Monthly Archives: November 2007

Zen and the art of deck repair

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Lately I’ve been trying work on my Zen habits and one of the tenets of this philosophy is to get rid of things that you are no longer using. An item in our lives that added cost and complexity and was no longer providing equivalent value was our hot tub. It came with the house and we used it for a while, but got out of the habit after a few years. It just continued to require energy, chemicals, and periodic repair that was out of proportion to the value we were getting from it. So we decided to give it away. I removed the decking surrounding it and with the help of a sawsall and eventually a chainsaw, I eventually liberated the deck structure that had been built around it. An ad for a functioning free hot tub on Craigslist resulted in 9 eager takers in less than 4 hours. Two people arrived for it around the same time and after a coin toss, the tub had a new owner. I wrote up a blog entry about it in July.

If you’re ever considering whether you should put a hot tub on top of your deck or build it into your deck, please choose on top of the deck. You’ll be much better off in the long run. Hot tubs require maintenance and building the tub into a deck makes maintenance much more difficult.

So for a few months, the gaping hole in the deck stared at me and I stared back at it wondering what would be the best way to fill it in. We joked about putting in a fish pond to entertain the cat and quickly realized that it would contain water and pumps and probably be a bigger maintenance headache than a hot tub. Thus it would definitely not be aligned with my desire to be more zen-like.

After removing the hot tub I soon realized that the deck had an oddity to it that wasn’t apparent prior to the tub’s removal. The main joists where the decking met were not aligned on the opposite sides of the hot tub. I wondered if this would present a problem if I were to have visible mismatch where the joists met in the middle or if it might look artsy. I drew it up in Autocad and realized that it would be very strange looking as you can see in the image below.

I decided I probably had to do some more surgery on the deck to get the main joists in alignment. After making another drawing, this time with the joists meeting at a center, I was much happier with the result. I removed the misaligned joists so that new ones could be installed that would align with the other joists.

I had previously met a handyman through Craigslist when I needed some work done on my siding. He was very professional and let me provide a lot of input, buy the materials, and didn’t charge me any extra for my help. I decided to hire him again for the deck work because I knew with some professional help, the job would go very quickly once it got started. A colleague of Terri’s joked that I must have been in the corporate world too long because I was outsourcing my handyman jobs. Maybe, but I know good help when I see it and I’m more than happy to pay for it.

The hole in the deck left by removing the hot tub.


I was in charge of the design and the materials. Here we have the pressure treated 2 x 8 joists and the 2 x 6 redwood planks.


Here are the joists with the redwood decking just starting to be installed. The joists were supported every 2 feet on the concrete pad in case anyone ever wants to put another hot tub on top of the deck. I also left the access door for the electrical wiring in the deck.

And here it is, all finished and looking like new. As the wood ages the colors will blend in. Right after a pressure washing, all the wood looks new like the new decking in the middle. That will be job for next spring.

UPDATE 2007-Dec-05:

We received a pleasant surprise in our electric bill today. It was 40% less than last year’s bill for November. The electricity cost to run a hot tub was one of those things that I never really wanted to contemplate when we owned it. Now that it’s gone, I’m only too happy to know what the savings will be. Based on some web research, a reasonable estimate for hot tub energy consumption appears to be between $400-$600/year and much of that is incurred in the winter when the difference between the outside temperature and the water in the tub is at a maximum. The cost of the chemicals and periodic repair added up too, easily adding a few hundred more per year to the overall cost. So the missing tub is already beginning to pay for the deck repair with negawatts and also by eliminating the cost of chemicals and maintenance.

Wind Turbine Efficiency

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At an NCRES meeting last night the question of wind turbine efficiency came up and I was about to explain it based on my understanding of the Betz limit, but realized it was a bit too complex an issue to summarize in a few sentences, so I decided to put it in a blog article. In fact, it’s even a little challenging to put in the blog, because it requires a table and the blog composing interface doesn’t seem to properly display tables or the characters pi or rho for some reason. So you can find a table and a few more details here, if you’re curious.

I use both the units of mph and m/s for speed since the U.S. has never bothered to convert to the metric system. For U.S. readers, an easy trick to convert from m/s to mph is to double the number and add 10%. What follows is rather technical, so if you’re not interested in math, physics, or wind energy, you may just wish to skip this article.

In order to understand how much power you can generate with a wind turbine, you must first know how much energy is available in the wind. This energy is primarily determined by wind speed and the size of the wind turbine’s rotor. Power generated is proportional to how much kinetic energy can be extracted per unit time.

Kinetic energy of a moving mass is defined by the equation ½ mv2. We need to know the kinetic energy of the air moving across the swept area of the turbine’s rotor. Multiplying energy by its rate of movement will provide its power.

The air’s mass per unit time can be computed with the formula pAv where:

p = density of the air
A = swept area of turbine’s rotor
v = velocity of the wind

Thus combining the equations for kinetic energy and wind speed, the power available in wind comes out to:

½ pAv3

Air density (p) is about 1.2 kg/m3 at sea level and a temperature of 20 °C. This number varies depending on temperature and altitude. For example, in Colorado air density is about 1 kg/m3 or about 20% less than at sea level.

Let’s take the example of a Vestas V80 turbine with an 80 meter rotor. The amount of wind energy available in a 20 mph (9.8 m/s) wind for this turbine with 5027 m2 of swept area is:

½ × 1.2 kg/m3 × 3.14 × (40 m)2 × (8.9 m/s)3


= 2.3 × 106 kg·m2/s3 = 2.3 MW

However, this number is the theoretical power of all the wind moving across the swept area, and you cannot completely stop the wind to get 100% of its energy. In 1920, a German physicist named Albert Betz figured out that the maximum energy that can be extracted by a wind turbine is about 59.3% of the theoretical energy present in the wind. This has become known as Betz’s Law. This means that you can only get about 1.35 MW from a 20 mph wind at sea level in the example mentioned above in the best case. Looking up the specifications for the Vestas V80 wind turbine in the graph below, we see that it generates about 950 kW in a 20 mph wind, which means it achieves about 70% of its Betz limit efficiency. This number is impressive considering there are losses at every stage of energy conversion, including the drag on the blades, the gearbox, the generator, and the transformer and losing only 30% through all these stages is quite good.


As the wind speed increases, the energy present in it goes up by the cube of its velocity. However, the maximum output of the V80 turbine stops at about 28 mph (12.5 m/s) when it reaches 2 MW. At this point, this turbine generates at about 54% of its Betz limit efficiency. From this point on, the wind turbine will not generate more than its 2 MW rated power despite the fact that the Betz limit power will climb to nearly 30 MW by the time the cutoff of the turbine is reached at 56 mph (25 m/s). Around the time of the cutoff, therefore, the turbine will be operating at 7% of its Betz limit. The turbine cuts off in high winds to protect itself from damage.

In the grand scheme of things, much of this ‘wasted’ power is mostly hypothetical since the wind speeds even at some of the best sited wind farms tend to average between 15 to 26 mph throughout the year. If the components were to be sized to handle 30 MW of power, they would be much heavier and much more expensive. So sizing the turbine for 2MW optimizes overall cost considerations over the life of the turbine.

So, how efficient is a wind turbine? The answer is that ‘it depends on how you define efficiency’. In the case where you measure efficiency as the amount of energy that is theoretically available to what is actually extracted, it can look like a very small number, about 40% maximum. However, if you consider that without the wind turbine, 100% of the energy it provides would be wasted, then the answer is that it is infinitely efficient.

Colorado Wind Energy

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I was out last week flying in the LongEZ and I decided to check the progress of the large wind farms that are under construction in Northern Colorado. One of these wind farms called Cedar Creek is right at the Wyoming-Nebraska-Colorado border and the other is farther east in Colorado, just south of Sidney, Nebraska. It is called the Peetz Table Wind farm. Between them, they have 500 wind turbines with a peak generating capacity of 700MW.

One of the things that impresses me most about wind farms is how fast they get built. These two facilities were just in the discussion stages 2 years ago. Early this spring they were just setting up the towers and now all towers are nearly complete and generating power. When I was growing up in Pennsylvania, nuclear power projects like the Susquehanna Steam Electric Station took a very long time to build, with an average build time of 12 years. By contrast these wind projects are going up in a year or less, and the amount of land available on which to build them is substantial so I would expect to see many more going up over the next few decades. Out west we also don’t have nearly the number of people objecting to them with NIBMY excuses. I suppose when your closest neighbors include 220 Minuteman silos, you have a different perspective on what constitutes a “good neighbor.” Some people can be very picky about what they allow in their backyards, as evidenced by Cape Wind.

My previous blog posting on Colorado wind power included an aerial shot of Colorado’s Ponnequin wind farm near Cheyenne, and I now have some new photos of the new wind farms I mentioned, each which has more than 200 wind turbines.

There are also some photos of the new Vestas Blades factory which is under construction in Windsor. It will produce about 1200 40-meter wind turbine blades per year when it is completed next spring. They are even talking about expanding it to increase the rate of production by 50% within a year of commencing operation.

Blending E85 at the pump

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I previously wrote about using ethanol as an aviation fuel. After noticing that the national average for aviation fuel is now around $4.60/gallon, and E85 is available for $2.19/gallon, it seems fitting to revisit the subject. As oil heads toward $100/barrel, pushing regular gasoline over $3/gallon again it would seem that E85 is poised see some renewed interest at the fuel pumps around the country.

In order to take advantage of E85’s lower pricing in comparison to gasoline, it requires that you have a ‘flex-fuel’ vehicle that is approved for use with E85…or does it? I began to ponder the question of whether you can safely run E85 in a vehicle that is not specifically designed for it. I decided to do some research and experimentation on the subject. There is a lot of misinformation floating around about ethanol, much of it by people who don’t have the slightest understanding of fuel chemistry. It’s sometimes so often repeated that you have to wonder if there is some sort of conspiracy against ethanol. I have a little more experience than the average man off the street about gasoline and ethanol. I worked in HP’s Chemical Analysis group for 7 years (now part of Agilent Technologies) where one of the instruments I helped to design and support measured oxygenate content in gasoline. So I am constantly amazed at how people with no technical background in the subject will confidently repeat common myths about ethanol. I covered a few of those in the aviation fuel article so I won’t repeat them here.

I was interested to know if anyone had developed a kit to convert a conventional car into an E85 flex fuel vehicle. I found that there are several conversion products on the market that splice into a car’s fuel injection system that allow any fuel-injected vehicle to use E85 fuel. Just about all cars manufactured in the past 15 years use fuel injection systems instead of carburetors to adjust the air-to-fuel ratio to the engine. The advantage of fuel injection is that it can be computer-controlled to vary the air-to-fuel ratio based on a number of factors such as throttle position, engine speed, manifold pressure, engine temperature, and oxygen content of the car’s exhaust. The ability to monitor all of these parameters and adjust the mixture accordingly has helped significantly with advances in fuel economy and emissions reductions. The computer is able to adjust the fuel amount by pulsing the fuel injection valves to allow just the right amount of fuel to enter the intake manifold. The air-to-fuel ratio is thus determined by how many milliseconds the injector valve is opened each cycle. By monitoring the oxygen content in the exhaust, it’s possible to tell whether the fuel injectors are providing too much fuel (too rich a mixture) or too little fuel (too lean a mixture) and that information can be used to help close this control loop. Although I haven’t been able to find any technical descriptions on the theory of operation of these conversion devices, the only thing that one can assume that they do is to stretch the pulse generated by the car’s computer to compensate for the air-to-fuel ratio difference required by E85 to extend it beyond what the car’s computer had included in the lookup table for the air-to-fuel ratio settings. It needs to do this because the air-to-fuel ratio for ethanol is about 30% lower than it is for gasoline. So the effect of adding one of these devices to your car is to shift the lookup table to favor E85 fuel in the event that the standard lookup table cannot reach the lower air-to-fuel ratio required to keep the mixture rich enough when running ethanol.

I would estimate that the cost of the electrical components to implement a simple scheme like this would be well under $50, and so you would think a conversion kit would sell for somewhere around $150 or less, but they are charging as much as $500 to $750, which is more that I wanted spend to run some E85 experiments. So I won’t be discussing the efficacy of E85 conversion kits. Instead, I will concentrate on blending ethanol with gasoline at the pump.

Ethanol has about 28% less thermal energy (measured in BTUs) than gasoline. However, the process to convert the BTUs into mechanical energy on cars is rather inefficient, usually less than 30%. Thus it doesn’t automatically follow that your fuel economy will be reduced by exactly 28% when you run E85 in place of gasoline if you can improve the conversion efficiency. In fact, E85 may deliver similar fuel mileage if your car’s computer can advance the timing of the ignition and convert more of the BTUs into usable mechanical energy. This is possible due to ethanol’s superior octane rating, which is a measure of resistance to engine knocking, also known as ‘pinging’ or detonation.

E85 has a 105 octane rating, which exceeds the octane rating of even the most expensive premium gasoline by a wide margin. For example, in Colorado we have 3 commonly available grades of fuel: 85 octane, 87 octane, and 91 octane. These are lower than what you’d find at sea level because at Colorado’s higher altitudes, the risk of detonation is lower and thus you can safely use lower octane fuels

Gasoline’s price goes up with increased octane rating because of its higher ‘grade’ and to cover the expense of the blending agents required to enhance the octane rating. I’ve noticed that the price goes up approximately 7% per grade here in Colorado. I’ve often wanted to use 85-octane gasoline since that’s the lowest price for fuel advertised on the gas station signs, but I know how destructive detonation can be to an engine, so I always use at least 87 grade on my Dodge Durango. On the few occasions I tried 85 octane, I could hear the tell tale signs of knocking when climbing hills. The knocking goes away in a few seconds since the computer is able to monitor a ‘knock sensor’ on the engine and retard the ignition timing accordingly but I still don’t like to hear that sound so I stick with 87 or higher octane.

I noticed that there is a rather extensive Wikipedia article dedicated to using E85 in standard engines. Although there are a number of warnings about all the things that could happen when running E85 in a vehicle not specifically designed to run on E85, most of them don’t apply to vehicles manufactured after 1990. For example, much of the rubber seal material in automotive fuel systems was changed after ethanol became a common blending agent. Ethanol is typically mixed at the rate of 10% ethanol to 90% gasoline to help reduce emissions, and most cars can run fine on a mixture with as much as 20% ethanol. I became curious to see what would happen if I tried running on 30% ethanol, so lately I’ve been filling my tank w
ith 2/3 of the less expensive 85 octane gasoline mixed with 1/3 of E85. This gives me something close to a 30% ethanol ratio (E30) with an expected octane rating of around 91 and a BTU content that would be 90% that of gasoline. Since I’m saving 7% per gallon on the gasoline, and 30% per gallon on the E85, my fuel bill effectively is reduced by about 15%.

I have a fuel computer in my Durango that gives me instantaneous and average MPG and I’ve noticed about a 10% drop in MPG on my E30 blend, so it’s still about 5% cheaper to do this than to fill up with regular gas.

I’m not blending my own E30 for the savings, but rather to satisfy a curiosity about using ethanol. I suppose if one is of a mindset to reduce our nation’s dependence on fossil fuels, blending in E85 at the pump could have an immediate impact of reducing our demand for gasoline by about 30%, or 40 billion gallons per year while increasing the demand for ethanol by a similar amount. The ethanol industry doesn’t produce enough to satisfy this level of demand yet, but if more people started blending E85 with regular gasoline at the pump it may help to drive demand for E85 to help to increase its availability. One of the common shortcomings of E85 is the fact that it’s only available in a relatively small number of locations. For example, in my own town of about 77,000 people, we have only two stations that carry it.

What I’d really like to do is reprogram my car’s computer, often referred to as the ECU (engine control unit) or PCM (powertrain control module), to accommodate E85. However, the information to do something like this isn’t readily available. If you’re an automotive engineer with Daimler-Chrysler and know how to reprogram the ECUs to be E85 compatible, please contact me ;-).

My nephew is currently in the process of installing an open source-based ECU called a MicroSquirt II in his 1981 DeLorean and I have become his technical support hotline, giving him tips on proper soldering techniques and electronic debugging issues with the device. The more I read about it, the more I like the idea of a completely user accessible and reprogrammable ECU. That would make it easy to experiment with various ethanol ratios and once it’s debugged, the data could easily be made available to anyone with a similar vehicle who wants it.

The EPA is concerned about aftermarket products in this category, of course, because the ECU is largely responsible for keeping the tailpipe emissions compliant with clean air regulations. But I see that as a relatively easy problem to solve because using oxygenated fuels such as alcohol and reducing tailpipe emissions tend to be mutually compatible goals. The EPA has issued laws against altering the ECU in a way that makes the vehicle non-compliant with clean air standards. This was a problem when people were converting cars to run on propane and natural gas back during the first energy crunch but today I think those laws are mainly aimed at companies selling ‘performance chips’ which tend to sacrifice fuel economy and tailpipe emissions for more power.

It will be interesting to see what happens with E85 because the stock market seems to be predicting a glut of ethanol in the near future, but with the recent increase in gas prices it may take care of any potential ethanol over supplies, especially if the idea of using it in standard vehicles becomes popular.