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Compost-powered Shower

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Thermometer showing ideal temperature
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Hot showers for all
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Watering the final layer
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The final set-up
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Put the sprinkler on when you take a break
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Tamping the sides

Whether you are a gardener with a passion for compost making, or a child who has felt the warmth of a pile of grass clippings, you will be familiar with the heat created by decomposing material. Our aim is to capture and use this heat to create hot showers.

A few years ago we were inspired by Jean Pain’s compost hot-water system and, as we frequently have extra people on the farm (particularly during our two week live-in PDCs), we needed another shower with good hot water. So began our compost-powered shower journey.

Since our original trial we have made about a dozen compost heaps to power showers, the best of which gave us five months of continuous hot water. It is joy to stand under a warm shower knowing you are benefitting from the energy and compost cycle, and watching the run-off flow onto the citrus.

This system works particularly well in our environment: we live in a fire prone area and need to manage the fire risk from the many trees that we have planted, especially acacias. Cutting and mulching branches reduces the fuel level and provides good compost, which also generates heat.

The most important thing to remember is that you need anaerobic compost – without air. The microorganisms in anaerobic compost work slowly and give off heat for many months. This is different from the more common aerobic compost, which needs plenty of air, attracts microorganisms that need oxygen and works fast – although the heat generated is not useful for heating water. In a compost-powered hot-water system we are looking for a constant heat, between 43 C and 55 C, over a long period.

Materials

You will need:

  • a shower, including drainage (ours goes directly to a citrus orchard)
  • a water supply with enough pressure for a shower (you’ll need cold water too, to adjust the temperature)
  • 100 metres of 20 mm poly-pipe
  • a collection of 20 mm fittings (e.g. valves, joiners)
  • a compost thermometer
  • about six cubic metres of freshly mulched plant material.

Experiment with plant material you have. Freshly cut, small size woodchips are ideal, and we have used eucalypts, acacias and grasses. Such material will have a good carbon/nitrogen ratio, and maximum surface area for holding moisture. Be careful to discard sharp material that could puncture the pipe.

Method

Make a large anaerobic compost heap between your water supply and your shower. We have enough room to create two heaps, and as one heap cools we use a valve to switch to the other.

You’ll need plenty of time to create the right conditions – a moist, compact environment – so set aside a couple of days, and invite some friends over to help.

Build the heap slowly, add water constantly and tamp it down continually. When the heap is about 30 cm high, add your first coil of pipe, and take care where you place it: keep it off the centre of the heap so that it doesn’t get spiked by the thermometer later; and don’t put it too close to the edge as it should be well insulated. Take care not to kink or cross the pipe – when it is warm it will be much more flexible, and any twists can turn into kinks. Undoing the heap later to find and fix a problem is not desirable. Have the pipe full of water when you are building, and add another coil about every 20 cm.

Continually walk or jump on, or tamp the heap as you are building it, including tamping the sides to create a compacted heap. But be gentle directly after laying pipe. Keep the heap wet during the building; put a sprinkler on it when you take a break.

When your heap in finished check the temperature in the middle with the thermometer. The temperature should rise slowly over the next week until it reaches an ideal shower supply temperature of 50 C. Once the heap is made we tend to cover it with black plastic but this is just to protect it from outside conditions. No other maintenance is required.

Now simply enjoy your shower. Oh and did I mention that you get great compost at the end!

Problem solving

Temperature rises too quickly. The heap is attracting aerobic bacteria > squeeze the air out with more water and compaction.

Temperature fails to rise. Too dry > add more water.

Smell. Although the compost smell may be absorbed through the pipe – and some people will notice – this isn’t a problem.

Lack of pressure. May be caused by kinks or leaks in the pipe > avoid these when building your heap.

Temperature cools down quickly. Look around the heap for puddles as the pipe may have leaked inside > fix any leaks.

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