The human powered student building is self-sufficient in terms of energy use and produces no CO2. However, humans need extra food when they produce power, and producing this food also requires energy.
Assuming a typical Dutch diet, one kilowatt-hour of human generated electricity produces up to 30 times more greenhouse gases than one kilowatt-hour of grid electricity. How do we keep the human powered community carbon neutral?
***
Humans need energy -- food -- to survive. Moderately active adults require 2,000 to 2,200 Calories per day, which equals 2.4 kilowatt-hour of energy, or an average of 100 watts of power. Most of this energy (70-90 watts, depending on the person) is used to maintain basic functions such as breathing, digesting, pumping blood, regenerating cells and thinking. [1]
Daily activities typically increase power usage by 30%, which brings the total roughly to between 90 and 120 watts. [1] However, the students in the human powered community are more active than average people, because they generate power for several hours per day.
Students produce energy in their private rooms and on the communal power generating floors. They also need to climb stairs, pedal their washing machine, pump the water for their shower, and do the dishes.
If we assume a student to produce 100 watts of power for four hours per day (room energy use + work duties on the communal energy floors), how much extra food is needed?
How Much Food Do We Need?
The human body is not very efficient: the production of 100 watts of power requires 300 to 500 watts of energy in the form of food -- similar to the conversion efficiency of a combustion engine. [1] This comes down to roughly 300 to 500 Calories per hour above the basal metabolism, or a total of 1,200 to 2,000 extra Calories for 4 hours.
For a daily intake of 2,000 to 2,200 Calories, the typical western diet (including more than 100g of meat per day) generates about 5 to 7 kg of CO2-equivalents per day. A vegetarian diet causes roughly 4 kg of CO2-equivalents, while a vegan diet produces the least greenhouse gas emissions, less than 3 kg of CO2-equivalents. [2] Note that these are averages: the energy use and greenhouse gas emissions depend on the ingredients and the location.
CO2-Emissions of Human Power
If a meat eater produces 100 watt of power for four hours per day, he or she would generate 2.5 to 5 kg extra CO2-emissions. On the other hand, if 400 watt-hour of electricity would be taken from the Dutch electricity grid, the CO2-emissions would be only 0.148 kg. That's 16 to 32 times less. A switch to a vegan diet can lower the carbon emissions of human power to 1.5 to 3 kg, but this is still much higher (10 to 20 times) than the CO2-emissions of grid electricity.
However, because students generate their own power, they have a strong incentive to use less power than students in other buildings. Energy use in the human powered building is at least 10 to 20 times lower than in a common student building. In combination with a vegan diet, the CO2-emissions of human powered electricity would thus be similar to those of grid electricity.
The Dutch eat too much: they could produce power for 2 to 3 hours without extra food intake.
But many people in the Netherlands already consume much more than 2,000 Calories per day, even if they’re not generating energy. The average daily food intake in the Netherlands is 3,000 Calories, which means that the Dutch have a surplus of 1,000 Calories, sufficient for two to three hours of power production.
Some people do sports to burn this extra energy, while others don’t – obesity has become a major health issue in the Netherlands, just like in other industrialised societies. This 'excess' energy could be used to produce power without raising the CO2-emissions of food production.
Cheese, Protein Shakes, and Dumpster Food
To further limit the CO2-emissions of food, and because we are in the Netherlands, the students have opted to produce their own cheese. The waste product of that process -- the whey -- is used to make protein shakes.
Protein shakes, which are popular in health clubs, are convenient because they allow active people to ingest sufficient proteins without grilling steaks and steaming vegetables almost continuously. This saves time eating and cooking. Protein shakes are purely nutritional and are not to be confused with steroids.
Protein shakes allow active people to ingest sufficient proteins without grilling steaks and steaming vegetables almost continuously.
To add surprises to the diet, students on cooking duty go dumpster diving in the city, mainly at the big supermarkets. This can bring food on the table that has a large CO2-footprint, however rescuing it from the garbage is obviously a good thing.
The making of cheese and protein shakes requires thermal energy, which is supplied by the biogas power plant. This means that cheese and protein shake production happens on days that the kitchen -- which depends on the biogas power plant for cooking -- serves raw foods.
***
[1] "The Human-Powered Home: Choosing Muscles Over Motors", Tamara Dean, New Society Publishers, 2008.
[2] Scarborough, Peter, et al. "Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK." Climatic change 125.2 (2014): 179-192. Abeliotis, Konstadinos, Vassiliki Costarelli, and Konstadinos Anagnostopoulos. "The effect of different types of diet on greenhouse gas emissions in Greece." International Journal on Food System Dynamics 7.1 (2016): 36-49.
You need carbohydrates, not protein, to keep going.
Posted by: Dave | 01 October 2017 at 09:02 AM
I find this hypothetical student building fascinating. It reads as a modern day secular monastery.
It’s easier to poke holes in an idea than to construct one, so I’ll try to keep my commentary constructive.
I think you should re-examine the role that fat plays in society and the body. Reducing it to simply “excess energy” ignores the incredible benefits of seasonal feast and famine conditions. Fat is a battery.
Additionally, it is deeply linked to mental health through things like temperature regulation, neurotransmitter production. All kinds of signals that tell you whether you are secure for the future or not.
Production of crops within biking distance means that a seasonal bounty can be stored for off season use without needing to can it.
Hope that helps.
Posted by: Sam A | 30 December 2017 at 02:30 PM
"Moderately active adults require 2,000 to 2,200 Calories per day, which equals 2.4 kilowatt-hour of energy, or an average of 100 watts of power."
These are false numbers based on people under-counting what their intakes. Real caloric needs are way higher.
“The FDA wanted consumers to be able to compare the amounts of saturated fat and sodium to the maximum amounts recommended for a day’s intake–the Daily Values. Because the allowable limits would vary according to the number of calories consumed, the FDA needed benchmarks for average calorie consumption, even though calorie requirements vary according to body size and other individual characteristics. From USDA food consumption surveys of that era, the FDA knew that women typically reported consuming 1,600 to 2,200 calories a day, men 2,000 to 3,000, and children 1,800 to 2,500. But stating ranges on food labels would take up too much space and did not seem particularly helpful. The FDA proposed using a single standard of daily calorie intake–2,350 calories per day, based on USDA survey data. The agency requested public comments on this proposal and on alternative figures: 2,000, 2,300, and 2,400 calories per day. Despite the observable fact that 2,350 calories per day is below the average requirements for either men or women obtained from doubly labeled water experiments, most of the people who responded to the comments judged the proposed benchmark too high. Nutrition educators worried that it would encourage overconsumption, be irrelevant to women who consume fewer calories, and permit overstatement of acceptable levels of “eat less” nutrients such as saturated fat and sodium. Instead, they proposed 2,000 calories as: - consistent with widely used food plans - close to the calorie requirements for postmenopausal women, the population group most prone to weight gain - a reasonably rounded-down value from 2,350 calories - easier to use than 2,350 and, therefore, a better tool for nutrition education Whether a rounding down of nearly 20 percent is reasonable or not, the FDA ultimately viewed these arguments as persuasive. It agreed that 2,000 calories per day would be more likely to make it clear that people needed to tailor dietary recommendations to their own diets. The FDA wanted people to understand that they must adjust calorie intake according to age, sex, activity, and life stage. It addressed the adjustment problem by requiring the percent Daily Value footnote on food labels for diets of 2,000 and 2,500 calories per day, the range of average values reported in dietary intake surveys.”
—
Why Calories Count: From Science to Politics
To get something close to real caloric needs you need to use a BMR calculator and then adjust it with activity book. I used to use it when I was still into dieting (getting cold and hungry all the time until I regained more than I lost - which was 10kg in less than half-of-a-year has finally cured me from such eating disorders) to get caloric deficits like 400kcal per day, so it's quite precise.
A 180cm 25 years old weighting 80kg will have resting metabolic rate of 1806kcal. If we assume "moderately active" means 15 hours of sitting work and 1 hour 4km walk, you get caloric use of 2520 kcal.
If it means more active - like moderately physically active means a light physical job like sweeping you'll easily end up with caloric requirements over 3000kcal.
Posted by: Sturm | 17 August 2018 at 02:49 PM