Performance Of Ground Source Heat Pump System Research Articles

Performance analysis of ground source heat pump systems for constant temperature and humidity air conditioning in industrial buildings: a case study

Abstract The ground source heat pump (GSHP) system has gained widespread popularity for its provision of efficient and environmentally sustainable cooling and heating solutions for buildings. While the performance of GSHP systems has raised significant concerns, research predominantly focuses on residential and office buildings, leaving a gap in understanding their applicability in industrial settings with constant temperature and humidity air conditioning needs. This study aims to address this gap by evaluating the performance of a hybrid ground source heat pump (HGSHP) system implemented within a cigarette factory located in the hot summer and cold winter (HSCW) of China. Through a comprehensive analysis of operational data and long-term monitoring under three cooling conditions, essential parameters including water temperature characteristics, indoor temperature and humidity, system efficiency, power consumption, and soil temperature distribution were examined. The findings revealed that the weighted average coefficient of performance (COP) of the heat pumps (COPhp) and the whole system (COPsys) was decreased from 5.05 to 4.32 and 3.32 to 2.89, respectively. A positive correlation was observed between low cooling load high energy consumption, and low COP. The inlet temperature of the condenser exhibited a declining trend, which was attributed to the intermittent operation of condensation heat recovery. Furthermore, a comprehensive analysis of indoor temperature and humidity distribution within the controlled room was presented and found that almost all the rooms serviced by this system meet the specified design requirements. This research contributes to an enhanced understanding of the viability of HGSHP systems in industrial settings and provides valuable references for improving their energy efficiency and overall performance.

Performance prediction of a ground source heat pump system using denoised long short-term memory neural network optimised by fast non-dominated sorting genetic algorithm-II

The ground source heat pump (GSHP) is a commonly employed technique that utilises geothermal resources to heat or cool buildings, offering an advantageous alternative for reducing conventional energy consumption. Considering that the output energy of GSHP system is a critical criterion for evaluating the geothermal energy extraction, this study proposes an improved long short-term memory (LSTM) model for predicting the energy output of geothermal heat exchangers (GHE) EGHE-PT and the electrical energy consumption EEC-PT of a GSHP system. The model is trained and validated using a comprehensive real-time monitoring dataset gathered over a four-year period from a three-story residential house situated in Cleveland, Ohio, USA. To process the raw data, the wavelet denoising method is employed, while the fast non-dominated sorting genetic algorithm-II (NSGA-II) is employed to automatically determine the optimal hyperparameters for the LSTM model. Comparative analyses with alternative prediction models demonstrate the superior performance of the Denoised-LSTM-NSGA-II model. The results indicate that the Denoised-LSTM-NSGA-II model yields reasonable prediction for the two performance indicators: EGHE-PT and EEC-PT (with the R2 of 0.91 and 0.89, respectively). Further examination reveals that outdoor temperature holds a significantly high importance rank within the Denoised-LSTM-NSGA-II model. This implies that the proposed method can achieve an acceptable level of accuracy by only utilising weather data from the preceding 5 days. The aforementioned findings present a potentially cost-effective approach for predicting the performance of GSHP system based on limited monitoring data.

Effect of soil moisture content on thermal performance of ground source heat exchangers: An electromagnetism topology-based analysis

Ground source heat pump (GSHP) technology has gained significant attention as a viable solution for the heating, ventilation, and air conditioning (HVAC) of buildings. One of the factors that can impact the performance of GSHP systems is the soil moisture content. In this study, an innovative approach, referred to as soil impedance topology, is introduced as an alternative to traditional methods for measuring soil moisture content in geothermal heat pump systems. This method is inspired by pipeline grid utilizes impedance measurement, which provides a direct measurement of soil moisture content without the need for sensors. The study also proposes a changing rule of impedance with varying moisture content, where capacitance increases and resistance decreases when the soil moisture content is less than 20% but stabilizes beyond a water content of 20%. The accuracy of the topological mechanism prediction method is high, as demonstrated through the verification of the Smith circle and measured data. However, it is noted that the performance may be insufficient in the high frequency band and high soil moisture content. The use of impedance topology provides a more accurate and reliable method for measuring soil moisture content as well as for modeling and predicting heat transfer rates and system performance. This technology has strong potential to improve efficiency, reduce energy costs, and enhance the environmental sustainability of geothermal heat pump systems.

Comparative analysis on the life cycle climate performance of ground source heat pump using alternative refrigerants

The ground source heat pump (GSHP) system is receiving increasing interest because of its potential to increase energy efficiency and thus reduce greenhouse gas emissions. Using low-GWP refrigerants is another effective approach to reducing emissions. However, alternative refrigerants also affect the energy performance of GSHP systems, so the life cycle climate performance (LCCP) is evaluated to facilitate reasonable refrigerant selection. The GSHP systems using five refrigerants (R134a, R152a, R1234yf, R1234ze(E), and R290) are simulated under the fixed and individual design methods, considering different climate zones. The results reveal that (1) R152a and R1234ze(E) are the optimum low-GWP refrigerants in four different climate zones under fixed and individual design methods, respectively. However, R290 and R1234yf are not good alternative refrigerants for their highest total emissions, though their GWP is low. (2) Changchun has the largest direct emissions (0.04–67.92 tCO2eq) and indirect emissions (2628.27–3065.76 tCO2eq) for its severe cold climate. (3) The refrigerant leakage rate (RLR) has a great impact on the total emissions of GSHPs with a high-GWP refrigerant, while the refrigerant charge has the least impact. The carbon emission factor (CEF) also has a rising influence on the LCCP. This research aims to provide suggestions for the selection of GSHP refrigerants towards carbon neutrality.

A revised sizing method for borehole heat exchangers in the Chinese national standard based on reliability and economy

The total length of borehole heat exchangers (BHEs) is an essential issue for ground source heat pump (GSHP) systems. An insufficient number of BHEs may lead to the attenuation of long-term performance and may fail to meet the cooling or heating demands of buildings. Meanwhile, too many BHEs that exceed the system reliability requirement lead to excessive investment. In China, the total length of BHEs calculated using the current Chinese national standard GB50366-2009 is increased when a constant is simply multiplied by engineers; this approach is not economic nor reasonable. Therefore, this study revised the calculation method of the total length of BHEs in Chinese national standards by introducing a parameter called temperature penalty (Tp) to ensure the long-term performance of GSHP systems and minimise the economic cost. A comparison of system reliability under the original BHE length calculation method and the optimised method was performed by simulation. The simulation method was verified through experimental measurement. Regression equations for the thermal conductivity of soil, specific heat capacity of soil, thermal conductivity of grout, daily operation time and Tp were also proposed.

Experimental study on the thermal imbalance and soil temperature recovery performance of horizontal stainless-steel ground heat exchanger

Soil thermal imbalance has become a common problem for ground source heat pump (GSHP) system, leading to the fluctuation of ground temperature and decline of heat transfer efficiency. However, compared with vertical ground heat exchanger (GHE), there is a lack of research and evaluation on the soil thermal imbalance for horizontal GHE. Therefore, in this paper, to investigate the extent of soil thermal imbalance and its effects on performance of GSHP system, a sandbox experiment embedded with horizontal stainless-steel GHE was implemented. Various operation conditions were designed to explore effects of intermittent time, water content (rainfall) and buried depth of pipes on soil temperature distribution and restoration performance. The experimental data was validated by a numerical simulation. The results indicated that 5-day intermittent operation of GSHP leads to an increase of 6.41 ℃ in soil temperature. After 2-day natural recovery, soil temperature recovery rate can only reach 0.72. Increasing soil moisture content and intermittent control are effective solutions to mitigate thermal accumulation and improve thermal performance. The heat transfer performance of GHE with an intermittent ratio of 6:18 which GSHP system runs for 6 h and stops for 18 h during a day is 33% higher than that with the intermittent ratio of 14:10 and 10:14. The higher the water content, the lower the soil temperature fluctuation and the stronger the soil temperature recovery capacity. This can be attributed to the increase of soil thermal conductivity and capacity, while the decrease of thermal diffusivity.

Does it pay to develop a ground source heat pump system? Evidence from China

The application potential and environmental benefits of ground source heat pump (GSHP) systems have become the focal points of decarbonization in the building sector. Synchronized and scientific analysis of GSHP systems' environmental and economic performance, however, remains lacking. This study analyzes the application prospects of GSHP systems via a life cycle assessment-based life cycle costing method, and considers China's actual status quo. The internal and external annual costs of a GSHP system per square meter are $ 4.05 and $ 1.37, respectively. Electricity generation and steel production are key processes to improve the environmental performance of a GSHP system further. Compared with coal-based heating, a GSHP system can mitigate 65%–95% of the environmental impact and 85% of external costs, except for the metal depletion impact which is 1.5 times higher than that of coal-based heating. In Shandong Province, promoting GSHP systems can substitute up to 69.4% of the district heating area, which implies reductions in fossil depletion, greenhouse gas emissions, human health impact, ecosystem quality impact, and external costs by up to 2.37 × 1010 kg oil eq, 1.08 × 1011 kg CO2 eq, 3.87 × 105 DALY, 1.18 × 103 Species. year, and $ 2.51 × 1010, respectively. In consideration of environmental and economic aspects, a GSHP system can exhibit benefits compared with coal-based heating after 2.34 years of operation. To improve the economic and environmental performance of GSHP systems, a series of recommendations on financial subsidies, renewable energy development, inter-regional power transmission, steel scrap utilization, and hydrogen reduction steelmaking is provided.

Operation performance test and energy efficiency analysis of ground-source heat pump systems

The improper operation of a ground source heat pump (GSHP) system is a significant cause of poor energy efficiency. Despite the increasing popularity of GSHP systems in China, few field test has been conducted on the operation of GSHP systems in the southwest and western regions of the country, and there is a lack of comprehensive comparative study. This study tested the operation performance of 26 GSHP systems in Sichuan, Chongqing, and Shaanxi under typical operation conditions. The performances indexes of the systems were calculated and investigated, including the coefficients of performance of the heat pump and system, water transfer factor of the water pump, and energy efficiency ratio of the system. These parameters were then compared and analyzed based on existing literature and relevant domestic standards concerning energy efficiency. Accordingly, suggestions were proposed for improving the operation performance of GSHP systems from the aspects of system design, construction, and operation. Results show that the average coefficient of performance (COP) of the tested systems was less than 3.0 under heating conditions, which did not meet the requirements for energy-saving operation stipulated by the national standard and fail to achieve the initial intention of saving energy in buildings by using GSHP systems. Based on the analysis, typical problems were diagnosed in GSHP systems. Specifically, the heat pumps usually operate in part-load conditions and at low efficiency for a long time; the transfer and distribution systems operate with small temperature differences and large flows; and the settings of room temperatures tend to be unreasonable. In view of the operation performance, ground-coupled heat pump (GCHP) systems are recommended for use in the western regions of China.

Evaluation of thermal imbalance of ground source heat pump systems in residential buildings in China

The thermal comfort level of Chinese residents in the hot-summer and cold-winter zone is increasing with economic development in recent years. More district heating and cooling systems were installed in these areas. Supported by the government, ground source heat pump (GSHP) is used as a common environmentally friendly district heating and cooling system in many residential communities. However, the evaluation of the real performance of GSHP is limited, especially limited understanding of the common issue of thermal imbalance of GSHP systems over several years—the mismatch between heat extraction from and rejection to the ground. Performance of GSHP systems can deteriorate over years if the thermal imbalance is significant and not addressed. For GSHP in the hot-summer and cold-winter climate zone, there are few thermal imbalance studies based on real field data and modeling. To address this gap, this paper proposes an integrated simulation model to evaluate thermal imbalance of GSHP systems considering key influencing factors including occupant behavior and heat pump performance. A case study was conducted to simulate and analyze the actual operation of GSHP in Chinese residential buildings. The indoor comfort temperature setting and flexibility of residents’ control on indoor terminal air-conditioning units determine the actual heating and cooling demand in residential buildings, which resulted in differences in thermal imbalance for GSHP systems. It was found that GSHP systems with radiant floor only for heating lead to the most severe thermal imbalance, while GSHP systems with fan coil units or radiant ceiling for cooling and/or heating achieved much better thermal balance. The proposed thermal imbalance ratio is an important indicator that can be used to evaluate thermal imbalance of GSHP systems and thus inform their design and operation for energy efficiency.

The influence of groundwater seepage on the performance of ground source heat pump system with energy pile

Both initial cost and land area can be saved while ground source heat pump (GSHP) system employs energy pile as the ground heat exchanger (GHE), and the energy pile exchanges heat with the surrounding underground medium. Groundwater seepage exerts influence on the heat transfer, and this is because the convection of groundwater alleviates the heat or cold accumulation around pile and then improves the heat transfer effect of energy pile. The existing researches regards the velocity of groundwater seepage as the one-dimensional vector, or the available models are not accurate enough though three-dimensional groundwater seepage is considered. The paper describes the spiral line heat source models with three-dimensional groundwater velocity, and the analytical solutions of temperature response are obtained. Afterwards, the performance of GSHP system is studied based on the proposed models, and the factors that have impacts on the coefficient of performance (COP) of heat pump unit are explored. The differences are explained while every factor employs different cases, but the common results of all cases are that the COP is indeed improved by groundwater seepage, and therefore the advantages of groundwater seepage should be noted. The researches of the paper attach importance to the seepage role, and the findings of the paper are favorable for the further development of GSHP technology.

Effects of ground heat exchangers with different connection configurations on the heating performance of GSHP systems

The connection configurations of ground heat exchangers (GHEs) have a significant impact on the ground temperature and the performance of ground source heat pump (GSHP) systems. In this paper, the heating performance of a GSHP system implemented in a net zero-energy building with two different GHE connection configurations, including series and parallel connections, was experimentally and numerically investigated. A mathematical model was developed based on ANSYS fluent to analyze the thermal performance of the GHEs and the model was validated against the experimental data. The experimental results showed that the parallel configuration of the GHEs achieved a better heating performance when the mass flow rate was 2.58 kg·s−1, as compared to that of the series configuration. The system heating performance with both series and parallel configurations of the GHEs increased with the decrease in the fluid flow rate under the same heating load condition. The pressure drop between the inlet and outlet of the GHEs with the series configuration was also higher when compared to that with the parallel configuration.

Constant-temperature thermal response test (TRT) with both heat injection and extraction for ground source heat pump systems: Methodology and a case study

Abstract An accurate estimate of site-specific underground thermal properties from thermal response tests (TRTs) is vital to the efficient and sustainable use of ground source heat pump (GSHP) systems. During a conventional TRT, the ground is perturbed by a heat injection and the response is measured in time. Despite the simplicity of the concept, conventional TRT fails to take into account the ground thermal response to heat extraction, which may affect the reliability of the thermal properties derived. To address the problem, an improved TRT based on both heat injection and extraction was proposed in this study. The improvements were demonstrated with an in-situ test carried out in Taiyuan, China. The measurement results showed that the ground thermal conductivity in Taiyuan was 1.56 W/(m K) and the borehole thermal resistance was 0.22 (m K)/W. The results also showed that, in the case of Taiyuan, ground thermal conductivities derived solely from heat injection test and heat extraction test were, respectively, 7.6% higher and 8.3% lower than that from the improved TRT. Thus, compared with the conventional TRT, the improved TRT consisting of both heat injection and extraction tests can provide test data more accurately reflect the annual performance of GSHP systems.

수치해석을 이용한 수직밀폐형 지열 시스템 영향인자의 민감도 분석 : 난방운전을 중심으로

Purpose: Recently, in order to realize eco-friendly buildings, studies on renewable energy technologies have conducted in field of building energy. Among these technologies, a ground source heat pump (GSHP) system can achieve higher performance than conventional air source system. However, the GSHP system has been delayed due to high initial cost and lack of guidelines for performance analysis of various design factor. Therefore, this paper aims to proposed design and operation method to improve the performance of the GSHP system and to minimize the additional cost. Method: In this study, numerical simulation was conducted to accurately predict the heat exchanger rate (HER) and entering water temperature (EWT) of the GSHP system. The numerical simulation was coupled with soil model, ground heat exchanger (GHX) model and ground surface heat flux model. Furthermore, the performance of GSHP system was analyzed according to the operation method of the system such as flow rate, operation time, and limit temperature. Result: As a result, the HER and the EWT of base case were 34.3W/m, 10.26℃ respectively in the condition of 9.3lpm flow rate, 9 hours per day operation, and 5℃ limit temperature.

Evaluation of a transient borehole heat exchanger model in dynamic simulation of a ground source heat pump system

The performance of a vertical ground source heat pump system (GSHPS) largely depends on the fluid temperature leaving the borehole heat exchanger (BHE) that may be affected by the short-term behavior of the BHE. Although considerable research has been carried out to analyze the short-term transient response of the BHEs, few studies have investigated its impact on dynamic simulation of GSHPS. Therefore, this paper presents a numerical approach based on a transient BHE model to evaluate the performance of a residential GSHPS over short and long timescales. The numerical results are compared with the results of EnergyPlus software. It is shown that the proposed model can appropriately predict the dynamic behavior of the system. Moreover, effect of borehole thermal capacity on the performance of the GSHPS is investigated in comparison with a quasi-steady state model. It is found that including the borehole thermal capacity substantially affects the design borehole length. Using the transient model instead of the quasi-steady state model leads to a 16% reduction in the required borehole length.

The performance prediction of ground source heat pump system based on monitoring data and data mining technology

This paper studies the performance prediction of ground source heat pump (GSHP) systems by real-time monitoring data and data-driven models. A GSHP system, which is installed in an office building of Shaoxing (29.42°N, 120.16°E), China, is real-time monitored from Nov. 2012 to Mar. 2015. Data mining (DM) technologies were simultaneously applied to process the monitoring data and find the required inputs for data-driven models. Back-propagation Neural Network (BPNN) algorithm was selected from six classical sorting algorithms to establish the data-driven models. The performance of the GSHP system from Nov. 2012 to Mar. 2015 was evaluated by the monitoring data. And the long-term performance was predicted by the data-driven models. The monitoring results show that the application effectiveness of the GSHP system is unsatisfied because of the high pumping power. Moreover, the relationship between the short-term and long-term performance of GSHP system is investigated for the purpose of predicting the long-term performance of GSHP system by a short-term monitoring data. The monitoring data of different days in several modes are needed to predict the long-term performance of GSHP system under a certain deviation.

Numerical investigation on thermal performance of ground heat exchangers using phase change materials as grout for ground source heat pump system

In order to solve the increasing deterioration of the energy shortage problem, ground source heat pump (GSHP) systems have been widely used. The ground heat exchanger (GHE) is a significant component of GSHP systems and the backfill materials have a dominating effect on thermal performance of GHEs. Therefore, phase change materials (PCM) were proposed to use as backfill material instead of common materials to improve the performance of GSHP systems. This paper first established a finite element model to investigate thermal performance of GHE, which was verified by experimental data of other researchers. Evaluation methodologies, such as effectiveness and thermal effects radius, were then proposed. The thermal performance of four backfill materials, including soil, paraffin RT27, acid and enhanced acid, was discussed, respectively. Finally, the effects and the combined effects of initial ground temperatures and pipe spacing on thermal performance of GHEs were studied. The results show that PCM has certain advantages over ordinary soil, because of its small thermal effects radius and consistent temperature in the phase change process. Meanwhile, the lower initial ground temperature and the larger pipe spacing of U-tube were beneficial to heat transfer, while it increased thermal effects radius and decreased liquid fraction of PCM. Furthermore, the thermal effects radius growth rate with pipe spacing increased with an increase in initial ground temperature.

Shallow geothermal energy: emerging convective phenomena in permeable saturated soils

Ground source heat pump (GSHP) systems efficiently heat and cool buildings using sustainable geothermal energy accessed by way of ground heat exchangers (GHEs). Thermal performance of GSHP systems is typically investigated considering either pure conduction in the surrounding ground or the hydrogeological conditions (i.e. groundwater flow). However, in saturated soils, the temperature gradient in the ground induced by the GSHP systems heating/cooling operations may result in natural movement of groundwater due to the changes in water density, which leads to an emerging natural convective heat transfer in the ground. This usually ignored convection may influence the thermal performance of GHEs; therefore, to capture and quantify this effect, a GHE field consisting of 16, 30 m-long GHEs installed in a fully saturated soil is modelled using a state-of-the-art three-dimensional finite-element model. The effect of carrier fluid velocity on natural convective heat flux in the saturated soil is investigated in this study and is compared with cases where buoyancy-driven convection in the ground is ignored. Results show that for saturated soils with relatively high hydraulic conductivity, natural convection affects the thermal performance of GHEs significantly and ignoring this effect may lead to overdesign of GSHP systems.

Analysis of the effect of global climate change on ground source heat pump systems in different climate categories

Ground source heat pump (GSHP) systems exhibit high thermal performance. Consequently, they are increasingly used to heat and cool buildings. The thermal performance of GSHP systems strongly depends on the operation ground temperature and thermal quality of the building envelope (TQBE). The operation ground temperature is a function of mean annual air temperature and annual thermal load of the building. The thermal load depends on the TQBE and outside temperature. Given that ongoing global climate change (GCC) affects air temperatures, it also affects the performance of GSHP systems. The magnitude of this impact on a given GSHP system strongly depends on local weather conditions and the TQBE.The overall aim of the current study is to investigate the impact of GCC on the performance of GSHP systems in different climate. To achieve this aim, three cities located in three climate categories were considered: Stockholm, Sweden (cold), Istanbul, Turkey (mild), and Doha, Qatar (hot). In each city, two buildings were modeled. One was built according to current local building regulations, while the other was built to have a TQBE lower than the standard TQBE. Simulations were run for present (2014) and future (projected for 2050) outdoor designing conditions.

업무용 건물의 지열 히트펌프 시스템에 대한 성능 예측

Ground-source heat pump (GSHP) systems have become an efficient alternative to conventional cooling and heating methods due to their higher energy efficiency. These systems use the ground as a heat source and the heat sink for cooling mode operation. The purpose of this simulation study is to evaluate the performance of a hypothetical GSHP system in an office building and to assess the energy saving effect against the existing HVAC systems (boiler and turbo chiller). We collected monthly energy consumption data from an actual office building (32,488 m 2 ) in Seoul, and created a model to calculate the hourly building loads with EnergyPlus. In addition, we used GLD (Ground Loop Design) V8.0, a GSHP system design and simulation software tool, to evaluate hourly and monthly performance of the GSHP system. The energy consumption for the GSHP system based on the hourly simulation results were estimated to be 582.6 MWh/year for cooling and 593.2 MWh/year for heating, while those for the existing HVAC systems were found to be 674.5 MWh/year and 2,496.4 MWh/year, respectively. The seasonal performance factor (SPF) of the GSHP system was also calculated to be in the range of 3.37∼4.28.

The quantitative evaluation of design parameter's effects on a ground source heat pump system

The main solution for the reduction of energy consumption in the field of HVAC is the development of new and renewable energy technologies. Among the various renewable energy systems, ground source heat pump (GSHP) systems have been spotlighted as efficient building energy systems because of their great potentials for energy reduction in building air conditioning and reducing CO2 emissions. However, higher initial cost works as a barrier to the promotion of their use. Therefore, it is critical to reduce the initial costs by optimizing the design of the system. In this paper, parameters that affect the performance of the GSHP system and the size of ground loop heat exchanger (GLHX) have been investigated. Ratio of GLHX length to unit capacity (L/Q) decreased according to increasing value of thermal conductivity, but L/Q increased according to increasing value of borehole heat transfer resistance. In cooling mode, L/Q decreased according to increasing EWT of underground circulating water and borehole distance but increased in heating mode. The value of L/Q tended to increase according to increasing underground initial temperature in cooling mode, but decreased in heating mode. L/Q decreased according to increasing U-tube separation distance and decreasing underground circulating water flow rate, because the thermal interference effect of underground circulating water and heat absorption and emission rate from the ground decreased. The reduction of the size of GLHX is very important in the aspect of saving total installation cost of a GSHP system. Therefore, the size of GLHX and the performance of GSHP system should be considered together for optimum design of the GSHP system.