Optimal design of rainwater tanks

Rainwater harvesting from water tanks will play an increasingly important role in securing our future urban water supply. The use of rainwater tanks has been shown to effectively reduce drinking water demand. But relatively little information is available on the energy consumption of distributed rainwater systems. A new CSIRO research project aims to close the knowledge gap.

“Adoption of rainwater tanks in urban areas was initially aimed at reducing the use of mains water for irrigation of gardens”, says Alan Gregory, CSIRO Urban Water Research Theme Leader.

“But nowadays a greater emphasis is placed on reducing the overall water consumption within the household through indoor uses such as toilet flushing and laundry use. Such uses require the water to be pressurised.”

There are a range of technologies and brands available for pressurizing rainwater for household applications. But information on the energy use for such applications is scarce.

Research to date indicates that the energy footprint of individual rainwater systems varies considerably and in some cases can be much higher than the energy footprint for traditional, centralised water distribution. The energy requirements across different systems on the market that perform the same purpose vary markedly.

“Our initial research indicates that there is considerable opportunity to optimise system designs to maximise water production while minimising energy use. This research project will explore different system configurations to supply rainwater for various uses such as the laundry and toilet flushing,” says Mr Gregory. “We aim to objectively evaluate the energy needs and performance of a range of systems used for rainwater supply within the home.”

CSIRO scientists will use a mini-house set up at the CSIRO Highett laboratories in Victoria, where they will be able to simulate the use of a range of system parts, plumbing, pumping and end-use configurations.

At the mini-house scientists will replicate an average household water demand and conduct a laboratory-based evaluation on different system configurations. This set-up will allow them to take detailed and frequent measurements to understand where energy is used in rainwater systems, such as when the pump starts up and and how long the pump runs for under reproducible regimes.

According to Mr Gregory, research outcomes will provide governments, system designers and suppliers and consumers with scientifically-based advice to consumers on the environmental impact of their rainwater systems, e.g. through extension of the energy rating systems to pump systems.

The outcomes might also help the water sector to better predict the growth in uptake of distributed systems on overall energy consumption and carbon footprint.

It will also help gain pump and equipment manufacturers more understanding of the operating requirements for their equipment so they can optimise their design and create optimal products.

The project will run for approximately 18 months and outcomes are expected mid 2011.

Contact:
Dr Ashok Sharma, CSIRO Land and Water
Email: Ashok.Sharma@csiro.au

Mr Alan Gregory, CSIRO Water for a Healthy Country Flagship
Email: Alan.Gregory@csiro.au