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• An absorption-resorption heat pump (ARHP) experimental prototype was developed. • Actual heating performance was tested and discussed under different conditions. • Possible solar contribution and the sequent lift of primary energy efficiency was analyzed. • Solar heat utilization by its temperature zones based on the ARHP was designed and examined. Among thermally-activated heat pumps, absorption-resorption heat pump (ARHP) is dominant by the ability of combining with low-temperature heat for efficient space heating. In this work, an ARHP experimental prototype is developed based on the previous thermodynamic cycle and tested to obtain the operation details such as coefficient of performance (COP), supply water temperature, heating capacity and so on. The experimental and the previous theoretical results are compared and mutually verified. The exact performance of the solar-assisted ARHP heating system is then investigated and compared with that of the conventional vapor compression heat pump (VCHP) in terms of primary energy ratio (PER) and primary energy saving ratio (PESR). The experimental results show that the COP increases greatly from 1.125 to 1.353 when the heat source temperature increases from 90 °C to 150 °C at the ambient temperature and return water temperature of 0 °C and 30 °C, respectively. Under given conditions, the measured heating capacity reaches a maximum value of 18.5 kW, 9.0 % lower than the rated value. The theoretical results reveal that solar fraction above 30 % can make PER of the solar-assisted ARHP heating system comprehensively greater than that of the reference VCHP system. Optimal solar contribution to space heating can be achieved based on the proposed ARHP if solar heat is dividedly utilized in its temperature zones of 10–35 °C, 35–83 °C and above 83 °C. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a solar heating system, which combines the technologies of evacuated tube solar air collector and rotary desiccant humidification together, has been configured, tested and modeled. The system mainly includes 15m2 solar air collectors and a desiccant air-conditioning unit. Two operation modes are designed, namely, direct solar heating mode and solar heating with desiccant humidification mode. Performance model of the system has been created in TRNSYS. The objective of this paper is to check the applicability of solar heating and evaluate the feasibility and potential of desiccant humidification for improving indoor thermal comfort. Experimental results show that the solar heating system can convert about 50% of the received solar radiation for space heating on a sunny day in winter and increases indoor temperature by about 10°C. Compared with direct solar heating mode, solar heating with desiccant humidification can increase the fraction of the time within comfort region from about 10% to 20% for standalone solar heating and from about 30% to 60% for solar heating with auxiliary heater according to seasonal analysis. It is confirmed that solar heating with desiccant humidification is promising and worthwhile being applied to improving indoor thermal comfort in heating season. [Copyright &y& Elsevier]

Multi-energy system is currently under rapid development due to their potential to reduce the use of fossil fuel resources and improve system stability. A systematic simulation-based, multi-objective optimization model of for solar hybrid heat pump heating and cooling system is presented. A combined energy, economic and environmental analysis of the system is conducted to calculate the primary energy use as well as the levelized total annual cost. A multi-objective optimization model is formulated using a genetic algorithm to simultaneously minimize these objective. Linear programming technique for multidimensional analysis of preference (LINMAP) is used to select the optimal point from the Pareto front. A sensitivity analysis is also performed to assess the influence of fuel cost, capital cost of innovative components and the annual interest rate on the Pareto front of the optimal solution. • Systematic simulation and MOO model for solar hybrid heat pump system are presented. • Genetic algorithm is used for the model to minimize energy and economic objectives. • Sensitivity analysis of the influence of parameters on the Pareto front is made. [ABSTRACT FROM AUTHOR]

• The efficiency factor of direct expansion PVT module is derived and validated. • Proposed a novel design method for PVT module employing roll-bond evaporator. • Parameter analysis is conducted to evaluate the thermal performance of four different channel patterns. • Hexagon and rectangle types have better temperature uniformity while grid and linear types have lower pressure loss. Direct expansion solar assisted PVT (photovoltaic/thermal) heat pump is a combination of PVT technology and heat pump technology, which can improve the comprehensive conversion efficiency of solar energy, and it is suitable for solar heating applications. In this paper, the efficiency factor of direct expansion PVT module employing roll-bond panel has been theoretically derived, modified, and validated by experimental results. Moreover, the efficiency factor could be used to design, evaluate, and optimize the thermal performance of direct expansion solar assisted heat pump systems. In addition, parameter analysis of four evaporator unit types has been conducted, and the recommendation values of each parameter have also been presented. The simulation results show that the roll-bond evaporator (fluid channel width: 10 mm) with hexagon and rectangle patterns have better temperature distribution uniformity than grid and linear types, and their temperature differences are both 0.038 °C while their dimensionless pressure losses are 0.109 and 0.230, respectively. To specifically design different kinds of PVT collector/evaporator or direct expansion evaporators, a novel design method for roll-bond evaporator is proposed, and a combination of hexagon and grid types is recommended for PVT module. Moreover, the recommendation fluid channel width of the roll-bond panel is 8 mm to 13 mm while the scaling ratio is 0.8 to 1.2. The modified efficiency factors are 0.521, 0.564, 0.549, and 0.342 of hexagon, grid, rectangle, and linear types when the fluid channel width is 10 mm, respectively. [ABSTRACT FROM AUTHOR]

• A solar PV/T heat pump is proposed for residential heating in high latitude area. • Design of build-in PCM heat storage unit is proposed and simulated. • The overall efficiency of this solar PV/T heat pump system can reach above 75%. PV/T (photovoltaic/thermal) technology is a combination of PV module (photovoltaic utilization) and collector (photothermal utilization), which can improve the comprehensive utilization efficiency of solar energy and has a broad application prospect. In this paper, PV/T module is coupled with heat pump evaporator to form a direct-expansion solar PV/T heat pump which is suitable for heat application in high latitude area. To achieve stable residential heating, a solar PV/T heat pump system coupled with build-in PCM (phase change material) heat storage is therefore proposed and simulated. Meanwhile, the mathematical model of solar PV/T heat pump coupled with build-in PCM heat storage system is established and verified. The simulation results show that the temperature of underfloor heating which using build-in PCM heat storage can reach 22–31 °C after 39 h when the circulating water is 40 °C. Moreover, the heating COP (Coefficient of Performance) increases with the increase of solar radiation, ambient temperature and area of PV/T collector, and decrease of wind speed, respectively. A 20 m2 PV/T panel module can output 21.4% of the electricity to power grid when the solar radiation intensity is 600 W/m2 and meet the heat demand of a 100 m2 room while maintain the operation of the system. Meanwhile, the heating COP can reach 5.79 which is 70% higher than the conventional air conditioning system and the electrical, thermal, overall efficiencies are 17.77%, 55.76% and 75.49%, respectively. [ABSTRACT FROM AUTHOR]

• Combination of the absorption and vapor compression heat pump. • Maximum performance enhancements for heating is 45.8%. • Maximum performance enhancements for cooling is 18.9%. • Power savings for heating and cooling are 16.0% and 31.4%, respectively. • Lower the heat-driven temperature for absorption to 60 °C. Decarbonizing the energy sector becomes a key topic to solving man-made climate change. For achieving indoor thermal comfort conditions, conventional heating, ventilating, and air-conditioning systems consume so much energy in both residential and public buildings. In this paper, a novel solar-assisted absorption-compression system for both heating and cooling is proposed to utilize solar thermal energy throughout the year for the heating/cooling supply. The experimental prototype was built and operational modes including solar-assisted heating/cooling mode and vapor compression individual heating/cooling mode. The performance enhanced by assisted heat input of the proposed system is evaluated by comparing it with air-source heat pumps operated under the same ambient conditions. Performance indices consisting of COP ele increment, power-saving ratio (PSR) and energy-saving ratio (ESR) are presented. The results indicate that the combination of the absorption heat pump subsystem and the vapor compression subsystem lowers the heat-driven temperature to 60 °C and thus makes higher solar collection efficiency possible. The maximum of the COP ele increment and the PSR under solar-assisted heating mode are achieved at conditions with 80 °C hot water temperature, of 45.8% and 31.4%, respectively, and the corresponding value for solar-assisted cooling mode are 18.9% and 16.0%. The speed of compressor as well as fan frequency of terminal has a greater influence on heating performance that on cooling performance due to the different coupling mechanisms. [ABSTRACT FROM AUTHOR]

Absorption-resorption heat pumps (ARHPs) have great potential in utilizing low-temperature solar heat for efficient winter heating, but are limited by their weak adaptability to cold climates relative to absorption heat pumps (AHPs) and vapor compression heat pumps (VCHPs). In this work, a resorption-compression cascade system consisting of ARHP and VCHP subsystems is proposed and investigated, with the goal of achieving efficient winter heating with improved solar contribution in cold climates. Thermodynamic models of the two subsystems and of the whole cascade system are developed for system feasibility verification and performance evaluations. Feasible operation temperature and pressure conditions are identified in terms of internal subsystem matching. Based on these operation conditions, the primary energy ratio (PER) – which is a key performance evaluation index – is investigated over a range of solar fractions (f). The results show that for cases without solar contribution, the PER can be generally >0.95 under feasible operating conditions. In addition, the primary energy saving ratio (PESR) and heating capacity lift ratio (ε lift), as well as the heat source temperature (T h) and ambient temperature (T amb) restriction, are all investigated and compared to those of other, competing heating systems. The results show that the proposed system can reduce the T h demand to 69 °C (with a minimum T amb of −21 °C) and extend the operational T amb to −31 °C (with a minimum T h of 90 °C), while importantly achieving PESR > 0.20 and ε lift > 20 % under the above extreme conditions. Moreover, when integrating the system with solar heat with f > 43 %, the proposed solar-assisted system has a clear PER advantage over an equivalent VCHP system in the T amb range from −31 °C to 10 °C, highlighting the possibility of achieving higher solar contribution in cold climates. • A novel resorption-compression cascade heat pump system was proposed. • Performances were compared with those of the VCHP and subcooling coupled system. • Potential of high solar contribution to heating in cold climates was stressed. • The system could be operated in ambient above −31 °C with heat source over 90 °C. • The system with solar fraction over 43 % has advantage over the equivalent system. [ABSTRACT FROM AUTHOR]

In this study, a distributed aerobic composting system was proposed and simulated assisted by a solar photovoltaic thermal (PV/T) heat pump. The PV/T heat pump was adopted to provide the electrical energy and heat energy required by the aerobic composting system. In addition, the area of solar photovoltaic panels required for compost fermenter at different volumes was calculated, and the effects of ambient temperatures, wind speeds and solar radiation intensities on the performance exhibited by the hybrid system were investigated. As indicated from the result, when the temperature of the composting tank was maintained at 60 °C, the C/N ratio can be reduced to 11.5:1 and the GI can reach 101.7%, satisfied the compost maturity standard. Moreover, as the ambient temperature decreased, the heat loss of the composting system and the energy consumption of the hybrid system increased. The wind speed did not significantly impact the comprehensive performance exhibited by the system. Under the average solar radiation of 600 W/m2, a maximum of 10 m2 PV/T panels could be installed on the top of a standard container, and a maximum of 6000L of aerobic composting system could be installed within the container. Accordingly, the 6000L composting system coupling with PV/T heat pump could generate 85.64 kWh electricity in one period (10 days) without consuming energy. [ABSTRACT FROM AUTHOR]

A novel solar assisted heat pump (SAHP) system for in-bin grain drying was proposed to solve the problems of poor uniformity and long drying time of grain in depot with higher initial water content in high grain piles. The effects of different operational parameters on the drying performance were numerically and experimentally investigated. The experimental results indicated that the thermal efficiency of the solar collector and the COP of the heat pump reached 63% and 5.03 under given conditions. The average heating capacity of the SAHP system was 130.2 kW, consistent with the simulation results under a typical sunny day in winter. The average water content of 3,760 tons of grain dropped from 12.9% to 12.5% after 42 h of drying. The specific moisture extraction rate of the proposed system and the exergy efficiency of the grain bin were 1.934 kg/kWh and 40.27%, respectively. The operating cost of SAHP grain drying decreased from 5.57 $/t to 1.43 $/t compared with the grain drying machine for the same drying weight. The daily drying capacity increased from 166 t/d to 334 t/d compared with the mechanical ventilation drying for the same water content reduction rate. This investigation provided guidance for expanding future researches on the SAHP system applied for in-bin grain drying. • A novel in-bin grain drying system using solar collectors coupled with air source heat pump is proposed. • The drying performance of the proposed system is numerically and experimentally investigated. • The average moisture content of 3,760 tons of corn dropped from 12.94% to 12.5% after 42 h of drying. • The specific moisture extraction rate of the SAHP grain drying system was 1.934 kg/kWh. • The payback period of the SAHP grain drying system was 0.33 years. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ETSC with inner concentrating by reflective coating was proposed and fabricated. • The best coating angle was 180° and efficiency increased with eccentric distance. • The thermal efficiency of the novel inner concentrating ETSC was increased by 10%. • The heat loss coefficient of the ETSC-IC was decreased by 27% to 48%. Evacuated tube solar collector (ETSC) is widely used for domestic and industrial applications. Using reflective coating in an ETSC to realize concentration is a method to heighten the thermal efficiency due to solar irradiation could be reflected by the coating on the lower half of the outer glass tube and concentrated to the eccentric inner absorber. In this paper, an evacuated tube solar collector with inner concentrating (ETSC-IC) by reflective coating was proposed and fabricated. A series of experimental tests of the ETSC-IC was conducted to investigate the thermal performance. In addition, the mathematical model of the novel collector with inner concentrating was developed, and the structural parameters of the inner reflective concentrating evacuated tube, including the coating angel and the eccentric distance, have been analyzed. The optical and thermal analysis revealed that the best coating angle of the evacuated tube was 180°, and the thermal performance of the ETSC-IC enhanced with the increase of the eccentric distance under the best coating angle. The thermal efficiency of the ETSC-IC could reach 0.65 to 0.72 on the condition that the solar irradiation was around 950 W/m2 and the temperature of inlet water varied between 45 °C and 70 °C, and the ambient temperature was 31.2 °C. The thermal efficiency of the ETSC-IC was improved by approximately 10% compared with the conventional evacuated tube due to the enhanced irradiation concentrating and the reduction of heat loss caused by the coating on the outer glass tube. [ABSTRACT FROM AUTHOR]

Borehole heat exchanger (BHE) is a promising method for extracting heat from the deep geothermal energy which has been widely used for residential heating in high latitude areas. The solar assisted photovoltaic/thermal (PV/T) heat pump could convert solar energy into useful heat efficiently, and could be further used to heat water from the BHE to a higher temperature level. In this paper, a residential heating system using BHE coupled with solar assisted PV/T heat pump is therefore proposed with further performance analysis. The simulation results show that a larger mass flow rate could increase the BHE's heat extract capacity but also increase the flow resistance and pump power under nominal conditions. The circulating water would not extract heat from rock-soil if the inlet temperature exceeds 48.5 °C when mass flow rate is 12 kg/s. Furthermore, the maximum water temperature from this hybrid system could reach 40.8 °C while the solar fraction is 67.5% when the area of PV/T module is 1000 m2, solar irradiation is 600 W/m2 and depth of the BHE is 2500 m. In the meantime, the heating COP of this hybrid system could reach 7.4 and the system could operate independently without power input from electrical grid. • A hybrid residential heating system using borehole heat exchanger coupled with solar assisted PV/T heat pump is proposed. • The structure and operating parameters of this hybrid system have been analyzed. • The heating COP of this hybrid system could reach 7.4, while the solar fraction is 67.5%. • The maximum thermal effect radius of a 2500 m borehole heat exchanger is within 8 m. • Higher mass flow rate and inlet temperature lead to lower heating COP and temperature difference between outlet and inlet. [ABSTRACT FROM AUTHOR]

Absorption-resorption heat pumps (ARHPs) can efficiently utilize low-temperature solar heat for winter space heating, but are restricted by the relatively weak low ambient temperature adaptability. By combining the different strengthens of vapor compression heat pump (VCHP) and absorption-resorption heat pump (ARHP), a novel solar-assisted resorption-subcooled compression hybrid heat pump system with higher heating capacity under cold climate condition for space heating is proposed. Thermodynamic models for the hybrid system involving two subsystems are developed for performance evaluation under different operation conditions. Feasible high pressure/low pressure (P H / P L) and evaporation temperature/condensation temperature (T e / T a) ranges for the hybrid system are revealed for component design. Based on that, performance evaluation indices like total coefficient of performance (COP tot), primary energy ratio (PER), primary energy saving ratio (PESR), coefficient from solar irradiation to heating capacity (SCOP) are investigated in terms of different P H / P L and T e / T a values. The results showed that for the base-case, the above indices are 2.41, 1.66, 0.35 and 1.21, respectively. In addition, heat source temperature demand, heating capacity and ambient air temperature need of the hybrid system are compared with those of the conventional absorption heat pump (AHP), single ARHP and single VCHP under the same operation conditions. The results show that the hybrid system can extend the operation heat source temperature to above 72 °C, highlighting the possibility of integrating with common non-tracking solar collectors, and can extend the feasible ambient air temperature to above −20 °C. Moreover, by recovering the sub-cooling heat of VCHP subsystem for ARHP subsystem operation, the hybrid system can lift the heating capacity by over 50% based on the equivalent VCHP system. • A resorption-subcooled compression hybrid heating system was proposed and analyzed. • The heating capacity is lifted by over 49.8% based on the equivalent VCHP system. • Heat source temperature demand of the hybrid heating system is over 72 °C. • The hybrid system can be efficiently driven be CPCs and ETCs for space heating. • The system has greater cold climate adaptability than the ARHP and AHP system. [ABSTRACT FROM AUTHOR]

In the past decades, solar heat for industrial processes (SHIP) have been rapidly developed and applied, and also getting more and more attention all over the world. China is the largest energy consumer with industry accounting for almost 70% of its total energy consumption. Low- and medium-temperature heat takes up 45% of process heat, covering 50–70% of industrial energy consumption, which provides a favorable condition for solar application in industrial processes. China has built developed some demonstration projects to make industrial processes well integrated with solar heating systems. This paper briefly summarizes the status of China's energy consumption, integration of SHIP, as well as available matching solar technologies. Ten typical industrial sectors are selected to specifically describe their potential of SHIP. Moreover, 26 SHIP cases covering the selected 10 sectors are presented by field researches, with capacity of energy saving and emission reduction previously investigated according to their own proportion of SHIP. The potential of SHIP in the 10 sectors are further predicted by optimistically and conservatively making their proportion in SHIP 5.5% and 2% respectively during the period of 2016–2020. The results show that at least 39.40 million tons of coal equivalent and 98.22 million tons of CO 2 emission is expected to be reduced in 2020 in China's all industrial sectors although solar can meet different proportions of heat demand in different industrial sectors. [ABSTRACT FROM AUTHOR]

Combining renewable energy with building energy supply is an effective way to pivot the building sector to carbon–neutral. This paper proposes a novel solar-assisted energy supply system which is applied in residential buildings for heating, cooling and domestic hot water. The heating/cooling output of the proposed system is mainly contributed by a vapor compression system to address the supply–demand mismatch of solar energy supply system, and the other part is assumed by a solar driven absorption system that is operating with lower generation temperature and higher evaporation temperature to assist the vapor compression system. Therefore, a solar-assisted absorption-compression system (SAACS) exploits the full potential of solar heat for annual energy supply by improving the contribution of per unit solar collection area, with considerable electricity-saving compared to air-source heat pumps. A thermodynamic model is established and validated by the results of the built experimental prototype which is testing. Solar-assisted heating mode and solar-assisted cooling mode are compared in comprehensive evaluation criteria to illustrate the performance differences caused by the assisted solar energy. The results indicate that solar heat at 60 °C is feasible for heating and cooling, revealing the great potential for efficient conversion from solar energy for heating and cooling. Due to the introduction of solar energy, the cooling and heating COP ele increases by 10.3 % ∼ 17.6 % and 32.3 % ∼ 56.3 %, respectively. Despite the lower increase in COP ele , electricity-saving ratio shows greater value at low hot water temperatures, varying from 24.3 % to 19.6 % for cooling and from 44.1 % to 39.7 % for heating as hot water temperature increases from 60 °C to 85 °C. The maximum SCOP is 0.63 for cooling, and 1.14 for heating. Yearly investigation shows that the SAACS combined with 20 m2 CPC collector has an annual average solar fraction of domestic hot water of 0.85 and a discounted payback period of 3.12 years. These results demonstrate the feasibility and flexibility of the SAACS applied to residential buildings toward decarbonization. • Flexible modulation of solar energy enable application for residential buildings. • Thermodynamic model and experimental prototype are implemented. • Both heating and cooling supply make use of solar energy. • Heat driven temperature is as low as 60 °C. • Discounted payback period is 3.12 years. [ABSTRACT FROM AUTHOR]

• A clapboard-type internally circulating fluidized-bed solar reactor was introduced. • The gas flow rate had a significant effect on the particle circulating rate. • Solar-to-thermal conversion efficiencies of SiC, alumina, and sand were reported. • The bed mass had an apparent effect on the solar-to-thermal conversion efficiency. • SiC presented the highest solar-to-thermal conversion efficiency of 10.7 ± 0.4%. Fluidized-bed based solar reactors for the gasification of biomass have been widely recognized as a promising approach to produce high-quality syngas due to the merits, e.g. continuous operation and superior heat and mass transport. In this work, a novel high-temperature solar reactor with a clapboard-type internally circulating configuration that can efficiently mitigate the overheating of the bed wall affected by non-uniform solar radiation, is designed, constructed, and experimentally investigated under Singapore's first 28 kW e high-flux solar simulator. To investigate the flow dynamics in the high-temperature solar reactor, a transient 3D computational fluid dynamics multi-phase model is developed accordingly and validated by the experimental data. The simulated results can well clarify the flow and thermal behaviours in experiments. The effects of the gas flow rate and bed mass on the thermal performances of different Group-B particle materials are studied through experiments and simulation. The results indicate that increasing the bed mass in the solar reactor is capable of mitigating the overheating of the absorber surface caused by hot spots. The gas flow rate is dependent on the particle thermo-physical properties and shape as well as the clapboard geometric parameters. The highest solar-to-thermal conversion efficiency (defined as the ratio of the accumulated sensible heat of the particles to the solar power input) of 10.7 ± 0.4% is achieved by SiC due to its superior thermal conductivity. [ABSTRACT FROM AUTHOR]

The adoption of vapor injection (VI) cycle could overcome the defects of the conventional one-stage air source heat pump (ASHP) system under extremely low ambient temperature conditions. Nevertheless, the ASHP system with VI cycle still could not operate efficiently due to the low evaporating temperature in the fin-tube evaporator. For such a situation, the PVT (Photovoltaic/Thermal) collector/evaporator could reach higher evaporating temperature attributed to its physical structure, thereby improving the system COP. This study proposes the detailed mathematical model of the vapor-injection heat pump system by incorporating PVT collector/evaporator and verifies the effectiveness of the proposed system. Parametric studies have been then conducted. The proposed system can operate off-grid and its COP can reach 4.0 at the ambient temperature of −10 °C and the solar irradiation of 500 W/m2. The practical electrical efficiency of PV panels achieves at 15.1%, whereas the thermal efficiency of the system is 44.8%. A hybrid control method including three modes has been also proposed based on the results for improving the system performance. The levelized cost of heat (LCOH) of this system is 0.054 $/kWh, which is 51.5% lower than that of electric heating system (0.111 $/kWh). • A PVT based vapor-injection heat pump system was proposed for residential heating. • A hybrid control method was established for better system performance. • The influences of real-time working conditions on system performance were studied. • The comparative analysis was conducted between the proposed system and ASHP system. [ABSTRACT FROM AUTHOR]

• A two-stage GAX-based absorption-resorption heat pump cycle was built and studied. • The novel cycle can work in much colder ambient condition than single-stage cycle. • The cycle can greatly reduce the heat source temperature demand to above 73 °C. • The cycle is feasible for efficient building floor heating or fan coil heating. • The cycle can greatly lift solar fraction and working time in winter space heating. Ammonia-water absorption-resorption heat pumps have great potential in efficiently utilizing low-temperature heat for space heating or hot water supply. However, single-stage absorption-resorption heat pumps have disadvantages of poor low ambient temperature adaptability and low heat supply temperature over conventional absorption heat pumps, which limit their applications in cold regions. In this paper, a novel GAX-based two-stage absorption-resorption heat pump cycle with multiple internal heat recovery is proposed aiming to expand the application scope at lower ambient temperatures, to raise the heat supply temperature and more significantly to utilize solar heat for space heating for longer solar working time with higher contribution. Feasible operation pressure combinations to enable the cycle were investigated. Coefficient of performance, ambient air temperature restrictions, heat source temperature demand, heat supply temperature level, heat inputs/outputs and solution circulation ratios of generators in terms of different operation pressure combinations were revealed by comparing with those of the single-stage cycle. Under given operation conditions, maximum COP value of 1.367 and heat supply temperature of 46.1 °C can be obtained and the cycle could be operated at ambient air temperatures above - 15.6 °C. The heat supply temperature is generally above 42 °C, which is suitable for building floor heating or fan coil heating. The cycle can be driven by heat source above 73 °C, highlighting the possibility of integrating it with more economical solar collectors for high efficiency space heating. [ABSTRACT FROM AUTHOR]

To find an optimal economic solution for solar district heating (SDH) in China, an evaluation model based on the levelized cost of heat (LCoH) is developed. A Python program is developed to calculate the LCoH of SDH systems using the quasi-dynamic test method. Based on these calculations, the trend of LCoH with solar collector area under different heating load intensities, heating terminal units, heated areas and land rents is discussed. The optimal solar collector area and the solar fraction are determined for combinations of solar thermal with four types of auxiliary heat sources, including air source heat pumps, ground source heat pumps, gas boilers and gas boilers with seasonal heat storage. The calculations show an economic optimal solar fraction of 11%–33% for a SDH system with heat pumps. High dependency of LCoH on network temperature is found for a SDH system with gas boilers. Seasonal heat storage minimizes LCoH of a SDH system with gas boilers at 100% solar fraction. The findings can be used as a reference for local authorities, consultants and engineers in the early energy planning to determine the optimal proportion of solar energy in a district heating system with the lowest operating cost. • An optimal solar fraction of 11%–33% for a SDH system with heat pumps. • High dependency of LCoH on network temperature for a SDH system with gas boilers. • Heat storage minimizes LCoH of a SDH system with gas boilers at 100% solar fraction. • The higher the heat demand, the greater the solar contributed economic benefits are. • With biomass >1100 CNY/ton, the biomass heating system reduces LCoH by adding solar. [ABSTRACT FROM AUTHOR]