Riding the Crest of the Wave
Janet Hughes
The Project
Water heating accounts for around 40% of typical household power usage, and a good deal of it is wasted. For example, roughly 12 litres of water goes down the shower drain per minute, still at a temperature of about 40 degrees. Haydn's project, "Energy from Effluent", aimed to develop a heat exchange device for recovering heat from warm wastewater, and using it to pre-heat incoming cold water, thus saving power by reducing the draw-off from the hot-water cylinder for each shower. His preliminary research established that no such device was available.
Dr Deans provided a computer model, with which Haydn examined possible design concepts. A model using two coils of 3/8" copper pipe, one inside the other, promised the best compromise between cost-effectiveness and efficiency. The pipes were coiled on a former, which had to be constructed from scratch. Among other problems to be solved, the reduction in cold water pressure had to be minimised, and the cold/hot contact and differential maximised.
Haydn built a prototype, and tested it on a rig at the School of Engineering using thermocouple temperature readings at various temperatures and flow rates. Modifications after testing increased the power output from 4.5kWto 4.8kW.
The unit potentially recovers about 40% of its cost per year, and has real commercial potential; but Haydn decided against patenting the system because of the cost involved, and the difficulty of exploring manufacturing and marketing feasibility while he is engaged in university studies.
CREST depends upon the goodwill of volunteer consultants. IPENZ Members who are interested in contributing to the CREST programme as consultants can contact Angela Christie ([email protected]) at IPENZ, or Jessie McKenzieat the Royal Society ([email protected]).
