7.5 Energy and Use of Sun
Efficient use of energy is one of the key targets of high performance buildings. There are two main strategies pursued: (i) conservation of energy through more efficient building design and (ii) on-site power generation through energy-conversion technologies. The options for the power generation include renewable and no-emission resources, such as solar, wind, and geothermal energy, depending on the building setting preferences. A sustainable building can be still connected to the grid, but should be much less reliant on it and, in some cases, can even feed some of the extra energy produced on site back to the grid (net-zero energy building concept).
Let us start with the following chapter reading. This reading will introduce you to the main systems and energy interactions inside a building. It also contains useful terminology.
Armstrong, J., Chapter 4. Efficient Use of Energy and Other Resources (pp. 83-115), in Green Building: Project Planning and Cost Estimating, RSMeans, John Wiley & Sons Inc., 2011. (See E-Reserves in Canvas.)
Read pages 83-90 to learn about the main aspects of energy regulation in buildings, and scan through pages 90-112 to become familiar with the main strategies and technologies used in green design.
One of the ideas we can get from this reading is the importance of flexibility and tunability of design. Designing and building for variable conditions allows for significant energy savings and more efficient use of resources when it is needed. For example, one of the cornerstones of green building designs is proper ventilation. Sensitive ventilation, such as adjusting ventilation requirements based on human occupancy, is one of the sources of energy saving.
Such tunable designs require special technologies for monitoring and control. For example, Air monitoring technologies, such as sensors, "smart controls" can be of great benefit in the regulation of high occupancy spaces (conference rooms, auditoriums) in terms of total required energy. Technology is currently available that monitors the CO2 levels in the space. Occupancy sensors can be used to turn off light in occupied spaces.
Net Zero Energy Building
One of the very attractive concepts in building design is net zero energy building (NZEB). In brief, it means that energy generated by the building offsets the consumed energy by the building operation. In that case, ideally, the building does not require grid and can sustain itself. This concept is currently under development, but some successful examples of its implementation already exist. Read the following web article to get a deeper insight into this topic.
"The Future of Green Buildings May Be Closer than You Think", Press release, Wharton University of Pennsylvania, May 06, 2013.
This article discusses the Net Zero Energy Building (NZEB) philosophy and some successful examples of it in several locations of the U.S. We will continue discussing this concept on the forum this week!
Optimizing use of the sun
Many existing homes and buildings heavily rely on oil, coal, and natural gas as fuels to heat and cool our homes. If not burning those fuels directly, we consume electricity from the grid, anyway, much of that electricity coming from the fossil fuel power plants. Those fuel resources are expensive, create pollution, and they are also being depleted rapidly. This makes attractive the strategy to adapt buildings for using the solar energy, which is an unlimited resource.
There are active and passive strategies for sun use:
Active strategies use solar photovoltaic (PV) panels or solar collectors to turn the solar radiation into electric energy or thermal energy. The technical principles of operation of PV and solar thermal technologies will be considered in more detail in another lesson, specially devoted to energy. Currently, many residential and commercial buildings are being evaluated for installation of active solar systems. While some are very well positioned to accommodate such on-site energy converters, others may be less suitable. Decision may be driven by such factors as: building design, shading structures, solar resource at the location of interest, building energy need compared to the system capacity, available roof or ground area for installation, and building aesthetics.
Passive strategies include features and adaptations in the building envelope and smart use of the natural solar activity. The passive approach does not imply installation of a separate solar energy conversion system, but rather utilizes features of building design. For example, a house can be oriented to minimize summer afternoon solar heat gain and to maximize winter solar heat gain. If the building is located in the Northern Hemisphere, the long sides of the house are made facing south and north while roof overhangs and landscaping are built to shade the east, south, and west sides. Alternatively, house design can take advantage of prevailing breezes during the spring, summer, and fall. Natural air movement is valuable for cross-ventilation of the house. In addition, foliage of trees and shrubs that create shade around your house helps keep the house cool, while bare branches in winter let the sunlight through to warm the house.
In passive system design, many physical parameters are manipulated to achieve the balance of heat distribution. There is a lot to learn in terms of how the light transmitting and absorbing surfaces are geometrically positioned, and what materials are used. You would have to turn to an architectural design course to become better educated on this topic, should you have interest. A couple of links below would give you some examples of passive solar strategies, if you are interested to learn more.
Read more about the passive strategies for optimized use of the sun:
"Passive Solar Design" Sustainable Sources, 2014.
Check Your Understanding:
Check your physics background. Name three types of heat transfer in the buildings.
Click for answer.
Heat conduction, Convection, Radiation
What is the difference between these heat transfer mechanisms?
Click for answer.
Conduction (or diffusion) of heat occurs due to temperature gradient across a space or material. After reaching thermal equilibrium, both temperatures become equal. Convection is transfer of heat associated with a flow - for example: air flow due to a pressure gradient. Radiation is emission of thermal energy in the form of electromagnetic waves - for example: emission of heat from the sun or a hot object. Unlike conduction and convection, radiated energy can be concentrated and used for power generation.
What are the main sources of heat gain in the buildings?
Click for answer.
Solar gain through windows, electric lighting equipment, people occupying space, heat conduction through roof and walls.
How trees can be part of green envelope design?
Click for answer.
For example, trees can provide seasonal shade, reducing the need for mechanical cooling.