10:00
System design and optimization III
Chair: Prof. Martijn van den Broek
10:00
20 mins
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EXERGOECONOMIC COMPARISON OF ORC CONCEPTS AT DIFFERENT SCALES
Christoph Wieland, Dominik Meinel, Hartmut Spliethoff
Abstract: Exergoeconomic investigations are carried out for different cycle designs (e.g. the Standard-Cycle, the Recuperator-Cycle and the Saturator-Cycle) and at different scales (0.5, 1.0 and 5.0 MWth). The focus of the simulations will be R245fa as a working fluid. The simulations are carried out with Aspen and the heat exchangers are modelled in Aspen-Plus with a shell-tube-design. The costs of these are estimated with available cost functions. The following question is answered: Which optimization measure in the cycle design is economic and beneficial for which size of the waste heat source?
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10:20
20 mins
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TECHNICAL, ECONOMICAL, AND ENVIRONMENTAL COMPARISON USING EXERGY ABOUT UTILIZING WASTE HEAT OF A COGENERATION SYSTEM FOR COMFORT COOLING USING ORC DRIVEN CHILLERS OR HEAT PUMPS VERSUS ABSORPTION/ADSORPTION CYCLES
Birol Kilkis, San Kilkis
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.
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10:40
20 mins
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THERMODYNAMIC ANALYSIS OF THE PARTIALLY EVAPORATING TRILATERAL CYCLE
Steven Lecompte, Martijn van den Broek, Michel De Paepe
Abstract: The potential of Organic Rankine Cycles (ORC) to recover low grade waste heat is well known. The high heat recovery potential is partially attributed to a good match of the temperature profiles between working fuid and waste heat stream in the evaporator. This preferable characteristic is mainly induced by the selection of an appropriate working fluid. However, because of the constant temperature evaporation of the working fluid, the heat recovery potential is restricted. In order to overcome this limitation the trilateral cycle (TLC) has already been investigated. A Trilateral cycle (also called Triangular cycle) is a modified Rankine cycle. The main difference is that the working fluid is not evaporated but only heated to the saturation temperature. Compared to the ORC, the heat carrier stream can be cooled further and the thermal efficiency is lower. In this study the effect of partial evaporation of the working fluid is investigated.
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