Tag Archives: efficiency

Georgian interior design and efficient radiators

My lecture last week, to first year students studying thermodynamics, was about energy flows and, in particular, heat transfer.  I mentioned that, despite being called radiators, radiation from a typical central heating radiator represents less than a quarter of its heat output with rest arising from convection [see post entitled ‘On the beach‘ on July 24th, 2013 for an explanation of types of heat transfer].  This led one student to ask whether black radiators, with an emissivity of close to one, would be more efficient.  The question arises because the rate of radiative heat transfer is proportionate to the difference in the fourth power of the temperature of the radiator and its surroundings, and to the surface emissivity of the surface of the radiator.  This implies that heat will transfer more quickly from a hot radiator but also more slowly from a white radiator that has an emissivity of 0.05 compared to 1 for black surface.

Thus, a black radiator will radiator heat more quickly than a white one; but does that mean it’s more efficient?  The first law of thermodynamics demands that the nett energy input to a radiator is the same as the energy input required to raise the temperature of the space in which it is located.  Hence, the usual thermodynamic definition of efficiency, i.e. what we want divided by what we must supply, does not apply.  Instead, we usually mean the rate at which a radiator warms up a room or the size of the radiator required to heat the room.  In other words, a radiator that warms a room quickly is considered more efficient and a small radiator that achieves the same as large one is also considered efficient.  So, on this basis a black radiator will be more efficient.

Recent research by a team, at my alma mater, has shown that a rough black wall behind the radiator also increases its efficiency, especially when the radiator is located slightly away from the wall.  Perhaps, it is time for interior designers to develop a retro-Georgian look with dark walls, perhaps with sand mixed into the paint to increase surface roughness.


Beck SMB, Grinsted SC, Blakey SG & Worden K, A novel design for panel radiators, Applied Thermal Engineering, 24:1291-1300, 2004.

Shati AKA, Blakey SG & Beck SBM, The effect of surface roughness and emissivity on radiator output, Energy and Buildings, 43:400-406, 2011.

Image details:

Verplank 2 002<br />
Working Title/Artist: Woodwork of a Room from the Colden HouseDepartment: Am. Decorative ArtsCulture/Period/Location: HB/TOA Date Code: Working Date: 1767<br />
Digital Photo File Name: DP210660.tif<br />
Online Publications Edited By Steven Paneccasio for TOAH 1/3/14


Subtle balance of sustainable orderliness

129-2910_IMGI wrote this short essay a couple of weeks for another purpose and then changed my mind about using it.  So I thought I would share it on this blog.

Whenever we do something, some of our useful resource gets converted into productive activity but some is always lost in useless waste.  In other words, 100% efficiency is impossible – we can’t convert all of our resource into productive activity.  Engineers call this the second law of thermodynamics.  Thermodynamics is about energy transitions, for instance converting chemical energy in fossil fuels into electrical energy in a power station, and in these circumstances, the useless waste is called entropy.  At the time of the industrial revolution, Rudolf Clausius recognised that entropy can be related to the heat losses which occur whenever we do something useful, such as generating electricity in a power station, cleaning the house with an electric vacuum cleaner or running to catch the bus.

Clausius’s definition of entropy was really useful for designers of 19th century steam engines but it is difficult to use in other walks of life.  Fortunately Ludwig Boltzmann gave us a more valuable description.  He equated entropy to the number of states in which something could be arranged, or its lack of orderliness.  In other words, the more ways you can arrange something, the less ordered it is likely to be and the higher its entropy.  So a box of children’s building blocks has a low entropy when the blocks are packed in their box because there is a relatively small number of ways of arranging them to fit in the box.  When the box is emptied onto your living room floor, there are very many more possible arrangements and so the blocks have a high entropy.  The chance of knowing the whereabouts of a particular block is small. Whoops!  Now we’ve wondered into information theory.

Let’s get back to the second law, which using Boltzmann’s description of entropy, we can express as the level of orderliness should always decrease.  Stephen Hawking describes this as the arrow of time.  Because, if someone shows you a video clip in which steam gathers itself together and returns into a cup of coffee, or that box of children’s blocks repacks itself, then we know the video is being run backwards because these processes involve decreasing entropy and this can only happen spontaneously if we reverse the direction of time.  If this is true then why do we exist as highly ordered structures?

Erwin Schrödinger in his book, ‘What is Life’ says that organisms suck orderliness out of the environment in order to exist, so that the orderliness of the universe, that’s the organism and its environment, decreases.  Humans digest highly-ordered food to sustain life and food, in the form of plants, is brought into existence by metabolising energy from the sun and releasing entropy in the form of heat.  When we die these processes cease and the orderliness is sucked out of us to sustain insects, maggots and bacteria.

We are organisms, known as Sapiens, that organise ourselves into cultures and societies.  Organisation implies an increase in the level of orderliness in apparent contradiction of the second law.  So, we would expect to find a corresponding increase in disorder somewhere to counterbalance the order in society.  The more regimented society becomes the greater the requirement for counterbalancing disorder to occur somewhere in order to satisfy the second law, which might happen unexpectedly and explosively if the level of constraint or regulation is too great.  This is not an argument for anarchy or total deregulation, the financial sector has already demonstrated the risks associated with this path, but for an optimum and sustainable level of orderliness.  This requires subtle judgment just like in elegant engineering design and living a healthy life, both physically and psychologically.

Where there is muck there is an engineer

Dr Lou Balmer-Millar at the FPC 2015 & the CAT 366E

Dr Lou Balmer-Millar at the FPC 2015 & the CAT 366E

Here’s a second post on what engineers do [see my post entitled ‘Press button for exciting ride‘ on March 25th, 2015].

Dr Lou Balmer-Millar leads a team that develops new technology for off-road vehicles.  She is Director of Research and Advanced Engineering at Caterpillar Inc. and she gave a keynote talk at the  Future Powertrains Conference, which I wrote about a couple of weeks ago.  She talked about the innovations that Caterpillar are developing to increase the efficiency of their vehicles.  This includes driverless giant trucks.  If you are worried about driverless cars then what about driverless 226 tonnes trucks?  It is already a reality –   watch the Caterpillar video.

However, what stuck in my mind from her presentation was not the enormous mining trucks but the way in which Caterpillar measure the efficiency of their diggers, such as the CAT 366E Hybrid.  They are not so much interested in miles per gallon as tonnes of dirt (or muck) shifted per gallon.  Efficiency is defined as what you want out of a machine divided by what you have to put in to a machine, or work done for energy supplied [see post entitled ‘Energy efficiency‘ on June 18th, 2014].  So for a passenger car, miles travelled divided by energy used is a reasonable measure of efficiency.  But for digger, tonnes of earth moved is what you are want done, so tonnes moved per gallon is the right measure of efficiency.   The machine in the picture does not look like anything special but Caterpillar claim it is 30% more efficient than its competitors.

So there is money to be made in shifting earth more efficiently than your competitors.  If you enjoy watching machines move earth the watch this video.

Photo credit: Joshua Tucker http://www.apcuk.co.uk/2015/03/future-powertrain-conference-2015-report/