body heat

Soundjenluc I am in Portland for the day, having dragged myself out of bed at an ungodly hour (4 AM) to catch my flight. (On the plus side, there is almost no traffic on LA freeways at that hour.) The reason: to visit the city's Green Microgym founded by personal trainer Adam Boesel last year. Perhaps you read some of the press coverage the opening generated: Boesel has retrofitted much of his exercise equipment (stationary bikes, treadmills, elliptical machines) so that gym members can produce a little bit of usable energy during their workouts — not a lot, mind you, but enough to run the fans, for example, or the stereo system. Combine that with other strategies for improving energy efficiency, and Boege keeps his electricity costs to a bare minimum. In time, he thinks he can break even, and maybe even turn a small profit.

He's not the first to ponder the potential of all those city dwellers — ahem! like me! — spending hours upon hours running or cycling in place to stay fit and trim, like hamsters on one of those little wheels, with little else to show for it other than improved health (which, admittedly, is a valuable thing). Lots of amateur engineers over the years have tried building their own energy-generating bikes to, say, run their coffeemaker in the morning. Several companies have cropped up in recent years specializing in retrofitted exercise equipment: in St. Petersburg, Florida, for example, which installed a set of retrofitted elliptical machines in a 28,000 member gym in Gainesville, or entrepreneur Jim Whelan's Green Revolution. There's an entire research program devoted to human-powered energy at the Delft University of Technology in The Netherlands.

For the Green Microgym, Boesel started with four linked Team Dynamo stationary bikes connected to a bank of batteries, capable of generating up to 200 watts for every hour of exercise — enough to run an LCD TV and stereo system for the entire workout period. It's a team effort, too, with all four riders helping to charge the batteries.

Sounds good in theory; Boesel found in practice that the battery option isn't nearly as efficient in generating useful energy as a machine with a "grid-tie" inverter that sends the generated energy directly into the power grid. (That's a device that lets people with solar panels, for instance, "spin the meter backward" and sell power back to their local power company. Boesel literally plugs those machines right back into the wall socket.) There is a greater conversion loss when you feed that generated energy back into the battery, for some reason.

See, that's why you need to do the experiment. Nonetheless, Boesel has reduced his energy costs significantly: he consumes on the order of 9 kilowatt hours per month, which is ridiculously low for a commercial enterprise. In addition to retrofitted machines, he employs a lot of common-sense conservation measures, like turning off machines and TVs when they aren't in use, and judicious use of the A/C and lighting. Apparently the average treadmill takes 1500-2000 watts to operate; you'd need nine Lance Armstrongs chugging at full power to keep just one of those suckers operating. Incremental improvements can add up over time, particularly for a small business like the Green Microgym. He estimates he saves between $75 and $150 a month, which isn't going to set Wall Street on fire — but it can help defray the creeping costs of running your own gym.

I don't know exactly how much energy my gym in LA uses, but it's a hell of a lot more than the Green Microgym's consumption. Granted, it's a lot bigger, with more machines (each with its own little TV monitor), a cutting-edge sound system, large mounted TVs all over the gym, a heated pool, large locker rooms with sauna and steam room and showers, etc. But there's a lot of little ways to eliminate waste here and there — like turning off the mounted TV screen on your elliptical machine after you're done working out, or feeding the energy produced by the exerciser back into running the little TV screen. And given the amount of sunshine LA gets in a typical year, I'm constantly surprised by how few places make use of solar panels. Yeah, yeah, they're expensive, and existing buildings can be difficult to adapt to that kind of renewable energy source. But it's a terrific future investment in sunny SoCal.

In general, we routinely overestimate how many calories we burn when we exercise (and underestimate how many food calories we consume). Seeing just how little energy I produce on Boesel's retrofitted elliptical is an eye-opener in itself, particularly since the resistance increases the harder I work. I'm breaking a sweat, starting to breathe hard, and the little light bulb he's hooked up to the front of the machine as part of the test phase barely stays lit. (The retrofitted elliptical was built with help from students at the local university.) I always suspected my gym's machines were overly optimistic about my physical exertions. Boesel has actually worked really hard to make sure his retrofitted machines feel just like the old ones, giving the user control over the resistance level. But once you're talking about watts instead of calories burned, you're dealing with smaller numbers. Some of that is related to body mass: Boesel figures he can produce 75-80 watts consisently — that is, at a pace he can sustain for a full hour's workout — compared to my measly 40 watts (and frankly, half the time during my mini-workout the gauge dips into the 30s — the shame!).

The body is a heat engine, as physicists well know, and thermodynamics is a tricky thing, with many different factors coming into play. It's easy to come up with a wrong or misleading answer — hence the recurrence of folks convinvecd they've just invented a perpetual motion machine. (Once again, for the record: there is no such thing as "free" energy.)  Matt over at Built on Facts had a terrific post about this last December, just in time for Christmas, about the effect climbing a steep hill has on how many calories someone would burn during the climb. "If you're going a long way uphill your height changes quite a bit, and correspondingly, so does your potential energy," he explains.

Being a thorough sort of guy, Matt actually crunched some numbers for how many calories a 160-pound man would burn climbing the stairs of the Empire State Building, based on that increase in potential energy. He assumes you reach the top 1050 feet above ground, and assumes a gravitational acceleration of 9.8 meters per second squared. The answer: he found a total change in potential energy of 230,000 joules. Woo-hoo! At least until you convert that into calories. It's about 54 food calories. Now you're less ecstatic, aren't you? Let Matt explain what's going on here:

Surely something that difficult would burn a lot more calories, you'd think. And it does. The immense effort you expend in climbing is mostly budgeted to different bodily processes. You have to move extra air in and out of your lungs. You have to circulate blood at a much higher rate. You have to process the complicated chemistry required to keep your muscles moving. All of these things take energy and by the time the shoe meets the stair most of the energy has already been lost, eventually ending up mostly in the form of heat. Your body can't afford to overheat and so you begin sweating to carry the excess heat away. All that energy had to come from somewhere and it came from the food you ate. By the time you're on the observation deck looking over Manhattan, you'll have used up a lot more than 54 calories.

In other words, it takes energy to run your body's machine. That's great news, potentially, for your waistline (depending on one's total caloric consumption), but the human body is an energy hog. In that respect, it's a highly efficient little heat engine, because by the time it gets done extracting energy for all those functions, there's precious little available to be harnessed as usable work. We see the same effect in Boesel's Green microgym. The BBC ran an article about this back in 2006, quoting energy consultant Graeme Bathurst, who said bluntly, "The key issue in this case is that human don't use very much energy."

If someone eats 2000 calories a day, that translates into just enough energy to run a 100-watt bulb for 22 hours — assuming 100% efficient conversion, which doesn't exist. Something is always lost in the conversion — in the case of exercisers, we lose energy by sweating off excess body heat, for example — which is why many physicists refer to those pesky laws of thermodynamics as the laws of "thermogoddammics."  Or as Bathurst puts it (far less colorfully), "The energy burnt is not converted directly into mechanical movement, and so it is not possible to harness the full energy usage."

How about that rowing machine mostly sitting idle in my gym? Let's say I rowed furiously on that thing for 10 minutes, thereby burning 100 calories. (We are being optimistic; it would be much less, particularly given my pathetic lack of upper body strength these days.) That's enough to run a 100-watt bulb for one hour on paper, but we'd be lucky to harness 50% of that. For a gym with 40 machines of all sorts — rowing, cycling, running, walking, ellipticals — that means users could generate some 25kWh of electrical energy during the two-hour peak period of the gym. Again, we're being idealistic, assuming all the machines would be in use and "that all individuals were genuinely attempting to work out," according to Bathurst. (We're looking at you, Princess, the girl in full makeup and swanky color-coordinated gym togs talking on her cellphone while strolling on the treadmill, not breaking a sweat. Get moving! You're ruining our overall energy output!)

That's not going to save the gym much money in terms of overall operating costs, but it's equivalent to running a few households for a day. It's probably sufficient to run your little TV monitor, or recharge your iPhone before heading home. According to an article last year in the Christian Science Monitor, a gym in Boston has a special stationary bike retrofitted to have a laptop built into the top. The laptop has no battery. It is powered entirely by the person pedaling, so someone can get in a decent spinning workout and still surf the Web and answer a few emails.

I am not sure this approach would work for me: I like to push myself and really work up a sweat at the gym, which means I get winded. When I get winded, I can't really focus on things like responding coherently to an email. Plus, the article doesn't say anything about whether sweat dripping onto the keyboard would damage it; anyone who's spilled tea or soda on their keyboard can attest that these are fragile things. But I could definitely be motivated to run a DVD player or small TV monitor or my iPod from my own exertions. Boesel actually sells retrofitting kits for home exercise equipment, and assured me I could probably find a refurbished spinning cycle for half price on E-Bay. (He's right; I checked.) It wouldn't take up much space in the downstairs guest room. I must take this matter up with the Spousal Unit, because even if I don't end up generating much overall energy, it would be kinda fun to do the experiment.

My gym is a long ways off from being able to break even on its energy costs, even if they retrofitted all their equipment tomorrow. Even Boesel's Green Microgym hasn't achieve 100% efficiency yet; the poor economy hasn't helped. But he's getting close! Add in the investment costs for retrofitting equipment, adding solar panels and other energy efficient approaches, and it's easy to see why venture capitalists might not be keen on the idea of green microgyms as a business prospect. It might not be a model that can scale up beyond a community gym, but I'm rooting for Boesel as he tries to take things to the next level.

Personally? I think they're missing the larger perspective. Sure, the current gym "culture" is one of energy waste, and such habits can be hard to break en masse. Nonetheless, it can be done. Regular readers know I drive a Prius since moving to Los Angeles (before that, I was a public transport kind of girl, which is easy to do in NYC and Washington, DC). My favorite feature is the graphical display that shows you exactly how many miles per gallon you're getting at any given moment. And that constant influx of real-time information makes me appreciate all the more just how much energy we consume when we drive our 3000+-pound cars. It has literally altered my driving behavior. I accelerate more slowly, take advantage of downhill sections of the road to coast a bit, brake less suddenly, etc., all for the thrill of the occasional tiny inch upwards in my overall average MPG. (I'm currently at 49.5 MPG over 2-1/2 years of combined city/highway driving, and counting.) This combination of practices is common among Prius drivers, and even has its own term: "hypermiling."

Are we saving the planet? Not really — not when you consider the energy costs that go into building and transporting our cars in the first place, and other peripheral costs. Ours is a complex, highly interconnected energy environment; that's what makes even basic thermodynamics such a bear to contend with. But I am personally saving money on gas. And the Prius has made a difference, in thousands of tiny, hard-to-quantify ways. Just like driving a Prius has made my hyper-aware of how much gas I burn, so, too, can retrofitting exercise machines help raise people's awareness of just how much hard work it takes simply to light a 60-watt bulb. And that can only be a good thing. Adam Boesel can bring a Green Microgym to Echo Park whenever he wants. I'll be his very first gym member…

11 thoughts on “body heat”

  1. I know you provide “physics with a twist” but really, “Watts per hour” is a twist too far.

  2. @Dave: Did you miss the part about being up since 4 AM? 🙂 There’s a lot of little typos and errors in wording in this post that I noticed when I finally got some sleep. They’ll be corrected eventually.

  3. Very interesting 🙂 I’ve read a bit about green gyms before, and I think it’s a great idea. If you can capture / feed back to the grid the energy people create using those machines, why the hell not? I wonder if I can rig up my elliptical bike-thing to power a radio (judging by what you wrote about the light bulb though, I’m thinking not…)

  4. I’m sure I’m not the first person to point this out but…
    lost in conversion sounds a lot like lost in translation.
    poetry, science, Sofia Coppola, exercising…the world’s not so different.

  5. What I remember when the Prius first came out in America (around 2000) is the engineers at GM’s R&D Center baffled by its success. They had “run the numbers,” and especially considering the economic and environmental cost of the nickel hydride battery pack – manufacturing, maintenance, replacement, and recycling – the Prius (and hybrid technology for cars in general) didn’t make economic sense.
    This was a narrow view, as engineering feasibility analyses often are, and it didn’t take into account the bigger picture: rising oil prices, improvements in the technology over time (the Prius is now over 10 years in commercial production), and of course the emotional impact of the Prius. Although these mechanical engineers were not experts in marketing, anyone working in the auto industry should have been aware that a car-buying decision is not entirely rational. That is, “money rational.” Jennifer has caught the flavor of this: “The Prius has made a difference, in thousands of tiny, hard-to-quantify ways.”
    Basically, the “economic sound barrior” of greener technology can be broken by enthusiasm for a longer term vision. The Green Microgym seems to have been inspired by such a vision, and (as Jennifer reports in her blog) contributes to the vision, raising consciousness (to use an archaic phrase) about “how much hard work it takes to light a 60-watt bulb.”

  6. I just want to clarify the “watts per hour” issue…I wouldn’t want you to continually fall victim to the ‘unit cops’. Saying “watts for every hour” is no different from “watts per hour”.
    A watt (power) is a rate of energy consumption, which represents 1 joule per second. A 100 watt light bulb uses energy at a rate of 100 watts. The four stationary bikes generate 200 watts of power, regardless of whether they are pedaled for an hour or only 5 minutes. It’s the amount of energy (joules) produced that increases with time.
    In any case, it’s an informative post. I’ve often wondered myself why gyms don’t try to benefit from all of that human-generated energy.

  7. “He’s not the first to ponder the potential of all those city dwellers — ahem! like me! — spending hours upon hours running or cycling in place to stay fit and trim, like hamsters on one of those little wheels, with little else to show for it other than improved health (which, admittedly, is a valuable thing).”
    True story: I watched Sean Carroll lectures (among others, from The Teaching Company) while on my treadmill at home. A little headphone amplifier, some noise-suppressing ear phones, and every word came through loud and clear over the fans and treadmill motor. How come his incipient second chin doesn’t show on his photos?

  8. This has been implemented here in the Philippines with Quezon City Jail where the inmates are required to take turns in recharging a car battery so that they could have their share with the power. If you want to see the full article you can read it here:
    Wouldn’t it be more economical idea if they purchased used stationary bikes instead? It would save them hundreds of dollars and fitness equipment is one of those that you can confidently buy 2nd hand. I saw this guide about used stationary bikes that might help people who plan on starting this kind of concept.

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