The round trip efficiency of compressed air for energy storage is greatly limited by the significant increase in the temperature of the compressed air (and the resulting heat loss) in high-ratio adiabatic compression. This paper introduces a multi-stage compression scheme with low-compression-ratio compressors and inter-compressor natural convection cooling resulting in a quasi-isothermal compression process that can be useful for large-scale energy storage. When many low pressure ratio compressors work inline, a high overall compression ratio can be achieved with high efficiency. The quasi-isothermally compressed air can then be expanded adiabatically in turbines to generate power with the addition of thermal energy, from either fuel or a solar thermal source. This paper presents mathematical models of such an energy storage system and discusses its round-trip performance with different operating schemes.

This paper presents results of the combined cycle power plant (CCPP) modeling when the ambient temperature is varying. The model of the CCPP was developed using a gas turbine and a heat recovery steam generator (HRSG) models that had been already developed and validated. The model of the components was developed based on an actual existing power plant and then the operational data of the power plant was used to validate the model. The results of running the model for various ambient temperatures demonstrated that the performance of the gas turbine part of the cycle was heavily affected by the changes in the ambient temperature, particularly the output power of the gas turbines. However, the performance of the steam cycle was almost untouched by the changes of ambient temperature. This suggests that operation of the CCPP is more stable than stand-alone gas turbine in hot summer days especially if the cycle is not equipped with an inlet air cooling system.

Because of the performance of the power generation equipment is almost perfect, how to integrate the thermally-activated technologies and use the waste heat deeply are a critical issue for CCHP (Combined cooling heating and power) system. According to the characteristics of a typical end user’s demands, a CCHP system with the flue gas and geothermal energy is proposed. The system is composed of an internal combustion engine, a soil source absorption heat pump driven by the flue gas, and other assistant facilities, such as pumps, fans, and end user devices. In the winter, the flue gas is used to drive absorption heat pump to recover the waste heat of the soil source and the condensation heat of the flue gas simultaneously, and in the summer, the waste heat of the flue gas is used to drive absorption heat pump to cooling, and the heat sink is the soil. In the paper, the energy analysis of the system is done. Compared with the conventional CCHP system, the operation cost is lowered greatly and the increased investment could be returned within one year. It is show that the system is the efficient integration of clean energy, renewable energy, the discharge of the flue gas could be reduced to below 30°C, and the water steam could be catch to avoid the white smoke of the stack.

As an energy-saving and environmentally friendly technology, the combined cooling heating and power system (CCHP) had been applied in the field of heating and air conditioning. Chinese researchers recently designed a CCHP system with the condensation heat recovery of the flue gas, which composed of a gas-powered internal combustion engine (ICE), an exhaust-gas-driven absorption heat pump (AHP), a flue gas condensation heat exchanger (CHE), and other assistant facilities, such as pumps, fans, and end user devices. The system was built and operated in 2011. We tested the parameters of the system on the heating and cooling status from the ICE to the CHE, including the temperature and flux of water, the inlet and outlet parameters of different facilities, and the performance of different facilities for a typical operation status. Based on the test results, the overall COP of the system in the heating and cooling mode was computed, and the energy efficiency level was analyzed. The results indicated that the energy utilization efficiency is about 94% on the heating status, and the energy utilization efficiency is about 84% on the cooling status. These results could serve as a reference for designing or evaluating the CCHP systems.

With the process acceleration of China’s energy conservation and the full development of the market economy, the environmental protection is to coexist with the power plants’ benefits for thermal power plants. Relative to the traditional mode named “determining power by heat”, it is not adequate that the heating demand is only to be met, the maximizations of economy benefits and social benefits are also demanded. At present, several large-scale central heating modes are proposed by domestic and foreign scholars, such as the parallel arrangement and series arrangement of heating system for the traditional heating units and NCB heating units (NCB heating unit is a new condensing-extraction-backpressure steam turbine and used to generate the power and heat, it has the function of extraction heating turbine at constant power, back pressure turbine or extraction and back pressure heating turbine and extraction condensing heating turbine.), and running mode with heating units and absorbed heat pumps, and so on. Compare and analyze their heating efficiency, heating load, heating area, power generation, and the impact on the environment. The best heating mode can be found under the different boundary conditions, it can be used to instruct the further work. The energy utilization efficiency will be further improved.

Combined cooling heating and power (CCHP) systems based on natural gas is widely applied abroad, which have resulted in increasing domestic attention to distributed energy systems (DES). In order to reduce heat loss of exhaust-gas and recover condensation heat of it, an innovative system is advanced by Tsinghua, which can recover exhaust-gas condensation heat utilizing an exhaust-gas-driven absorption heat pump (AHP). In 2007, Tsinghua bears a research task from National Ministry of Science and Technology, that is, ‘Integration and Demonstration study of high-efficiency natural gas CCHP technique’. As a part, a natural gas CCHP system based on AHP has been set up at the Tsinghua University energy-saving building, in Beijing, China, and a lot of research has been made. As another part, a combined cooling heating and power (CCHP) project based on the gas-powered internal combustion engine (ICE) (electricity volume MW) is built in Beijing Southern Station. This paper mainly analyzes and introduces the running condition of this demonstration project.

Combined Cooling, Heating, and Power (CCHP) systems have been widely recognized as a key alternative for heat and electricity generation because of their ability to consume fuel more efficiently, which translates into a reduction in carbon dioxide emission, considered the main factor contributing to global warming. However, economic analyses do not always favor the implementation of this technology. Even though CCHP systems offer other benefits such as power reliability, power quality, and fuel source flexibility, they are often negated as a feasible alternative because of these poor economic indicators. Therefore, a more comprehensive evaluation of the system should be considered. This is particularly true in an environment where economic, environmental, political, and logistical problems associated with increasing centralized electrical power production are becoming more difficult to overcome. In addition, as consumers continue to be more involved and to develop a better understanding of energy choices, the demand for technology that better meets their energy needs is increasing. To promote the development of CCHP projects, it is important to facilitate, without any cost, a first order analysis of this technology to determine if a more cost intensive, in-depth analysis should be performed. This analysis can be done by using screening tools such as the CCHP Screening Tool for Existing Office Buildings (CCHP-ST-EOB) proposed in this study. Screening tools should be as accurate as possible while maintaining the simplicity of their data input in order to make it easy to use by a broad audience that may include building owners and managers without engineering background. In this sense, the CCHP-ST-EOB uses a methodology that translates energy consumption from utility bills as input into hourly energy consumption for a more accurate analysis of the matching between the demand and supply sides. This tool takes into consideration partial load efficiencies for the power generation unit and absorption chiller for a more realistic simulation of the system performance. Results are presented in terms of cost, primary energy consumption, and CO 2 emission. The tool is available to be downloaded free of charge at http://microchp.msstate.edu/thankyou.html.

Pending or recently enacted greenhouse gas regulations and mandates are leading to the need for current and feasible GHG reduction solutions including combined heat and power (CHP). Distributed generation using advanced reciprocating engines, gas turbines, microturbines and fuel cells has been shown to reduce greenhouse gases (GHG) compared to the U.S. electrical generation mix due to the use of natural gas and high electrical generation efficiencies of these prime movers. Many of these prime movers are also well suited for use in CHP systems which recover heat generated during combustion or energy conversion. CHP increases the total efficiency of the prime mover by recovering waste heat for generating electricity, replacing process steam, hot water for buildings or even cooling via absorption chilling. The increased efficiency of CHP systems further reduces GHG emissions compared to systems which do not recover waste thermal energy. Current GHG mandates within the U.S Federal sector and looming GHG legislation for states puts an emphasis on understanding the GHG reduction potential of such systems. This study compares the GHG savings from various state-of-the-art prime movers. GHG reductions from commercially available prime movers in the 1–5 MW class including, various industrial fuel cells, large and small gas turbines, micro turbines and reciprocating gas engines with and without CHP are compared to centralized electricity generation including the U.S. mix and the best available technology with natural gas combined cycle power plants. The findings show significant GHG saving potential with the use of CHP. Also provided is an exploration of the accounting methodology for GHG reductions with CHP and the sensitivity of such analyses to electrical generation efficiency, emissions factors and most importantly recoverable heat and thermal recovery efficiency from the CHP system.

This paper evaluates the economic, energetic, and environmental feasibility of using two power generation units (PGUs) to operate a combined heat and power (CHP) system. A benchmark building developed by the Department of Energy for a full-service restaurant in Chicago, IL is used to analyze the proposed configuration. This location is selected since it usually provides favorable CHP system conditions in terms of cost and emissions reduction. In this investigation, one PGU is operated at base load to satisfy part of the electricity building requirements (PGU1), while the other is used to satisfy the remaining electricity requirement operating following the electric load (PGU2). The dual-PGU configuration (D-CHP) is modeled for several different scenarios in order to determine the optimum operating range for the selected benchmark building. The dual-PGU scenario is compared with the reference building using conventional technology to determine the economical, energetic, and environmental benefits of this proposed system. This condition is also compared to a CHP system operating following the electric load (FEL) and to a base-loaded CHP system, and it provides greater savings in operating cost, primary energy consumption, and carbon dioxide emissions than the optimized conditions for base loading and FEL.

Gas turbine-based power plants generate a significant portion of world’s electricity. This paper presents the modeling of a gas turbine-based cogeneration cycle. One of the reasons for the relatively low efficiency of a single gas turbine cycle is the waste of high-grade energy at its exhaust stream. In order to recover this wasted energy, steam and/or hot water can be cogenerated to improve the cycle efficiency. In this work, a cogeneration power plant is introduced to use this wasted energy to produce superheated steam for industrial processes. The cogeneration system model was developed based on the data from the Whitby cogeneration power plant in ASPEN PLUS ® . The model was validated against the operational data of the existing power plant. The electrical and total (both electrical and thermal) efficiencies were around 40% and 70% (LHV), respectively. It is shown that cogenerating electricity and steam not only significantly improve the general efficiency of the cycle but it can also recover the output and efficiency losses of the gas turbine as a result of high ambient temperature by generating more superheated steam. Furthermore, this work shows that the model could capture the operation of the systems with an acceptable accuracy.

Combined heat and power (CHP) or cogeneration systems provide both electricity and useful heat to a building. CHP systems can result in lower operational cost, primary energy consumption (PEC), and carbon dioxide emissions when compared to the standard alternative of purchasing electricity from the grid and supplying heat from a boiler. However, the potential for these benefits is closely linked to the relationship between the ratio of power to heat supplied by the CHP system and the ratio of power to heat demanded by the building. Therefore, the benefits of the CHP system also vary with the size of the prime mover. In the model presented in this paper, the CHP system is base-loaded, providing a constant power-to-heat ratio. The power-to-heat ratio demanded by the building depends on the location and the needs of the building, which vary throughout the day and throughout the year. At times when the CHP system does not provide the electricity needed by the building, electricity is purchased from the grid, and when the CHP system does not provide the heat needed by the building, heat is generated with a supplemental boiler. Thermal storage is an option to address the building’s load variation by storing excess heat when the building needs less heat than the heat produced by the CHP system, which can then be used later when the building needs more heat than the heat produced by the CHP system. The potential for a CHP system with thermal storage to reduce cost, PEC, and emissions is investigated, and compared with both a CHP system without thermal storage and with the standard reference case. This proposed model is evaluated for three different commercial building types in three different U.S. climate zones. The size of the power generation unit (PGU) is varied and the effect of the correspondingly smaller or larger base load on the cost, PEC, and emissions savings is analyzed. The most beneficial PGU size for a CHP system with the thermal storage option is compared with the most beneficial PGU size without the thermal storage option. The need for a supplemental boiler to provide additional heat is also examined in each case with the thermal storage option.

A recently patented hybrid technology may prove to be an energy game-changer. This innovative integrated combined cycle uses two fuels and a large gas (combustion) turbine in tandem with a small, efficient helium nuclear reactor to cleanly produce electrical power. The hybrid approach to energy sustainability combines the strengths of individual energy assets to yield an optimal solution to meet the planet’s needs. This integration is more effective than the sum of the individual technologies by themselves. The hybrid is able to efficiently use all of fuel resources available in the US in a single power plant. The hybrid-nuclear family of technologies is a fail-safe, environmentally friendly and evolutionary new direction for nuclear power and energy production.

This paper presents a solar Organic Rankine Cycle (ORC) for electricity generation; where a regression based approach is used for the working fluid. Models of the unit’s sub-components (pump, evaporator, expander and condenser) are also presented. Heat supplied by the solar field can heat the water up to 80–95 °C at mass flow rates of 2–12 kg/s and deliver energy to the ORC’s heat exchanger unit. Simulation results of steady state operation using the developed model shows a maximum power output of around 40 kWe. Both refrigerant and hot water mass flow rates in the system are identified as critical parameters to optimize the power production and the cycle efficiency.

Data centers play an important role in modern business. They require a large amount of electricity and cooling energy simultaneously. In 2007, the percentage of total energy consumed by data centers in total US energy doubled over seven years and it is estimated to be double again by 2012. Currently data centers typically employ separate cooling, heating and power (SCHP) systems. The Combined Cooling Heating and Power (CCHP) system is an efficient, clean, and reliable approach to generating power and thermal energy from a single fuel source simultaneously on site. They could be suitable energy supply systems for data centers since demands from data centers match with the energy generation of the CCHP systems. This paper assesses the energy performance of a CCHP system for the Qualcomm data center in San Diego, California, by means of modeling and operational data analysis. The CCHP system mainly consists of four gas turbines, one exhaust fired absorption chiller, three hot water fired absorption chillers, three electrical chillers and seven cooling towers. System performance models have been developed and validated by experimental data in TRNSYS. The modeling result shows that the CCHP system is capable of meeting the electricity and cooling demands with an overall system efficiency of 46%. As a result, the CCHP system could approximately save 12.9GWh of energy per year compared with SCHP systems. Therefore, the CCHP system is a sustainable and green option for data centers.

Combined heat and power (CHP) has the potential to decrease greenhouse gas emissions by utilizing waste heat that is typically rejected to the environment. CHP systems have been used to satisfy loads on university and corporate campuses but there may be other clusters of mixed used buildings that are viable for a CHP system. In an urban environment, such as New York City, high electricity loads and space heating loads are located in close proximity to each other, whether in a single building or in a neighborhood. This indicates a potential for clusters of buildings demand that could be satisfied by CHP. The analysis presented attempts to determine the potential for CHP systems for the 28,840 blocks of New York City many of which incorporate buildings of mix use. The systems are sized to meet the electrical base load and are considered viable if the CHP efficiency (useful electrical and thermal energy divided by the fuel input) is greater than 60% and the system size is larger than 30kW. The analysis determined that of the 28,840 blocks in New York City, 3,205 could be considered for a CHP system.

Pacific Northwest National Laboratory (PNNL) is working with industry to independently monitor up to fifteen distinct 5 kilowatt-electric (kWe) combined heat and power (CHP) high temperature (HT) proton exchange membrane (PEM) fuel cell systems (FCSs) installed in light commercial buildings. This research paper discusses an evaluation of the first six months of measured performance data acquired at a one-second sampling rate from real-time monitoring equipment attached to the FCSs at building sites. Engineering performance parameters are independently evaluated. Based on an analysis of the first few months of measured operating data, FCS performance is consistent with manufacturer-stated performance. Initial data indicate that the FCSs have relatively stable performance and a long term average production of about 4.57 kWe of power. This value is consistent with, but slightly below, the manufacturer’s stated rated electric power output of 5 kWe. The measured system net electric efficiency has averaged 33.7%, based on the higher heating value (HHV) of natural gas fuel. This value, also, is consistent with, but slightly below, the manufacturer’s stated rated electric efficiency of 36%. The FCSs provide low-grade hot water to the building at a measured average temperature of about 48.4°C, lower than the manufacturer’s stated maximum hot water delivery temperature of 65°C. The uptime of the systems is also evaluated. System availability can be defined as the quotient of total operating time compared to time since commissioning. The average values for system availability vary between 96.1 and 97.3%, depending on the FCS evaluated in the field. Performance at Rated Value for electrical efficiency (PRV eff ) can be defined as the quotient of the system time operating at or above the rated electric efficiency and the time since commissioning. The PRV eff varies between 5.6% and 31.6%, depending on the FCS field unit evaluated. Performance at Rated Value for electrical power (PRV p ) can be defined as the quotient of the system time operating at or above the rated electric power and the time since commissioning. PRV p varies between 6.5% and 16.2%. Performance at Rated Value for electrical efficiency and power (PRV t ) can be defined as the quotient of the system time operating at or above both the rated electric efficiency and the electric power output compared to the time since commissioning. PRV t varies between 0.2% and 1.4%. Optimization to determine the manufacturer rating required to achieve PRV t greater than 80% has been performed based on the collected data. For example, for FCS unit 130 to achieve a PRV t of 95%, it would have to be down-rated to an electrical power output of 3.2 kWe and an electrical efficiency of 29%.The use of PRV as an assessment metric for FCSs has been developed and reported for the first time in this paper. For FCS Unit 130, a 20% decline in electric power output was observed from approximately 5 kWe to 4 kWe over a 1,500 hour period between Dec. 14th 2011 and Feb. 14th 2012.

A power plant concept with the potential to replace the large fleet of ageing, small-scale (< 50 MW e ), inefficient, polluting, and soon-to-be obsolete coal-fired power plants is proposed. The proposed plant comprises a bituminous coal-fed oxygen-free gasifier, low-temperature syngas cleanup system and an open-cycle gas turbine with heat recovery. Heat is supplied to the gasifier through combustion of a portion of the cleaned syngas produced by it. Since the proposed plant employs only a gas turbine, with no steam bottoming cycle, heat recovery from the gas turbine and its integration with the rest of the plant is crucial. A thermodynamic model of the plant has been created to assess its feasibility based on overall efficiency and emissions of CO 2 , SO 2 , mercury and particulates. The model comprises submodels for feedstock composition and enthalpy, as well as first-order thermodynamic models for each of the plant components including the gasifier, feedstock preparation, heat exchangers and steam generators, contaminant removal, combustors and turbomachinery. The results of the analysis show base case plant thermal efficiency of 38.2% on a HHV basis, which is roughly 5% points higher than that for a similarly-sized pulverized coal combustion (PCC) plants. Emissions of CO 2 , SO 2 , mercury and particulates per unit electrical energy produced in the base case are: 0.774 kg/kWh, 47.2 g/MWh, 2.37 g/GWh and 28.2 g/MWh, respectively. These values are well below emissions from similarly-sized PCC plants, which have been assessed using a spreadsheet model. The model of the proposed plant has been used to assess overall performance when torrefied pine wood is co-gasified with coal. Results show a slight decrease in plant efficiency with increasing co-gasification, with large decreases in CO 2 , SO 2 and mercury emissions. Emissions of particulates increase slightly with co-gasification. Finally the model has been used to perform sensitivity analysis on the proposed system. Sensitivity analysis highlights the need for greater understanding of gasifier performance under a range of conditions.

Optimization of thermodynamic cycles is important for the efficient utilization of energy sources; indeed it is more crucial for the cycles utilizing low grade heat sources where the cycle efficiencies are smaller compared to high temperature power cycles. This paper presents the optimization of a combined power/cooling cycle, also known as the Goswami Cycle, which combines the Rankine and absorption refrigeration cycles. The cycle uses a special binary fluid mixture as the working fluid and produces power and refrigeration. In this regard, multi-objective genetic algorithms (GA) are used for Pareto approach optimization of the thermodynamic cycle. The optimization study includes two cases. In the first case the performance of the cycle is evaluated as it is used as a bottoming cycle, and in the second case as it is used as a top cycle utilizing solar energy or geothermal sources. The important thermodynamic objectives that have been considered in this work are, namely, work output, cooling capacity, effective first law and exergy efficiencies. Optimization is carried out by varying the selected design variables; boiler temperature and pressure, rectifier temperature, and basic solution concentration. The boiler temperature is varied between 70–150 °C and 150–250 °C for the first and the second cases, respectively.

In recent studies, plasma gasification has shown great potential as an effective method for solid waste treatment and energy recovery. In this study, a plasma gasification process is simulated based on a chemical equilibrium model developed in Aspen Plus. The model takes into account the properties of different feedstock, used for gasification, and the input plasma energy and evaluates the output syngas composition following a Gibbs free energy minimization approach. The model is used to evaluate plasma gasification of three types of feedstock i.e. industrial waste (shredded tires), construction waste (plywood), and baseline bituminous coal. The process is optimized for two different types of plasma gas: air and steam. Process metrics are evaluated and compared for the considered feedstock. Results showed an obtained plasma gasification efficiency of 46.4% for shredded tires and 41.1% for plywood and bituminous coal. Energy recovery potential is also evaluated using an integrated plasma gasification combined cycle (IPGCC) power plant model. Thermal efficiencies of the process are evaluated and compared for the different feedstock. Plasma gasification of waste tire material resulted in an energy efficiency of 28.5%, while the efficiency for coal and plywood was lower at 20.0% and 18.3%, respectively.

In recent years, due to the increased fossil fuel costs and environmental concerns, there has been a renewed interest in absorption cooling (using low-grade heat source) systems for refrigeration and space cooling applications. Although, the stand-alone coefficient of performance (COP) is a concern with such systems, absorption cooling can be a useful add-on that improves the overall efficiency of conventional vapor compression cooling cycle. A local company based in Las Vegas which is involved in the development of advanced HVAC technologies, has developed a natural gas fueled internal combustion (IC) engine driven heat pump. This system recovers the rejected heat from the IC engine during the heating cycle, thus, increasing the heat delivered and improving the system’s overall efficiency. However, during the cooling cycle the rejected heat is dissipated to the ambient air through radiators. The overall efficiency of the system can be improved if the heat rejected during the cooling cycle can be recovered and used for space cooling or refrigeration applications. In this study, a vapor compression refrigeration system coupled with an absorption cooling system is simulated using MATLAB. The vapor compression system is driven by a natural gas fueled IC engine and the waste heat from the engine is used to drive the absorption cooling system. The waste heat is recovered both from gas exhaust and engine cooling systems. The developed simulation model is used to find the transients of both the vapor absorption and compressions systems for varied cooling demands. Important parameters such as coolant temperature and exhaust gas temperature are obtained from experimental data. This paper presents the most efficient load distribution between the vapor compression and absorption cooling systems.