Feedback: your letters

Topics under discussion this fortnight: lifting the veil on green truths; wearable technology to free prisoners; Australia's death train; a lot of wind and more.

Are this year's models the greenest?

Much has been written on the need to reduce our carbon footprint and thus global warming. All sorts of goods have been promoted as reducing global warming by using less energy. I have yet to see any real data on the overall lifetime carbon footprint of such goods.

What personal experience has been brought to my attention is that the lifetime of a product is of extreme importance in this matter. With 15 ecofriendly lamps in my home I am trying to help with global warming, but two have failed after much less than 1,000 hours in spite of claims of 10,000-15,000 hours life. This seems far too near the extreme of a normal failure distribution to be a coincidence. Since they are complex structures with heavy metals in their construction, the carbon impact of their manufacture and disposal must be considerable.

Additionally, I find the claims for their light output grossly exaggerated as my stairs are more dimly lit by a 75W equivalent ecolamp than the 60W GLS it replaced despite the fact that it is less shrouded by the lampshade. I wonder therefore which is best for global warming.

Another aspect of this problem is illustrated by the life of modern consumer goods. I am now using the third kettle I have bought in just over three years. The first had a fancy lever system to open the lid. I gave up trying to repair it after the third failure. It used enough plastic to have made a mechanism that would last but there was not enough where the stresses were greatest. The second failed with a break in the connection to the heating plate right at the plate.

I have a fridge and a chest freezer both of which are more than 25 years old. Both use more energy than modern equipment but I believe they are more ecofriendly than their modern equivalents, which, from my friends' and neighbours' experience, have a life of about five to seven years.

The manufacture and disposal of consumer goods are responsible for a large part of their carbon footprint, so it is up to engineers to design them for a long life if global warming is to be a consideration. Unfortunately visual impact, low cost and need for replacement sales appear to have more attention than properly engineering products for long-term reliable performance.

Other bad influences are fashion - as in mobile phones, where having last year's model is not good - and forced obsolescence - as in computing, where a new more powerful PC is needed just to do the same work at the same speed in an operating system for which support will continue to be available. We need a real full-life analysis of products before considering them ecofriendly.

Alfred Reading MIET, Surrey

Clothes to replace prisons

Articles on wearable electronics in the 25 October issue of E&T missed out one piece of technology - the electronic tag, which could open up a whole new area of crime prevention and crime fighting.

One can see that, in the future, designer garments could have a tag of some sort embedded into the fabrics to make them glow when a detector is nearby thus giving the customer an indication that the clothing in question is genuine. Or stores could use the technology to check if it's being stolen.

The clothing could be used to light up when offenders stray out of their designated areas, or set off an alarm if, say, a sex offender were to stray too close to a school, or some place where the venerable congregate.

Maybe some sort of positive feedback could be built into the clothing to deliver an increasingly severe reminder to the criminal if they stray beyond their designated areas.

Just think, wearable technology could spell the end of prisons for all but the really dangerous to society.

Reid Thomas MIET, Cranleigh, Surrey

RFID nightmare

The idea of RFID tags being used to track articles by type from manufacturer through to the point of sale and beyond, as described in your View from Brussels column (#18) is bad enough. This might extended so that every item could be identified, which raises some nightmarish possibilities.

Just imagine walking past a hidden detector which identified every individual item that you had with you. This would then give access to all the associated information - where they were purchased, how they were paid for, who paid for them etc.

In this way your every movement could be tracked. Automatic deactivation at point of sale is imperative.

Chris Pryor MIET, Ely

Rail's dead end

Australian readers of E&T might take issue with the claim that the London Necropolis Railway was "unique in the world" ('Final Destination', 8 November). A similar service was provided in New South Wales from a separate 'Mortuary Station' in the yard of Sydney Central Station to - by coincidence - Rookwood Cemetery in the city's western suburbs. A branch into the cemetery connected to the main railway line between Flemington and Lidcombe. Rookwood station was used by visitors to the cemetery latterly at weekends only, and was closed permanently in 1967. The Sydney station, renamed 'Regent Street', featured in a commercial on British TV earlier this year.

Ian Ross, Ilford, Essex

Further to the article describing London's Necropolis Railway, can I draw readers' attention to a very good detective novel written by Andrew Martin and also called 'The Necropolis Railway' (ISBN 0-571-22878-x). It provides a detailed account of the working of the Waterloo to Brookwood railway in 1903 through the eyes of a young worker who is also an amateur sleuth. Not exactly an engineering textbook but full of details, especially the engines used to pull the Coffin Train.

Wally Waltho MIET, Portchester Hants

IVF and cryonics

Excuse my world-weary scepticism about this creepy old stuff, but I can see a parallel between cryonics ('A Science Without a Deadline', 8 November) and in-vitro fertilisation techniques. It may not be common knowledge, but some 50 per cent of frozen human embryos do not survive the freeze/thaw process. A further 25 per cent are so badly damaged by it that they are deemed 'unusable'. All of these end up poured down the laboratory sink.

IVF is a very wasteful procedure, with only about three live births out of every 100 laboratory-conceived human embryos. Studies (notably one carried out in Sweden) indicate that IVF children also have a higher incidence of abnormalities such as Down's syndrome and spina bifida.

We simply cannot interfere with nature with impunity, as any engineer worth his salt would tell you.

Patrick McKay IEng MIET, Ampthill, Beds

Idle turbines

Dr R Barnes (Letters, 8 November) can learn about idle wind turbines from manufacturers' website, from which he will see that nothing is generated in winds below 4m/s; full power requires 15m/s, Beaufort Force 7, 'Near Gale'. At 4m/s, the 15kW produced by a 2500kW machine barely drives the yaw motors. Wind turbines have an annual load factor of 25 per cent, implying long spells of low or zero power output, and about 5,000MW is needed to deliver the same energy as Sizewell B (1350MW, 94.5 per cent load factor last year).

Dr Barnes might also look at REISI Wind, which gives masses of factual data on Germany's 23,044MW subsidised wind installation. For example, it produced less than 1000MW of power between 9pm on 3 November this year to midnight on 5 November, the lowest point being 20MW at noon on 4 November, an anticyclone.

We don't have that detail available in the UK, so I built a spreadsheet that converts Met Office anemometer speeds to MW at hub height. That same large high-pressure system gave us winds good enough for 0.5 per cent of installed power at peak load around tea time on 4 November. We had three such spells lasting ten days or more in winters of 2005-06, and 2006-07 and again in 2007-08.

In my career I had responsibility for reliability of supply in various roles in London and the Home counties for 37 years. On the distribution side, you get to talk to the customers, from cement works, HM Dockyard, oil refineries, paper mills, pharmaceuticals, to individual domestics.

As we replace ageing power stations with subsidised unreliable renewables, I'll tell you what I learned. Customers don't like blackouts - especially the home dialysis people. I ask renewable fans what generation they would use to supply our 60,000MW maximum demand - numbers please, not adjectives - "and answer comes there none".

Bill Hyde DFH CEng FIET, Offham, Kent

Creative engineering 

Stuart Bridgman (Letters, 8 November) describes constructing a home-made audio-frequency induction-loop system, of the type which are quite widely used in Europe and some other countries. (See standards BS 7594 and IEC 60118-4.) I note that the project was "a few decades ago" but for reasons that will become clear, a few comments are necessary.

The transmission response rises at 6 dB/octave because of the loose magnetic coupling between the under-floor loop and the pick-up coil. This is not normally compensated in the receiver. But the loop is inductive, especially if it has more than one turn. A rule of thumb is "2 microhenrys per metre of perimeter multiplied by the square of the number of turns" (yes, the inter-turn coupling is close enough in a multi-core cable). This restricts the high frequency response when the inductive reactance approaches the loop resistance.

It may be that Mr Bridgman found that the DC resistance of the loop was less than the audio amplifier device would accept as a load resistance, and so included a fixed resistance in series with the loop.

This is quite okay, if theoretically a low-efficiency solution. For larger loops, current feedback is used to give the amplifier a high enough output source resistance to produce a high-frequency half-power point at 5kHz, in accordance with the standards. The low-frequency half-power point is specified there as 100Hz. A lower extension can cause problems with mains hum pickup.

John Woodgate, Rayleigh, Essex

Not so hot

According to 'Catwalk Goes Techno' (25 October), the heat from a person's temples "can provide an average power of more than 1MW indoors". So all our power needs will be provided by a couple of hundred 'wired up' slaves for each city!

Malcolm Nicholls, Alicetown, Lower Hutt

Apologies to readers. That 'M' should of course have been a lower case 'm'. - Ed

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