What fails first

SLOP4761 · Week 12 · Integration and the investment recommendation

Where we are

Last teaching week. Eleven weeks have each produced a sized piece, and each one assumed it had first call on water, area and the daily energy allowance.

This tutorial is ungraded. It is assembly for Assignment 2.

This week’s question

Put them in one model, run the year, and find out which one gives way first.

Almost every design fails somewhere the student did not expect, because the subsystems compete for three shared resources and each week sized its piece as though it had first call on all three.

By the end you can

  1. Run five whole-system checks in order, and trace a failure back to the week that caused it
  2. Report a peak-month energy figure that a marker can reproduce
  3. Name what fails first in a dry year, and what you would change

Check 1 — do the mass balances close?

  • Water in = water used + overflow + loss
  • Dry matter in = dry matter out + a stated respiration term
  • Nitrogen in = nitrogen applied + stored + exported

A stream that appears in no balance has been forgotten.

Check 2 — does the energy fit?

Peak-month average daily load, with the month named. Every counted load with its power and duty cycle. Uncertain loads at their upper estimate.

The reference designs declare 0.65 kWh/day of uncertain load on top of what the model computes, and land between 2.18 and 4.01 kWh/day against the 5 kWh/day cap.

A mushroom chamber, a controlled fermentation space, a dehydrator and a heated digester together come to about 1.65 kWh/day upper estimate — more headroom than some sites have left.

Check 3 — does the budget fit?

Every line from the published schedule, plus the required 10 % contingency.

The excellent reference designs cost $24,860 to $28,875. At Darwin that leaves $1,125 of a $30,000 allowance — inside the noise of a screening model priced from retail listings.

Treat a design that lands within a few thousand dollars of the cap as untested, not as compliant.

Checks 4 and 5

4. Do the indicators pair? Water closure is never reported without garden water satisfaction. Alice Springs’ excellent reference design reaches 97 % water closure with 16 % garden water satisfaction, and a design showing only the first number is hiding the second.

5. What happens in a dry year? Re-run against the synthetic dry-year dataset and name what fails first.

Your tutorial task

  1. Quiz 5, twenty minutes, on weeks 11 and 12 and the integration material
  2. Run the five checks in order on your recommended option. Most people fail check 2 or 3 — work back and find the load or line item that never made it into the summary
  3. The cross-site comparison: groups of five, one per home, one design idea through all five
  4. The uncertainty list, with a range on each item

Output: the proposal skeleton — the ten numbered items of the brief — plus an uncertainty list.

And the boundary

Energy supply and shelter are out of scope. Biogas is recorded and not credited; only the digestate’s nutrients count.

Those belong to SLOP4762 — Designing the Closed-Loop Household II: Energy and Shelter, a proposed follow-on course that adds energy physics and introductory thermodynamics to the prerequisites.

Before you leave

  • Do all three balances close, with loss terms rather than residuals?
  • Is the peak month named, with uncertain loads at their upper estimate?
  • Is garden water satisfaction beside every water closure figure?
  • Can you name what fails first in the dry year, in which month?

What is left is assembly, drawing and writing — not new subsystems.