Harvesting Waste Energy


Gerard Hillenbrand, P.E.

Harvesting waste energy.

That was the interesting subject presented at the Metropolitan Sections Technical Meeting held on Thursday, November 18th 2009 in Cooper Union’s New Academic Building on Third Avenue and East Seventh Street in Manhattan. Professional Engineering Licensees attending this meeting qualified for one continuing education credit hour toward satisfying the requirements established several years ago by the N.Y. State Department of Education.

The evening’s speaker was professor Robert Dell of Cooper Union’s Mechanical Engineering Department who reported extensively on research he and other department representatives and students conducted in response to funding provided by Con Edison, the Cooper Union Research Foundation, and the Agricultural University of Iceland, among other generous supporters. Several years ago Professor Dell served a very productive term as faculty advisor to Cooper Union’s student ASME Section under the Met Section Presidencies of James Oussani, Jr. and Wasyl Kinach, PE. As a result, this meeting offered the Met Section a unique opportunity to welcome Professor Dell when returning to section activities.

An important aspect of the Green Building movement is the considerable energy saving inherent in developing greenery of the roofs of the buildings. Such developments provide environmentally advantageous conditions for enhancing internal climate control within buildings – cooling in summer and heating in winter. In New York and other major cities a substantial amount of waste steam is vented to the atmosphere – a significant loss of energy. In green roofs, rainwater is collected and heated through heat exchangers utilizing waste steam. Professor Dell’s report summarized research, which optimized the growing conditions for the greenery on these roof installations. Similarly, in agricultural areas especially those with potential access to sources of geothermal energy, similar systems can be developed to increase farm production several fold.

At the Albert Nerken Engineering school at Cooper Union several test beds were constructed and exposed to the atmosphere on the building’s roofs and other non-sheltered areas. Soil was added to the trays and appropriate greenery planted. Waste steam from the buildings heating system heated the water, which was circulated through the pipes in the test beds. Results of these experiments included:

    • Heated test beds produced more growth in plants rather than non-heated beds. Maintaining a bed temperature of 30oC (86oF) produced the best results throughout the growing season.
    • Various soil depths were tested in the beds and six inches of soil was most productive no fertilizers were added to the soils.

Other experiments included optimizing the depth and pattern of the piping in the beds, various piping materials (metal vs. plastic), several types of pipe insulation, and varying the pattern of planted greenery roots relative to the pipe patterns.

Extensive experiments were also conducted in the Old Blue Lagoon area in Iceland where geothermal steam is plentiful. A hole is bored into the earth in a hot spring area and very hot water and steam extracted at temperatures varying from 98o – 130oC (208o – 266oF). This geothermal energy is exchanged into hot water at 64oF (147oF) which is circulated through test beds containing soils 10 centimeters deep. The test beds, located in green houses, also have heated sidewalks and water exit temperatures of 40o – 50oC (104o – 122oF). Similar experiments were conducted varying soil depth, soil temperature, piping materials, sizing, patterns and spacing versus a no-heated control garden also located in a green house. Results were essentially the same, with even tropical fruits such as bananas successfully grown, despite harsh weather conditions existing in Iceland. Similar experiments have succeeded in growing delicate flowers such as pansies in Germany. Countries with substantial geothermal energy sources include Japan and New Zealand. Using these techniques agricultural output can be substantially increased and growing seasons extended in these hostile environments.

The extensive installation of green roofs in cities could result in substantial savings in water consumption. In New York City, for example, water savings of as much as 96 Billion pounds per year have been projected. This figure correlates to six inches in water height in reservoirs. Correspondingly, building-heating costs would be reduced with an equivalent increase in storage of runoff water. A Con Edison spokesman at this meeting reported that this organization uses huge amounts of city water to cool down its boiler condensate sot that it can be safely conducted through underground piping for disposal. With green roofs commonplace in New York City, Con Edison would experience substantial heat and water savings.

Met Section congratulates Professor Dell and his associates for their excellent research both domestically and overseas and extends sincere thanks for their very impressive presentation.

 Posted by at 2:42 pm