What crosses the fence line#
SLOP4761 · Week 1
Designing the Closed-Loop Household I
A household is not self-sufficient because it produces everything.
It is self-sufficient when the output of one system is the input to another.
So we are not closing the loop#
We are measuring how much of it closes.
And being equally precise about what still comes through the gate.
The household. Fixed for everyone.#
Two adults. Two children, 9 to 13.
| Demand | Per year |
|---|---|
| Food energy | 3.49 million kcal |
| Protein | 67.5 kg |
| Water | 219 kL |
| Excreted nitrogen | 13.6 kg |
| Food waste | 380 kg |
Five climates. One household.#
- Canberra — cool temperate, 616 mm
- Alice Springs — hot arid, 284 mm
- Brisbane — subtropical townhouse, 1,146 mm
- Adelaide — Mediterranean, 525 mm
- Darwin — tropical wet-dry, 1,733 mm
Climate is the only variable. That is the experiment.
Closure#
What the site supplied and the household used
÷ everything the household used
including imports
Three consequences#
- Carting water in lowers your score. It does not vanish.
- Fish fed on bought pellets are bought fish.
- A bigger garden can never lower your water score.
That third one was a bug we had to fix.
Why not just divide production by demand?#
It can exceed 100 %.
So it rewards growing food nobody eats.
And it cannot see a single imported kilogram.
Today’s calculation#
Roof runoff, enHealth Appendix B, after Martin (1980):
runoff (L) = A × (rainfall − B) × roof area
A = 0.80 · B = 2 mm per month
Canberra#
300 m² of roof. 616 mm of rain.
0.80 × (616 − 24) × 300 = 142,080 L
142 kL
Household demand: 219 kL
65 %#
The largest roof in the set, in a climate nobody calls dry, before a single plant is watered.
And the others#
| Site | Roof yield | Of domestic demand |
|---|---|---|
| Darwin | 411 kL | 188 % |
| Brisbane | 153 kL | 70 % |
| Canberra | 142 kL | 65 % |
| Adelaide | 92 kL | 42 % |
| Alice Springs | 73 kL | 33 % |
Darwin collects twice what it drinks#
And still runs out in September.
That is week 9, and it is the most useful thing in this course.
What is out of scope#
Energy and shelter.
Your digester will make biogas. You will record it and it will earn you nothing.
Only the digestate’s nutrients count here.
Because crediting it would be a lie#
Biogas is energy.
Energy is SLOP4762 — Energy and Shelter, a proposed follow-on course.
Part one has to stop somewhere honest.
Two hard constraints#
$30,000 of new spend, including 10 % contingency.
5 kWh a day of process energy, peak month, counted loads.
Uncertain loads counted at their upper estimate.
This week#
Claim a site.
Build the sheet: plot, growing area, roof, tanks, bore.
Twelve rows of Bureau of Meteorology data, with the station named.
A source for every value.
The sheet comes to every tutorial#
Everything after this week writes into it.