Energy - Wikipedia
A zero-energy building, also known as a zero net energy (ZNE) building, net-zero energy . Under this definition the carbon emissions generated from on-site or off -site .. convert a whole campus off of fossil fuels has to date only been theoretical. .. well-insulated walls, radiant heat barriers, ducts in insulated spaces, etc. The dating app helps you meet people and spend your time together in Internet dating love story · Energia radiante definicion yahoo dating. En fotometria, l' energia lumínica o lluminosa és l'energia fracció percebuda de l' energia transportada o com si fos matèria, però el més normal és que es desplaci com una ona i interaccioni amb la matèria de manera material o física. L'energia lluminosa no s'ha de confondre amb l'energia radiant. . Eines personals.
The magnitude of the electromagnetic force, whether attractive or repulsive, is given by Coulomb's lawwhich relates the force to the product of the charges and has an inverse-square relation to the distance between them. Electric charge gives rise to and interacts with the electromagnetic forceone of the four fundamental forces of nature.
The most familiar carriers of electrical charge are the electron and proton. Experiment has shown charge to be a conserved quantitythat is, the net charge within an electrically isolated system will always remain constant regardless of any changes taking place within that system.
The charge on electrons and protons is opposite in sign, hence an amount of charge may be expressed as being either negative or positive. By convention, the charge carried by electrons is deemed negative, and that by protons positive, a custom that originated with the work of Benjamin Franklin.
Charge is possessed not just by matterbut also by antimattereach antiparticle bearing an equal and opposite charge to its corresponding particle. Electric current The movement of electric charge is known as an electric currentthe intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Electric current can flow through some things, electrical conductorsbut will not flow through an electrical insulator.
Current defined in this manner is called conventional current. The motion of negatively charged electrons around an electric circuitone of the most familiar forms of current, is thus deemed positive in the opposite direction to that of the electrons. The positive-to-negative convention is widely used to simplify this situation. An electric arc provides an energetic demonstration of electric current The process by which electric current passes through a material is termed electrical conductionand its nature varies with that of the charged particles and the material through which they are travelling.
Examples of electric currents include metallic conduction, where electrons flow through a conductor such as metal, and electrolysiswhere ions charged atoms flow through liquids, or through plasmas such as electrical sparks. While the particles themselves can move quite slowly, sometimes with an average drift velocity only fractions of a millimetre per second, : That water could be decomposed by the current from a voltaic pile was discovered by Nicholson and Carlisle ina process now known as electrolysis.
Their work was greatly expanded upon by Michael Faraday in Current through a resistance causes localised heating, an effect James Prescott Joule studied mathematically in The level of electromagnetic emissions generated by electric arcing is high enough to produce electromagnetic interferencewhich can be detrimental to the workings of adjacent equipment.
These terms refer to how the current varies in time. Direct current, as produced by example from a battery and required by most electronic devices, is a unidirectional flow from the positive part of a circuit to the negative.
Alternating current is any current that reverses direction repeatedly; almost always this takes the form of a sine wave. The time-averaged value of an alternating current is zero, but it delivers energy in first one direction, and then the reverse.
Alternating current is affected by electrical properties that are not observed under steady state direct current, such as inductance and capacitance. Electric field See also: Electrostatics The concept of the electric field was introduced by Michael Faraday. An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field.
The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two massesand like it, extends towards infinity and shows an inverse square relationship with distance.
Gravity always acts in attraction, drawing two masses together, while the electric field can result in either attraction or repulsion. Since large bodies such as planets generally carry no net charge, the electric field at a distance is usually zero. Thus gravity is the dominant force at distance in the universe, despite being much weaker.
As the electric field is defined in terms of forceand force is a vectorso it follows that an electric field is also a vector, having both magnitude and direction. Specifically, it is a vector field. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field.
This concept was introduced by Faraday,  whose term ' lines of force ' still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines.
The field is therefore zero at all places inside the body. The principles of electrostatics are important when designing items of high-voltage equipment.
There is a finite limit to the electric field strength that may be withstood by any medium. Beyond this point, electrical breakdown occurs and an electric arc causes flashover between the charged parts. This principle is exploited in the lightning conductorthe sharp spike of which acts to encourage the lightning stroke to develop there, rather than to the building it serves to protect : Voltage and Battery electricity A pair of AA cells.
The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work. The electric potential at any point is defined as the energy required to bring a unit test charge from an infinite distance slowly to that point. It is usually measured in voltsand one volt is the potential for which one joule of work must be expended to bring a charge of one coulomb from infinity.
An electric field has the special property that it is conservativewhich means that the path taken by the test charge is irrelevant: Beside the energy balance, Net ZEBs can be characterized by their ability to match the building's load by its energy generation load matching or to work beneficially with respect to the needs of the local grid infrastructure grind interaction.
Both can be expressed by suitable indicators which are intended as assessment tools only. The information is based on the publications,   and  in which deeper information could be found. Design and construction[ edit ] The most cost-effective steps toward a reduction in a building's energy consumption usually occur during the design process. Sunlight and solar heat, prevailing breezes, and the cool of the earth below a building, can provide daylighting and stable indoor temperatures with minimum mechanical means.
ZEBs are normally optimized to use passive solar heat gain and shading, combined with thermal mass to stabilize diurnal temperature variations throughout the day, and in most climates are superinsulated. Sophisticated 3-D building energy simulation tools are available to model how a building will perform with a range of design variables such as building orientation relative to the daily and seasonal position of the sunwindow and door type and placement, overhang depth, insulation type and values of the building elements, air tightness weatherizationthe efficiency of heating, cooling, lighting and other equipment, as well as local climate.
These simulations help the designers predict how the building will perform before it is built, and enable them to model the economic and financial implications on building cost benefit analysisor even more appropriate — life cycle assessment. Zero-energy buildings are built with significant energy-saving features. The heating and cooling loads are lowered by using high-efficiency equipment such as heat pumps rather than furnaces.
Heat pumps are about four times as efficient as furnaces added insulation especially in the attic and in the basement of houseshigh-efficiency windows such as low-E triple-glazed windowsdraft-proofing, high efficiency appliances particularly modern high-efficiency refrigeratorshigh-efficiency LED lighting, passive solar gain in winter and passive shading in the summer, natural ventilationand other techniques.
These features vary depending on climate zones in which the construction occurs. Water heating loads can be lowered by using water conservation fixtures, heat recovery units on waste water, and by using solar water heating, and high-efficiency water heating equipment.
And miscellaneous electric loads can be lessened by choosing efficient appliances and minimizing phantom loads or standby power. Other techniques to reach net zero dependent on climate are Earth sheltered building principles, superinsulation walls using straw-bale constructionVitruvianbuilt pre-fabricated building panels and roof elements plus exterior landscaping for seasonal shading.
Once the energy use of the building has been minimized it can be possible to generate all that energy on site using roof-mounted solar panels.
See examples of zero net energy houses here. Zero-energy buildings are often designed to make dual use of energy including that from white goods. For example using refrigerator exhaust to heat domestic water, ventilation air and shower drain heat exchangersoffice machines and computer servers, and body heat to heat the building.
These buildings make use of heat energy that conventional buildings may exhaust outside. They may use heat recovery ventilationhot water heat recyclingcombined heat and powerand absorption chiller units. By far the most common way to harvest energy is to use roof-mounted solar photovoltaic panels that turn the sun's light into electricity. Energy can also be harvested with solar thermal collectors which use the sun's heat to heat water for the building.
Heat pumps either ground-source otherwise known as geothermal or air-sourced can also harvest heat and cool from the air or ground near the building. Technically heat pumps move heat rather than harvest it, but the overall effect in terms of reduced energy use and reduced carbon footprint is similar.
In the case of individual houses, various microgeneration technologies may be used to provide heat and electricity to the building, using solar cells or wind turbines for electricity, and biofuels or solar thermal collectors linked to a seasonal thermal energy storage STES for space heating.
An STES can also be used for summer cooling by storing the cold of winter underground. To cope with fluctuations in demand, zero energy buildings are frequently connected to the electricity gridexport electricity to the grid when there is a surplus, and drawing electricity when not enough electricity is being produced. Energy harvesting is most often more effective in cost and resource utilization when done on a local but combined scale, for example, a group of houses, cohousinglocal district, village, etc.
An energy benefit of such localized energy harvesting is the virtual elimination of electrical transmission and electricity distribution losses.
Renewable energy - Wikipedia
On-site energy harvesting such as with roof top mounted solar panels eliminates these transmission losses entirely. Energy harvesting in commercial and industrial applications should benefit from the topography of each location. However, a site that is free of shade can generate large amounts of solar powered electricity from the building's roof and almost any site can use geothermal or air-sourced heat pumps.
The production of goods under net zero fossil energy consumption requires locations of geothermalmicrohydrosolarand wind resources to sustain the concept. This may in some cases include district heatingcommunity chilled water, shared wind turbines, etc. There are current plans to use ZEB technologies to build entire off-the-grid or net zero energy use cities. The "energy harvest" versus "energy conservation" debate[ edit ] One of the key areas of debate in zero energy building design is over the balance between energy conservation and the distributed point-of-use harvesting of renewable energy solar energywind energy and thermal energy.
Most zero energy homes use a combination of these strategies. Entire additions of such homes have appeared in locations where photovoltaic PV subsidies are significant,  but many so called "Zero Energy Homes" still have utility bills. This type of energy harvesting without added energy conservation may not be cost effective with the current price of electricity generated with photovoltaic equipment depending on the local price of power company electricity.
The cost, energy and carbon-footprint savings from conservation e. For new builds, and with expert design, this can be accomplished with little additional construction cost for materials over a conventional building. Very few industry experts have the skills or experience to fully capture benefits of the passive design. Photovoltaic-generated electricity becomes more cost-effective when the overall demand for electricity is lower.
Occupant behavior[ edit ] The energy used in a building can vary greatly depending on the behavior of its occupants. The acceptance of what is considered comfortable varies widely. Studies of identical homes have shown dramatic differences in energy use in a variety of climates. An average widely accepted ratio of highest to lowest energy consumer in identical homes is about 3, with some identical homes using up to 20 times as much heating energy as the others .
Occupant behavior can vary from differences in setting and programming thermostatsvarying levels of illumination and hot water use, window and shading system operation and the amount of miscellaneous electric devices or plug loads used.
Utility companies typically own this infrastructure up to the property line of an individual parcel, and in some cases own electrical infrastructure on private land as well. Utilities have expressed concern that the use of Net Metering for ZNE projects threatens the Utilities base revenue, which in turn impacts their ability to maintain and service the portion of the electrical grid that they are responsible for.
Utilities have expressed concern that states that maintain Net Metering laws may saddle non-ZNE homes with higher utility costs, as those homeowners would be responsible for paying for grid maintenance while ZNE home owners would theoretically pay nothing if they do achieve ZNE status. This creates potential equity issues, as currently, the burden would appear to fall on lower-income households. A possible solution to this issue is to create a minimum base charge for all homes connected to the utility grid, which would force ZNE home owners to pay for grid services independently of their electrical use.
Additional concerns exist that local distribution as well as larger transmission grids have not been designed to convey electricity in two directions, which may be necessary as higher levels of distributed energy generation come on line. Overcoming this barrier could require extensive upgrades to the electrical grid, however this is not believed to be a major problem until renewable generation reaches much higher levels of penetration than currently realized. Federal, and especially California, subsidies and financial incentives.
Led by the CEO of United Technologies and the Chairman of Lafargethe organization has both the support of large global companies and the expertise to mobilize the corporate world and governmental support to make ZEB a reality. Their first report, a survey of key players in real estate and construction, indicates that the costs of building green are overestimated by percent.
Survey respondents estimated that greenhouse gas emissions by buildings are 19 percent of the worldwide total, in contrast to the actual value of roughly 40 percent. Much has been learned from many significant successes, and a few expensive failures.
Among these, the Canadian R and the German passive house standards have been internationally influential. Collaborative government demonstration projects, such as the superinsulated Saskatchewan House, and the International Energy Agency's Task 13have also played their part. Gas for cooking at the same level. Net Zero Carbon Conversion Example[ edit ] Many well known universities have professed to want to completely convert their energy systems off of fossil fuels.
The very idea that one could convert a whole campus off of fossil fuels has to date only been theoretical.