Kitchen extractor fans, and their fans

What about ventilation in the kitchen then? 

The manufacturers of Best cooker hoods recommend you exchange something like ten times the volume of your kitchen per hour, which for a regular kitchen is between three and four hundred cubic metres per hour. Passive House recommends you need to ventilate the whole house around 35 cubic metres per person per hour. So these kitchen hoods need two or three times more ventilation than the whole house. Obviously this is a peak load, and the kitchen is not going to be ventilated the whole time.

Japanese cooker hoods typically have three settings: Strong, medium and weak. It may be my Japanese web-searching inability, but numbers don't seem to jump out when I try to find them. Instead there are rather a lot of sites asking why their extractor fans don't seem to be extracting very well.

This site of notes about making your own home (in Japanese) provides a lot of data about different fuels, and some calculations giving a figure of 1,166 cubic metres per hour (assuming three gas rings), or 551 if there are only two rings. Other sites and some of Mitsubishi's extractor fans go into the thousands. 

There are probably differences in peak cooking intensity between Japan and the UK. The former has a culinary history based on wood as a fuel, which gives a strong high heat, ideal for steaming and stir frying. The latter, on the other hand, used peat or coal, which give a lower, longer heat more suited to baking or roasting. Hence the Japanese language has one work—yaku—which can translate into English bake, roast or grill, while there are various different Japanese words for fry, whether itameru (stir fry) or ageru (deep fry). But I'm supposed to be writing about ventilation here, not deep culinary thermodynamics.

The choice in Japan is typically between extractor only fans and those that will bring air into the house at the same time as they are expelling air. The latter are often recommended for houses that are airtight. In our house we got an extractor only fan, with the reasoning that it would only have one hole in the wall rather than two, and therefore make the house less leaky since extractor fan ducts are major causes of reduced airtightness. I'm not sure whether we made the right choice; w hen we switch the kitchen fan on, the front door becomes difficult to open.

In other countries, at least for passive house, another choice is recirculating hoods that will send the air through a charcoal filter to remove the oil and kitchen crap before releasing the scrubbed air back into the kitchen. The heat will then stay in the thermal envelope, and the air will sooner or later pass through the heat recovery ventilation. 

Lloyd Alter on Mother Nature Network has interesting insights into the lack of clarity on the subject. And some very nice pictures of dream kitchens. He discusses how some people rail against recirculating kitchen ducts, while the people wanting low-energy buildings see them as essential. He points out that in Ireland you're allowed to connect a kitchen duct to a heat exchanger but in Canada it's illegal. 

So what should you do? Recently I've been thinking about making a pizza oven in the garden. I know that doesn't entirely answer the question, but if you want to have a low energy house, do you want high-energy cooking inside? We then get into the question of whether low energy buildings should be enforcing low-energy lifestyles, or whether they should allow people do whatever they want while reducing the energy use. 

By the way, if you were wondering why there are so many people complaining that their extractor fans don't work well, it's because they need cleaning. 

Rechargeable batteries half the size, or double the charge

There's an interesting story here in all about circuits about new battery technology that could double the density. In a lot of applications, battery weight is critical. Remote control helicopters is one example, since the power inside the battery must be used to lift the battery itself. These first appeared in the mid 1990s with nickel-cadmium batteries, but later became popular as toys when lithium-ion polymer batteries provided sufficient current for the weight. The development in battery technology marches on, and now a solar-powered plane has flown around the world. It takes a while to find information about the batteries  on the Solar Impulse website, but without the four lithium polymer batteries, which make up a quarter of the plane's weight, it would have struggled to stay up through the nights, or get through any clouds on the way to or from the stratosphere. 

Although solar power is the biggest part of the solar impulse story in the media, the batteries may be more significant, making possible hydro-electric or nuclear-fusion powered flight. Where toys and explorers play, the industrial economy often follows, and I will not be surprised to see some commercial battery-powered flight in the next ten years. It will certainly start off expensive and short-haul, perhaps flying from airports in built-up areas where noise and pollution are bigger issues. Flexible solar panels may be used cosmetically, but the batteries will be the power source.

Anyway, one of the reasons why lithium is a more popular battery choice than nickel-cadmium is that it's lighter. Anyone who has seen the periodic table knows that lithium comes in at number three, right after hydrogen and helium. Electricity is basically stored in the outer electron of each atom, so the light weight of the lithium atom means more free electrons per weight. The first lithium batteries were made with mixtures of other metals, like iron or manganese. In lithium-ion batteries, lithium atoms freed from their out electrons float through the electrolyte from one side of the battery to the other. Once these were put in plastic cases, they started to be called lithium polymer batteries. In its more technical meaning, lithium-ion polymer batteries have a polymer electrolyte.

Image from of Business Wire.

As far as the travelling ions are concerned, batteries have an anode on one side and a cathode on the other. The first lithium batteries used the metal case as the cathode, and a large chunk of lithium as the anode. Lithium-ion batteries use graphite for the anodes. This new technology uses a thin film of lithium as the anode, which means it can hold extra charge with less weight.

These batteries are still using the ions to carry the charge rather than the electrons. Looking at the relative size of the electrons and ions, this is a bit like playing tennis where the players have to go back and forth over the net, rather than the ball. Battery technology is progressing, but still has a long way to go!

You can see an infographic of how other kinds of batteries work here.

Cross leakage and cross contamination

So the big issue with Energy Recovery Ventilation is that along with the moisture, other things are going to be transferred from the exhaust air to the incoming air, compromising its freshness.
This is also called cross leakage, or how much of the outgoing air will end up coming back in again. It even has an acronym: EATR (Exhaust Air Transfer Ratio).

Air xchange.com refers to US ASHRAE standards on cross leakage. Exhaust air is classified into four different groups: Class 1 air has low contamination, for example from office spaces, classrooms or corridors. Class 2 air has moderate contamination, for example from rest rooms, dining rooms, warehouses. Class 3 has significant contamination, for example kitchens, beauty salons, pet shops. Class 4 air has highly objectionable fumes or potentially dangerous particles, for example paint spray booths, laboratory fume exhaust or kitchen grease exhaust.

The US standard states that less than 10% cross contamination is acceptable for class 2 air. This seems like a lot, but in practice you will never get 0% contamination, even with a heat recovery system that is not trying to transfer moisture. Energy recovery systems can get as low as 1%.

Mitsubishi has a report on their Lossnay ventilation system with evidence from a test in 1999 that their membranes are fine enough to prevent bacteria from passing from exhaust to incoming air. They have more information about their systems in English here.

If the membranes are this good, then perhaps we should be using ERV after all, and they should be recommended for kitchens and bathrooms. 

Another compounding factor with kitchens in Japan is that a lot of stir frying, deep frying and grilling seems to take place in Japanese kitchens, and there is usually an extractor fan with three or four times the ventilation needed for the whole house. More about kitchens later!

Green Building Advisor has a useful comparison of ERV and HRV, with a nice aside: "...assuming, of course, that the designer or installer hasn't made any blunders. (Sadly, this can be an optimistic and risky assumption.)"

Energy efficient homes will 'boost economy'

News from the BBC here about Scottish investment in housing energy efficiency, which will pay itself off for years.

They include this stock photo to symbolise an energy efficient house.



What does the photo tell us?

On a superficial level, it's a thermograph, which tells us that houses are giving off heat, and the fact we've taken a picture of the house means that we care about heat. So, it says low energy building.

A brief analysis of the photo tells a different story. The different colours indicated different temperatures, going from black for the coldest part of the picture (deep space high in the sky) to white for the hottest part of the picture, which is the parts of the upstairs wall away from the lintels.

The windows are colder than the walls.

Does this mean that the windows are doing a better job at insulating than the walls? I guess this is possible for an old house where nice new double-glazed windows have been installed, but no effort has been made to insulate the walls. Or are we seeing through the windows into the room inside, which is colder than the outside walls and the roof?

The gable end is cooler too.

Does that mean the gable end is better insulated than the front of the house? This would be a good idea as end terraces have a lot more external surface area, and need more insulation to reach the same energy efficiency as the rest of the terrace. But I thought there was no insulation in the front wall?
The front gate looks pretty warm too. Interesting. Is it heated?

The house next door seems to be equally red along the wall, and along the roof, except for an area going up into a point on the roof. Could that be the shadow of a tree?

Just a guess, but this picture was probably taken on a sunny afternoon. All the heat it shows has come from the sun, hence the warm gate and south-facing walls. The east-facing gable end has been in the shade for a while, as has the neighbour's wall and roof in the shade of the tree. The windows are cooler because a lot of the heat is going through them into the house rather than warming them up or reflecting into the camera. The bushes and trees in the garden are cooler still, because they do an even better job at absorbing the heat. Also the trees, and probably the windows too, have lower emissivity, so even if they are hotter, they'll radiate less and the thermograph won't know about it.

A thermograph taken in the day time will tell you almost nothing about the energy efficiency of a house. You need to take the picture on a cold night, when the heating inside is turned up high. Even then it's not obvious what the picture is telling you. 

Other kinds of ventilation system

There are two more kinds of heat recovery ventilation systems beyond the heat exchange and energy exchange cross flow or counterflow systems previously mentioned.

One is the enthalpy wheel. Enthalpy is not completely sensible. It is a measure of the total energy of a system, including latent heat, so they could probably have just called this an energy wheel. It is also called a thermal wheel, or a heat wheel. The wheel rotates with the incoming air going through one half of it, and the outgoing air through the other half, parallel to the axis of the wheel. If it's hot inside and cold outside, the exhaust air will warm up the part of the wheel passing through that side, then when it passes through the other side, the wheel will warm up the incoming air.  

These wheels have the advantages of energy recovery, potentially meaning more savings than a heat recovery system, and also reducing the risk of frost in the out-going air since the moisture is taken out of the air before it leaves the building. Also, the speed of the wheel can be adjusted to change the amount of energy recovery. This may be useful in seasons when you don't need to exchange much heat, or cooler nights in hot summers when you want to bypass the heat exchanger. 

Enthalpy wheels also have the disadvantage of cross contamination, as some of the exhaust is going to get back in again. Enthalpy wheels may be suited to large buildings which need constant temperatures and humidities, with relatively low ventilation rates. For example, the Passive House-certified Hereford archive and records centre uses one.

An even simpler heat exchanger is the single room energy recovery vent, or ductless vent.

This looks a bit like a regular extractor fan, but it both inhales and exhales air, and passes it through a ceramic core that stores and releases heat. Typically these systems inhale air for something like 70 seconds, pause, then exhale air for 70 seconds. 

More than one of these ventilators can be added in different parts of a building so that while one is blowing air in, another is sucking air out. 

This system has the advantage of not needing any ducts, and being very easy to retrofit, as Guy Marsden in Maine, USA explains. As it is recovering energy there is a potentially higher efficiency, better humidity control and lower risk of frost.

Also it has a remote control. I'm inclined to see this as a disadvantage, rather than an advantage, since we already have too many remote controls in our lives, and we really shouldn't need another one to breathe. Some people do like to have buttons to press though!

Another concern is that it's difficult to be sure that air blown out of the building is not going to be sucked straight back in again. Of course there is a potential problem with any ventilation system that badly positioned exhaust and fresh air outlets and inlets will just lead to a recirculation that makes irrelevant any worries of cross contamination within the system.  

Also, with the inherent problem of cross contamination in the energy exchange system, it's difficult to see how this would work with toilets, kitchens and bathrooms, where you would really only want to remove air, but not supply it. 

It's possible to imagine a configuration where the unit is placed next to an internal wall, and incoming air goes into one room, while outgoing air is expelled from another. I have no idea whether this is possible outside my imagination, but it may be worth trying!

Thanks to Devatech for the image of the wheel, which I shamelessly downloaded from your website! 

And to Nihon Stiebel who supply a "Twin air fresh" ductless, decentralised ventilation system with energy recovery. 

Air xchange.com has more technical considerations here about energy wheels. 

Turf laid... Time to get a lawn mower

Lawns are not really a big thing in Japan, so the lawn mower culture is very different. I remember lawn mowing in England as a childhood chore. First we used an old petrol-engine Mountfield that collected the clippings in a case at the back. I have bitter memories of lugging it around the lawn, and later trying to clean all the grass crud that had accumulated in the nooks and crannies. Next we got a Flymo that cut the grass as it hoovered around the lawn.

We also had one of those manual cutters that had no engine and relied on you pushing to spin the blades around. This didn't seem to cut the grass and we never used it.

I thought these would be long obsolete, but they sell them in Japan. Not so much as a cheaper option for the lawn-owning poor (who do not exist) or the congenitally tight-fisted. The tag line is that these lawn mowers are quieter, so they won't disturb the neighbours.

They also have these:

Honda Demonstrates Robotic Lawn Mower - WSJ

I can think of many things that would hinder the robot on its path. 

Can't read the air

Building culture changes around the world. People talk about "vernacular architecture" as if buildings are all having conversations with each other, but often the languages seem to be mutually unintelligible. 

Heat recovery ventilation is one area where a lot seems to be lost in translation. And there was plenty of hot air to start with.

In Japan, ventilation systems are usually called ２４時間換気 niju-yo-jikan kanki  i.e. 24-hour ventilation. It seems like a strange name, as if you would call your refrigerator a 24-hour refrigerator, or your roof a 24-hour roof! They have been mandated in new buildings since 2003, but a lot of people switch them off. So they are not really 24-hour after all. There are plenty of reports of people who have switched off their ventilation because it makes the house cold, but if you do that, as Last resort blog (in Japanese) warns, you're going to get condensation.

顕熱交換 ken netsu koukan  is heat recovery ventilation (HRV), while 全熱交換 zen netsu koukan is energy recovery ventilation (ERV) which also recovers moisture, and is probably the more common choice in Japan when any kind of heat is being recovered. Translation aside, this may be a shock for those who read the first law of thermodynamics and thought heat and energy were the same thing. My dictionary gives Ken netsu as "sensible heat". And that's not a very sensible expression in English where "sensible" usually has a different meaning. The opposite of "sensible heat" is not "foolish heat" but is "latent heat".

The Japanese language often uses abbreviations of English words that are not commonly used in English. For example PA is used for parking area, and IC for interchange, and you will find these driving on the expressways. KY is an abbreviation of kuuki yomenai, ie cannot read the air. Reading the air means reading a situation, so KY refers to someone who is out of touch with the rest of the room.

Japanese building plans with ventilation systems will show SA for supply air, RA for return air, EA for exhaust air and OA for outside air. These abbreviations are occasionally used in English.

There is a page here that:

proposes a housing environment that has a "Flow of healthy air" and is "Clean and safe".

It should be pointed out that inverted commas are used in Japanese for emphasis, so the inverted commas around "flow of healthy air" and "clean and safe" do not mean that somebody said it was healthy, clean and safe, but they're actually being sarcastic. 

Energy Thoughts and Surprises: How much electricty does the solar hot water panel pump use?

Here's someone else blogging about energy.

https://energy-surprises.blogspot.com/

I'm not the only sane person in the asylum after all!

Forgot to boil the water

In the jumble of pros and cons for ventilation systems recovering heat and moisture, the moisture advocates point out the extra energy in the water. This Polaris site (in Japanese) tells us the different heat contained in dry and humid air: apparently air at 20 degrees centigrade has 11.9 kCal of heat at 80% humidity, but only 9.2 kCal at 30%. He doesn't say how much air contains that much heat, perhaps a kilogram, or a cubic metre, or your living room? And he doesn't give a reference point for the heat, whether it is per degree, relative to zero degrees centigrade or the total heat relative to absolute zero. And how do we understand those numbers anyway? I usually only think about calories in food, and whether it's 11.9 or 9.2 it's still only about half a jelly baby.  

Whatever the actual meaning of these numbers, humid air is going to hold more heat than dry air, since the extra water in the air is holding more heat. 

But not only does the water in the air hold more heat, it also needs to have been vaporised. Most of us are familiar with water vaporisation, as it happens when we boil a kettle. Although 100 degrees is the boiling point of water, it doesn't all suddenly turn to steam when it reaches that temperature. It takes some extra heat to turn it from one phase to another. While it takes one calorie to raise one gramme of water by one degree, it takes over five hundred calories to turn a gramme of water into steam. 

This is not just true of the water in a kettle, but of any water that is evaporating. For example the water in clothes hung out to dry inside, or water that has been poured on a plant, or water in our skin. Water evaporating from skin is our main mechanism for losing heat, and our sense of temperature depends largely on how much heat we are losing. This makes humid places feel hotter, because less moisture will evaporate into humid air than into dry air. 

According to the ever-reliable Engineering Tool Box saturated air at 20 degrees centigrade has almost three times more energy than dry air relative to dry air at freezing, so the above figures would be more like 12.1 kCal per kilogram at 80% humidity and 7.5 at 30%. That's 60% more heat. 

The consequence for ventilation is that if you have a system that is exchanging heat but not moisture (HRV), then in the winter you're going to be losing a lot of energy in the airborne water vapour you expel as you bring in dry air. And in summer you're going to be bringing in a lot of heat to the house embodied in the humid air. 

So an energy recovery system will lose less energy, and is probably a good idea if you have dry winters or humid summers.

Of course you're unlikely to be choosing between 30% and 80% humidity. In the summer you may have 80% humidity and want 30%, and in the winter you're likely to get 30% humidity, but probably wouldn't want as much as 80%.

However, as the Polaris site points out, energy recovery systems transfer moisture back into the house. They usually do this across a paper membrane. Along with that moisture you can also get some bacteria and odours, which often makes people reluctant to use energy recovery ventilation in kitchens, bathrooms and toilets, putting simple extractor fans there instead. For example Mitsubishi suggests a dedicated extractor fan for the kitchen, and offers a system with additional drying, heating and direct ventilation options for the bathroom. 

Since kitchens, bathrooms and toilets are the places you usually want to extract air from, while supplying fresh air to bedrooms and living spaces, you may end up only using heat recovery ventilation for a fraction of the house, and any efficiency gains are lost, perhaps along with improvements in interior humidity. Unless of course you can recover heat and moisture without letting anything else through.

Acknowledgment:
Special thanks to Ben Shearon for asking questions that lead me to investigate this topic.

Note from Wikipedia: In SI units, cs = 1.005 + 1.82H where 1.005 kJ/kg°C is the heat capacity of dry air, 1.82 kJ/kg°C the heat capacity of water vapor, and H is the specific humidity in kg water vapor per kg dry air in the mixture.