End of the cam?

Valve actuatorI spotted an article recently about moving away from mechanical cam-driven valves on engines to computer controlled rapid acting “electro-hydraulic-pneumatic actuators” permitting far more precise control of valve movements without the “part open / part closed” stage of their mechanical counterparts. Why is this innovation important? Simple – it appears to offer a 16-17% improvement in fuel efficiency at a stroke – or to put it another way, a potential 16-17% reduction in CO2 emissions from transport (and any other engine-driven process) if it was adopted worldwide.

Steam engineWhich reminded me about “cams” and changing technology- especially as I have one on my desk as I write this! In my youth (well, for my Engineering Workshop Theory and Practice A-Level) I made a vertical D-slide double acting steam engine which uses a cam to control which side of the piston receives the steam, and which side is open to atmosphere. Because of this, the piston drives in both directions, rather than requiring the flywheel to drive the piston back to the top for older single-acting cylinders – at the time a major improvement in steam engine technology. And, in time, this very simple mechanical gizmo made its way into petrol & oil engines as a simple way to control valve movements, and now, for the first time in literally hundreds of years, we’re now seeing a step-change on the technology.

And made me wonder. Given that a move from a simple but commonly used mechanical system to a precise electronic system can radically alter the fuel consumption of the engines of potentially every car, lorry, bus, boat, ship … etc in use on the planet, where else could a bit of lateral thinking make big changes to our efficiencies, resource use, waste, and emissions whilst permitting us to continue to enjoy our tech-rich lifestyles?


60W lightbulb alternatives

The promise of a new LED equivalent to the now-phased-out 60W tungsten filament bulb prompted me to do a quick energy & cost comparison of the original tungsten lamps and the available alternatives. Here’s what I found.

60W tungsten filament lamps lasted approximately 1000 hours, over which time they used 60 kWh of electricity, for which I pay roughly 14p/kWh, or £8.40 over the life of the bulb.

The current alternative, a 13W CFL bulb, varies hugely in cost depending upon where you buy it, but you should be able to get a decent quality one for around £5.00. Over the same 1000 hours as a tungsten lamp, it will use 13 kWh of electricity at a cost of £1.82 – a total cost of £6.82 for the first 1000 hours.

CONCLUSION 1 – Even if you have a stock of unused tungsten filaments bulbs, don’t bother “using them up” – throw them away now and replace them with 13W CFL bulbs – you will save money very quickly.

As a decent CFL can be expected to last around 10 000 hours, the savings get even better, and over its life the total cost of a CFL would be around £23.20, This is equivalent to ten 60W filament bulbs used one after the other (if you had them) which would cost you £84.00 in electricity alone.

Not everyone likes CFLs though, so it’s good to see that the UK Technology Strategy Board held a competition for proposals to develop a low energy equivalent to the “standard” 60W bulb that would fit into the same “envelope”. The contract was won by Zeta LED Technology, and they have recently announced that the lamp should be available in 2012. As might be expected, the lamp is LED-based, has an 8W energy use, gives off 650 lumens at a “warm white” colour temperature of 2800 – almost identical to tungsten lamps – and has a life expectancy of 36 500 hours. The manufacturers anticipate an initial cost of £20/unit, dropping to £10/unit once into volume production.

So, over the 10 000 hour life of the CFL lamp, the new LED lamp will use 80 kWh of electricity at a cost of £11.20 – £31.20 in total at £20 / unit – but only £21.20 in total once the new lamp is in volume production, less than the lifetime cost of the equivalent CFL (£23.20).

CONCLUSION 2 – Unless you feel very strongly against CFL’s, on the basis of cost alone you should stick with them for a few years until volume production brings down the price of LED lamps. 

In the same way as CFLs last far longer than filament lamps, LEDs are expected to last far longer than CFLs. Over its 36 500 hours life, the LED lamp will use £40.88 in electricity, whereas 3.65 CFLs will have used £66.43 in electricity. You will also have had to buy four CFL lamps rather than just one LED lamp, so there are long term economies there too. (Note that 36 500 hours is 25 years at 4 hours per day!)

CONCLUSION 3 – In the long run, LED lamps offer the best value, especially once the unit price has dropped, or even straight away if you run them a long time every day.

(CONCLUSION 4 – If you buy the new LED lamps for your own home, take them with you when you move!)

More information on the new LED lamps can be found here:

(Note that the cost comparison ignores any increase in the cost of electricity over the period being considered. Increases in energy cost will always favour lower energy alternatives.)

Halogen vs LED GU10s

How does an expensive LED “spotlight” compare to a cheaper halogen one when their running costs are taken into account?

Just about everywhere you look these days, your eyes get seared by cheap-and-cheerful halogen spotlights – shops, restaurants, pubs, hotels – perhaps even in your own home. But how many of us realize just what carbon-greedy wallet-draining little critters they are?

This is the typical halogen spotlight – a GU10 base with a 50 Watt rating giving off about 250 lumens of light for about 1500 hours before it fails. But as it’s cheap, (and 1500 hours is a whole year at around 4 hours a day) it doesn’t really matter does it? Well, let’s start to crunch numbers. 50 Watts over 1500 hours is 75kWh of electricity, which if you pay the same sort of price as me (about 14p / kWh) is £10.50. So, over the 1500 hr life of the spotlight, it’s going to cost you about £11.85 all up, including initial purchase. And now you need to buy another, and start all over again.

Here’s the modern dimmable LED alternative – 10x the cost on the face of it, but notice the power rating – 3W rather than 50W. OK, it’s a slightly lower light output – 170 lumens (for 50,000 hours!), but I have used a “dimmable” comparison as this gives the LED version the highest initial cost to illustrate the point. So over the same 1500 hours to the halogen spot failing, it will use 4.5 kWh of electricity, which costs about £0.63, so the total for the first 1500 hours is £13.13.

But the LED bulb is still good for another 48,500 hours (roughly!), and while the next 1500 hours with your replacement halogen bulb will cost you another £11.85, the LED will continue doing its job for further 1500 hours using all of 63p in electricity. And the same will happen for the next 1500 hours after that, and the one after that. So, unless you’re planning to use the bulb for less than 1500 hours, the LED version is quickly cheaper overall even though it costs 10x as much as the halogen bulb to buy.

(And I’ve not factored in the hassle or cost of getting to the fittings to change the bulbs when they fail, or ordering / maintaining replacement stock, etc – someone has to do it, and it all has a cost. Or running an air-conditioning system to keep the places where you use halogen bulbs cool as they convert a lot of that 50W into heat …)

That’s my “wallet-draining” comment sorted, so what about the “carbon-greedy” bit? UK grid electricity gives off about 500g of CO2e for every kWh of electricity in the grid, so over its lifetime, a single halogen bulb is responsible for about 37.5 kg of CO2e emissions from its power use alone (equivalent to driving about 170 miles in an average car), while the LED alternative is responsible for a mere 2.25kg (10 miles) – a 94% reduction.

It’s a bit of a no-brainer really, isn’t it? So bite the bullet – next time you need to replace a halogen spot, pop in an LED one instead and not only save yourself money (and buffer yourself against future electricity price hikes …), but reduce your carbon emissions too.

I often provide cost/carbon comparisons like this on selected existing fittings and my alternatives as part of my services when reviewing the energy consumption of premises.

(Prices quoted & lamp images are taken from http://tinyurl.com/3vv63pa on date of posting and include VAT but exclude delivery)

Transport emissions “Magic Numbers”

A few years ago, I bought a new car that told me the average mpg I was achieving on the current tank of petrol and I started to wonder about what gCO2/km this meant I was achieving at any fuel economy. A little bit of empirical research revealed a fairly linear relationship between mpg and gCO2/km that was true for almost any car for a given fuel type, and a bit more thinking made me realise that complete combustion of a fixed quantity of any given fuel would give off the same quantity of CO2 irrespective of the engine it was burnt in.

Which led me to develop a “magic number” for my car which, divided by the mpg I was achieving gave me a good idea of its emissions – “6600” for “petrol”. (“Petrol” is a blend of compounds rather than a single compound, but I’ve generally found it works well for any 95 octane petrol engine within a percent or two). So, if I achieved 40mpg, my emissions were roughly 165 gCO2/km, 50mpg gave 132 gCO2/km and 60mpg gave 110 gCO2/km. And I did exactly the same exercise for diesel & LPG.

However, in the future fuels will be blended with biofuels, particularly bioethanol in the case of petrol (“E10” and “E85” for 10% and 85% bioethanol contents respectively), and the CO2 calculation for this is much more straightforward as it is a single chemical compound and you can use the combustion reaction to calculate the carbon:

C2H5OH + 3O2 = 2CO2 + 3H2O

Which in terms of molecular weights looks like :

46.068 (ethanol) + 95.996 (oxygen) = 88.019 (carbon dioxide) + 54.046 (water)

So, 1 kg of ethanol will produce 1 x (88.019 / 46.068) = 1.911 kg of carbon dioxide on complete combustion. Given that the density of ethanol is 789 g/l, one litre of ethanol will give off 1508 g of CO2 when it burns, and a gallon (4.546 litres) will give off 6854 g of CO2. But as we commonly measure transport emissions in terms of “gCO2/km”, but think in terms of fuel economy in “mpg”, this needs to be divided by 1.6093 (ie 1.6093 km = 1 mile) to give my bioethanol “magic number”: 4259, rounded to 4250. So, for pure Bioethanol, CO2 emissions in g/km = 4250 / mpg.

Which surprised me, as it is so much less than the figure for “petrol” at 6600 and more akin to LPG at 3250, suggesting that fuel economy should drop off markedly as bioethanol is blended in, but I also found an interesting snippet on the web that went: “By blending ethanol with gasoline we can also oxygenate the fuel mixture so it burns more completely and reduces polluting emissions.” (1)  And if it enables the petrol to burn more completely, perhaps it liberates more power from the mix, giving improved performance that offsets its lower carbon content?

By knowing the number for pure bioethanol, and that for petrol, simple maths gives the numbers for the E10 and E85 blends, and my current list of Magic numbers for different fuels looks like:

  • Diesel — CO2 emissions in g/km = 7575 / mpg
  • Petrol — CO2 emissions in g/km = 6600 / mpg
  • E10 Bioethanol — CO2 emissions in g/km = 6365 / mpg
  • E85 Bioethanol — CO2 emissions in g/km = 4600 / mpg
  • LPG — CO2 emissions in g/km = 3250 / mpg

I’ll update this list if I ever find any info on biodiesel! (Although I suspect it will be very much like “fossil” diesel.)

(1) http://www.esru.strath.ac.uk/EandE/Web_sites/02-03/biofuels/what_bioethanol.htm