Electricity demand in southern Europe to soar with air con

After the hurricane in Texas, there has been a lot of news about how the weather will affect energy use. Of course the big story is how energy use is already affecting weather! I'm sure I heard people twenty years ago warning about global warming making storms bigger and more frequent. 

Another angle is news from the Guardian here about the increase in electricity demand in southern Europe for air conditioning due to increased temperatures. The UK will probably also need more cooling, but will need less heating, so in terms of energy may break even. Obviously the increase in temperature depends partly on whether we do anything about carbon emissions, and of course there will be some feedback if Europe does not de-carbonise the electricity supply.

The article does mention increasing insulation as a way to maintain comfortable temperatures, which is good.

The picture accompanying this shows an array of air conditioners from four different manufacturers, all Japanese.

Here is a report on global demand from the Japan Refrigeration and Air Conditioning Industry Association which shows that demand for air conditioners is already increasing around the world. They estimate 2016 global demand to be around 100 million units, growing 2.9% from the previous year.

In terms of market size, China is the biggest with 40% share, followed by Rest of Asia, North America, Japan, Latin American and then Europe with 6 million unit sales. In terms of market growth there is a very different picture, with Europe growing at over 12%, followed closely by Latin America, then Rest of Asia growing at over 8%. The more mature air conditioner markets of North America and Japan show the lowest growth rates of 1.8% and 2.8% respectively.

Since they can work as heaters as well as coolers, and since they run off electricity which is the medium of choice for renewable energy, split-unit heat-pump-based air conditioners may increasingly become the unit of choice for domestic heating and cooling needs. I may even get one myself.

Is that factoid true?

I came across this comment as I was preparing a lesson on cooling: 

"US uses more electricity on cooling than Africa does on everything."

As often happens, the factoid gets divorced from its source, and just stays there, overly confident in its truth. But is it true? And how do I find out? As Churchill said, "A lie gets halfway around the world before the truth has a chance to get its pants on." He said this long before the internet was invented and the term "social media" was coined, but some things do not change. Or perhaps, and somewhat more scarily the world today is similar to the 1920s, and we are heading towards a repeat of the 1930s. 

According to this article in Mother Jones (July, 2015), the US spends 11 billion dollars on air conditioning, and in the process emits 100 million tons of CO2.

According to the Carbon Dioxide Information Analysis Centre (2008) Africa's carbon emissions 311 metric tonnes. But that's all emissions, not just electricity. 

Wait a minute, was the Mother Jones statistic metric tonnes, long tons or short tons? The latter are 10% more or less the former. Also, the factoid said "electricity" and Africa presumably has other carbon emissions than electricity. So it may be true.

According to accountants KPMG, Africa's electric generation capacity was 680 billion kWh in 2012. The US average 12 cents per kWh. So, I can work back from the 11 billion dollars to get 90 billion kWh. Now we're even further out and Africa is using over seven times more energy for everything than the US does for cooling.

US Energy Information Administration's website gives around 2 pounds CO2 per kWh of electricity. If a short (US) ton is 2000 pounds, that's 1000 kWh per ton of CO2. So 100 billion kWh on air conditioning in the US.

Interestingly, if the above emission figures are correct, Africa's energy generation is at least twice as clean as the US. This is possible if Africa has a higher proportion of hydroelectricity, and a lot of the plant is newer and more efficient. 

Or perhaps this factoid was just talking about domestic air conditioning, rather than commercial or industrial.

This is neither US nor Africa, but may have some air conditioning

Or maybe the article was just wrong. This US Department of Energy site claims $29 billion were spent by homeowners on air conditioning, emitting 117 million metric tonnes of CO2. 

But where did I actually get that factoid from in the first place? It probably came from this July 2012 article on Yale Environment 360 by Stan Cox. It was probably true at some point, since the US has a long history of air conditioning, and Africa is still rapidly developing as an electricity consumer. 

Oh for that world of long ago, when all good things were true...

Lesson 13: How do air conditioners work?

I made a bit of a miscalculation. There were three lessons left and three student presentations, one of which was on low-energy buildings in hot climates, and another on generating your own power. I had planned to do a lesson on cooling, and had some leftover material on solar electricity, and should really have had these presentations on three different days, then filled in the rest of the class with my information, assuming that the students had not covered it in their presentations. Or if they had, then continue the lesson with discussions on the relevant topics. Unfortunately they both ended up in week 14, so week 13 became empty, and the only material ready for it was the left-overs on cooling and solar electricity. 

If I'd been doing a full lesson on cooling, I would have started with a brainstorm of different ways to stay cool, with my non-exclusive list ready in the wings: windows, insulation, thermal mass, trees, heat-exchange ventilation, fans, air conditioners, de-humidifiers, and ice—preferably large blocks. Another thing that was not on my explicit list, which probably should be, was shading. 

Not wanting to take away too many options for the following week's presentation, and keen to teach some science, I skipped this and went straight into an exposition of the workings of air conditioners. 

Before getting into the details, we needed to understand four concepts relating to gases: volume, pressure, temperature and heat. These are all interrelated. Other things being equal, if a fixed amount of gas is in a smaller volume, it will have a higher pressure. Other things being equal, if the amount of heat in a fixed amount of gas goes up, the temperature will rise. If you don't add any heat to some gas, but squash it in to a smaller volume, then the amount of heat won't change, but the temperature will go up. And if you expand it, the temperature goes down. 

A heat pump sends a fluid in a circuit through a hot area and then a cold area. The Fluid is compressed as it goes into the hot area, which will increase the temperature and allow it to transfer heat to the hotter area. It is then allowed to expand when it goes into the colder area so the temperature will drop and heat well flow from the cold area into the fluid. 

That's the Carnot cycle. Heat pumps are basically trying to defy the second law of thermodynamics, by getting heat from a colder place to a hotter place. We use them in our fridges and air conditioners, and increasingly they are used for space heating and water heating. 

The coefficient of performance is used to measure the efficiency of a heat pump, and it measures the amount of heat that is transferred divided by the amount of energy that goes in. Typical domestic heat pumps have average COPs of 3 to 5, but precise numbers are very difficult to find. 

There are limits to the COP, and as the temperature difference goes up, the COP will go down. If a heat pump is used for generating hot water in the winter, using cheap night-time electricity, the COP can get very low, and the heat pump is not performing much better than an electrical heating element.  

How fans do and do not cool

It's now air conditioner season. We have one at home but it is just in one room and so far we have hardly used it. We have an electric fan, which seems to work. 

There are three ways of looking at how fans work. There's the science-free way, the way with a little science, and the heavy science way. 

The unscientific way of looking at it is that the fan is sending out cold air. The air feels cool, and the fan makes you feel colder so this view has some logic. 

If a little science is applied, it's tempting to think that the fan is not sending out cool air, and that it is simply cooling by helping the moisture on our bodies to evaporate by blowing the air away from next to our skin. This view will, quite correctly, note that fans are not going to make the room cooler, because the fan motor is generating friction and electrical resistance is heating up the coils and there is generally an increase in entropy all round. 

While an air conditioner will cool down the room by pumping heat outside, a fan will, if anything, make the room warmer by bringing in electricity, looking at a closed thermodynamic system. 

But this is ignoring Bernoulli. One way of looking at the Bernoulli effect, recently mentioned on an episode of the BBC's In Our Time talking about the completely irrelevant subject of cosmic rays, is by blowing on your hand. If you open your mouth and breathe, it feels warm. If you purse your lips, it feels cool. The reason it feels cool when you purse your lips is because the air is at a lower temperature. The reason it is at a lower temperature is because it is at a lower pressure. Since temperature relates to the amount of heat, and lower pressure means that the gas is spread out over a larger volume, so the temperature drops. The reason for the pressure drop is that the air is moving faster.

Another way of looking at it is what happens on narrow streets at Matsumoto Bon Bon. This is an annual festival where a few thousand people dance around the streets for three or four hours. Some of the streets are wide dual carriageways and some narrow one-way streets. What usually happens, as the evening goes on and more of the beer carted around behind each group gets drunk, is that the procession ceases to have a uniform density of people, and instead has some very crowded areas where nobody is moving, and some completely empty sections. The narrow streets always become empty, so the dancers have to run along these to catch up with the next group, often having been dancing on the spot before. What is happening is that the narrow street is making people go faster, and because they are going faster there is more space between each person and the density has gone down. Exactly the same thing happens between the atoms in a gas. This, incidentally, is what keeps planes in the air. 

It also means that the air coming out of a fan is actually colder, since it is moving faster and has lower pressure. But unless you keep the whole house at a low pressure, the overall temperature is not going to stay down. The fan will only cool you down if you are standing in front of it. Otherwise, it should be switched off. 

(fan graphic taken from: http://blingee.com/ without permission)

AC DC fans

We were looking at fans in the electric shop the other day. There were a few new DC fans. The shop shows the rating of each fan, and DC seem to consume about half the electricity. This seems a little counter-intuitive since I thought AC motors were more efficient than DC motors. I guess DC fans are more efficient because the control circuit of a DC fan will change the current electronically. The AC fan, on the other hand, is probably going to use a variable resistor, turning some of the electricity into heat, and running the AC motor at a speed where it's not so efficient. 

But surely, if you're running the AC motor at the design value, it's going to be more efficient?

All electric motors basically work with electromagnets making a rotating magnetic field. AC electric motors can be very simple. Effectively the alternating current goes straight to an electromagnet making a rotating magnetic field.  A fixed magnet on the shaft then rotates. Depending on how well the frequency of the current synchronises with the speed of the motor will change the efficiency. 

I had a record player with a direct-drive AC motor that I brought to Japan many years ago. The UK has mains current at 50 Hz, while Japan has 60 Hz. This made my Bruce Springsteen records sound like Dolly Parton. 

I didn't use it to play heavy metal. 

Eventually I got a 60 Hz motor, then took it back to the UK where I briefly had the opposite problem, although unfortunately no Dolly Parton records. Now it's back in Japan but I'm not sure where the correct motor is.

DC motors can be brushless or with brushes. If they use brushes, the polarity of the electromagnet changes as the shaft rotates. The brushes cause friction which adds to the inefficiency.

Brushless DC motors, also called stepper motors, have the fixed magnet on the shaft, and two sets of electromagnets which are swithed on and off to create a changing magnetic field. 
Another loss of efficiency is in the resistance of the electromagnets, which will be more for DC with its constant current, rather than a current rising as the electromagnet needs more power. The electromagnets are going to be applying their full forcefield the whole time, even when their field is in the same direction as the fixed field and the power is not going to help move the shaft around. AC, on the other hand, is sinusoidal and the power will rise to the challenge of providing torque when it is most effective and most needed. The sine wave in the AC is just circular motion repeated onto the timeline, so it's going to convert easily back into rotation.

So AC motors would seem to be more efficient.

Or maybe the DC fans have AC motors in them, and an electronic inverter converts DC into AC at the optimum frequency, while the AC motors are stuck with the mains frequency.  Even then, the AC fans should be more efficient because there's no conversion from AC to DC in the power supply then back from DC to AC in the inverter.

It may just be that the DC fans aren't more efficient than the AC ones; just less powerful. Apparently they are really good at supplying a gentle breeze.

There's an interesting, but inconclusive, discussion of the efficiency difference between AC and DC in electric vehicles here.

Fans for power conditioners

You really have to read the small print. 

The rating of the Power conditioners is 4 kW, but this is at a temperature of 30 degrees. It drops to 3.2 kW when the temperature goes up to 40 degrees. 

This is a big deal if we have two power conditioners, which we do, and the panels are producing over 8 kW, which they will on many sunny days. 

I don't have much solid data at hand on the hourly generation. I started off copying it from the display panel, but gave up after about three weeks and have just been recording the daily figures since then. The 22 days of recorded data, of which 16 were sunny, and what I see when I walk past the display panel, show that it's rare for the power conditioners to be producing more than 7kW. Of the hours we'd expect maximum output, we got 7.2 kWh per hour once, but the normal maximum is about 6.9 kW.  

Since the temperature of the power conditioners mostly depends on the heat they put out, and the heat they put out is a percentage of the electrical power going through them, they are unlikely to deliver 4kW. 

If they could be cooled, we may get an extra half kilowatt out of each power conditioner when it is generating a lot. That could be for four or five hours on a good day. Maybe an average of two hours a day. 2 kWh, 100 yen in the bank every day. 

Cooling them is easy. You can put a fan in front of them. The room with the power conditioners gets hot, and the thermometer in there shows that it's over 30 between about 10:30 and 16:30, but circulating the air is going to cool the machines down. 

I put a fan in there the other day and watched the numbers on the power conditioners go up from 3.2 to 3.99 while they were blown on. 

The fan is going to use electricity, of course, but probably only around 20 Watts. Fixing it to a timer to run between 11:00 and 16:00 each day would cost us 100 Wh, but this is only 5% of the extra 2 kWh we could make, so we'd be winning. 

Of course we have to offset these financial savings with the capital investment. We may need to get another fan since the time we want to cool down the power conditioners coincides with it being hot downstairs when we want to circulate air in the house. 

It would be really good to have a fan connected to the DC output of the panels, that would start working when it got to around 4kW. This is part of a broader desire to take power straight off the panels without sending it through the power conditioner, for example in running a heat pump for hot water. I don't think it would be very difficult technically, but I'm really not sure whether I'll be able to find anyone interested in doing it. 

The pursuit of ambience

It's going to take us a year or two to work out exactly what to do with the cooling and heating of the house. It will probably boil down to three different strategies: cooling, passive heating and active heating. There may be some gaps in between where we don't have to worry, but I suspect at any given time we should either be cooling the house in anticipation of impending heat or heating it in anticipation of impending cold. The weather and climate are changing but the seasons are here for a while.

We switched off the active heating April 10th, and the house has not been cold since. The last night below zero outside was 8th April, when it was minus 2, according to tenki.jp, although it was down to 3 degrees above freezing in the wee hours of 13th May and this year it didn't start getting really hot until the middle of July. 

We're now in cooling mode and have begun a routine of opening up the windows when it drops below about 25, which is often at 7 pm, and closing them when the temperature outside rises above 25, which is around 7 am. July 21st was cool and rainy, in the low 20s all day, so the house was cooled a little more.

The bypass system on the ventilation is now working, so it will be pumping cooler air into the house throughout each night, exchanging all the air every two-and-a-half hours. Opening the windows substantially increases the air flow and cooling. In an ideal world they would open and close automatically, like the heat-exchanger bypass switches on and off automatically, depending on temperature difference.

The daily indoor temperature variation is bigger than I expected, probably due to the size of the windows on the south wall, and the lack of a decent awning to keep the heat off the terrace. At the moment we just have a little camping tarp over it.