for the worst case and not for continuous energy-saving. Amit Gitterman, who is Becker’s and Dr Raphael Linker’s PhD student working towards candidacy, is looking at optimal automatic dynamic control to bridge between the conflicting demands for continuous indoor air quality and energy conservation.
Another energy-saving device concerns lighting control. Current practice does not take into consideration the quantity of natural light that penetrates the building, resulting in superfluous artificial lighting. A smart system that incorporates occupancy sensors, automatic dimmers, and proper design of the electrical lighting system, can achieve up to 80 percent energy saving of the electricity spent on daytime lighting in classrooms and in offices that have external windows. This does not work for internal rooms or open-space offices, Becker says.
Appropriate shading and smart glazing are additional considerations. To allow day-lighting, window glazing should not be tinted dark, but should comprise what is known as a low-e (low emissivity) coating. The glazing should have selective features that reduce solar radiation in summer but allow natural light during the entire year. It is more costly than regular double glazing, but can save a great deal of energy consumption and is suitable for windows facing in any direction. Furthermore, windows facing north, south, east and west should be of different size to maximize daylight and optimize between winter positive and summer negative heat gains. Glass-faced curtain-walls act as solar collectors. Becker says, “What works just fine in a Chicago skyscraper is not suitable for our hot country.”
“There is always a conflict between initial costs and the end saving. If the smart systems are used more, then the initial costs will drop too.”