Hybrid Ground Source Heat Pump Research Articles

Heat exchange performance of an energy-pile group in a hybrid GSHP system and effects of pile spacing

In long-term operations, seasonal imbalance in the thermal load may adversely affect the heat transfer performance of the energy piles, potentially resulting in thermal accumulation within the ground and eventual system failure. The heat transfer performance of energy pile systems during long-term operation under unbalanced thermal loads must be investigated. Moreover, the design parameters of energy piles are usually constrained by the requirements of foundation structural design, resulting in energy piles being densely arranged. Hence, the influence of pile spacing on the heat exchange performence of energy piles must be comprehensively understood. In this study, two- and three-dimensional energy-pile heat transfer models were established and innovatively coupled based on an engineering project currently under design. Numerical simulations were performed to investigate the heat transfer behavior of energy-pile groups subjected to unbalanced thermal loads and the effect of pile spacing on their heat exchange performance. Furthermore, design recommendations regarding the determination of the proportion of thermal loads to be borne by the energy piles in a hybrid GSHP system were provided. The results indicate that the proposed 2D-3D coupled modeling approach is able to simulate the heat exchange performance of large-scale energy pile groups. Pile spacing considerably affects the long-term thermal performance of energy-pile groups, especially in cases with small pile spacings. The influence of pile spacing on the heat exchange capacity of energy piles can be considered in the design phase by incorporating a group effect coefficient η, which are calculated to be 0.165, 0.470, 0.732, and 1 for pile spacings of 2 m, 4 m, 6 m, and 10 m, respectively.

Implementation of Adaptive Network-Based Fuzzy Inference for Hybrid Ground Source Heat Pump

Implementation of Adaptive Network-Based Fuzzy Inference for Hybrid Ground Source Heat Pump

Feasibility and investigation of residential HVAC system with combined ground source heat pump and solar thermal collectors in different climates of Iran

Geoexchange is one of the most energy-efficient, environmentally clean, and cost-effective space-conditioning systems available on the market. Seasonal storage of solar energy in geothermal boreholes is sharply interesting as a means of heating and cooling in buildings with different applications. In this study, a closed-loop geo-exchange and solar thermal system with two different heat exchangers are examined in an energy-efficient house. TRNSYS, a simulation software tool, was used to model the yearly performance of the hybrid ground-source heat pump (GSHP) system. Two different types of ground heat exchangers, e.g., tube-in-tube and U-tube were employed. The mass flow rate through the heat exchangers and the solar collector was examined to choose the best scenario for each of them. The economic benefits of a gray water heat recovery system and solar collector were studied; the results show that 517 and 536 US Dollars/Year can be saved from each of them, respectively. System performance analysis was carried out in different cities with various climates in Iran. Moreover, a complete economic assessment was evaluated for all cases. The results show that for the same inlet water temperature to GSHP, the tube-in-tube heat exchanger can pass 45% more flow than the U-tube heat exchanger for the same size as the HP. Furthermore, in the absence of the solar collector, a 2.7 × 108 kJ increase was conducted in the auxiliary heater component yearly. Finally, four different climates were evaluated for the launching of the GSHP system with a solar thermal collector. The hot and dry climate with 27 °C fluid inlet to a heat pump, a total borehole depth of 220 m, and an initial cost of $ 25,047 was selected as the most appropriate weather conditions for launching the system in Iran.

Design of High-Performing Hybrid Ground Source Heat Pump (GSHP) System in an Educational Building

Underground thermal imbalance poses a challenge to the sustainability of ground source heat pump systems. Designing hybrid GSHP systems with a back-up energy source offers a potential way to address underground thermal imbalance and maintain system performance. This study aims to investigate different methods, including adjusting indoor heating and cooling setpoints and dimensioning air handling unit (AHU) cooling coils, heat pump and borehole field, for improving the long-term performance of a hybrid GSHP system coupled to district heating and an air-cooled chiller. The system performance, life cycle cost and CO2 emissions were analyzed based on 25-year simulations in IDA ICE 4.8. The results showed studied methods can significantly improve the hybrid GSHP system performance. By increasing the AHU cooling water temperature level and decreasing indoor heating and cooling setpoints, the ground thermal imbalance ratio was reduced by 12 percentage points, and the minimum borehole outlet brine temperature was increased by 3 °C in the last year. However, ensuring long-term operation still required a reduction in GSHP capacity or an increase in the total borehole length. The studied methods had varying effects on the total CO2 emissions, while insignificantly affecting the life cycle cost of the hybrid GSHP system.

Development of a group control strategy based on multi-step load forecasting and its application in hybrid ground source heat pump

Development of a group control strategy based on multi-step load forecasting and its application in hybrid ground source heat pump

Zoning operation of energy piles to alleviate the soil thermal imbalance of ground source heat pump systems

• Zoning operation of energy piles is investigated to alleviate soil thermal imbalance. • Dense heat injection into the central piles can relieve the cold accumulation. • Heat extraction from the outer layer piles can relieve the cold accumulation. • A reasonable strategy is proposed to achieve good system efficiency and reliability. Energy piles have attracted increasing interest for application in ground source heat pumps, because it is environment-friendly, energy-efficient, and without additional drilling cost. However, when there is a large difference between the heating and cooling loads, the system will suffer from a soil thermal imbalance which may further decline the system performance and even cause a system failure. A hybrid ground source heat pump system that integrates auxiliary equipment can solve the problem, however, it needs additional investment and a complicated control strategy. In this paper, the zoning operation of energy piles can effectively improve the temperature recovery ability of soil in the energy pile group and thus alleviate the soil thermal imbalance. Specifically, a heating-dominated residential building in Beijing is selected for a case study, with 144 energy piles arranged in a 12 × 12 layout. An analytical model of the spiral-coil energy pile group with seepage will be adopted, which can consider the groundwater flow, the geometry of spiral coils, and the thermal interaction among different energy piles, achieving high calculation accuracy and fast calculation speed. Based on this analytical energy pile model, a system model will be built to investigate the system performance influenced by different zoning operation strategies. Results show that intensive heat injection into the center of the pile group (Strategy 2 and Strategy 3) or heat extraction from the outer layer of the pile group (Strategy 4) can relieve the cold accumulation. Strategy 2 can relieve the outlet temperature decline from 5.54 °C to 4.46 °C and improve the heating COP from 3.297 to 3.423 compared to the conventional full operation strategy. Although the annual heat pump COP of Strategy 2 is a little lower than that of conventional full operation strategy, Strategy 2 has the shortest unmet heating or cooling time. Therefore, the proposed zoning operation strategy can achieve good system efficiency and excellent system reliability compared to the conventional strategy.

Numerical study on seasonal operation of solar assisted hybrid borehole heat exchange array

The combined use of solar energy and ground-source heat pump system may provide a reasonable solution to the energy crisis and low utilization efficiency of single energy. Herein, a numerical model of a solar assisted hybrid ground-source heat pump (SAHGSHP) system composed of multiple types and lengths of borehole heat exchanger (BHE) array was developed. The effectiveness of this model was validated by experimental data of a SAHGSHP system located in Tongzhou, Beijing. The verified model was used to study the performance sustainability of SAHGSHP system under different seasonal operation modes and its influence on the temperature of rock and soil. It was shown that for different types of BHEs in heat extraction periods of SAHGSHP systems, the outlet temperature decline rate decreases by an average of 2.30%, the temperature decline rate of rock and soil at the reference point under single-season operation decreases by an average of 0.78%, and the temperature increase rate of rock and soil at the reference point under double-season operation increases by an average of 0.53% compared with that of hybrid ground-source heat pump (HGSHP). The results of this study could provide a further understanding for analyzing the seasonal operation mode of SAHGSHP.

Hybrid ground source heat pump system capable of year‐round heating and its application in liquid natural gas vaporization

One of the challenges in using a ground source heat pump (GSHP) system is the long-term increase or decrease in underground temperature due to an imbalance between heat extraction and injection. To eliminate this imbalance, we proposed a hybrid GSHP (HGSHP) system combined with air–water heat exchangers (AWHEs) capable of year-round heating and applied it to the hot water supply for liquid natural gas (LNG) vaporization in a satellite station. In this paper, the authors demonstrate the year-round heating capability of the HGSHP system and the energy conservation benefits of installing the HGSHP system for LNG vaporization. First, a field experimental apparatus was constructed for a gas vaporization system with the HGSHP; thereafter, an experimental proof of gas vaporization was obtained. The experimental results showed that it was possible to stably vaporize liquid nitrogen that was used instead of LNG by supplying hot water at 25°C. Additionally, in the gas vaporization experiment with the HGSHP system in the summer season, the SCOP measured was over ten. A calculation model for the AWHE was then established using the field test data; thereafter, a simulation tool for the HGSHP system was developed by combining it with one for the GSHP system. The simulation results indicated that the average surface temperature of all GHEs in the HGSHP system decreases from first year to second year. However, the average surface temperature of all GHEs stabilizes at a reduced level after the third year. These results indicate that the HGSHP system can operate long-term for year-round heating because the average surface temperature stabilize in the long-term.

Optimal design of a hybrid ground source heat pump for an official building with thermal load imbalance and limited space for the ground heat exchanger

This work presents the optimal design of a hybrid ground source heat pump (GSHP), taking into account thermal imbalance and space limitation for the ground heat exchanger field (GHE), applied to an official building. Once the building loads are calculated and devices selected, experiments carried out from a single vertical borehole obtain the ground thermal characteristics, including a local short-term period function (STGF). From them, the Finite Line-Source (FLS) model simulates the GHE behavior, from decomposing the ground thermal loads in hourly linear steps for 50 years. A set of input variables, such as geometric configuration data of boreholes field, and additional terms associated with this hybrid operation, must be provided to the model. For optimization purposes, a design of experiments (DoE) considers the thermal ground characteristics and input factors, providing both energy savings and the internal rate of return as outputs (objective functions). Pareto's optimal solutions method provides the selected case, considering a compromise between economic and environmental benefits. It has been established for 18 boreholes (rectangular disposition) of 120 m deep, providing a 33.12% energy saving and an internal rate of return of 3.9%, also showing 89% of the total building load supported by the GHE.

A method for fast economic optimization of large hybrid ground source heat pump systems

This paper presents a novel simulation-based method for fast economic optimization of large hybrid ground source heat pump systems. Rapid evaluation of the objective function is achieved by the joint use of previously developed efficient algorithms, including Delaunay triangulation, successive flux estimation and fast spectral convolution. The resulting objective function is concave and composed only of continuous parameters. The global optimal solution of a problem composed of several dozens of boreholes operating over a 30 year time span is found using the Ant Colony Optimization algorithm for continuous domains, and convergence is achieved in under 12 min of computation time. Results show that optimization is key for proposing a financially viable hybrid ground source heat pump project for large commercial buildings. We also show that proper project financing, such as government guaranteed loans, can significantly contribute towards achieving better economic performance. The proposed approach is fast, convergent, practical, and can help promoters present hybrid GSHP projects under a less risky type of business.

Environmental and energy performance assessment of hybrid ground source heat pump coupled with TABS emission system in the EU non-residential building typologies

Hybrid Ground Source Heat Pump (GSHP) coupled with radiant emission system is a storage-integrated renewable HVAC technology. Previous attempts that assessed the potential of such a system either employed steady-state estimates or were limited to a few cases. However, incorporating system and building dynamics is crucial to accurately estimate the GSHP's share in the total final energy delivered to the building, hence its energy performance. This paper assesses the environmental and energy performance of the system in non-residential building typologies in the EU. It provides a robust quantification of its potential in the building sector's clean energy transition. We developed an automated method employing dynamic models to estimate building thermal loads. Parametric archetypes were developed to represent the diverse characteristics of the EU non-residential building stock. The analysis of 94,000 cases showed that the storage-integrated hybrid GSHP system covers more than 50% of the annual energy demand in 55% of the cases. The system reduced annual median primary energy and CO2 emissions by half compared to conventional systems, reaching 25 kWh/(m2.a) and 5 kgCO2/(m2.a), respectively. These results suggest that a significant reduction in CO2 emissions is achievable by implementing storage-integrated hybrid GSHP in the EU non-residential buildings.

Modeling and optimization of hybrid ground source heat pump with district heating and cooling

Hybrid heating systems with ground source heat pumps (GSHP) and district heating and cooling offer flexibility in operation to both building owners and energy providers. The flexibility can be used to make the heating system more economical and environmentally friendly. However, due to the lack of suitable models that can accurately predict the long-term performance of the GSHP, there is uncertainty in their performance and concerns about the long-term stability of the ground temperature, which has limited the utilization of such hybrid heating systems. This work presents a hybrid model of a GSHP system that uses analytical and artificial neural network models to accurately represent a GSHP system's long-term behavior. A method to improve the operation of a hybrid GSHP is also presented. The method was applied to hospital buildings in northern Sweden. It was shown that in the improved case, the cost of providing heating to the building can be reduced by 64 t€, and the CO2 emissions can be reduced by 92 tons while maintaining a stable ground temperature.

Optimal Design of a Hybrid Ground Source Heat Pump for an Official Building with Thermal Load Imbalance and Limited Space for the Ground Heat Exchanger

Optimal Design of a Hybrid Ground Source Heat Pump for an Official Building with Thermal Load Imbalance and Limited Space for the Ground Heat Exchanger

Comparative study of hybrid ground source heat pump in cooling and heating dominant climates

The ground source heat pump system (GSHP) has been an accepted technology to provide energy efficient and renewable air conditioning to the buildings. However, imbalanced heating and cooling load during the winter and summers especially in the regions with heating and cooling dominant climates may degrade the performance of the system over a long-term operation. Hybrid GSHP system which uses supplemental energy sources such as solar panel or cooling tower can balance the imposing load on the ground heat exchanger (GHE) and benefits the system by minimizing the GHE length in short-term and improves the overall performance in long-term. This research presents a study of application of hybrid GSHP system with an intention to compare its applicability in the regions with dominant heating and cooling loads. In this study, a student office and an actual heat pump system in Akita City, northern Japan was modeled in TRNSYS software and was validated using in-situ measured data. The hybrid system which coupled with a supplemental heating and cooling source devices was simulated to test its viability for the different heating and cooling loads in different regions within the country. The results revealed that hybrid system plays an effective role in both climates to balance the load on GHE, keeps constant the soil temperature, and consequently improves the long-term performance. Moreover, in short-term, it can reduce the GHE length and decrease drilling cost based on the meteoroidal condition of the region such as solar radiation. For instance, the GHE length was reduced to around half in cooling dominant region using cooling tower, while it was negligible in heating dominant region.

Energy demand reduction in the built environment using shallow geothermal integrated energy systems: Part II – Hybrid ground source heat pump for building heating

Abstract The research collection aims at finding the various possible opportunities for the effective integration of shallow geothermal energy (SGE) to decrease the energy demand in the built environment and to reduce emission associated with it. The direct utilization of SGE using a ground source heat pump (GSHP) has been reviewed in comprehensive review part I and part II. From the extensive review, it is found that the hybrid GSHP is needed to avoid ground thermal imbalance and peak demand. Hybrid GSHP can adopt various supplemental heat sources and sinks according to the local climatic conditions and the balance of energy demands. The primary focus on the integration of subsystems such as biomass, solar energy (PV, PVT, and collector), phase change material, micro gas turbine, and absorption heat pump with GSHP is presented for heating application. This comprehensive review part III highlights the recent research findings and a potential gap in hybrid GSHP for further research and developments

Feasibility and performance analysis of hybrid ground source heat pump systems in fourteen cities

Ground source heat pump systems (GSHP) for residential building heating, cooling, and hot water are highly energy efficient but capital intensive when sized for peak demands. The use of supplemental sources of energy with GSHP systems enables improved life-cycle economics through the reduction in the size and cost of the GSHP components. This paper investigates the life-cycle economics of hybrid solar-assisted ground source heat pump systems (SAGSHP) using simulations validated from field data. The economics and optimal sizing of SAGSHP systems for heating dominant climates in four locations in Australia and ten locations elsewhere are evaluated in order to explore the suitability and relative merits of SAGSHP systems in a range of heating dominant climates. In locations having high or moderate levels of solar irradiation, high electricity prices, and high or moderate gas prices, SAGSHP systems are shown to have the lowest life cycle cost amongst alternatives, with predicted savings of up to 30%.

Hybrid ground source heat pump system for overcoming soil thermal imbalance: A review

Soil thermal imbalance becomes the main obstacles to the efficient and sustainable operation of ground source heat pump (GSHP) system. There is evidence that hybrid ground source heat pump (HGSHP) system is an advanced alternate to eliminate soil thermal imbalance and improve system performance. Therefore, this paper presents a comprehensive overview of recent developments and applications of hybrid ground source heat pump system, aiming to conclude some valuable remarks and recommendations for the future research in this direction. Based on the difference of cooling or heating load requirements and application areas of GSHP, different types of HGSHP coupled with auxiliary heating source devices, auxiliary cooling source devices, sensible and latent thermal energy storage devices are presented in section 3, section 4 and section 5, respectively. Furthermore, recent progress in control strategies of HGSHP system are summarized and reviewed. Finally, some conclusions and suggestions for the applications of HGSHP system are proposed to provide an overview of HGSHP system and facilitate more extensive applications of HGSHP system.

Determination of the ground source heat pump system capacity that ensures the longevity of a specified ground heat exchanger field

This paper presents an iterative spectral approach for the determination of the maximum heat pump capacity that ensures the longevity of a specified ground heat exchanger field in hybrid ground source heat pump systems. Fast fluid calculation is obtained by spectral convolution of the incremental ground load signal and the ground heat exchanger transfer function. A correction function is used in an iterative scheme to determine the maximum heat pump capacity that maintains fluid temperature within the operation limits. Results show that the maximum capacity is case dependent, and that long-term simulation is important for its determination. The proposed approach is fast, convergent, general and can manage different building load profiles, either balanced or imbalanced, and different heat pump controls.

Optimizing the Operation of a Hybrid Ground Source Heat Pump System Under Uncertainty

Hybrid renewable energy systems that combine conventional heating, ventilation, and air conditioning (HVAC) systems and ground source heat pumps (GSHP) have become an attractive alternative for conventional HVAC systems due to their higher cost and energy efficiency.Furthermore, control strategies that exploit predictive information about weather and building occupants' activity can further reduce the system operating costs. This study proposes a Stochastic Model Predictive Control (SMPC) for hybrid GSHP systems considering the stochastic nature of the building space heating demand. In SMPC, near-optimal control decisions are found for the current and future states of the system through the application of Regression Monte-Carlo techniques. We compare the performance of SMPC to that gained by using setpoint Control (SPC) and Model Predictive Control (MPC) which uses a deterministic forecast. It is found that by taking uncertainty into account via SMPC, the operating cost reduction compared to SPC is approximately equal to half of the cost-optimality gap between SPC and an idealized controller that is represented by MPC with perfect future information. Furthermore, we find that MPC using a forecast based on expected values leads to greater operating costs compared to the simpler SPC strategy when variability and uncertainty are present.

Comparative heating performance evaluation of hybrid ground-source heat pumps using serial and parallel configurations with the application of ground heat exchanger

Hybrid ground-source heat pumps (HGSHPs) were introduced to prevent performance degradation under thermal imbalance between heating and cooling loads. However, the performance of an HGSHP with a parallel configuration has been rarely investigated in heating-dominated areas. In this study, the heating performances of HGSHPs with serial and parallel configurations are analyzed experimentally by varying the entering secondary fluid temperature (EFT) and flow rate of the supplementary heat exchanger as well as the ground temperature. Compared with the serial configuration, the parallel configuration demonstrates a 16.3% greater heating capacity and 12.6% higher coefficient of performance at an optimal flow rate of 10 LPM with an EFT and ground temperature of 19 °C and 14 °C, respectively. Moreover, for EFTs less than 22 °C, the parallel configuration demonstrates a reduced heat extraction rate from the ground as well as a higher exergy efficiency. Overall, the parallel configuration exhibits superior heating performance, even under severe ground thermal conditions.