Dust and Water

Dust by Jay Owens and The Three Ages of Water by Peter Gleick.

Friends, I have recently read two books that have caused me to re-evaluate – in the words of Peter Gleick – the true value of water. The first book, Dust, considers the role of dust in human culture. And the second, The Three Ages of Water, describes the critical importance of fresh water for all life on Earth. Partly to help me recall the contents, I thought I would write a précis of the two books, and I hopefully you will find this of interest too.

Dust

Dust may seem an odd topic for a book, but it in fact dust is an intrinsic part of the natural world and plays an outsize role in many geophysical processes. As materials break down, they turn into small and smaller particles and at some point – below around about a tenth of a millimetre or so – we somehow lose consciousness of them as individual particles. But the materials are still there. Crucially, when not bound by water, particles of this size are small enough to be lifted by the wind and held aloft.

Jay Owens begins her assessment of the significance of dust in her own flat as she reflects on the astonishing amount of otherwise invisible dust made visible in the beams of sunlight. This is the start of a world-wide journey.

She first revisits the origin of the concept of ‘dusting’ – a task which arose from combination of the appalling particulate pollution from coal burning, and the development of consumer goods which needed to be displayed. She argues that the idea of household cleaning as “women’s work” led to the oppression of women throughout the 19th and 20th Centuries.

She visits Owen’s Valley, California where in the 1920’s entrepreneurs from Los Angeles acquired – through techniques of dubious legality – water rights that underpinned the growth of Los Angeles and led to the destruction of Owen’s lake, which became a source of toxic dust, and led to the desolation of a fertile valley. And she visits the land at the heart of the creation of the dustbowl in the US in the 1930’s.

Likewise she visits the Aral Sea where in the 1960’s soviet planners re-directed the sources that fed the Aral Sea in order to grow cotton. Since then the sea has all but disappeared, leading to toxic dust storms that have led to the desertification of a once fertile ecosystem.

Click on image for a larger version. USGS Landsat images of the Aral Sea in 1992 and 2020. Even in 1990 the sea, once the 4th largest freshwater lake on Earth, had already undergone significant contraction.

She visits the areas around atomic bomb test sites and investigates the lasting impact of the clouds of invisible radioactive dust that spread across the USA from the explosions.

Click on Image for a larger version. From the Downwinders Website, this graph shows the dose of radioactive Iodine -131 at locations across the US as a result of dust particles from atomic bomb tests.

And she visits Greenland to see the effect of particles of black carbon on the melting of the ice sheet.

Click on Image for a larger version. The upper image from the American Museum of Natural History shows a section of an ice core from the Greenland Ice sheet. The yearly bands are clearly visible. The lower graph shows analysis of such ice cores revealing the amount of black carbon dust deposited year by year over the last 800 years.

Throughout all her travels, Jay Owens emphasises the outsize role that tiny particles of dust play, and notes that somehow it always the less powerful groups in society that suffer. Although her writing is polemical at times, I feel that the book has nonetheless raised my consciousness of dust. Previously I had thought of dust as being incidental or peripheral, but in fact, if you look for it, dust is everywhere.

Water 

We all know that water is important, but Peter Gleick’s aim in writing this book is to urge is to see the true value of water.

In the first age of water, he discusses the role of water in the prehistory of the solar system, our planet, and the development of life, and leads us eventually to the critical role of water in the first civilisations that we know of, circa 5,000 BC.

What I had not fully appreciated is the profound extent to which control of water – via the construction of dams and irrigation structures – was at the base of all of the activities of these civilisations. And that loss of control – either via floods or drought or conflict – led to the collapse of societies, over and over again.

The second age of water – the age in which we are now living – is the age in which we ‘mastered’ fresh water. We can now control the flow of water from mountains to the sea, and we can ‘mine’ water from deep underground. And we know how to create potable water almost anywhere on Earth. And yet after perhaps 150 years of mastery, we find ourselves in a very difficult place.

Most critically, despite the UN declaring water to be a fundamental human right – with a nominal target of 50 litres per day – millions of people on Earth still lack basic facilities for drinking and hygiene.

Click on Image for a larger version. Based on weekly meter readings, the graph shows the household usage of water for myself and my wife is on average around 100 litres per person per day.

Additionally, and I don’t need to tell this to UK readers, many of our rivers and water courses are polluted to the point where ecosystems have been damaged.

Perhaps the defining feature of the second age of water is that we have treated water as being “ours” and considered any water which is not captured or used to be wasted or ‘lost’.

And worldwide we have mined “fossil” water collected in aquifers over thousands of years to create agricultural systems that have flourished for a few decades, but which are – literally – unsustainable. If we run out of almost any other substance, we can find a substitute, but there is no substitute for water.

The third age of water is the age which Gleick believes we are entering, and age in which we truly value water as the unique element around which all ecosystems are constructed. Some features of this age are:

• Reduction of the amount of water that we use, domestically, industrially and agriculturally – but with no reduction in the utility we extract from the water.
• Valuing potable water for the wonderful product that it is and using ‘grey’ water for many of the functions for which we currently use potable water.
• Valuing the ecosystems within which all life exists, even to the point of giving rivers and ecosystems legal representation. Already, the US is removing dams to allow the slow re-building of natural water courses, and wetland restoration projects are underway world -wide.

I found the book by turns educational and inspiring. Although hearing of the phenomenal degradation left over from the second age of water, I feel that we have now universally accepted that it’s generally a bad thing when rivers catch fire. [Note added: Randy Newman wrote a song about one of the better known river fires]

As I was reading the book reports were unfolding of the appalling behaviour of Thames Water, the company that supplies my own water. And I was reminded that water is still of fundamental importance and that as in the civilisations of Early Mesopotamia, kingdoms could fail if water was not well-managed.

Water & Dust 

As regular readers will know, I am personally immersed in issues around our Climate Crisis. And I try to avoid becoming too involved in our other ongoing ecological crises – things can get very depressing! But together these books have raised my consciousness without getting me down too much. The Three Ages of Water in particular sets out a very positive and achievable agenda for change.

The Gas Man Cometh… for the last time

Friends, today was a special day for me. Today, the gas man came and disconnected my house from the gas grid. We haven’t used any gas for a year now – but being physically disconnected from the grid just feels sooooo good.

The gas grid

The gas grid is an international network of pumps and pipes constructed on a scale which is hard to grasp. In extent, it sprawls across Europe – take a look at this astonishing map. And locally, it extends into most individual dwellings in the UK.

When I consider the astonishing magnitude of the decades-long endeavour required to construct such a network, two thoughts occur to me: one depressing and the other uplifting.

Depressing thought

Depressingly, the people who have invested in this network will fight tooth and nail to keep extracting ‘value’ from it.  To these people – which probably includes my pension fund – the fact that the toxic gas they transport is leading to climate change is of no interest. In their perception, Climate Change is indeed an existential threat, but not because it is a threat to humanity. Instead they see Climate Change as an existential threat to their business model. They have no corporate interest in humanity.

The businesses that operate on this grid extract value from shipping stuff through it. And if governments restrict their right to sell methane – so-called ‘natural’ gas – because of its climate impacts, then they will see shipping hydrogen as an opportunity, despite its unsuitability for domestic heating.

Because they take no responsibility for the climate impacts of their business, they will use their power to lobby on behalf of using hydrogen or hydrogen-blended with methane. This is just an insidious attempt to try to continue to extract ‘value’ from their network: it is not based on rapidly reducing carbon dioxide emissions. Rather their aim is to prolong methane extraction which they will process, at a cost, to produce hydrogen.

The uplifting thought

The uplifting thought is that the colossal gas grid was constructed over decades, one project at a time. And this gives me hope. Because every new wind or solar farm, every new battery storage plant, every new electricity grid interconnection is another step in the construction of the infrastructure for renewable energy.

I believe that eventually we will look back with horror at the idea of delivering toxic, asphyxiant, explosive gas directly into people’s homes. Gas which people burned for cooking, emitting toxic irritant combustion products directly into their kitchens. And we will be appalled at the idea that we ever thought it acceptable to allow the average UK dwelling to emit more than  two tonnes of carbon dioxide every year: TWO TONNES of a gas which is changing the climate of Earth.

Friends, the future is coming, one gas-meter-removal at a time.

Gas and Gaslighting

Click on image for a larger version. BBC News stories detailing gas explosions this autumn: See end of article for links.

Friends, welcome to 2023.

I would have liked to start the year talking about something positive, but I can’t!

Over the Christmas break it struck me just how astonishing it is that we still allow homes to be heated by burning methane gas.

And we even build new homes incorporating this deadly and disgusting technology.

In case you didn’t know:

• Over 100 people a year in the UK die from carbon monoxide poisoning, mainly arising from poorly-maintained gas-burning equipment.

Click on image for a larger version. Graph showing data from the Office for National Statistics on the number of people killed each year from carbon monoxide poisoning (link).

• Even when gas-apparatus functions correctly, gas cookers emit toxic fumes into the homes of people who cook with gas. It is likely the highest exposure to mixed oxides of nitrogen (NOX) that you will experience anywhere in the UK is not by a roadside, but in a kitchen.

Click on image for a larger version. While cooking with gas in this US household, NO2 levels rose to almost 300 ppb. This figure is modified from the linked article.

• And on top of it all, every year gas causes more than 300 explosions in the UK, killing or maiming around 100 people each year.

Click on image for a larger version. There are over 300 fires involving gas and an explosion every year. About 100 of these incidents result in a casualty or a fatality (Data Source).

• And on top it all again, burning it emits tonnes of carbon dioxide, a gas which is destabilising the climate on which we depend.

So how is it that we tolerate such a technology? Why are we not outraged?

Gaslighting

Friends, we are being ‘gaslighted‘ by the Gas Industry.

Gaslighting – as Wikipedia puts it – is a term that:

…”may also be used to describe a person (a “gaslighter”) who presents a false narrative to another group or person, thereby leading them to doubt their perceptions and become misled, disoriented or distressed. Often this is for the gaslighter’s own benefit.

The gas industry – and the media it influences – suggest that the deaths and appalling climate impacts of burning gas are in some way ‘normal’ and ‘acceptable’.

Because we are familiar with gas, they propagate a false narrative that ‘burning gas’ is somehow ‘safe’, ‘natural’, ‘warming’ and ‘friendly’.

To understand how shocking and deceitful this really is, try the following exercises:

• Imagine that Wind Turbines killed more than 100 people a year.
• Imagine that Heat Pumps killed more than 100 people a year.
• Imagine that Solar Panels killed more than 100 people a year.

Do you think there would be media outrage? Of course there would! But with gas – these consequences are literally just ignored.

The Reality

The reality is this: gas is a filthy polluting technology and burning gas damages our climate, our health, and kills over 100 people a year in the UK alone, as well causing 300 explosive fires per year.

I urge you not to be misled into thinking that gas is anything other than a toxic mistake. If you can, I urge to eliminate gas appliances from your life.

BBC News Story Links

• 10 dead in Jersey
• Critical Injury in Evesham
• Barnsley Explosion
• Gas Canister Explosion in Glasgow
• Nottingham Gas explosion
• Four year-old girl killed in London
• Man dies in Scotland

 

2022 to 1978: Looking Back and Looking Forwards

Friends, it’s been two years since I retired, and since leaving the chaos and bullying at NPL, retirement has felt like the gift of a new life.

I now devote myself to pastimes befitting a man of my advanced years:

• Drinking coffee and eating Lebanese pastries for breakfast.
• Frequenting Folk Clubs
• Proselytising about the need for action on Climate Change
• Properly disposing of the 99% of my possessions that will have no meaning to my children or my wife after I die.

It was while engaged in this latter activity, that I came across some old copies of Scientific American magazine.

Last year I abandoned my 40 year subscription to the magazine because it had become almost content free. But in its day, Scientific American occupied a unique niche that allowed enthusiasts in science and engineering to read detailed articles by authors at the forefront of their fields.

In the January Edition for 1978 there were a number of fascinating articles:

• The Surgical Replacement of the Human Knee Joint
• How Bacteria Stick
• The Efficiency of Algorithms
• Roman Carthage
• The Visual Characteristics of Words

and…

• The Carbon Dioxide Question

You can read a scanned pdf copy of the article here.

This article was written by George M Woodwell a pioneer ecologist. The particular carbon dioxide question he asked was this:

Will enough carbon be stored in forests and the ocean to avert a major change in climate?

The article did not definitively answer this question. Instead it highlighted the uncertainties in our understanding of the some of the key processes required to answer the question.

In 1978 the use of satellite analysis to assess the rate of loss of forests was in its infancy. And there were large uncertainties in estimates of the difference in storage capacity between native forests, and managed forests and croplands.

The article drew up a global ‘balance sheet’ for carbon, and concluded that there were major uncertainties in our understanding of many of the physical processes by which carbon and carbon dioxide was captured (or cycled through) Earth’s systems.

Some uncertainty still remains in these areas, but the basic picture has become clearer in the subsequent 44 years of intense study.

So what can we learn from this ‘out of date’ paper?

Three things struck me.

Thing#1

Firstly, from a 2022 perspective, I noticed that there are important things missing from the article!

In considering likely future carbon dioxide emissions, the author viewed the choices as being simply between coal and nuclear power.

Elsewhere in the magazine, the Science and the Citizen column discusses electricity generation by coal with no mention of CO2 emissions. Instead the article simply laments that coal will be in short supply and concludes that:

“There is no question… coal will supply a large part of the nation’s energy future. The required trade-offs will be costly however, particularly in terms of human life and disease.

Neither article mentions generation of electricity by gas turbines. And neither makes any mention of either wind or solar power generation – now the cheapest and fastest growing sources of electricity generation.

From this I note that in it it’s specific details, the future is very hard to see.

Thing#2

Despite the difficulties, the author did make predictions and it is fascinating from the perspective of 2022 to look back and see how those predictions from 1978 have worked out!

The article included predictions for 

• The atmospheric concentration of CO2
• CO2 emissions from Fossil Fuels

Click on image for a larger version. Figure from the 1978 article by George Woodwell. The curves in green (to be read against the right-hand axis) shows two predictions for atmospheric concentration of CO2. The curves in black (to be read against the left-hand axis) shows two predictions for fossil fuel emissions of CO2. In each case, the difference between the two curves represents the uncertainty caused by changes in the way CO2 would be cycled through (or captured by) the oceans and forests. See the article for a detailed rubric.

The current atmospheric concentration of carbon dioxide is roughly 420 ppm and the lowest projection from 1978 is very close.

The fossil fuel emissions estimates are given in terms of the equivalent change in atmospheric CO2, and I am not exactly sure how to interpret this correctly.

Atmospheric concentration of CO2 is currently rising at approximately 2.5 ppm per year, and roughly 56% of fossil fuel emissions end up in the atmosphere. So the annual emissions predicted for 2022 are around 2.5/0.56 ~ 4.5 ppm /year, which is rather lower than the lowest prediction of around 6 ppm/year.

The article also predicts that this will be the peak in annual emissions, but that has yet to be seen.

The predictions did not cover the warming effect of carbon dioxide emissions, the science of which was in the process of being formulated. ‘Modern’ predictions can be dated to 1981, when James Hansen and colleagues published a landmark paper in Science (Climate Impact of Increasing Atmospheric Carbon Dioxide) which predicted:

A 2 °C global warming is exceeded in the 21^st century in all the CO₂ scenarios we considered, except no growth and coal phaseout.

This is the path we are still on.

From this I note that the worst predictions don’t always happen, but sometimes they do.

Thing#3

The final observation concerns the prescience of the author’s conclusion in spite of his ignorance of the details.

Click on the image for a larger version. This is the author’s final conclusion in 1978

His last two sentences could not be truer:

There is almost no aspect of national or international policy that can remain unaffected by the prospect of global climatic change.

Carbon dioxide, until now an apparently innocuous trace gas in the atmosphere may be moving rapidly toward a central role as a major threat to the present world order.

 

Heating Degree Days:4:Three numbers you need to know about your home

Friends, after the previous three posts (1, 2, 3) about Heating Degree Days, you may be wondering:

• Is Michael OK? He seems to be obsessed with Heating Degree Days?
• Hasn’t he been keeping an eye on the COVID figures?

Well, I have indeed been focussed on Heating Degree Days, and in this short (!) article I would like to summarise why.

The Heating Degree Day (HDD) concept enables two calculations for numbers you really should know about your dwelling:

• It’s thermal leakiness: technically its heat transfer coefficient (HTC)
• The size of heat pump your dwelling requires.

When combined with an estimate for how good the insulation is, you will be in a great position to make rational choices about improving the thermal performance of your dwelling.

Here are the three calculations:

#1:Heat Transfer Coefficient.

How much does heating power does it take to make your dwelling 1 °C warmer?

The answer to this question is known as the Heat Transfer Coefficient (HTC) for a dwelling.

A first estimate of your HTC can be made by dividing your annual gas consumption (in kWh) by 57.3:

Note: This formula was revised on 21/3/2022 due to a typo in the original text.

This assumes your dwelling (flat or house) is in the southern half of the UK (i.e. South of Manchester) and that you set your thermostat to 20 °C.

• If you live between Manchester and Edinburgh, reduce your estimate of HTC by 10%.
• For each 1 °C above 20 °C that you set your thermostat, reduce the first estimate of HTC by 10%.
• For each 1 °C below 20 °C that you set your thermostat, increase the first estimate of HTC by 10%.

#2:Heat Pump Size.

How big a heat pump do I need?

It’s the question everyone wants an answer to!

A first estimate of the size of heat pump you require can be made by dividing your annual gas consumption (in kWh) by 2,900.

This assumes your dwelling (flat or house) is in the southern half of the UK (i.e. South of Manchester) and that you set your thermostat to 20 °C.

• If you live between Manchester and Edinburgh, increase your estimate of heat pump power by 10%.
• For each 1 °C above 20 °C that you set your thermostat, increase your estimate of heat pump power by 10%.

#3:Insulation

Do I need more insulation?

If your home is a house (rather than a flat), then you can assess how good your home is compared to the best possible as follows.

Divide your annual gas consumption (in kWh) by the floor area of all the floors in your home that live in i.e. include the loft if its part of the domestic space but not if it’s just used for storage.

• The best possible is < 15 kWh/m^2/year: this is the Passivhaus standard
• The best possible retrofit is < 25 kWh/m^2/year: this is the Enerphit retrofit standard
• The AECB retrofit standard is < 50 kWh/m^2/year.

My house was ~ 90 kWh/m^2/year before external wall insulation and triple-glazing reduced it to around 45 kWh/m^2/year. The only way to significantly improve on this would be with underfloor insulation and air-tightness work.

If the figure for your home is very much above 100 kWh/m^2/year then I would suggest you consider insulation work.

Summary

If you know these numbers – even approximately – for your home, then you will be in a position to make reasonable choices about what to do next.

Please bear in mind that all the figures are approximate. I can see ways in which they could be wrong by 10%, but I would be surprised if they were 20% wrong.

Estimating Rates of Air Change in Homes

Air flow in modern homes

Modern homes are built with low air leakage rates and then mechanically ventilated to keep the air ‘fresh’. To prevent heat losses associated with this air exchange, the outgoing ‘stale’ air is flowed through a heat exchanger to warm the incoming ‘fresh’ air.

However this Mechanical Ventilation with Heat Recovery (MVHR) is not suitable for many older homes – such as mine – which are too leaky.

My home has gaps between floorboards on the ground floor and the air can flow in and out easily through the underfloor void.

To seal my home to modern standards would require re-building the entire ground floor – adding insulation as one worked. One would then add MVHR to the newly-sealed house. This would be very disruptive, and so I have instead chosen to remain married.

So in my old house and many like it, heat losses from air flow are highly uncertain.

Wouldn’t it be great if there were some way to measure air flow in older homes which was cheap and convenient!

Measurement 

Air flow through a building is commonly characterised by the number of air changes per hour – ACPH. But how can this be measured if one doesn’t know where the air is coming in or going out?

This building wiki suggests:

Tracer gas measurement can be used to determine the average air change rate for naturally’-‘ventilated spaces’ and to measure infiltration (air tightness)’. To do this, a detectable, non-toxic gas is released into the space and the reduction in its concentration within the internal atmosphere is monitored over a given time period.’

By ‘tracer gas measurement’ the wiki means that a gas is released into the air at a known rate, and its concentration measured versus time. If the rate of production of tracer gas is known, then the final stable concentration allows one to work out the number of air changes per hour (ACPH).

• If the number of ACPH is small, the final concentration will be high.
• If the number of ACPH is high, the final concentration will be low.

What this wiki frustratingly fails to point out is that carbon dioxide is an ideal tracer gas and has been used for years for this purpose.

This essential fact is pointed out in the first paragraph of an outstandingly clear and authoritative paper from Andrew Persily and Lillian de Jonge.

Carbon dioxide generation rates for building occupants Persily A, de Jonge L. Indoor Air. 2017;27:868–879. https://doi.org/10.1111/ina.12383 . It’s also available with alternate formatting here.

The first line of the abstract is:

Indoor carbon dioxide (CO2) concentrations have been used for decades to characterize building ventilation and indoor air quality.

This surprised me because in all my reading about this subject in the UK I have never seen it mentioned. But then, in the first line of the paper itself, Persily and de Jonge point out just how old the idea is:

Indoor CO2 concentrations have been prominent in discussions of building ventilation and indoor air quality (IAQ) since the 18th century when Lavoisier suggested that CO2 build-up rather than oxygen depletion was responsible for “bad air” indoors.

The gist of their paper is a thorough review and examination of the factors which affect the rates at which human beings emit carbon dioxide. I won’t deprive you of the pleasure of reading the paper but factors discussed include:

• The ratios of fat, protein and carbohydrate in people’s diet.
• Age, gender and ethnicity.
• Body size and mass.
• Levels of activity.

The paper is very readable and I recommend it in the highest terms.

A worked example: my bedroom.

At night my wife and I sleep in a room which is about 7 m long, 3.5 m wide and 2.2 m high. So it has a volume of 7 x 3.5 x 2.2 = 54 cubic metres, or 54,000 litres.

There are no obvious draughts and I had no idea how many air changes per hour there were.

But overnight, the concentration of carbon dioxide rises from about 450 parts per million (ppm) characteristic of fresh air, and stabilises around 1930 ppm.

I can work out the number of air changes per hour ACPH using the formula below.

In this formula:

• The room volume in litres
  • In my case 54,000 litres
• c is the measured stable CO2 concentration in ppm
  • In my case 1930 ppm
• c₀ is the concentration of CO2 in ‘fresh’ air in ppm
  • In my case around 450 ppm
• 10^-6 is the scientific way of saying “divide by a million”
  • 1/1,000,000
• CO2 production rate is what Persily and de Jonge’s paper tells us:
  • For sleeping males over the age of 11, the answer is within 10% of 12.7 litres per hour.
  • For sleeping females over the age of 11, the answer is within 10% of 10.2 litres per hour.
  • So our joint CO2 production rate is about 23 litres per hour

Putting all those numbers in the formula……we find the rate of change of air is around 0.29 ACPH – with the answer probably being within 10% of that value.

Some other factors.

Persily and de Jonge’s paper is extraordinarily thorough and tackles some of the tricky problems about using this technique for estimating air flow in buildings.

Firstly, there is the question of the level of activity of the people in a particular space. The metabolic rate is generally measured in units of mets with 1 met being roughly the metabolic activity during sleep. Very roughly it corresponds to around 58 watts.

The paper has extensive tables showing the CO2 production rate in litres per second for different levels of activity of different sexes at different ages. (Remember to multiply these numbers by 3600 to convert them into CO2 production rate in litres per hour before using them in the formula above.)

Secondly, there is the wider question of which volume of air is relevant. My bedroom represents a small volume with well understood rates of CO2 production.

But is a CO2 meter placed in a ground floor room measuring the characteristic concentration of the room it is in, the whole ground floor, or the entire house? Resolving questions like this may take a few experiments, such as moving the meter around.

Additionally, the amount of CO2 generated in a house over a day may not be clear. For example, the number of occupants and their level of activity may be hard to determine.

Mi casa no es tu casa

The situations encountered in your home will be different from those in my home.

Nonetheless, if you are trying to assess air flow within your home, I would recommend that you consider using carbon dioxide measurements as part of your arsenal of measurement techniques.

I use two CO2 meters and can recommend them both:

• This one records onto a microSD card
  • https://www.amazon.co.uk/gp/product/B079L5VD7P/
• This one also measures particulates PM2.5 and PM10 but doesn’t record the results – you have to read it ‘live’.
  • https://www.amazon.co.uk/gp/product/B07DQRPM3Z/

Air Conditioning versus Air Source Heat Pump

Click for a larger version. Similarities and differences in how an air source heat pump (ASHP) or an air conditioning (AC) system warms a home. All the components inside the dotted green line are contained in the external units shown. A key design difference is whether or not the working fluid is completely contained in the external unit. See text for more details.

Regular readers will probably be aware that – having reduced the heating demand in my house – my plan is to switch away from gas heating and install an electrically-powered air source heat pump to heat the house and provide domestic hot water.

But next week I am also installing air conditioning, something which is traditionally not thought of as very ‘green’. What’s going on?

Why Air Conditioning?

I have two reasons.

My first reason is that, as you may have heard, the whole world is warming up! Last year it reached 38 °C in Teddington and was unbearably hot for a week. I never want to experience that again.

During the summer the air conditioning will provide cooling. But assuming the heating comes with good weather, the air conditioning will be totally solar powered, and so it will not give rise to any CO2 emissions to make matters worse!

My second reason is that in the right circumstances, air conditioning is a very efficient way to heat a house. That’s what this article is about.

Heat Pumps

Air Conditioners (AC) and Air Source Heat Pumps (ASHP) are both types of heat pumps.

In scientific parlance, a heat pump is any machine that moves heat from colder temperatures to higher temperatures at the expense of mechanical work.

Note: to distinguish between the general scientific idea of a heat pump, and the practical implementation in an air source heat pump, I will use abbreviation ASHP when talking about the practical device.

The general idea of a heat pump is illustrated in the conceptual schematic below.

As shown, the pump uses 1 unit of mechanical energy to extract two units of heat energy from air at (say) 5 °C and expel all 3 units of energy (1 mechanical and 2 thermal) as heat into hot water at (say) 55 °C.

Click for a larger version. Traditional representation of the operation of heat pump.

Heat pumps can seem miraculous, but like all good miracles, they are really just applied science and engineering.

A heat pump is characterised using two parameters: COP and ΔT.

• A heat pump which delivers 3 units of heat for 1 unit of work is said to have a coefficient of performance (COP) of 3.
• The temperature difference between the hot and cold ends of the heat pump is usually called ‘Delta T’ or ΔT.

Obviously engineers would like to build heat pumps with high COPs, and big ΔTs and they have used all kinds of ingenious techniques to achieve this.

But it turns out that heat pumps only operate with high COPs when the ΔT is small and when the heating power is low. There are two reasons.

• Firstly, the laws of thermodynamic set some absolute limits on the COP achievable for a given ΔT.
  • Most practical heat pumps don’t come close to this thermodynamic limit for a variety of mundane reasons.
  • The maximum COP for moving heat from 5 °C to 55 °C is 6.6.
  • The maximum COP for moving heat from 5 °C to 20 °C is 19.5.
• Secondly, in order to heat a room to (say) 20 °C, the hot end of the heat pump needs to be hotter than 20 °C.
  • Typically the hot end of the heat pump must be 5 °C to 10 °C warmer than the room in order that heat will flow out of the heat pump.
  • Additionally the cold end of the heat pump must be 5 °C to 10 °C colder than the external air in order that heat will flow into the heat pump.
  • The interfaces between the ends of the pump and the environment are called heat exchangers and designing ‘good’ heat exchangers is tricky.
  • A ‘good’ heat exchanger is one that allows high heat flows for small temperature differences.

So now we have seen how heat pumps are characterised, let’s see how heat pumps are used domestically.

Air Source Heat Pump (ASHP) versus Air Conditioner (AC)

The schematic diagrams  below show how a house is heated by an ASHP and an AC system. Both systems operate using a working fluid such as butane, which is ingeniously compressed and expanded. The details of this process are not the topic of this article so here I am glossing over the fascinating details of the device’s operation. Sorry.

Click for a larger version. How an air source heat pump (ASHP) warms a home. All the components inside the dotted green line are contained in the external unit shown. A key design feature is that the working fluid is completely contained in the external unit and heat is transferred to the central heating water by a heat exchanger.

Click for a larger version. How an air conditioner (AC) warms a home. All the components inside the dotted green lines are contained in either the external unit or the fan coil unit shown. A key feature is that the working fluid itself flows into the fan coil unit and heats the air directly.

We can compare the operation of the two systems in the table below.

Air Conditioner	Air Source Heat Pump
Air at (say) 5 °C is blown over a heat exchanger and evaporates the working fluid.	The same.
The working fluid is then compressed – that’s the bit where the work is done – and liquefies, releasing the captured heat.	The same.
The hot working fluid – now at ~30 °C then flows through a pipe to an indoor heat exchanger (fan coil unit) where air is blown over the pipe and heated to 20 °C.	The hot working fluid – now at ~60 °C then flows through a heat exchanger and transfers the heat to water in my central heating system at ~55 °C
No corresponding step	The 55 °C water then flows through a radiator in my room, heating the room by radiation and by convective heat transfer to air at ~20 °C.

Looking closely at the figures and table above, one can see that the operation of the ASHP and the AC system are broadly similar.

However the ASHP has to operate with a bigger ΔT (~55 °C versus ~25 °C) than the AC system, and also has to transfer heat through an extra heat exchanger.

Both these factors degrade the achievable COP and so for my application, the specified COP for an ASHP is just over 3, but for the AC system, it is just over 5.

In my well-insulated house, when the external temperature is 5 °C, I require typically 36 kWh per day of heating, equivalent to 1.7 kW continuous heating. I can achieve this in several ways:

• Using gas I must burn ~40 kWh of gas at 90% efficiency costing 40 x 3p (£1.20) and emitting 40 x 200 g = 8 kgCO2
• Using an ASHP with a COP of 3, I must use ~36 kWh/3 = 12 kWh of electricity costing 12 x 25p (£3.00) and emitting 12 x 200 g = 2.4 kgCO2
• Using an AC system with a COP of 5, I must use ~36 kWh/5 = 7.2 kWh of electricity costing 7.2 x 25p (£1.80) and emitting 7.2 x 200 g = 1.4 kgCO2
• Using a domestic battery and buying the electricity at night for 8p/kWh, I can reduce the cost of using an ASHP or AC system by a factor of 3 to £1.00/day or £0.60/day respectively.

[Note: In these calculations I have assumed that the carbon dioxide emissions per kWh are same for both gas and UK electricity (200 gCO2/kWh) which is roughly correct for 2021]

So using an AC system I should be able to achieve domestic heating with lower carbon dioxide emissions than an ASHP.

My plan

In my case I need to heat water for my home to 55 °C for use in showers and basins. So I need an ASHP for that. And since I already have radiators in every room, hooking up the ASHP to the radiator circuits is smart double use.

The AC system I am having installed will have 1 external unit and 2 internal ‘fan coil units’. One unit will be in my bedroom (a sheer indulgence) and the other will be high up on the stairs, allowing air to be either blown down to the ground floor where I hope it will circulate, or blown towards the bedrooms.

My hope is that, when used together, the AC system (COP~5) will reduce the heating output required from the radiators so that I can reduce the flow temperature of the water from 55 °C to perhaps 40 °C. This reduces their heat output, but increase the COP of the ASHP from 3 to perhaps 4.

The main difficulty that I foresee is the extent to which the AC heating will actually permeate through the house and so reduce the amount of heating required by the ASHP.

So I am not sure how much heating will be required by the ASHP acting through the radiators, and whether the radiators will work at low flow temperatures. It is possible I might need to replace a few radiators with ones which work better at low temperatures.

It is not at all obvious that this plan will actually work at all – but I think it is worth a try.

Kit

The air conditioning I am having installed is a Daikin 2MXM40 multi-split outdoor unit with two FTXM25 indoor air units. (Brochure)

The model of heat pump I will have installed is a Vaillant Arotherm plus 5 kW. It can supply up 5 kW of heating at 55 °C with a COP of 3  – i.e. it will use just 1.6 kW of electrical power to do that – and heat water to 55 °C. Water storage will be a 200 litre Unistor cylinder. A brochure with technical details can be found here, and a dramatic video showing the kit is linked at the end of this article.

When I have come to terms with how much money I am spending on this, I will share that information. But at the moment it hurts to think about it!

Anyway: the adventure begins next week!

 

Battery Day: One month on…

Click for larger version. The graph shows daily electricity drawn from the grid (kWh). Before the solar panels were installed average usage was 10.9 kWh/day. After the solar panels were installed this fell by a couple of kWh/day. After an increase over Christmas when our son returned, we were back to normal. In the last month the solar electricity generated on the lengthening days have reduced the electricity drawn from the grid. Since the battery was installed a month ago, we have not drawn any electricity from the grid, but daily usage has been unchanged.

Friends, I have been so busy I have been forgetting to blog! So I thought I’d just post a quick update on the Powerwall Installation.

One month on now and we are still “off grid”: we haven’t used a unit of grid electricity for a month. But as the graph above shows, our usage has continued unchanged.

My experience has convinced me that solar installations should all be accompanied by a battery of some sort.

As I have mentioned before, from a national perspective, local batteries are a bad idea: they consume energy.

But from from a user’s perspective, they allow me to benefit from my investment.

And the prospect of not using any grid electricity until maybe September leaves me giddy.

Longer term goals

Click for a larger version. Summary performance of the battery system on 17th April 2021. The battery supplies the house overnight, and is then re-charged by solar generation in the morning. When the battery is full (around 1 p.m.) solar generation is exported to the grid. In the evening the battery takes over again as the solar generation dwindles.

We haven’t experienced a summer of solar power yet, but the longer days are amazing – even in April!

On sunny days the panels generate over 20 kWh of electricity, and the battery is full in the middle of the day.

Once the battery is full, the system exports electricity to the grid in the afternoon and we don’t need to use the battery until perhaps 7 p.m.

These exports are an important part of our plan.

In the winter, we will need to buy electricity from the grid – especially as next winter we will be using a heat pump for heating and hot water.

But ideally we hope the exports of electricity in the summer should match imports in the winter.

Looking at the cumulative generation and export from the system (below), and remembering that exports should be larger in the summer, it looks like yearly exports might just reach 1000 kWh – much more than I had expected.

This would be enough to ‘balance’ 100 days of 10 kWh per day in the winter, assuming no solar power. But even in mid-winter there is typically 2 or 3 kWh per day and so we might just be able to achieve year-round balance.

Click for a larger version. Cumulative generation and export of solar electricity. The dotted green line was my initial guess for generation through the year.

Battery Day: First Results

Me and my new Tesla. This unit contains 13.5 kWh of battery storage along with a climate control system to optimise battery life. We have placed it in the porch so that (when visits are allowed again) everyone who visits will know about it!

Last September, Tesla held their ‘Battery Day‘ during which they unveiled their road map towards cheaper, better, batteries.

Not to be outdone, last Monday VW held their own ‘Battery Day‘ during which they unveiled their road map towards cheaper, better, batteries.

And last Thursday was my own battery day, when Stuart and Jozsef from The Little Green Energy Company came and installed a Tesla Powerwall 2 at Podesta Towers in Teddington. I was (and still am) ridiculously excited.

I am still evaluating it – obviously – but here are a couple of notes.

How it works

The system has two components. An intelligent ‘gateway’ that monitors loads and supplies, and a climate-controlled battery storage unit.

Click for a larger version. The left-hand graphic shows how AC power enters our house, and how DC power generated by solar panels is linked to the grid. When the Solar PV is sufficient ,power is exported to the grid. The right-hand graphic shows how the TESLA ‘gateway’ device monitors the solar PV, domestic loads and battery status and intelligently decides what to do.

The gateway (and the battery) are electrically situated between the electricity meter and all the loads and power sources in the house. So all energy enters or leaves the battery module as AC (alternating current) power.

But its internal batteries must be supplied with DC (direct current).

This makes it ideal for storing power from the AC grid, but less than ideal for storing the DC current generated by solar PV panels.

One might have expected that a device designed to store solar power might intrinsically operate using DC and indeed, some battery systems – positioned between the solar PV and the inverter – do this.

So the choice to place the Powerwall™ where it is, is a compromise between the extra functionality this location offers – it can back up the entire house – and the inefficiency of storing solar PV which is first converted to AC by the inverter, and then re-converted back to DC by the Powerwall. The support document states that the conversion from AC to DC and back to AC has 90% round-trip efficiency.

The photograph below shows the gateway installed under the stairs in our house.

Click for a larger version. The Tesla ‘Gateway’ installed in our house. The unit is positioned in between the electricity meter and all the domestic loads. The black conduit leads under the floor to the battery which is installed in the porch.

Control

The system is controlled by an app which is – frankly – mesmerising. It shows how electrical power flows between:

• the grid,
• the battery,
• our home, and
• our solar panels

Click for a larger version. Screenshots from the app at various times yesterday.

There is less room to adjust the parameters of the system than I had anticipated. This appears to be because, in exchange for a guarantee that the battery will retain at least 80% capacity (10.8 kWh) after 10 years, one is required to relinquish detailed control to the Tesla Brain.

Through a built in network connection, the device is in constant touch with Tesla who monitor its performance and can detect if it is abused in some way. I am not sure how I feel about that – but then guaranteed long-term performance is certainly worth something.

One feature of this relinquishing of detailed control concerns ‘time-of-use’ tariffs. I anticipate that – especially in winter – I will need to charge the battery overnight on cheap rate electricity.

The system supports this mode of operation but is not yet operational. Apparently it needs to study the patterns of household use for 48 hours before being enabled.

When operational, one gives the system general instructions and then allows it to choose when, and by how much, to charge. There is for example no way to force the battery to charge to 100% on command.

In practice I suspect it will be fine, but at the moment it still feels a little weird.

Performance on Day#1

The simplest way to show how the Powerwall™ works is by looking at the data which the ‘App’ makes available.

The first graph shows the household demand through the day. It’s fascinating to look at this data which has 5 minute and 0.1 kW resolution. The metrologist in me would like more – but in honesty, this is enough to understand what is happening.

Click for a larger graph. See text for details.

Now we can look to see how that demand was met. Overnight, we relied mainly on the grid.

Click for a larger graph. See text for details.

The battery could have supplied this overnight electricity, but it had been set to hold a reserve of 16% of its capacity (~2 kWh) in case we required backup after a power cut. We have lowered that setting now because, thankfully, power cuts are rare in Teddington. The battery drew power from the grid overnight in two short periods to maintain this reserve.

Additionally, at the end of a sunny day in which the solar PV filled the battery, there was brief period where we returned electricity to the grid.

During the day – which was very sunny 🙂 – the household electricity demand was met by the electricity from the solar panels.

Click for a larger graph. See text for details.

Without the battery, most of this 16.91 kWh of electricity would have been sent to the grid. But now only a tiny fraction was returned to the grid, most of it being captured by the battery – see below.

Click for a larger graph. See text for details.

The graph above shows the battery maintaining its reserve charge at night, and then charging from the solar PV during the day. At peaks of household demand, the charging is paused. At around 16:00, the battery was briefly full, and shortly thereafter it began discharging to meet household demand.

As I write this at 1:00 p.m. on the day after the day shown (a rather dull day 😦 ), the battery is 56% full and charging.

The graph below shows all the above curves together.

Click for a larger graph. See text for details.

Overall

The Powerwall system is an object of wonder. It is beautifully engineered and miraculous in its simplicity.

It transforms the utility of the solar PV allowing me (rather than electricity companies) to benefit from the investments I have made.

I will post more about the performance in terms of cost, electricity and carbon dioxide when I have more data.

But for the moment I will just thank Jozsef and Stuart from The Little Green Energy Company for their professionalism and attention to detail. And ‘No’. I am not being paid to say that – quite the opposite!

Stuart and Jozsef from The Little Green Energy Company. You can’t see it, but they assure me they were both smiling. Click for a larger version

 

Sometimes I find it hard to like EDF

Click for larger version. EDF wrote to me today to say they are increasing the price of ‘night rate’ electricity by 73.7%.

Energy is a wonderful thing. But sometimes it can be hard to like the companies which sell it to us…

…especially when they increase the price of their product by 73% overnight!

As regular readers will know, since 2018 I have been working hard to reduce my household energy consumption and the concomitant carbon dioxide emissions.

My 3-step plan has been:

1. Reduce household heating requirement with insulation and triple-glazing.
2. Switch from gas heating to electrical heating with a heat pump.
3. Use solar panels and a battery to generate low-emission electricity and reduce the cost of switching to electrical heating.

Part#1 is complete: winter is not yet at an end, but heating demand appears to about 50% lower.

Part#2 is underway and I hope to have a heat pump installed this summer. But electrical heating is more expensive than gas heating.

Part#3 is underway: the solar panels are performing well and a battery should be installed this Thursday. The battery should allow me to use mainly my own solar electricity, or EDF off-peak electricity for most of the year.

I carried out extensive modelling of the effect of varying patterns of electricity consumption and compared different ‘tariffs’.

• Domestic Batteries: Purchase decisions and realistic models (1st February 2021)
• Thinking more about batteries (9th January 2021)
• Thinking about domestic batteries (3rd January 2021)

I had based my costings on the fact that the night rate for electricity would be about 5p/kWh and day rate would be about 25p/kWh. Of course I knew these costs could vary over time.

Nonetheless, it would be an underestimate to say that I was ‘disappointed’ when EDF wrote to me this morning to say that price of night time electricity was to rise from 4.99 p/kWh to 8.67 p/kWh…

…a 73% rise!

Like I said, sometimes it can be hard to like the companies which sell us energy.

Switch!

I am thinking about it.

But switching is, in my opinion, a distraction. It is a way of distracting us ‘fish’ from the fact that we are in a ‘barrel’ and at the mercy of the confusopolists.

 

Previous articles about the house.

2021

• Domestic Batteries: Purchase Decisions and Realistic Models (1st February)
• In the Bleak Mid-Winter (19th January)
• Domestic Batteries: Thinking More about Batteries (9th January)
• Domestic Batteries: Thinking about Domestic Batteries (3rd January)
• External Wall Insulation: Day-by-Day Analysis (1st January)

2020

• External wall insulation: How well is it working? (23rd December) after a month or so
• External Wall Insulation: How well does it work? (16th November) just after installation.
• The Beginning of the External Wall Insulation Project (15th October)
• Passivhaus? Or Michaelhaus? (August 26th)
• Measuring the thermal conductivity of insulation (August 24th)
• I am becoming an insulation bore. (August 21st)
• My House: comparing models and measurements (July 28th)
• Estimating the expected thermal performance of my house (July 22nd)
• Be Constructive! (July 5th)
• House of Shame#1 (June 24th)

2019

• The OTHER front in the fight against climate change (September 22nd)
• Why does heating my house require 280 watts per degree Celsius above ambient? (August 18th)
• What it takes to heat my house: 280 watts per degree Celsius above ambient (August 16th)
• Should I still be using gas? (May 6th)