Human Powered Gym?- Part 1

I was in the gym the other day, when I thought "hang on a minute, I'm on a cycling machine, which is just basically making a wheel turn (the basis of electricity generation). Why can't we use this to power the gym- lights, the tvs, the radio, the air conditioning and the machines themselves?"

I suppose a more reasonable question is:
Is it economically viable to install generators attached to the machines in a gym? Noting that:

1.  Almost certainly new exercise equipment would be required.
2. All the machines aren't going to be used all time, so either you need a backup supply system (if the average energy output isn't as large as the energy requirement) or a method of storing the energy (if the average energy is larger than the energy requirement).
3. Generators require something spinning, preferably constantly. This is fine on a bike, but rowing machines, treadmills and cross-trainers won't be quite as simple.

 As I imagined, I am not the first person to think of this idea (nice as it would have been!). In fact, there is a gym in Portland across the pond which does exactly this:

http://news.bbc.co.uk/1/hi/technology/7796215.stm

There are also gyms in Hong Kong using this concept:

http://www.inhabitat.com/2007/03/08/human-powered-gyms-in-hong-kong/

And, as a blue sky "gym concept" island:


http://www.alternative-energy-news.info/human-powered-workout-gym-concept/

For this last article, I am not so interested in the article itself, but the comments after it.

This is all very interesting, but let's examine (using the figures found on the companies websites, as well as other sources I will mention) the actual numbers.




_______________The Numbers_________________

First of all, what is the power output of a human on (say) a cycling machine?

• The first article states "if you figure a 100 watts per machine" and this is backed up on their website (http://www.humandynamo.com/technical_info.html) as "60-120 watts"
• The second states "One person has the ability of producing 50 watts of electricity per hour when exercising at a moderate pace"

(Note that this is actually slightly wrong units-wise. watts is a unit of power, the rate of producing energy [or the "amount of energy produced each second"] , so producing 50 watts per hour doesn't really make sense. The quoted Steve Clinefelter probably means a person can produce 50 watts for an hour [i.e 50 Joules per second x an hour] )

• In the comments of the third article, the result of the discussion is that about 75-100 watts useful work is produced.

 Let's go with an estimated value of 80 watts, as I reckon many people at the gym either won't be working at their highest power output, or won't be great athletes.

The Human Dynamo website (the system in the first article) claims that their system is "70% efficient", which seems reasonable after looking at general generator efficiency ranges, so our estimated output for one person is 56W.

Right, now we have our estimated output, let's see what we can power with that.

Air conditioning
From the excellent online book Sustainable Energy- Without the Hot Air by David MacKay (http://www.inference.phy.cam.ac.uk/withouthotair/c7/page_51.shtml) an air conditioning unit will use 0.6 kW or 600W, so you'd need more than 10 people using a "dynamo bike" to power the cooling system in the gym.
(Note that this is for a domestic room, the use for a large gym may be much more)

Lights
Let's assume that the gym is using relatively efficient fluorescent tubes, which have a variety of powers (http://www.firstlightdirect.com/mcp/Fluorescent_Tubes.html). So, depending on the exact lighting system in the gym (let's say 20W per tube), our one person could probably light up at least a couple of tubes while he's on the bike.
From Without Hot Air, a home sound setup uses about 10W (http://www.inference.phy.cam.ac.uk/withouthotair/c11/page_70.shtml) and from the Human Dynamo site, a "stereo" uses 30-70 watts. So our one person could conceivably power the stereo system for the whole gym (obviously depending on the individual gym system!).

Looking at the same page of Without Hot Air, a tv uses 100W. This seems to agree with a quick google search of tv power usage, including large tvs of 32" and above, although these power values are much lower than those given in the Human Dynamo site:
Small TV: 60-100 watts. (I am assuming that since people will be watch the tvs from a distance, they will go with larger ones)
Large TV: 400-600 watts (This is the value I am comparing with)
So two of our estimated bikers could power a tv. Obviously if they are powering the tv, they can't also be powering the lights! I am taking each usage in turn, I'll conclude at the end about joint usage.

Phone/mp3 player charger
Again, a quick google search will yield a host of results for various ipods, phones and other such devices. They all tally fairly well with the Without Hot Air value (still on the same page) for mobile phone charger: 5W or so. You could, then, charge your phone/mp3 player/whatever device with the power you generate. [However, there is still the question of how cost-effective it is to get this electricity from you rather than just a grid, as you will still need all the dynamo and storage systems.]

The machine itself
You might think that the biker should be able to power the screen which gives information about the current exercise. This is true, as there are some machines on the market which are self-powered (e.g the r3, club series and c3 bikes in http://uk.home.lifefitness.com/content.cfm/lifecycles_1 ). Many other machines are battery powered (particularly rowing machines). There is a problem, though. The machines linked above have simple black/white LCD screens (like this http://www.getprice.com.au/images/uploadimg/791/350__1_Athletics-20--20IDM-20Basic-20Countdown-20Timer.jpg) but many of the newer machines have fancy colour and touch capabilities, which surely increase their power consumption.
Unfortunately, I haven't been able to find detailed information about the power usage for exercise machines (please comment below if you have!). We do know, however, that they can be powered by either batteries or the person using it. I'll guess (although please don't assume that this is accurate!) of a value of around 20W.

________________Conclusions of Part 1_________________________________

Let's review. We have an average person using a bike producing a (useful) 56W.
What can we power with that? (Taking each case individually)

Air conditioning:              600W        - would requre more than 10 people to power it

Lights:                             20W          -  could power a few of the lights in the gym

Music System:               ~30W          - could power the gym sound system

TV:                                100W         - two bikers could run a television

gadget charger:               2W            - could easily power this

The machine screen:       20?W        - could power, depending on the screen itself

So in total, a normal gym goer could power the machine, charge his phone and maybe power a light or two.
That's enough for part 1. In part 2, I'll talk about the gym production as a whole, storing the energy, weights machines and the economic feasibility.