The Evaporative Cooler (4 easy steps to using a psychrometric chart)



A few years back in mid-2015 I moved to a dry hot place and happened to rent out a house that had an extremely inefficient air conditioner. The electric bill was horrible, and I had no water bill. The most obvious solution was a swamp cooler. Being inexperienced in everything related to evaporative coolers and how they work, it took some time to come to understand the ins and outs of these machines.


First, the basics:


Put some rubbing alcohol on your hand, and let it dry. This will feel cool on your hand. After you get out of the pool, you feel cool as the water evaporates off your skin. Once all the water dries off your body, you feel hot and want to jump back in. This describes the mechanism at work here. As water evaporates it cools. Thus if you blow a bunch of hot dry air over/through something wet it cools and moistens the air. Thus the basic thing to visualize is a fan, a ‘medium’, and some water.


We could go into the science and start talking about the phase change of the water, and all the specifics. However, the basic idea is a wet towel being being blown by a fan. That’s how they did it in antiquity and it hasn’t changed much since then.


My specific situation:


My first month’s electric bill was $600! The half ton A/C unit was a rust bucket, and by my estimate this house should have a 1-ton unit. The thing ran 22-24 hours a day and used 4 kwh. 22-hours x 30-days x 4-kwh x $.30. This comes out to ~$800. To explain the discrepancy: In California they have this screwed up electric bill system that increased the price per kilowatt the more you use, with the max being around .30 cents, so some of the cost was in using up the lower cost tiers.


It took some time to figure out exactly how much energy the A/C system was using, but not until after a whopper $600 electric bill had come in and been paid. I made a spreadsheet to calculate the california electricity billing system, it was quite complicated. I looked at the meter a lot; When I turned off the ‘always-on’ A/C the drop in usage was 4 kw! Sure enough it was an honest bill. I considered moving out, forcing the landlord to fix the A/C (very doable in CA), and a lot of other options.


Then I found the swamp cooler!


Some more details on Swamp Coolers:


There are several varieties of swamp coolers. The big boxy ones that re-circulate water, and look like A/C units. The roller ones for shop floors. Also, window type units. However, the efficiency of the unit is based on the medium inside and not the shape. Sizing the unit is based on the square footage you want to cool. Well, sizing is really based on the volume so if you have vaulted ceilings it’s not the same as regular ceilings.


The medium inside the cooler governs its efficiency. The blue-green plastic mats are not very efficient. The pink stuff isn’t either. The wood-shaving stuff is somewhat efficient. However, the cardboard looking stuff is the most efficient!


A swamp cooler must move all the air in your house through in a few minutes. In short, the best strategy is to ALWAYS oversize in order to get the best results. There should be a path for the air though the house/building, and a cracked window or two on the far side. Not a wide open window.


Lastly, in a lot of places that you can use swamp coolers, the water is hard. Thus units that re-circulate water don’t fare so well.


The Find, the buy, and the usage:


I was in the local big-box store and was wandering through the swamp cooler section. All the prices were way out of range for me, but then I noticed a $650 window unit for the exact square footage of the house I was renting. This caught my eye and I went home and researched the hell out of it.


The result of the research was that the thing would pay for itself in about a month and a week. I won’t link to the thing here, but there are various brands of window mounted plastic swamp coolers at big box stores in desert areas. They all look alike and function pretty much the same, but the key thing is to make sure they use the waxy cardboard looking medium. These window type units are not for the type of person that calls a repairman. It’s more of a diy type machine with lots of interesting design choices meant to fool you into breaking it. By reading forums online I learned from others mistakes.


It took a weekend, several trips back and forth to the hardware store, and roughly $800 in stuff (cooler + hose + fittings + other materials). The thing worked wonders. It barely used 1 kwh. It reduced the cost of electricity down to 13 cents per kwh. By the numbers it actually paid for itself in 33 days, and then kept going. The electric bill went down to $100/month. It was a great success.


However, there was a weird problem. On random days it would just not work. Out of the blue on a random day the house would get hot and muggy. These days sucked.  Also, sometimes it would just half work. No amount of opening the windows more, fans, or anything would help. It was as if the swamp cooler turned off of it’s own accord.


The solution, and the point (swamp cooler advanced lessons):


Prior to starting this I had zero experience with swamp coolers. Thus, there was a missing bit of knowledge that I hadn’t considered. I was discussing the ‘random day’ issue with a friend and his response was, “It’s monsoon season what did you expect.” Obviously it took a few days for those words to sink in.


The reason the swamp cooler stopped working randomly was because of spikes in the humidity. There are three key tools that are necessary for having a swamp cooler. Those tools are namely,


  1. A temp/humidity sensor
  2. A website that can show you the predicted temp AND humidity on a given day.
  3. A psychrometric graph


First spend some time (read days) moving the temp humidity sensor around the house and observe thing. For example, I learned that the particular swamp cooler could raise the humidity 40% on a good day, and 30% on a bad day. The reason this tool is needed is to asses if things are working correctly.


Second, find a good website that can show you humidity predictions. This is key. You need to know the humidity and temperature. My go to here is wunderground.org. They have a graph prediction for the next 10-days. On the graph you can customize it to display temp and humidity.


Third and most important is you need to print out a good large psychrometric graph. This is where the magic comes in. By using this graph I figured out how to predict the days where the swamp cooler would not work, also when it would work great. It takes some getting used to, but to the uninitiated it looks like some kind of sorcery.


4 Easy steps to Using a Psychrometric Graph:


  • Put your finger on the bottom x-axis at the temperature that it is going to be (or is) outside.
  • Slide your finger up to the curve that matches the humidity (or an estimation of the curve)
  • Slide your finger diagonally past 30% to 40% (the amount of humidity that your swamp cooler will add to the air)
  • Slide your finger back down to the x-axis and this is an estimation of the temp that the swamp cooler will output (not the temp of your house).


(see chart below)


It is key to understand that this is an estimation, and if the cooler outputs 80 degree air, your house will be hotter than that. In my case the far side of the house could be 3-6 degrees hotter than the output of the swamp cooler. Also, some swamp coolers only add 20% to the air and are horribly inefficient.




It is 100 degrees out, and 20% humidity. What temperature will a swamp cooler output if it adds 40% humidity?


  1. Start at 100 on the bottom
  2. Slide up to the 20% curve
  3. Slide up-left to the 60% curve
  4. Slide down to 80 on the bottom.


Thus a swamp cooler adding 40% humidity to 100 degree air that has 20% humidity will output 80 degree air.





http://www.cpuc.ca.gov/ (they try very hard to hide the info here)


https://docs.google.com/spreadsheets/d/18UmuYY2MZNcGBXqYW7B66MbqC8hdJqXPIF9RA_oOsV0/edit?usp=sharing (my complicated spreadsheet for calculating energy costs in my location)




http://imgur.com/a/GF0gx (imgur backup of image)



Composites and Planned Obsolescence

Being an engineer, and a particularly old school engineer, I spent the early part of my career trying to avoid composites. The thing was that I didn’t trust what I was being told and learning about the material. Technically, any material that lattices two different materials together is a composite: concrete and metal, glass and plastic, clay and stainless steel, wood and gypsum for a few. There are good reasons for compositing materials, but there can be huge pitfalls. I must stress that it’s not all a rosy picture, but there are some good things.


In basic chemistry we learn about covalent and ionic bonds. It isn’t until organic chemistry (usually in college) that we learn about van der waals bonding. This is the type of bonding that keeps plastics together. This isn’t the same as the previous two. There are a ton of extra caveats to this type of bond, it is much weaker than ionic, covalent, or even the crystalline structure of metals. It breaks down in light, is more prone to corrosion, has certain toxicity malfunctions, and even degrades over time. Overall plastic is an inferior material when considering durability, robustness, cyclical use, safety, and product lifetime.


Planned obsolescence is a term coined to describe what economists have decided to call durable goods. One of the most glaringly obvious and hideously polluting faults of durable goods is the usual failing of a small plastic part. This is why industrial equipment rarely incorporates the material, and when said industrial equipment makes use of plastics it is different. They amp up the thickness, choose particularly durable plastics, and hedge all bets.


Not to be redundant (he he) but typically redundant systems are robust and rarely fail. The chemistry of plastics dictates that they will fail, fail often, fail under corrosion, break down in light (UV) and fail, spew tiny amounts of toxins that are imperceptible, and generally make our lives hell. Yes, there are benefits, and we all know those benefits, but why the railing against plastics?


Aircraft composites are plastics. Albeit plastic with something else inside, but still contain plastics. This material is extremely strong for its weight (referred to as strength-to-weight by engineers). Another caveat is that this composite is extremely strong in one direction, and weak in the others. This is called anisotropy. Metals are not perfectly isotropic (uniformly strong in all directions) but they are close enough to generally consider them so. Composites are not isotropic at all and can be very strong in one direction, but very weak in another.


For decades, there were three main aircraft structural materials namely, aluminum,corrosion resistant steel, and titanium. Hopefully, the materials were used in this order because the strength to weight relied highly on the use of aluminum with titanium and cres filling in only the gaps. This new ‘composite’ material throws a whole lot of junk into the mix that confuses everyone. This confusion is particularly true of executives, reporters, and generally anyone who doesn’t understand math and physics well.


— warning note: be aware of the term ‘factor of safety’ here —


If I was a billionaire, and I wanted to fly around in a jet, I would completely ban plastics and composites from my aircraft on the mere grounds that it was a bad investment. At the point that a salespeople interjected some random composite material benefits, I would ask for a deep discount for the aluminum equivalent. I consider aluminum to be the superior material. At this point we are going to have to go over the differences and start splitting hairs.


Aluminum has several widely used variants. Its main advantage is that for its weight it is very strong and relatively cheaply bought strength. It is highly corrosion resistant, has a long lifetime, and is the choice metal for durability in aircraft over time. However, it has a lifetime. This lifetime is very predictable. So predictable, that you can calculate very precisely when it will fail, but it will eventually fail. This failure mode is called fatigue.


Steel has many variants, but only cres can be used in conjunction with aluminum. Two metals tend to create a battery, and one corrodes away. Cres is the way to avoid this battery-corrosion problem. Steel (and corrosion resistant steel) have a particular behavior that causes it to have potentially/possibly infinite fatigue strength, whereas aluminum is not capable of this infinite behavior. However, steel is much heavier per strength than aluminum and a fully steel aircraft would suffer extreme performance/weight problems.


Titanium is pretty much relegated to two jobs. One, where there is a high temperature application, as it is hard to melt. Two, where there is a particular shortcoming that steel will not suffice for. Titanium might as well be called ‘incorruptible unmeltable brittle steel’. It is expensive, hard for communists to obtain, and serves pretty much as a replacement for steel as their strength to weights are pretty close. Although titanium is a bit stronger. Also, titanium corrodes far differently (less) than steel does.


Keep in mind that balsa wood and burlap/cloth ply are the ‘really old school’ materials, but are no longer used widespread. Also, ultralights are aluminum tubes with nylon cloth.


Composites are the new kid on the block. This material has ‘huge’ strength to weight benefits. The material has annoyingly hard to calculate stresses that only apply in one or two directions, take more manpower to produce, and confuse the crap out of everyone who isn’t a scientist/engineer. The benefit is that the strength-to-weight can be off the chart if put together right. However, the achilles heel is not the lack of understanding, or high cost of production. The achilles heel of this material is the almost fraudulent lack of lifecycle, effectivity, or longevity calculations.


— Please read the last sentence of the previous paragraph a few times. The last sentence of the previous paragraph is the point of this article/post —


Let that sink in.


To be clear, composites have a clear advantage over the other material choices. For example, in non-reusable rockets it should be the prime material due to its peculiar properties. Let’s say that the thrust reversers on an engine are ‘replaceable’ then this would definitely be the place to use them. Imagine a case where something needs to be extremely strong, but need not last past 5 years of repeated use, and this is the place for this material.


A Glow-in-the-Dark Truck?

I don’t have to worry about scratches on my door in the parking lot, but you do.


I had this really great idea for a passive air-conditioning system for my truck. This plan was years in the making. However, the end output is that my truck glows in the dark and just doesn’t look quite right (a good thing). To tell the story we must begin at the start of things.


I bought an old used pickup from a private party. It was one of those cases where you could absolutely tell that the guy had taken good care of it, but was ready to move on. The original mats were still in it, and it was kept clean. There were several problems with the truck, but it ran good. One of the problems was that the clear coat was peeling off on the roof, hood, and doors. I don’t mind this actually, because I had the bright idea that I would paint it myself… eventually. It would take several years to plan out the details. Rust happens slowly, so why not take our sweet time in getting the money, tools, and ability to do the thing.


After several years the rust was beginning to start to take hold in some places, and the clearcoat degradation had reached critical mass. Also, I recently moved into a place that has a nice big garage, and space enough to paint a vehicle. More, I happened to have enough money to buy the supplies that I had planned out in my notes for several years or occasional looking. I decided to buy some samples and test out the ideas I had.


The original idea was to use a pigment that changes color based on temperature. Turning black when cold and white when hot. Thus, the paint could function as a passive air conditioning system in a small way. Since there are other types of pigments out there I ordered some samples of these as well. Namely, a pigment that changed color based on UV, and one that glows in the dark.


The secondary idea was to improve durability and reduce the possibility of getting dings and knicks by painting the whole vehicle in some kind of epoxy or truck bed-liner like stuff. This would also alleviate corrosion (rust) over all


I put a big piece of plywood on the ground in the backyard, in a place that it would get a lot of sun. It was August at the time and I knew that the heat would test it to the max. I rolled out about half a dozen samples on this large piece of plywood that I had leftover from a previous project. All of the pigments worked fine. However, after day one the UV pigment stopped working. After a couple of weeks the temperature sensitive paint turned an ugly blotched brown-toast looking and stopped working. However, the glow in the dark pigment continued to work.


I planned according to the results. I purchased some tintable truck bed liner, and enough glow pigment to do the entire vehicle. About a decade ago I had tried a DIY roll on bedliner, so I had some ideas about how/what I wanted. I’ll spare you the specifics of all of the tape/papering, scuffing mixing, 1st, rescuffing 2nd, scuffing, and 3rd coat. The whole project took a lot of energy over an entire 3-day weekend to complete.


Inevitably, there were setbacks, and mistakes, but it got done. There is a place where some of my hairs were imbedded and ar visible. I discovered the mil thickness required removing the door handles, so decided to not paint close to them. At one place of 2”x2” adhesion didn’t work well on layers 2 and 3, but tearing it away and using a sponge with acetone and some fresh resin covered it up. There some large runs, and all the things you would expect from a non-professional DIY (2nd timer) project. The end result was good enough.


There was some intent to make the thing look ugly so that it would be avoidable in traffic and to thieves. However, the ugly didn’t happen. I chose grey as a tint on the assumption that it would be more stealthy and generally unattractive. Instead, of looking kinda ugly and stealthy it comes off looking more just off and sticks out as different. Like a glitch in the matrix during the day and at sunset. At dusk it softly, on the edge of perception, glows. However, at night the glow isn’t really effective (weird).


It is somewhat of a disappointment that the glow actually doesn’t realistically show up unless you drive into an unlit tunnel or parking lot from broad daylight. Even when I get gas at a bright gas station, it isn’t particularly obvious when I drive away. I’ve seen it noticed by pedestrians, but not other drivers after dark. The glow is extremely subdued in the light of streetlamps, and most of the roadway lights around. Only in that weird occasion where light changes too fast for people to turn on their headlights does it ever become obvious. Now, it’s far more subtle.


The truck does get looks, but more looks of squinting eyes trying to figure it out. The glow is not obvious, thus people can’t quite figure out what they are looking at.


The picture was taken by decreasing the shutter speed on the camera.



My Truck - Glows

Daylight photo of my truck




Oil Pulling, the great fad of 2016

The concept is really way too simple to explain. Oil pulling is using cooking oil (coconut, canola, olive, etc) as a mouthwash. It can also be applied to other areas like the scalp, legs, or forearms. However, the term is meant to describe using it as a sort of mouthwash. There are other caveats like DO NOT use mineral oils, and all the other stuff about keeping the oil as organic-clean-hipster as possible.


I’ve been watching this fad and it grow somewhat over the past year or so. I’m not sure I would actually classify it as a fad, but that would be the easiest way to communicate it. Right now it appears to be in that formative stage of things that only a few people know about it, and I’m pretty sure it’s going to stay there because there appears to be no way to capitalize on the opportunity. This is because it is just freakin cooking oil.


The only reason I know about this is because I was oil pulling long before I even knew what it was called. Since I was a teenager I’ve had really bad dandruff. Not eczema, just bad itchy dandruff, it was pretty annoying. Nothing worked to solve it. I tried all sorts of things: coal tar shampoo, selsun blue, tea tree shampoo, and everything over the counter. The only thing that worked was this thing I called an ‘oil shower’.


I would plan on it being a long shower and make sure I had an extra towel, some cooking oil, and lots of shampoo/soap. Once in the shower I would pour cooking oil in my hand and rub it vigorously into my scalp and keep putting more in until it was sopping with oil. After a lot of scrubbing I would scrape it off. I would repeat this process until the oil no longer contained the white ‘dandruff’ that it was taking off my scalp. I could tell that I was done when the oil no longer turned white. How I could tell this would be by scraping my hand over my head until I had enough in my hand to inspect it for clarity.


As you can imagine this process was really messy. It would take a ton of soap to clean all the oil out of my hair and off my skin. I would have to wash everything at least twice. Inevitably I’d get oil in my eyes, and this sucks just as much as soap but lasts longer. Sometimes I would have to dry and take another shower a couple of hours later just to clean off the oil. However, I would be dandruff free for 2-6 weeks depending on the stress I was under. I’ve told a lot of people about this, but not really received much feedback.


As a side note this process became extremely neat and tidy when I (apparently along with everyone else) discovered coconut oil. Only the discovery was not about the ‘health benefits’ for me. Coconut oil is partially solid at room temp the stuff doesn’t run down my back and get all over the place. It makes the whole operation easy… So now I’ve pretty much solved my dandruff problem by keeping some coconut oil in the shower. I’ve also realized that crisco could be used as a cheap alternative, but we have to keep things hip here.


Technically my ‘oil shower’ was oil pulling, but of the scalp instead of the mouth. So last year when I heard about oil pulling I was confused. I had never considered putting the stuff in my mouth, rinsing like mouthwash and spitting it out in the toilet (because it might clog the sink). I tried it and I liked it. I felt like an idiot from 12+ years of honing my ‘oil shower’ technique without ever considering tasting the cooking oil. It was as if once I decided to put it on my scalp it became shampoo, and therefore soapy, and not tolerable in my mouth.


After a good brushing and flossing doing an oil pull makes my teeth feel as smooth as if I’ve just come back from the dentist. However, after discussions with others not everyone gets this feeling. Others have said that it makes their gums feel better, or that it does nothing for them. So obviously results vary.


Two theories/opinions come to my mind. One that it might be old forgotten tech/methods, and two that on a macroscopic level it works out. From some of my research it is apparent that thousands/hundreds of years ago people did do things like oil pulling (mouth, scalp, and skin variants). Also, the idea is pretty sound and it would be hard for an honest (and I stress this word honest) scientist or doctor to realistically debunk something so simple that it’s worked for thousands of years. Keep in mind that oil pulling is not a replacement for the normal brushing with toothpaste thing… well it’s not a replacement for me at least.


Theory/Opinion 1: I read in the iliad a while back and remember that they put olive oil in their hair back then, when they wanted to look ‘handsome’ or something. It would also be understandable to try to polish one’s teeth with the oil remaining from a hunted animals boiled fat. This would act as something like a cross between lip balm and toothpaste. I’m sure that if you do some research you can find thousands of other instances of this type of curiosity, but the point is simple. It’s damn old school to use oil as a hygiene product. Quick trivia fact: old school soap is oil/fat, lye, and water. That is a pretty big hint about being hipster-natural-simple.


Theory/Opinion 2: Imagine you’ve just poured the foundation of your house today, the guys just got done and are about to go home at 5pm. Just then some idiot shows
up with a truckload of cooking oil and pours it right in the setting concrete. He also takes good measure to pour it all over you, the workers, their equipment, and the whole lot. This is essentially what you’re doing to the little bastards in your mouth trying to build houses ‘plaque’ on your teeth. While it may not be an petroleum oil spill, it still mucks everything up and wreaks havoc on operations. At the same time its none too toxic to you. Besides you spit it out along with all the stuff it absorbed anyways.


In the end oil pulling (as long as you don’t use mineral oils) is probably as proven as you can get, and likely the cheapest value added thing you can do for your health. I talked with a hair stylist in some depth about the concept, and her response was that the regulations prevent her from claiming that it had any effect on dandruff. I would assume the same for a dentist. In other words don’t expect your professionals, leaders, bourgeoisie, or pilot bureau to tell you about it.

Projects & Links

Colonize the Moon
About moon/mars/asteroid colonies and space stuff

Computer Dungeon
linux/raspberry-pi/bitcoin and computer stuff

A video upload server I coded myself