Archive for the ‘Personal’ Category

Controlling Tap Temperatures with a Blending Valve

October 6, 2021

Friends, I wrote the other week about how controlling for Legionella in a domestic hot water system could lead to overly hot temperatures at hot water taps.

This presented the risk of scalding people using hot water for a day or two after the anti-legionella heating cycle had run.

The solution was to install a thermostatic blending valve on the output of the hot water cylinder.

This article is a short follow-on, showing how the blending valve behaves.

Blending Valve

Click image for a larger version. A blending valve mixes cold water with hot water from a domestic hot water tank to achieve a blended flow with a thermostatically-controlled temperature.

The Caleffi 5218 series valve I installed (data sheet as pdf) was specified to be settable for output flows between 45 °C and 65 °C, with each unit on the thermostatic control corresponding to a 2 °C change in flow temperature.

Obviously, this had to be checked!

Click image for a larger version. Testing the temperature of the tap water.

I tested the flow temperature using a thermocouple inserted in the water flow and waited for the temperature to stabilise.

As the data sheet makes clear, on first operation, there can be a short-period where the water temperature at the taps exceeds the set temperature. This seemed to be limited to about 10 to 15 seconds after which the water temperature was stable to within ±0.1 °C.

Click image for a larger version. The graph shows the measured flow temperature versus the thermostatic setting of the blending valve. The cylinder temperature was – evidently – about 56 °C, and the sensitivity of the setting was very close to its specified 2 °C per setting unit.

As the graph above shows, the valve performed exactly as specified. And although there is still a small risk of scalding due to the transient response of the valve, in practice, I think this risk is low.

Why? Because if the pipes through which the blended water is delivered are initially cold, then the over-temperature water will lose heat to the cold pipework.

I have now set the valve to a nominal 49 °C, and I propose to stop thinking about this problem. It’s a lovely day and I really want to get outside!


October 5, 2021

Friends, I gave a talk last week to the Richmond U3A – The University of the Third Age.

Disappointingly it was still a Zoom affair, but it appeared to be pass adequately.

After the talk I rashly thought I would run through it again and create a video presentation that I could share.

Having stared at my own face for several hours while trying every possible permutation of sound and video options in Windows™, I am no longer sure it was such a good idea.

But I’ve done it now. And as the saying goes, “I’ve suffered for my art, now it’s your turn…

You can download the Powerpoint file here.

The video of the presentation is in three parts, respectively 12, 16 and 24 minutes long.

Carbonaut: Part 1: 12 minutes

The first part is about the Climate Crisis and features a nice version of the Keeling curve – the curve that shows the increase in atmospheric carbon dioxide since 1959 – but expressed in tonnes of carbon dioxide in the atmosphere rather than concentration.

This makes it easier to understand how tonnes of emissions per person can lead to gigatons of emissions globally.

Carbonaut: Part 2: 16 minutes

The second part is about my ‘personal’ carbon dioxide emissions and explains how I have assessed the carbon dioxide emissions from house.

The key recommendation is to start reading your gas and electricity meter once a week.

Carbonaut: Part 3: 24 minutes

The final part is about what I have done to reduce carbon dioxide emissions from my house by 80%. It covers the installation of:

  • External Wall Insulation
  • Triple Glazing
  • Solar Panels
  • Battery
  • Air Source Heat Pump

It also covers what all this cost, the embodied carbon cost, and the likely carbon savings before the estimated date of my death. It’s quite a bit!

Carbon and Debt

September 12, 2021
There are parallels between the 'debt crisis and the carbon emissions crisis?

There are parallels between the ‘debt’ crisis and the carbon emissions crisis?


This article is about the similarities between financial debt and ‘carbon’ debt. 

I wrote it almost 10 years ago back in December 2011, but the subject has been on my mind again recently. 

  • The financial situation was very different back then, but also very much the same! 
  • The carbon situation is now much worse: we have had 10 wasted years and emitted another 360 billion tonnes of carbon dioxide.


I have been struck recently by profound similarities between the debt crisis and the carbon crisis. Here are seven points: see what you think:

1. Both these crises arise from a choice to consume now and pay later.  

With the debt issue, this is true both at a personal and a national level. Politicians have shied away from making people aware of the true cost of their policies for fear of unpopularity. Similarly, because of the potential unpopularity of the policies required to address carbon emissions, politicians have held back from policies that would dramatically cut carbon emissions.

2. Both these crises require us to address intergenerational morality.  

In the same way that it is unfair to spend money now and expect our children to pay it back, so it is unfair to emit carbon now, and expect our children to deal with the consequences.

3. Both these crises require international solutions.  

National politicians have failed us: they are unable to resist spending and borrowing more in order to stay popular. And so the Eurozone have now called for central oversight of national budgets to make sure countries do not surreptitiously borrow too much. Similarly, the nations of the world require external limits to be imposed upon them. Only in this way can politicians tell their people: ‘its not our fault’.

4. Neither of these crises will ever be ‘solved’.

Rather, they are perpetual struggles not isolated events.  Recent events in Europe may make it seem that a particular path to a solution has been found. But it hasn’t. The forces which drove Europe into its difficulties and which created spectacular indebtedness in the UK are still all in play. Similarly, the outcome of the Durban conference is neither a cause for celebration or depression: it is just another step on the path, and we really don’t know what lies ahead. [Note: I have no idea now what that conference was about!]

5. Accounting is difficult and dull and boring. 

But accounting is essential. This has been true of financial accounting for many years, and it will be equally true of carbon accounting when the concept becomes established. But what appears to be a constraint on freedoms or our growth, is simply a way of staying honest.

6. Spending money you have borrowed is like burning carbon.

Why? makes us feel good now. Building a hospital we can’t afford brings benefits and so does burning carbon – we get improved lifestyles today – and much cheaper than the sustainable lifestyles we might aspire to. But eventually we will have to pay the cost. In financial terms this can involve reduced incomes which will the harm people’s health as well as their wealth. In carbon terms, we really don’t know what the costs will be, or who will be required to pay them.

7. Paying back debt is really hard.

If you have ever had to pay back any significant amount of debt, then you know how hard it is. This is as true for nations as it is for people – with the additional unfairness in that the people who borrowed the money and benefitted are not the people who have to pay it back. If we are to ever get back to some kind of carbon neutral economy then it will involve real pain as we wean ourselves off carbon emitting technologies. Real pain – and most probably real reductions in quality of life.

I could go on because I think the parallels are quite deep, but I think I have made the point.

However, I do want to add that in both cases, there is no need to despair. The world is very beautiful, and very resilient. And we have each other. If we can learn a lesson, and teach our children, then we can still make things better than they otherwise would have been.

Heat Pumps: Power, Noise and Condensation

August 30, 2021

Friends, I had a visit the other day from a couple who were considering installing a heat pump in their home, but were concerned about the noise.

To get the heat pump to operate, I ran the hot water for 10 minutes and then requested a hot water ‘boost’ using the app on my phone.

We then stood around the heat pump chatting until the visitors started to get cold. The reason? The heat pump had started up and was blowing cold air over their legs. But they had not heard a thing!

I told them to wait – and slowly the heat pump speeded up and became audible. But it was not what I would call ‘noisy’. In the garden, 5 metres away – you would not be aware of it as a separate sound against the (quiet) suburban background.

In fact, the need for heat pumps to be quiet constrains their design significantly and actually determines their physical size! It would be possible to make heat pumps differently – but they would be either noisier or drippier!

Let me explain…

Click for a larger version. How a heat pump works. A fan rotates and blows air out of the heat pump cabinet. This draws in air which flows over a so-called heat exchanger. This consists of many small diameter pipes containing coolant. The coolant absorbs heat from the air which is later delivered to the house.

Thermal power and air volume

When designing a heat pump, the first thing one needs to know is the thermal power the heat pump must deliver: Let’s say its 6 kW.

If it operates with a coefficient of performance (COP) of 3, then 2 kW out of those 6 kW will be from the electrical motor, and 4 kW will be extracted from the air.

Heat pumps obtain this energy by cooling outside air by roughly 3 °C using a so-called heat exchanger. The heat capacity of air is (more or less) fixed, ~ 1 kJ/kg/°C (source) and 1 kg of air occupies a volume about 0.83 cubic metres.

So, if the heat pump extracts heat from 0.83 cubic metres of air per second, cooling it by 3 °C, then it will extract 3 x 1 kJ = 3 kJ of heat per second i.e. 3 kW.

So to achieve its target of extracting 4 kW of heat, it must pass 33% more air over its heat exchanger i.e. about 1.1 cubic metres of air.

Air speed and noise

Heat pump noise arises from air flow over and around surfaces, and the noise increases with the speed of air flow.

A heat pump can draw a given quantity of air over its heat exchanger in (broadly) two ways.

  • By increasing the speed of air flow over a given area of heat exchanger
  • Or by increasing the area of heat exchanger and keeping the air speed low.

In practice, the faster the air flows, the noisier the heat pump becomes.

So when more heating power is required, manufacturers can speed up a fan a little to increase air speed, but  generally they increase the area of the heat exchanger.

Click for a larger version. Heat pumps made by Vaillant. In order to extract more heat while keeping the air speed low, heat pumps need to be physically larger to accommodate larger area heat exchangers.

Heating Power and Condensation

The heating power of a heat pump is linked directly to the volume of air it passes across its heat exchanger, and the amount by which the air is cooled.

So one other option for increasing the heating power extracted from the air while maintaining low air speeds (i.e. low noise) is to cool the air more.

However when air is cooled, then depending on…

  • the air temperature,
  • the initial humidity, and
  • the temperature drop,

…water may or may not condense. The larger the temperature drop, the more likely water is to condense.

Water condensation is not especially harmful, but at low temperatures, condensation can freeze around the heat exchanger and stop the heat exchanger working.

Heat pumps can detect this and intermittently melt any ice on the heat exchanger – but this makes the operation of the heat pump less efficient.

To cope with condensation all heat pumps are equipped with a drain which allows condensed water to simply drip out the bottom of the casing. This is why it is important to mount heat pumps level – so the designed draining port is actually at the lowest point.

But where does the water go after it drains away?

Allowing water to just drip on the ground – and potentially freeze is not a great idea.

Plumbing the drain into an existing drainpipe may seem adequate but it is not. In winter, when the heat pump is operating below zero, this will freeze and may cause icy spillages, and blockages.

So best practice is dig a ‘soak-away’. For my heat pump we used a ground auger to drill a 15 cm diameter hole a full 1 metre deep. We then filled this with small stones.

The drain hose from the heat pump has a 30 cm long internal heater that prevents icing until the condensate is about 15 cm below ground level. Hopefully the temperature there will be above 0 °C!

Click for a larger version. Arrangement for removing condensation from a heat pump. The casing must be level and water is drained away from the lowest point in the cabinet into a soak-away. The drain is heated along its length to prevent it freezing up at low temperatures.

How much condensation is there?

The amount of condensation depends on many factors but because I knew you would ask, I wrote a spreadsheet to calculate it. (Excel .xlsx file: Calculation of Condensate Volume)

A typical output is shown below. The graph shows the number of litres per day of condensation for a heat pump which delivers 6 kW of heating when the external temperature is 0 °C.

This calculation assumes the relative humidity of the air is 85% and that the temperature drop across the heat pump heat exchanger is either 3.5 °C or 7.0 °C – potentially extracting double the heating power.

In this case the larger temperature drop causes a roughly 10-fold increase in the rate of condensation

The reason for the shape of the curves is that:

  • At low external temperatures, the heat pump must run at high power and so extract heat from a larger volume of air.
  • At low external temperatures, the amount of water in the air is much less than at high temperatures.

Together these two factors combine to produce maximum condensation at temperatures between 5 °C and 10 °C.

Click for a larger version. The graph shows the amount of condensation (litres per day) expected when a heat pump is operating at the external temperature shown so as to maintain an internal temperature of 19 °C. The thermal power at 0 °C is 6 kW and heat pump is assumed to cool the air by ΔT = 3.5 °C  or by ΔT = 7.0 °C. The relative humidity of the air is assumed to be 85%. Notice that cooling the air more drastically increases the amount of condensation.

Non-combatants may wish to stop reading here.

But for those interested, I will explain the calculation below.

Click for a larger image. Spreadsheet for calculating the amount of water which condenses from a heat pump. The text below explains each column in the calculation. The actual spreadsheet is downloadable from a link in the text.

The basic inputs are the shown in red text with a yellow background.

  • The desired internal temperature (19 °C)
  • The thermal power required to maintain 19 °C when the external temperature is 0 °C. (6000 W = 6 kW)
  • The Coefficient of performance of the heat pump (3) which is assumed to be constant.
  • The humidity of the air (85%)
  • The amount (ΔT) by which the heat pump cools the air (3.5 °C)

Column 1: shows the external temperature.

Column 2: shows the temperature demand, the difference between the internal and external temperatures

Column 3: shows the thermal power required to heat the dwelling, assuming it is proportional to temperature demand.

Column 4: shows how much thermal power must be extracted from the air based on the COP.

Column 5: shows the volume of air per second that must be cooled by ΔT in order to extract the required heating power. More air flow is required at low temperatures as the heating demand increases

Next we work on the humidity

Column 6: shows the specific humidity of saturated air with the numbers entered from a data table. This expresses the maximum density (in grams per cubic metre) of water that air can hold without condensing.

Column 7: shows the the same quantity as column 6 but derived from a formula designed to closely match the actual data. This allows me to interpolate between the points in the data table.

Column 8: shows the specific humidity of the air under consideration i.e. with relative humidity less than 100%.

Column 9: shows the specific humidity of saturated air which is ΔT colder than the external temperature.

Column 10. If the specific humidity of the actual air (Column 8) exceeds the specific humidity of saturated air at its new lower temperature, then condensation will occur.

Column 11. If condensation occurs, then the excess water (the difference between columns 8 and 9) will become liquid.

Column 12. Expresses the condensation per cubic metre in terms of condensation per second.

Columns 13, 14, 15 and 16. Expresses the condensation rate in terms of litres per second, per minute, per hour and per day respectively.

Know your onions

August 9, 2021

Click for a larger image. New Zealand onions were on sale in my local supermarket at the same price as UK onions. How?

Friends, while shopping in my local supermarket, I noticed that there were two crates of onions next to each other.

Both offered onions for sale at a very reasonable 85p per kg.

I have been trying recently to preferentially buy produce from the UK, and so I looked at the labels to see if the onions were from England or Spain.

I was pleased to see that one crate of onions was indeed from the UK.

But I was shocked to see that the other crate of onions was not from Spain, but from New Zealand!


Click for a larger image. New Zealand is literally on the other side of the Earth from the UK. It is a very long way for onions to travel.

Friends. I am not a xenophobe.

And I welcome the import of New Zealand produce to the UK. It makes perfect sense for us to import kiwi fruits for example, or wine. I can even understand a seasonable argument for apples.

But importing onions from New Zealand makes no sense to me.

I am, literally, lost for words

Our Old Car is Dead. Long Live The New Car!

July 28, 2021

Click for larger image. Our old and new Zafira cars

After 20 years and 96,000 miles, our 2001 Vauxhall Zafira is close to death.

We bought it for £7000 when it was three years old in 2004. Back then it was all shiny and new, but over the last 17 years it has developed a very long list of faults.

Alexei Sayle once said of his car: “When one door closes, another one opens.”. This was one of the faults our car did not have. But it did have a feature such that: “When one door closes, all the electric windows operate simultaneously.”

Over the last few weeks the engine has begun making horrific noises, the engine warning light is on permanently, and there is an acrid stench of burning oil in the cabin.

After much deliberation, we have replaced it with a closely similar car, a 2010 Zafira with only 52,000 miles on its ‘clock’. The new car lacks our old car’s charmingly idiosyncratic list of faults, but what can you expect for £3,200?

In this post I would like to explain the thinking behind our choice of car.

Do we need a car?

Strictly speaking, no. We could operate with a combination of bikes and taxis and hire cars. But my wife and I do find having a car extremely convenient.

Having a car available simplifies a large number of mundane tasks and gives us the sense of – no irony intended – freedom.

Further, although I am heavily invested in reducing my carbon dioxide emissions, I do not want to live the life of a ‘martyr’. I am keen to show that a life with low carbon dioxide emissions can be very ‘normal’.

So why not an electric car? #1: Cost

Given the effort and expense I have gone to in reducing carbon dioxide emissions from the house, I confess that I did want to get an electric car.

I have come to viscerally hate the idea of burning a few kilograms of hydrocarbon fuel in order to move myself around. It feels dirty.

But sadly buying a new electric car didn’t really make financial sense.

There are lots of excellent electric family cars available in the UK, but they all cost in the region of £30,000.

There are not many second-hand models available but amongst those that were available, there appeared to be very few for less than £15,000.

Click for larger version. Annual Mileage of our family cars since 1995 taken from their MOT certificates. The red dotted line is the Zafira’s average over its lifetime.

Typically my wife and I drive between 3,000 and 5,000 miles per year, and we found ourselves unable to enthuse about the high cost of these cars.

And personally, I feel like I have spent a fortune on the house. Indeed I have spent a fortune! And I now need to just stop spending money for a while. But Michael: What about the emissions?

So why not an electric car? #2: Carbon Dioxide

Sadly, buying an electric didn’t quite make sense in terms of carbon emissions either.

Electric cars have very low emissions of carbon dioxide per kilometre. But they have – like conventional cars – quite large amounts of so-called ’embedded’ carbon dioxide arising from their manufacture.

As a consequence, at low annual mileages, it takes several years for the carbon dioxide emissions of an electric car to beat the carbon dioxide emissions from an already existing internal combustion engine car.

The graph below compares the anticipated carbon dioxide emissions from our old car, our new car, and a hypothetical EV over the next 10 years. The assumptions I have made are listed at the end of the article.

Click for larger version. Projected carbon dioxide emissions from driving 5,000 miles per year in: Our current car (2001 Zafira); Our new car (2010 Zafira); and a typical EV. The dotted line shows the effect of grid carbon intensity falling from around 200 gCO2/kWhe now to 100 gCO2/kWhe in 2030.

For an annual mileage of 5000 miles, the breakeven point for carbon dioxide emissions is 6 or 7 years away. If we reduced our mileage to 3000 miles per year, then the breakeven point would be even further away.

Click for larger version. Projected carbon dioxide emissions from driving 3,000 miles per year in: Our new car (2010 Zafira); and a typical EV. The dotted line shows the effect of grid carbon intensity falling from around 200 gCO2/kWhe now to 100 gCO2/kWhe in 2030.

However, we are a low mileage household. If we drove a more typical 10,000 miles per year then the breakeven point would be just a couple of years away. Over 10 years, the Zafira would emit roughly 12 tonnes more carbon dioxide than the EV.

If we took account of embodied carbon dioxide in a combustion engine car, i.e. if we were considering buying a new car, the case for an EV would be very compelling.

Click for larger version. Projected carbon dioxide emissions from driving 10,000 miles per year in: Our new car (2010 Zafira); and a typical EV. The dotted line shows the effect of grid carbon intensity falling from around 200 gCO2/kWhe now to 100 gCO2/kWhe in 2030.


By replacing our old car with a closely similar model we have minimised the cognitive stress of buying a new car. Hopefully it will prove to be reliable.

And however many miles we drive in the coming years, our new car will reduce our carbon dioxide emissions compared to what they would have been in the old car by about 17%. And no new cars will have been built to achieve that saving.

Assuming that our new car will last us for (say) 5 years, I am hopeful that by then the cost of electric cars will have fallen to the point where an electric car – new or second-hand – might make sense to us.

Additionally, if the electricity used to both manufacture and charge electric cars increasingly comes from renewable sources, then the reduction in carbon dioxide emissions associated with driving electric cars will (year-on-year) become ever more compelling.

However, despite being able to justify this decision to myself, I must confess that I am sad not to be able to join the electric revolution just yet.


For the Zafiras:

  • I used the standard CO2 emissions per kilometre (190 and 157 gCO2/km respectively) in the standard government database.

For the hypothetical EV

  • I took a typical high efficiency figure of 16 kWh per 100 km taken from this article.
  • I assumed a charging inefficiency of 10%, and a grid carbon intensity of 200 gCO2/kWhe reducing to 100 gCO2/kWhe in 10 years time.
  • I assumed that the battery size was 50 kWh and that embodied carbon emissions were 65 kg per kWh (link) of battery storage yielding 3.3 tonnes of embodied carbon dioxide.
  • I assumed the embodied carbon dioxide in the chassis and other components was 4.6 tonnes.
  • For comparison, the roughly 8 tonnes of embodied carbon dioxide in an EV is only just less than the combined embodied carbon dioxide in all the other emission reduction technology I have bought recently:
    • Triple Glazing, External Wall Insulation, Solar Panels, Powerwall Battery, Heat Pump, Air Conditioning

I think all these numbers are quite uncertain, but they seem plausible and broadly in line with other estimates one can find on the web


Not-blogging: What I did on my holidays

July 25, 2021


View from our holiday cottage,

Friends! Hello again.

I have been on holiday in delightful Kent, visiting many of the same attractions I visited last year, and a few new ones.

I have also been busy not-blogging.

Blogging about a topic forces me to clarify my thoughts.

And similarly not-blogging allows me to avoid clarifying my thoughts. Which has been a relief.

I did notice the extreme weather events world-wide and the pandemical nihilism in the UK, but it has been a blessing to not have to focus on these events too closely.

While away I…

  • Enjoyed the kindness of strangers and reflected on how steadfast this was in even the most difficult of times.
  • Noticed how tough the pandemic has been for small businesses, and reflected on my own good fortune.
  • Required no cash at all not even once in even the smallest of establishments and reflected that cash will soon become extinct.
  • Gazed in wonder at Canterbury Cathedral and reflected on the enduring power of martyrdom.
  • Visited the Brogdale National Fruit Collection and reflected on how hard it is to buy British Fruit even in the Garden of England.
  • Discovered an airfield unmarked on the OS map and reflected on the pleasure of discovery.
  • Saw many beautiful flowers and plants and reflected on their resilience and perfection.
  • Noticed how different country foxes were from from their town cousins: country foxes have beautiful coats and run like the wind when they spot you.
  • Visited Leeds Castle and reflected on the unimaginable wealth of Lady Bailey – an heiress of an ESSO founder who used the vast estate as her weekend retreat. And I thought about the storms my children will endure as a result of that companies success.
  • Visited Rochester Castle and was astounded by this carcass of a skyscraper with astonishing views.
  • Visited Chatham Dockyard and reflected on how different the world was now from my father’s world which transported him to North Africa and Burma.
  • Visited Teapot Island Museum and reflected on the way in which this non-native plant (tea was apparently smuggled from China and planted in India) had led to (amongst other things) a bizarre form of cultural expression.
  • Spent time with my children and reflected on my great good fortune.
  • Realised that after 96,000 miles and 20 years of neglect, our car was about to die. The stench of burning oil highlighted my appreciation that its carbon-based effluents were polluting the planet.
  • Walked through wheat fields and reflected on wonder of my daily bread.
  • Ate fish and chips on the beach in the rain and reflected on how English I feel while still not disliking other cultures.
  • Saw wind ‘farms’ at sea and solar ‘farms’ on land and reflected on the sheer wonder of their engineering and the hope for a non-polluting future that they embody.

And I let all this and more wash over me.

And after returning to a heatwave that I believe may have extended beyond Teddington, I enjoyed solar-powered air conditioning at home – even as I slept – and allowed these memories and reflections to ferment in my dreams.

I have put some pictures below and after my non-blogging indulgence, I will be back blogging very shortly

I hope you too can have a holiday of sorts.


Click the images for larger versions.

The World Set Free

June 26, 2021

I recently re-readThe World Set Free” by H.G. Wells, a book which has a decent claim to being the most influential work of fiction of the 20th Century.

Written in 1913, a central theme of the book is that access to energy is central to the advance of global civilisation.

In the prologue, he imagines early humans wandering over the Earth and not realising that, first coal, and then later nuclear fuel, was literally under their feet.

Rendering of the gigantic planned SunCable solar farm. Copyright SunCable.

I had revisited the text because I realised that Wells had ignored the energy in the sunlight falling on the Earth, of which we require just 0.01% to power our advanced civilisation.

And so now, we can simply collect the largesse of energy that falls on the Earth everyday.

But it is unfair to criticise a futurist for what they omitted – getting anything right at all about the future is hard.

But re-reading the book I realised that Wells’ imagined vision of the future has been – I think – profoundly influential. Let me explain.

The Most Influential Book of the Twentieth Century?

The book initially follows a scientist (Holsten) who uncovers the secret of what he calls “induced radio-activity” – allowing the controlled release of nuclear energy.

And eventually a world of atomic-powered planes and automobiles follows.

But the political institutions of the world remained archaic and unsuited to the possibilities of this new world.

And in a stand-off broadly following the divisions of the actual World Wars, he foresees a global war fought with atomic weapons – a phrase which I think he must have invented.

Fictional Atomic Bombs

Of course in 1913, atomic bombs did not exist. H G Wells envisaged them as follows.

“…the bomb-thrower lifted the big atomic bomb from the box and steadied it against the side [of the plane]. It was black sphere roughly two feet in diameter. Between its handles was a little celluloid stud, and to this he bent his head until his lips touched it. Then he had to bite in order to let air in upon the inducive. Sure of its accessibility, he craned his neck over the side of the aeroplane and judged his pace and distance. Then very quickly he bent forward, bit the stud, and hoisted the bomb over the side.

“Never before in the history of warfare had there been a continuing explosive… Those used by the allies were lumps of pure Carolinum, painted on the outside with un-oxidised cydonator inducive enclosed hermetically in a case of membranium. A little celluloid stud between the handles by which the bomb was lifted was arranged so as to be easily torn off and admit air to the inducive which at once became active and set up the radioactivity in the outer layer of the Carolinum sphere. This liberated fresh inducive and so in a few minutes the whole bomb was a blazing continual explosion.

Carolinum belonged to the beta group of Hyslop’s so-called ‘suspended degenerator’ elements, [and] once its degenerative process had been induced, continued a furious radiation of energy and nothing could arrest it. Of all of Hyslop’s artificial elements, Carolinum was the most heavily stored with energy and the most dangerous to make and handle. To this day it remains the most potent degenerator known. What earlier 20th Century chemists called its half-period was seventeen days; that is to say, it poured out half the huge store of energy in its great molecules in the space of seventeen days, the next seventeen days’ emission was half of that first period’s outpouring and so on…. to this day, the battle-fields and bomb fields of that frantic time in human history are sprinkled with radiant matter, and so centres of inconvenient rays

“A moment or so after its explosion began, [the bomb] was still mainly an inert sphere exploding superficially, a big inanimate nucleus wrapped in flame and thunder. Those that were thrown from aeroplanes fell in this state, they reached the ground mainly solid, and, melting soil and rock in their progress bored into the earth. There, as more and more of the Carolinum became active, the bomb spread itself out into a monstrous cavern of fiery energy at the base of what became very speedily a miniature active volcano. The Carolinum, unable to disperse, freely drove onto and mixed up with the boiling confusion of molten soil and superheated steam, and so remained spinning furiously and maintaining an eruption that lasted for years or months or weeks according the size of the bomb…

“Once launched the bomb was absolutely unapproachable and uncontrollable until its forces were nearly exhausted, and from the crater that burst open above it, puffs of heavy incandescent vapour and fragments of viciously punitive rock and mud, saturated with Carolinum, and each a centre of scorching and blistering energy, were flung high and far.

“Such was the crowning triumph of military science, the ultimate explosive that was to give the ‘decisive touch’ to war…

Actual Atomic Bombs

Of course almost every detail of the account above is wrong.

But qualitatively, it is spot on: a single weapon which could utterly destroy a city not just at the time of its detonation, but have effects which would persist for decades afterwards: the “ultimate explosive”

And critically, the book was read by Leo Szilard, a man with a truly packed Wikipedia page!

On September 12, 1933, having only recently fled Germany for England, Szilard was irritated by a Times article by Rutherford, who dismissed the possibility of releasing useful amounts of nuclear energy.

And later that day, while crossing Southampton Row in London, it came to him how one could practically release nuclear energy by making a nuclear chain reaction. He patented his idea and assigned the patent to the UK Admiralty to maintain its secrecy.

In the following years he was influential in urging the US to create a programme to develop nuclear weapons before the Germans, and so he came to be present in Chicago when Fermi first realised Szilard’s chain reaction on December 2nd 1943.

On seeing his invention work, he did not rejoice. He recalls…

“There was a crowd there and when it dispersed, Fermi and I stayed there alone. Enrico Fermi and I remained. I shook hands with Fermi and I said that I thought this day would go down as a black day in the history of mankind.

I was quite aware of the dangers. Not because I am so wise but because I have read a book written by H. G. Wells called The World Set Free. He wrote this before the First World War and described in it the development of atomic bombs, and the war fought by atomic bombs. So I was aware of these things.

But I was also aware of the fact that something had to be done if the Germans get the bomb before we have it. They had knowledge. They had the people to do it and would have forced us to surrender if we didn’t have bombs also.

We had no choice, or we thought we had no choice.

Was the book really influential?

Of course I don’t know.

But it is striking to me that by merely imagining that such terrible weapons might one day exist, and feasibly imagining the circumstances and results of their use, H.G. Wells placed this idea firmly into Szilard’s mind.

And Szilard was a man who – with good reason – feared what the German regime of the time would do with such weapons.

And so when recalling the first sustained and controlled release of atomic energy in Chicago, he immediately recalled H.G. Wells vision of a war fought with atomic bombs.


“The World Set Free” is fascinating to read, but it is not – in my totally unqualified opinion – a great work of literature.

The characters are mainly implausible, and the peaceful and rational world government Wells envisages would follow nuclear devastation might be better characterised by George Orwell. (Scientific American contrast Orwell and Wells’ ideas about science and society in an interesting essay here.)

By contrast, some of the plot twists are strikingly plausible. I was struck in particular when – after the declaration of World Government from a conference in Brissago in Switzerland – one single monarch held out.

In what might now be called “a rogue state”, a conniving ruler – “a Fox” – sought to conceal some “weapons of mass destruction”. After an attempted pre-emptive strike on the World Government was foiled, an international force searched the rogue state, grounding its aeroplanes, and a search eventually unearthed a stash of atomic bombs hidden under a haybarn.

Perhaps George Bush had been reading “The World Set Free” too!



Back Down to Earth

June 22, 2021

Friends, at the end the last article I wrote:

The combination of 12 solar panels and a Tesla Powerwall battery has been sufficient for us to be practically off-grid for the last 3 months. And that will probably continue for another 3 months. feels astonishing to be sustaining a good quality of life powered entirely by the Sun.

As we approach the summer solstice, I feel like I have reached apogee in a solar-powered rocket, and I am briefly floating weightless.

A week of miserable weather has brought me firmly back down to Earth.

After 87 days drawing no electricity from the grid, as the chart below shows, we have had to re-connect.

Click for a larger version. The graph shows daily electricity drawn from the grid (kWh) since November last year. After the battery installation, this fell to almost zero. Also shown is daily electricity used from the battery and solar panels (kWh). This has risen recently because electricity is now being used for air conditioning, cooking and domestic hot water.

We have now switched the mode of operating the battery so that it charges itself at night using off-peak electricity.

Solar Statistics: Summer Solstice Review

The summer solstice is probably a good point to review the performance of the solar panels installed last November 2020.

The £4200 system consists of 12 Q-Cells Duo BLK-G8 panels tilted at 40°. Six panels facing 25° East of South and six facing 65° West of South. A fuller description can be found here.

Click for a larger version. The graph shows daily solar generation (kWh) versus day of the year along with a 5-day running average. Also shown are two estimates for expected generation (kWh)alongside typical daily consumption.

The last 5 days have seen very poor generation. Last Friday 18th June, generation was just 2.3 kWh – more typical of mid-winter than mid-summer! And a battery with 13.5 kWh capacity is not big enough to see us through this dip.

Click for a larger version. The graph shows cumulative solar generation (kWh) versus day of the year along with a cumulative exports (kWh). Also shown are lines showing the estimated annual and semi-annual generation as specified by the installer.

Total generation so far this year is 1780 kWh – very close to 50% of the installer’s annual estimate.

The system has exported 590 kWh, my benevolent contribution to the grid, and I have used around 1200 kWh saving me around £250 compared to the situation without solar panels and batteries. If the panel’s performance is similar in the second half of the year, this would give a modest 3.5% return on my investment.

Carbon dioxide emissions 

Some fraction of this generation will have displaced gas generation which would have given rise to 0.45 kgCO2 per kWh, and some fraction will have displaced a typical generating mix which would have given rise to roughly 0.2 kgCO2 per kWh.

So depending on the assumptions made, my electricity generation has probably avoided emissions of between 350 kg and 800 kg of carbon dioxide so far this year, and will probably have avoided between 0.7 and 1.6 tonnes of CO2 by the end of the year.

The bigger plan 

The installation last week of the Air Source Heat Pump, a Vaillant Arotherm plus 5 kW model, together with a domestic hot water cylinder, marks the end of my investments in reducing carbon dioxide emissions from the house.

The ‘magic’ of the heat pump is that it uses 1 kWh of electrical energy to extract typically 2 kWh of thermal energy from the air, yielding around 3 kWh of heating.

This is central to reducing my carbon dioxide emissions. It has allowed me to replace the polluting gas boiler.

To compare carbon dioxide emissions with what what would have happened if I had made no changes, I have made a month-by-month estimate of household carbon dioxide emissions over the next 20 years.

These calculations are still preliminary, but the figure below shows their general form. It charts the anticipated carbon dioxide emissions if I had done nothing, alongside the anticipated carbon dioxide emissions in my plan.

Click for a larger graph. This chart shows month-by-month calculations of anticipated household carbon dioxide emissions based my current plan, or the do nothing alternative.

The green line shows an initial rise due to the 10.5 tonnes of carbon dioxide emitted during the manufacture of:

  • External Wall Insulation Boards (1.6 tonnes)
  • External Wall Mortar (1.0 tonnes)
  • Argon Triple Glazing (1.9 tonnes)
  • Solar Panels (1.6 tonnes)
  • Battery (1.4 tonnes)
  • Heat Pump (1.5 tonnes)
  • Air Conditioning (1.5 tonnes)

The green line then shows a much lower slope. The calculations indicate a break-even in terms of carbon dioxide by the end of 2023, and the non-emission of around 60 tonnes of carbon dioxide by 2040 when compared with the ‘do nothing‘ alternative.


It’s disappointing to be back ‘on grid’ for a few days, but overall the solar panels are performing pretty much as anticipated, already avoiding the emissions of hundreds of kilograms of carbon dioxide.

And they are just one part of the plan. The installation of the Air Source Heat Pump is the last part of the plan, and I will now monitor the house to see if my expectations are fulfilled.

Boiler Killer Strikes Again

June 12, 2021

Teddington: 10 June 2021:

Vaillant Ecotec, 10, a hardworking combination boiler, was today found dead in the garden of his family home in Teddington, West London. His torso was found in the front garden, with body parts gruesomely strewn across the grass. This grizzly discovery marks the fifteenth unexplained death of a boiler in Teddington this year.

We understand that he had been in good working order just recently, and his death has left other household appliances in a state of shock.

Bosch Fridge Freezer, 8, was lost for words. “He put in a fine performance over the winter, emitting almost 1.5 tonnes of carbon dioxide. You really couldn’t ask for a better boiler. And now it’s summer and he had been hoping for a bit of rest, just heating water for the odd shower. I can’t believe he’s gone.”

Early reports suggest that the slaying was pre-meditated and the killer was probably operating on a so-called ‘contract’. An Air Source Heat Pump was seen in the back garden just before the incident, and a Police spokesman confirmed that they considered that sighting was significant.

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