I’d like to know the level of protection from ultraviolet rays that my current eyeglasses and sunglasses provide. In this post, I don’t actually do the test, but I set up all the background information. The test has to wait for materials to arrive from Amazon. Continue reading Post #1654: Testing eyeglasses and sunglasses for UV protection. Part 1, the set-up.
Category: Analysis
Anything that I have tested empirically, or explain with detailed calculations, or just generally bother to get all the facts straight.
Post #1641: Of Freon and Schrader Valves
Let me get to the punch line first, and tell the story second.
Yesterday, I found out that:
- I own about $5,000 worth of R-22 refrigerant, a.k.a., Freon. That’s at full retail, the price I’d have to pay currently to replace it.
- That $5K worth of refrigerant is held in place by a less-than-reliable $1 device that was invented in the late 1800s.
As an economist, I goggle at the mismatch.
But there appears to be nothing I can do about it. Except to wait for the inevitable leak.
Now I’ll tell the story. And try go get up to speed on modern refrigerant options. And try to plan ahead.
My world and welcome to it.
My house came with an exceptionally quirky HVAC system.
The key elements are a pair of ground-source heat pumps. That sounds pretty eco-friendly and high-tech, right?
As actually implemented, my home HVAC is a Rube Goldberg machine. There’s a mile of plastic pipe buried in the back yard. Two pumps circulate water through that mile-long loop, terminating at two commercial (not home) AC compressors. These grumble away in the basement, feeding refrigerant lines running to air handlers — the things that actually blow the hot or cold air around the house. Those air handlers were clearly part of an earlier system, and to reach the one in the attic, the installers ran about 100′ of refrigerant lines outside, up the side of the house, and over top of the roof. The whole mess is controlled by a mix of wired and wireless thermostats of dubious reliability. These, in turn, interface with the 65-year-old three-zone baseboard hot water heat via a high-tech high-efficiency gas furnace and electronic interface, that actually turns the hot water baseboards on and off via valves than run on melted wax. (That’s not sarcasm, that’s a Taco (pr. Tay-co) valve.)
I mean, what could possibly go wrong?
In any case, we fired up the heat pumps this past weekend, only to find that one of the two heat pumps wasn’t. Pumping heat, that is.
A service call later, and the diagnosis is that the unit is drastically low on refrigerant.
Normally, that’s not much of an issue. Find the leak, fix it, and refill the system.
But in this case, it’s a problem. That’s because the bozos who installed those heat pumps less than 20 years ago cheaped out and installed units that use R-22 refrigerant, also known as Freon. Of ozone destruction fame. That can no longer be made in the U.S. or imported into the U.S.
(At the time they installed these, it was already well known that Freon was on its way out. When I replaced the AC in my prior house, years before, I opted for the newer “Puron” (R410-A) refrigerant. Buying a new R-22 unit at that time would have been foolish. But now I own two of them.)
Normally, that’s not much of an issue either. There are now drop-in replacement refrigerants like R-421A. These don’t destroy the ozone layer, and in most cases you can simply vacuum out the R-22, replace with R-421A (or similar), and get on with your life. (They have a huge global warming potential, though, as discussed below.)
But in this case, it’s a problem. Apparently those replacements won’t work in every system. My HVAC guy assures me that mine is one such. Maybe the 100′ long refrigerant lines have something to do with that. Maybe it’s the fact that these are oddball commercial units, not home units.
So in my case, the options were to fix the leak and top up the leaking unit with R-22, or throw it away and get a new one. Which, owing to the unique setup, is almost certainly going to cost a mint. Assuming my HVAC guy is giving me the straight story.
So I had my HVAC guy repair the leak and top up the system. Which is when I found out that this company now charges more than $300 a pound for R-22. I expected it to be expensive — that’s been in the works since 2010, when the decision was made to phase it out in the U.S. Which means my replacement cost for the 14+ pounds of R-22 in my two units is somewhere around $5000.
(But I didn’t expect it to cost me more than $300 a pound, but it was a decision that I made on the fly. I now see that the wholesale price of R-22 is around $40 a pound. As shown below. So my HVAC guy apparently took a roughly 800 percent markup. Because, hey, my system wasn’t going to run without that additional R-22. So they got me. But this definitely means I’m looking for a new HVAC firm. And I’m also wondering whether I got the straight scoop regarding whether or not drop-in replacement refrigerants will work.)
And what caused the leak, for which I had to purchase about $1500 worth of R-22? That was due to a faulty Schrader valve. Which is a roughly 70 cent part, using a design patented in 1893.
And that’s just the way it is. The valves that made sense when they were holding in the (then) $1 a pound Freon are now are all that stands between the atmosphere and my precious antique R-22.
Looking ahead.
Given the dollars involved, I probably ought to think through what my next steps are. As opposed to panic-purchasing something the next time there’s a problem.
There are a lot of considerations.
Source: US EPA
First, with no new production or import allowed in the U.S., at the current price, it’s a pretty good bet that R-22 is now a zero-sum game. That is, everything currently residing in appliances will get reclaimed and re-used, until it all eventually leaks into the atmosphere.
(In theory, per the EPA, you can ship your R-22 off to have it destroyed at a certified destruction facility. Or you can plan on storing it safely, indefinitely. But I don’t see that happening if you can re-sell it to your customers at $300+ a pound.
This means there is no environmentally benign way to get rid of the R-22 that came with my house. If I opt for new equipment, the HVAC techs will, by law, recover (pump out) all the R-22 in the current system. But surely they’ll sell that to be reclaimed and re-used. Which means that it will be used in somebody else’s leaky system. And one way or the other, it’s going to end up in the atmosphere.
I should mention here that in addition to R-22’s destruction of the ozone layer, all these refrigerants — even the ozone-benign ones — have a horrifically high global warming potential (GWP). R-22 isn’t the worst, but it’s bad enough, with a 100-year GWP of 1850 (reference). Or, in other words, a pound of that stuff has as much impact as 1850 pounds of C02. My little R-22 leak had as much global warming impact as releasing about four tons of C02. That’s about the same global warming impact as an entire year’s worth of electricity use, in my house.
I think that gives me my first and most obvious decision point: As long as my current heat pumps don’t leak, I should make every effort to keep them running. Even though the equipment is old, it’s still a reasonably efficient heating and cooling plant because it’s a ground-source system. I don’t think any marginal efficiency improvements from new equipment could plausibly offset the GWP from the earlier-than-necessary release of my 14 pounds of R-22.
The fact that I own this R-22 is nothing for me to feel guilty about. I’m not the one who installed the R-22 heat pumps. But now, I’m the custodian of it. It’s on me to address any leaks, to try to keep this crap bottled up for as long as possible.
Conversely, as soon as a unit develops an irreparable leak, I should decommission it. With one caveat. My HVAC guy actually gave me the option of just refilling the system, and not bothering to find the leak. With a slow leak, plausibly I could have kept this running for years on maybe a pound of R-22 per year. But if I could not fix the leak, it would be better that the R-22 go into somebody else’s system, with the chance that it doesn’t leak, than to keep it in a known leaky system.
(And so, that’s the first benefit of thinking this through. Because, had this occurred in some sort of emergency situation, such as a deep cold snap, I’d probably have opted to keep the system running at all costs. Now I have my head screwed on straight regarding the environmentally sound(er) thing to do.)
The caveat is that the systems you can get today all use refrigerants with high global warming potential. So much so that refrigerants that were cutting-edge replacements for R-22 twenty years ago are themselves now being phased out. Puron (R410-A), for example, has a GWP of more than 2000. It came on the market in 1996, and it’s slated to be phased out sometime in the 2030s.
So the caveat boils down to this: If we’re only a year or two away from new units that use a truly benign refrigerant (no ozone destruction, minimal GWP), it might make sense to limp along for that year or two, rather than install new equipment with soon-to-be-outdated refrigerant.
Right now, as I read it, the world of low-GWP refrigerants is in flux. For heat pumps, Carrier now makes a large commercial ground-source unit using R-1234ze, with claimed GWP of less than 1 (reference). Looks like some other manufacturers are jumping on that bandwagon. So, plausibly, if that trend continues and they enter the home heating and cooling market, by the time I have to replace these old R-22 ground-source heat pumps, I ought to have a fairly efficient and environmentally benign alternative.
In the meantime.
Meanwhile, I remain appalled that the same century-old tech that keeps my car tires inflated is all that stands between my precious R-22 and the outside world. When my HVAC guy comes back for a routine maintenance visit in the spring, I’ll be grilling him about options for making sure I never get another Schrader valve leak on these systems. Maybe I can have him replace those prophylactically (there are tools for replacing them with out losing the R-22). Maybe it’s a question of putting gas-tight caps over them.
One way or the other, there has to be a more secure way to keep this particular genie in the bottle. The valves that made sense 20 years ago seem ridiculously out of place for a gas that’s going for hundreds of dollars a pound.
Post #1636: Countertop water filtration.
This is my overview of simple (no-plumbing) water filtration systems currently on the market. As with many of my posts, I’m writing this up to make sure I understand the topic. I doubt anyone will read the detail.
To cut to the chase, after 20 years, we’re abandoning our standard Brita water filter in favor of the upgraded version, the Brita Elite. The new Brita filter fits the old pitchers, but appears to do a much better job at filtration.
This, while I continue to look over our options for a more sophisticated filtration system.
In brief:
Post #1635: First frost
Source: Analysis of historical weather data from NOAA.
Stealth frost
It looks like we’re going to have a few nights with freezing temperatures this week, here in Vienna, VA.
I’ve been doing a few chores in and around the garden to get ready for that. The most important of which was moving a large potted lime tree into the garage. Even a touch of frost and that would likely die back to the ground. I’ve also drained all the water barrels, and I’m bringing hose timers and other frost-sensitive objects inside.
This means it’s also time to redo my prior analysis of trends in first frost. It’s been unseasonably warm in the East, so it would be no surprise if this year’s first frost were a bit later than usual.
But when I actually looked at the data, I got a surprise: Dulles Airport (my standard for this frost analysis) recorded a frost about three weeks ago, on October 21. I missed that, and clearly we didn’t get a frost in Vienna, based on (e.g.) the fact that my okra plants are still alive.
That said, on average, first frost in my area is now about 20 days later than it was in the 1960s. As you can probably see from the graph, virtually all that change has been in this century. That couple-of-weeks shift in the first frost date appears to be a fairly widespread phenomenon (per this reference).
That’s consistent with the continued northward shift of the USDA hardiness zones. They update those every so often, using more recent historical weather (i.e.) climate data. With the most recent up date (2012, using the 30 years of weather ending 2010), most of the zone boundaries slid north, compared to the prior map (using the 30 years ending in 1990). Apparently, the average rate of travel of the hardiness zone boundaries is reported at 13 miles (north) per decade (per that same reference). That varies widely, as zone boundaries at the coast shift more slowly, due to the moderating effects of ocean temperatures.
In any case, it will be sometime around 2040 before Vienna, VA makes it into Zone 8 — or Zone 8 makes it to Vienna — take your pick.
Source: NOAA, via the New York Times
So I guess it’s still a bit early to expect climate change to save me from these frost-related chores. But give it enough time, and we our descendants our descendants, if any, will have no problem growing palm trees around here.
As was true at last year’s first frost date (Post G21-057), indoor relative humidity remains high. That said, I’m keeping an eye on it, and when it drops below 40%, I’ll start running my humidifiers. I summarized why that’s important for prevention of respiratory infections in Post #894.
Source: American Society of Heating, Refrigerating and Air-Conditioning Engineers
Post #1629: Worst economic advice ever?
What is wrong with this picture?
This is a political ad that has aired repeatedly in the past few weeks in the Washington, DC area. It’s an ad for a candidate for U.S. Representative from one of the Virginia suburban districts.
That’s the candidate and her father.
Have you figured out what’s wrong?
Sure, this is a campaign ad. You’re supposed to respond to the images emotionally. You aren’t supposed to think about what they are actually saying. But instead of just basking in the warm glow of that aw-shucks fiscal conservatism, try actually reading the words.
Crudely put, savings + spending = income. Which means that the candidate is endorsing the notion of spending less than 50% of one’s income. As a matter of logic, that’s the only way that you can save more than you spend.
Let me walk through the implications of that, one step at a time.
Microeconomics: Not feasible for the middle class.
Source: Federal Reserve Bank of St. Louis (FRED) system.
OK, let’s just take that at face value. The printed advice above boils down to “you should save at least half of your income”.
First, to be clear, for the U.S. as a whole, that’s never happened and never will. Above you can see more than a half-century of the U.S. personal savings rate. It has typically ranged from 5% to 15%, with a secular trend toward less savings. In recent years, 5% would be roughly normal.
But that doesn’t tell the full story. Almost all that savings is done by the well-to-do. The top 10% and top 1% of earners. Here’s a graph — of unknown quality — of savings rates by wealth.
Source: financialsamurai.com
That looks about right to me.
For the vast majority of Americans, the idea of saving half your income is absurd. It’ll never happen, for the simple reason that you need to pay the bills.
Even more absurdly, this same candidate has made much of how middle-class families must struggle to make ends meet. So the message here is that the middle class is struggling, but it should be saving more than half of its current income.
So, look, if you make tons of money, sure, you can look down on the great unwashed masses and their pitiful savings rates. I’ve had years where my little business was so successful that I did, literally, save more than I spent. But I can also recall the single-digit checking account balances of my youth. So if people with modest incomes don’t save much money — and they never have — I find it hard to fault them. Personally, I’ve always been extremely financially conservative. But I don’t think that somebody with two minimum-wage jobs should be expected to save half their income.
Macroeconomics: Economic suicide.
It goes without saying that if, in some imaginary world, Americans suddenly decided to save half their income, the economy would immediately tank. We’d have the next Great Depression.
Oh, wait, didn’t that just happen? The top graph below is personal savings, which appears to have hit nearly 35% recently. The bottom graph is the unemployment rate, which hit 15%. That was, in fact, the highest unemployment rate since the Great Depression. Which we just had, during the pandemic.
Source: Federal Reserve Bank of St. Louis FRED system. I should note that this is a bit of a cheat, on the savings side, because individuals largely saved their first round or two of COVID-19 payments. (Which is why they needed additional rounds of stimulus, get it?) That artificially gooses the observed savings rate, but only by a bit. Basically, from the standpoint of economics, people were pretty much panicking, as they had during the Great Depression. And as everyone individually reduced spending, the macroeconomic results were inevitable.
My first point being that if Americans were suddenly to follow that folksy bit of economic wisdom, that would guarantee that we’d have the next great depression.
So, why didn’t we slide into an economic depression?
The answer is the COVID-19 spending bill that Trump signed. Followed by the two COVID-19 spending bills that Biden signed. All of which force-fed money to U.S. corporations and citizens, to counteract the collapse of demand that occurred during the pandemic.
Which was matched by similar programs undertaken by all of the industrialized nations. This wasn’t a U.S. idea. This is what everybody with any sense did.
Anyway, all that money is now coming out of people’s savings, and going into spending. That’s my interpretation of why the U.S. personal savings rate is now just about 3%, which is low compared to recent history. It’s also why the unemployment rate is about 3.5%, also low by recent history. And, to some significant extent, why prices are up.
It may seem like the Federal government spent a lot of money to keep the COVID economic crisis from snowballing. We did, in fact, run the largest deficit (as % of GDP) since WWII.
But the point is, that was almost undoubtedly cheaper than having the next Great Depression. Which is what the entire industrialized world was facing. Which is why everybody threw money at their economies. They didn’t do it because they were stupid. They did it because it was smart. It was cheaper than the alternative.
Are we living with the consequences now? Yep, sure are. Are people going to squabble about how much was spent, try to use it to political advantage? Yep, sure are. Will folks forget why the money got spent in the first place? No doubt.
Will this candidate ever get called to task for suggesting that middle-class people ought to save more than half of their income? Nah, I bet nobody even noticed what that ad implied. Will anyone ever point out that uniform adoption of that policy is collective economic suicide? For sure not.
That’s just the way the world works. Please feel free to say anything, no matter how stupid, as long is riles up the right people. And never, ever apply logical analysis to anything that is said.
Don’t worry, be happy.
Post #1624: 80 MPG?
Not quite. But I think I’m finally figuring out how to drive my wife’s Prius Prime.
Above is the gas mileage on my wife’s Prius Prime, after a round trip from Vienna VA to Harper’s Ferry WV. This is all after resetting the odometer once the battery was depleted. So it’s straight-up gas mileage.
This trip contained a short section of high-speed driving, but was mostly hilly primary and secondary roads in western Virginia and West Virginia. And I think I finally understand how I’m getting such great mileage.
The Prius Prime loves hilly roads. It is an excellent car for a particular style of pulse-and-glide driving.
Post #1618: There ain’t no disputin’ Sir Isaac Newton: Efficient driving in an EV.
Driving an electric vehicle (EV) efficiently is forcing me to learn some new driving habits. And, in particular, I have to un-learn some cherished techniques used for driving a gas-powered car efficiently.
When I look for advice on driving an EV efficiently, all I get is a rehash of standard advice for driving a gas car. But the more I ponder it, and the more I pay attention to the instrumentation on my wife’s Prius Prime, the more I’m convinced that’s basically wrong.
An electric motor is fundamentally different from a gas engine. With an electric motor, you want to avoid turning your electricity into heat, rather than motion. That boils down to avoiding “ohmic heating”, also known as I-squared-R losses.
To minimize those heating losses, you want to accomplish any given task using or generating constant power. That task might be getting up to speed after stopping at a red light, or coming to a stop for a red light, in some given length of roadway.
Here’s the weird thing. Assuming I have that right — assuming that an efficient EV driving style focuses on providing or generating constant power over the course of an acceleration or deceleration — that implies a completely different driving style, compared to what is recommended for efficient driving of a gas-powered vehicle.
In particular, the standard advice for gas cars boils down to accelerating and decelerating with constant force. When you take off from a stop light, aim for a constant moderate rate of acceleration. When you are coming to a stop, aim for a steady rate of deceleration. Constant acceleration or deceleration boils down to constant force on the wheels, courtesy of Sir Isaac Newton’s F = MA (force is mass times acceleration).
But power is not force. As I show briefly, in the next section. In a car, power depends on speed. Constant force on the brake pedal (and so, on the brake rotors in a traditional car) generates far more power at high speed than at low speed. Similarly, a constant rate of acceleration consumes more power at high speed than at low speed.
And so, there seems to be a fundamental conflict between the way I was taught to drive a gas car efficiently, and what seems to be the right way to drive an EV efficiently.
In a nutshell, to drive an EV efficiently, you should be more of a lead-footed driver at low speeds. And taper off as the car speeds up. Conversely, hit the brakes lightly at high speed. And press the brakes harder as the car slows.
That’s the driving style that aims for production and consumption of power at a constant rate, over the length of each acceleration or deceleration. And that’s completely contrary to the way I was taught to drive a gas vehicle.
Think of it this way. Suppose you apply a certain level of force to the brake pedal of a traditional car. The resulting friction between brake pads and rotors will generate heat. That rate of heat production is, by definition, power, as physicists define it. You’re going to generate a lot more heat per second at 80 MPH than you are at 4 MPH. (In fact, 20 times as much.) Restated, for a given level of force, you are bleeding a lot more power off the car’s momentum at 80 MPH than at 4 MPH. And those big differences in power, over the course of an acceleration or deceleration, are exactly what you want to avoid in an EV with regenerative braking, in order to avoid I-squared-R losses.
Force and power: A brief bit of physics and algebra
1: Two definitions or laws of physics
Work = Force x Distance
Power = Work/Time
2: A bit of algebra
Substitute for the definition of work:
Power = (Force x Distance) / Time.
Re-arrange the terms:
Power = Force x (Distance/Time)
Distance/time = speed (definition)
Power = Force x speed.
For a constant level of force applied to or removed from the wheels, the rate of power consumption (or production) is proportional to the speed.
Upshot: To accelerate or decelerate at constant power, the slower you are going, the heavier your foot should be. The faster your are going, the lighter your foot should be. For the gas pedal and the brake pedal.
Ohmic heating: Why a long, hard acceleration trashes your battery reserve.
Anyone who drives a PHEV — with a relatively small battery — will eventually notice that one long, hard acceleration will consume a big chunk of your battery capacity. On a drive where you might lose one percent of battery charge every few minutes, you can knock several percent off in ten seconds if you floor it.
Another way to say that is that getting from A to B by flooring it, then coasting, consumes much more electricity than just gradually getting the car up to speed.
I’m not exactly sure why that is. But I am sure that it is universally attributed to I-squared-R or ohmic heating losses in the motors, batteries, and cables.
Any time you pass electric current through a wire or other substance, it heats it up. From the standpoint of moving your car, that heating is a loss of efficiency. The more current you pass, the more it heats up the wire. And that heating is non-linear. Watts of heat loss are proportional to I-squared-R, in the argot. They go up with the square of the current that you pass through that wire.
Again, I’m not completely sure here, but my takeaway is that your heating losses, at very high power, are hugely disproportionate to your losses at low power. At constant voltage, I believe those losses increase with the square of the power being produced by the electric motors. In other words, ten times the power produced to move the car creates 100 times the ohmic heating losses.
And that’s how ten seconds of pedal-to-the-metal can use up as much electricity as 10 minutes of moderate driving.
That said, I have to admit that I’m relying on “what everybody says” for this. For sure, hard acceleration seems to trash your battery capacity far in excess of the distance that you travel at that rate of acceleration. Whether the root cause for that is I-squared-R losses, or something else about the car, I couldn’t say.
Either way, my takeaway is that if losses are proportional to the square of power consumed or generated, then to accomplish any given task (any fixed acceleration or deceleration episode), your aim should be to do that at constant power. Because that’s what will minimize the overall energy loss from that acceleration or deceleration episode.
Drive like you are pressing on an egg — that was a real thing. EV drivers should chuck the egg.
Source: Duke University Libraries, via Internet Archive.
Those of us who grew up during the 1970s Energy Crisis will probably recall public service announcements that asked you to drive as if there were a raw egg between your foot and the gas pedal. I managed to find a Texaco ad of roughly that era, laying out that egg-on-gas-pedal meme. The picture above is from that video.
As kids, that was pretty much beaten into us. Responsible driving means no jackrabbit starts, no tire-smoking stops. Easy does it. We’re in the middle of a prolonged gasoline shortage, after all.
So now I come to the part that is absolute heresy for someone of my generation. If you’ve absorbed the prior two sections, you realize that this advice probably isn’t correct for an EV. Why? To consume power at a constant rate over the course of an acceleration, you should start off with a brisk rate of acceleration, then diminish that as the car speeds up.
In other words, if you drive an EV, drive with a lead foot. Not all the time. But at the start of every acceleration. And the end of every deceleration.
If you drive an EV, chuck the egg.
The Prius Prime Eco display
Source: Underlying picture is from Priuschat.
With that understanding in hand, I’m finally starting to make some sense of the “eco” display on my wife’s Prius Prime.
In theory, this little gauge is giving you guidance on how to drive the car most efficiently. In practice, I could never make head or tail out of it, except that it seemed to be telling me to drive with a lead foot.
Which, I now understand, it was.
On this display, if you put your foot on the gas, it will show you your actual throttle (gas pedal) position, and the gas pedal position that will, in theory, give you greatest efficiency.
By contrast, when you put your foot on the brake, it doesn’t show you the brake pedal position. Near as I can tell, it shows you the amount of power than you are generating. That is, a constant brake pedal position will lead to a shrinking bar, as the car slows down and less energy is generated.
Watch what happens if I try to accelerate gently:
It’s possible that all the meter is actually telling me is that a very lightly-loaded electric motor will operate inefficiently. I don’t think the Prius eco monitor is actually trying to get me to drive at constant power.
Edit 3/11/2024: After driving around with a ScanGauge III, my conclusion is that accelerating at constant power is exactly what the eco-meter is trying to get you to do. It wants you to start off with a heavy foot, and then, as you accelerate, it wants you to back off. Near as I can tell, that bar is set up to keep you at around 23 HP of power output, or 50 amps of discharge current, or a “2 C” rate of discharge, for this battery.
In particular, my diagram above is labeled wrong. The two red arrows should be labeled “desired power output” and “actual power output”. You will notice that if you don’t move the gas pedal, the “actual power output” line will creep up as you speed up. The only way to keep that line in the same place is to back off the gas as your speed increases. So that line isn’t the throttle position, it’s the power output (power = force x speed).
But no matter how I arrive at it — from theory, or from finally paying full attention to the Prius eco meter — the whole drive-like-there’s-an-egg-between-foot-and-gas-pedal is clearly obsolete. Gentle acceleration may get you your best mileage in a gas-powered vehicle. But it’s not the correct way to drive an EV.
Post #1617: When will the tear-down boom end, the sequel.
It hasn’t been possible to buy a small house in Vienna, VA for at least a decade now. Every small house that goes up for sale is purchased by developers, who then proceed to tear it down and build the largest house that will fit onto that lot.
This sustained destruction of middle-class housing, replacing it with lot-filling McMansions, is what I have termed “the tear-down boom”.
I have written about the various implications of the tear-down boom. Among other things, this continual replacement of small houses with gigantic houses means that:
- Post #519. Town revenues from residential real estate have been pushed materially higher by the resulting increase in the price of the houses.
- Post #308. There’s a tremendous mis-match between the stock of houses in the Town of Vienna, and the houses available for sale. Middle-class people can live here — if they already own a house — but they can’t move here, because all the middle-class houses are replaced with McMansions before being re-sold. As a result, increasingly, Vienna is a town for the wealthy, not the middle class, something I termed the “Mcleanification” of Vienna.
And yet, some of the economics of the tear-down boom just didn’t seem to make a lot of sense, simply as way to generate housing stock. People really don’t need 10,000 square foot houses, and everything I read about the next Gen X and later is that they have no interest in buying such gigantic pieces of real estate. Seemed like a classic case of “sell it to whom?”.
The best explanation I could give for the tear-down boom is that it was the result of two toxic Federal economic policies. These were the huge tax advantages to home ownership, including both tax sheltering of current income and tax-exemption of any capital gains, and near-zero real (inflation-adjusted) interest rates. In 1997, the Federal government eliminated capital gains on housing. (With some limits.) That was on top of the tax sheltering that housing provides via income-tax deductibility of mortgage interest and property taxes. Then, in 2008, the Fed dropped inflation-adjusted interest rates to zero or below, following the near-collapse of the U.S. financial system.
Between those two policies — the tax advantages and the free money — it became ludicrously cheap to finance the purchase of a mega-home. And that mega-home was a highly-leveraged investment that was, ultimately, better than tax-free.
But trees don’t grow to the sky. Back in 2019, I asked “When will the tear-down boom end?” That was Post #217.
Even then, the market was showing some oddities. Oddity #1 is that these mega-homes were appreciating less rapidly than adjacent lower-priced homes. Oddity #2 is that the changes in tax law in 2018 made it much more expensive to own homes costing over about $850,000. Here’s the analysis of just how much more expensive it became to carry the cost of a $1.4M house after the 2018 changes in Federal tax law:
Not only did it suddenly cost a lot more to carry that $1.4M house, almost all of the additional cost came from the housing value just in excess of $850,000. Basically, the law reduced the size of what I would term the “tax efficient” house, that is, the house that earns you the maximum tax breaks as a percent of cost.
As a result, in 2019, I looked at that and said, isn’t this going to put the brakes on the tear-down boom?
And so far, the answer is no. Just casually driving around town, these still seems to be a tear-down on pretty much every block.
So far.
Today’s mortgage interest rates.
In this last section, all I want to do is assess the impact of the rise in mortgage interest rates. Literally, dig up the spreadsheet above, and replace the then-current 4% mortgage interest rate with the current 7% (or so) rate.
Source: Federal Reserve Bank of St. Louis (FRED) system.
Redoing the analysis, I find that the carrying cost of a $1.4M (small) McMansion in Vienna is now about 50% higher then it was back in 2018. And 86% higher than it was in 2017, before they changed Federal tax law to reduce the tax advantages of owning an expensive home.
So, to be clear: Those houses are still big money-makers for the owners, as housing prices have risen steeply in the past year. That said, if home prices merely stabilize, new McMansions will have after-tax carrying costs in today’s environment that are 86% higher than they were in 2017.
My belief is that this plausibly is going to put a damper on tear-downs in Vienna.
I’ve been wrong about that before.
But I believe it strongly enough that I spent last week painting the front of my house. That’s a real change for me, because I had simply stopped doing any maintenance on my house that didn’t directly affect occupant health and safety. I figured, why bother to keep the place up, when they’re just going to tear it down when I eventually move?
I was letting the house deteriorate, peeling paint and all. But now I have about a decade’s worth of deferred basic maintenance to do. Because in today’s environment, it’s no longer a given, I think, that this house will be torn down when I leave it.
Post #1613: How the Prius does its thing.
Introduction: The U.S. market for gas-powered cars in 2005.
Source: Analysis of US EPA gas mileage and vehicle specification data, 2005 model year.
Back in 2005, my wife needed a car. And by that I mean, we were interested in a gasoline-powered passenger car. Not a truck, crossover, van, SUV or the like. And not a diesel. We’d done that, and didn’t much like the drawbacks of the diesels of that era. A passenger sedan, in the parlance of the era. Fueled by gasoline.
I was interested in buying something that was efficient. But the raw MPG numbers were a jumble, driven largely by the size of the vehicle. I didn’t really want to try to squeeze into some tiny econobox just because it got better mileage than a bigger car. I was interested in identifying something that was efficient at converting gasoline into movement of passengers and luggage. Not just the tiniest car I could fit into.
I took data from the EPA and calculated fuel efficiency in a way that put large and small cars on more-or-less equal footing. Instead of looking at miles per gallon, I calculated cubic-foot-miles per gallon. Where “cubic foot” is combined interior passenger and luggage room, measured in cubic feet. Under this approach, a car that was twice as big, but got half the gas mileage, would count the same as a car that was half as big, but got twice the gas mileage. They both used the same amount of gas to move a given volume of passengers and luggage.
My “cubic-foot-miles per gallon” for passenger cars is similar to the concept of ton-miles per gallon for freight vehicles. For the simple reason that miles-per-gallon doesn’t tell you how much you were able to haul. Trains, after all, burn a lot of diesel fuel per mile. But they also move a lot of tonnage with that fuel. In some sense, what matters isn’t the amount of fuel burned, it’s the usable carrying capacity that the fuel consumption provides.
The idea was to make this a two-step process. First, I would separate out the vehicles that were efficient, regardless of size. Then, from the lineup of vehicles that rose to the top of that listing, we could try to make an informed choice about what size of car we wanted to buy. Given the choice of efficient vehicles on the market at that time.
Things did not quite turn out as planned. I figured I’d get a “spectrum” of efficiencies, with a few dozen cars to choose from at the high end of the spectrum.
When I did that calculation– and so removed the variation that was driven merely by the size of the car — the data resolved into the amazingly simple picture, shown above. For gasoline passenger cars, the 2005 American market consisted of three pieces:
- The Prius
- The Honda Civic Hybrid
- Everything else.
The real eye-opener, to me, was the extent to which “everything else” was just that. Basically, all non-hybrid cars were roughly equally inefficient.(!) Sure, you had some muscle cars come in at the bottom of the heap. But the point is that there wasn’t some nice, smooth distribution of cars in terms of their efficiency. There was crowded mass of vehicles with little to distinguish one from another. There was the Honda Civic Hybrid, poking up above that mass. And there was the Prius, running about three times as efficiently as the average.
The upshot is that if you wanted an efficient gas car in 2005, the decision was a no-brainer. You bought a Prius. The only other gas car that came close to it was the Honda Civic Hybrid, and that was just a bit too small for me.
The best way I know of to illustrate how different the Prius was from other offerings at the time is to ask this simple question: In the 2005 car market, what was the most efficient gas-powered vehicle capable of moving six people? The answer? Two Priuses. Every six-passenger sedan, van, or SUV got less than half the gas mileage of the Prius. It was that far ahead of its time.
(As a footnote, I never put pickups, vans, or other special purpose vehicles (SUVs, etc.) on this graph because I couldn’t get the interior volume information. The EPA showed the MPG for those vehicles, but in 2005, the EPA only tracked interior volumes of passenger cars. And, as it turns out, that’s still the case. They only note the interior volume of traditional passenger cars.)
Redo: The U.S. market for gas-powered cars in 2022.
Now fast-forward to the 2022 model year, and ask the same question. If you were interested in buying an efficient gas-powered car, what would your options be? (I use 2022, not 2023, because the 2023 model year data from the U.S. EPA are not yet complete).
First, you have to acknowledge how much the market has changed.
In 2005, there were no electric vehicles (EVs) or plug-in hybrid electric vehicles (PHEVs). For passenger cars, 99% of the offerings were straight-up gas vehicles. There were a couple of hybrids, and a couple of diesels. Roughly speaking, 99% of the models offered were standard gas cars.
In 2022, here’s how the U.S. passenger car market shaped up. (Recall, this is just cars, not pickups, vans, SUVs, and the like.) In 2022, three-quarters of the offerings are still standard gas vehicles. But more than one-quarter are alternatives — hybrids, plug-in hybrids, or EVs.
Now let me ask the gas-car-efficiency question, for 2022. I’m ignoring EVs, and for the PHEVs, I’m using just their gas-only mileage. How do gas-powered cars shape up, in terms of my efficiency measure (cubic-foot-miles per gallon)?
Source: Analysis of US EPA gas mileage and vehicle specification data, 2022 model year.
Unlike 2005, the Prius now has quite a bit of company. The 2022 Prius is slightly more efficient than the 2005 model, but now there are a couple of gas-powered cars that top it, and many that are nearly as efficient.
Unsurprisingly, everything at the top of the efficiency charts, for gas-powered cars, is a hybrid of some sort. The entire cluster of gas sedans at the top consists of hybrids and PHEVs (where only the gas portion of the PHEV mileage has been counted.)
For the record, the two Prius-beaters on that graph are the Hyundai Ioniq and Ioniq Blue. For reasons that must make sense to Hyundai, those are no longer being made as gas hybrid versions. Hyundai discontinued those cars as of June 2022 (reference).
So, by the time we get to the 2024 model year, the Prius will be back at the top of the heap. As it should be. But now, at least, it has some close company.
Finally, I have to emphasize that this was for gas-powered vehicles. On paper at least, there are many fully-electric (EV) and partially-electric (PHEV) cars that get MPG-equivalents in excess of the 54 MPG for the Prius Eco (highlighted in the chart above). But here, I wanted to look at gas-powered cars, for comparison to my 2005 analysis. And I don’t want to get into what those MPGe numbers actually mean. It’s not straightfoward.
How does the Prius achieve such efficiency?
You see a lot of bad information about how the Prius achieves its high efficiency, for a gas-powered car. Some is just plain confused, some gets the orders-of-magnitude wrong. Some explanations appear to violate basic physics, such as the law of conservation of energy.
To be clear, Toyota did optimize many aspects of the operation of that car. If you look at a list of where energy gets dissipated in a typical car, the Prius addresses every area.
Source: Energy.gov
Take wind resistance, for example. Once you actually manage to get energy to the wheels of the car (Power to wheels line, above), about half of that energy gets dissipated as wind resistance. If you want decent mileage, you need to keep that to a minimum. The Prius has a “coefficient of drag” of 0.24, among the best ever measured for a mainstream U.S. passenger car (see the extensive list in Wikipedia.) By contrast, your basic brick-on-wheels design — a Jeep Wrangler — has a coefficient of drag of about 0.45. What people perceived in 2005 as the somewhat odd shape of the Prius was all about providing interior volume while minimizing air resistance.
There are other minor contributors. The Prius comes with low-rolling-resistance tires. It minimizes losses from braking by using regenerative (electrical) braking where possible. It reduced the parasitic losses from (e.g.) air conditioning by employing a more efficient compressor design. And so on.
But as you can see from the chart above, most of the energy wasted by a standard gas car is wasted by the engine. As I understand it, the single largest driver of Prius efficiency — and the reason it had to be made as a hybrid in the first place — is that it uses a different type of gasoline engine. It’s an Atkinson-cycle (or maybe Miller-cycle) engine, instead of a standard car Otto-cycle engine.
Why do I think the use of an Atkinson engine is key? Well, here’s a list of the top 20 most-efficient gas cars offered in the U.S. in 2022, listing their specs and the type of engine they use.
Notice anything?
What was unique to the Prius in 2005 is now the standard way to achieve good fuel efficiency in a gas-powered car. But, as explained below, in most cases, you have to add some secondary propulsion (electric motors) to get adequate on-road acceleration.
Here’s the explanation in brief.
The chemistry of gasoline dictates that you need a fairly “rich” gas-air mixture in an internal combustion engine. If you make the mix too lean — too little gasoline relative to the air — the spark plug can’t ignite it and/or it burns poorly and/or it generates a lot of nitrous oxides. To get reliable ignition and a clean burn, you more-or-less need to mix gas and oxygen in the ratio needed for complete combustion of the gas. Too little gas in the mix and the engine stumbles and dies, or runs dirty.
But if you fill the engine cylinder with that relatively rich gas mix, you end up with more chemical energy in that cylinder than you can use. Sure, you can compress it and ignite it. But there’s so much energy that you’ve still got quite a bit of usable gas pressure left when the piston gets to the bottom of the cylinder. (The number I see cited most often is that, under load, the gas pressure in the cylinder is still at five atmospheres when the piston hits the bottom of its range of motion.) At that point — once the piston bottoms out — all you can do is open the exhaust valves and let all that potentially usable energy — that still-usable gas pressure — escape out the exhaust.
And that’s exactly what a standard Otto-cycle car engine does. The intake stroke and power stroke are the same length, the valves open and close within a few degrees of the piston being at bottom dead center/top dead center. At the end of each power stroke, there’s plenty of pressure left in the gas inside the cylinder. And with each cycle, that energy gets tossed out the exhaust port.
This has been known for decades, i.e., that gas engines would run more efficiently if you could put a much leaner mixture into the cylinder. The problem was getting that leaner mix to ignite and burn well. Back in the 1970s, Honda tried to address this with its stratified-charge engine (reference). That used two carburetors — one rich, one lean — and two intake valves. It filled the top of the cylinder with a richer mixture that the spark plug could ignite. And the rest of the cylinder with a leaner mixture that would itself be ignited by the rich mix at the top. It was moderately successful, and I recall that the Honda CVCC with that engine was among the most fuel-efficient cars of its generation.
A better way to put less gasoline into the cylinder, and yet have it burn well, is to fill only part of the cylinder on the intake stroke. Where I need to define “the cylinder” as the full length of the resulting power stroke. That way, the air-to-fuel mix is correct for consistent ignition and clean burn. You simply have less total fuel in the cylinder before you ignite it.
And that’s exactly what the modern Atkinson (or Miller) cycle engine does. And it does that by closing the intake valve well after the piston hits bottom dead center. This allows the piston to push out maybe 30% of the total air-fuel mix, then compress and explode what’s left. As a result, you get both the right chemistry (the right air-to-fuel ratio) and the right amount of fuel to allow the resulting energy to be used efficiently.
In the Prius engine, more-or-less, the intake valve closes when the piston is 30% of the way up the bore. (The engine has variable valve timing, so, well, that varies). That works out to be, in effect, about a 10.5:1 compression ratio, and a 13.5:1 expansion (power stroke) ratio.
And so, while the standard Otto-cycle engine has nearly-identical compression and expansion (power stroke) ratios, the Atkinson-cycle engine has a much lower compression ratio, compared to its expansion (power stroke) ratio. The whole point of which is to allow you to put the right fuel-air mix into the cylinder, just less of it.
But this comes at a cost. With less fuel, and a longer expansion stroke, there’s less power with each power stroke. And part of that power stroke now occurs at pressures much lower than you would get in an Otto-cycle engine.
As a result, the Atkinson engine is efficient, but it has a relatively poor power-to-weight ratio. In the case of the Prius, the older 1.6 liter engine might have produced maybe 140 horsepower configured as run as a standard Otto-cycle engine. But as an Atkinson-cycle engine, I think it barely broke 90 horsepower.
The result would have been a car with unacceptable on-road performance. (Yeah, even for Prius drivers.) So, the engineers at Toyota (and Ford) added electric motors, a big battery to run the motors, and so on. And the hybrid was born.
To be clear, the electrical side of the modern hybrid is more-or-less a necessary evil. It was something tacked on after the fact, to allow the engineers to replace the inefficient Otto-cycle engine with a more efficient, but less powerful, Atkinson-cycle engine.
So, now you know the primary source of Prius efficiency. And you know why the 20 most efficient gas-powered cars offered in the U.S. all use Atkinson-cycle engines.
Post #1612: CO2 emissions from gas versus electric leaf blowers.
Source: Xerces Society for Invertebrate Conservation
To be clear, I think the right thing to do with your fallen leaves is to leave them alone, to the extent that you can (Post G22-034). But if you’re going to use a leaf blower, how do gas-powered ones compare to electrics, in terms of generating C02 emissions?
Bottom line: 7-to-1. At Virginia’s current electrical generation mix, a gas-powered leaf blower produces about seven times as much C02 emissions as an electric leaf blower. I show the calculation below.
In part, that’s because the grid just keeps getting cleaner. A couple of decades ago, the difference would have been more like three-to-one. But mostly that’s because small two-stroke engines, as used on leaf blowers, are inefficient.
Note that this 7-to-1 ratio is just for C02. In terms of total air pollution, gas powered leaf blowers stack up far, far worse compared to electrics. In particular, smoky two-stroke gas engines produce huge volumes of unburned hydrocarbons, as anyone who has ever seen and smelled the exhaust from a two-stroke can attest.
To be clear, leaf blowers don’t use enough gasoline to matter, in terms of our annual C02 emissions. They are a drop in the bucket. And not that there aren’t a lot of other reasons to skip leaf blowers entirely, let alone gas-powered ones. But this is a statistic that I wanted to pin down. So here is the calculation, with citations as to source.
Background
My wife asked me a simple question today regarding gas-powered versus battery-powered leaf blowers. How do they compare in terms of C02 emissions? I did a quick back-of-the-envelope and got numbers that didn’t appear credible. So I decided to do a more formal calculation, with the metric being pounds of C02 produced per 100,000 cubic feet of air moved.
It’s already well-established that gas-powered leaf blowers produced a tremendous amount of air pollution, per amount of work performed. That owes mainly to the use of small two-stroke engines.
No shock there — these are the engines where you mix the oil with the gas, and burn that mixture to produce a smoky blue exhaust. That exhaust is every bit as dirty as it looks. You can look that up anywhere, and as far as I know there’s more-or-less zero disagreement about that. Here’s what appears to be a fairly sophisticated test (reference Edmunds).
In terms of pollutants (e.g., unburnt hydrocarbons) and such, that’s the pretty much the end of the story. Except to note that a part of the resulting air pollution is black carbon, which is increasingly being recognized as a major contributor to global warming (See Post G22-058). So, these two-stroke gas engines contribute to global warming beyond their emissions of C02 alone.
But my question was in terms of C02 emissions.
In absolute terms, obviously, the gas consumed in lawn care is a drop in the bucket, compared to the gas consumed by cars and trucks. (So, priding yourself on using an electric mower, while you drive an inefficient car, is straight-up greenwashing, in terms of impact on C02 emissions. It might ease your conscience, but in the grand scheme of things, your lawn mower is rounding error in your household carbon budget.)
That said, just exactly how do the C02 emissions compare, between gas and electric leaf blowers? My first rough cut seemed to say that gas leaf blowers produced vastly more C02, compared to electrics, than gas cars did compared to electric cars. (Which, for a Prius, is about 2.5:1. Gas miles in our Prius Prime produce about 2.5x as much C02 as do electric miles.). So I decided to do a more careful and better-documented calculation.
A virtual trip to Home Depot, and a surprise.
I went to the Home Depot website and began with the first gas-powered leaf blower that showed up. This is an ECHO gas-powered backpack leaf blower. I downloaded the manual to see what I could find out.
My first shock was in finding that this can be fitted with air pollution controls. For example, this model has a catalytic converter and a gasoline evaporation control system, at least in some areas. This, apparently, is required by law, and has been required, in at least some areas, since the mid-2010s.
Source: Manual for the ECHO backpack leaf blower referenced above.
I then looked at a similar Ryobi model, and it too has a catalytic converter as an option. That said, the owners’ manual says that it must be replaced every 50 hours.(!) Hard to find it labeled as catalytic, but it appears that the muffler assembly is a $50 part. I’m guessing the average user will not bother to replace that after 50 hours of use.
Source: Manual for the Ryobi backpack leaf blower cited above.
The important implication of this is that older comparisons — such as the 2010 testing done by Edmunds, cited above — may (or may not) be vastly out-of-date. Those older studies predate catalytic-converter-equipped units. It’s not clear to me whether all units are now equipped with catalytic converters, or whether the typical owner bothers to maintain those catalytic converters. But this does make me wonder just how much all of the often-cited literature on the dirtiness of these engines is out-of-date. I certainly see recent articles that still cite the remarkable findings of that Edmunds comparison.
It also appears that most of the advocacy articles focus on the high levels of unburned hydrocarbons. That’s where the blue-smoke-spewing two-strokes do the worst. All of them also seem to add in a huge amount of spilled gasoline, though how they could possibly know the average spill rate for the average consumer is beyond me.
Anyway, catalytic converters on two-stroke leaf blowers — that was news to me. (Though if you Google it, you can find many examples.). Maybe I’ll investigate further at some point.
For now, I’m looking for fuel consumption (which will dictate C02 output) and work produced, probably measured as cubic foot of air moved per minute.
Moving on.
After looking at a few more gas-powered leaf blowers, it’s clear that they use so little fuel that homeowners don’t care what the fuel consumption is. The issue of fuel consumption per hour, or typical run time on a tank of gas, is simply not addressed in any of the consumer literature for these devices.
You really have to dig to get it. Luckily, Stihl introduced some fuel-efficient models about a decade ago, and as part of that, they produced statistics on typical gasoline consumption per hour. These were aimed at demonstrating cost savings to professional users such as landscape maintenance companies.
With that in hand, it’s just a question of comparing some off-the-shelf plug-in electric models to a couple of efficient Stihl gas models. Here’s the calculation.
Discussion
The bottom-line figure seems completely credible to me.
For a Prius, the equivalent number would be 2.5 to 1. That’s my best estimate (presented in long-ago prior posts), based on our experience with a 2021 Prius Prime.
It’s no surprise that the ratio would be not quite 7 to 1 when comparing small two-stroke engines to electric motors. In general, engine efficient drops with size, due to proportionately larger heat losses in small engines. And two-stroke engines are designed for a good power-to-weight ratio, not for fuel efficiency. Meanwhile, electric motor efficiency — at least at this size — varies only modestly by size. And as a result, what was a 2.5 to 1 advantage for electric cars becomes a 7 to 1 advantage for electric leaf blowers.
That said, the global warming impact of these devices is almost negligible, at least in terms of C02 emissions. Note, from the table above, that you’d have to run those leaf blowers for about three hours to use up one gallon of gasoline. Compare that to the U.S. average of about 650 gallons of gasoline per licensed driver per year, and it’s obvious that leaf blowing really doesn’t much matter, in the overall U.S. carbon budget.
That said, this is just another illustration of something that I hope is becoming increasingly clear to most Americans: The future is electric. The rapid de-carbonization of the grid means that more and more frequently, the low-carbon option is going to be the electric option. Whether that’s for transportation, heating with heat pumps (Post G22-058), or for moving your leaves from place to place.
On the smugness of raking, or, TANSTAAFL
I’m sure that at least some readers have thought to themselves, “Why use a leaf blower at all? I rake my leaves, therefore I don’t use any fossil fuels to collect my leaves.”.
Well, it just ain’t that simple.
- Raking consumes energy.
- We supply that energy with fuel.
- That fuel is a highly refined substance called “food”.
- Food production and distribution consumes enormous amounts of fossil fuel.
One way or the other, everybody wants to think that there’s a free lunch. In this case, the free lunch is the illusion that if you don’t consume fossil fuels directly, then you can ignore the fact that you’re consuming them indirectly.
And I’m the guy who gets to tell you that nope, there ain’t no such thing as a free lunch. The facts are that:
- it took a lot of fossil fuels to make your lunch, and
- if more exercise means you eat a bigger lunch, then
- more exercise means you consume more fossil fuels.
The only trick is that you consume those fossil fuels indirectly, via increased food consumption, not directly, by gassing up your power tools.
I was introduced to this concept in an article entitled “Bicycling Wastes Gas?“. I can do no better than suggest that you read it.
Here’s the story of how I finally came to understand this. In my youth, for two years, I biked to work about three times a week, during the warm weather. Work, in this case, was downtown Washington DC. The round-trip distance was about 32 miles. For a guy my size, that burns about 1600 calories.
Lo and behold, I found myself eating a lot more. Conservation of energy, and all that. Those 1600 calories of daily exercise had to come from somewhere. And if my weight remained stable, they had to come from an additional 1600 calories of food.
The kicker is that, for the standard American diet, it takes about 10 fossil-fuel calories to make and deliver one edible calorie. Estimates vary, but that’s a nice round credible number. So, while 1600 calories doesn’t sound like much energy (for comparison, a gallon of gas contains about 31,000 (kilo) calories of energy in it), once you factor in how the fossil fuel energy required for one edible calorie, suddenly, you realize that your 1600 calories of typical-American-diet embodies as much fossil fuel as … roughly half-a-gallon of gasoline.
Here’s a reference that, at the end, comes to the same conclusion that I’m about to state. Bottom line: As a bicyclist, eating the average American diet, I get about 63 MPG equivalent. That is, when you divide the additional fossil fuels required, to produce the additional food I consumed, when I biked 32 miles a day, at the standard U.S. diet, by the total miles traveled, that worked out to be 63 MPGe. (Where the “e” means that it’s compared the total fossil fuel energy to the amount of energy in a gallon of gasoline.)
(You have to be careful when you do such a calculation, because exercise calories-per-hour data are always the gross calories, including your basal metabolism. Nobody cites the additional calories consumed by the exericise, over and above basal metabolism — the amount you would burn in any case. You have to derive that before doing the calculation.)
Your mileage will, of course, depend on what you eat. Potatoes embody very little fossil fuel. Beef embodies an almost unbelievably large amount. And many have pointed out that typical ovo-lacto-vegetarian diets embody about half as much fossil fuel as typical carnivorous diets (reference, Pimental, Cornell U.).
But to make this clear, assuming 10 fossil fuel calories per edible calorie, if my wife and I bike together, and maintain a stable weight, we actually consume more fossil fuel than if we drove together in a gas Prius. And me, by myself, bicycling (while eating the average American diet) consumes more fossil fuel per mile than traveling on electricity in a Prius.
In other words, if I parked my electric Prius and did all my travel by bike — while eating the standard American diet — if my travel miles were held constant, I would increase my fossil fuel consumption.
Weird, huh? And saying that inevitably makes bicycling advocates angry. Nevertheless, it’s just math. And a belief in basic physics, i.e., conservation of energy.
Arguably, the biggest fossil fuel savings from committing to using a bike rather than a car comes from total miles traveled. Because, in fact, if I have to power them myself, my total miles traveled will not remain constant. Not even when considering local transport only. A short jaunt to the hardware store by car becomes a major investment in time and effort by bike. Consequently, if my only option were biking, I’d be making a lot fewer trips to the hardware store.
What about leaf raking? With that as preamble, at my weight, this calculator says I’d burn a gross total of 481 calories per hour, raking my lawn, from which I need to net out about 135 an hour for basal metabolism (e.g., just sitting and reading). For me, then, leaf raking is a net ~350 calories per hour. Supplying an additional 350 calories, with the average American diet, requires 3500 (kilo) calories of fossil fuel energy. Or about as much as you’d get in 0.11 gallons of gas. Inverting that, by raking leaves (and replacing those calories with the average American diet), I consume gasoline-equivalents at the rate of about one gallon every nine hours.
Compare that to the gallon-every-three-hours of the smaller gas-powered leaf blower above.
Conclusion: Once you factor in the “fuel” for your leaf raking, you consume about one-third as much fossil fuel as you would using a small leaf blower. That’s per hour.
How that stacks up per cubic yard of leaves is anybody’s guess. But my guess is that, as with my example of bicycling above, your fossil fuel consumption from food-powered leaf raking is not hugely different from gas-powered leaf blowing. All due to the fossil fuels embodied in the extra food required to replace the calories burned in raking.
And, as with the bicycling example above, it’s a pretty good bet that electrically-powered leaf collection — your electric leaf blower — beats hand raking, in terms of total fossil fuel impact.
There are plenty of good reasons to rake leaves by hand. Less noise. Great exercise. Commune with nature.
And, as with bike-versus-car, if you are powering the operation with your own muscles, you’re probably going to do a lot less. You’ll likely to be motivated to move the leaves less, and maybe be motivated to #leavetheleaves. All of those are positives.
But in terms of the implications of that for fossil fuel use, that’s far from clear. Raking requires energy. That comes from food. If your weight is stable, more energy output requires more food input. And food production in the U.S. requires large amounts of fossil fuels. Bottom line is that there ain’t no such thing as a free lunch.