Solar-ground Source Heat Pump System Research Articles

Heat transfer and system performance of a novel solar ground-source heat-pump system with borehole heat exchangers using a combined parallel and series connection

Heat transfer and system performance of a novel solar ground-source heat-pump system with borehole heat exchangers using a combined parallel and series connection

Thermal performance of solar ground source heat pump system for rural buildings in Chinese cold zone

In response to China's national policy of “achieving carbon peak by 2030 and carbon neutrality by 2060″, and to promote the heating system of rural buildings in China's severe cold zone. Two heating schemes of the GSHP (Ground Source Heat Pump) system and the SGSHP (Solar Ground Source Heat Pump) system are designed and simulated for a single rural residential building in Harbin city. The results present that the outlet temperature of buried pipe in SGSHP system is 13.86 % higher than that in GSHP system, and coefficient of performance (COP) correspondingly increases 9.2 %. There is a better comprehensive performance for the SGSHP system in cold climates. The standard coal consumption of SGSHP system is about 72.35 % less than that of biomass boiler system, showing a greater energy efficiency. Compared to the local conventional biomass boiler system, the dynamic cost payback period of the SGSHP system amounts to 11 years, while yielding a net present value (NPV) of 10,800 CNY throughout the project's life cycle. The emissions of CO2, SO2, and dust are reduced by 2617.13 kg, 19.38 kg, and 14.535 kg respectively. The results indicate a great overall performance of the SGSHP system for residential heating in the cold climate zone. This research offers an energy efficient and eco-friendly alternative for the space heating of Chinese rural buildings in cold climates.

Simulation study on the system performance of solar-ground source heat pump using return water of the district heating network as supplementary heating

In order to mitigate the extreme climate change and improve the utilization of renewable resources, a solar-ground source heat pump system using return water of the district heating network as supplementary heating(SGSHP-DHNSH)has been proposed. This system compared with parallel and series connections of solar assist ground source heat pump systems for simulation and analysis. The results indicate that the SGSHP-DHNSH system raises the evaporation temperature, demonstrates a high rate of renewable energy utilization, and efficiently stores heat within the buried pipes. Notably, the soil temperature in the SGSHP-DHNSH system experiences only a 0.16 °C decrease, which represents reductions of 8 % and 9.8 % compared to the series and parallel systems, respectively. Furthermore, the system COP demonstrates a commendable improvement of 20 % and 13.7 %, the evaporator inlet temperature is higher than the series and parallel systems by 6.7 °C and 5.3 °C, respectively. Moreover, the total energy consumption throughout the heating season stands at 63 MW h, reflecting a substantial 24 % and 19 % reduction in comparison to the series and parallel systems, respectively. The SGSHP-DHNSH system plays a crucial role in improving the utilization rate of renewable resources and alleviating the soil heat imbalance caused by ground source heat pump operation.

Study on optimization of winter operation characteristics of solar-ground source heat pump in Shanghai

The operational characteristics of the combined solar-ground source heat pump system (referred to as SGSHPS) are influenced by local solar resources, climate characteristics, and operating modes. This paper aims to study the operational characteristics of SGSHPS in Shanghai under different operation modes, providing a reference for engineering applications of SGSHPS.Three operation modes were selected for this study: operation of the soil source heat pump, tandem operation mode 1, and tandem operation mode 2. The tandem operation mode 1 represents the heat pump source-side outlet fluid passing first through the buried pipe and then through the thermal storage tank, The tandem operation mode 2 represents the heat pump source-side outlet fluid passing first through the thermal storage tank and then through the buried pipe. The highest system COP was experimentally measured for tandem mode 1. TRNSYS software was used to construct the three oeration modes and obtain parameters such as unit COP, system COP, and buried pipe heat exchange.By comparing and analyzing the winter typical january month average system COP values obtained from experiments and simulations for each operation mode, The maximum error between the experimentally derived conclusions and the simulated conclusions is 9.9 %. The winter typical month january average system COP for the operation of the soil source heat pump was 3.26, while for tandem mode 1 it was 3.5, and for tandem mode 2 it was 3.44. Tandem mode 1 exhibited a 7 % higher system COP compared to the operation of the soil source heat pump, and a 1.7 % higher system COP compared to tandem mode 2. This indicates that the tandem operation of the solar-ground source heat pump is more energy-efficient than the operation of the soil source heat pump system. Therefore, tandem mode 1 is considered the optimal operating mode for SGSHPS in Shanghai during winter.

Analysis of the operation performance of a hybrid solar ground-source heat pump system

The operational performance of a hybrid solar ground source heat pump (HSGSHP) system built at the Hebei University of Technology and composed of a ground source heat pump (GSHP) system and a solar-assisted ground source heat pump (SAGSHP) system is investigated in this work. For the GSHP system, the coefficient of performance (COP) of heat pump unit and system of the GSHP system varies from 4.59 to 5.07 and 3.87 to 4.28, respectively, in the cooling seasons from 2012 to 2016. During the heating season, the COP of heat pump unit and system of the GSHP system varies from 4.59 to 5.07 and 3.87 to 4.28, respectively. The annual COP of heat pump unit and system of the GSHP system increases from 3.19 to 4.18 and 3.03 to 3.63, respectively. For the SAGSHP system, solar space heating can improve performance by nearly 79.0%. For the HSGSHP system, increasing the proportion of the heat supply of the SAGSHP system within a certain range can effectively improve the COP of the HSGSHP system in the heating season. The results show that solar space heating can improve the performance of the HSGSHP system by nearly 25.8%.

Thermal behavior of a combi-storage in a solar-ground source heat pump system for a single-family house

Experimental investigations on thermal behavior of a combined solar and ground source heat pump (SGHP) system for a single-family house are presented. The SGHP system was installed at the Lyngby campus of Technical University of Denmark. Detailed experiments were carried out on the system in 2019 under real weather conditions covering domestic hot water (DHW) consumption and space heating (SH) demand. Depending on the contributions of the energy inputs to the combi-storage, five typical daily operation modes are classified. The focus of the investigations is on the dynamic thermal behaviors of the heat storage under different operating conditions. When the combi-storage was primarily heated by solar energy, the inlet stratifier in the storage performed well, ensuring thermal stratification and a good utilization of solar energy. Water temperature in the storage reached up to about 68℃ at the end of the solar heating process. When the combi-storage was primarily heated by the ground heat, the water temperature near the outlet for SH was kept at a temperature range from 26℃ to 31℃ in the heating process to ensure the outlet temperature level of SH, and the water temperature near the outlet for DHW was in the temperature range 47℃∼51℃ in DHW volume. When there was no heat input to the combi-storage, the pre-stored heat can meet the daily heating demand, and the number of days on this mode was up to 9.4% of the total experimental days. The paper gives valuable inputs for researchers and engineers who plan to integrate the combi-storage in a renewable heating system with solar collectors and ground source heat pumps.

Study on solar-ground source heat pump and combined heating system in severe cold area

This paper studies the operation strategy and economy of solar-ground source heat pump gas heating system in severe cold region. Two operation modes of the system are introduced: series operation and parallel operation, and the two operation modes are simulated. This paper compares and analyses the heat exchange of the ground pipe, the change of the water temperature at the inlet and outlet of the ground pipe heat exchanger, the heating efficiency coefficient cop and the refrigeration efficiency coefficient EER of the heat pump unit during the five-year operation of the combined heating system, and studies the change of the soil temperature, Finally, the economic analysis is made from the initial investment cost and operation cost of two different heating schemes. The results show that the maximum heat transfer efficiency of the parallel system is 2.5 times that of the serial system, and the total heat transfer between the parallel system and the heat network is 83.2 % higher than that of the serial system. The inlet and outlet water temperature of the buried pipe decreased under both operation modes. After five years of operation, although the operation cost of the parallel combined heating system is higher than that of the serial combined heating system, the parallel combined heating system has more advantages than the serial combined heating system in terms of the overall heating effect of the system and the influence degree of the system on soil temperature.

Experimental performance evaluation and parametric study of a solar-ground source heat pump system operated in heating modes

The dual heat source coupling modes of solar-ground source heat pump system (SGSHPS) directly determine its operation characteristics. In this paper, the thermal performance of a SGSHPS operated in different dual heat source coupling modes were studied experimentally. The unit COP, solar collecting efficiency and inlet and outlet temperatures of GHE were tested for various modes. The results show that for the combination operation mode, solar and ground heat source are dynamically coupled by the water tank and plate heat exchanger, and the average unit COP and collecting efficiency are 3.61 and 51.5%, respectively. For the water tank heat storage mode, the inlet water temperature of evaporator in the daytime stop mode of GSHP is 1.85 °C higher than daytime operation mode of GSHP, and the average unit COP and collecting efficiency are respectively 3.43 and 34.8%, 3.91and 34.9% for the daytime stop mode of GSHP and daytime operation mode of GSHP. For the ground heat storage mode, the ground temperature can be improved effectively for ground continuous heat storage mode and the outlet temperature of GHE can be increased significantly for ground intermittent heat storage mode. The average unit COP and collecting efficiency are 3.65 and 47.9%, 3.8 and 41.5% for the ground intermittent and continuous heat storage mode, respectively. A TRNSYS dynamical simulation model of the SGSHPS was established to explore the influences of key parameters on the system performance. The results indicate that the collector area and GHE number have evident influences on the system efficiency, but the impact of water tank volume is very small. The suitable collector area and GHE number are found to be 80 m2 and 9, respectively, and the water tank volume should be set as small as possible with the permission of actual conditions.

Optimization design and compare of different solar-ground source heat pump system of office building in cold regions

This paper presents two different operation modes of Solar-Ground Source Heat Pump System (SGSHP(S)). With the simulation tool TRNSYS, two different SGSHP system models were built to taking simulation. After making analysis and compare of different simulation results, series operation mode was believed to be better than parallel in the target building.

MULTI-ENERGY COUPLING SYSTEM BASED ON PLC AND WINCC

The development and utilization of multi-energy coupling platform has been completed by the software of Siemens S7-200 and configuration software WinCC. PLC of Siemens is used to collect temperature, flow rate, quantity of heat, power, etc. and calculate the COP of heat pump and the system. The detecting system is composed of the slave computer PLC and the host computer WinCC. The real-time monitoring and control function are realizedbythis system.And six operational modes of the solar-ground source heat pump system are designedaccording to different external conditions, which is an effective way to make up the shortcomings of the solar energy and GSHP (Ground Source Heat Pump) individually.

Experimental investigations of the performance of a solar-ground source heat pump system operated in heating modes

Solar-ground source heat pump system (SGSHPS) is a new type of high efficiency, energy saving and environmental protection air-conditioning technology. In this paper, experimental studies and numerical simulation on the performance of a SGSHPS operated in different heating modes were carried out. The experimental system was installed in Nanjing of China and solar collectors were coupled with ground heat exchangers (GHE) through an insulated water tank. Four operation modes including ground source heat pump (GSHP), combined operation mode, day and night alternate operation mode and solar U-tube feeding heat alternate operation mode were investigated during winter season. The heat pump performance, solar collecting performance and borehole wall temperature variations were analyzed and compared for various modes. The experimental results indicate that for the combined operation mode, the system operation efficiency during day can be improved by the assistance of solar energy, and the excess solar energy collected during day can be stored in ground by the GHE to improve the operation performance of GSHP during night. The proportions of heat source burdened by solar and geothermal energy are 43.3% and 50.2% respectively. For the alternate operation modes, the temperature resumption of ground surrounding the GHE can be well achieved due to the intermittent heat extraction of GHE or feeding solar heat into ground and thus the overall utilization efficiency of solar and geothermal energy can be improved greatly. During the whole experimental period, the average COPs are 2.37 and 2.72 for GSHP and SAHP operation mode respectively, and the corresponding parameters are 2.69, 2.65 and 2.56 for the combined operation mode, day and night alternate operation mode and solar U-tube feeding heat alternate operation mode, respectively. The average solar collecting efficiency are 43.6%, 47.3% and 38.8% for the combined operation mode, SAHP operation mode and solar U-tube feeding heat operation mode, respectively. Based on the unit modeling, a dynamic simulation program was constructed to investigate the seasonal performance of the SGSHPS operated in different heating modes, the simulation results show that the seasonal average COP are 3.67, 3.64, 3.52 and 3.48 for the combined operation, day and night alternate operation, solar U-tube feeding heat and GSHP mode, respectively. From the view of improving the overall efficiency and increasing heat source fraction of solar energy, the combined operation mode is the best.

Experimental Study of A Solar Assisted Ground Source Heat Pump for Heating

researchers in order to analyze the performance of solar-ground source heat pump systems, while most studies are performed by theoretical and simulation means, the studies related to experiment are few in numbers. The lack of experimental data of solar-ground source heat pump system leads to weak awareness of operating performance. Therefore, it is important for mastering the operating performance to do the experimental study on solar-ground source heat pump system. The objective of this study is to experimentally analyze the performance of solar assisted ground source heat pumps by using a solar-ground source heat pump hybrid system in the city of Ningbo, then obtained the variation of operating performance of SAGSHP, and verified the heating performance of solar assisted ground source heat pumps is better than ground source heat pump. SAGSHP for heating is feasible in technology.

Performance evaluation and optimization of a novel solar-ground source heat pump system

This paper presents a novel solar-ground source heat pump system (SGSHPS) designed for an office building in Beijing for heating, cooling, and producing domestic hot water. An operation strategy of the system in transition seasons is proposed to keep the heat pump off and connect ground heat exchanger (GHE) directly to the heat exchangers of fan coils, as indoor conditioning terminal equipment. With the simulation tool TRNSYS, the important parameters of the system were optimized and the operation strategy was shown to be feasible. Two mainstream operation plural strategies in winter were analyzed and compared, and the system with GHE and solar collectors installed in series (SGSHPS(s)) showed better performance than SGSHPS(r) in cold regions.

Thermal Contribution Rates of Double-Heat Sources of the Direct-Expansion Solar-Ground Source Heat Pump System in Hot Summer and Warm Winter Area

According to the energy-consuming characteristics of buildings in hot summer and warm winter area, a direct-expansion solar-ground source heat pump system is put forward. This system runs the direct-expansion solar heat pump system in summer and direct-expansion solar-ground source heat pump system in transition season and winter to produce hot water. The article analyses the thermal contribution rates of double-heat sources of the system under various working conditions in different seasons. Results indicate that the total area of solar evaporators matches the power of units and the matching value is 2.18m2/kW. When the average daily total solar radiation is 15.8MJ/m2 in summer, 11.2MJ/m2 in transition season and 11.2MJ/m2 in winter, the unit area heat transfer are respectively about 1.48kW/m2, 1.1kW/ m2 and 0.43kW/m2. The annual solar thermal contribution rate is 46.4% and the annual soil thermal contribution rate is 32%, which can reduce 57.96% quantity of heat absorbing from the soil.

Seasonal Underground Storage of SGSHP System Design Based on Equilibrium Geothermal Temperature

Constant geothermal temperature is necessary to the long-term efficient operation of the ground source heat pump. SGSHP (Solar-Ground Source Heat Pump) system adopts solar energy as assistant heat source to maintain the geothermal temperature in cold regions. A design method based on equilibrium geothermal temperature was illustrated with an example of a villa in Beijing, China. Flowchart and control strategy of the combined system were introduced. Average heat collection efficiency and necessary area of the solar collector were derived on the basis of energy balance equation. Geothermal temperature variation was also researched to test if the solar energy and geothermal energy were reasonably matched. Results show that the combined system can maintain a constant geothermal temperature if it is well designed. The solar-ground source heat pump system is efficient, reliable and energy-saving.

A multi-integrated renewable energy system in a commercial building in Beijing: lessons learnt from an operating analysis

In this case study, calculations and analyses were performed mainly for a solar-ground source heat pump system using a newly built office–factory building. Calculations for the collector panels, the water heater system and the saving for natural lighting system were also performed. Results have shown that the energy consumption in ground source system is 34.1% more efficient than that of air source system in normal days in winter. The required data for the calculations were measured using calorimeters and electricity meters which form part of the building automation system (BAS). The BAS works through a direct digital control system. On the basis of the observation and research on the actual operation, suggestions related to the design, operation and inspection are given. Copyright , Oxford University Press.

Performance prediction of a hybrid solar ground-source heat pump system

This paper presented a novel hybrid solar GSHPS (HSGSHPS) composed of a GSHPS and a solar assisted GSHPS (SAGSHPS) used in an office building for heating and cooling. The key issues of designing the HSGSHPS were introduced and a simulation model was developed in TRNSYS to predict the multi-year performance of this system. The simulated results showed that the proposed HSGSHPS was reasonably designed to resolve the ground temperature imbalance problem on an annual basis. The suitable control strategy for the solar collection and storage was found according to the coefficient of performance (COP) of SAGSHPS. The first-operation time has impact on the operation of SAGSHP and GSHPS. Injection of thermal energy into the borehole heat exchanger (BHE) or borehole thermal energy storage (BTES) before the heat extraction from BHE/BTES was favourable to the overall COP of system. It is very important to SAGSHPS to store sufficient solar thermal energy in the BTES because of its small spacing between boreholes. 32% of the electrical energy consumption in the HSGSHPS could be saved if the load circulation pump was turned off when no fan-coil was running, rather than always keeping it running at all times.

Energy analysis of a solar-ground source heat pump system with vertical closed-loop for heating applications

A heat pump system is the ideal way to extend the heat supply of existing oil or gas fired heating system. Consumption costs are lowered through the use of free energy from the environment, and the dependence on fossils fuels simultaneously reduces. In order to investigate the performance of the solar-ground source heat pump system in the province of Erzurum having cold climate, an experimental set-up was constructed. The experimental apparatus consisted of solar collectors, a ground heat exchanger (GHE), a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement equipments. In this study, the performance of the system was experimentally investigated. The experimental results were obtained from October to May of 2008–2009. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP) and the system performance (COPS). The coefficient of performance of the heat pump and system were found to be in the range of 3.0–3.4 and 2.7–3.0, respectively. This study also shows that this system could be used for residential heating in the province of Erzurum being a cold climate region of Turkey.

Numerical Simulation of Solar Ground-Source Heat Pump with Latent Heat Storage

Solar ground-source heat pump (SGSHP) system is unsteady when used to heating. Latent heat storage tank (LHST) was used appropriately in which phase change material (PCM) - CaCl2•6H2O was encapsulated in plastic kegs setting on the serpentine coil. PCM which was as controlling unit of the phase change heat transfer model were solved numerically by an enthalpy-based finite differences method and was validated by experimental data. In order to reflect the effect of the system, two days were chosen to compare the numerical results with experimental data. Inlet and outlet temperature of the water in the LHST, temperature of PCM and storage & emission heat of LHST were measured. The trends of the variation of numerical results and experimental data were in close agreement. Numerical results can reflect the operation mode of the system very well.

Solar and ground source heat-pump system

Theoretical and experimental studies were performed for a solar-ground source heat-pump (SGSHP) system with a vertical double-spiral coil (VDSC) ground heat-exchanger (GHX). The heating mode of the SGSHP system is alternated between a solar energy-source heat-pump (SSHP) and a ground-source heat-pump (GSHP) using a low-grade energy utilization system built by the authors. The measured performances were for the SSHP, GSHP and SGSHP systems, as well as the ground heat-exchanger (GHX). The heat absorption rate per unit of ground surface area occupied by the GHX is shown to be 18 times greater than a single-pipe horizontal heat-exchanger. The coefficient of performance (COP) of the system with GHX is a 21% improvement over the system with the single-pipe horizontal heat-exchanger. The underground two-dimensional symmetry temperature field of the GHX was simulated using the volume-control method. The analytical results are compared with the experimental data. The mathematical model presented herein may provide design guidance for the design of a GHX for GSHP systems. The heat-output performance of a solar collector, which was used for a solar-ground source heat-pump with the heating mode, is also predicted. Valuable numerical results were obtained in the experimental study of the real SGSHP system.