Operation Of Heat Pump System Research Articles

Investigation on ejector design for CO2 heat pump applications us-ing Dymola

In this paper, the Dymola modelling tool is used to study the influence of ejector design onto the whole heat pump cycle working with carbon dioxide. The cycle is built using the components provided by the TIL Modelica library. It is found that the ejector models in TIL are quite limited, namely by their inability to properly capture the on-design plateau and rapid decrease in performance in off-design operation. Therefore, an in-house state-of-the-art ejector model, originally developed in Python, is implemented as a Dymola object. This model is then calibrated onto CO2 experimental data. The operation of a simple CO2 heat pump system is investigated, with focus on the ejector sizing at fixed geometry. It is found that there exists an ejector size that maximises the COP of the cycle. Furthermore, critical ejector pressure is not reached at this optimum COP point; the ejector is operating well under the on-design regime.

Modeling and operational characteristics analysis of a dual-source synergetic heat pump based on air energy and biomass waste heat

Air source heat pumps have gradually become a widely used heating solution worldwide due to their advantages of high efficiency, energy conservation, and environmental protection. However, air source heat pumps also face some challenges in practical applications, such as unstable heating and performance degradation in low-temperature environments. In order to improve these problems, based on the cascade heat technology, a new type of dual-source synergetic heat pump system is designed using air energy and biomass waste heat dual heat sources. In order to study its performance, a simulation model of the heat pump system was first constructed using distributed-parameter method. In order to verify the effectiveness of the model, an 18-kW heat pump experimental unit was constructed. By comparing the three key parameters of user side outlet water temperature, high-temperature compressor power, and system coefficient of performance (COP), the results show that the maximum error does not exceed 11 %; Secondly, in order to improve the stability and operational efficiency of the system, a three-level control strategy was designed based on considering the coordination of different grade heat sources; Finally, based on the above, the operating characteristics of the heat pump system were investigated through testing under different external input conditions. The research results indicate that by utilizing cascade heating and parallel heat exchange technology, the heat pump system can achieve stable heating even under large fluctuations in external working conditions. At the same time, compared with air source heat pumps, the COP can be improved by 69.7 % in low-temperature environments. The system results not only provide reference for the design and operation of new heat pump systems, but also provide practical and feasible solutions for the problem of decreased heat pump performance in low-temperature environments.

A variable water flow rate control method of hybrid geothermal heat pump systems

In the long-term operation of a geothermal heat pump system, when the cooling load is high, the temperature rise in the ground due to heat accumulation occurs. Changes in ground temperature hinder recovery of the temperature on the heat source side of the heat pump, and the performance of the geothermal system deteriorates because the heat exchange efficiency of the circulating water decreases. This problem can be solved by operating a hybrid geothermal system composed of an additional heat source system to the geothermal system. Therefore, in this paper, a method for operating a hybrid geothermal heat pump system was proposed to solve the degradation of system performance due to the temperature rise in the ground due to heat accumulation. The operating conditions for starting the operation of the hybrid geothermal heat pump system were derived, and the coefficient of performance prediction model was proposed for flow rate control considering the energy of the pump and the heat pump system. In addition, the proposed control method was evaluated for energy saving and performance improvement through simulation, and was also evaluated in terms of economic feasibility.

Research on the influence of underground seepage on regional heat accumulation of ground source heat pump heat exchanger

During the long-term operation of the ground source heat pump system, the temperature imbalance of the rock and soil around the heat exchanger results in the deterioration of the performance of the ground source heat pump system. Through previous projects, it has been found that in the area of underground seepage speed, it is helpful to alleviate the heat or cold accumulation of rock and soil mass around the ground source heat pump system. Based on this, two test sites in Zhangqiu District, Jinan City, Shandong Province, were selected to conduct pumping and irrigation tests to change the underground seepage velocity, determine the flow velocity through isotopic tracer tests, obtain soil thermal physical parameters and simulate heat accumulation through thermal response tests, and establish long-term numerical simulation through Opengeosys to synthesize the conclusion that the seepage velocity increases. The more efficiently the temperature of the rock and soil mass is restored to the initial condition, the more efficiently the heat exchange performance of the buried pipe heat exchanger and the surrounding rock and soil mass is maintained, and the efficient operation of the ground source heat pump system in winter and summer is ensured.

Seasonal performance of an energy pile heat pump system and prediction of building thermal load

Ground source heat pumps (GSHPs) are widely used for cooling and heating buildings, which can reduce the burning of fossil fuels and contribute to the reduction of carbon emissions. Energy piles, as underground heat exchangers, have advantages over conventional buried borehole pipes, saving drilling costs and accelerating the construction period. However, few studies have focused on the actual operation of an energy pile heat pump system, and the prediction of the building thermal load can reduce the instrument arrangement and test recording time. Hence, a heat pump system was built in this study to serve a single lab using energy piles with a cap structure as the energy supply, and summer cooling and winter heating tests were conducted. Under the test conditions in this study, the GSHP had a faster start-up speed and less power consumption than the air source heat pump (ASHP), and the average coefficient of performance (COP) of the energy pile heat pump system was 3.78, which is 40.0 ∼ 51.2% higher than that of the corresponding ASHP (the normative reference COP is 2.50 ∼ 2.70). The methods of higher-order surface fitting and an artificial neural network model were both suitable for predicting building thermal load.

Study on long-term operation characteristics of the medium-deep ground source heat pump system with solar heat storage

Long-term heating operation of the medium-deep ground source heat pump (MGSHP) system will cause the underground temperature around the mid-deep borehole heat exchanger (MBHE) significantly lower than its initial value, which will reduce the operating efficiency of the MGSHP system. In some cases, the temperature of the circulating water in MBHE even is lower than the lowest value required by the heat pump unit, which will lead to operation failure of the unit. Attenuating the ground temperature decrease by storing heat underground during non-heating seasons is an effect way to maintain the heat extraction capacity of the MBHE. In this paper, the influence of storing solar energy underground during non-heating seasons on the long-term operating characteristics of the MGSHP system is studied. The MBHE heat transfer model which considers the heat storage process is developed and embedded in the software of TRNSYS. Based on the numerical simulation model of solar assisted mid-deep ground source heat pump (SAMGSHP) system built by TRNSYS, the long-term characteristics including the variations of the fluid temperature of the MBHE, the ground temperature distribution and the COP of the heat pump unit of the MGSHP system with heat storage during non-heating seasons are analyzed and compared with the case without heat storage. The results show that storing solar energy underground during non-heating seasons can effectively improve the ground temperature, significantly slow down the decline of the circulating water temperature of the MBHE in heating seasons and apparently increase the COP of the heat pump unit. The results can serve as a reference for engineering applications of MGSHP systems, especially those cannot completely meet the original design heating load.

Analysis of the performance and operation of a photovoltaic-battery heat pump system based on field measurement data

Photovoltaic-heat pump (PV-HP) combinations with battery and energy management systems are becoming increasingly popular due to their ability to increase the autarchy and utilization of self-generated PV electricity. This trend is driven by the ongoing electrification of the heating sector and the growing disparity between growing electricity costs and reducing feed-in tariffs in Germany. Smart control strategies can be employed to control and optimize the heat pump operation to achieve higher self-consumption of PV electricity. This work presents the evaluation results of a smart-grid ready controlled PV-HP-battery system in a single-family household in Germany, using 1-minute-high-resolution field measurement data. Within 12 months evaluation period, a self-consumption of 43 % was determined. The solar fraction of the HP amounts to 36 %, enabled also due to higher set temperatures for space heating and domestic hot water production. Accordingly, the SPF decreases by 4.0 % the space heating and by 5.7 % in the domestic hot water mode. The combined seasonal performance factor for the heat pump system increases from 4.2 to 6.7, when only considering the electricity taken from the grid and disregarding the locally generated electricity supplied from photovoltaic and battery units.

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.

Research on thermal performance of ground source heat pump based on artificial neural network predictive model

The long-term operation of ground source heat pump systems can affect the soil environment, causing a decrease in heat transfer performance of underground heat exchangers. Based on a real project, this study aims to determine the actual soil thermal property and propose optimization schemes. A combination of 1D-3D heat transfer model and artificial neural network model was proposed. This research confirms the possibility of using the outlet water temperature as input to predict the soil thermal property parameters. Through model calculations, the soil comprehensive thermal conductivity of 1.78 W/(m·K) and comprehensive heat capacity of 1909.8 J/(kg·K) was determined. On this basis, the impacts of burial depth, spacing, and initial ground temperature on the heat transfer of the underground heat exchangers was investigated. The results showed that the heat exchange is logarithmically related to the depth and spacing of the boreholes, but the heat exchange decreases as the initial ground temperature increases, following a quadratic function relationship. For the current hourly cooling demand, it is recommended to have the pile spacing of 5.5 m and the depth of 110 m. With the addition of a cooling tower that takes on 2/3 cooling load, the system's average coefficient of performance can reach 5.62, resulting in a 19.6 % improvement.

Sustainability assessment of hydrochemical and microbiological disturbances in shallow aquifer by thermal utilization

The use of geothermal systems with shallow groundwater to achieve global carbon neutrality has increased substantially. However, they not only have hydraulic and thermal effects on the environment, but also induce hydrochemical and microbial changes that can worsen the sustainability of water resources. This study focused on evaluating groundwater mixing and pollution in a surrounding shallow aquifer induced by operation of a groundwater heat pump (GWHP) system. To explain these phenomena, hydrogeochemistry, multiple isotopes (O, H, and Sr), Rn, and microbial data were combined with geochemical modeling of the test system. Few studies have been conducted on field measurements using these combined approaches. The hydrogeochemical and microbial data showed specific characteristics accompanying the thermal use of groundwater. The calculated saturation index values and PHREEQC modeling results indicated a high probability of clogging effects in wells located near the boundary of the thermal plume. There was also a decrease in the microbial diversity index. Rn and stable isotopes indicated active mixing between circulating water and ambient groundwater along the main groundwater flow direction during the operation. This study demonstrated that subsurface hydrological and microbial environments, such as those of the GWHP system, responded to impacts of moderate intensity. Because the applied data were able to derive possible environmental and operational problems of shallow geothermal systems, hydrological and microbiological signatures should be considered for sustainable management of groundwater in geothermal sites. Our study can have implications for energy reuse from storage within an aquifer, such as aquifer thermal energy storage (ATES) based on field tests, using combined analysis.

Low-pressure steam generating heat pump – A design and field implementation case study

Steam is commonly used in industries for cooking in their kitchens, and diesel or LPG-fired boilers are often used to generate it. The use of a high-temperature heat pump to generate steam can help reduce emissions and lower the CO2 footprint by eliminating these fired sources. The following study details the design and consistent operation of a steam-generating heat pump (SGHP) system that employs a high-temperature scroll compressor and functions on the principles of a vapour compression system. SGHP generates steam with a stagnation pressure of 1.5 bar, a flow rate of 81.43 kg/hr, and a temperature of 108.52 ℃. The system was simulated using DWSIM under steady-state conditions with no pressure drop, and steam was generated through a flash tank. SGHP was also installed in a canteen that previously used a diesel boiler, and data from 31 days of operation was analyzed to evaluate system performance, environmental impact, and overall savings. The system COP was 2.2. The analysis showed that an average daily energy savings of 57.79 kWh and an average cost savings of Rs. 1125.46 were achieved. SGHP (with high temperature circuit only) increased carbon emissions by 20.3 % compared to diesel, based on India's emission factor of 790 g CO2/kWh. However, considering the emission factor of the European Union, the steam-generating heat pump has the potential to reduce carbon emissions by 57.8 %.

Research on designated calibration method of fault sensor in photovoltaic thermal heat pump system based on fault detection and virtual calibration

With the increasingly serious global energy problem, clean energy sources such as solar energy have become the mainstream focus of development. Among these, solar Photovoltaic thermal (PVT) heat pump systems have promising prospects. However, incorrect data transmitted by sensors can significantly impact the operation and control of the entire heat pump system, leading to reduced efficiency. Given the specific nature of PVT heat pump systems, their internal sensors are prone to errors during operation. To address these challenges, the Autoencoder Virtual in-situ calibration (AE-VIC) is applied to PVT heat pump systems. Preliminary studies have shown that this method can effectively reduce systematic and random errors in sensors. However, the current AE-VIC method faces certain issues, including unclear calibration targets and inefficient calibration of multiple sensors simultaneously, making it difficult to implement in practical systems. In order to overcome the limitations, fault detection is integrated with AE-VIC. By combining the feature extraction capability of Autoencoder with a Softmax classifier, sensors with faults can be identified before the overall calibration process, making the calibration objective of the AE-VIC more targeted. Following fault detection, inputs of the AE model are optimized using the mRMR algorithm for the identified faulty sensors. This optimization alleviates the difficulty of calibration. Through validation with actual system, the improved method effectively diagnoses and locates faulty sensors, and subsequently calibrates them. After calibration, the sensor system error can be reduced by over 95%. The improved calibration method surpasses the original AE-VIC method in terms of both time and accuracy.

Study on the influence of buried pipe fault on the operation of ground source heat pump system

In order to analyze the influence of fault buried pipes on the operation of ground source heat pump system, a simulation model of unit considering both the influence of inlet fluid flow and temperature is developed, which is coupled with the three-dimensional dynamic model of 3 × 3 pipe group. The results show that the influence degree caused by different blocked positions is basically same. When one, two and a group of pipes are blocked, the annual power consumption of unit increases by 3.78%, 8.81% and 15.91% respectively. Besides, the system annual average coefficient of performance decreases from 3.28 to 3.21, 3.12 and 2.98. The ratio of cooling to heating load demands studied is 1.44, and the pipe blockage exacerbates the soil thermal imbalance, which cause a continuous deterioration of cooling performance. When the cooling load is high, the system is difficult to meet the demand. Because of design margin of total length, the time for not meeting the cooling demand after blocking one pipe is the same as normal condition, but the time after blocking two and a group of pipes increases 37.5 h and 88.5 h. Moreover, the amount for not meeting the demand increases 25.4%, 52.11% and 129.94% on average respectively.

Study on heat exchange of groundwater under complex geological conditions in karst area of south China

This paper takes a groundwater source heat pump in the region as the research object and based on field research, experimental tests combined with comparative analysis, the data on its operation is monitored and analyzed in terms of operation, energy saving, and environment. The results show that the cooling temperatures of the test rooms were all below 26°C, the average coefficient of performance of the units was 4.61–4.93 and the average coefficient of performance of the system was 3.08–3.27. In addition, compared to conventional water-cooled chillers, 466 tons of standard coal could be saved in one cooling season, resulting in a reduction of 1,150.8 tons of carbon dioxide emissions, 9.3 tons of sulfur dioxide emissions and 4.7 tons of dust emissions The savings in operating costs are 793,000 RMB. This shows that the groundwater source heat pump has good energy efficiency and economy. The research results obtained in this paper provide a reference for improving energy efficiency and optimizing the operation of the groundwater source heat pump system. It is of great significance to the application of groundwater source heat pump systems in areas with complex geological environments.

Can heat pump heat storage system perform better for space heating in China’s primary schools? A field test and simulation analysis

The space heating system has a significant influence on the energy consumption and comfortable indoor environment for primary schools in China’s cold area. This study investigated the operational performance of heat pump systems in two primary schools. Results showed that the primary school buildings had high heating load at turn-on period every morning, which then quickly decreased when the students came to classroom. With this wide-range variation of heating load and unreasonable control strategy, the mismatch between heat source and heating demand happened very easily among the whole heating season. It then led to typical issues and poor energy efficiency of heat pump systems, including excessive space heating after school, low load ratio and frequent start-stop operation of heat pump systems, small water temperature difference and excessive water flow rate of water distribution system, etc. In allusion to those core issues, the heat pump heat storage system (HPHS) was raised for space heating in primary schools to decouple the heat supply side and the heat demand side. Then this study simulated and analyzed the operational performance of HPHS. Results showed that with reasonable control strategy, the excessive heat supply after school was effectively avoided to save almost 51% of the total heat consumption. Besides, the heat pumps could operate stably with almost full heating load for heat storage, thus reaching better energy performance with annual average COP of 5.13. Also the water distribution systems in the ground side, heat storage side and user side could reach better energy performance with high energy efficiency and reasonable water temperature difference among the heating season. Therefore, the HPHSs with reasonable control strategy could effectively solve those typical issues and are more suitable for primary schools.

Optimal Operation Control of Composite Ground Source Heat Pump System

During the operation of the ground source heat pump (GSHP) system, the operations of the chiller system should be controlled by adjusting the difference between water temperature and wet bulb temperature. Therefore, it is important to consider the control strategy for the switch time (ST) and wet bulb temperature difference (WBTD) of the chiller system. This paper sets up two control strategies, namely, the strategy to control the ST of system operations, and the strategy to control the WBTD. Then, theoretical modeling was carried out to compare the system energy consumption and borehole wall temperature under different strategies. The modeling results were referred to optimize the control strategy for composite GSHP systems. It was found that, under the ST control strategy, the best wet bulb temperature is 2℃, and the best chiller operation hours are 3h; under the WBTD control strategy, the best wet bulb temperature is 3.5℃, and the best WBTD is 1.5℃. In addition, the ST control strategy is superior to the WBTD control strategy, in terms of system energy consumption, borehole wall temperature and initial investment.

Machine learning based refrigerant leak diagnosis for a vehicle heat pump system

• Detect the charge fault in cooling, heating, and series dehumidifying operating modes. • The extremely randomized trees achieve the best accuracy out of 25 models. • Use advanced feature recursive elimination method to select best system sensor scheme. • Achieve the optimal diagnostic accuracy of 95.69% while utilizing the fewest sensors. • The approach taken in this paper is broadly applicable to other diagnosis problems. The detection of refrigerant leak is critical for the effective operation of heat pump systems and vehicle maintenance. Using feature selection methods, machine learning methods, and system sensors schemes, this article optimizes the performance of refrigerant leak detection for vehicle heat pump systems that operate in cooling, heating, and series dehumidifying modes. The extremely randomized trees (EXT) model was chosen as the best model for refrigerant leak detection in heat pump systems out of 25 machine learning models, with the highest f1 score of 95.73%. The advanced feature recursive elimination strategy developed in this study is effective at increasing model accuracy, with an improvement of 1% in model diagnostic accuracy while reducing the number of features for modeling. By comparing different sensors schemes for vehicle heat pump system, this article analyzes the importance of different sensors for refrigerant leak detection. The accuracy of refrigerant leak detection in vehicles reaches 95.69% based on the optimal sensors scheme. The results demonstrate that the methods proposed in this paper not only reduce the cost of sensors used in the heat pump system, but also improve the heat pump system's performance for refrigerant leak diagnosis across three operation modes. In addition, the approach taken in this paper is broadly applicable to diagnosis problems in other fields to facilitate the application of diagnosis in the real world.

Operation optimization of the coaxial deep borehole heat exchanger coupled with ground source heat pump for building heating

• The transient numerical model of the coaxial heat exchanger is established. • Operation optimization method for the heat pump system is developed. • The underground heat transfer model is validated using test data from literature. • The operation of the system before and after optimization is compared. Geothermal is considered to be one of the most promising renewable sources for district heating. Ground source heat pump systems coupled with the coaxial deep borehole heat exchanger have been widely applied because of their high efficiency. However, in order to reduce the total energy consumption of the system, there are few studies on the optimization of the water flow rates in the coaxial deep borehole heat exchanger by time to meet the load change during the heating season. In this paper, an optimization method for the two flow rates which are set at two time periods respectively every day in the coaxial deep borehole heat exchanger during the operation of the ground source heat pump system is proposed. The application of the method is to determine the applicable flow rates when the temperature of the next day is predicted. Space heating of a building (located in Tianjin, China) is taken as a scenario, comparisons were carried out on system operation before and after optimization, which shows that the method has a good effect on the energy-saving operation of the system. After optimization, the total power consumption of the system is reduced, the total performance coefficient of the equipment as well as the temperature difference between the inlet and outlet of the underground heat exchanger is increased, and the trend of flow rates changes with time is the same as the indoor and outdoor temperature difference.

Holistic optimization of the operation of a GCHP system: A case study on the ADREAM building in Toulouse, France

Ground-source heat pumps are more energy-efficient, especially when compared to their water and air source counterparts. However, when operating and design conditions are vastly different, the expected gains in efficiency could be easily negated. Under such scenarios, measures to improve energy performance are explored through performing mathematical optimization on the appropriate model of the system.Components of a heat pump system are often operated at pre-defined setpoints or independently optimized, disregarding the overall performance. Formulation of a holistic optimization problem which expresses the system in its tuneable variables, while capturing the tight-coupling between its components results in a complex mixed-integer non-linear program. Our paper concerns itself with the mathematical modeling and optimization of the hourly operation of a ground-coupled heat pump system for improving energy and operating cost. We judiciously abstracted and decoupled the component models of the system, so that the problem could be formulated as a mixed-integer linear program. This vastly benefited the solvability of the optimization problem.For illustration, we implemented this methodology on a system in the ADREAM building of the LAAS-CNRS laboratory in Toulouse, France. Four case studies are defined in the lead up to holistic optimization, allowing the results to be easily understood. The results reveal significant limitations, which prompted the hybridization of the system with a hypothetical water-to-air heat exchanger. Results indicated electricity and cost savings of up to 35.0% and 12.7% respectively, depending on the objective function. Our findings postulate that the additional investment is recoverable within five years.

Influence of Groundwater Heat Pump system operation on geological environment by Hydro-Thermal–Mechanical–Chemical numerical model

Groundwater Heat Pump (GWHP) systems have gained attention for space heating and cooling due to its efficiency and low installation costs. It is known that thermal transfixion and land subsidence are main geological environmental hazards in the application of GWHP. But few studies paid attention to groundwater quality. In this research, a three-dimensional Hydro-Thermal–Mechanical–Chemical numerical model was established based on Biot’s consolidation theory, solute and heat transport in porous media theory. The numerical model could evaluate geological environment from four aspects: hydraulic head, temperature, groundwater quality, and land subsidence. The coupling effect of building load and extraction–injection groundwater is considered to study land subsidence. The model is applied to a GWHP in Nantong, China. The results show that increasing the temperature change and decreasing the circulation ratio of GWHP will alleviate thermal accumulation, thermal transfixion, and freshwater salinization of the confined aquifer III. But it will aggravate the occurrence of land subsidence. The geological environment involves four factors. The development of shallow geothermal energy should be considered comprehensively. Optimizing operation scheme by changing the groundwater seepage field would alleviate geological environment deterioration.