In building and construction, the R-value is a measure of how well a two-dimensional barrier, such as a layer of insulation, a window or a complete wall or ceiling, resists conductive flow of heat. R-values measure the thermal resistance per unit of a barrier's exposed area; the greater the R-value, the greater the resistance, so the better the thermal insulating properties of the barrier. R-values are used in describing effectiveness of insulating material and in analysis of heat flow across assemblies under steady-state conditions. Heat flow through a barrier is driven by temperature difference between two sides of the barrier, the R-value quantifies how the object resists this drive: The temperature difference divided by the R-value and multiplied by the surface area of the barrier gives the total rate of heat flow through the barrier, as measured in watts or in BTUs per hour; as long as the materials involved are dense solids in direct mutual contact, R-values are additive. Note that the R-value is the building industry term for what is in other contexts called "thermal resistance per unit area."
It is sometimes denoted RSI-value. An R-value can be given for an assembly of materials. In the case of materials, it is expressed in terms of R-value per unit length; the latter can be misleading in the case of low-density building thermal insulations, for which R-values are not additive: their R-value per inch is not constant as the material gets thicker, but rather decreases. The units of an R-value are not explicitly stated, so it is important to decide from context which units are being used: an R-value expressed in I-P units is about 5.68 times larger than when expressed in SI units, so that, for example, a window, R-2 in I-P units has an RSI of 0.35. For R-values there is no difference between imperial units; as far as how R-values are reported, all of the following mean the same thing: "this is an R-2 window". The more a material is intrinsically able to conduct heat, as given by its thermal conductivity, the lower its R-value. On the other hand, the thicker the material, the higher its R-value.
Sometimes heat transfer processes other than conduction contribute to heat transfer within the material. In such cases, it is useful to introduce an "apparent thermal conductivity", which captures the effects of all three kinds of processes, to define the R-value in general as R = thickness of the specimen apparent thermal conductivity; this comes at a price, however: R-values that include non-conductive processes may no longer be additive and may have significant temperature dependence. In particular, for a loose or porous material, the R-value per inch depends on the thickness always so that it decreases with increasing thickness. For similar reasons, the R-value per inch depends on the temperature of the material increasing with decreasing temperature. In construction it is common to treat R-values as independent of temperature. Note that an R-value may not account for radiative or convective processes at the material's surface, which may be an important factor for some applications; the R-value is the reciprocal of the thermal transmittance of a assembly.
The U. S. construction industry prefers to use R-values, because they are additive and because bigger values mean better insulation, neither of, true for U-factors. The U-factor or U-value is the overall heat transfer coefficient that describes how well a building element conducts heat or the rate of transfer of heat through one square metre of a structure divided by the difference in temperature across the structure; the elements are assemblies of many layers of components such as those that make up walls/floors/roofs etc. It measures the rate of heat transfer through a building element over a given area under standardised conditions; the usual standard is at 50 % humidity with no wind. It is expressed in watts per meter squared kelvin; this means. A low U-value indicates high levels of insulation, they are useful as it is a way of predicting the composite behavior of an entire building element rather than relying on the properties of individual materials. In most countries the properties of specific materials are indicated by the thermal conductivity, sometimes called a k-value or lambda-value.
The thermal conductivity is the ability of a material to conduct heat. Expanded polystyrene has a k-value of around 0.033 W/m
International standards are technical standards developed by international standards organizations. International standards are available for use worldwide; the most prominent organization is the International Organization for Standardization. International standards may be used either by direct application or by a process of modifying an international standard to suit local conditions; the adoption of international standards results in the creation of equivalent, national standards that are the same as international standards in technical content, but may have editorial differences as to appearance, use of symbols and measurement units, substitution of a point for a comma as the decimal marker, differences resulting from conflicts in governmental regulations or industry-specific requirements caused by fundamental climatic, technological, or infrastructural factors, or the stringency of safety requirements that a given standard authority considers appropriate. International standards are one way of overcoming technical barriers in international commerce caused by differences among technical regulations and standards developed independently and separately by each nation, national standards organization, or company.
Technical barriers arise when different groups come together, each with a large user base, doing some well established thing that between them is mutually incompatible. Establishing international standards is one way of preventing or overcoming this problem; the implementation of standards in industry and commerce became important with the onset of the Industrial Revolution and the need for high-precision machine tools and interchangeable parts. Henry Maudslay developed the first industrially practical screw-cutting lathe in 1800, which allowed for the standardisation of screw thread sizes for the first time. Maudslay's work, as well as the contributions of other engineers, accomplished a modest amount of industry standardization. Joseph Whitworth's screw thread measurements were adopted as the first national standard by companies around the country in 1841, it came to be known as the British Standard Whitworth, was adopted in other countries. By the end of the 19th century differences in standards between companies were making trade difficult and strained.
The Engineering Standards Committee was established in London in 1901 as the world's first national standards body. After the First World War, similar national bodies were established in other countries; the Deutsches Institut für Normung was set up in Germany in 1917, followed by its counterparts, the American National Standard Institute and the French Commission Permanente de Standardisation, both in 1918. By the mid to late 19th century, efforts were being made to standardize electrical measurement. An important figure was R. E. B. Crompton, who became concerned by the large range of different standards and systems used by electrical engineering companies and scientists in the early 20th century. Many companies had entered the market in the 1890s and all chose their own settings for voltage, frequency and the symbols used on circuit diagrams. Adjacent buildings would have incompatible electrical systems because they had been fitted out by different companies. Crompton could see the lack of efficiency in this system and began to consider proposals for an international standard for electric engineering.
In 1904, Crompton represented Britain at the Louisiana Purchase Exposition in St. Louis as part of a delegation by the Institute of Electrical Engineers, he presented a paper on standardisation, so well received that he was asked to look into the formation of a commission to oversee the process. By 1906 his work was complete and he drew up a permanent constitution for the first international standards organization, the International Electrotechnical Commission; the body held its first meeting that year with representatives from 14 countries. In honour of his contribution to electrical standardisation, Lord Kelvin was elected as the body's first President; the International Federation of the National Standardizing Associations was founded in 1926 with a broader remit to enhance international cooperation for all technical standards and specifications. The body was suspended in 1942 during World War II. After the war, ISA was approached by the formed United Nations Standards Coordinating Committee with a proposal to form a new global standards body.
In October 1946, ISA and UNSCC delegates from 25 countries met in London and agreed to join forces to create the new International Organization for Standardization. List of international common standards List of technical standard organisations
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit. It uses the degree Fahrenheit as the unit. Several accounts of how he defined his scale exist; the lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice and salt. Further limits were established as the melting point of ice and his best estimate of the average human body temperature; the scale is now defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure. At the end of the 2010s, Fahrenheit was used as the official temperature scale only in the United States, its associated states in the Western Pacific, the Bahamas, the Cayman Islands and Liberia. Antigua and Barbuda and other islands which use the same meteorological service, such as Anguilla, the British Virgin Islands and Saint Kitts and Nevis, as well as Bermuda and the Turks and Caicos Islands, use Fahrenheit and Celsius.
All other countries in the world now use the Celsius scale, named after Swedish astronomer Anders Celsius. On the Fahrenheit scale, the freezing point of water is 32 degrees Fahrenheit and the boiling point is 212 °F; this puts the freezing points of water 180 degrees apart. Therefore, a degree on the Fahrenheit scale is 1⁄180 of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water are 100 degrees apart. A temperature interval of 1 °F is equal to an interval of 5⁄9 degrees Celsius; the Fahrenheit and Celsius scales intersect at −40°. Absolute zero is −273.15 °C or −459.67 °F. The Rankine temperature scale uses degree intervals of the same size as those of the Fahrenheit scale, except that absolute zero is 0 °R — the same way that the Kelvin temperature scale matches the Celsius scale, except that absolute zero is 0 K; the Fahrenheit scale uses the symbol ° to denote a point on the temperature scale and the letter F to indicate the use of the Fahrenheit scale, as well as to denote a difference between temperatures or an uncertainty in temperature.
For an exact conversion, the following formulas can be applied. Here, f is the value in Fahrenheit and c the value in Celsius: f °Fahrenheit to c °Celsius: °F × 5°C/9°F = /1.8 °C = c °C c °Celsius to f °Fahrenheit: + 32 °F = °F + 32 °F = f °FThis is an exact conversion making use of the identity −40 °F = −40 °C. Again, f is the value in Fahrenheit and c the value in Celsius: f °Fahrenheit to c °Celsius: − 40 = c. C °Celsius to f °Fahrenheit: − 40 = f. Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale, the zero point was determined by placing the thermometer in a mixture "of ice, of water, of ammonium chloride or of sea salt"; this combination forms a eutectic system which stabilizes its temperature automatically: 0 °F was defined to be that stable temperature. The second point, 96 degrees, was the human body's temperature. According to a story in Germany, Fahrenheit chose the lowest air temperature measured in his hometown Danzig in winter 1708/09 as 0 °F, only had the need to be able to make this value reproducible using brine.
According to a letter Fahrenheit wrote to his friend Herman Boerhaave, his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained, he re-calibrated his scale using the melting point of ice and normal human body temperature. Fahrenheit soon after observed; the use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. Under this system, the Fahrenheit scale is redefined so that the freezing point of water is 32 °F, the boiling point is 212 °F or 180 degrees higher, it is for this reason that normal human body temperature is 98° on the revised scale. In the present-day Fahrenheit scale, 0 °F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above.
Instead, that eutectic is at 4 °F on the final Fahrenheit scale. The Rankine temperature s
International System of Units
The International System of Units is the modern form of the metric system, is the most used system of measurement. It comprises a coherent system of units of measurement built on seven base units, which are the ampere, second, kilogram, mole, a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units; the system specifies names for 22 derived units, such as lumen and watt, for other common physical quantities. The base units are derived from invariant constants of nature, such as the speed of light in vacuum and the triple point of water, which can be observed and measured with great accuracy, one physical artefact; the artefact is the international prototype kilogram, certified in 1889, consisting of a cylinder of platinum-iridium, which nominally has the same mass as one litre of water at the freezing point. Its stability has been a matter of significant concern, culminating in a revision of the definition of the base units in terms of constants of nature, scheduled to be put into effect on 20 May 2019.
Derived units may be defined in terms of other derived units. They are adopted to facilitate measurement of diverse quantities; the SI is intended to be an evolving system. The most recent derived unit, the katal, was defined in 1999; the reliability of the SI depends not only on the precise measurement of standards for the base units in terms of various physical constants of nature, but on precise definition of those constants. The set of underlying constants is modified as more stable constants are found, or may be more measured. For example, in 1983 the metre was redefined as the distance that light propagates in vacuum in a given fraction of a second, thus making the value of the speed of light in terms of the defined units exact; the motivation for the development of the SI was the diversity of units that had sprung up within the centimetre–gram–second systems and the lack of coordination between the various disciplines that used them. The General Conference on Weights and Measures, established by the Metre Convention of 1875, brought together many international organisations to establish the definitions and standards of a new system and standardise the rules for writing and presenting measurements.
The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metre–kilogram–second system of units rather than any variant of the CGS. Since the SI has been adopted by all countries except the United States and Myanmar; the International System of Units consists of a set of base units, derived units, a set of decimal-based multipliers that are used as prefixes. The units, excluding prefixed units, form a coherent system of units, based on a system of quantities in such a way that the equations between the numerical values expressed in coherent units have the same form, including numerical factors, as the corresponding equations between the quantities. For example, 1 N = 1 kg × 1 m/s2 says that one newton is the force required to accelerate a mass of one kilogram at one metre per second squared, as related through the principle of coherence to the equation relating the corresponding quantities: F = m × a. Derived units apply to derived quantities, which may by definition be expressed in terms of base quantities, thus are not independent.
Other useful derived quantities can be specified in terms of the SI base and derived units that have no named units in the SI system, such as acceleration, defined in SI units as m/s2. The SI base units are the building blocks of the system and all the other units are derived from them; when Maxwell first introduced the concept of a coherent system, he identified three quantities that could be used as base units: mass and time. Giorgi identified the need for an electrical base unit, for which the unit of electric current was chosen for SI. Another three base units were added later; the early metric systems defined a unit of weight as a base unit, while the SI defines an analogous unit of mass. In everyday use, these are interchangeable, but in scientific contexts the difference matters. Mass the inertial mass, represents a quantity of matter, it relates the acceleration of a body to the applied force via Newton's law, F = m × a: force equals mass times acceleration. A force of 1 N applied to a mass of 1 kg will accelerate it at 1 m/s2.
This is true whether the object is floating in space or in a gravity field e.g. at the Earth's surface. Weight is the force exerted on a body by a gravitational field, hence its weight depends on the strength of the gravitational field. Weight of a 1 kg mass at the Earth's surface is m × g. Since the acceleration due to gravity is local and varies by location and altitude on the Earth, weight is unsuitable for precision
Horsepower is a unit of measurement of power, or the rate at which work is done. There are many different types of horsepower. Two common definitions being used today are the mechanical horsepower, about 745.7 watts, the metric horsepower, 735.5 watts. The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses, it was expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery. The definition of the unit varied among geographical regions. Most countries now use the SI unit watt for measurement of power. With the implementation of the EU Directive 80/181/EEC on January 1, 2010, the use of horsepower in the EU is permitted only as a supplementary unit; the development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, Thomas Savery wrote in The Miner's Friend: So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, for which there must be kept ten or twelve horses for doing the same.
I say, such an engine may be made large enough to do the work required in employing eight, fifteen, or twenty horses to be maintained and kept for doing such a work… The idea was used by James Watt to help market his improved steam engine. He had agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines; this royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined; the wheel was 12 feet in radius. Watt judged. So: P = W t = F d t = 180 l b f × 2.4 × 2 π × 12 f t 1 m i n = 32, 572 f t ⋅ l b f m i n. Watt defined and calculated the horsepower as 32,572 ft⋅lbf/min, rounded to an 33,000 ft⋅lbf/min. Watt determined that a pony could lift an average 220 lbf 100 ft per minute over a four-hour working shift. Watt judged a horse was 50% more powerful than a pony and thus arrived at the 33,000 ft⋅lbf/min figure. Engineering in History recounts that John Smeaton estimated that a horse could produce 22,916 foot-pounds per minute.
John Desaguliers had suggested 44,000 foot-pounds per minute and Tredgold 27,500 foot-pounds per minute. "Watt found by experiment in 1782 that a'brewery horse' could produce 32,400 foot-pounds per minute." James Watt and Matthew Boulton standardized that figure at 33,000 foot-pounds per minute the next year. A common legend states that the unit was created when one of Watt's first customers, a brewer demanded an engine that would match a horse, chose the strongest horse he had and driving it to the limit. Watt, while aware of the trick, accepted the challenge and built a machine, even stronger than the figure achieved by the brewer, it was the output of that machine which became the horsepower. In 1993, R. D. Stevenson and R. J. Wassersug published correspondence in Nature summarizing measurements and calculations of peak and sustained work rates of a horse. Citing measurements made at the 1926 Iowa State Fair, they reported that the peak power over a few seconds has been measured to be as high as 14.9 hp and observed that for sustained activity, a work rate of about 1 hp per horse is consistent with agricultural advice from both the 19th and 20th centuries and consistent with a work rate of about 4 times the basal rate expended by other vertebrates for sustained activity.
When considering human-powered equipment, a healthy human can produce about 1.2 hp and sustain about 0.1 hp indefinitely. The Jamaican sprinter Usain Bolt produced a maximum of 3.5 hp 0.89 seconds into his 9.58 second 100-metre dash world record in 2009. When torque T is in pound-foot units, rotational speed is in rpm and power is required in horsepower: P / hp = T / × N / rpm 5252 The constant 5252 is the rounded value of /; when torque T is in inch pounds: P
Natural gas prices
Natural gas prices, as with other commodity prices, are driven by supply and demand fundamentals. However, natural gas prices may be linked to the price of crude oil and/or petroleum products in continental Europe. Natural gas prices in the US had followed oil prices, but in the recent years, it has decoupled from oil and are now trending somewhat with coal prices; the current surge in unconventional oil and gas in the U. S. has resulted in lower gas prices in the U. S; this has led to discussions in Asian oil-linked gas markets to import gas based on the Henry Hub index, which was, until recently, the most used reference for US natural gas prices. Depending on the marketplace, the price of natural gas is expressed in US dollars per 1 million British thermal units, thousand cubic feet, or 1,000 cubic meters. Note that, for natural gas price comparisons, $ per MMBtu multiplied by 1.025 = $ per Mcf of pipeline-quality gas, what is delivered to consumers. For rough comparisons, one million Btu is equal to a thousand cubic feet of natural gas.
Pipeline-quality gas has a BTU value higher than that of pure methane, which has 1,012 BTU per cubic foot. Natural gas as it comes out of the ground is most predominantly methane, but may have a wide range of BTU values, from much lower to much higher than standard pipeline-quality gas; the natural gas market in the United States is split between the financial market, based on the NYMEX futures contract, the physical market, the price paid for actual deliveries of natural gas and individual delivery points around the United States. Market mechanisms in Europe and other parts of the world are similar, but not as well developed or complex as in the United States; the standardized NYMEX natural gas futures contract is for delivery of 10,000 mmBtu of energy at Henry Hub in Louisiana over a given delivery month consisting of a varying number of days. As a coarse approximation, 1000 ft3 of natural gas ≈ 1 MMBtu ≈ 1 GJ. Monthly contracts expire 3–5 days in advance of the first day of the delivery month, at which points traders may either settle their positions financially with other traders in the market or choose to "go physical" and accept delivery of physical natural gas.
It should be noted that most financial transactions for natural gas take place off exchange in the over-the-counter markets using "look alike" contracts that match the general terms and characteristics of the NYMEX futures contract and settle against the final NYMEX contract value, but that are not subject to the regulations and market rules required on the actual exchange. It is important to note that nearly all participants in the financial gas market, whether on or off exchange, participate as a financial exercise in order to profit from the net cash flows that occur when financial contracts are settled among counterparties at the expiration of a trading contract; this practice allows for the hedging of financial exposure to transactions in the physical market by allowing physical suppliers and users of natural gas to net their gains in the financial market against the cost of their physical transactions that will occur on. It allows individuals and organizations with no need or exposure to large quantities of physical natural gas to participate in the natural gas market for the sole purpose of gaining from trading activities.
In 2015-Nov Henry Hub Natural Gas Spot price was - 2.09 за Million Btu Generally speaking, physical prices at the beginning of any calendar month at any particular delivery location are based on the final settled forward financial price for a given delivery period, plus the settled "basis" value for that location. Once a forward contract period has expired, gas is traded daily in a "day ahead market" wherein prices for any particular day are determined on the preceding day by traders using localized supply and demand conditions, in particular weather forecasts, at a particular delivery location; the average of all of the individual daily markets in a given month is referred to as the "index" price for that month at that particular location, it is not uncommon for the index price for a particular month to vary from the settled futures price from a month earlier. Many market participants those transacting in gas at the wellhead stage add or subtract a small amount to the nearest physical market price to arrive at their ultimate final transaction price.
Once a particular day's gas obligations are finalized in the day-ahead market, traders will work together with counterparties and pipeline representatives to "schedule" the flows of gas into and out of individual pipelines and meters. Because, in general, injections must equal withdrawals, pipeline scheduling and regulations are a major driver of trading activities, quite the financial penalties inflicted by pipelines onto shippers who violate their terms of service are well in excess of losses a trader may otherwise incur in the market correcting the problem; because market conditions vary between Henry Hub and the 40 or so physical trading locations around United States, financial traders u