Barra system

Barra system

The Barra system is a passive solar building technology developed by Horazio Barra in Italy. It uses a collector wall to capture solar radiation in the form of heat. It also uses the thermosiphon effect to distribute the warmed air through channels incorporated into the reinforced concrete floors, warming the floors and hence the building. Alternatively, in hot weather, cool nighttime air can be drawn through the floors to chill them in a form of air conditioning.

Barra's are said to be a lot more comfortable than other passive solar housesFact|date=February 2007, with more uniform north-south temp distribution. Many successful systems were built in Europe, but Barra seems fairly unknown elsewhere.

Passive solar collector

To convert the sun's light into heat indirect a separate, insulated space is constructed on the sunny side of the house walls. Looking at the outside, and moving through a cross section there is an outside clear layer. This was traditionally built using glass, but with the advent of cheap, robust Polycarbonate glazing most designs use twin- or triple-wall polycarbonate greenhouse sheeting. Typically the glazing is designed to pass visible light, but block IR to reduce losses, and block UV to protect building materials.

The next layer is an absorption space. This absorbs most of the light entering the collector. It usually consists of an air gap of around 10cm thickness with one or more absorption meshs suspended vertically in the space. Often window fly screen mesh is used, or horticultural shade cloth. The mesh itself can hold very little heat and warms up rapidly in light. The heat is absorbed by air passing around and through the mesh, and so the mesh is suspended with an air gap on both the front and back sides.

Finally a layer of insulation sits between the absorption space and the house. Usually this is normal house insulation, using materials such as polyisocyanurate foam, rock wool, foil and polystyrene.

This collector is very agile - in the sun it heats up rapidly and the air inside starts to convect. If the collector were to be directly connected to the building using a hole near the floor and a hole near the ceiling an indirect solar gain system would be created. One problem with this that, like Trombe walls, the heat would radiate back out at night, and a convection current would chill the room during the night. Instead, the air movement can be stopped using automatic dampers, similar to those used for ventilating foundation spaces in cold climates, or plastic film dampers, which work by blocking air flow in one direction with a very lightweight flap of plastic. The addition of the damper makes the design an efficient isolated solar gain system.

Thermal store

To store the thermal energy from the collector, the Barra system suspends a "spancrete" slab of concrete as a ceiling to store heat. This is fairly expensive and requires strong support. An alternative is to use water, which can store 5 times as much heat for a given weight . A simple, cheap and effective way is to store the water in sealed 100 mm diameter PVC storm pipe with end caps.

Whether water or concrete is used, the heat is transferred from the air in the collector into the storage material during the day, and released on demand using a ceiling fan into the room at night.

Where "spancrete" slabs are used, the ceiling also heats the house by radiation. Some houses are fitted with louvres (similar to those used on satellites) to adjust the radiation transfer. Warm air travels through the slab tunnels from south to north, where it exits and travels back north through the bulk of the room to the air heater inlet near the floor.

Intermediate thermal store

In most places a system designed for 5 successive days of no sun provides enough storage for all but a few days in a hundred years. Heat can be stored over a number of days using a large container of water. A 8 foot cube of water in the basement might store 15 kL of water, which is heated using a copper tube with fins in the collector. The performance of this can be improved by putting the finned tube inside another layer of glazing at the back of the main collector, allowing the temperature to build up more than the surrounding air stream. On cloudy days the heat is transferred back out of the store to heat the house.

ee also

References

*The Barra system is described on pages 169-171 and 181 of Baruch Givoni's Climate Considerations book (Wiley, 1998.)
*The basic reference is Barra, O. A., G. Artese, L. Franceschi, R. K. Joels and A. Nicoletti. 1987. "The Barra Thermosyphon Air System: Residential and Agricultural Applications in Italy, UK, and in the Sahara." International Conference of Building Energy Management. Lausanne, Switzerland.

External links

* [http://www.ambthair.com/coolingandlowenergy.html#barra The Barra system]


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Barra (disambiguation) — For the similar sounding Burra see Burra (disambiguation) Barra may refer to:Places in Europe: *Barra, Scotland, United Kingdom *Barra (Naples), Italy *Barra de Mira, Portugal *Gougane Barra, a settlement in County Cork, IrelandPlaces in Africa:… …   Wikipedia

  • Barra da Tijuca — is a borough in the city capital of state of Rio de Janeiro, Brazil, and also denominates an administrative region in which we find Barra de Tijuca as a borought along with some others like: Joá, Itanhangá, Camorim, Vargem pequena, Vargem grande …   Wikipedia

  • Barra Honda National Park — Infobox protected area | name = Barra Honda National Park iucn category = II caption = locator x = locator y = location = Costa Rica nearest city = Nicoya lat degrees = lat minutes = lat seconds = lat direction = long degrees = long minutes =… …   Wikipedia

  • Barra del Colorado Wildlife Refuge — Infobox protected area | name = Barra del Colorado Wildlife Refuge iucn category = caption = locator x = locator y = location = Costa Rica nearest city = lat degrees = lat minutes = lat seconds = lat direction = long degrees = long minutes = long …   Wikipedia

  • Sistema Barra — El sistema Barra es un sistema de la tecnología solar pasiva desarrollado por el Dr. Horazio Barra en Italia. Utiliza un muro colector de la radiación solar, con la particularidad respecto al Muro Trombe en que detrás de la pintura oscura hay una …   Wikipedia Español

  • Ford Barra engine — The Barra engines are a family of straight 6s and V8s assembled by Ford Australia since 2002. The V8s are built in the USA by the Ford Motor Company and are shipped un assembled to Australia, for assembly at the FPV Factory. Production of the… …   Wikipedia

  • Pasquale Barra — is a former Italian Camorrista who was a senior member and hitman for the Nuova Camorra Organizzata (NCO), a Camorra organization in Naples. Barra has the distinction of being the first NCO member to become a pentito, when he decided to… …   Wikipedia

  • Protocolo base de X Window System — Saltar a navegación, búsqueda Logo del Protocolo X del Sistema core de Windows. El Protocolo base de X Window System[1] …   Wikipedia Español

  • Robert Barra — Robert D. Barra (born 1960) was a Republican elected to serve his constituents of the New York 21st Assembly District in November 2000. Because of redistricting due to the census, Assemblyman Barra became the Assembly member from the newly formed …   Wikipedia

  • X Window System — en GNOME 2.20. Logotipo de X Window System X Windo …   Wikipedia Español

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”