Theoretical thermal performance analysis of two solar‐assisted heat‐pump systems

The thermal performance of two different schemes of solar‐assisted heat‐pump systems has been theoretically studied. In first scheme, the evaporator of the heat pump is taken directly as the solar collecting plate and always maintained at the ambient temperature. As there is no heat loss from the collecting plate, the thermal efficiency of the collector is high and equals the solar absorptivity of the collecting plate. As suggested, the heat‐pump evaporator of the second scheme is placed in a novel fresh water solar pond/tank with high efficiency. Since the evaporator operates at a relatively high temperature, the COP of the heat pump can be increased. The calculated results show that the COP of a solar‐assisted heat pump using the second scheme is considerably higher than that of the first scheme. Copyright © 1999 John Wiley & Sons, Ltd.     

Performance analysis of an industrial waste heat‐based trigeneration system

The thermodynamic performance of an industrial waste heat recovery‐based trigeneration system is studied through energy and exergy efficiency parameters. The effects of exhaust gas inlet temperature, process heat pressure, and ambient temperature on both energy and exergy efficiencies, and electrical to thermal energy ratio of the system are investigated. The energy efficiency increases while electrical to thermal energy ratio and exergy efficiency decrease with increasing exhaust gas inlet temperature. On the other hand, with the increase in process heat pressure, energy efficiency decreases but exergy efficiency and electrical to thermal energy ratio increase. The effect of ambient temperature is also observed due to the fact that with an increase in ambient temperature, energy and exergy efficiencies, and electrical to thermal energy ratio decrease slightly. These results clearly show that performance evaluation of trigeneration system based on energy analysis is not adequate and hence more meaningful evaluation must include exergy analysis. The present analysis contributes to further information on the role of exhaust gas inlet temperature, process heat pressure, ambient temperature influence on the performance of waste heat recovery‐based trigeneration from a thermodynamic point of view. Copyright © 2009 John Wiley & Sons, Ltd.     

Exergetic,environmental and economic analyses of small‐capacity concentrated solar‐driven heat engines for power and heat cogeneration

In this paper, the exergy interactions, environmental impact in terms of CO₂ mitigation, and the economics of small‐capacity concentrated solar power‐driven heat engines for power and heat generation are analysed for residential applications. Starting from a base case study that assumes mass production in Ontario, it is shown that the investment in such a system, making use of a heat engine and having 9 m² of aperture area, could be about CN$10 000 for a peak electrical efficiency of 18% and thermal efficiency of 75%. The average CO₂ mitigation due to combined savings in electricity and heat is ～0.3 kgCO₂ kWh^?1, a figure 3–4 times larger than for photovoltaic panels. If 25% government subsidy to the investment is provided, the payback period becomes 21.6 years. Additionally, if the financing benefits from a feed‐in‐tariff program (at 25% electrical sell‐back to the grid) and deductions from CO₂ tax are realized, then the payback time drops to 11.3 years. These results are obtained for a conservative scenario of 5.5% annual incremental increase in energy price. For the moderate consideration of all factors, it is shown that within the financial savings over the entire lifecycle, 7% are due to carbon tax, 30% are due to electrical production and the largest amount, 63%, is the result of reducing the natural gas heating capacity with solar heating from the proposed system. Copyright © 2011 John Wiley & Sons, Ltd.     

Preliminary investigation of a transcritical CO2 heat pump driven by a solar‐powered CO2 Rankine cycle

In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO₂ Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO₂ as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO₂ heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO₂ heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO₂ flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental analysis of a two‐axis tracking system for solar parabolic dish collector

In this paper, an attempt has been made to develop a two‐axis tracking system for solar parabolic dish concentrator and experimentally evaluated the performance of the tracking system. In this proposed design, the sensor design uses the illumination produced by the convex lens on the apex of a pyramid to align the dish in‐line with the sun. The change in incident angle of the solar rays on the lens surface shifts the area of illumination from the apex of the pyramid towards its faces. Photodiodes placed on the faces of the pyramid are used as the sensitive elements to detect the movement of the sun. The sensor output is fed to a microcontroller‐based system to drive the stepper motor on the basis of the programmed algorithm such that it receives normal incidence of sunlight on the sensor. To evaluate the performance of the proposed system, a conventional available 1‐W photovoltaic (PV) panel is placed at the focal point to measure the short circuit current and open circuit voltage. With respect to the conventional solar PV panel, it is observed that the positioning accuracy of the proposed tracking system enhances the short circuit current of 0.11 A by 86%. Thus, the proposed tracking system can be used in a stand‐alone parabolic dish with concentrating PV module as the focal point for further studies.     

Design of a solar‐driven cogeneration system using flat plate collectors and evacuated tube collectors

The objective of this work is the investigation of a novel solar‐driven cogeneration system, which combines both flat plate collectors (FPCs) and evacuated tube collectors (ETCs). This system includes an organic Rankine cycle in order to produce electricity and heat exchangers in order to produce useful heating at 50°C, which is a usual temperature level for domestic applications. The combination of FPCs and ETCs aims to reduce the investment cost and so to design a cost‐effective solar‐driven cogeneration system. The FPCs are located before the ETCs in order to work at lower temperature levels and the ETC at higher temperature levels, a design which provides optimum compatibility between temperature levels and solar thermal efficiency values. The system is examined energetically, exergetically, and financially. The power production is selected at 5 kW, while the heating production is studied from 5 kW up to 35 kW. According to the final results, it is found that in the typical case of 20‐kW heating production, the simple payback period of the system is around 11 years, while the energy and exergy efficiency at 16% and 4%, respectively. The analysis is conducted with a developed model in Engineering Equation Solver under steady‐state conditions.     

Study on a direct‐expansion solar‐assisted heat pump water heating system

Analytical and experimental studies were performed on a direct‐expansion solar‐assisted heat pump (DX‐SAHP) water heating system, in which a 2 m² bare flat collector acts as a source as well as an evaporator for the refrigerant. A simulation model was developed to predict the long‐term thermal performance of the system approximately. The monthly averaged COP was found to vary between 4 and 6, while the collector efficiency ranged from 40 to 60%. The simulated results were used to obtain an optimum design of the system and to determinate a proper strategy for system operating control. The effect of various parameters, including solar insolation, ambient temperature, collector area, storage volume and speed of compressor, had been investigated on the thermal performance of the DX‐SAHP system, and the results had indicated that the system performance is governed strongly by the change of solar insolation, collector area and speed of compressor. The experimental results obtained under winter climate conditions were shown to agree reasonably with the computer simulation. Copyright © 2003 John Wiley & Sons, Ltd.     

Evaluation of a solar driven trigeneration system with conventional and new criteria

Solar-driven trigeneration systems are able to cover all the building energy needs in heating, cooling and electricity using only the solar energy. The objective of this paper is to evaluate a solar trigeneration system under different criteria in order to make clear that there are numerous factors which have to be taken into consideration in the trigeneration system design. The examined system consists of parabolic trough solar collectors, a storage tank, an organic Rankine cycle and an absorption heat pump. The system is evaluated using different evaluation criteria which are associated with the energy, the exergy and the financial performance of the system. Moreover, a new criterion which takes into account the building energy needs is introduced and is investigated in different scenarios. The final results of this work clearly indicate that the optimisation of the solar driven trigeneration systems is depended on the desired design conditions and goals.

Abbreviations: COP, Coefficient of performance; ECO, Economizer; EES, Engineering Equation Solver; EVAP, Evaporator; ORC, Organic Rankine Cycle; PTC, Parabolic trough collector; SC, Scenario     

Design and energy evaluation of a stand‐alone copper‐chlorine (Cu‐Cl) thermochemical cycle system for trigeneration of electricity,hydrogen, and oxygen

In this article, a new stand‐alone Cu‐Cl cycle system (SACuCl) for trigeneration of electricity, hydrogen, and oxygen using a combination of a specific combined heat and power (CHP) unit and a 2‐step Cu‐Cl cycle using a CuCl/HCl electrolyzer is presented. Based on the self‐heat recuperation technology for the CHP unit and the heat integration of the Cu‐Cl cycle unit, the power efficiency of the SACuCl for 5 prescribed scenarios (case studies) is predicted to achieve about 48% at least. The SACuCl uses the technologies of the dry reforming of methane and the oxy‐fuel combustion to achieve a relatively high CO₂ concentration in the flue gas, and CO₂ emissions for power generation could be almost restricted by 0.418 kg/kWh. From the aspect of the electricity required for hydrogen production, it is verified that the 2‐step Cu‐Cl cycle system is superior to the conventional water electrolyzer because the CHP process supplies the heat/electricity for Cu‐Cl thermochemical reactions and a thermoelectric generator is connected to the exhaust gas for recovering the power consumption from the compressor and the CuCl/HCl electrolyzer. Finally, the heat exchanger network and the pinch technology are employed to determine the optimum heat recovery of the Cu‐Cl cycle. In case 5 analyzed for the SACuCl, the electricity required for the heat‐integrated 2‐step Cu‐Cl cycle is predicted to dramatically decrease from 4.39 to 0.452 kWh/m³ H₂ and the cycle energy efficiency could be obviously increased from 23.77 to 31.97%.     

Experimental investigation of the performance of a solar‐assisted ground‐source heat pump system for greenhouse heating

The main objective of the present study is to investigate the performance characteristics of a solar‐assisted ground‐source heat pump system (SAGSHPS) for greenhouse heating with a 50 m vertical 1¼ in nominal diameter U‐bend ground heat exchanger. This system was designed and installed in the Solar Energy Institute, Ege University, Izmir (568 degree days cooling, base: 22°C, 1226 degree days heating, base: 18°C), Turkey. Based upon the measurements made in the heating mode, the heat extraction rate from the soil is found to be, on average, 54.08 Wm^?1 of bore depth, while the required borehole length in meter per kW of heating capacity is obtained as 12.57. The entering water temperature to the unit ranges from 8.2 to 16.2°C, with an average value of 9.1°C. The greenhouse air is at a maximum day temperature of 25°C and night temperature of 14°C with a relative humidity of 40%. The heating coefficient of performance of the heat pump (COP_HP) is about 2.13 at the end of a cloudy day, while it is about 2.84 at the end of sunny day and fluctuates between these values in other times. The COP values for the whole system are also obtained to be 5–15% lower than COP_HP. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparative analysis of a solar‐driven novel salt‐based absorption chiller with the implementation of nanoparticles

The present study exemplifies the comprehensive thermal analysis to compare and contrast ammonia‐lithium nitrate (NH₃‐LiNO₃) and ammonia‐sodiumthiocynate (NH₃‐NaSCN) absorption systems with and without incorporation of nanoparticles. A well‐mixed solution of copper oxide/water (CuO/H₂O) nanofluid is considered inside a flat‐plate collector linked to an absorption chiller to produce 15‐kW refrigeration at ?5°C evaporator temperature. Enhancements in heat transfer coefficient, thermal efficiency, and useful heat gain of the collector are evaluated, and the effect of these achievements on the performance of both absorption chillers have been determined for different source temperatures. A maximum 121.7% enhancement is found in the heat transfer coefficient with the application of the nanofluid at 2% nanoparticle concentration. The maximum coefficient of performance observed for the NH₃‐NaSCN chiller is 0.12% higher than that for the NH₃‐LiNO₃ chiller at 0°C evaporator temperature. Contradictory to this, the average system coefficient of performance of the NH₃‐LiNO₃ absorption system has been found 5.51% higher than that of the NH₃‐NaSCN system at the same evaporator temperature. Moreover, the application of the nanofluid enhanced the performance of the NH₃‐NaSCN and NH₃‐LiNO₃ systems by 2.70% and 1.50%, respectively, for lower generator temperature and becomes almost the same at higher temperatures, which altogether recommends the flat‐plate collector–coupled NH₃‐LiNO₃ absorption system be integrated with a nanofluid.     

Exergy analysis of direct expansion solar‐assisted heat pumps using artificial neural networks

Artificial neural network (ANN) is applied for exergy analysis of a direct expansion solar‐assisted heat pump (DXSAHP) in the present study. The experiments were conducted in a DXSAHP under the meteorological conditions of Calicut city in India. An ANN model was developed based on backpropagation learning algorithm for predicting the exergy destruction and exergy efficiency of each component of the system at different ambient conditions (ambient temperature and solar intensity). The experimental data acquired are used for training the network. The results showed that the network yields a maximum correlation coefficient with minimum coefficient of variance and root mean square values. The results confirmed that the use of an ANN analysis for the exergy evolution of DXSAHP is quite suitable. Copyright © 2009 John Wiley & Sons, Ltd.     

Maximum overall efficiency for a solar‐driven gas turbine power plant

A general model for an irreversible solar‐driven Brayton multi‐step heat engine is presented. The model incorporates an arbitrary number of turbines (N_t) and compressors (N_c) and the corresponding reheating and intercooling processes; thus, the solar‐driven Ericsson cycle is a particular case where N_t, N_c → ∞. For the solar collector, we assume linear heat losses, and for the Brayton multi‐step cycle, we consider irreversibilities arising from the non‐ideal behavior of turbines and compressors, pressure drops in the heat input and heat release, heat leakage through the plant to the surroundings, and non‐ideal couplings of the working fluid with the external heat reservoirs. We obtain the collector temperatures at which maximum overall efficiency η_max is reached as a function of the thermal plant pressure ratio, and a detailed comparison for several plant configurations is given. This maximum efficiency is obtained in two cases: when only internal irreversibilities are considered and when both internal and external irreversibilities (which corresponds to the fully irreversible realistic situation) are simultaneously taken into account. Differences between both situations are stressed in detail. In the fully irreversible realistic case, it is possible to perform an additional optimization with respect to the pressure ratio, . In particular, this double optimization leads to a valuable increase in efficiency (between 34% and 65%) for a plant with two turbines and two compressors compared to the simple solar‐driven one‐turbine one‐compressor Brayton engine. Copyright © 2012 John Wiley & Sons, Ltd.     

Sustainability accounting for the construction and operation of a plant‐scale solar‐biogas heating system based on emergy analysis

Domestic heating systems have long been playing a significant role in China's energy structure. The sustainability of a hybrid solar‐biogas heating system (SBHS) under various feedstock fermentation scenarios was evaluated using emergy analysis. Representative emergy indices such as transformities, emergy yield ratio (EYR), environmental loading ratio (ELR), emergy sustainability index (ESI), ratio of waste treatment (%W), feedback yield ratio (FYR), and emission mitigation intensity (EMI; g/10¹⁰ sej) were selected to evaluate the sustainability performance of different feedstock scenarios including cow dung (CD), swine manure (SM), and poultry manure (PM). The results showed that PM fermentation scenario had greater market competitiveness, lower environmental pressure, better sustainability, and self‐organizing ability than the other two options. However, both the emergy efficiency and the CO₂ emissions mitigation intensity of PM scenario were worse than that of the SM and CD. Moreover, compared with other biogas systems and traditional agricultural systems, the hybrid SBHS was proved to be a promising mode for the treatment of rural manure waste with favorable economic benefits and environmental sustainability.     

Experimental adjustment and validation of a generalized solar‐assisted cogeneration system model

A solar‐assisted absorption cooling and water heating system model is adjusted and experimentally validated in this study. Conservation laws are combined with available heat and mass transfer empirical correlations to quantify the diverse types of flows that cross the system. The model is generalized by nondimensionalizing the variables, and the resulting system of ordinary differential equations is solved for dimensionless temperatures with respect to time. Next, the model is experimentally adjusted through the solution of the inverse problem of parameter estimation, through which geometric, operating parameters and physical terms are identified and adjusted (or added) according to a first set of measured temperature data. The adjusted model is then validated using a second experimental data set, and the results are presented in normalized form for design, control, and optimization of similar systems.     

Effect of storage options on price-based scheduling for a hybrid trigeneration system

Trigeneration is efficient to supply cooling, heat, and power demands. Also, hydro (pumped) storage with zero fuel costs can increase profit when price-based scheduling problem is solved. The goal of this study is to investigate the effects of electric boiler, hydro storage, and heat storage tank on price-based scheduling problem for hybrid trigeneration (trigeneration-conventional-gas boiler) system. A heuristic algorithm is applied to a power system where in validation case, total cost reduction of 0.63% to 0.91% is reached as compared with reported in literature. The results show that the utilization of electric boiler, hydro storage, and heat storage tank leads to profit improvement by 4.58%. Also, a critical sensitivity analysis is conducted and the results show the significant effects of several factors on scheduling results.     

Parametric study on the thermoelectric conversion performance of a concentrated solar‐driven thermionic‐thermoelectric hybrid generator

A concentrated solar‐driven thermionic‐thermoelectric hybrid generator composed of solar heat collector, thermionic generator (TIG), thermoelectric generator (TEG), and radiator is introduced in this paper. A theoretical model of thermoelectric conversion performance for the hybrid generator is built up based on the heat source of the concentrated solar radiation rather than isothermal heat source. Based on the model, the impacts of related parameters on the internal temperature distributions, output power, and efficiency have been discussed. Moreover, the optimal operating conditions of the TIG‐TEG hybrid device at its maximum output power and efficiency have been determined. Results show that when cascading the TEG with the TIG, there is very little change of the TIG cathode temperature in most conditions, namely, T_C ≈ T_C′. Meanwhile, the anode temperature becomes higher, and the TEG cold end temperature T₂ is close to the anode temperature T_A′ for the single TIG system, ie, T_A > T_A′ ≈ T₂. In theory, the optimal concentrated solar radiation I₀ for the maximum output power P_max and the maximum efficiency η_max differs, which are I_0,P = 2.5 × 10⁶ W/m² and I_0,η = 2 × 10⁶ W/m², respectively, whereas the output power and efficiency of the TIG‐TEG hybrid system simultaneously reach their maximum values when the optimal TIG anode temperature T_A,opt = 1025 K, the optimal TIG output voltage V_opt = 2 V, and the optimal ratio of load resistance to internal resistance (R₂/R)_opt = 2. However, in practice, the parameter values of I₀, Φ_A, and T_A should be strictly controlled under 1.8 × 10⁶ W/m², 1.4 eV, and 660 K, respectively. Generally, the maximum output power and efficiency of the hybrid TIG‐TEG system are, respectively, 35% and 4% higher than that of the single TIG.     

Modelling and testing of a hybrid solar‐biomass ORC‐based micro‐CHP system

Expanders employed recently in organic Rankine cycle (ORC)‐based systems suffer from key problems including excessive working fluid leakage, thermal losses, low isentropic efficiency and high cost. The majority of the units available in the market are for medium and large‐scale applications (>100 kW) with no commercial micro‐scale expanders available and applicable for ORC units for residential and building applications. Moreover, the majority of the studies conducted on ORC expanders employed HFC and HCFC working fluids which have high global warming potential leading to negative environmental impacts. In this study, a micro‐scale CHP system based on the ORC technology is theoretically and experimentally investigated to provide the thermal needs and part of the electrical demands for residential applications. An innovative design for a hybrid ORC‐based micro‐CHP system is proposed using a biomass boiler and a solar concentrator to run the CHP system providing more reliable and clean operation compared to conventional natural gas‐driven units. The micro‐CHP system employs a new type small‐scale scroll expander with a compact design, integrating the generator and the turbine in a single unit. A numerical model was developed using the Engineering Equation Solver (EES) software to simulate the thermodynamic behaviour of the ORC unit predicting the thermal and electrical performance of the overall CHP system. In addition, an experimental setup was built to test the whole ORC–CHP system performance under different conditions, and the effect of various operational parameters on the system performance has been presented using an environmentally friendly HFE7100 working fluid. The maximum electric power generated by the expander was in the range of 500 W at a pressure differential of about 4.5 bars. The attained expander isentropic efficiency was over 80% at its peak operating conditions with no fluid leakage observed. Being mass‐produced with low cost in the automotive industry along with the high isentropic efficiency and the leakage‐free performance, the proposed compact scroll expander represents a potential candidate to be used in the development of micro‐scale ORC–CHP units for building applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigation of a combined solar–heat pump system for residential heating. Part 1: experimental results

In order to investigate the performance of the combined solar–heat pump system with energy storage in encapsulated phase change material (PCM) packings for residential heating in Trabzon, Turkey, an experimental set‐up was constructed. The experimental results were obtained from November to May during the heating season for two heating systems. These systems are a series of heat pump system, and a parallel heat pump system. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load meet by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. Copyright © 1999 John Wiley & Sons, Ltd.