Essay on Human-Powered Gym

My essay on the feasibility of a Human-Powered Gym has gained a lot of hits since I originally wrote it in 2010, and so I have decided to reproduce it as a separate page for ease of access. Enjoy!

Human powered gyms

As we increasingly look for alternative sources of energy, could there be an untapped potential power plant within each of us? David Pickup examines the possibility and economics of a human-powered gym.

Energy supply is one of the most pressing and controversial issues of recent times. It is widely accepted that climate change and greenhouse gas emissions are linked, and it is also established that the world fossil fuel reserves are running out [1]. Thus, as the electricity needs of the world increase, it is vital to start looking for alternate sources of energy for electricity production. Of these, the main options are nuclear, wind, solar, wave and hydroelectric power. However, a dynamo could be attached to any turning wheel and some cardiovascular gym machines do turn a wheel, so it is conceivable that gyms could be a potential source of electrical power. In particular, exercise classes, where groups of 20 or so people are all on the same type of gym machine at the same time, might be a useful source of electricity.

The Warm-up

Before discussing the concept in detail, it would be constructive to outline some data on gyms to provide context. The growth of fitness suites is a relatively recent phenomenon across the landscape of Britain: their numbers have risen from less than 200 in the 1980s to 5,714 in 2010 [2]. The industry is still growing in the UK with a 1% rise in 2010 by to £3.8 billion. However, this growth may slow or stop, as new membership has recently decreased: a Times writer, Peta Bee, even claimed that “the gym's heyday has come and gone” [2].  She explains that the general trend has changed so that people are trying to be more active in their daily lives, rather than doing focussed fitness training at a gym. This potential lack of membership could be a significant problem for human-powered gyms in the future, but it remains to be seen whether this dip in gym membership is a legitimate concern.

There are various types of exercise machine, and these have different effectiveness for electricity production. The simplest and most efficient way of producing electricity is by continuously turning a wheel at a constant speed. Both cycling machines and cross-trainers operate in this way and are thus the most effective and widespread of the electricity generators; this is reflected in the use of these machines by human-powered gyms in Hong Kong [3] and Portland, Oregon [4]. Another electricity generation technique that is applicable to gym equipment is a wheel spinning discontinuously, i.e. without a constant speed. A good example of this action is a rowing machine, where each stroke forces a resistance wheel to rotate. This method is also applicable to a self-powered treadmill, although most gym treadmills currently require electricity to run rather than being self-powered. These powered treadmills allow the speed can be kept constant, rather than having the user trying to keep a consistent pace. However, there is no definitive answer on whether this causes better fitness training [5]. Weights machines are a popular piece of equipment in any gym, and although it is conceivable to generate electricity lifting weights in a similar way to the rowing machine – by having a weighted wheel turned when a force is applied, for example – much of the useful work fitness-wise is done when lowering a weight as well as lifting it. Therefore, it is unlikely that these machines could be adapted to produce electrical power while retaining their optimum training functions.

Power Consumption of the Gym

Device	Total Power Estimate
Air conditioning	1800W
Lights	200W
Televisions	500W
Music System	50W
Total:	2550W
Table 1: communal gym power consumption.

Before estimating the power generation capabilities, it would be helpful to discuss the power consumption of the gym; i.e. how much power the devices in the gym use. There are many resources online of homeowners measuring the power use of devices in homes, which will provide the bulk of the estimates given below. This is a reasonable assumption as some of the devices used in gyms, such as televisions and stereo systems, are often simply the same as their domestic equivalents. Where typical systems are required for estimated values, the example of Addlestone Leisure Centre (ALC) in Surrey, UK is used [6]. This is a gym attached to a school which the author attended in August-September 2010, and so provides an accurate and recent set of gym data. Through visiting several gyms over the years, it was clear that this one was a typical setup. There is an important distinction to be made between communal gym power usages, i.e. equipment that everyone will use, and individual power usages, i.e. each person’s machine.

Firstly, the air conditioning will be considered. An estimate for the power used by a standard air conditioning unit is 600W [7]. In a typical gym there would be more than one of these machines, so this is one of the main power users in the gym. In ALC there were 3 such units, giving a total power estimate for air conditioning as 1800W.

Lights and music are also regular occurrence in gyms, and different lighting and music systems will vary hugely in power consumption. A reasonable estimate for the power usage of the lights in the typical gym is 10 20W fluorescent tubes, leading to a total value of 200W, while the power consumption value for the music system in ALC was 50W [8].

Televisions are a relatively new addition to the gym, but are very popular. A typical large TV uses around 100W [9]. There will usually be multiple televisions around the gym, leading to a much higher power usage; there were 5 in ALC, giving a total of 500W.

Many people now take their own gadgets, such as phones and iPods, into the gym with them. If the batteries run out, it is highly inconvenient; it would therefore be a good idea if the gym machine could charge these devices. It does not take much power either, only about 5W [10]. It is important to note that this is a power consumption of the individual machine, rather than a communal consumption of the gym.

The communal gym usage values are collected into a table [Table 1]. The total communal gym power consumption is 2550W, while the individual consumption is 5W. This total value is by no means complete: it does not include the reception equipment such as computers and phones, for example, or changing room equipment like showers or hairdryers. However, as a first estimate it gives a good basis for the actual consumption of the gym workout area, which is where the power generation would also occur.  

Power Generation

An estimate of the power generated by one exercise machine will now be made. For the purpose of simplicity and the availability of information, this machine will be an exercise bike. There are several estimates of the total power generated by a human on an exercise bike: 60-120W [8], 50W [4] and 75-100W [11]. The value of 80W will be taken, as many people working at a gym will not be willing or able to work at a high level for an extended period of time. Not all of the power generated by the person will be converted to useful electricity, however; gym machines are not 100% efficient. The efficiency of these machines is around 70% [8]. This gives a final useful power of 56W.

Using ALC as an example, there are 14 machines which could be used. In terms of electricity generation, cross-trainers and exercise bikes are considered equivalent, while rowing machines, treadmills and weights machines are ignored. These 14 machines could generate 784W, but observations over a month at ALC show that, on average, only half of the machines were in use, giving a power of 392W, which will be rounded up for clarity to 400W. This shows that the machines are able to generate around 16% of the communal power usage of the gym, even when ignoring the individual machine’s power consumption. Therefore, the machines in a gym would not be able to power it, without very severe energy saving schemes. There are other problems, too, such as the storage of the energy. The energy produced by the gym would need to be stored in order to cope with fluctuations in the production rate corresponding to peak or off-peak times, which would require a further monetary investment for batteries, or other similar energy storage techniques. Despite all of these problems, the gym is generating 400W of electricity when it is open rather than buying this from an electricity company. Could this save money for the gym?

Is it worth it?

A typical gym, ALC, is open 42 hours a week [12], so 42 x 52 = 2184 hours a year. This weekly figure may seem small; this particular gym reduced its opening hours in September 2010 by 24 hours during the working week due to lack of membership. It will be assumed that the rate of electricity production, 400W, stays constant throughout this period; this is reasonable as there will be roughly equal peaks and troughs in production corresponding with busier and quieter times in the gym. Therefore, the energy generated by the gym in a year will be 400W x 2184h = 873.6 kWh. Industrial electricity costs roughly 9p per kWh (8.66p per kWh in 2009 [13]), so the gym will save ~£76 annually. This offset is hugely outweighed by the costs of machines and generating equipment (roughly £3750 for one machine [14]). Although this cost may well come down as the machines start to be mass-produced and the cost of electricity is likely to increase, the economic benefits will still be minimal.

It seems, then, that the concept of a human-powered gym is a non-starter. Even with significant energy saving schemes and changes in the attitude of gym members, there is simply not enough power generated to be economically viable, as the costs would outweigh the potential savings. However, this was not a pointless experiment. With the age of cheap fossil-fuelled electricity starting to reach its end, it is worthwhile exploring every nook and cranny for alternative power sources. Although the concept doesn’t work in a commercial setting, there could be space in the home for an electricity-generating gym machine that, say, charges your gadgets and powers a music system. Changes in energy production in the next 50 years are inevitable, but sadly it looks like power to the people will not be power from the people.

BIBLIOGRAPHY

References:

[1] Intergovernmental Panel on Climate Change 2007, Fourth Assessment Report. Available from: <http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html> [26 November 2010]

[2] Peta Bee 2008, Britons are leaving the gym. The Times, March 4, 2008. Available from: <http://www.timesonline.co.uk/tol/life_and_style/health/features/article3476487.ece> [26 November 2010]

[3] Tylene Levesque 2007, HUMAN-POWERED GYMS in Hong Kong.  Available from: <http://www.inhabitat.com/2007/03/08/human-powered-gyms-in-hong-kong/> [26 November 2010]

[4] Peter Bowes 2009, a gym powered by sweat and tears. BBC News, 2 January 2009.  Available from: <http://news.bbc.co.uk/1/hi/technology/7796215.stm> [26 November 2010]

[5] Lori Newell 2010, Self-Powered vs. Electric Treadmill. Available from: <http://www.livestrong.com/article/127936-selfpowered-vs.-electric-treadmill> [26 November 2010]

[6] Addlestone Leisure Centre information 2010. Available from: <http://www.runnymede.gov.uk/portal/site/alc/menuitem.0283cc2d9e7dbe9b1512d754af8ca028/> [30 November 2010]

[7] David J.C. MacKay, Sustainable Energy – without the hot air. (UIT Cambridge, 2008.) p. 51. Available free online from www.withouthotair.com. [30 November 2010]

[8] Human dynamo Technical Information n.d. Available from: <http://www.humandynamo.com/technical_info.html> [30 November 2010]

[9] HDTV Power consumption compared n.d. Available from: <http://reviews.cnet.com/green-tech/tv-consumption-chart/> [30 November 2010]

[10] Edward Ho n.d., Gadget Power Usage. Available from: <http://www.edho.com/power/> [30 November 2010]

[11] Human Powered Workout Gym Concept 2009. Available from: <http://www.alternative-energy-news.info/human-powered-workout-gym-concept/> [30 November 2010]

[12] Addlestone Leisure Centre Opening Times n.d., Available from: <http://www.runnymede.gov.uk/portal/site/alc/menuitem.168fda1ea550e7ec6712d754af8ca028/> [30 November 2010]

[13] Department of Energy and Climate Change 2010, Domestic electricity prices in the EU and the G7 countries. Available from:  <http://www.decc.gov.uk/assets/decc/statistics/source/prices/qep551.xls> [30 November 2010]

[14] Human Dynamo Pricing n.d.  Available from:  <http://www.humandynamo.com/howtobuy.html> [30 November 2010]