Tag Archives: lifehack

Saving ventilation cost by using the wind

Most large modern buildings have active ventilation built in, meaning that electric fans drive the air through the building. The airflow direction is usually fixed at construction time. However, if the wind happens to blow from the opposite direction to the ventilation flow, then the fans require extra energy to counter the wind. On the other hand, if the wind agrees with the airflow in the building, then the fans may not need to be run at all. To save electricity, a building could have a wind direction sensor (a weather vane) on the roof connected to a switch that reverses the ventilation fans, so that the fans always pump air in approximately the same direction as the wind. If the wind is strong enough, a wind speed sensor (a small windmill or windsock) on the roof could stop the ventilation fans altogether.
The tradeoff for this adaptive ventilation system is the initial fixed construction cost and the ongoing maintenance of the weather vane, windsock and controller of the fans. All the extra components of the system (relative to the current unidirectional ventilation) are cheap and robust, so the both the fixed cost and the maintenance should be negligible.
Current ventilation systems have differently shaped air inlets and outlets in the rooms, which suggests that the system requires a particular airflow direction. In this case, adaptive ventilation may be much more expensive than the current ones, because the ventilation shafts and air vents need to be doubled. To avoid the need to build twice as many shafts and vents, have just the air inlets and outlets of the whole building switch roles with the wind direction. The rest of the system can remain unidirectional when the valves from the building’s inlet and outlet to the rest of the system switch appropriately. The air inside the building can then move in the opposite direction of the wind some of the time. In this case, the electricity saving is only realised if the building is sufficiently airtight, which is the case for modern highrises that have unopenable windows. If the air is allowed to move through the building independently of the ventilation and the wind is opposite the airflow in the system, then the fans have to overcome the air pressure difference like in the current systems. This wastes electricity.

When to open windows to cool or warm a building

My uninsulated apartment building went from too cold to too hot in about a week, which is normal in Canberra. People have started to open the windows in the stairwell in addition to their apartment windows. The timing of the opening seems a bit misguided – people open the windows in the morning. During daytime, the air outside is warmer than the air inside the stairwell, but during the night the outside air is colder. To state the obvious: to cool down the building, open the windows for the night and close them for the day. Currently the opposite seems to happen, although I counter this trend by closing the windows in the morning when I notice them open.
In general, if you want the building cooler and the outside air is colder than the inside, then open the windows, but if the outside is warmer, then close them. If you want the building warmer and the outside air is colder than the inside, then close the windows, but if the outside is warmer, then open them. This could easily be automated with temperature sensors outside and inside the building connected to a thermostat and small electric motors opening and closing the windows. Such a system would save some of the heating and cooling costs of the building.
There may be non-temperature reasons to open and close the windows, for example to let smell out of the stairwell or to keep insects from coming in. The second reason is not relevant for my building, because all windows have bugscreens and the exterior doors have a gap an inch wide under them, which the insects can easily use to get in.

Tenancy Ending Checklist

Before the final inspection:
Give or receive valid notice of ending tenancy in writing, resolve any dispute about this.
Confirm any arrangements for agent/landlord to access property in writing.
Schedule final inspection.
Disconnect all utilities connected in your name.
Calculate rent payable until end of tenancy and pay that amount.
Cancel direct debit if necessary.
Clean property as needed when compared to incoming condition report.
Arrange for carpet cleaning if necessary.
Remove any additions, alterations you have done to property.
Print 1) bond refund form, 2) move-in condition report (keep a copy), 3) filled or blank move-out condition report, 4) key receipt to take to final inspection. 5) Put the move-in photos and video on a laptop/other device or print them to take to final inspection.

On the day of final inspection or move-out day:
Take photos of meters (date stamped).
Take photos/videos of condition of property and do your own condition report.
Bring the required forms, photos and video to the final inspection. Attend final inspection.
Return keys and get a receipt or sign a photocopy.
Resolve any issues with condition of property.
Sign bond refund form and lodge with Office of Rental Bonds (you or the agent can do this).

Rigid skirt to prevent falls

Falls are a major cause of hospitalisation in the elderly and people with impaired balance or strength. A fall may cause a vicious cycle: the bad experience leads to a fear of falling, which makes people avoid exercise. Not exercising leads to worse balance and muscle condition. Weakness and a lack of balance cause more falls.
To prevent falls, people should train their sense of balance and their stabilising muscles, but in a way that does not risk injury via falls during training. One device that would allow practising balance while preventing falling over is a rigid wide-flared skirt attached above a person’s centre of gravity (the attachment could be almost under the armpits). The hem of the skirt would be above the ground when the body is upright, but its edge would touch the ground if the body tilts too much in any direction. Support from the rigid skirt would then prevent further tipping in that direction. The lack of support in a central position (and for slight tilts around it) allows practising balance, for example by standing on one leg and trying to stay upright. The principle is the same as for helper wheels (training wheels) on childrens’ bicycles, which are off the ground while the bike is in a central position, but touch the road and stop too great a tilt to the side once the bike tips away from the centre. Other analogies to the rigid skirt are hands-free crutches pointing in all directions simultaneously, or a walking frame that surrounds the body, as opposed to being pushed in front.
The advantage of the skirt for fall prevention over crutches or a walking frame is that the skirt is hands-free. The advantage over a fixed training frame, or somewhat slack ropes tied to the upper body that also prevent a fall, is that the skirt moves with the person. This makes training easier by allowing walking and jogging.
The skirt can be home-made from many materials, such as tent poles or bamboo sticks tied or duct taped to a belt at the top and a hula hoop at the bottom. Using modern materials such as carbon fiber ski poles can make the skirt light, yet strong and rigid.
Of course the rigid skirt looks strange and attracts notice if not too many people are using it. On the one hand, the skirt does not have to be used in public if in-home training is enough. On the other hand, the first walking frame or the first crutches must also have looked strange to bystanders, but are now accepted mobility aids that almost nobody reacts negatively or even curiously to.
For using the skirt on the street, one problem is the wide-flared base (about 2m in diameter) that makes it difficult to pass other pedestrians. One (expensive) solution is to make the skirt out of sticks that can be moved independently and add a robotic controller that keeps the skirt narrow if the body is upright, but when the tilt angle becomes large enough, flares the skirt out in the direction of the tilt to stop the fall. Flaring the skirt means moving the sticks outward and lengthening them.

Heating my apartment with a gas stove

There is no built-in heating system in my Australian-standard un-insulated apartment, and the plug-in electric radiators do not have enough power to raise the temperature by a degree. In the past two winters, I used the gas stove as a heater. It is generally unwise to heat an enclosed space without purpose-built ventilation (such as a chimney) by burning something, because of the risk of CO poisoning. Even before CO becomes a problem, suffocation may occur because the CO2 concentration rises and oxygen concentration falls. Therefore, before deciding to heat with a gas stove, I looked up the research, made thorough calculations and checked them several times. I also bought a CO detector, tested it and placed it next to the gas stove. The ceiling has a smoke alarm permanently attached, but this only detects soot in the air, not gases like CO.
For the calculations, I looked up how much heat is produced by burning a cubic metre or kilogram of CH4 (natural gas), how much the temperature of the air in the apartment should rise as a result, how much CO2 the burning produces, and what the safe limits of long-term CO2 exposure are.
The energy content of CH4 is 37.2 MJ/m3, equivalently 50-55.5 MJ/kg. A pilot light of a water heater is estimated to produce 5.3 kWh/day = 20 MJ/day of heat, but a gas stove’s biggest burner turned fully on is estimated to produce 5-15 MJ/h, depending on the stove and the data source.
The chemical reaction of burning natural gas when oxygen is not a limiting factor is CH4 +2*O2 =CO2 +2*H2O. The molar masses of these gases are CH4=16 g/mol, O2=32 g/mol, CO2=44 g/mol, H2O=18 g/mol, air 29 g/mol. One stove burner on full for 1 hour uses about 0.182 kg =0.255 m3 of CH4 and 0.364 kg of O2, which depletes 1.82 kg = 1.52 m3 of air. The burning produces 2.75*0.182 = 0.5 kg = 0.41 m3 of CO2. The CO2 is denser than air, which is why it may remain in the apartment and displace air when the cracks around the windows are relatively high up. On the other hand, the CO2 also mixes with the air, so may escape at the same rate. Or alternatively, the CO2 is hot, so may rise and escape faster than air. For safety calculations, I want to use a conservative estimate, so assume that the CO2 remains in the apartment.
The volume of the apartment is 6x5x2.5 m =75 m^3. The density of air at room temperature is 1.2 kg/m^3, thus the mass of air in the apartment is 90 kg. The specific heat of air is 1005 kJ/(kg*K) at 20C. The walls and ceiling leak heat, thus more energy is actually needed to heat the apartment by a given amount than the calculation using only air shows. It takes 900 kJ of heat to raise the temperature of the air, not the walls, by 10C (from 12C to 22C). This requires 9/555 kg = 9/(16*555) kmol of CH4 with estimated energy density 55500 kJ/kg. Burning that CH4 also takes 9/(8*555) kmol of O2 and produces 9*11/(4*555) kmol = 9/200 kg of CO2.
The normal concentration of CO2 in outside air is 350-450 ppm. Estimate the baseline concentration in inside air to be 1/2000 ppm because of breathing and poor ventilation. Adding 1/2000 ppm from heating, the CO2 concentration reaches 1/1000 ppm. This is below the legal limit for long-term exposure.
CO is produced in low-oxygen burning. As long as the CO2 concentration in the air is low and the oxygen concentration high, the risk of CO poisoning is small.
For the actual heating, I first tested running the smallest burner all day while I was at home, and paid attention to whether I felt sleepy and whether the air in the apartment smelled more stale than outside or in the corridor. There seemed to be no problems. For nighttime heating, I started with the smallest burner in the lowest setting, similarly paying attention to whether the air in the morning smelled staler than usual and whether I felt any different. Because there were no problems, I gradually increased the heating from week to week. The maximum I reached was to turn on the largest burner to less than half power, and one or two smaller burners fully. Together, these burners produced much less heat than the largest burner on full, as could be easily checked by feel when standing next to the stove. At night, the stove prevented the temperature in the apartment from dropping by the usual 2C, but did not increase it. The CO2 produced was probably far less than the bound I calculated above by assuming a 10C increase in temperature. Empirically, I’m still alive after two winters of letting the gas stove run overnight.

Reducing reflections off eyeglasses

Spectacle shops try to sell customers more expensive lenses with glare-reducing coatings. Such coatings are often fragile, which benefits the sellers, because the glare-reducing lenses would need frequent replacement. Another way to reduce glare reflecting into the eye is to find its source and block it. For example, standard flat-lens eyeglasses reflect rays coming from behind and slightly to the side into the eye. If the light source behind can be eliminated, e.g. curtains drawn across a window, then the glare disappears.
There may be many sources of light that reflect from the glasses into the eye, for example due to multiple head orientations and light sources all around. In that case, blocking the light at the source is infeasible, but the rays causing glare can still be blocked closer to the eye. One way is to put side panels on the earpieces of the glasses. The side panel must touch the head with the edge closer to one’s back, so rays from behind cannot get between the earpiece and the head, so cannot reflect off the lens into the eye. The side panels can be cut from cardboard and slipped on the earpieces, as shown in the photo below.

The side panels will also block unwanted light coming from one side into one eye directly (without reflecting off the lens). An example is the Sun shining through a window to the side, causing eye strain.

Joining together detached houses saves energy

Suburbs in many countries consist of detached houses that very close to each other – I have seen neighbours’ walls half a metre apart. Both houses could save energy by joining their adjacent walls together, which reduces heat loss in cold weather and heat entry (thus the need for air conditioning) in hot temperatures. Ideally, the joining should happen at the construction stage, but it is not difficult to do after the houses are built. Just enclose the space between the sides of two houses by extending the front and back wall and the roof of each house. It is not a load-bearing construction, it just has to keep the wind out from the space between the houses and provide some insulation to the space.
An added bonus is the creation of a covered storage area (a door to the space between houses should be created if the houses don’t already have a door on that side). A possible downside is that to get from the front of the house to the back, now one has to pass through the house or the storage area. But given the narrowness of the typical walkway between suburban detached houses, passing through the house may be the best route anyway. Also, when enclosing the walkway, a door can be made in each end to keep it open for passage.
Another downside is that windows on the side of the house now look into a covered storage area, not outside. But if the houses are so close together, then the only view from the window is the wall or window of the neighbour. After enclosing the side, this view becomes darker, but that does not seem a great loss. If it is, then energy-efficient lights can be installed in the enclosed area and kept on during waking hours, so people can admire their neighbour’s wall or window. Really, windows with such views can be replaced by a poster-size print-out of a photo of the view, because if the window looks into the neighbour’s window, then the neighbour probably keeps the curtains closed to prevent spying. And a wall through a window looks pretty similar to a photo of the wall stuck over the window.
The real reason to not join the houses is probably marketing and the desire to show off that it targets. People want to boast of owning a detached house, even if it is less than two metres from the neighbour’s. Knowing this, property developers construct such dwellings and market them as detached (“own your own house”, really owned by the mortgage issuer for 25 years). This is similar to the reason why McMansions are built, only the income of the buyers differs. Also similar are the pride and marketing that make people buy large SUVs, pickups and all-terrain vehicles for driving solely on paved roads.

Silly sunglasses

Most sunglasses do not cover the eye fully. For example, any design where the lenses are close to flat (aviator, retro) or small does not protect the eye from rays coming from above or the side. Sunlight commonly comes from above, so these sunglass designs do not block a significant part of it. If the lenses are tinted (not clear), then they worsen the outcome for the eyes, because the dark glass in the centre of the visual field makes the pupils expand. When that happens, the pupils let in more light from any direction, including sunlight from the unprotected top and side directions.
In comparison, the polycarbonate safety glasses that currently cost 2 AUD in a construction shop have a wrap-around design and large lenses that leave only a small gap between the forehead and the glasses. Light from the side and nearly all other directions has to pass through the glasses before reaching the eye. The material for the safety glasses is polycarbonate, which block 99.9% of UV light. In order for sunglasses to provide better UV protection than the safety glasses, they have to block a larger percentage of UV light or cover more ray paths into the eye.
Suppose that sunglasses were made from a material that blocks 100% of UV. Then to improve on the safety glasses, the sunglasses would have to cover at least 99.9% of the ray paths into the eye that safety glasses cover. In other words, the sunglasses would have to have the same wrap-around design and as large or larger lenses.
An improved design for both safety glasses and sunglasses would take the wrap-around design one step further: cover the eyes from top to bottom as well as from side to side. One way to achieve such cover is a half-dome over each eye that touches the forehead above the eye and the cheek below, as well as the bridge of the nose and the temple.
A brimmed hat that blocks light coming from above compensates to some extent for flat-lensed or small sunglasses. The hat does not protect the eyes from light coming from the side and below the brim, so the classic sunglass designs are still inferior to wrap-arounds even combined with a hat.

Taking your own fingerprints

Some jobs, visas, etc, require a criminal record check from the FBI, which requires sending the FBI your fingerprints. Where you live, it may be difficult to find a professional who will take your fingerprints on an FBI-approved fingerprint card. But no problem, it is quite feasible to take your own fingerprints.
Supplies needed:
1. Scrap paper to practice on
2. Printouts of the FBI fingerprint card on standard office paper (5-10 copies, because you will make mistakes)
3. Ink pad from a stamp (with some black or blue ink in it). For most brands of stamps, the internet has instructions on how to slide the ink pad out.
4. Piece of smooth rubber a little larger than a fingertip, e.g. a piece of bicycle inner tube, a piece of unlubricated condom, or a rubber ball about 5 cm in diameter
5. Paper towels or tissues for wiping ink from fingertips
6. Stick of glue for gluing paper
7. Small sharp straight scissors, or a razorblade and a smooth cutting board, for cutting paper
8. Large envelope for mailing the fingerprint card to the FBI without folding it. Postage stamp(s).

The piece of smooth rubber is for painting the ink of the stamp pad onto the ridges of the fingerprints. Just dipping the fingers in ink or touching them to the stamp pad will put ink in the troughs of the fingerprints as well. Too inky fingers will create a uniform splotch on the paper, not the lines and whorls of a fingerprint. Also, if the stamp pad holds the impression of the writing on the stamp, then the fingers will get that writing on them as inkless areas.
The ink should not be quick-drying, e.g. alcohol-based from a marker pen. This will dry on warm fingertips before the finger reaches the paper. The ink must be liquid, not the paste from a ballpoint pen, because the paste sticks to the fingertip in small chunks. These will create uniform dark splotches on the paper, with the adjacent areas blank white. The ink used in stamp pads is good.
With inky fingers, it is easy to get ink stains on the table or anything else within reach, so the paper towels or tissues should be held ready to clean the ink up while it is still wet.
Procedure:
1. Read the FBI’s online instructions for taking legible fingerprints (https://www.fbi.gov/services/cjis/fingerprints-and-other-biometrics/recording-legible-fingerprints), the Guidelines for Preparation of Fingerprint Cards (https://ucr.fbi.gov/fingerprints_biometrics/guidelines-for-preparation-of-fingerprint-cards-and-association-criminal-history-information) and the Capturing Legible Fingerprints poster (https://www.fbi.gov/file-repository/capturing-legible-fingerprints.pdf).
2. Lightly rub the bulging side of the piece of rubber on the stamp pad to coat it with an even thin layer of ink. Then lightly paint the ink on one fingertip, the first priority being to coat all the ridges from the crease of the first joint to the nail and from one side of the nail to the other. The second priority is to avoid coating the troughs of the fingerprint. Some ink in the troughs is unavoidable, but minimising it will make the print clearer.
3. Roll the fingertip on the scrap paper from nail to nail, like the FBI instructions say. Compare the result to the Capturing Legible Fingerprints poster. The goal is to get a roughly rectangular imprint with the ridges and troughs of the fingerprint visible. Empty spots on the fingerprint indicate too little ink, inky splotches indicate too much. Lightly pressing the second joint of the finger down with the thumb and forefinger of the other hand may help, or alternatively holding the tip of the nail down with the thumb and forefinger of the other hand. Practicing repeatedly with the same finger helps. The ink on the fingertip needs renewing from time to time. If there is too much ink on the fingertip, rolling it on the scrap paper will reduce the amount.
4. Estimate how much ink on the fingertip leaves the best print. If the first roll after inking a finger always creates splotch, estimate how many rolls on the scrap paper are needed (without renewing the ink) to make the fingerprint legible.
5. Once the fingerprints on the scrap paper are looking good, use the same amount of ink and pre-rolls to put the same finger’s print on all the FBI fingerprint cards.
6. Wipe this finger clean of ink.
7. Repeat points 2-6 with each finger. When reaching the thumbs, also put their flat impressions on the fingerprint card (flat thumb impressions require less practice). Doing one finger at a time minimises ink stains on the fingerprint card and the furniture, and gives practice for each finger just before that finger’s print is taken.
8. Ink the four fingers of one hand and practice taking the four-finger flat impression a couple of times. Then put the four-finger impression on all the fingerprint cards. Clean the fingers. Repeat with the other hand.
9. Choose the fingerprint card with the largest number of clear fingerprints. It doesn’t matter how bad the unclear prints on the card are – these will be covered in the next step.
10. For each unclear print on the chosen card, pick the clearest print of the same finger from the remaining cards. Cut out that fingerprint, following the edges of the box it is in. Glue the cutout over the unclear print on the chosen card, making sure all four corners of the cutout are glued down. Hopefully you only need to cut and glue at most 3 prints.
11. Fill out the form at the top of the fingerprint card with black or blue pen, as the instructions say. The required codes for hair and eye colour, etc, can be found in the Guidelines for Preparation of Fingerprint Cards.
12. Without folding the fingerprint card, put it in the envelope together with the printout of the email confirmation of paying the appropriate fee on the FBI website. Address the envelope correctly and mail it. From Australia, sending the A4 envelope to the FBI using regular mail cost under 3 AUD in 2018. In my case, the pdf of the criminal record check was accessible from the FBI’s website less than two weeks after mailing my fingerprint card.

Urination technique 101

Many urinals are shaped so that if your centreline is aligned with the urinal’s centreline, then no matter where you aim, the spray splashes right back to your centre.

The solution is to stand slightly to one side, not directly in front of the urinal, but still aim straight ahead (perpendicular to the wall when viewed from above, not necessarily when viewed from the side). The urine starts flowing or splashing forward almost parallel to the wall of the urinal. This is the principle in a squash game – the more bounces off the wall, the slower the ball moves. If the energy for backward reflection is dissipated, then the ball falls down under gravity. The same applies to a urine stream – the more forward splashes off the wall of the urinal, the more energy dissipated and the more the urine flows downward.