Solar-assisted Ground-source Heat Pump System Research Articles

Performance Study of a Hybrid Solar-Assisted Ground-Source Heat Pump System Used for Building Heating and Hot Water Demands

Performance Study of a Hybrid Solar-Assisted Ground-Source Heat Pump System Used for Building Heating and Hot Water Demands

Performance of a solar ground source heat pump used for energy supply of a separated building

In order to achieve the carbon peak and carbon neutrality strategy in China, A SAGSHP (solar-assisted ground source heat pump) system is developed and four partition operation schemes of quarterly multi-mode switching buried pipe were designed in this research. Four types of buried pipe interconnection were schemed including central type, N type, H type, diagonal type, and the field tests were conducted. The system performance, soil heat balance, economic characteristics of the SAGSHP system were analyzed and compared with the ASHP&CFB (Air source heat pump & Coal-fired boiler) system. The results show that the energy supply by the SAGSHP system can meet the heating, cooling and domestic hot water needs of separated buildings after adopting the partitioned multi-mode switching operation scheme. Meanwhile, the system's heat loss is decreased, soil heat balance is well maintained, and the system flexibility is improved. The graded use of solar and soil energy is well realized. The COPs of SAGSHP system in heating period and cooling period were 3.62 and 5.76 respectively under the control of the central zoning operation scheme of buried pipes. Solar energy can provide 49.97 % of the total heat supply of the system. Compared with the ASHP&CFB system, the SAGSHP system can save 9.84 t of standard coal after operating 13 years, and the equivalent reductions of CO2, SO2, and dust are 26.568 t, 0.1968 t, and 0.1476 t, respectively. The system economy is the most sensitive to the project's initial cost whereas the least sensitive to electricity prices. The research in this paper provides a feasible alternative for the energy supply of separated office buildings in Chinese the severely cold regions of China.

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%.

Dynamic modeling of solar-assisted ground source heat pump using Modelica

Traditional rural energy sources, such as straw, firewood, and coal are the main energy resources in developing countries; however, these resources are associated with low efficiency and can cause considerable air pollution. With the rapid development of renewable energy worldwide, existing energy frameworks in rural areas need to be urgently transformed. Developing a universal and reliable dynamic modeling framework for multi-source heat pumps remains an unresolved issue. To this end, this paper proposes an integrated energy system based on a solar-assisted ground source heat pump (SGSHP), which can facilitate the utilization of renewable energy, reduce the electricity consumption, and provide demand response (DR) resources in rural houses. A 150-m2 rural house on the outskirts of Shanghai, China was considered as a case building. A novel Dymola modeling framework of an SGSHP system was established, and the heating performance was analyzed. Considering the variation in the energy demand in winter, four practical operation modes were implemented to maximize energy efficiency. The results show that the coefficients of performance of the system are 4.2 and 3.5 with and without solar collectors, respectively. The contributions of solar energy, geothermal heat, and electricity in the system are 27%, 18%, and 55%, respectively. Moreover, approximately 79.6% of AC loads can be shaved during evening peak load time in our proposed energy system.

Energy, economic and emission assessment of a solar assisted shallow earth borehole field heat pump system for domestic space heating in a north European climate

The performance of a solar assisted ground source heat pump (SAGSHP) system was evaluated and compared with a conventional gas boiler system using simulation, for a central England location. The earth energy bank was the long-term heat store element of the system and consisted of a very shallow field (1.5 m deep) of borehole heat exchangers (BHE). The mathematical model of the system was formulated, and parametric analyses were carried out by varying the number of BHEs and their spacing. The energy performance was expressed using four energy metrics, while its economy and CO2e emissions were compared with a natural gas boiler (NGB) system via the life cycle cost method and the fractional CO2e savings, respectively. The system can be energy self-sufficient by installing 40 BHEs at 1.25 m spacing or with 32 BHEs at 1.5 m spacing. The NGB system appears more economic than the SAGSHP system, due to low natural gas prices, the high price of the imported electricity, the low price of the exported electricity and the higher capital cost of the SAGSHP system. However, the SAGSHP system was found to have net negative carbon emissions, in contrast to the high positive emissions of the NGB system.

Solar-assisted ground source heat pump system operated in heating mode: A case study in Tunisia

The endeavor of this paper is to investigate the feasibility of a solar-assisted ground source heat pump (SAGSHP) system for space heating in the climatic condition of Northern Tunisia. Therefore, an experimental set-up was installed and tested in the Research and Technology Center of Energy. The SAGSHP system consists of a ground source heat pump (GSHP) system with a horizontal ground heat exchanger and a buried tank, buried both 1 m deep, and a solar flat-plate collector (SFC) with an area of 2 m2 as an auxiliary heat source. Two configurations are set and technically evaluated: (a) space heating by SFC only, and (b) SAGSHP. The results show that: (a) standalone SFC for heating increases the indoor air temperature by about 3 °C, but it cannot guarantee thermal comfort (22 °C), and (b) The tested SAGSHP achieves a significant high performance for space heating.An exergetic analysis proves high performance of the SAGSHP system, in addition an economic evaluation shows good cost-benefit of the SAGSHP system as compared to other conventional heating systems.

Energy and economic evaluation of a solar assisted ground source heat pump system for a north Mediterranean city

In this study, a PVT based solar assisted ground source heat pump (SAGSHP) system was investigated regarding its energy performance and cost-effectiveness for the city of Thessaloniki (Greece). The SAGSHP system was set to cover the space heating and domestic hot water needs for a low-rise dwelling. A mathematic model formulated in TRNSYS was used with the aim to carry out parametric analysis by varying the number of the PVTs. It is worth noting that, two of the most important components of the employed model, the PVT collector and the geothermal heat exchanger, have already been validated via experimental data. Simulations were conducted and through the results seven energy metrics were estimated, with the objective to examine the system’s energy performance from various perspectives. The SAGSHP system with 16 PVTs was found capable to covering 73% of the heating load and to generate 1.22 times more electricity than that consumed by the system. The electricity yield of PVTs was not affected throughout the parametric analysis, and the maximum specific productivity was estimated at 301.5 kWhe PVT−1 per year. The results suggest that a SAGSHP system equipped with about 14 PVTs can reach energy self-sufficiency. As regards the economics of the SAGSHP system, this was compared with a natural gas boiler system via two methods, the life cycle cost (LCC) and the life cycle savings (LCS). A sensitivity analysis with major economic parameters of the systems was carried out. It was found that the cost-effectiveness of the SAGSHP system is influenced mainly by its capital cost and by the price of the natural gas. Systems equipped with less than 12 PVTs can be cost-competitive by subsiding from 8% up to 42% of their capital cost. Also, system with more than 12 collectors were found of more benefit than the smaller ones, in the case where feed-in-tariff schemes are applied, or the bank loan’s interest rate is low. It can be concluded that, the proposed system can be an attractive monetary solution for covering the heating load in comparable dwellings with a similar climate to Thessaloniki.

Low-energy opportunity for multi-family residences: A review and simulation-based study of a solar borehole thermal energy storage system

The multi-family residential building sector is the least energy efficient in the United States, thus allowing for ample opportunities for significant cost-effective energy and carbon savings. In the present study, we propose a district solar borehole thermal solar energy storage (BTES) system for both retrofit and new construction for a multi-family residence in the Midwestern United States, where the climate is moderately cold with very warm summers. Actual apartment interval power and water demand data was mined and used to estimate unit level hourly space and water heating demands, which was subsequently used to design a cost-optimal BTES system. Using a dynamic simulation model to predict the system performance over a 25-year period, a parametric study was conducted that varied the sizes of the BTES system and the solar collector array. A life-cycle cost analysis concluded that is it possible for an optimally-sized system to achieve an internal rate of return (IRR) of 11%, while reducing apartment-wide energy and carbon consumption by 46%. Both a stand-alone and solar-assisted ground-source heat pump system were designed and simulated for comparison to the BTES system, and found to be less economically favorable than the solar BTES system. Thus, the promise for district-scale adoption of BTES in multi-family residences is established, particularly for new buildings.

A novel solar-assisted ground-source heat pump (SAGSHP) with seasonal heat-storage and heat cascade utilization: Field test and performance analysis

To maintain the energy quality with high temperature and reduce the energy loss of seasonal heat-storage in solar-assisted ground-source heat pumps (SAGSHPs), a novel SAGSHP system with the heat-cascading of borehole heat-exchangers was designed and its field-test was conducted in this paper. The borehole heat-exchangers were divided into two regions: the core region and the peripheral region. The core region can maintain a high temperature (e.g. 45 °C), which is much higher than in previous studies, and the heat from this region can be used directly, without the operation of a heat pump. A field-test was conducted in a community in the province Shandong, China. The results indicate that a sufficient soil-temperature gradient (the temperature is high in the core but low at the periphery) can be created and maintained. The monthly averaged borehole-wall-temperature difference between the borehole heat-exchangers (BHEs) at the core and the periphery can be as high as 30.1 °C. This means that both cascaded heat-storage and heat-utilization can be realized. In addition, an average performance of CCOP = 5.15 and SCOP = 4.66 can be achieved. Compared with previous studies, despite the lower CCOP, a higher SCOP can be attained, thanks to heat cascade storage and -utilization. The novel approach described in this paper represents a viable alternative for space heating in North China.

Simplified method to determine the collector area of solar-assisted ground-source heat pump system

This paper mainly presents the numerical simulation on the long-term performance of a solar-assisted ground-source heat pump (SAGSHP) system for heating and cooling in a commercial building in cold areas of China. A simplified method of determining the optimal solar collector area of the SAGSHP system was proposed based on the yearly heat balance of the ground in the storage volume and the system economy. The verification of the system design is carried out by TRNSYS and a numerical simulation is performed for continuous operation of 10 years under the meteorological conditions of Dalian. Simulating results show that the underground load imbalance problem for a heating load dominated ground-source heat pump (GSHP) system is solved by soil recharging in the transition season, and the average temperature of ground in the storage volume keeps nearly unchanged at the end of every year.

Study on the methods for predicting the performance of a hybrid solar-assisted ground-source heat pump system

It is critical to find suitable setting parameters for designing a hybrid solar-assisted ground-source heat pump system in the practical engineering application, but the heat pump performance is unpredictable after many years of operation. This paper used 2000 sets of performance data collected from solar-assisted GSHP systems that keep operating over 20 years to simulate long term used heat pump with a professional software called GeoStar. Adopted the classification and regression tree (CART) method, the design of solar energy collector areas can be predicted. The multi-linear regression is also utilized to predict average monthly per meter borehole heat exchange. Seasonal factor decomposition and exponential smoothing are used to analyze the average monthly temperature of the circulating fluid, circulating fluid inlet and outlet temperatures of the heat pump after 20 years when we perform the time series prediction. Experimental results demonstrate that CART, multi-linear regression, seasonal factor decomposition and exponential smoothing are promising for practical applications.

Simulation of the thermal performance of a hybrid solar-assisted ground-source heat pump system in a school building

ABSTRACTA hybrid solar-assisted ground-source heat pump (SAGSHP) system was designed, in the frame of an energy upgrade study, to serve as a heating system in a school building in Greece. The main scope of this study was to examine techniques to reduce the capacity of the heating equipment and to keep the primary energy consumption low. Simulations of the thermal performance of both the building and of five different heating system configurations were performed by using the TRNSYS software. The results are presented in this work and show that the hybrid SAGSHP system displays the lower primary energy consumption among the systems examined. A conventional ground-source heat pump system has the same primary energy consumption, while the heat pump’s capacity is double and the ground heat exchanger 2.5 times longer. This work also highlights the contribution of simulation tools to the design of complex heating systems with renewable energy sources.

Energy End-use and Grid Interaction Analysis of Solar Assisted Ground Source Heat Pumps in Northern Canada

This paper presents an analysis conducted on a ground source heat pump (GSHP) system coupled with evacuated tube solar thermal collectors to reduce the borefield size in Northern Canada. The annual energy consumption, utility costs, grid impact, greenhouse gas emissions, and economics of a solar assisted GSHP system are compared to several conventional and heat pump (HP) space heating, cooling and domestic hot water systems for mid-rise apartment buildings located in Whitehorse, YK and Yellowknife, NT. In both regions the solar assisted GSHP system demonstrated energy savings over a conventional space heating system, while successfully overcoming an annual ground energy imbalance and reducing the required borefield size. From a grid perspective, although the HP systems shifted the space heating fuel source from fuel oil to electricity, the solar thermal system is able to help minimize the use of inefficient auxiliary heat to meet the space heating loads. The high associated capital costs of a GSHP system coupled with a solar thermal system make the economics difficult to justify; however for regions where energy security is of high importance, the energy savings achieved with these systems can have a substantial impact.

Heat Imbalance Analysis of a Hybrid Ground-Source Heat Pump System

Operating data in the last two years of a hybrid ground-source heat pump system (HGSHPS) were analyzed, and were contrasted to TRNSYS simulation results. Heat extraction from the borehole heat exchanger (BHE) of ground-source heat pump system (GSHPS) was too much larger than the heat injection, but heat extraction from the borehole thermal energy storage (BTES) of solar assisted GSHPS (SAGSHPS) was too less than the heat storage, in 2012. Serious problem of heat imbalance of BHE occurred, and the GSHPS almost could not work in the late heating season of 2012. An adjusted operating strategy was utilized in 2013. The ground temperature imbalance for GSHPS and heat excess for SAGSHPS were resolved. It is important to monitor the operation of HGSHPS to resolve the heat imbalance problem.

Experimental performance analysis of a solar assisted ground source heat pump system under different heating operation modes

This paper presents an experimental study on the influence of operation modes on the heating performance of a solar assisted ground source heat pump system (SAGSHPS). Through experiments conducted in January, the characteristics of the SAGSHPS were investigated under different heating operation modes. The results indicate that the solar thermal could be used to accelerate the soil recovery when the heat pump unit is turned off, but the duration of solar use to recharge boreholes should be optimized according to the water temperature in the solar heat storage water tank to avoid unnecessary power consumption of the circulation pump. In addition, the solar heat storage water tank is beneficial for the stable operation of the SAGSHPS. The volumetric flow rate in the water tank has a significant impact on the electricity consumption of the SAGSHPS. From comprehensive analysis of the integral effect of the SAGSHPS under different modes, the mode in which the water tank is connected with the ground heat exchangers (GHES) in series is the recommended mode for the SAGSHPS in the coldest month in Dalian.

Optimization of solar assisted ground source heat pump system for space heating application by Taguchi method and utility concept

In the present research, a methodology is proposed to optimize the solar collector area and ground heat exchanger length for achieving higher COP of Solar Assisted Ground Source Heat Pump (SAGSHP) system using Taguchi method and utility concept. Four operating parameters for solar collector and four parameters for ground heat exchanger have been selected with mixed level variation using an L18 (21, 37) orthogonal array. The key parameters such as solar collector area, ground heat exchanger length and COP of the SAGSHP system are optimized to predict the best levels of operating parameters for maximum COP of SAGSHP system. Lower the better concept has been used for the solar collector area and ground heat exchanger length whereas higher the better concept has been employed for the COP of SAGSHP system and the results have been analyzed for the optimum conditions using signal-to-noise (SN) ratio and ANOVA method. Computations were carried out for 18 experimental trial runs by considering 2ton heating load in winter season. The optimum COP for SAGSHP was estimated to be 4.23 from the utility concept, which is 8.74% higher than the optimum COP predicted by Taguchi optimization. Optimization of solar collector area and ground heat exchanger length by the utility concept has shown only about 2.3% reduction in area and 1.6% reduction in length respectively compared to those values optimized by the Taguchi method.

Experimental investigation on system with combination of ground-source heat pump and solar collector

This paper presents the heating performance and energy distribution of a system with the combination of ground-source heat pump and solar collector or a solar-assisted ground-source heat pump system (SAGSHPS) by calculation and experiment. The results show that the average absolute error is less than 0.6 °C and the relative error is less than 5% under the pulse load when the analytical solution to the 2-D solid cylindrical source model is used for the SAGSHPS. The coefficient of performance (COP) of the SAGSHPS is 2.95–4.70. The average fluid temperature in the borehole heat exchanger can increase by 3 °C with the assistance of solar collector, which will improve the COP of the heat pump by approximately 10% from the experimental data. The energy contributions to the total heating load of soil, electricity and solar are 56.30%, 36.87% and 6.83%, respectively.

Simulation of embedded heat exchangers of solar aided ground source heat pump system

Aimed at unbalance of soil temperature field of ground source heat pump system, solar aided energy storage system was established. In solar assisted ground-source heat pump (SAGSHP) system with soil storage, solar energy collected in three seasons was stored in the soil by vertical U type soil exchangers. The heat abstracted by the ground-source heat pump and collected by the solar collector was employed to heating. Some of the soil heat exchangers were used to store solar energy in the soil so as to be used in next winter after this heating period; and the others were used to extract cooling energy directly in the soil by circulation pump for air conditioning in summer. After that solar energy began to be stored in the soil and ended before heating period. Three dimensional dynamic numerical simulations were built for soil and soil heat exchanger through finite element method. Simulation was done in different strata month by month. Variation and restoration of soil temperature were studied. Economy and reliability of long term SAGSHP system were revealed. It can be seen that soil temperature is about 3 °C higher than the original one after one year’s running. It is beneficial for the system to operate for long period.

06/00781 Performance analysis of a solar-assisted ground-source heat pump system for greenhouse heating: an experimental study: Ozgener, O. and Hepbash, A. Building and Environment, 2005, 40, (8), 1040–1050.

This paper investigates the techno-economic feasibility of geothermal deep direct-use for heating, cooling, and thermal energy storage in the United States. The six 2017–2019 deep direct-use projects funded by the U.S. Department of Energy are reviewed and evaluated using the simulation tool GEOPHIRES, and results are compared with prior studies, existing geothermal district heating systems in Europe and the United States, as well as non-geothermal centralized and non-centralized heating, cooling, and thermal energy storage systems. Analysis indicates that deep direct-use feasibility varies widely, depending on subsurface characteristics, system design, and financial conditions. Project base case levelized cost of heat values ranged between $13 and $350/MWh; key drivers lowering the levelized cost of heat include higher reservoir temperatures, shallower reservoir depths, higher well flow rates, higher utilization rates, lower drilling costs, and lower discount rates. Incentives such as grants and an investment tax credit resulted in small improvements in project economics. Base case levelized cost of heat values for four projects fell within the range of levelized cost values for existing systems in Europe and the United States, and were comparable to values found in previous studies, including the 2019 GeoVision study. The lowest-cost projects for district heating had comparable levelized cost of heat values to existing fossil-fuel-driven district heating systems, and lower values than decentralized heating with natural gas boilers or heat pumps. Chilled water production with absorption chillers driven by a high-quality geothermal resource obtained attractive levelized cost of cooling values, in line with values from typical centralized cooling production facilities and lower than domestic decentralized cooling with air-conditioning units. Also, thermal energy storage is a potential deep direct-use application, where levelized cost of storage values can be obtained that are comparable to those of other thermal storage techniques such as borehole thermal energy storage and hot water storage tanks. Other aspects of deep direct-use, which are not captured in a standard levelized cost of energy metric, include the ability to decarbonize the heating and cooling supply, and provide reliability and resiliency to the energy infrastructure. These attributes are gaining increased attention and improve overall project feasibility. Finally, this paper identifies technical, market, policy, and social barriers for deep direct-use development in the United States, and provides potential approaches for reducing these barriers.

05/02782 Experimental investigation of the performance of a solar-assisted ground-source heat pump system for greenhouse heating

05/02782 Experimental investigation of the performance of a solar-assisted ground-source heat pump system for greenhouse heating