47 views of scaffolding

I started off taking pictures of our house as they were building it. Then the scaffolding came to obscure my view.

In this pictues, you can see where they added an airtightness sheet around the upstairs floor, which becomes very difficult to make airtight after the walls have gone in, if your airtight layer is inside the structure.  

Then they started covering the scaffolding with sheets.

This happened all around the house.

Other, greater buildings are blighted with scaffolding. Here is an old building in Athens which I believe Victorian engineers tried very hard to "repair" by straightening all the lines on the structure. It turns out it had been carefully designed with non-straight lines so that it would look right.

I remember visiting Tokyo Disneyland and seeing the centrepiece, Cinderella Castle, surrounded with scaffolding, which had been carefully covered with sheets depicting the castle. I wasn't sure whether this made the building seem more real or more fake.

Here is another view of our house.

Changing groups

Time to shuffle the students a bit.

The lesson on windows went well, and I think the estimation of the room's window U value was not too overwhelming for the students. This was partly because I had structured the problem solving a bit more. Scaffolding is also very helpful in the construction of knowledge. Also I had them change groups at the beginning and tried to get mixed skill sets together.

I had put them into groups in week four and it's a good idea to change after two or three weeks have passed. The dynamics of groups have been characterised by the stages of Forming, Storming and Norming. After norming we hope for performing, but instead it can get boring! Changing groups every week is a bit too disruptive, but leaving the same groups for too long risks unfairness for people who have ended up in a dysfunctional group as well as a missed opportunity for having the students meet more people and make more friends.

The first time I put them into groups, I began by asking everyone these questions:

• What is your major?
• Are you good at maths?
• Are you good at English?
• Are you good at drawing?
• What is your favourite subject?

Then I asked them to make groups of four, with different majors, different favourite subjects, and new friends. I told them that maths was going to be useful, so if they weren't good at maths they should find someone who is. Also, if possible, I wanted different nationalities and mixed genders. The class is about 85% Japanese and 70% male, so this was not going to happen with every group.

In the first couple of weeks, and in previous years, I had tried to have Japanese-speaking and English-speaking groups, but last year I realised that resulted in me having a false sense of the English level of the room, and some parts completely lost. Spreading out the English speakers means they can work more to mediate between my English explanations and instructions, and the Japanese of the students who often have more interest in, and aptitude for, the topic.

Three weeks later they were still more or less in those groups of four, but a group of women had formed in the back corner of the class, and I'm sure the same couple of architecture students had been sitting next to each other every class. It's not really bad to sit next to the same person every week, but a changing environment is conducive to learning since memories are formed by connections and associations. Also they may meet some new people.

So I asked them, within their groups, to first decide who was best at writing. Next, I asked who was best at English. The writer then had to write down those names. Next I asked who was best at communicating. If it was their best English speaker, they should choose the next best English speaker as their English speaker. Finally I asked who was best at mathematics, and if it was their best communicator or best English speaker, they should choose a different best communicator or English speaker.

Then I shuffled the deck by having each writer stay put, each English speaker move around the class clockwise to the next group, the communicator move two groups clockwise, and the mathematician move one group anti-clockwise. I figured the mathematician would be able to handle the negative number. As usual, I had to do some traffic direction, partly because there was one group in the middle of the class, and it wasn't completely obvious which way was clockwise and which was anti-clockwise.

Now I had a high chance of diverse groups. They had all worked in different groups before and would hopefully bring the best experiences into the new group.

When it came to calculating the U value of the windows, I asked them to pick a leader, a designer, a calculator and a checker.


I reminded them of the problem solving steps:
1. Formulate problem, ideally drawing it!
2. Plan a strategy, making sure they write it down!
3. Find equations
4. Find data, but not until they had done the first three steps
5. Calculate
6. Check
7. Check again

After a while I reminded them about surface resistance, then gave them some equations, thermal conductivities and dimensions.

A little later, as I wandered the class looking at their calculations, I noticed a couple of U values of over thirty for the glazing, which looked way out. I went back to check and noticed I'd given them the wrong value for conductivity of air by a factor of ten. It should be 0.024 W/Km but I'd given them 0.24. A great example of how everyone makes mistakes, and how important checking is. Making mistakes is not a problem in itself—everyone does that!—you have to realise when you have made mistakes, and then fix them.

How big a battery would I need?

Our house produces more electricity than we use, so in theory it would be very easy to unplug from the grid and become self sufficient. We don't do this for three reasons:

First, being connected to the grid means that we have electricity when the sun is not shining, its rays are blocked by heavy clouds, or by snow on the roof. We don't need to worry about batteries or generators because the grid is our back-up power supply.

Second, since we produce more energy than we use, we can supply energy to the grid and contribute electricity to the community. We wanted the house to produce more energy than it consumes, and we like to feel that the extra energy is being used and making a difference.

Third, they pay us for any electricity that we supply. They pay us very well: about twice what we pay for day-time electricity and five times the amount for night-time electricity. This is similar to the second reason, since we can see from the negative bills that our electricity is making a difference. We can safely assume that there is more demand and less supply in the day time, so we are filling some kind of need by selling our electricity. It's less safe to assume that our electricity is worth twice as much as their electricity, and easier to see the feed-in-tariff as a boost to the solar industry. Even then it is probably a good thing as the renewable energy industry and its exploitation of a resource that literally falls from the sky still seems to be getting less subsidy than exploiting fossil fuel reserves, and if we are to transition from fossil fuels we will need solar panels.

Regardless of the politics, the highly tangible and easily countable financial considerations mean that we try to sell as much of our day-time electricity as possible, and use their night-time electricity instead. Looking just at energy use this is a bad idea. Our main power consumption is for heating water, which we mostly use in the evening. Currently we are heating hot water at night and it is sat in the tank steadily losing heat for most of the day. Also, the tank is heated by an atmospheric heat pump, getting heat from night-time air, which is colder than the daytime temperature by something like 10 degrees at any time of the year. If we were using electricity in the day time from our own panels, then the heat pump would do a lot less work to get the heat from the outside temperature up to the temperature in the water tank, and the hot water tank would be losing a lot less heat before we use it. This could save us as much as 25% of our electricity, but we don't do it because using our electricity in the day time is over 300% more expensive.

Our contract for selling electricity runs out after ten years and we certainly will not be able to get the same price, but it's not clear yet what the financial calculation will be. If we were to start using daytime electricity, we would also think about trying to use the hot air under the solar panels, which would be even hotter and need even less work to provide us with hot water, but that's another blog post.

Back to the question in the title: If we were to disconnect from the grid and wanted to get a battery to keep us in power, how big would the battery need to be? I have seven years of generation and consumption data to give me an answer.

When I said that we produced more power than we consumed, this has been true for every year and every month. The lowest producing month was October 2017 (670 kWh), which was the least sunny October since 1917 with only 100.9 hours of sunlight. September 2018 had even fewer hours of sunlight (94.4), but we made 800 kWh. That's the same as our highest monthly consumption, 800 kWh, in February 2013.

The longest period when generation stayed above consumption every day was 153 days from 20th April to 20th September, 2016.

The longest period where consumption stayed above generation was for five days between 12th and 17th October, 2017.

If we need a battery to cover all our energy needs, then it may be for these five days. In the simplest calculation, we need a battery of 33.1 kWh (the shortfall between the 70.5 kWh consumption over those five days and the 37.4 kWh generated). That's one or two Nissan Leafs.

There were five times when the consumption stayed above the generation for four days: from 14th January, 18th June, and 23rd October, 2013, from 6th September, 2015 and from 19th October, 2017. Many of these grey-outs are in September or October, when consumption is at its lowest. The snowy days in the middle of January 2013 were at a time of much higher consumption, and for those we would have needed to store 53 kWh to make up the gap between 61 kWh generate and 114.2 kWh consumed. The Teslas have 60kWh batteries.

Although the meteorological data confirms September and October as the months most prone to sunlight shortages, when the roof is covered with 22 cm of snow, our heating needs may also peak.

So the short answer is, we would need a 53kWh battery. Anything smaller and we are still going to need to rely on the grid and pay the monthly connection charge, or we would need some other backup, so the value of a smaller battery is limited.

Since most of our energy is for heating, it may make sense for us to look at storing heat rather than electricity. Phase-change materials may be useful for this.

Also, a more thorough answer would look at charging efficiency, discharging efficiency and electricity leakage. The figures above assume 100% of the electricity goes into the battery, 0% of the charge is lost over time, and 100% of the charge comes out.

Squaring the Circle for Traditional Buildings

It often seems that there is a battle going on between traditional building techniques and high-insulation high-airtightness approaches such as Passive House. Advocates and practitioners of traditional buildings have a strong case that years of experience will show how and when buildings fail, and how they can be built to last. They claim natural materials can absorb and release moisture and are free from dangerous chemicals, so they are better for the building and more healthy for the inhabitants.

But traditional buildings do not use a lot of insulation and are not airtight, so here are two questions: 

How do you keep a traditional Japanese building warm in the winter? 

How does ventilation work in traditional Japanese buildings to ensure good air quality?

I'll get to the answers soon.

High airtightness is sometimes achieved with synthetic membranes, but concrete, plaster on stone or brick, and oriented strand board (OSB) can also play a part in a building's airtight layer. Insulation materials are often polymer-based, especially where a high performance is needed. To get the same insulation as ten centimetres of top-grade foam, you need over 30 centimetres of thatch, over 80 centimetres of wood, a similar thickness of clay mixed with straw, or over two metres of rammed earth. Cellulose fibre insulation is better than all those traditional alternatives, but you would still need over twice the thickness to match foam.

It is interesting to note that a mixture of clay and straw has a similar insulation level to wood, which means that a structure of wooden posts and pillars filled with traditional walls may have an even layer of insulation, avoiding cold spots. But a typical passive house wall has something like ten times higher insulation than a traditionally-built house, so for those walls to perform in the same way, they would need to be ten times thicker.

So how do you keep a traditional Japanese building warm in the winter?
Short answer: You don't. 

When it's cold outside, it gets cold inside. The walls are porous so moisture does not tend to build up. If you want the house to be warm you have to start burning stuff. Today that stuff is usually fossil fuel, either directly, or indirectly with electricity generated from fossil fuels. So you certainly can build with traditional, natural materials, but the inhabitants are only going to be comfortable with a steady flow of un-traditional, unnatural fossil fuels. 

Traditional Japanese heating is with wood burnt in an irori open fire or charcoal smouldering under a kotatsu table heater. Irori are open fireplaces in the middle of the room. Traditional Japanese buildings don't have chimneys, so the smoke finds its way up though the house, killing any bugs on the way, and then out through the ample gaps in the structure.

Traditonal kotatsu burn charcoal in a small irori pit, with a table over the top covered in quilts and blankets. The kotatsu just provides a warm space to sit in rather than warming the whole building, which in some ways is a very efficient use of fuel. This 1820 woodblock by Eisen Keisai also hints at other ways couples kept warm on long winter nights. 

Today people do not want open fires because of the risk of the house burning down, and the increased soot and extra cleaning. Charcoal-burning kotatsu are also a carbon monoxide risk so modern kotatsu use electric heating elements. They are still occasionally fatal because of the heat shock when elderly people get in or out of them. Many people in Japan love their kotatsu, but if they start living in an insulated house, they do not miss them!

Most Japanese homes do not have any central heating system, often relying on kerosene fan heaters, electric carpets, or air conditioners in heating mode. Some houses have underfloor heating, but there are frequent stories of people who use it for one year, see the electricity bill, then never switch it on again. None of these heating techniques is traditional or natural. 

Wood burning stoves may be a more natural method, and cast iron stoves from New England or the west coast of Ireland do look very nice in Japanese houses. The rituals of preparing wood and the cleaning and maintenance may not suit everyone's lifestyle, the smoke may not please the neighbours, and unless the house is in the middle of a forest the source of wood may not be sustainable. An increase in wood-burning stoves has been blamed for poor air quality in London, and since London is not a major producer of wood, you also have to wonder about the carbon footprint of transporting the fuel. 

Wood pellets are much more efficient than burning wood directly, which not only means less wood, but also less ash to clear from the stove and less pollution going through the chimney. The first wood pellets were made from sawdust waste from timber mills. However, as demand increases, and efficiency leads to less waste, trees need to be specially cut and grown for wood pellets. Economically speaking, pellets may have started off being made from a waste product with zero cost, but as and demand increases, the price may go up. The impact is not zero and while burning wood pellets may be better than burning fossil fuels, they do not provide a solution to the world's energy problems, and whatever you are burning, it's still better to burn less. Ideally some of the trees in our dwindling forests will be left as habitat, and end up falling to the ground and emerging in a few millennia as a carbon source for future inhabitants of the planet. But I may be digressing from the topic of traditional buildings. On the other hand, preservation of the environment may be exactly what advocates of traditional building want. 

If I may return to more urgent matters of survival, when a building is airtight, it must be ventilated. The solution used in most passive houses is a mechanical ventilation system with heat recovery. Advocates of traditional building techniques often have a visceral reaction to the idea of mechanical ventilation as it is clearly not a traditional way to ventilate buildings. It uses electricity, so how could that ever be natural?

It is not natural. But what exactly does "natural" mean? When people call for natural materials, what are they asking for? Asbestos occurs naturally in the ground, but I'm guessing you wouldn't want that in your natural building! Polyethylene and polypropylene are completely synthetic and harmless to taste and touch.

If you really want nature, you should go and live outside. Buildings are not natural. Rather than asking a binary question whether specific materials or techniques are natural or not, we need to look at health, comfort and energy use, over the lifetime of the building and make the least bad decisions to get the best health and most comfort for the least energy use and lowest environmental impact.

So how do you ventilate a traditional building? 

I'm temped to say that you don't, but of course traditional buildings are ventilated—just not in a very systematic way. If there is a fire in the building then it is also working as a ventilation system by sending hot air up and out of the building while drawing air in through those thoughtfully provided gaps and porous surfaces. When there is no fire, air must find its way in and out through open windows and doors. The amount of natural ventilation then depends greatly on the outside temperature, wind speed and direction. So if a house is designed to always have fresh air, it will usually have too much ventilation. This will lead to uncomfortable drafts and a steady loss of heat. If it is designed to minimise drafts and heat loss, then there won't be enough ventilation for good air quality and control of moisture. 

The traditional builders will usually choose too much ventilation because that is the only way to guarantee there will be no moisture build up. So the house should not be airtight. If the builders do make the house airtight, they need to put in mechanical ventilation. They could ensure ventilation by providing a fire for you to keep stoked, but if they do that, they need to make sure there is no risk of carbon monoxide poisoning, which again will probably mean avoiding airtightness.

Mechanical ventilation does use electricity, but it provides fresh air, takes excess humidity out of the house, and keeps you warm very cheaply by recovering the heat from the expelled air. Heat recovery ventilation will only work if a building is airtight, making sure that air is coming in and out through the heat exchanger. Also, the insulation will only work effectively and without risk of condensation within the walls if the building is airtight. And if the building is airtight, active ventilation is needed because natural ventilation is unreliable.

Without active ventilation and airtightness, extra insulation is a risk as air leaking out of the house in winter drops in temperature and hits the dew point, producing condensation.

So the traditional builders are going to hand you a choice: 

Pay a lot for heating, or be cold. 

On the other hand, a traditional structure can be wrapped in an airtight insulating layer, and include a ventilation system. This will protect the structure and make it last longer, and will make it nice for the inhabitants, who probably do not want to live a traditional life that is not as comfortable and not as long.

In the fight for survival of traditional building, insulation, airtightness and active ventilation are not the enemy. They may be the saviour! 

References:

Pollutionwatch: wood burning worsening UK air quality, Guardian (2018, February 1st)

Steven Goodhew and Richard Griffiths (2004) Sustainable earth walls to meet the building

regulations

Emissions from Wood:

Roger Drouin (2015) Wood Pellets: Green Energy or New Source of CO2 Emissions?

How to Solve Problems

Teaching is a constant learning process. At least it should be. One problem with being a teacher is that you often get into situations where you think you're right, which can make it difficult for you to change what you're doing. In the classical model of the teacher, you can be expected to be right in your knowledge, otherwise you wouldn't be there. But when it comes to how to share that knowledge, or in what order to present it, there is less clear right and wrong and just a whole range of choices.

I believe in the power of problem solving for teaching. This translates to a belief in the power of learners to solve problems, and for them to learn something in the process. The problem is, not all learners are good at solving problems, and many have been through educational systems where they have not been expected to solve them. At least not the kind of problems that I give them. 

So how do I solve this problem?

Given that I want to teach problem solving skills, I probably just have to be a lot more open and transparent about it. I have been mentioning a few things to the students in passing: like suggesting they draw diagrams to help them work out problems, or advising them to write their calculations out carefully and clearly on lots of paper so it's easy to go back later and see what they did. I need to be much more explicit about the steps of the problem solving process, and give them a bit more practice in each step rather than just throwing a problem at them and hoping they'll work it all out. Too often the problem I've been throwing at them is how to solve problems, which is way too abstract.

Here are some steps:

• Formulate the problem

The first step is to work out exactly what the problem is. Draw a picture. Write down what you know. Draw another picture. Put question marks where you need to find an answer. 

• Find solutions

Now that you know the problem, you can think about solutions. What strategies are available? Are there different ways to solve the problem. Make a list!

• Choose a solution

Which is the best way to solve the problem? What are the steps? 

• Prepare tools

If you are calculating, your main tools are equations. If you are using a computer, the tool is the software. You also needs data. There will be physical properties that need to be looked up from tables, some things may need to be measured. Some will need to be estimated.

• Calculate

Use lots of paper. Avoid any shortcuts that will not be obvious to someone looking at the calculations later. If you miss out steps on paper, there's a higher chance you'll make a mistake.

• Check the calculation

Ideally get someone else to check your calculation. It's often difficult to see your own mistakes.

• Check the answer

Eyeball it. Compare it with your real world experience. So you calculated that this pencil weighs a million tonnes? Maybe you should think again.

• Check the error

Answers in the real world are never perfect. Their accuracy depends on the accuracy of the numbers going in, and the accuracy of any equations you used. Know how wrong you are!

That's eight steps, and no fancy acronym to go with them. I can start building them into my lessons and watch what happens.

It's probably also worth talking about engineering problems and how they are different to the problems that come up in education. They have often been conditioned to find one correct answer, but over in the real world there is usually more than one answer, and more than one way of finding the answer. Good engineering will find the best solution to a problem, given a range of criteria. The most important considerations are often cost, safety and performance, and the best solution may be optimised between them. Cost itself can be in materials, equipment and construction processes. 

Of course one factor in this optimisation is the length of time the engineer spends on the problem itself, since engineers are a scarce resource and their time precious.

So I think I've written enough on this topic for now.

[Image taken from https://schooltutoring.com. not sure where they got it from!]