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Archive for the ‘engineering’ Category

how far can you transport wood pellets before losing the carbon benefit?

Posted in biofuel, biomass, climate change, energy, engineering, house, renewable energy on April 19, 2007| 9 Comments »

pelletsAt least around 3000 kilometres. Here’s why:

The BRE gives a carbon intensity of 0.025kgCO2/kWh for biomass. This includes an allowance for planting, harvesting, processing, and delivery to point of use. See the 2001 emissions report and the 2003 update.

But we need to vary the emissions figure based on distance travelled. The European Environment Agency gives a figure of just over 0.12 kgCO2 per tonne per kilometre for road transport, quoted here. Even more pessimistic, the Royal Commission on Environmental Pollution says 0.18 – 0.27 kgCO2 per tonne per kilometre (see table 4.4). (more…)

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using mass to cool your house

Posted in architecture, climate change, energy, engineering, house, italy, renewable energy on April 4, 2007| 11 Comments »

A few weeks ago at the end of a post about the myth of stone walls as insulation, I mentioned that high mass materials can be useful when included inside the insulation layer. Here’s why. (more…)

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new single-house CHP unit

Posted in chp, climate change, energy, engineering, micro chp on March 27, 2007| Leave a Comment »

I saw on zerochampion that GTC Europe have got together with Cambridge Consultants to produce a single-house micro CHP unit. The key difference between this unit and the Mircogen or Whispergen is that it’s based on a Rankine cycle engine rather than a Stirling engine.

It’s got a similar electric-to-heat output ratio as the Whispergen and Microgen (1 kWe/9 kWt) but they claim that it operates at high efficiency at part load. They also say 2000 units will be available for sale by the end of this year at around €5000 each. It’ll be impressive if they hit the release target as the unit seems to have come out of nowhere. (more…)

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biofuel not so bio

Posted in biofuel, biomass, climate change, energy, engineering, renewable energy on March 23, 2007| 1 Comment »

Biofuel is all over the news right now. The recent agreement between US and Brazil, Al Gore’s presentation at the World Biofuels Conference, and the latest UK budget are just a few examples. At first glance biofuels promise to be a key element in a sound strategy to mitigate climate change. But under the surface rages a fierce debate. (more…)

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the myth of stone walls as insulation

Posted in climate change, energy, engineering, house, italy on March 5, 2007| 13 Comments »

In Italy, building professionals often tell you that thick stone walls will keep you warm in winter. Our first geometra said so. And recently my friend’s architect told him it wasn’t worth adding insulation to his walls since they were porous tufa stone, which the architect claimed was a good insulator. But it’s not true.

A good insulator has a high thermal resistance – it prevents heat from flowing from the warm side to the cool side. Polystyrene, rockwool, and sheep’s wool are all examples of good insulators. In many cases you can compensate for lower thermal resistance by increasing the thickness of material: if your insulation isn’t good, just use more of it. But with stone, the thermal resistance is so low that in order to offer a reasonable level of insulation, the walls need to be unrealistically thick.  (more…)

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end of domestic-scale chp?

Posted in chp, climate change, energy, engineering, micro chp on February 27, 2007| 9 Comments »

It was announced this month that BG Microgen are closing their doors. Microgen is one of two major players in the much hyped and still nascent domestic-scale CHP market. Why would a company backed by British Gas, with over £50m already invested, and poised to take a significant share of a huge market (so we’re told) close their doors just like that? (more…)

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forget insulation. install a display meter

Posted in climate change, energy, engineering on February 14, 2007| 4 Comments »

Engineers spend a lot of time during the design of a new building predicting how much energy it will consume, banging away on spreadsheets or simulation software and ending up with deceptively precise numbers. The predictions are useful as a like-for-like comparison with buildings of a similar type but the problem comes when you treat the results as a reflection of real energy use in the building.

Simulation results are almost meaningless once the occupant comes on the scene, even in a low-energy house. The Passiv Haus Institute monitored over a hundred houses built to the German Passiv Haus standard (homes so efficient they don’t need conventional heating) and found that mean levels of consumption were almost always higher than predicted, in some cases more than three times higher. And there are many examples of monitoring studies for commercial and domestic buildings with similar results. (more…)

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solar thermal panels in winter

Posted in energy, engineering on January 19, 2007| 1 Comment »

As part of the design of a UK secondary school, we were looking at using solar thermal panels. Normally, solar thermal doesn’t work well in schools because in the UK almost half of your energy is harvested in the summer when the building isn’t in use.

As a solution, we talked about trying to bias the output of solar thermal panels towards winter months by increasing their inclination. By putting them at a steeper pitch, you expose less collector area to direct sun in summer and, providing the spacing is sufficient, more area to low angle winter sun. (more…)

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