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Session: System design and optimization III
Session starts: Tuesday 08 October, 10:00
Presentation starts: 10:20
Room: Ruys & Rijckenvorsel Zaal

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Birol Kilkis (Baskent University)
San Kilkis (TU Delft)

Abstract:
A typical tri-generation system satisfies comfort cooling loads by heat operated absorption and/or adsorption cycles. This paper presents and investigates another option, namely an ORC-based system. This system generates electric power first in the ORC unit utilizing the cogeneration heat. Then this power is utilized either by an electric power driven compression-cycle chiller or a ground-source heat pump. These two equipment subsets of the ORC-based system options, namely chiller and heat pump were evaluated for a large hospital building retrofit, of which the original design involved a 6,4 MW electric power-capacity cogeneration system, absorption and adsorption cycle cooling equipment in tandem, ice storage tank, and chillers. Analyses were based on energy efficiency, rational exergy management efficiency, coefficient of performance, simple pay-back period, and CO2 emissions reduction potential compared to the original retrofit design. The new retrofit case study showed that ORC-based system alternative with a ground-source heat pump option is preferable, because it gives the highest energy and exergy efficiencies. Although these results are project specific, further parametric analyses indicated that this preference is generally valid when annual heating and cooling seasons are similar. When the cooling season is dominant, then electric power driven chillers may be more economical compared to ground-source heat pump option with higher cooling COP values. When the heating season is dominant with little cooling loads, then absorption chillers without ORC unit may be economically preferable unless the electric power supply from the ORC is sufficient such that it may be directly used in the building besides for cooling purposes. The overall conclusion is that ORC is a better alternative for tri-generation systems and more effectively utilizes the cogeneration heat for comfort cooling and also comfort heating cases if applicable, in a specific design. Furthermore it has been also found that the use of low-exergy cooling and heating systems and equipment in a building like chilled beams and radiant panels improve the overall performance of ORC-based trigeneration systems, their economy, efficiency and environmental benefits. For the latter case, the same argument also holds true for CO2 emissions that a trigeneration system is responsible. REFERENCES [1] S. M. Sami, “Energy and exergy analysis of an efficient organic Rankine cycle for low temperature power generation”, International Journal of Ambient Energy, Vol. 29, No. 1, pp. 001-010, 2008. [2] Kilkis, B., Rational Exergy Management Model Guided Green Mechanical Systems for Low-Exergy Health Care Buildings, ASHRAE 2012 Winter Meeting in Chicago, January 25-29, Seminar Proceedings on CD and on-line, Chicago, 2012. [3] Manning, K. Opportunity for Cogeneration, ASHRAE J., October Issue, pp. 57-59, ASHRAE: Atlanta, 1996. [4] DOE, Combined Heat & Power (CHP) Resource Guide for Hospital Applications, Midwest CHP Applications Centre, 80 p., 2007. [5] Prudenzi, A., Caracciolo, V., and Silvestri, A. Identification of Electric Load Typical Patterns in Hospitals for Supporting Energy Management Strategies, Proceedings, 20th Congress of IHVE, October 19-22, Barcelona, 2008. [6] WHO and HCWH, Healthy Hospitals, Healthy Planet, Healthy People, Discussion Draft, 32 p., Health Care Without Harm Centre, Geneva, 2010. [7] Kılkış, Ş. A Rational Exergy Management Model to Curb CO2 Emissions in the Exergy-Aware Built Environments of the Future, Doctoral Thesis in Civil and Architectural Engineering, KTH, Stockholm, Sweden, 189 p., 2011. [8] Kilkis, B., Exergy Metrication of Radiant Panel Heating and Cooling with Heat Pumps, Energy Conversion and Management, Vol: 63, pp. 218-224, 2012. [9] Marija Todorović, Successful Composition of The Geo Co- and Tri-Generation Projects, International Geothermal Days, Conference and Summer School, Session 5, Proceedings of the International Conference on National Development of Geothermal Energy Use, Paper V.1., Belgrade, Serbia, 2009.