electricity from a gym: quick calcs

1. Credit for power put into the grid is much higher than cost of power taken out of the grid in many states. For example, in WA, you get paid as much as $.51/kW-hr to add solar or wind energy to the grid.
2. Many exercising machines convert effort more or less directly to heat. In winter, this can subtract from the heating requirements of the building, much as waste heat from lighting fixtures does. Of course, if taken too far, this heat can cause the cooling system to kick in, even in winter. In summer, the heat from exercising generally adds to the cooling load.

Paul Mathews

Wow, I'm really living in the wrong state, then! Here in CA, you're lucky to get a fraction of the rate they charge you...

Excellent point.

Ah, here's a link to the dance club generator:

SUSTAINABLE NIGHTCLUB

Energy can be harvested from just about anywhere: rivers, the sun, wind . . . and hyperactive club kids. The latter is the rationale behind Club Double Dee, which dubs itself the world's first sustainable dance club.

Scheduled to open in Rotterdam, the Netherlands, the club is a cooperative project between Enviu, an international organization promoting sustainable entrepreneurship; Doll Lab, a Dutch architecture firm; and Off Corso, a local dance club. Not only is Double Dee considering serving organic beer and using a rainwater collection system for toilets, but it may actually be powered by dancing: Springs beneath the floor would capture motion energy to be converted into electricity. Enviu is remaining tight-lipped about the specifics of the project until its public presentation on Oct. 7, an event that the organization's Web site,

, touts as "the beginning of a new era; an era in which sustainability will be hip and trendy."

You failed to consider the conversion efficiency of the people doing the work... Currently the US Government is looking into harvesting energy from soldiers as they walk around. They are looking at a variety of techniques, but all have fairly low conversion efficiencies. You might have some luck, but I'm not holding my breath.

Brad

Yep, conversion efficiencies all around are likely to be low. Then again, some folks might be able to put out 200W continuously.

I did the math intending to prove that this was a complete waste of time, but my results do not conclusively prove that... although, I do not intend to open a gym of any sort anytime soon.

Michael

So, do they just surround the dance floor with induction coils and strap large supermagnets to the dancing kiddies? ;-)

Cheers! Rich

Just strap TVs to exercycles, and sell them to everyone. It'll save energy, and help alleviate the obesity epidemic. ;-)

And, of course, if the user turns off the TV and, say, reads a book while still pedaling, it can feed back to the grid for credits. That would encourage reading instead of TV. ;-D

Cheers! Rich

High gas prices help too, according to The Independent:

Best regards, Spehro Pefhany

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If you frequent gyms as I do you'll know that probably around 90% of the people on the equipment like treadmills, bikes and rowers are complete slackers. They don't work hard, and most come off barely having raised a sweat.

Also, cables are a trip hazard, so lots of bikes and rowers are self powered, only switching on when you start rowing. Can't feed those one back to the grid unless you have an expensive facility retrofit.

Dave.

How expensive? Most of the gym equipment I see already has a generator of some sort installed - to operate the equipment screen/control system. There is likely excess capacity already built-in, even for the slacker-user.

All that is needed is some cabling and an inverter to feed back to the grid or power the gym lights, etc.

It might be economically feasable after all.

John

The "slacker" user would barely generate enough power to turn the machine on and power the flashy LED display panel. There is a huge difference between the potential power output a "slacker" would generate compared with a super freak going at full speed.

Yes, and that's my point. That cabling might be expensive to install because you can't just lay it on the floor because it's an OH&S trip hazard. You might have to cut channels into the concrete floor or whatever to conceal the cabling. I have no idea how much that costs, but I'm sure it ain't trivial. That's how it is at many gyms I've been too, and that is why a lot of the machines are self powered, no need for the gym to install a costly power outlet for each machine.

Dave.

In a typical gym you wouldn't recover the energy needed to light the place, let alone sell power back to the grid.

So you have to play the "what-if" game, where you can make (unrealistic) assumptions: highly efficient generators,

100% equipment usage, lowered requirements for lighting, heat, ventillation, etc, high output power from each user and so forth.

Of course, if you could somehow harvest the energy expended by the free-energy crowd ...

Ed

Yep. 10 kW *maximum*, assuming 100 pieces of equipment. That already is a lot. *Can* one pack more than 100 pieces of exercise equipment into a gym?

24 Hour Fitness is downright empty at times... not always fully packed, as my optimistic calcs assumed. If only 10% occupied, 1kW... can that power the fluorescent lights...? It definitely won't keep the indoor pool heated...

Then it just boils down to the economics of reduced electricity purchases - never mind the grid intertie. Hmm... replace the inverter with a shelf of deep cycle batteries to store energy from the peak crowds, and just use that energy to heat the pool...???

M

If springs beneath the floor capture energy from dancers, it will be harder to dance. (Compare to one of those exercise machines with dampers hooked to foot pedals - your going down of your own weight, but your muscles are still applying a force through a distance, costing energy.) So everyone will go home early, giving further savings in lighting costs.

--
John

It's worse - *far* worse - than that. In a typical gym, most of the equipment is idle. On top of that, most of the exercisers generate power intermittently rather than continuously while they are exercising, with a lot of idle time between exercise sets.

The energy the human puts into some repetitive motion machines must be "given back" to move the mechanisms back to the initial condition. If it were all converted from kinetic to electrical, the machine would not return to the initial condition for the next cycle. Repetitive motion (push and relax) machines would yield a very low efficiency.

Even if on a stationary bicycle type generator where power is provided 100% of the time, a typical human can produce and maintain about 75 watts, not 100, according to:

So to produce and maintain 1KW, you would need 13 people producing a bit above average on continuous effort machines, like a bike, which is not found in the typical gym. But say it was. If that's 10% of the equipment, it implies 117 other machines, all of which occupy space, and all of that space needs to be lighted. So, since we're into "what-if" territory assuming

13 bikes producing 75 watts each, how many square feet will all the (130) machines occupy, and how many square feet can 12 4 foot (80 watt, two tube) watt fluorescant fixtures illuminate, meeting commercial building code requirements? I'm not going to do the math, as I don't know how many square feet each machine needs nor what commercial code requires - but I doubt that that the fixtures can each provide enough illumination for 11 machines per fixture. And then there is the requirment for emergency lighting, lighting in the showers, bathrooms, reception area, battery charging (so you can turn the lights on when you enter the room and no one is generating at the moment, or so you can keep the lights on when the last person stops exercising) etc.

Ed

I've had occasion to ride a bus past one of those exercise joints, and I wonder, do these people drive to this place to pay to walk on the treadmill? Why didn't they just walk to the gym, and they wouldn't have to use the treadmill? And the other question I'm always impelled to ask - isn't life itself enough of a treadmill already? ;-)

Cheers! Rich

Wrong to start with. 100W is our standby dissipation. Driving a generator with 300W continous is doable, 500W continous will be hard.

It's a social thing, they spend half their time chatting or watching the big screen TV's.

I'm the only one who rides a bike to my gym.

Dave.

Accordding to this link, 75 watts is sustainable on average:

Where did you get yoyr 300 watt figure?

Ed

average:

Maybe he's a Tour de France rider?

I also didn't specify whether my 100W was power input or power output. If it's power output, the rider will have to ride harder due to inefficiencies in the power conversion, of course... 200W? what's a typical small generator efficiency? 50%? 90%?

Michael