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  • 51.
    Lundqvist, Per
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Öhman, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Global Efficiency of Heat Engines and Heat Pumps with Non-Linear Boundary Conditions2017In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 19, no 8, article id 394Article in journal (Refereed)
    Abstract [en]

    Analysis of global energy efficiency of thermal systems is of practical importance for a number of reasons. Cycles and processes used in thermal systems exist in very different configurations, making comparison difficult if specific models are required to analyze specific thermal systems. Thermal systems with small temperature differences between a hot side and a cold side also suffer from difficulties due to heat transfer pinch point effects. Such pinch points are consequences of thermal systems design and must therefore be integrated in the global evaluation. In optimizing thermal systems, detailed entropy generation analysis is suitable to identify performance losses caused by cycle components. In plant analysis, a similar logic applies with the difference that the thermal system is then only a component, often industrially standardized. This article presents how a thermodynamic "black box" method for defining and comparing thermal efficiency of different size and types of heat engines can be extended to also compare heat pumps of different apparent magnitude and type. Impact of a non-linear boundary condition on reversible thermal efficiency is exemplified and a correlation of average real heat engine efficiencies is discussed in the light of linear and non-linear boundary conditions.

  • 52.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    The Ground Source Heat Pump: A System Analysis With a Particular Focus on The U-Pipe Borehole Heat Exchanger2010In: 2010 14th International Heat Transfer Conference, Volume 4, 2010, p. 395-402Conference paper (Refereed)
    Abstract [en]

    The mass flow rate of the secondary refrigerant flowing in the borehole heat exchanger of a ground source heat pump is an influential system parameter whose variation can influence the pumping power, efficiency of the pump, heat distribution in the borehole, heat pump heat capacity, and above all, the system Overall Coefficient Of Performance (COP). The present paper uses both in-situ field measurements and modeling to evaluate these effects. From the field measurements, it can be concluded that the thermal contact between U-pipe channels increases as the brine mass flow rate decreases. Furthermore, the modeling results show that there is a certain optimum brine mass flow rate which gives a maximum overall system COP. Different optimum mass flow rates are obtained for different compressor speed and it is shown that their relation is almost linear. However, concerning system COP maximization, it can be concluded that a constant but carefully-selected brine mass flow rate can still be an appropriate option for the variable capacity heat pump unit studied in the present paper where the compressor frequency changes between 30Hz and 75Hz. Concerning the heat capacity maximization in the system, a variable speed brine pump can be used to help the insufficiently-sized compressor to cover the peak heat demand of the building.

  • 53.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ahmadi, Navid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental Analysis of a Variable Capacity Heat Pump System Focusing on the Compressor and Inverter Loss Behavior2010In: Proceeding International Refrigeration and Air Conditioning Conference, Academic Conferences Publishing, 2010Conference paper (Refereed)
    Abstract [en]

    Capacity control with variable speed compressors in heat pump systems is one of the techniques having a potentialfor efficiency improvement in heat pump systems. It is anticipated that the compressor and inverter efficiency areinfluenced by changes of the compressor speed. The present experimental study evaluates these losses in a variablespeed heat pump system.The experimental results show that increasing the compressor speed reduces the heat pump COP up to 30%. Theinverter loss increases as the compressor speed is increased, although the inverter loss as the percentage of the totalcompressor power decreases. Increasing the compressor speed increases the pressure ratio from 2.7 to 5.8,increasing the loss due to the pressure ratio mismatch drastically. Finally, the highest total isentropic efficiency ofthe compressor is obtained when the compressor frequency is close to 50Hz.

  • 54.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundquist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Capacity control in ground source heat pump systems part II: Comparative analysis between on/off controlled and variable capacity systems2011In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 34, no 8, p. 1934-1942Article in journal (Refereed)
    Abstract [en]

    In the present paper, as the second part of two, modeling and simulation was carried out for a Ground Source Heat Pump (GSHP) system in the presence of all the most important interacting sub-systems such as building, ground heat source, electrical auxiliary heater, and the heat pump unit in order to make a fair and comprehensive comparison between the annual performance of on/off controlled and variable capacity systems. The annual modeling showed that dimensioning of the on/off controlled GSHP based on the peak heat demand of the building plays a significant role when the two control strategies are compared: if the on/off controlled GSHP is dimensioned to cover only 55% of the peak heat demand of the building, the electrical auxiliary, which then covers about 10% of the annual heating demand of the building, makes the SPF of the on/off controlled GSHP to be lower than the one of the variable speed system. On the contrary, when the on/off controlled system is dimensioned to cover more than 65% of the building's peak heat demand, i.e. more than 95% of the annual heat demand of the building, there is no considerable difference between the SPFs of the on/off controlled and variable capacity systems.

  • 55.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A descriptive and comparative analysis of three common control techniques for an on/off controlled Ground Source Heat Pump (GSHP) system2013In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 65, p. 1-9Article in journal (Refereed)
    Abstract [en]

    In the present paper, three common methods in order to control an on/off controlled Ground Source Heat Pump (GSHP) system called "Constant hysteresis", "Floating hysteresis", and "Degree-Minute" methods are comprehensively described. Then, the generic model already developed by the authors is used in order to do the dynamic simulation of the systems with three different control methods over a year and making the comparison between them. The results from annual modeling of the systems show that the mean temperature of the heating water supplied to the building for the system controlled with degree-minute method is always close to the required temperature, regardless of the climatic boundary conditions over a typical year, whereas, the average supply temperature for the system with constant hysteresis method is mostly higher or lower than the required temperature, depending on the boundary condition. Regarding the annual energy use, the degree-minute and constant hysteresis methods have the lowest and highest annual energy use respectively. Switching from constant hysteresis to floating hysteresis method, the annual energy use will become lower and the mean temperature of the heating water supplied to the building will be closer to the required one.

  • 56.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Retrofitting a variable capacity heat pump to a ventilation heat recovery system: modeling and performance analysis2010Conference paper (Other academic)
  • 57.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Variable capacity heat pump systems, modeling and simulation2008In: 9th International Energy Agency Heat pump conference, 2008Conference paper (Refereed)
    Abstract [en]

    Variable speed compressor is one of the most promising ways to modulate thecapacity of heat pump units. The paper describes some common obstacles in the evaluationof variable speed heat pump systems. The inconsistencies between the compared systemcomponents, the complexity in the measurement of some detailed parameters, too muchfocus on unit efficiency solely, but also not considering the effect of system dynamics aresome of the mentioned problems. Dynamic modelling and simulation of a heat pump systemtaking all system components into consideration and validation of the model based onexperiments are suggested as the solution. This paper describes a parameter estimationapproach to variable speed heat pump unit modelling that requires a relatively low demand ofmeasured input data. The outputs of the model are a number of parameters such as totalisentropic efficiency of compressor as a function of frequency, superheat temperature andsub-cooling temperature, etc. Making use of the model provides the opportunity to evaluatethe dynamics of the whole system including building and heat source in TRNSYS.

  • 58.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Evaluation of the annual performance of Ground Source Heat Pump systems: A comparison between single speed and variable speed systems2011In: 23rd IIR International Congress of Refrigeration, International Institute of Refrigeration, 2011, p. 3741-3748Conference paper (Refereed)
    Abstract [en]

    In the present paper, modelling and simulation was carried out for a Ground Source Heat Pump (GSHP) system in the presence of all the most important interacting sub-systems such as building, ground heat source, electrical auxiliary heater, and the heat pump unit in order to make a fair and comprehensive comparison between the annual performance of on/off controlled and variable capacity systems. The annual modelling showed that dimensioning of the on/off controlled GSHP based on the peak heat demand of the building plays a significant role when two control strategies are compared: if the on/off controlled GSHP is dimensioned to cover only 57% of the peak heat demand of the building, the electrical auxiliary, which covers about 10% of the annual heating demand of the building, makes the SPF of the on/off controlled GSHP be lower than the one of the variable speed system. On the contrary, when the on/off controlled system is dimensioned to cover about 70% of the building’s peak heat demand, i.e. about 98% of the annual heat demand of the building, the SPF of the on/off controlled system can higher than the variable capacity systems.

  • 59.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    P5 – Dynamic heat pump system with capacity control2010Report (Other academic)
  • 60.
    Madani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Variable capacity heat pumps, modelling and simulation2008In: IEA Heat Pump conference Proceeding (2008) 9th International Energy Agency Heat Pump Conference, Academic Conferences Publishing, 2008Conference paper (Refereed)
  • 61.
    Madani Larijani, Hatef
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundquist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Capacity control in ground source heat pump systems Part I: modeling and simulation2011In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 34, no 6, p. 1338-1347Article in journal (Refereed)
    Abstract [en]

    The present paper, as the first part of two, suggests a method to approach the challenge of capacity control in Ground Source Heat Pumps (GSHP). The paper describes the development of a model of the system which includes several sub-models such as the heat pump unit, building, ground source, thermal storage tank, auxiliary heater, and climate. The developed computer model can be used for comparative analysis of different control methods and strategies aiming at the improvement of the system seasonal performance. With this model, on/off controlled and variable capacity GSHPs, with a single speed or variable speed pumps in the systems, can be evaluated in a wide range of operating conditions and more energy efficient methods of the system control can be found. The computer model is developed in the two environments EES and TRNSYS utilizing so-called co-solving technique.

  • 62. Marimón, M. A.
    et al.
    Arias, Jaime
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per G.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bruno, J. C.
    Coronas, A.
    Integration of trigeneration in an indirect cascade refrigeration system in supermarkets2011In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 43, no 6, p. 1427-1434Article in journal (Refereed)
    Abstract [en]

    This article presents an energy and economic analysis of a trigeneration configuration for supermarket applications. The energy system in a supermarket is relatively complex, because it includes lighting, air conditioning, cabinets, refrigeration system, etc. A trigeneration system could be used to simultaneously satisfy heating, refrigeration and electricity demands in supermarkets. More specifically, this article studies the integration of a trigeneration system and an indirect refrigeration cascade compression system in a supermarket in Barcelona. The trigeneration system consists of a cogeneration engine and an ammonia/water absorption chiller unit. The results of simulating energy usage, life cycle costs and CO2 emissions have been compared with a conventional indirect refrigeration cascade compression system for the supermarket studied. Several trigeneration configurations have been studied. They all show a payback time of less than 6 years but the profitability of the investment depends strongly on the ratio between the prices of natural gas and electricity. This study shows that this novel trigeneration system is economically feasible and environmentally more viable than conventional supermarket systems.

  • 63.
    Nemariam, Teclemariam
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per
    KTH, Superseded Departments, Energy Technology.
    Modeling and Simulation of Solar-Assisted Absorption Cooling System2004Conference paper (Refereed)
  • 64.
    Nemariam, Teclemariam
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per
    KTH, Superseded Departments, Energy Technology.
    Modeling of Solar Cooling System: A Systems Approach2004Conference paper (Refereed)
  • 65.
    Palm, Björn E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Andersson, Klas
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Samoteeva, Oxana
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Designing a Heat Pump for Minimum Charge2005In: IEA HPC newsletter, Vol. 232, p. 17-1§Article in journal (Refereed)
  • 66.
    Palm, Björn E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fernando, Primal
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Andersson, Klas
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Samoteeva, Oxana
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Designing a Heat Pump for Minimum Charge of Refrigerant2005In: Proc. IEA Heat Pump Conference, Las Vegas, USA, June 2005, Academic Conferences Publishing, 2005Conference paper (Refereed)
  • 67.
    Poppi, Stefano
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. KTH, Centres, SeRC - Swedish e-Science Research Centre. Dalarna University, Sweden.
    Sommerfeldt, Nelson
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Bales, Chris
    Madani, Hatef
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Techno-economic review of solar heat pump systems for residential heating applications2018In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 81, p. 22-32Article, review/survey (Refereed)
    Abstract [en]

    Solar heat pump systems (SHPs) have been investigated for several decades and have been proven to increase the share of renewable energy and reduce electric energy demand in residential heating applications. Many review articles have been published on the subject, however literature discussing the techno-economics of different solar technologies (thermal, photovoltaic and hybrid thermal/photovoltaic) in combination with heat pumps is lacking, and thus to directly compare the merits of different SHPs is not an easy task. The objectives of this study are: a) review the different system boundaries and the main performance indicators used for assessing energetic and economic performances; b) review techno-economic studies in the literature and identify which studies give enough information and are compatible enough for making an economic inter-comparison; c) present an economic inter-comparison based on the identified systems. The results show that there is a lack of studies including an economic assessment of solar photovoltaic and heat pump systems. Additionally, there are no consistent boundaries or approaches to the study structures, making comparisons between systems difficult. In conclusion, a standardized or broadly accepted definition of technical and economic performance for SHPs is needed. Despite this, the study has shown that there are clear trends for decreasing payback times for SHPs, both solar thermal (ST) and photovoltaic (PV), with decreasing heating degree-days and with increasing solar resource.

  • 68.
    Pridasawas, Wimolsiri
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per
    KTH, Superseded Departments, Energy Technology.
    Butane, as a Refrigerant for a Solar-Driven Ejector Refrigeration System2004Conference paper (Refereed)
  • 69.
    Pridasawas, Wimolsiri
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per
    KTH, Superseded Departments, Energy Technology.
    Optimization of a small-scale solar-driven ejector refrigeration system2004Conference paper (Refereed)
  • 70.
    Pridasawas, Wimolsiri
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per G.
    KTH, Superseded Departments, Energy Technology.
    An exergy analysis of a solar-driven ejector refrigeration system2004In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 76, no 4, p. 369-379Article in journal (Refereed)
    Abstract [en]

    Energy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m(2), an evaporator temperature of 10 degreesC, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 degreesC as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 degreesC.

  • 71.
    Pridasawas, Wimolsiri
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvisti, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A year-round dynamic simulation of a solar-driven ejector refrigeration system with iso-butane as a refrigerant2007In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 30, no 5, p. 840-850Article in journal (Refereed)
    Abstract [en]

    In this paper, the performance of the solar-driven ejector refrigeration system with iso-butane (R600a) as the refrigerant is studied. The effects that both the operating conditions and the solar collector types have on the system's performance are also examined by dynamic simulation. The TRNSYS and EES simulation tools are used to model and analyze the performance of a solar-driven ejector refrigeration system. The whole system is modelled under the TRNSYS environment, but the model of the ejector refrigeration subsystem is developed in the Engineering Equations Solver (EES) program. A solar fraction of 75% is obtained when using the evacuated tube solar collector. In the very hot environment, the system requires relatively high generator temperature, thus a flat plate solar collector is not economically competitive because the high amount of auxiliary heat needed to boost up the generator temperature. The results from the simulation indicate that an efficient ejector system can only work in a region with decent solar radiation and where a sufficiently low condenser temperature can be kept. The average yearly system thermal ratio (STR) is about 0.22, the COP of the cooling subsystem is about 0.48, and the solar collector efficiency is about 0.47 at Te 15 °C, Tc 5 °C above the ambient temperature, evacuated collector area 50 m2 and hot storage tank volume 2 m3.

  • 72. Primal, F.
    et al.
    Lundqvist, Per G.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Refrigeration systems with minimized refrigerant charge: system design and performance2005In: Proceedings of the Institution of mechanical engineers. Part E, journal of process mechanical engineering, ISSN 0954-4089, E-ISSN 2041-3009, Vol. 219, no E2, p. 127-137Article in journal (Refereed)
    Abstract [en]

    Independently of the choice of refrigerant, environmental and/or safety issues can be minimized by reducing leakage and the amount of refrigerant charge in heat pump or refrigeration systems, preferably both. In the investigation reported here, a laboratory test rig was built, simulating a water-to-water beat pump with a heating capacity of 5 kW. The system was designed to minimize the charge of refrigerant mainly by use of minichannel aluminium heat exchangers and a compact system design. It was shown that the system could be run with 200 g of propane at typical domestic heat pump operating conditions without reduction in the heating coefficient of performance (COP,) compared with a traditional design. Additional charge reduction is possible by selecting proper compressor lubrication oils or by employing a compressor simply using less lubrication oil.

  • 73.
    Rader Olsson, Amy
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies. KTH Centrum för hållbart samhällsbyggande.
    Stoltz, David
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Håkansson, Maria
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Hult, Anna
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ekener, Elisabeth
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Yin, Ying
    Frostell, Björn
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Förstudie av det bilaterala svensk-kinesiska samarbetet kring ekostäder2015Report (Other academic)
    Abstract [sv]

    Sverige har under flera år haft ett samarbete med Kina angående utveckling av ekostäder. Ett flertal myndigheter, företag och forskare har medverkat i planeringen av två stadsutvecklingsprojekt i Kina – Tangshan Bay Eco-City och Wuxi Sino-Swedish Eco-City. Denna förstudie syftar till att skapa en ram för en eventuell utvärdering av samarbetet mellan svenska och kinesiska aktörer. Förstudien omfattar en inventering av tidigare forskning och andra relevanta rapporter, identifiering av nyckelaktörer och aktiviteter inom det svensk-kinesiska samarbetet samt intervjuer med representanter från medverkande företag och kontor. Resultatet av inventeringen och intervjuerna analyseras med hänsyn till befintlig forskning angående effektiva institutioner för planering och finansiering, tillämpning av innovativ energi-och miljöteknik, och planering som beaktar stadens metaboliska funktioner samt faktorer som påverkar socialt hållbarhet. Förstudien har genomförts av forskare vid KTH från institutionerna för Energiteknik, Samhällsplanering och miljö samt hållbar utveckling, miljövetenskap och teknik under perioden oktober 2014-februari 2015.

  • 74.
    Sakellari, Dimitra
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Forsén, Martin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Investigating Control Strategies for a Domestic Low-Temperature Heat Pump Heating System2006In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 29, no 4, p. 547-555Article in journal (Refereed)
    Abstract [en]

    Despite energy conservation regulations and efforts for improving HVAC operations, numerous domestic buildings do not perform energy efficiently and many times the indoor environment is far away from specified comfort levels. Especially in houses served from low-temperature heating systems the low ability of the heating system to respond to fast changing thermal loads is common. In such cases, the implementation of new, sophisticated controls is an important issue. In this study, we use a reference model of a domestic low temperature heat pump heating system developed in TRNSYS-EES and analyse its operation. Several methods of control strategies have been applied for specified time periods in order to keep the comfort within reasonable ranges. Prognostic climatic control and increased ventilation rates when required are some of these methods. The results depict the influence of the control method on the indoor temperature and the comfort indexes of PMV and PPD. The highest indoor temperature difference for a chosen day reaches 4 degrees C when there is no shading and when there is internal shading with the option of applying prognostic climatic control. Generally, the findings highlight the importance of dynamics in controlling functions and the difficulty of incorporating in models unpredictable factors as the solar radiation.

  • 75.
    Sakellari, Dimitra
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per
    KTH, Superseded Departments, Energy Technology.
    Influence of the Design Criteria on the Operation of a Domestic Heat Pump Heating System2003In: Proceedings of the 21st IIR International Congress of Refrigeration, 2003, Vol. 28, no 1Conference paper (Refereed)
  • 76.
    Sakellari, Dimitra
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per
    KTH, Superseded Departments, Energy Technology.
    Modelling the Performance of a Domestic Low-Temperature Heating System based on a Heat Pump2002Conference paper (Refereed)
  • 77.
    Sakellari, Dimitra
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per Gunnar
    KTH, Superseded Departments, Energy Technology.
    Energy Analysis of a Low-Temperature Heat Pump Heating System in a Single-Family House2004In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 28, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

     Energy costs and environmental concerns have made energy optimisation a viable option for buildings. Energy-efficient heating systems together with an effective use of buildings thermal mass and tightness have a significant impact on the energy requirement and on the possibility for sizeable running cost savings. In this study we use the simulation tool TRNSYS-EES to model and analyse the performance of a residential house and the low-temperature heating system that serves its thermal needs. The building is a single-family house with controlled ventilation and the chosen heating system is a hydronic floor heating system connected to an exhaust air heat pump. The aim of the simulation is to study the performance of the building, the heating system and the controls in an integrated manner. Overall, the results indicate that the energy efficiency issue implicates system design and system thinking concerns as well as techno-economic difficulties. Them controls and the choice of the operation mode are of a great importance.

  • 78.
    Sakellari, Dimitra
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Modelling and Simulation Results for a Domestic Exhaust-Air Heat Pump Heating System2005In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 28, no 7, p. 1048-1056Article in journal (Refereed)
    Abstract [en]

    Energy consumption in residential buildings has gained an increasing interest the latest years due to the rising demand for efficient energy use and higher comfort standards. In tight building constructions with controlled ventilation, heat recovery with exhaust-air heat pump connected to floor heating is regarded as energy efficient heating system that optimises the energy use in buildings while maintaining an acceptable level of thermal comfort. In this study, we use the computational tools TRNSYS and EES to model and analyse the performance of a residential house, its ventilation system and its floor heating system based on an exhaust air heat pump. The system analysis focuses particularly on the influence of internal and solar gains on the operation of the heating system and the thermal comfort of the house. Furthermore, the way that gains influences the performance of the floor heating system is examined. Overall, the results bring to light the impact of factors that are not easy to predict on the indoor climate and the thermal comfort.

  • 79.
    Sakellari, Dimitra
    et al.
    KTH, Superseded Departments, Energy Technology.
    Lundqvist, Per Gunnar
    KTH, Superseded Departments, Energy Technology.
    Towards Energy-Use Optimisation of a Domestic Heating System based on a Heat Pump2001In: Strojniski vestnik, ISSN 0039-2480, Vol. 47, no 8, p. 506-511Article in journal (Refereed)
    Abstract [en]

    The overall efficiency of a heat pump system i.e. heat source, heat pump unit and distribution system, is strongly affected by the design temperature levels of the system. The temperature levels influence the performance, in every single process from the time that energy flows from the ambient to the heat source until the heat is released from the building envelope to the environment. The heat exchanging processes in every step affect the energy flow, the losses and generally the energy efficiency of the heating system. The objective of this paper is to show how the different temperature levels influence the energy efficiency and the performance of a heat pump system for domestic applications. The heat pump unit and the heat distribution system are approached as an integrated system. Hence, calculations are performed in order to estimate possibilities for energy savings and for improving the overall efficiency of a heating system based on a heat pump. The results show mainly the increasing call reducing the supply temperature of heat distribution systems. The influence of the refrigerant characteristics on optimal heat pump designs will be discussed.

  • 80.
    Shafqat, Omar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Stoltz, David
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Arias, Jaime
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Participatory simulation for energy target identification in EcoCities2014Conference paper (Refereed)
    Abstract [en]

    Cities and Urban centers are hot beds for future innovation in the field of energy efficiency. At present, energy use in cities accounts for more than 60% of total world energy use and this trend is expected to increase with the growth in urbanization in various parts of the world. The role of Ecocities in this regard is of considerable importance. This paper discusses a model that was developed to assist the target setting in the planning process of an Ecocity in China. The Ecocity located in the Wuxi region in China, is currently in its planning stage. The model has been developed with a systems thinking approach, using STELLA. Different sectors comprising the Ecocity i.e. built environment, transport, water and waste management and energy generation have been considered. An effort has been made to take into account various possible synergies and feedbacks in the system that can be utilized to improve the performance of the overall system. An interactive interface has been provided to help different stakeholders in the decision making process. A participatory approach was adopted in the development of the model where different key parameters were identified as a result of a collaborative exercise with the various stakeholders. A framework for Participatory Modeling and Simulation has been developed. The model gives a possibility to visualize the energy saving potential for different technologies being proposed for implementation in the eco-city. Different scenarios have been created in conjunction with the identified sectors to reflect various levels of ambition towards energy saving in the eco-city.

  • 81.
    Shahrooz, Mina
    et al.
    KTH.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Nekså, P.
    Natural refrigerants for low temperature power cycles2018In: Refrigeration Science and Technology, International Institute of Refrigeration, 2018, Vol. 2018, p. 1373-1380Conference paper (Refereed)
    Abstract [en]

    Working fluid selection determines various characteristics of low temperature Rankine cycles. Among other factors, the selected working fluid affects thermal performance, apparatus size and economic feasibility of the cycle. Beyond only affecting characteristics of the system, unrealistic preconditions for the working fluid of the system may force the designers in using environmentally harmful mixtures and force the outcome beyond boundaries of environmental regulations. There has been numerous research and scrutiny on various working fluids, but due to the unstructured and unorganized orientation of previous studies, there is no comprehensive insight on relationship of different characteristics of the working fluid and overall performance of the system. This work intends to develop a numerical evaluation approach, using a modified stochastic optimization algorithm as a search engine. The paper further explores and questions the existing criteria for optimization of working fluids in Rankine cycle. Rather than just finding the optimum fluids for different cases, this study aims to investigate the behavior of different fluids around optimum points and see the bigger picture to find trends in different fluid behaviors. Analysis of results show two main behaviors among the fluids in subcritical cycles. In the first type behavior, the optimum points for output work, thermal efficiency and exergy efficiency lie very close to each other, while in second type, these optimum points are not close. There is a transition from first type behavior to second type for a ratio of critical temperature around 0.9 of heat source inlet temperature. These results also show the importance of key performance parameter determination.

  • 82.
    Stoltz, David
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Arrias, Jaime
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Categorization framework for systems innovation in EcoCities2015In: CLEAN, EFFICIENT AND AFFORDABLE ENERGY FOR A SUSTAINABLE FUTURE, 2015, p. 2466-2471Conference paper (Refereed)
    Abstract [en]

    With an increasing concern regarding climate change and the increasingly higher rate of urbanization worldwide, cities are expected to play a more important role in the future global energy system. Therefore, sustainable urban development projects, so-called EcoCities projects, are carried out globally. EcoCities are normally focusing on minimizing energy use and greenhouse gas emissions as well as to serve as platforms for innovation fostering. One good example is Royal Seaport in Stockholm, Sweden in which an Innovation Arena has been established by the utilization of the Triple Helix innovation model where academia, industry and the city are cooperating. Due to the fact that EcoCity projects often are focusing on Innovation creation, this study defines a multi-level perspective framework for systems innovation in such projects. Based on previous studies on systems innovation from a multi-level perspective, the framework explains the occurrence of EcoCity projects as a reaction to the change in climate and urbanization as well as how EcoCities are acting as innovation platforms by simplifying the integration of emerging technologies in the city system. This paper also presents a hypothesis that EcoCity projects enable a shortened time for vision and ideas to transform into inventions and furthermore into innovations by reaching acceptance. (C) 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

  • 83.
    Stoltz, David
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Shafqat, Omar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Arias, Jaime
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    On holistic planning in ecocity development: Today and in the past2014In: Energy Procedia: International Conference on Applied Energy, ICAE2014, Elsevier, 2014, Vol. 61, p. 2192-2195Conference paper (Refereed)
    Abstract [en]

    Cities are expected to play an increasingly important role in the future global energy system due to the rapid rate of urbanization. As a reaction to this, the concept of ecological cities, or EcoCities, has gained a foothold in the world and there are numerous commenced EcoCity projects worldwide. As an example, it is said that there are over 250 EcoCity projects in China alone. However, there is no definitive definition of what an EcoCity is per se and thus it is relevant to ask what lies behind the "eco" in these projects. EcoCity planning is generally recommended to be carried out through a holistic planning approach by incorporating a wide range of focus areas in the project. The holistic planning is often claimed to be the key to successful EcoCity projects. Therefore, this article has identified 10 focus areas and used these to evaluate EcoCity projects by analyzing how many of these focus areas that have been taken in consideration in the projects. The higher number of focus areas in consideration, the higher score and thus the higher level of ambition, i.e. The city is planned in a more holistic manner. The projects have also been analyzed by identifying the year of start and geographical location in order to compare whether the level of ambition is varying between different parts of the world and during different time periods and by that identify whether EcoCity projects are planned with a more holistic approach now than earlier.

  • 84. Su, Chang
    et al.
    Shafqat, Omar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Ice-storage device application in commercial buildings of Wuxi Sino-Swedish Eco-City2015In: Refrigeration Science and Technology, International Institute of Refrigeration, 2015, p. 5028-5035Conference paper (Refereed)
    Abstract [en]

    Wuxi Sino-Swedish Eco-City is a 2.4 km2 demonstration project for innovation in energy technology and integrated smart city solutions in southern China. Due to a high cooling demand from building sector in summer season, there is foreseen to be electricity peak load. The peak requires marginal electricity such as gas turbine to cover the demand, which will bring extra CO2 emission. Ice-storage system once equipped into the building energy system, can be a good solution for balancing the peak load and saving energy. This paper discussed the modelling process of the eco-city's commercial building electricity projection based on icestorage implementation and provides an operation strategy. The simulation results show that the electricity peak can be effectively balanced. A total of 630 ton carbon dioxide can be reduced per year in a certain scenario, and up to 40 thousand Yuan electricity cost can be reduced each year.

  • 85.
    Svane, Örjan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies. School of Computer Science and Communication (CSC), Centres, KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Sustainable Communications, CESC.
    Gustafsson, Stina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wangel, Josefin
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies.
    Jonsson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Höjer, Mattias
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Environmental Strategies. School of Computer Science and Communication (CSC), Centres, KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Sustainable Communications, CESC.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Jenny
    Linköping University, Dept. Technology and Social Change.
    Weingaertner, Carina
    University of Birmingham, Centre of Urban and Regional Studies.
    Situations of Opportunity in City Transformation: – enriching evaluative case study methodology with scenarios and backcasting, exploring the sustainable development of three Stockholm city districts2009In: Proceedings of the ENHR Conference 2009, Prague, 2009Conference paper (Refereed)
    Abstract [en]

    To keep global warming at 2°C, society faces challenges of a totally new magnitude. In Swedenlike any high-income country, it becomes a powerful driving force in city transformation. Tackling this challenge of urban sustainable development poses problems for planners and researchers alike: What planning processes, what urban structures enable transformation, how can planners and other actors combine forces to deliberate themselves from path dependency,extending their freedom of action? In this paper, we explore how evaluative case study methodology merged with techniques from Futures Studies provide a cross-disciplinary research approach that defines the challenge in scope and time while retaining its complexity. Case studies are in-depth analyses of a small number of units, enabling studies of complex phenomena; for us, complexity means integrating the issues of What to change and change by Whom in order to explore How change can come about and evaluate How much it could contributeto urban sustainable development. How can this approach be developed to explore the future? Futures Studies can indicate the probable or supply visions of the desirable, it can be normative or descriptive. For our purpose, it is normative, focusing on the long-term necessityof mitigating global warming. Through it, we develop scenarios that explore the path of transformation of three Stockholm City Districts, from today’s climate changing society towardsa 2060s vision of a low carbon, low energy society. From historical studies we learned that there are shorter periods – Situations of Opportunity – when inertia against change is low. This concept we now apply to future Situations, making these our cases proper. For each Situation in every district we develop three representations of their realisation in the upcomingdecades: the Final Scenario is a narrative of the whole, seen from the future; the computerisedEnergy Usage Model quantifies outcomes in terms of reduced energy use; the Transformative Governance Network illustrates the process of change, its agents and their forms of co-operation. Elements of the approach could contribute to the practice of planning.

  • 86.
    Vogel, Jonas Anund
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Arias, Jaime
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Categorizing barriers to energy efficiency in buildings2015In: CLEAN, EFFICIENT AND AFFORDABLE ENERGY FOR A SUSTAINABLE FUTURE, 2015, p. 2839-2845Conference paper (Refereed)
    Abstract [en]

    Introducing new technologies in buildings in Sweden have historically been connected with great portions of scepticism, hence influencing the speed of acceptance of new technologies. The speed is slow even though technologies are tested, evaluated, proven to make an impact, and economic efficient. In order to understand acceptance of energy efficient technologies in multifamily buildings and to identify the origin of barriers to energy efficiency this paper investigates barriers as consequences of the current system structure in the Swedish building sector. The study views the Swedish building sector as a sociotechnical system built from technical artefacts, institutions, and actors, thus often deeply embedded in our societies. The Swedish building sector is well structured, resulting in that innovation and development occurring outside of the existing sociotechnical regime might not be recognized as feasible investments. In order to identify the structures enabling barriers to energy efficiency adoption this paper aims at developing a framework for categorizing barriers depending on their structural origin. The categorization framework is inspired by theories of sustainable innovation journeys and of soft systems and distinguishes between three decision-levels for barriers to energy efficiency: Project level, Sector level and Contextual level. By implementing the proposed categorization framework it becomes obvious that problem areas in the building sector are not connected to any specific structural level. However, results in this study reveal that most barriers originate in the Contextual level, which implies that energy and sustainability are not yet key aspects when forming and transforming contextual preconditions on how to design and build multifamily buildings in Sweden. (C) 2015 The Authors. Published by Elsevier Ltd.

  • 87. Zampollo, M.
    et al.
    Madani, Hatef
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    The role of heat pumps in smart grids2015In: Refrigeration Science and Technology, International Institute of Refrigeration, 2015, p. 3905-3913Conference paper (Refereed)
    Abstract [en]

    The spread of intermittent renewable energy sources and distributed generation units make load management an even more delicate aspect of energy system operations. Heat pump technology can provide a major contribution to energy system management once properly integrated in its infrastructure, as foreseen by the Smart Grid vision. This paper tackles the challenge of Smart Grids and gives a clear representation of the role that heat pump technology can play through its applications in the Smart Grids context. A broad description of the evolution process taking place in the current energy sector is the starting point to outline the new role of heat pumps in this paper. This description is followed by an introduction of the vision of the highly integrated and distributed energy system fostered by Smart Grids, showing how the potential of so called "prosumers" can be unlocked. A conceptual model of the system is developed to highlight the role of major stakeholders and their interactions and also to identify the key role of heat pumps in the future energy system. In addition to this, an assessment of the potential impact of heat pump technology in the Smart Grid context has been evaluated considering the economic savings that could be achieved by a demand response strategy.

  • 88.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Comparison and analysis of performance using Low Temperature Power Cycles2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 52, no 1, p. 160-169Article in journal (Refereed)
    Abstract [en]

    Low Temperature Power Cycles have become increasingly interesting means of increasing energy efficiency of processes as well as for base load power generation from solar, and geothermal, heat. Theoretical understanding of the various processes, components and limitations is constantly increasing through extensive research. Practical utilisation of this knowledge is also increasing steadily though properly published field data is scarce. In this article a number of different solutions for power generation from low temperature heat sources have been gathered and analysed. Some of the studied units have not previously been described. A method for general evaluation of LTPC's is proposed and the outcome of the analysis is discussed as well as how to use it for practical purposes. By separating thermodynamic potential from irreversibilities the analysis indicates that the irreversibilities show limited dependency on temperature, size, thermodynamic cycle or working fluid. Instead performance of the studied units follows a relatively simple correlation with utilisation of the thermal potential. This correlation is defined and discussed. One conclusion is that the correlation allows for a possibility to express the maximum expected real power generation with knowledge of the characteristics of the heat source and heat sink only.

  • 89.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental investigation of a Lysholm Turbine operating with superheated, saturated and 2-phase inlet conditions2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 50, no 1, p. 1211-1218Article in journal (Refereed)
    Abstract [en]

    Low temperature power cycles can benefit from the use of multi-phase flow expansion devices from a thermodynamic cycle efficiency point of view. Particularly power cycles such as ORC, Kalina and Trilateral Flash Cycles can be improved by multi-phase expansion. This article presents the experimental findings in a series of laboratory tests on a semihermetic Lysholm Turbine operating with R134a with superheated, saturated and wet inlet gas conditions. The test arrangements are described as well as discussion on the relevance of such test data. Finally comparison is made with findings from other investigations and recommendations for further studies are made. A correlation between peak efficiency and sensitivity to inlet vapour fraction was discovered which allows for estimations of adiabatic efficiencies with 2-phase inlet conditions even when only test data, or simulations, from single phase inlet conditions exist. The conclusions made are that Lysholm Turbines are well suited for low temperature power generation and that further understanding of the performance during 2-phase conditions is required.

  • 90.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    On high level evaluation and comparison of ORC power generators2015In: Proceedings of the 3rd International Seminar on ORC Power Systems, 2015Conference paper (Refereed)
    Abstract [en]

    A review of the thermodynamic performance of ORCs from public, as well as non-public sources hasrevealed a correlation suitable to be used as a rule of thumb for  high-level performance estimation ofORC power generators. Using the correlation, the limited amount of available test data can begeneralised leading to a high level evaluation of the commercial benefits of any potential applicationfor ORCs.Power generators using ORC-technology exist in relatively low numbers. Furthermore, fieldinstallations seldom imply comparable boundary conditions. As ORCs generally  operate at lowtemperature differences between source and sink it has been shown that their relative sensitivity tovariations in temperatures i.e. the finiteness of source- and sink, is larger than the sensitivity of powergenerators operating with large temperature differences. Therefore the establishing of practical rule ofthumb performance estimation, similar to the figure of merit, Coefficient of Performance, COP, asused in refrigeration and air conditioning industry, has previously not been successful.In order to arrange field data in a manner suitable for comparison a refinement of suitable figures ofmerit was required. The suggested, refined terms are presented and explained as well as criticallyevaluated against the most common  efficiency terms traditionally used.The current lack of a performance rule of thumb leaves room for less serious vendors and laymen tomake performance claims unrealistic to practical achievements. Scrutinizing such questionablestatements requires detail process simulations and a multitude of technical assumptions. Henceargumentation becomes ineffective. If a suitable rule of thumb can be established argumentationagainst dubious claims would become significantly more forceful.This paper suggests a new term to be used as rule of thumb and explains a  method on how to use it.

  • 91.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Screw expanders in ORC applications, review and a new perspective2015In: Proceedings of the 3rd International Seminar on ORC Power Systems, 2015Conference paper (Refereed)
    Abstract [en]

    Performance of Organic Rankine Cycles is sensitive not only to the entry  temperature ratio betweenheat source and heat sink but also to the temperature  degradation of the heat source flow, caused bythe heat transfer to the process in pre-heater, evaporator and super heater. In order to adopt the cycleto the great variety of heat sources a multitude of fluids are required. Alternatively fluid mixtures,trans-critical or supercritical fluid conditions can be used to match the process temperatures with theheat source. Screw expanders offer an alternative, new approach to the matching problem of ORC’s asthey allow for flexible multi-phase expansion. Hereby the vapour fraction at the expander entry can beused to  partially match the temperatures of the process to a particular heat source. To provide aperspective on the use of such screw expanders in ORC-systems previous experimental andcommercial experience have been reviewed and discussed.Screw expanders are versatile machines used for the production of mechanical work in power rangesfrom 3kW to 1.5MW. As the functional characteristics differ significantly  from dynamic expandersthe explanatory models used to generalise results are different. Plenty of research has resulted in wellgeneralized explanatory models for dynamic expander analysis. For screw expanders similarexplanatory models exist mainly in commercially confidential environments. A few public sourcesdisclose test data. In the few cases data has been investigated the analyses tend to rely onthermodynamic models suitable for dry gas expansion. Typically that leads to reasonable replicationof test results but seldom to models suitable for detailed understanding of the process. In applicationswith 2-phase expansion the theories used to simulate functional characteristics is entirely insufficient.The main reason for  the scarcity of work in this field is probably the empirical difficulties in obtaininggood measuring data in multi-phase conditions.This paper describes a review of multi-phase screw expander experiences and explains why a uniquetheory is required to model its characteristics. In the absence of such a unique theory a correlationbased in empirical data is presented. This allow for estimations of screw expander efficiency in multi-phase conditions. Measured efficiency with dry expansion, or such efficiency simulated, can be usedto estimate adiabatic efficiency with expansion entry vapor fractions ranging from 0 to 1 by using thiscorrelation. Hence estimating expansion efficiency during multi-phase expansion is simplified,allowing for better optimisation of the ORC-systems. This way a new perspective of screw expanderpotential in ORC system integration can be presented.

  • 92.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Theory and method for analysis of low temperature driven power cycles2012In: Applied Thermal Engineering, ISSN 1359-4311, no 37, p. 44-50Article in journal (Refereed)
    Abstract [en]

    A new method, using a combination of traditional first law and second law analysis, is developed to facilitate characterization and comparison of power cycles using low temperature heat sources. In trying to determine the best thermodynamic cycle and working media for a given application one must take the strongly non-linear effects of matching the pinch points of a particular cycle with a particular working media into account. The new method allows unbiased comparison of arbitrarily chosen power cycles, working fluids and component characteristics. The method also allows for operating conditions with finite capacity heat source and heat sink. The usefulness of the method is illustrated by the analysis of the effects of local temperature difference distribution for three different fully reversible power cycles using three different working media.

    The driver for developing this method is to simplify comparison and communication among users and industrial professionals and thus enable a better understanding of characteristics and design criteria for low temperature heat driven power cycles.

  • 93.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Per, Lundqvist
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Organic Rankine Cycles with variable vapour fraction expansion entry: Reduced sensitivity to choice of working fluid in modified Organic Rankine Cycles by using wet vapour expansion entry conditions2014Report (Other academic)
    Abstract [en]

    The task of reducing global carbon dioxide emissions leads to a need to reduce the average CO2-emission in power generation. A more energy efficient mix of power generation on national, or regional level, will require the re-use of waste heat and use of primary, low temperature heat for power generation purposes. Low Temperature Power Cycles, such as Organic Rankine Cycles, Trilateral Flash Cycles, Kalina Cycles offer a large degree of freedom in finding technical solutions for such power generation.

    Theoretical understanding of LTPC’s advance rapidly though practical achievements in the field show very humble improvements at a first glance. Cost of applying the new knowledge in real applications seems to be an important reason for the discrepancy. One central reason for the high cost level is the diversity of process fluids required and consequently the lack of standardization and industrialization of equipment. Uses of supercritical power cycle technology tend to cause the same dilemma. Furthermore upcoming regulations prohibiting the use of several process fluids tend to lead to remedies increasing plant cost.

    By using 2-phase, variable vapour fraction, expansion inlet conditions the need to use many different process fluids is reduced, allowing simpler and more cost efficient LTPC’s by easier matching with heat source temperature characteristics. This article explores some of the associated effects on cycle output and cost efficiency. A waste heat recovery application is investigated simulating cost efficiency, thermodynamic efficiencies and power generation while using fundamentally different working fluids, lumped component efficiencies, variable utilization of the waste heat and optimisation on expansion inlet vapour fraction.

    The conclusion made is that the sensitivity to choice of working fluid is lower than intuitively anticipated, in contrast to common consensus in science. Furthermore it is shown that exceptional component efficiencies are not required in order to achieve a performance comparable to current practise and that a good business case is possible under the assumed economic conditions.

  • 94.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Per, Lundqvist
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Thermodynamic pre-determination of power generation potential in geothermal low-temperature applications2014In: Geothermal Energy, ISSN 2195-9706, Vol. 2, no 1, p. 1-10, article id 4Article in journal (Refereed)
    Abstract [en]

    Background: Small capacity, low temperature, geothermal heat sources providesignificant opportunities for distributed, small scale power generation. Projectdefinitions and pre-dimensioning however require advanced thermodynamicengineering at a cost independent of project size. In order to reduce this cost, anew method has been developed to allow basic level engineers to performpre-optimisation of thermodynamic potential as well as expected performance usingavailable power plant technology at such pre-optimized conditions.Results: By reducing the complexity of second-law computations, a simpletwo-dimensional diagram is shown representing the dimensioning criteria requiredfor maximum power generation using the particular heat source and sink whileconsidering expected power plant performance, using systems and componentson the market.Methods: By sensitivity analysis the combination of thermodynamic analysis and realworld data correlations was simplified and arranged for pre-dimensioning ofbusiness cases.Conclusions: Optimal pre-dimensioning of power generation system for anygeothermal heat source, with a defined heat sink, can be determined withoutadvanced thermodynamic expertise. This reduces the cost for business case proposals,pre-dimensioning and tender specifications of small-scale power generation systemsfor low temperature heat sources. The intended implication of this work is to increasethe use of low-temperature geothermal wells for distributed power generation.

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