Saturday, July 4, 2015

Does Outside Air Temperature Affect MPG?

Most of us that have driven vehicles in cold weather have recognized that they consume more fuel as the outdoor temperature drops. We might attribute it to letting our cars sit and idle in order to maintain a warm interior, or we might surmise that slippery road conditions reduce fuel efficiency. While both of those factors decrease fuel efficiency, I've gathered some data that indicates the temperature of the ambient air also affects the efficiency of internal combustion engines.

I began collecting data on February 9 this year using my 2013 Volkswagen Passat TDI SE with a diesel engine and manual transmission. My car has a meter that calculates average fuel economy (miles per gallon) for each trip, so I've been recording the fuel economy for my trip to work each morning. My route is identical each day and while my data doesn't represent an entire year, the temperature range is wide enough that I don't expect significant changes in the data over the next seven months. Road construction on my route added a detour beginning April 2, which increased the distance and added more 45 mph zone driving to the trip. I've noted the route change in my data, but what's presented here includes data from both routes.

My Volkswagen owner's manual includes this chart that predicts an increase in miles per gallon as trip length increases and also as temperature increases.  Volkswagen's chart implies that my fuel economy would increase further if my commute were longer than my current 30.8-mile trek. I attribute that effect to the inefficiency of an internal combustion engine at temperatures lower than the normal operating temperature, and to a lesser extent the higher losses in the powertrain due to cold lubricant. I have observed that it takes about 7 minutes for the temperature gauge to settle at the normal operating temperature in the winter, while it only takes about 5 minutes in the summer. Since my data covers nearly the same route every day, my chart doesn't duplicate Volkswagen's, but includes more temperature data than VW's two series.

My data indicates a pretty strong correlation between increasing ambient temperature and increasing fuel economy. The regression curve added to the chart reveals that the correlation is almost linear, but a slightly better fit to a second-degree polynomial with a stronger effect at colder temperatures. Although the coefficient of determination (R²) is relatively high at 0.8172, the scatter in the data convinces me that there are other variables affecting fuel economy besides temperature. Wind, traffic congestion, and speed are all obvious effects that probably contribute to the data scatter above. Some of these are out of the driver's control (wind or road conditions), while driving behavior clearly affects mpg and is clearly in the driver's control.

For my data, I've tried to accelerate consistently from one day to the next, I set the cruise control to the same speeds as much as possible, and fortunately traffic density does not often affect my speed at the time of day I make my commute. To reduce the variables related to air temperature, I drive no differently when the engine is cold in the winter than I do in the summer, i.e. my car doesn't sit stationary while "warming up" in the winter.

I chose one temperature each day based on the temperature recorded by the National Weather Service even though the thermometer in my car leads me to believe the temperature may vary by a few degrees over my route. More complex data gathering and analysis is possible, but is not included in the data I've presented. Since temperature alone does not represent the only effect on fuel economy, I've also collected data on other variables that should prove insightful in understanding fuel economy trends. Those data will be presented in future posts right here. In the meantime, it has been comforting each day to recognize a factor out of my control that can be used to predict fuel consumption for that trip.

Tuesday, June 30, 2015

Corn in the backyard, 2015 -- weeks 7 & 8

June 21

Although the stalks added about 21 inches of growth in the seventh week to reach 61 inches tall, the crop is beginning to show signs of stress in some areas.  Persistent rain over the last two weeks has resulted in standing water or very wet soil in the lowest spots of most of the fields in our area.  You may have noticed the stalks just right of center in the top image are lagging the other stalks, and have yellow leaves at their base.  That part of Farmer Wagenbach's field appears to be affected more than the rest, but continues to grow.

Even with the rain, the weather was warm enough to record 178 growing degree days versus a historical norm of 152 for the week.  There is no sign yet of tassels or ears, but we'll continue to monitor that closely.

June 28

The stalks added another 21 inches of height in the eighth week, reaching 82 inches.  Growing degree days totaled 174 which was slightly higher than the historical norm of 163 for the week.  More rain over the week gave the soil little chance to dry out, which affected the growth of some of the stalks.  Since there aren't any tassels or ears in the field yet, it's still too early to tell if yield will be affected in the wet portions of the field.

Friday, June 26, 2015

The Four Best Things About Homeschooling

I wrote this article last fall for the newsletter of our local homeschool association, and I share it again here for your edification.

I’m Kurt Riggenbach, and I’ve supported my wife, Karen, as she did most of the work in educating our daughters over the past 13 years. Lily finished high school five years ago, and Gretel just finished this spring. They say you can know someone by the things they value, and because homeschooling has changed us so dramatically, I’d like to introduce our family through what I consider to be the four best things about homeschooling.

We set our own schedule. Not only did we decide when to study each day, but we chose which days are “school” days, and when we would take breaks during the year. Our girls both attended the public school for a time (five years for our oldest, and one for our youngest), so we were all familiar with the hassle and anxiety of arriving at the school building in the morning before the bell rang. In contrast, setting our schedule based on the natural morning rhythm of our family was a true blessing that probably added 10 years to my wife’s emotional life. It was a rare day that our school requirements weren’t satisfied by the time the public school let out in the afternoon, even though we usually started later than they did. That wasn’t too surprising, however, since my wife was exposed to the inefficiency of the government system when she served as a room mother in our daughter’s class, and became convinced that even the most incompetent home school could be more efficient than the public school.

We typically scheduled school for Monday through Friday, but we didn’t hesitate for a moment to take vacations when the public school was in session. In fact, we prefer vacationing in the spring and fall now as the weather is more moderate, crowds are smaller at most of the places we visit, and “off peak” discounts sometimes apply. We even occasionally used summer months to catch up on schoolwork or get ahead in a subject area.

Our daughters both took thirteen years to complete their K-12 education, primarily because we didn’t have any goals that required they finish earlier. Now that the State of Illinois is satisfied with their education, they continue to study subjects that interest them, and aren’t afraid of learning in unconventional ways, and on their own schedule.

We choose our own curriculum. I remember well the paper our young daughter brought home from the public school on which she was asked to list a person she wished to meet. Her answer: Monica Lewinsky. I was too embarrassed for her to inquire how she knew that name, or in what context it was presented that would cause a grade-schooler to desire to meet her. I was troubled that at the time she knew few of the names of the current elected leaders of our state or country, but she knew the name of an infamous White House intern. That was probably one of the straws that were quietly piling on the camel’s back of our decision to teach our children at home, and represents the control one relinquishes when their child is part of the public school system. Even though evaluating and choosing books and resources for each child can be daunting, the peace that comes with knowing what they’re learning and what they are not exposed to is immeasurable.

Granted, the State of Illinois requires that we teach certain subjects, but it wasn’t until we began homeschooling that we realized how much latitude one has in satisfying the requirements of the law. The APACHE conference opened our eyes to resources that presented a perspective different from that presented by the public schools my wife and I attended. Books and speakers challenged our paradigms in history, math, science, government, and writing to the extent that I sometimes felt like I couldn’t trust anything I learned in my first 18 years of life! We gladly chose resources that were based on a biblical worldview, and as a result, my children are stronger creationists and better-balanced historians than I am, and that makes me happy.

We’re part of a great culture. Fourteen years ago I would not have guessed that some of our closest friends would be the homeschoolers we met while touring Colonial Williamsburg. We were in the early months of our homeschooling adventure when we realized our friendships with other homeschooling families were the closest friendships we had. Many of those friendships still thrive today, and we continue to add new friends as we travel to attend new conferences, events, or simply sightseeing. More often than not, we recognized common philosophies and values after only a few moments of conversation.

Homeschooling Christians often have so much in common that it’s not difficult to feel like we’ve known each other our entire life when, in reality, we’ve only just met. Shared goals and struggles help bind our homeschool culture together, and they often prove stronger than ethnic, geographic, economic, and even doctrinal differences. Our strongest bond, however, could be that we not only see our method of educating as consistent with scripture, but many of us feel compelled to teach our children at home. It’s not a trivial thing to reject the public school culture of our day, and our common resolution in that effort joins us closer together.

Maybe that’s why it’s not uncommon to find homeschoolers worshipping together in congregations in which they outnumber those that choose other education options. We eventually joined a church composed primarily of homeschoolers several years ago, and we find it a natural fit with many of the convictions God has forced us to face in the last 13 years. In fact, God continues to use His Spirit through many imperfect people in our culture to convict us in areas where we fall short of his will, and we appreciate that aspect of our homeschool culture.

We spend time together. When our oldest daughter was nine years old, the public school consumed all but 2 or 3 of her waking hours each week day. Recognizing then that she might leave our home in as few as nine years, we were startled by the realization that we may never know her very well if we continued at that rate. God opened our eyes then and allowed us to deepen our relationships with our children through something as simple as spending more time with them. My wife benefitted more than I since she did almost all the instruction while I spent a good part of my day working away from home, but our family slowly began acting more like a family and less like individuals living together.

We still have individual interests, individual friends, and times when we do activities individually, but our identity as a family is now as strong as our identity as individuals. Time will tell if we put too much emphasis on being together instead of building independence, but at the moment, we’re all enjoying our time together.

Few decisions in my life have changed as many aspects of my life as our decision to bring our children home for their education. That decision clearly seemed to be a test of our obedience to what we felt the Lord was commanding us to do, and required a good bit of faith at the time. Even so, it was a relief to obey as the conviction was so strong we knew we would be miserable if we didn’t. God has continued to challenge our beliefs or practices in many areas, frequently using people that we would not have met were we not part of the homeschooling culture. We pray God continues to challenge us for the rest of our lives.

Thursday, June 18, 2015

Corn in the backyard, 2015 -- week 6

June 14

The second week of June proved productive for corn stalk growth behind our house as the plants averaged about 40 inches tall, which is the tallest we've ever measured for this week in June.  The plants were aided by more than 40% more growing degree days than the norm, collecting 200 versus the historical average of 141.  Rain was also plentiful, to the extent that some fields experienced ponding and started to show plant damage.

You'll notice the sky in the top image was mostly cloudy on the morning of June 14, increasing our tally of cloudy Sunday mornings.

Finally, I chose to include this view from above one of the plants showing the growth pattern of the leaves that comprise the stalk.  It's not visible yet, but soon a tassel will emerge from the center of the plant designating the transition into the fruit-bearing mode.  You'll see that event documented here first!

Thursday, June 11, 2015

The Cherry Harvest Has Begun!

Other than picking a few cherries for nibbling here and there, we didn't really start harvesting until June 9. We've had a few friends collect about 3 gallons of cherries off the tree so far, but there's still plenty left to pick. As best I can determine, the variety is probably Montmorency, as the fruit is never huge or dark, but ripens to a moderately deep red. The taste is sour, but still pleasant to eat off the tree, and makes a wonderful cooking cherry. If any of our readers would like to come pick to their heart's delight, just come on over and help yourself. We have ladders available, and if you come while we're  home, we may keep you company while you pick!

Wednesday, June 10, 2015

Corn in the backyard, 2015 -- weeks 4 & 5

 May 31

The plants almost doubled in size the week before the 31st, reaching 15 inches with the help of extra growing degree days. We historically experience 110 growing degree days for that week, but received 160 this year. Rainfall has been adequate as well, leaving the soil in great shape as we headed into June.

 June 7

Although the week before June 7 was slightly cooler than the historical average (116 actual growing degree days vs. 126 average), the plants still added 11 inches to their height, ending the week at 26 inches tall.

The wide angle image above was taken a few minutes earlier than normal because a storm was approaching from the northwest (right in the image). That was one of several storms to roll through our neighborhood on June 7 depositing about 3 inches of rain in the process.

As I look at these photos, it occurs to me that our Sunday mornings have been more cloudy than not over the last five weeks: four cloudy days to one sunny one to be exact. I'd have to check the archives to be sure, but I doubt that we've ever had more cloudy Sundays than sunny ones in the summer.

Saturday, June 6, 2015

Almost like receiving a Christmas card!

Every year we hope to receive this card from our County Health Department, and this year they didn't disappoint.  I've tried to be diligent in the maintenance of our septic system, but I'm always a little anxious when I submit our annual sample.  For a summary of our septic experiences over the years, feel free to choose the septic system label in the right column to see all the posts together.

As always, our neighbors downstream are breathing a sigh of relief.

Friday, May 29, 2015

Corn in the backyard, 2015 -- week 3

May 24

The plants continue to thrive, but this year's growth rate lags many of the other third weeks we've observed.  We received 85 growing degree days from May 17 to 23, versus the historical average of 92 for that period, which was probably partially responsible for the slow growth.  Since the plants emerged, they've still received over 36% more than an average year's growing degree days.  The corn still needs to grow and develop quite a bit before we can make any judgment on this year's crop, so we'll just keep watching, and recording data, and reporting progress here.

Tuesday, May 26, 2015

Heating Season Temperature Data and a Couple More Charts

A few weeks ago, we shared the data that indicated our winter temperatures were about as close to average as possible this year.  As we look at the entire heating season, the data looks a bit different.  If these charts look unfamiliar, see the footnote at the bottom of this post for an explanation of the data presented in the charts.

The entire season can be summarized by the position of the red curve at the right side of the chart, where it's apparent that over the entire season our daily average temperatures were considerably warmer than normal.  We accumulated 361 degrees of daily deviation above the average, which means each of the 244 days of our heating season (yep, that's about 8 months!), averaged about 1.5 degrees warmer than normal.

An interesting phenomenon to note is that in early March our heating season was close to the historical norm.  Predominately warmer than normal temperatures since early March have produced our entire cumulative deviation from normal, indicating that the 78 final days of the season averaged over 4.6 degrees warmer than the historical norm.

Recently it occurred to me that all our readers may not have gleaned all the information these temperature charts can communicate, so I present the next chart as an educational tool.

I include the red cumulative deviation curve on these temperature charts for two main reasons: (1) the ability to determine how the data as a cumulative total compares to historical norms, and (2) to recognize trends in the temperature data that may not be easily apparent in the blue daily deviation bars.  On this chart I've added red (warmer) and blue (colder) arrows to illustrate the trends indicated by the red curve (feel free to click the chart for an enlarged view).  In case you hadn't noticed, when the red curve slopes up from left to right, that indicates that the daily deviations from normal have been predominately warmer than average.  Likewise, when the curve slopes down from left to right, colder deviations have predominated.  One can easily recognize at least seven extended temperature trends through the last heating season: four when warmer temperatures prevailed, and three when the daily averages below normal outweighed those above normal.

Since temperatures that were near normal would present a red curve that was roughly flat from left to right, I found it interesting that we seldom observe that characteristic in our temperature data.  Instead, it seems our temperatures are either well above normal or well below normal, leaving very few "normal" days!  This lead me to conjecture that a histogram of the daily temperature deviations for an entire year might look different than the normal distribution, or "bell curve" that one might expect.

To my surprise, the histogram showed our weather to be a lot more "normal" than I expected.  A histogram is a chart in which each bar represents the number of times (or frequency) that a certain temperature deviation was attained.  In the chart above, each bar actually represents a range of temperatures three degrees wide.  For instance, the short bar at the far right indicates that there was one day in which the deviation from average was greater than 21 degrees, but less than or equal to 24 degrees.  The next bar to the left shows five days in which the deviation from average was greater than 18 degrees, but less than or equal to 21 degrees, and so on.  As expected, there aren't many instances at the extreme temperature deviations represented, but there are quite a few days in which the average temperature was very close to the historical average.

The most populated group is that in which the average temperature was the same as the historical average or one or two degrees colder.  The number of days in 2014 when the mean temperature was within 5 degrees colder to 6 degrees warmer than the historical average was 182, just shy of half of the days of the year.  Since 2014 ended a little colder than normal, it might be surprising that 168 days were colder than the historical average, while 179 were warmer, and 18 days matched the historical mean.

Footnote: The blue bars in the upper two charts represent the daily temperature deviation from the historical average for Central Illinois as measured at the Greater Peoria Regional Airport.  Since each day has a historical average high and low temperature, the average of the high and low represents the historical daily average or mean.  The average of the actual high and low temperature represents the actual mean, and the difference between the historical mean and the actual mean represents the daily temperature deviation.  On these charts, all temperatures are shown in degrees Fahrenheit.

Saturday, May 23, 2015

Corn in the backyard, 2015 -- week 2

May 17

The plants sprouted to a height of about 5.5 inches for our second measurement which is about average by our experience, and the green covering of the field was noticeably thicker.  We had over 38% more growing degree days than the historical average for the seven days prior to these photos, which extended the warmer-than-normal trend started the week before.  After 11 days of growth above ground, the crop appeared to be making good use of the excellent conditions.