Risorse professionali

What is the British Standard for the design and installation of domestic sprinkler systems?

BS 9251.

Why are installations earthed?

In general an earthing system needs to satisfy three demands:

  • It must conduct lightning and short-circuit currents without introducing intolerable step and touch-voltages .
  • It must protect the occupants, equipment and fabric of the building against damage due to short-circuit currents and lightning strikes.
  • It must provide a suitable environment for electronic equipment by providing a low impedance path to interconnect equipment.

Although requirements for these three aspects are very different and are often specified separately, the implementation of them requires an integrated systems approach.

Il tubo per condizionamento e refrigerazione “funziona” in altre applicazioni?

Certo, per esempio in geotermia. Il tubo viene posato sottoterra per prelevare calore dal terreno: l’energia così ottenuta viene sfruttata per il riscaldamento degli edifici o per la produzione di acqua calda. Nel tubo di rame scorre un fluido frigorigeno, destinato ai cicli di condensazione ed evaporazione all’interno della pompa di calore.
Grazie al rame, si ottengono efficienze elevate non raggiungibili in altro modo, che si traducono in una minore occupazione di superficie del suolo.

Un’altra applicazione poco nota è la formazione del ghiaccio per le piste di pattinaggio: succede in Svezia, dove dal 2006 si è iniziato ad utilizzare il rame per questo scopo. Grazie al rame e alla COcome fluido refrigerante (al posto dei tubi plastici con acqua e sale), sono stati ottenuti enormi risparmi di energia e denaro.

Milyen típusú rezet használunk a villamosok, trolibuszok és vonatok felsővezetékében az elektromos áram átvitelére?

A tiszta réz túlságosan lágy a felsővezetékekhez, ezért rézötvözeteket használunk, melyeket az EN 50149:2012 szabvány ismertet. A felhasznált rézötvözetek kis mennyiségű ezüstöt, magnéziumot, ónt vagy kadmiumot tartalmaznak.

Why is copper so efficient in heat exchanger applications?

Because the thermal conductivity is so high – it is 23 times better than stainless steel or titanium and 1.6 times better than aluminum.

What is the current standard for copper fittings?

EN 1254 Parts 1 to 5.

Il verderame che si forma all'interno delle tubazioni per l'acqua potabile è dannoso per la salute?

No. Innanzitutto bisogna chiarire che quello che si forma nelle tubazioni non è verderame: l’equivoco nasce dal fatto che numerosi sali di rame hanno una colorazione verde o verde-azzurra.
Il verderame, che si usa in agricoltura, è oltretutto solubile in acqua quindi non potrebbe restare sulle pareti interne del tubo.
Qui si forma un sale di stechiometria non definita composto da numerosi anioni, che è protettivo, resistente e non dannoso per la salute umana.

Why is copper so efficient in heat exchanger applications?

Because the thermal conductivity is so high – it is 23 times better than stainless steel or titanium and 1.6 times better than aluminum.

Milyen tisztítást igényelnek a rézötvözetből készült ketrecek?

A rézötvözet-háló természetes módon gátolja a biológiai szennyeződés kialakulását, ezáltal javul a vízcsere és cirkuláció, a víz oxigén szintje magas marad, ami blokkolja a paraziták és patogén kultúrák fejlődését, azok nem fertőzik a halakat. Ezáltal csökkenthető a felhasznált antibiotikumok mennyisége, algagátló (antifouling) vegyszerek alkalmazása és a költséges ketreccsere. A rézötvözetből készült ketreceket átlagosan évente egyszer vagy kétszer kell tisztítani, ami lényegesen kevesebb, mint a hagyományos ketrecek esetében, főleg ha a számot az teljes élettartamra vetítjük.

What is the difference between a voltage regulator and a Dynamic Voltage Restorer (DVR)?

Both are used to mitigate the effects of voltage dips. Dips are characterised by the depth – the retained voltage – and the duration. Short and deep dips are best served by a DVR while long and shallow dips are the province of the voltage regulator.

A voltage regulator has no energy store. It has a transformer secondary winding in series with the supply. When the input voltage moves outside the tolerance band the primary of that transformer is driven to boost, or in anti-phase to reduce, the voltage appropriately. Because the load voltage is kept constant, the power to the load is constant so, when the input voltage falls, the input current increases. The current capability of the supply and the device itself limits the working range to about +/-30% of nominal voltage.

A DVR has an energy store, so requires no additional input power (in the short term) to boost the voltage during a dip. A DVR can correct a dip to 0% retained voltage. But the DVR has a limited energy store and so is suitable for short-term effects only – it cannot correct for long term under voltage, for example. Also, the store has to be recharged between events so it is not suitable multiple dips are expected frequently. Typically, DVRs use super capacitors, large secondary batteries or high-speed flywheels as energy stores.

Unsurprisingly, DVRs are more expensive than voltage regulators.

In long strip roofing what is the maximum length of a bay?

This depends on the pitch of the roof. For 3-4 degrees 14.6m, for 4-10 degrees 11.0m, for 10-30 degrees 9.7m and for over 30 degrees 8.1m.

Why is copper the preferred material for busbars?

There are several reasons. Firstly, the bars are more compact because copper has a higher conductivity than aluminium. Secondly, it is much easier to joint copper. A hard, highly insulating oxide grows very rapidly on the surface of aluminium, making it very difficult to make good reliable joints in the field. On the other hand, the thin oxide layer that forms, more slowly, on copper is not an insulator so jointing is simple. Finally, copper is much stronger than aluminium, less susceptible to creep and better at withstanding short circuit current forces.