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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 Ammonia-water absorption-resorption heat pump (ARHP) is a promising technology for promoting efficient utilization of low-temperature thermal for space heating. This paper proposes a novel unbalanced ARHP cycle by replacing the condenser and evaporator in the conventional absorption heat pump (AHP) cycle with a high-pressure absorber and a low-pressure generator, respectively. The proposed cycle can work just depending on the concentration difference of ammonia-water solution under different pressure levels. A numerical model has been developed to investigate the feasible high-pressure/low-pressure (P H / P L) values to effect the thermodynamic cycle. The cycle's coefficient of performance (COP) under different P H / P L pair values and other given working conditions are studied. The maximum COP is 1.550 and the corresponding optimum P H / P L pair to effect the cycle is 1.40 MPa/0.38 MPa at a heat source temperature of 95 °C. When P H / P L pair value is 1.40/0.38 MPa, heat supply temperature of 44.5 °C and COP value of 1.331 can be obtained, which can basically meet the temperature demand of building floor heating. In addition, effects of different P H / P L pair values on solution circulation ratios and vapor discharge scopes of generators are discussed. It is concluded that the ideal P H / P L candidates yield large concentration difference between the inlet and outlet of generators and absorbers. Meanwhile, the solution circulation ratios of the two generators at ideal P H / P L pairs are acceptable values between 2.0 and 12.0. The cycle can work when the ambient temperature is above −7.5 °C and the driving heat source temperature is larger than 85 °C, which is potential in efficient utilization of commonly used stationary solar collectors for winter heating. Highlights • An unbalanced absorption-resorption heat pump cycle was developed. • Mathematical model was developed to explore feasible inner operation pressures. • Effects of different operation parameters on the cycle's COP were analyzed. • Performance was compared with that of conventional absorption heat pumps. • COP of the whole solar driven space heating system was investigated. [ABSTRACT FROM AUTHOR]

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-driven GAX-based ammonia-water absorption heat pump was proposed. • Experimental and theoretical analysis on the system was carried out. • Thermal efficiency of the heat pump was optimized. • Effects of different operation parameters on system performance were analyzed. This research involves a GAX-based ammonia-water absorption heat pump, which utilizes solar energy and natural gas as heat source. The experiments of parabolic tough collector and GAX absorption heat pump were carried out separately. GAX absorption heat pump is operated when the ambient temperature is 4.31–11.07 °C, COP approaches 1.44–1.66. Thermal efficiency of the PTC varies from 0.50 to 0.60. A mathematical model of the coupled solar absorption heat pump is built. The effect of each heat exchanger size on the GAX cycle performance is investigated, results show that the heat exchanger size of solution cooled absorber has the greatest impact on the cycle. Both Solar driven mode and Solar-NG driven mode were studied. Solar driven mode is strict with solar energy, if the direct normal irradiance is below 560 W/m2 the system cannot work. Solar-NG driven mode could work under any solar radiation condition. In this mode, generation temperature could be controlled by changing the flow rate of natural gas. The optimal generation temperature is found to be around 180 °C when T amb = 7 °C, DNI = 800 W/m2, T wout = 45 °C. Besides, system analysis reveals that the heat pump could perform competitive in low ambient temperature if the solar radiation is abundant, which makes Lhasa a perfect site for the system. Economic analysis in Lhasa show that the addition of solar collector could reduce the operating cost by more than 25%. [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]

Abstract Ammonia-water absorption-resorption heat pump (ARHP) is a promising technology in efficient utilization of low-temperature heat for residential heating application. This paper proposes a balanced-type single-stage ARHP cycle based on the unbalanced ARHP cycle by eliminating the rectifier and depending on only one solution circulation pump. The proposed cycle can achieve internal mass and species conservation by changing the ammonia-water solution concentration difference at different pressure levels. A mathematical model is developed to obtain feasible high pressure/low pressure (P H / P L) pairs to enable the cycle. The cycle's coefficient of performance (COP) at different P H / P L pair values is investigated. The maximum COP is 1.51 and the corresponding heat supply temperature reaches 43.4 °C when P H / P L pair value is 1.50/0.48 MPa and heat source temperature is 95 °C. The maximum heat supply temperature can reach 53.4 °C and the minimum ambient air temperature to effect the cycle is − 5.8 °C. Other parameters like heat output/inputs, solution circulation ratios, and absorption and desorption concentration gradients in the absorbers and generators are studied. Inner pressure (difference), COP and heat source temperature demand have been compared with those of the conventional absorption heat pump (AHP) cycle and the unbalanced ARHP cycle. The results revealed that the proposed cycle could work at lower heat source temperature (above 82 °C) and within wider heat source temperature range than the conventional AHP cycle, indicating that the proposed cycle is potential in efficient utilization of commonly used solar collectors for space heating. In addition, the proposed cycle could be operated at higher COP values and lower inner pressure differences than the unbalanced ARHP cycle. Highlights • A balanced-type single-stage absorption-resorption heat pump cycle was studied. • Mathematical model was developed to explore feasible inner operation pressures. • COP values corresponding to different inner high/low pressure pairs were revealed. • Effects of different parameters on performance of the proposed cycle were analyzed. • Performance is compared with that of the AHP cycle and the unbalanced ARHP cycle. [ABSTRACT FROM AUTHOR]

The performance of a solar-assisted DX-PVT heat pump (direct expansion photovoltaic-thermal) is intimately relevant to the system configuration. Inappropriate system configuration will undermine the system performance. This work assessed the effect of the equipment area of PVT modules on the PVT heat pump system driven by novel direct-expansion roll-bond PVT modules, and aimed to propose optimal system configuration. An analytical model was developed for the PVT heat pump system and validated by the experimental results. Simulations were conducted to reveal the effect of A / V t h , a proposed parameter to describe the system configuration, namely the ratio of the modules' area to the theoretical displacement of the compressor. The results showed that the larger A / V t h lead to higher COP but lower HGF (heat gain factor). With A / V t h increasing from 0.768 to 2.303 m2 h/m3, the COP increases by 61.3% (from 3.1 to 5.0) but the HGF decreases by 39.6% (from 0.91 to 0.55). Higher levels of solar irradiation strengthens the positive effect of the increasing A / V t h on thermodynamics performance and weakens the negative effect of that on the heat collection performance. The enhancement in COP is 42.8%/70.9% with A / V t h increasing from 0.768 to 2.303 m2 h/m3 when solar irradiation is 500 W/m2/800 W/m2, while the decrease in HGF is 49.2%/39.2%, respectively. A configuration optimization was also conducted to balance the thermodynamics and heat collection performance. The A / V t h varying from 1.535 to 1.919 m2 h/m3 was suggested as the optimized configuration when solar irradiation is 500 W/m2. After optimization, the IPLV and HGF can exceed that of air-source heat pump and flat-plate collectors by 40%, showing considerable performance advantages. [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]

• Solar photovoltaic-assisted ground-source heat pumps are studied in Nordic climate. • Ground regeneration with solar thermal energy improves long-term performance. • Designs are compared in terms of energy efficiency, cost, and ground heat transfer. • Photovoltaic-thermal leads to lower investment costs by reducing the borehole size. Ground source heat pumps (GSHP), as a renewable energy technology, are highly efficient systems suitable for meeting the heating needs of buildings, particularly in heating-dominated regions like Scandinavia. This study aims to better define the scope of application and sizing of GSHP combined with photovoltaic-thermal (PVT) collectors in Nordic conditions. The study compares seasonal performance factors (SPF), average ground temperatures, and investment costs for heating different numbers of apartment blocks in two distinct Nordic climates: Baltic climate and cold continental climate. To assess the long-term effects on the energy performance of GSHP + PVT systems, dynamic simulations using the TRNSYS software are conducted over a period of 50 years. The results demonstrate that PVT improves the long-term system performance, particularly in large and compact borehole (BH) fields, while in smaller BH fields, natural regeneration keeps playing a substantial role. For instance, PVT added to a GSHP system with large BH field can limit the ground temperature reduction after 50 years by 33 % compared to the configurations without PVT. In contrast, this reduction is only 13 % for systems with small BH fields. Moreover, the results show that GSHP + PVT can lead to a reduction of up to 95 % in the required area for installing the BH field while maintaining (almost) the same energy performance compared to a conventional GSHP. Notably, this study shows that the utilization of GSHP + PVT leads to a substantial reduction in BH length (up to 50 %) while maintaining a similar system SPF. It leads to a decrease in investment costs of up to 9.32 % and 22.92 % for the scenarios located in Norway and Sweden, respectively, compared to the case with PV instead of PVT. These findings suggest that PVT integration holds promise for advancing the GSHP adoption in high-latitude regions, especially in larger installations and colder climates, by mitigating investment costs while preserving the system SPF and ground temperature stability. [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]

The photovoltaic-thermal heat pump system, which integrates multiple energy technologies, can meet the building's diverse energy needs. This study evaluates the energy, economic, and environmental performance of a direct-expansion photovoltaic-thermal heat pump system for domestic hot water supply through a life cycle approach. The annual thermal and electrical outputs are estimated. On this basis, economic analysis is conducted with indicators of life cycle cost, levelized cost of heat, and investment payback time. Moreover, a detailed life cycle assessment is performed to evaluate the environmental impact, following three methods: cumulative energy demand, IPCC 2021 global warming potential, and ReCiPe 2016 Endpoint. Results show that the proposed system is highly effective, with a 9.67% increase in annual electricity output over traditional photovoltaic systems and a self-sufficient rate of 88.21%. The system also has a significantly lower environmental impact than conventional heating systems, with a life cycle environmental impact of only 3–5% compared to electric boilers. The environmental payback time ranges from 0.33 to 5.18 years, according to the three methods used in the study, which is shorter than the investment payback time of 2.49–5.21 years, suggesting the need for cost reduction for future promotion. Moreover, electricity consumption during the operation stage accounts for 32–52% of the total environmental impacts. Thus, decarbonization of the power grid and improvements in system efficiency can significantly reduce the system's environmental footprint. Overall, the photovoltaic-thermal heat pump system is an intriguing strategy for building energy conservation, offering high energy efficiency, acceptable costs, and low environmental impact. • A direct-expansion photovoltaic-thermal heat pump system for hot water production. • Operation simulation, life cycle cost, and life cycle assessment are conducted. • Investment, energy, CO 2 , and total environment payback time are evaluated. • The main factors impacting environmental performance are identified. • The system outperforms conventional systems in energy and environmental aspects. [ABSTRACT FROM AUTHOR]

• A LiBr-H 2 O concentration difference cold storage system was proposed. • The system performance of hybrid cycles was investigated experimentally. • The energy balance between the subsystems was analyzed. Solar-powered LiBr absorption cooling system is of potential in the application of air-conditioning. A LiBr-H 2 O concentration difference cold storage system driven by vapor compression heat pump was proposed. This cold storage process is not affected by the environmental conditions, since the main energy input is low price electricity at night. The experimental results show that the energy storage density (ESD) can reach 77.8 kWh/m3 and the energy storage coefficient of performance (ESCOP) is 2.81 with low heat loss. The ESCOP means the energy stored in the cold storage process divided by the total electricity consumption in the absorption and heat pump subsystem. The heat transfer in the condenser of the absorption subsystem approximately equals that in the evaporator of the heat pump, and the electricity consumption of the circulating pump in the absorption subsystem is low. Therefore, the value of ESCOP should be slightly lower than the COP of the heat pump system but for higher than 1. These results indicate the feasibility of improving the system efficiency, the operation cost, and long term operation of the solar air conditioning system by coupling the absorption and vapor compression cooling cycles. Finally, the influence of working parameters on the system performance is discussed based on the experimental and simulation analyses. The energy balance between the absorption cycle and the heat pump cycle in the cold storage system is analyzed. It is found that the coefficient of performance of the heat pump (COP ele,HP) and ESCOP increase with a low initial LiBr-H 2 O solution concentration. The ESCOP decreases by 34.4% when the initial concentration increases from 52% to 57%. The average ESD increases to 140.2 kWh/m3 with a concentration difference of 8%. Based on the experiment results, the payback period of the proposed system is estimated as 2.4 years comparing with the traditional LiBr-H 2 O absorption system. [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]

Abstract With the increasing attention to indoor air quality (IAQ), the use of fresh air conditioning systems has become more widespread in recent years. However, the dew point dehumidification method of conventional air conditioning system results in high energy consumption because the temperature of the air needs to be reduced below the dew point temperature. In this research, a fresh air dehumidification system using heat pump with desiccant coated heat exchanger (DCHE) is presented and experimentally tested. The harmful effect of adsorption heat could be overcome and the efficiency of dehumidification could be improved due to the application of DCHE. Base on the experimental results, it can be noticed that maximum moisture removal 9.98 g/kgDA could be achieved on high humidity condition and the coefficient of performance of the heat pump system can reach 5.36. In addition, the system is more efficient for handling humid air with high relative humidity. Besides, energy saving ratio of the system is studied compared with conventional dew point dehumidification and the maximum energy saving ratio is 74.4% at the experimental condition. [ABSTRACT FROM AUTHOR]

In this study, we presented a detailed experimental investigation of an air source liquefied petroleum gas (LPG)-solar driven absorption heat pump (LSAHP) using Generator Absorber heat eXchanger (GAX). The GAX absorption heat pump with a nominal heating capacity of 55 kW uses ammonia-water as working pairs and is powered by hybrid energy sources: a 45 m 2 parabolic trough solar collector (PTC) and a direct-fired liquefied petrol gas (LPG) burner. The thermal performance of the PTC was characterized with selected on-sun conditions. Results showed that solar thermal efficiency can reach up to 53.55% with direct normal insolation of 450 W/m 2 and inlet thermal oil temperature of 191 °C. Three operation modes were identified based on the driven energy sources: ( i ) LPG-Solar hybrid mode, ( ii ) Solar only mode, and ( iii ) LPG only mode. Under the average ambient temperature of 17.52 °C, 20.0 °C, 8.77 °C the averaged COPs of three modes are 1.54 (mode i ), 1.63 (mode ii ) and 1.20 (mode iii ) respectively. Solar energy contributions reached 40.2% and 55.10% in mode i and mode ii separately which demonstrated the feasibility of the coupling of PTC and GAX heat pump to reduce the dependence on fossil fuel. The impact of operation conditions (ambient temperature, inlet hot water temperature, and LP gas flow rate) on the heating capacity and system performance were investigated under steady-state conditions. Results indicated that higher ambient temperature, higher gas flow rate, and lower inlet hot water temperature benefit the heat pump performance, among which the influence of ambient temperature is the greatest. COP reaches 1.47 with 19 °C ambient temperature and 35 °C inlet hot water temperature. It’s worth noting that COP’ achieves 1.82 under the same condition if we exclude the heat loss of flue gas. [ABSTRACT FROM AUTHOR]

Due to the high dehumidification performance realized by removing adsorption heat by inner cooing, desiccant coated heat exchanger (DCHE) has been proposed and widely studied. The heat pump is usually used as the cooling and heat sources of the dehumidification system composed of DCHE because the cooling and heat capacity could be provided by the heat pump at the same time. Moreover, considering the advantage of low-grade thermal energy utilization, solar thermal energy can be used to further enhance the regeneration of DCHE to improve dehumidification performance and energy efficiency. In this paper, the solar-enhanced fresh air dehumidification system using DCHE driven by heat pump was proposed and a series of experiments were conducted under typical Shanghai summer high humidity conditions. The typical moisture removal of the system can be increased by about 15% to 10.14 g/kgDA and the COP could be further increased by over 25% to 5.39. In addition, the influence of different regeneration temperatures enhanced by solar thermal energy on the system has also been studied. Considering the dehumidification performance improvement and energy utilization efficiency, the optimal regeneration temperature is between 60 °C and 65 °C for the system proposed in this paper. • Moisture removal and COP can be increased by 6%–28% by solar enhanced. • Performance enhanced is more obvious when regeneration temperature is below 65 °C. • Solar enhanced dehumidification 1.43 (g·kgDA−1)/kW and 1.12 kg/kWh can be achieved. • Higher efficiency solar collectors will achieve higher solar enhanced performance. [ABSTRACT FROM AUTHOR]

High source temperature demand (>100 °C) and inflexible working pressure restrict the widespread application of solution transportation systems. Absorption-resorption heat pump cycles stand out in significantly lowering the demand of heat source temperature (to 80 °C), as well as multiplying working pressure choices (lower to 500 kPa) attributed by solution concentration adjustment and simplifying system structure (no rectifier). In this paper, a novel solution transportation resorption system is proposed based on the single-stage absorption-resorption heat pump cycle by assigning high-pressure generator and high-pressure absorber on the source site while placing low-pressure generator and low-pressure absorber on the user site. Feasible working pressure combinations and outlet temperature of high pressure-absorber to effect the system are investigated, illustrating the pressure range difference between resorption cycle and cycle -based heat transportation system. Thermodynamic parameters such as thermal coefficient of performance, electrical coefficient of performance, heat supply temperature range of the system are revealed in this paper. Under the condition that transporting distance is 20 km, the maximum COP value of the proposed system could reach 0.53 when high/low pressure pair is 700 kPa/405 kPa. The highest supply water temperature could reach 53.84 °C with COP of 0.477, which is suitable for floor heating. Besides, hydrodynamic and economic analysis of the proposed system are conducted, indicating that when the transportation distance exceeds 4 km, the proposed system is more economical than conventional sensible heat transportation systems. According to restriction to pump power, the longest distance is supposed to be no more than 113 km when loading power is 20 MW. • A novel no-insulation long distance thermal transportation system was proposed. • Pressure range, COP and supply water temperature of STR system was investigated. • Energy density and distance effect on STR system was studied. • The economic advantage of STR system was studied. [ABSTRACT FROM AUTHOR]

Absorption heat pumps (AHPs) can be thermally activated by low-grade heat sources for space heating. The efficiency can be greatly improved by adopting GAX-based internal heat recovery, which lifts the heat source temperature demand and deteriorates the cold climate condition adaptability, and thus immensely limits the widespread application. In this paper, a hybrid GAX-based absorption-compression heat pump (ACHP) system is proposed to expand the geographical scope of application in extremely cold climate conditions, to lift the heat supply temperature, and more importantly to utilize heat sources of lower temperatures. A mathematical model was developed and validated in comparison with experimental and theoretical results from the literature. Feasible generation-evaporation temperature (T g - T e) conditions to enable GAX were presented in detail. Coefficient of performance (COP), primary energy ratio (PER), heat supply temperature, heating capacity, and heat duty of main components were investigated concerning different working conditions. The possible sensible and latent heat recovery ratio of the GAX was explored. The results show that when P r increases, the feasible T g - T e area moves towards the lower T g and T e sides. The system can be utilized for building floor heating with PER above 1.116, COP higher than 1.614, temperature lift (Δ T lift) up to 81.85 °C even when ambient air temperature (T amb) is down to −40.6 °C, and for fan coil heating when T amb is above −40.0 °C with PER above 1.074, COP over 1.615 and Δ T lift up to 85.92 °C. The system can utilize heat sources down to 80 °C by adjusting the working pressure ratio (P r), highlighting the possibility of integration with solar collectors for heating purposes. • A hybrid GAX-based absorption-compression heat pump (ACHP) system was proposed. • Feasible source-load temperature range and the heating performance were revealed. • Heat recovery ratio by GAX section and the effect on heating indices were reported. • Possible solar contribution to raising the primary energy efficiency was analyzed. [ABSTRACT FROM AUTHOR]

• The two-phase flow characteristics were investigated. • The effect of temperature uniformity on PVT module's electrical efficiency was considered. • The optimized fluid channel pattern was proposed. • The comparative and feasibility analyses were conducted of different fluid channel patterns. The two-phase flow characteristics of the roll-bond cooling component were investigated to design and optimize the fluid channel pattern for higher thermal and electrical efficiencies. The CFD method was applied to evaluate the thermal, electrical, and hydraulic performance of the PVT (photovoltaic-thermal) module employing different patterns of roll-bond panel. The influence of uneven working temperature of solar cell units on the PVT module's electrical efficiency was considered. Moreover, the proposed numerical model was validated by the experimental results. The optimized two-phase flow channel pattern was structured by hexagon-grid coupled fluid channel units with the one-way arrangement, and it showed significant improvement in temperature uniformity, thermal and electrical efficiencies, and hydraulic behavior. The feasibility analysis revealed that the optimized fluid channel pattern could reduce the PV module's working temperature by up to 47.3 °C and improve its electrical efficiency by 46.5% on a typical summer day. In this circumstance, the average system COP was 4.37 and the average temperature difference of the PVT module was 4.6℃, while the average electrical and thermal efficiencies were 16.7% and 47.6%, respectively. [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]