14 Nov 2020

Are heat pumps the way forward?

There is a lot of talk about heat pumps. Some tout them as the future of home heating, a surefire way of combatting our carbon intensive heat habit. There's no doubt it's a big problem, as this diagram clearly shows, but are heat pumps an easy fix?

First things first. What exactly is a heat pump? The clue is in the name. Heat pump. Unlike every other form of heating we have ever used, a heat pump doesn't actually produce heat, it shifts it. It takes the heat out of a large body of stuff (be it the air around us, the ground underneath us or some body of water nearby), and shifts this heat into a much smaller body of stuff, either air or water inside the house. 

That is the magic of the heat pump. 


Another way of looking at this is through the medium of colour. Imagine you had a large square drawn on a sheet of white paper and that this large square is filled evenly with very pale pink colour. It took just three drops of red inkwash to get that pale pink colour. Next to the large square is a small empty square, about a third of the size. If we were to somehow suck the red inkwash out of the large square and pour it into the small square, the three drops of red inkwash would be enough to turn the small square bright red, whilst the large square would now appear to be empty. We haven’t made any new red inkwash, we have simply moved it from one square to another, whilst increasing its concentration. The pale pink colour in the large square is gradually replenished by more red ink wash (incoming solar radiation): in this way, heat pumps are (mostly) a renewable technology.


Heat pumps are not new. They have been around almost as long as electricity has been wired into peoples’ homes. And heat pumps don’t just make small spaces hotter: the heat can flow the other way, in order to make spaces colder. Think of the domestic refrigerator. Every home you have ever lived in already has a heat pump working away in the background, at the back of the fridge. The same technology underlies the world of air conditioning as well. It’s a huge worldwide industry. 


But what concerns us here is the home heating aspect of it. It’s a technology that has energy-efficiency burned into it and, used well, it can achieve enormous energy savings with the potential to make the switch to electric heat a lot more palatable.


The key point of interest to engineers here is to measure the level of energy efficiency. This is conventionally expressed as the ratio of the amount of heat being pumped into a house set against the amount of electric energy required to run the heat pump. 


This ratio (heat in:power used) is known as the Coefficient of Performance or COP, and when you start getting versed in the world of heat pumps you will hear the term COP (or sometimes SCOP, where the S stands for Seasonal) used a lot. The higher the COP the better; it means the heat pump is more efficient and this makes it both cheap and green to run. 


The downsides for heat pumps is that they are relatively expensive to install and that they are electrically powered. Whilst electricity is now less carbon intensive than gas, and appears to be on course to become nearly carbon-free over the coming decades, domestic supply is currently three to four times the cost of gas.

If you want British consumers to switch over from gas boilers to heat pumps, you really need the heat pump to be at least three to four times more efficient in order to cancel out the pain of higher fuel bills. So if you manage to get a COP of 3 or 4 (which is technically quite possible), then your new electricity fuel bills will be comparable with your old gas bills. Get your COP higher than 4 (unlikely, but it has been known) and you will have the most thrifty heating system imaginable. Not only greener, but cheaper to run.

So why not just buy a heat pump with a very high COP? This is where it starts to get complicated. Unlike a gas boiler, which simply responds to a command to “Burn, baby, burn”, the actual performance of a heat pump is down to what you demand from it. Ask it to lift the internal water temperature by 30°C, and it will turn in a five-star performance with a COP way over 3. However, ask it to lift the water temperature by 60°C, and it will be a very different story. The same heat pump will be performing with a much lower COP and the cost of your home heating will appear to be astronomical. In fact, for every 1°C temperature increase you ask from your heat pump, the COP falls by 3%. The lab tests used to advertise the relative performance of heat pumps are all conducted at low temperature lifts.


So how much work will you require from your heat pump? 30°C lift (success) or 60°C lift (failure)?


There are some big variables to consider here.  Let’s look at the two most important.

The input temperature

The warmer the heat source, the less work the heat pump has to do, and therefore the more efficiently it runs. Not all heat pumps are the same. Air-source heat pumps (ASHP), as their name suggests, draw their heat from the surrounding air and they therefore have to deal with a very wide temperature range. In summer, they can be immensely efficient but homes don’t need space heating in summer. In mid-winter, when the air temperature falls below zero, they are starting with one arm tied behind their back and their efficiency (COP) falls substantially. In contrast, ground source heat pumps (GSHP) draw their heat from below ground where temperatures are much more even throughout the year. It follows that, over the course of a year, GSHPs are more efficient than ASHPs. The downside is that GSHPs are much more complicated and expensive to install.

The output temperature

The two key factors affecting your heating demand are space heating and domestic hot water. Space heating is conventionally delivered via radiators, or occasionally underfloor heating. The water flow temperature in your radiators can be as high as 70°C, which is enough to put a huge strain on any heat pump. The solution may lie in fitting bigger radiators capable of working at lower temperatures. Underfloor heating is designed to work at around 40°C  and therefore makes a good partner for heat pumps, but unfortunately very few homes in the UK have underfloor heating systems. 


Domestic hot water is another kettle of fish. Most UK homes, at least most small ones, now use a combination boiler (aka a combi) to supply their heating needs. A combi heats hot water instantly with a quick blast of gas. Heat pumps are unable to do this: they work by supplying a steady trickle of heat, so hot water for the tap or shower has to be sourced from a storage tank such as a cylinder.  


This is a problem for many homeowners in that combi-heated homes don’t have any hot water storage, nor do many of them even have space for hot water storage. If you are very desperate, you can probably find a place somewhere in your home for a hot water tank, but it will involve lots of plumbing and probably carpentry as well, to create an airing cupboard. 


If you are building a new home, these issues won’t be a problem. Hot water tanks, underfloor heating, good insulation, efficient glazing: all these things are easy to build in. But if we wish to make our existing housing stock all electric, we have some major issues to address here if we want to switch over to heat pumps. We have developed a housing stock that is based largely on high-temperature, gas-fired instant heating. Weaning us off this will not be easy.

Good installers know all this and will be able to advise you as to whether your home is heat pump ready or even heat pump compatible. Cowboys will just sell you a heat pump and let you suffer the consequences - cold homes with high fuel bills.


If you don’t have a heat pump ready home, and you are not inclined to undertake the upgrades required to do this, there are hybrid options available. Typically this might be keeping your gas boiler and using it for domestic hot water and for very cold days in winter when a heat pump will struggle, but using a heat pump for the main bulk of your space heating requirements. As space heating typically makes up something like 80% of your homes overall heating bill, such a solution will make quite a difference to your carbon footprint, but it’s unlikely to be any cheaper to run. Hybrid solutions can also be combined with solar thermal or PV which will further reduce your carbon footprint. But you won’t be on course for a fully electric home whilst you still have a fossil fuel boiler as a back up.

If you want to do that, you can always fit an electric boiler. They even make electric combis, but they are underpowered when compared to their gas-fired cousins. And of course, they will cost three to four times as much to run. Not really a very enticing option.



The government is indicating that it wants us to switch to heat pumps for all new homes within a few years. Technically this should be no problem, as new homes can be designed to be heat-pump ready. The problem resides in what we do with the existing housing stock, something like 25 million homes heated by gas or oil which won't take easily to a heat pump without a fair bit of adaptation. This is what needs to be the focus of policy over the coming years. The switch over to heat pumps isn't going to happen without a few carrots (incentives) and sticks (taxes on fossil fuels), and how these issues are approached by our government will be a measure of how serious they are about de-carbonised home heating. 

The only document they have published so far on this topic, the Future Homes Standard, is a very tepid dish indeed, which will have very little impact on the rate of heat pump deployment in the retrofit sector.








21 Apr 2020

On waste and recycling

I’ve always felt that it is a good idea to have a waste strategy for every home I have lived in. Something just a bit more sophisticated than sticking everything in the bin, which is what used to happen. Over the years, it is something which we as a country have been encouraged to do as well. Whereas when I was a child there was one bin, now there are at least three and we are expected to sort the waste we produce into the correct bins.

The first UK bottle bank was opened in 1977 (in Barnsley, naturally). Things started slowly but got moving on a national level in the 1990s. Then, in 2003. the Household Waste Recycling Act was passed. It required every local authority in England to provide each household with a separate collection of at least two types of recycled material by 2010. The age of the wheelie bin was well and truly with us and it seemed like we were entering a phase where the country would stop dumping everything in landfill and start to get to grips with all the waste we generated.

But looking at it now, it seems that perhaps our hopes were misplaced. It turns out an awful lot of our waste was simply being loaded onto vast container ships and sent to China where they did heaven knows what with it. In 2018, China said enough is enough since when we have finally had to confront the fact that, though we collect all this waste, we don’t really have much idea what to do with it. For whilst local authorities are mandated to collect different waste streams, they are free to decide what goes into which stream and they are under no obligation to see that any of it actually gets recycled.

So confusion reigns. Each local authority has its own rules and the rules themselves are often most unclear. Take the vexed example of plastic packaging: we are swimming in the stuff. But it turns out that some of it is recyclable whilst other stuff isn’t. So which is it? As you stand over your kitchen bins with some plastic packaging in hand, do you put it into the black bin for landfill or the blue bin for recycling? Or perhaps your bins are a different colour — they couldn’t even decide on that.

If you are like me, you hesitate then hazard a guess. I sometimes even refer to the council website to see what goes where. But too often I draw a complete blank as the thing I am trying to dispose of isn’t mentioned. Wheareas once upon a time I used to pride myself of recycling almost everything and hardly ever having to put something in the landfill bin, I now realise I was being hopelessly optimistic. 

Recycling itself is run as a market operation. If there is a market for the material you throw away, it can be separated, bundled up and sent of for reuse. All well and good. That’s what you hope will happen. But if the market price drops below what it costs to do the recycling, then what used to get sent to China now ends up back in landfill or in the incinerator, which is where the problem started.

Have we really spent 30 years deluding ourselves about recycling? In that time it’s become the mark of a good citizen that you take your recycling seriously, trying to send very little to landfill. But for all the effort we’ve made in our kitchens and bin stores, it appears that what actually gets recycled is pretty minimal, and it’s not even increasing. The recycling bin labelled "The Chinese will sort it out" has been closed for good.

8 Mar 2020

Wine bottles

I've drunk wine all my adult life. Just how much, I hate to think.  It's an infectious habit for sure, one which I share with probably half the UK population. It seems, from a trawl of the stats, that we consume something like 25 bottles each per annum. Seeing as half the population doesn't touch the stuff, that must be about a bottle a week for those of us that do.

But this blog post isn't about the wine we drink, but the way we drink it, which is almost always poured from glass bottles. Wine as a product is around 40% packaging by weight, which is incredibly wasteful, and would shame most other food and beverage suppliers into extinction.

A typical bottle of wine is 75cl by volume: the wine itself weighs about the same as water (i.e.750gms), the bottle anywhere between 500 and 600gms. And the great bulk of the wine we buy is bottled at source, which may well be on the other side of the world. Australia, New Zealand, Argentina, Chile, South Africa, California — we just love their wines. But what a waste it is to ship their wines in heavy glass bottles. Not that it's much better from nearer European vinyards — it is still a very strange way to organise a business based on the pleasure of drinking.

So why is wine placed into glass bottles? The short answer is that it is tradition. We consumers like to see a nice bottle with an attractive label, and to most of us the pleasure of drinking wine starts when we handle the bottle unopened in the shop. Ever wondered why there are just so many wine varieties in a supermarket? The idea here is that you are making a personal choice that says something about you, your wallet and your taste, something that can't be said for Diet Coke or any other soft drink.

The producers also like it because bottling at source gives them some protection over the content. As much as 37% (by volume) of the international wine trade is done in bulk shipping containers, to be eventually bottled in the country of consumption. But by value, that 37% volume reduces to just 11% in value, which shows you that bulk wines are really aimed at the bottom end of the market. Put another way, the average bottle of table wine enters the country of consumption at €2.84/bottle: with bulk wines, this figure per notional bottle reduces to just €0.60, a quarter as much.

Which begs the question, why don't quality producers think about BiB (Bag in a Box)? It's been available as a method of supplying wine for over 30 years but it only really covers the bottom end of the wine market, except in Sweden, where premium wines are widely available this way. There is nothing intrinsically difficult about pouring wine into bags, and it stores much longer than opened bottles. Only the very finest of wines, bought for their ageing potential, actually require a glass container: 99% of the wine market is designed to be drunk within a few weeks or months of purchase.

And the packaging? Instead of 500 to 600gms of glass per bottle, the equivalent weight in BiB is no more than 40gms,  a mix of cardboard outer and a plastic pouch. It makes sense both economically and environmentally, as currently the world's shipping lanes carry something like 9 billion bottles of wine each year.

The question which of course will bother wine drinkers is whether there are BiB wines on the market that are any good. I'm no expert in this. Maybe I can report back at a future date when I have sampled a few. But to get me started, I have ordered a red and a white from the BiB Wine Company and so far I have been impressed. At £10-£12/bottle equivalent, their offerings are bang in the middle of my price range sweet spot.

To learn more about the international wine trade, I found this site. And calculating the environmental impact, I found this site most helpful.

12 Feb 2020

The risks we face

Back in November 2019, I blogged about plate tectonics and, in particular, how we live - and die -with the earthquakes, tsunamis and volcanoes that result from us living on an unstable planetary surface. It set me thinking more about the more general risks we face and how we can categorise them.

Plate tectonics covers the below-ground risk. But what about things dropping on our heads from outer space? These could be solid, like meteorites or asteroids, but they could also be unwelcome rays from the Sun or elsewhere. We don't see much evidence of these risks but they do happen and very occasionally they can be very deadly. A single huge collision with another heavenly body 65 billion years ago is believed to have been  responsible for the extinction of the dinosaurs.

The third field of risk is atmospheric. The Earth's surface is surrounded by a relatively thin layer of gases which we depend on for life. As the Earth both rotates and tilts on its access, the resulting winds and weather patterns cause all manner of mayhem at the surface. Think Droughts. Storms and Hurricanes. Monsoons. Flooding. Extreme temperatures. Fog. Snow. Ice. Fires (albeit at one stage removed but remember that oxygen is an essential component of fire).

The atmosphere also dictates which life forms, if any, will occupy the surface. No rain = dessert. Frozen rain = snow = Arctic like conditions and glaciers. Lots of heat and rain = jungles. Lots of rain and coolish temperatures = Manchester.

We interact with our atmosphere in ways we don't with the ground beneath or space above. For instance, we can turn fog into smog by adding burnt carbon to the atmosphere. And we can alter the characteristics of the atmosphere itself by tinkering with its component gases. In particular, with carbon dioxide which, despite being only a trace gas making up just 0.04% of the Earth's atmosphere, is known to act as a thermostat for global temperatures.

A more nuanced example of this was our production of CFCs, a 20th century phenomenon, which then drifted into the upper atmosphere and reacted with ozone. This resulted in large holes in the ozone layer which acted as a dampening layer for incoming solar radiation. This made sunshine a far more dangerous factor for those outdoors and led to increases in skin cancer. The Montreal Protocol, in 1987, was a fine example of nations working together to ban the use of CFCs and to bring about a gradual repair of the ozone layer.

An even more nuanced example would be the current fear about the spread of the cornonavirus from China. The atmosphere carries with it not just the threat of challenging external weather conditions, but also as a carrier of communicable diseases.

So there you have it. We live on a Planet with an unstable surface, subject to bombardment by things from outer space and dependent on a thin zone of gases which behave in a somewhat chaotic manner, and which we have started to use as a waste dump.

Having said that, it's a beautiful morning here in Cambridge and it's good to sometimes feel that Earth is not such a bad place to be posited on for a while.

1 Feb 2020

Carbon-free electricity

The race is on to produce zero carbon electricity, which is the most straightforward way of slowing/stopping climate change. But how realistic is this goal, and how long will it take? Here's a summary of the situation in the UK.

When we say 'zero carbon electricity' we are referring to how electricity is made, not what's in it. Using fossil fuels to make electricity (the traditional method, if you like) burns lots of carbon which releases loads of carbon dioxide (CO2) into the atmosphere. Renewable technologies, hydro power and nuclear power produce electricity without burning any carbon and are therefore said to be zero carbon. The electricity we now use is from a mix of sources and therefore can be said to have a carbon intensity factor, depending on how much is derived from fossil fuels (carbon) and how much from zero carbon sources. The higher the proportion from fossil fuels, the greater the carbon intensity is said to be.

The standard measurement (or metric) used to express the carbon intensity of electricity is grams of CO2 equivalent per kWh (kilowatt hour) of power, written XXXgCO2ee/kWh. The word "equivalent" is in here because other climate changing gases (notably methane) are also released during the production processes and these have to be taken into account when considering the global warming effect of the different gases. It's a complex field and the maths is not quite as straighforward as we might hope for. Methane has a large global warming footprint, but only stays in the atmosphere for a few years, unlike CO2 which hangs around for centuries before slowly being absorbed by the oceans.

When we first started making electricity on a commercial scale, the preferred method of production was to use coal-fired power stations to drive huge turbines. Coal-fired electricity has a very high carbon intensity factor, as it releases masses of CO2: anywhere from 750 to 1,000g/kWh, depending on the type of coal and the efficiency of the plant. Coal also happens to be a dirty, toxic fuel which poisons a lot of people, but that is not what concerns us here. Using gas to make electricity is a much better option than coal (and it's cleaner) but it still produces a lot of CO2 —  it scores between 380 and 480g CO2ee/kWh/kWh.

In contrast, with the notable exception of biomass, all the non-fossil fuel production methods are zero-carbon. That doesn't mean there aren't other issues surrounding their use: nuclear power maybe zero-carbon but it is not zero-problem (Chernobyl, Fukashima etc). But from a carbon intensity point of view, they all score zero. Or 0g CO2ee/kWh. To be pedantic, there are carbon costs with renewables but they are solely to do with the construction or manufacture of the equipment — known as embodied carbon.

The carbon intensity of fuel table can be summarised thus (all in g CO2ee/kWh):
Lignite: 850 - 1100
Coal: 750 - 1000
Oil: 550 - 700
Natural gas: 380 - 480
Biomass: 50 upwards
Nuclear: 0
Wind, solar: 0
Hydroelectric: 0

More details via Google or Wikipedia but a good source is here.

The history of UK electricity production shows the carbon intensity was high, at around 700g CO2ee/kWh in the 1970s when it was almost all produced by coal-fired power stations. As the switch to gas took place over the following decades, the intensity falls to around 450g CO2ee/kWh. Here is a useful summary of the situation up till 2015.  However, since 2015, the rate of change has accelerated dramatically, as you can follow here. The principle reason for this is the switch to offshore wind farms, which have had a massive effect. Maybe because it is happening out at sea, we are only barely aware of this major infrastructural change. Other factors include decreasing demand for electricity overall (which makes it easier to drop coal from the energy sources), an uptake in solar PV and a switch from coal to biomass as the huge Drax power station in Yorkshire which alone accounts for around 8% of the UK electricity demand. Currently UK electricity averages around 230g CO2ee/kWh

What it means is that electricity has gone from being a much higher carbon intensity than gas to becoming much the lowest carbon intensity power source, all in the past five years. And it is due to head lower still over the next 15 years, as we move to decarbonise the grid. Electricity is, however, over three times the price of natural gas, so a switch to electric heating is still unlikely any time soon, especially as the cost of heat pumps, the obvious technology to employ here is way more than a standard gas boiler.

I for one hadn't realised quite how quickly this change would take place and as a result fitted a gas condensing boiler in our new home - a decision made in 2017 - on the basis that we had done everything possible to minimise the heat load and that, as electricity released rather more CO than gas, it made sense to go with the cheaper power source.

The government has recently published the Future Homes Standard which is a mixed bag of proposals outlining measures to decarbonise our housing over the coming decade. It's received a very lukewarm review from almost every commentator, but the headline move contained in the proposals is that ‘new homes should not be connected to the gas grid from 2025’. 

Given the huge change in the mix of energy sources we are using to make electricity, this single proposal will rank as the most significant decarbonising measure we have ever taken.