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• A constant-temperature thermal response test was proposed and demonstrated. • The new concept enables simultaneous heat injection and extraction tests. • A test data analysis method was developed based on the finite line source model. • Ground thermal conductivity was evaluated for both heat injection and extraction. • Convective effect enhanced ground heat transfer when heat injection was involved. Getting an accurate estimate of site-specific ground thermal conductivity from thermal response tests (TRTs) is crucial to the efficient and sustainable use of ground source heat pump systems. In a conventional TRT, the ground thermal conductivity is estimated by perturbing the ground with a positive heat injection and the response is measured in time. Despite the simplicity, the conventional TRT does not take into account the ground thermal response to cooling pulses. This may lead to mode-biased estimation due to the presence of natural convective effect. To address the problem, a constant-temperature TRT that comprises simultaneous heat injection and extraction was proposed. A test data analysis method was developed based on the finite line-source model. On this basis, a very first field test was performed in Taiyuan, China, demonstrating the use of the proposed TRT concept with full-scale measurements. Results show that, in the case of this field test, the ground thermal conductivities derived separately from heat injection and heat extraction are 1.83 W/(m K) and 1.65 W/(m K), respectively. The significant difference (10.9%) indicates that when heat injection is involved, the natural convective effect has enhanced ground heat transfer to increase the conductivity estimate. Thus, as compared to the conventional approach, the use of the proposed TRT can improve the characterization of the ground thermal response and conductivity. Relevant results and the test protocol reported in this study will be useful in providing the background information for this technology to be adopted in the ground source heat pump industry. [ABSTRACT FROM AUTHOR]

• A PVT collector with a roll-bond absorber is designed for rural home application. • Thermo-laminating is a novel and convenient method for PV-absorber connection. • The validated PVT model can simulate the roll-bond PVT performance accurately. • The model is available for predicting the dynamic performance of PVT systems. This paper mainly investigated the performance of a low-cost roll-bond water-type photovoltaic thermal (PVT) collector from both experimental and modelling approaches under the climatic conditions of Sichuan Basin of China. The design and manufacturing process of the PVT prototype adopted the available commercial PV panels for convenience and for reducing the manufacturing cost. The experiment measured all the main properties of the developed PVT module. The excellent heat transfer performance of its roll-bond absorber plate was also validated by outdoor steady-state tests. Then, the steady-state numerical models were used to simulate the performance of the PVT prototype in TRNSYS. By comparing the simulation and experimental results, two robust models were selected which have their own advantages in charactering the thermal and electrical properties of the PVT collector. Through validating the numerical models with experimental data, the deviation between the simulated and the measured values was further reduced. In addition, a complete photovoltaic thermal–domestic hot water (PVT-DHW) system with such PVT collectors was developed in TRNSYS, by which the annual system output and efficiency were predicted and analysed. [ABSTRACT FROM AUTHOR]

The rapid development and large-scale penetration of wind power would bring about substantial environmental benefits by substituting fossil fuel-based thermal power generation. In this paper, the environmental co-benefits synergized with energy saving benefit of wind power penetration in China were quantified. Moreover, the regional distribution of environmental co-benefits was mapped by considering the baseline emission factor of each region. Based on the co-benefits analysis results, the wind power deployment pathways were designed to enlarge the environmental co-benefits in the whole country level. The results show that the CO 2 , SO 2 , NO x , and PM 2.5 emissions reduced and water consumption saved due to wind power penetration account for respectively 2.58%, 2.71%, 2.66%, 1.58%, and 2.34% of total environmental emissions and water consumption from the whole power generation sector in China. In view of regional distribution, the environmental co-benefits of wind power to the power system is not proportional to the amount of fossil-fueled power that it displaces. The penetration of wind power results in the largest environmental co-benefits in the North China grid. The Northwest China grid has a higher environmental alleviating potential compared with the Northeast China grid even though the two regions has an equal magnitude of wind power penetration. Scenario analysis suggests that lowering the proportion of thermal power in power generation structure and the transmission of bundled wind power and thermal power from the north to the load centers are promising ways in enlarging the environmental co-benefits of wind power penetration. [ABSTRACT FROM AUTHOR]

• Analyzed the performance of tunnel lining exchanger under periodic boundary conditions. • A distinct 'inertia' phenomenon is observed for the temperature wave in the tunnel surrounding rock. • A critical heat transfer point exists along the CHE tube length. • Recommended CHE tube length was determined. In recent years, the number of subways has rapidly increased, as they can effectively alleviate urban traffic congestion. However, subways can also result in thermal pollution problems in underground spaces. The long-term operation of a subway causes thermal accumulation in the surrounding rock of a tunnel, severely affecting the safe and efficient operation of the subway. The metro source heat pump technology is an effective approach to address the foregoing problem. However, currently, the research on its systematic design methods remains inadequate. In particular, studies on the evolution law of heat transfer characteristics of its front-end heat exchangers during years of operation are limited. In this study, a numerical model of a front-end capillary heat exchanger (CHE) is formulated. The model is based on a practical subway source heat pump demonstration project located in a cold area in China. The annual heat transfer characteristics of the CHE under periodic boundary conditions are simulated and analysed. The results reveal that the temperature of the CHE and its vicinity fluctuates periodically and increases annually under typical design conditions. The fluctuation range of CHE wall temperature gradually decreases from 25.0 °C at 0 m from the CHE inlet to 9.6 °C at 10 m from the CHE inlet in the 10th year. A distinct 'inertia' phenomenon is observed when the temperature wave is transmitted to the rock surrounding the tunnel. With the increase in the surrounding rock depth from 0 to 25 m, the amplitude of temperature wave gradually decreases from 4.277 to 0.013 °C, and the reduction rate gradually declines from 24 % to 14 %. Meanwhile, the phase delay of temperature wave increased from 0° to 282.40°. Moreover, a critical heat transfer point exists along the CHE tube length, and the heat transfer law and efficiency before and after the critical point differ. Statistics show that the ratio of CHE average heat flux after the critical point to that before the critical point ranges from 1.11 % to 46.16 % in the heating season and from 30.19 % to 46.12 % in the cooling season, respectively. The recommended CHE tube length is determined to be 4.9–6.3 m based on the analysis results. This research can provide reference data and a theoretical basis for the design of front-end heat exchangers of subway source heat pump systems. [ABSTRACT FROM AUTHOR]

• A greenhouse heating approach utilizing energy transfer between greenhouses is presented. • A dual source heat pump with greenhouse and outdoor air sources is designed. • An innovative heating load model and a surplus air heat model are developed. • The greenhouse heating system was built and followed with a pilot study. • COP of heat pumps was improved by 23–26% due to usage of greenhouse air source. Multi-span greenhouses consume enormous amounts of energy for heating in northern China, resulting in poor profitability and unsustainability. A greenhouse heating system, utilizing energy transfer between greenhouses based on a dual source heat pump, was designed to remedy this issue. The system collects surplus air heat inside Chinese solar greenhouses (CSGs) for heating multi-span greenhouses. Through enabling a greenhouse energy transfer in time and space, improved utilization efficiency of surplus air heat in CSGs is achievable, resulting in an overall reduction of heating costs. This study defines the heating approach and describes the overall system design. The dual source heat pump acts as the core component, with two separate evaporators placed in the CSG and ambient air. Calculations for system sizing are then presented, including a heating load model of multi-span greenhouses, a surplus air heat model of CSGs, the selection of required equipment (dual source heat pump, heat storage tank, and surface air cooler of the combined air conditioning unit), and the area matching. Finally, a case study illustrates the implementation processes of the heating system. The available CSG surplus air heat ranged 100.8–112.6 W m−2 for system sizing, and the minimum area of CSGs was suggested to be twice the multi-span greenhouse area. The pilot test showed that the running status and heating effect of the system was stable. The coefficient of performance (COP) of the heat pump reached 4.3–4.8 when using CSG surplus air heat as the heat source, performing 23–26 % higher than when using ambient air over the same periods. Throughout the entire course of heat collection, dual source heat pumps, switching sources based on their setting, achieved a total COP of 3.4–4.2, increased by 6–11 % compared with air source heat pumps. This study provides a novel heating approach and an energy-saving system for multi-span greenhouses. [ABSTRACT FROM AUTHOR]

Abstract: Lightweight envelopes are widely used in modern buildings but they lack sufficient thermal capacity for passive solar utilization. An attractive solution to increase the building thermal capacity is to incorporate phase change material (PCM) into the building envelope. In this paper, a simplified theoretical model is established to optimize an interior PCM for energy storage in a lightweight passive solar room. Analytical equations are presented to calculate the optimal phase change temperature and the total amount of latent heat capacity and to estimate the benefit of the interior PCM for energy storage. Further, as an example, the analytical optimization is applied to the interior PCM panels in a direct-gain room with realistic outdoor climatic conditions of Beijing. The analytical results agree well with the numerical results. The analytical results show that: (1) the optimal phase change temperature depends on the average indoor air temperature and the radiation absorbed by the PCM panels; (2) the interior PCM has little effect on average indoor air temperature; and (3) the amplitude of the indoor air temperature fluctuation depends on the product of surface heat transfer coefficient h in and area A of the PCM panels in a lightweight passive solar room. [Copyright &y& Elsevier]