Central heating
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213605691
2008-05-20T01:23:59Z
137.186.182.122
/* Heat pumps */
:''For the [[Grand Central Records]] albums, see [[Central Heating (Grand Central album)]] and [[Central Heating 2]]. For the [[Heatwave (band)|Heatwave]] album, see [[Central Heating (Heatwave album)]].''
A '''central-heating''' system provides warmth to the whole interior of a building (or portion of a building) from one point to multiple [[room (architecture)|room]]s.
When combined with other systems in order to control the building [[climate]], the whole system may comprise a [[HVAC]] ([[heating]], [[Ventilation (architecture)|ventilation]] and [[Air Conditioning|air conditioning]]).
Central heating differs from [[local heating]] in that the heat generation occurs in one place, such as a [[furnace room]] in a house or a [[mechanical room]] in a large building (though not necessarily at the "central" geometric point). The most common method of heat generation involves the combustion of [[fossil fuel]] in a [[furnace]] or [[boiler]]. The resultant heat then gets distributed: typically by [[forced-air]] through ductwork, by water circulating through pipes, or by steam fed through pipes. Increasingly, buildings utilize solar-powered heat sources, in which case the distribution system normally uses water circulation.
In much of northern [[Europe]] and in urban portions of [[Russia]], where people seldom require air conditioning in homes due to the temperate climate, most new housing comes with central heating installed. Such areas normally use [[gas heater]]s, [[district heating]], or [[Heating oil|oil-fired]] systems. In the western and southern [[United States]] natural-gas-fired central forced-air systems occur most commonly; these systems and central-boiler systems both occur in the far northern regions of the USA. Steam-heating systems, fired by coal, oil or gas, feature in the USA, Russia and Europe: primarily for larger buildings. [[Electric heating|Electrical heating systems]] occur less commonly and are only practical with low cost electricity or when [[geothermal heat pump]]s are used. Considering the combined system of central generating plant and electric resistance heating, the overall efficiency will be less than for direct use of fossil fuel for space heating.
==History==
Cities in the northern [[Roman Empire]] used central heating systems c. 100 AD, conducting air heated by furnaces through empty spaces under the floors and out of pipes in the walls — a system known as a ''[[hypocaust]]''.<ref>{{cite web |url=http://www.bbc.co.uk/schools/romans/tech.shtml |title=BBC - Romans - Technology |publisher=[[BBC]] |accessdate=2008-03-24}}</ref> The [[Cistercian]] [[monk]]s revived central heating using river diversions combined with indoor wood-fired furnaces. The well-preserved [[Real Monasterio de Nuestra Senora de Rueda|Royal Monastery of Our Lady of the Wheel]] (founded 1202) on the [[Ebro River]] in the [[Aragon]] region of [[Spain]] provides an excellent example of such an application.
By about 1700 [[Russia]]n engineers had started designing hydrologically based systems for central heating. The [[Summer Palace (Russia)|Summer Palace]] (1710–1714) of [[Peter the Great]] in [[Saint Petersburg]] provides the best extant example. Slightly later, in 1716, came the first use of water in Sweden to distribute heat in buildings. [[Martin Triewald]], a Swedish engineer, used this method for a [[greenhouse]] at [[Newcastle upon Tyne]]. Jean Simon Bonnemain (1743–1830), a French architect,<ref>
Emmanuelle Gallo: "Jean Simon Bonnemain (1743-1830) and the Origins of Hot Water Central Heating" in ''Proceedings of the Second International Congress on Construction History'' (2006-06-17), pages 1043-1060; retrieved from http://halshs.archives-ouvertes.fr/halshs-00080479/en/
on [[2007-02-05]]
</ref>
introduced the technique to industry on a [[cooperative]], at [[Château du Pêcq]], near [[Paris]].
[[Angier March Perkins]] developed and installed some of the earliest steam-heating systems in the 1830s. The first was installed in the home of [[Governor of the Bank of England]] [[John Horley Palmer]] so that he could grow [[grape]]s in [[England]]'s cold climate.<ref>McConnell, A. (2004) "[http://www.oxforddnb.com/view/article/21967 Perkins, Angier March (1799–1881)]", ''[[Oxford Dictionary of National Biography]]'', Oxford University Press, accessed 14 Aug 2007 (subscription required)</ref>
== Water heating ==
{{main|Water heating}}
Common components of a central-heating system using water-circulation include:
* Gas supply lines (sometimes including a propane tank), oil tank and supply lines or [[district heating]] supply lines
* [[Boiler]] (or a [[heat exchanger]] for district heating) — heats water in a closed-water system
* [[Pump]] — circulates the water in the closed system
* [[Radiator]]s — wall-mounted panels through which the heated water passes in order to release heat into rooms
Engineers in the United Kingdom and in other parts of Europe commonly combine the needs of room heating with hot-water heating and storage. These systems occur less commonly in the USA. In this case, the heated water in a sealed system flows through a [[heat exchanger]] in a hot-water tank or [[hot water cylinder|hot-water cylinder]] where it heats water from the normal water supply before that water gets fed to hot-water outlets in the house. These outlets may service hot-water [[Tap (valve)|tap]]s or [[appliance]]s such as [[washing machine]]s or [[dishwasher]]s.
===Sealed water-circulating system===
A sealed system provides a form of central heating in which the water used for heating usually circulates independently of the building's normal water supply. A [[pressure vessel]] contains compressed gas, separated from the sealed-system water by a diaphragm. This allows for normal variations of pressure in the system. A [[safety valve]] allows water to escape from the system when pressure becomes too high, and a valve can open to replenish water from the normal water supply if the pressure drops too low. Sealed systems offer an alternative to open-vent systems, in which steam can escape from the system, and gets replaced from the building's water supply via a feed and central storage system.
==Electric and gas-fired heaters==
Electric heating or resistance heating converts electricity directly to heat. Electric heat is often more expensive than heat produced by combustion appliances like natural gas, propane, and oil. Electric resistance heat can be provided by baseboard heaters, space heaters, radiant heaters, furnaces, wall heaters, or thermal storage systems.
Electric heaters are usually part of a fan coil which is part of a central air conditioner. They circulate heat by blowing air across the heating element which is supplied to the furnace through return air ducts. Blowers in electric furnaces move air over one to five resistance coils or elements which are usually rated at five kilowatts. The heating elements activate one at a time to avoid overloading the electrical system. Overheating is prevented by a safety switch called a limit controller or limit switch. This limit controller may shut the furnace off if the blower fails or if something is blocking the air flow. The heated air is then sent back through the home through supply ducts.
In larger commercial applications, central heating is provided through an [[air handler]] which incorporates similar components as a furnace but on a larger scale.
==Hydronic and steam systems==
[[Hydronics|Hydronic heating systems]] are systems that circulate a medium for heating. Hydronic radiant floor heating systems use a boiler or district heating to heat up hot water and a pump to circulate the hot water in plastic pipes installed in a concrete slab. The pipes, embedded in the floor, carry heated water that conducts warmth to the surface of the floor where it broadcasts energy to the room.
Hydronic systems circulate hot water for heating. Steam heating systems are similar to heating water systems, except steam is used as the heating medium instead of water.
Hydronic heating systems generally consist of a boiler or district heating heat exchanger, hot water circulating pumps, distribution piping, and a fan coil unit or a radiator located in the room or space. Steam heating systems are similar except no circulating pumps are required.
Hydronic systems are closed loop: the same fluid is heated and then reheated. Hydronic heating systems are also used with antifreeze solutions in ice and snow melt systems for walkways, parking lots and streets. They are more commonly used in commercial and whole house radiant floor heat projects, while electric radiant heat systems are more commonly used in smaller "spot warming" applications.
==Heat pumps==
In mild climates a [[heat pump]] can be used to air condition the building during hot weather, and to warm the building using heat extracted from outdoor air in cold weather. Air-source heat pumps are generally uneconomic for outdoor temperatures much below freezing. In colder climates, [[geothermal heat pump]]s can be used to extract heat from the ground. For economy, these systems are designed for average low winter temperatures and use supplemental heating for extreme low temperature conditions. The advantage of the heat pump is that it reduces the purchased energy required for building heating; often geothermal source systems also supply domestic hot water. Even in places where fossil fuels provide most electricity, a geothermal system may offset [[greenhouse gas]] production since most of the energy furnished for heating is supplied from the environment, with only 15–30% purchased
== Environmental aspects==
From an energy-efficiency standpoint considerable heat gets lost or goes to waste if only a single room needs heating, since central heating has distribution losses and (in the case of forced-air systems particularly) may heat some unoccupied rooms without need. In such buildings which require isolated heating, one may wish to consider non-central systems such as individual room heaters, fireplaces or other devices. Alternatively, architects can design new buildings to use [[low-energy building|low-energy building techniques]] which can virtually eliminate the need for heating, such as those built to the [[Passive House]] standard.
However, if a building does need fully heating, combustion central heating offers a more [[environmentally friendly]] solution than electric-air central heating or than other direct [[electric heating]] devices. This stems from the fact that most electricity originates remotely using [[fossil fuels]], with up to two-thirds of the energy in the fuel lost (unless utilized for [[district heating]]) at the [[power station]] and in [[Electric power transmission|transmission losses]]. In Sweden proposals exist to phase out direct electric heating for this reason (see [[oil phase-out in Sweden]]). Nuclear and hydroelectric sources reduce this factor.
In contrast, hot-water central-heating systems can use water heated in or close to the building using high-efficiency [[condensing boiler]]s, [[biofuel]]s, or [[district heating]]. Wet [[underfloor heating]] has proven ideal. This offers the option of relatively easy conversion in the future to use developing technologies such as [[heat pump]]s and [[solar combisystem]]s, thereby also providing [[future-proof]]ing.
Typical efficiencies for central heating are: 85-97% for gas fired heating; 80-89% for oil-fired, and 45-60% for coal-fired heating.<ref>[http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12330 EERE Consumer's Guide: Selecting Heating Fuel and System Types<!-- Bot generated title -->]</ref>
==See also ==
* [[Central Heat Distribution]]
* [[Energy conservation]]
* [[Geothermal Systems]]
* [[HVAC]]
* [[Renewable energy]]
* [[Solar combisystem]]
* [[Underfloor heating]]
* [[Wind energy]]
==External links==
* [http://www.allhvacinfo.com HVAC Directory.]
* [http://emmanuellegallo.free.fr Emmanuelle Gallo site dedicated to heating history]
* [http://www.air-conditioners-and-heaters.com/central_heater.htm Electric and Gas fired Heaters]
* [http://www.air-conditioners-and-heaters.com/boilers_gas_oil.htm Gas and Oil Boilers]
* [http://www.high-performance-hvac.com High Performance HVAC site with central heating articles]
*[http://www.homeheatingguide.co.uk/central-heating-systems.html Central Heating] Information at Home Heating Guide
==References ==
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[[Category:HVAC]]
[[Category:Plumbing]]
[[Category:Residential heating]]
[[da:Centralvarme]]
[[de:Zentralheizung]]
[[el:Κεντρική θέρμανση]]
[[es:Calefacción]]
[[eo:Centra hejtado]]
[[fa:شوفاژ]]
[[fr:Chauffage]]
[[ko:중앙 난방]]
[[nl:Centrale verwarming]]
[[ja:セントラルヒーティング]]
[[pl:Ogrzewanie]]
[[pt:Calefação (sistema de aquecimento)]]
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[[yi:צענטראלע הייצונג]]