Groundwater Source Heat Pump Research Articles

Hybrid model-free control based on deep reinforcement learning: An energy-efficient operation strategy for HVAC systems

At present, most optimization objectives of heating, ventilation, and air-conditioning (HVAC) systems focus on the local optimization of equipment during cooling hours, usually ignoring the importance of the end conditions. In addition, traditional control methods may not perform well in complex or dynamic systems. Therefore, in this study, a hybrid model-free control (HMFC) strategy was developed that combines deep reinforcement learning (DRL) with L-BFGS-B and expert knowledge to improve its ability to cope with complex system environments. This strategy was used to optimize the cooling and heating periods of a groundwater source heat pump system in a bitterly cold region of China throughout the year, considering the end-of-system conditions. L-BFGS-B optimized the fresh-air ratios for the end air-handling unit, whereas DRL achieved global optimization of the heat pump outlet temperature, air-conditioning water circulation pump frequency, and submersible-pump frequency. To verify the effectiveness of the strategy, a simulation platform was built based on actual data and device parameters, and the simulation results of HMFC and model predictive control (MPC) were output, compared, and analyzed with data of the system measured in 2022 under expert rule-based manual control (RBC). The results show that HMFC was 7.38 % and 9.38 % more energy efficient than RBC during heating hours, respectively. HMFC was 24.26 % more energy efficient than RBC and 10.03 % more energy efficient than MPC during cooling hours. Moreover, the distribution of the system coefficient of performance under the HMFC method was more concentrated in the higher range, indicating that the proposed HMFC can save energy savings. Thus, it is a feasible optimization scheme for buildings without a large number of historical data. Finally, the strategy was applied to a real engineering experimental analysis, and the engineering practice results show that the strategy is robust and practical.

Physical experiment and pore-scale investigation of the clogging of polydisperse particles in saturated porous media during artificial groundwater recharge

Groundwater recharge engineering practices are usually accompanied by the migration and deposition of polydisperse particles. Solid particles may be retained in the pore space leading to clogging of the porous media and reducing groundwater recharge efficiency. However, the mechanism behind this clogging phenomenon remains poorly understood. Specifically, the relation of particle clogging at pore-scale and macroscale is unclear. Here, the influence of polydisperse particle size on clogging development patterns was studied utilizing a series of laboratory-scale column experiments in conjunction with pore-scale scanning electron microscopy (SEM) experiments. Particles with median particle sizes (dp50) of 0.66, 4.05, 11.83 μm were injected separately into the sand column to simulate particle clogging that occurs during groundwater recharge. SEM was used to directly observe particles deposition on porous media grain surface after the column experiments. By counting the size distribution of the particles on the media grain surface, the response of the particle deposition to the surface morphology of the media grains was analysed. Compared to dp50 of 4.05 and 11.83 μm, the spatial distribution of particles deposited in the sand column was more uniform at dp50 of 0.66 μm. The smallest particles (dp50 = 0.66 μm) used in the experiments ultimately formed mixed clogging, which was the result of the combined effects of particle deposition and aggregation. The particle deposition with dp50 = 4.05 and 11.83 μm ultimately exhibited hyper-exponential distribution and formed mixed and superficial clogging, respectively. At the same time, the concave region of the media grain surface played a dominant role in particle deposition. For dp50 = 4.05 μm, 69.41 % of the particles were deposited in the concave region, and for dp50 = 11.83 μm, the proportion was 90.1 %. The results help to better manage particle clogging in groundwater recharge and other engineering applications (e.g., groundwater source heat pump, and filtration project). In addition, these findings provide a theoretical reference for the development of numerical models to help recognize the probability of particles of different sizes to be captured in porous media.

Techno-Economic Analysis of the Heating System Robustness

A techno-economic analysis of different heating systems of a multi-apartment building is performed. The final energy savings and the economic benefit under different boundary conditions are investigated for a Passive House that has been realized and monitored in Innsbruck, Austria. Eight different system combinations are considered, varying the heat generation (direct electric (as-built), air/water heat pump (HP) and groundwater HP) as well as the size of the photovoltaic (PV) system. The systems are investigated with a building model with two different parameterizations: the pre-design stage and the model adapted to the monitored boundary conditions (BC: climate and user behaviour) and monitored energy consumption. The monitoring of the first two years of operation revealed a significantly higher space heating demand (29 kWh/(m2a) compared to 8 kWh/(m2a)). The most robust system (i.e. the system that performs best independent of the BC) for primary energy optimization is identified as an air-source heat pump with a 32 kWp photovoltaic system. This system also allows economic savings in case of high heating demand (adapted building model) and slightly higher costs in case of low heating demand (pre-design model). The groundwater-source HP is cost-effective only in scenarios with high heating demand due to significant investment and installation costs. Monthly primary energy factors are used to account for seasonal effects of the energy demand, providing an assessment of system efficiency that accounts for the so-called winter gap.

Clogging caused by coupled grain migration and compaction effect during groundwater recharge for unconsolidated sandstone reservoir in groundwater-source heat pump

In unconsolidated sandstone reservoirs, presence of numerous movable grains and a complex grain size composition necessitates a clear understanding of the physical clogging process for effective groundwater recharge in groundwater-source heat pump systems. To investigate this, a series of seepage experiments was conducted under in situ stress conditions using unconsolidated sandstone samples with varying grain compositions. The clogging phenomenon arises from the combined effects of grain migration and compaction, wherein the migration of both original and secondary crushed fine-grain particles blocks the seepage channels. Notably, grain composition influences the migration and transport properties of the grains. For samples composed of smaller grains, the apparent permeability demonstrates a transition from stability to decrease. In contrast, samples with larger grains experience a skip at the stability stage and directly enter the decrease stage, with a minor exception of a slight increase observed. Furthermore, a unique failure mode characterized by diameter shrinkage in the upper part of the sample is observed due to the combined effects of grain migration and in situ stress-induced compaction. These testing results contribute to a better understanding of the clogging mechanism caused by the coupled effects of grain migration and compaction during groundwater recharge in unconsolidated sandstone reservoirs used in groundwater-source heat pump systems.

Short- and long-term heating performances and optimization of solar heating coupled with groundwater source heat pump (SH-GWSHP) system for 24-h running buildings in Tibetan Plateau, China

Tibet is rich in solar energy and has significant heating demand for buildings. Hence, developing a multi-source complementary heating system based on solar energy is a feasible approach to address local heating issues in the Tibetan area. However, the design of a solar energy-based heating system for 24-h running buildings is challenging due to the mismatch between solar energy availability and nocturnal heating load. To fill this gap, a solar heating system coupled with a groundwater source heat pump (SH-GWSHP) is proposed in this study. The heating performance of the proposed SH-GWSHP system for 24-h buildings under Tibetan weather conditions is explored and optimized. A field test is conducted to assess the short-term performance of the SH-GWSHP system at Xigaze Peace Airport. Furthermore, a transient system simulation (TRNSYS) model of the coupled heating system is developed and utilized to analyze and optimize long-term system performance. The results show that the average temperature of a water tank is higher than 50 °C for 4 h and the measured energy efficiency ratios (EERs) of the SH system, combination heating mode, and GWSHP system are 8.52, 3.79, and 3.38, respectively. The maximum daily average collector efficiency is 0.4 and the average value is approximately 0.3 during the middle heating period. In addition, the overall solar fraction is only 0.20 over the entire heating season. The optimal volume of the water tank for performance optimization is 30 m3. The collector area should be maximized to fully utilize solar energy for heating, and the temperature of the heating water should be minimized to achieve optimal heating efficiency.

Analysis and simulation of ecological environment response of ground source heat pump system under thermal equilibrium

This work is designed to study the thermodynamic equations of groundwater source heat pump in hot summer and cold winter, and to determine the optimal operating conditions of groundwater source heat pump by means of the thermodynamic analysis of source heat pump, flow, unit, pump power, evaporation side and condensation side. Practice has proved that the equipment runs stably and with high efficiency. By comparison, the ground source heat exchangers were compared with conventional chillers and boiler. The results showed that the underground heat pump had higher energy consumption, lower primary energy consumption, reduced CO2 emissions, and reduced environmental pollution during operation, proving that the underground heat pump had obvious advantages over the conventional cooling and heating system. Meanwhile, this also shows that the long-term operation of ground heating system has caused the instability of ground heating system, the accumulation of cold and heat in ground-water, and the variation of ground temperature, which not only reduces the system efficiency, but it also affects the physical properties of soil itself and the soil heat flow, and will also cause changes in soil microbial environment and vegetation ecological environment, thus affecting the whole ecological environment.

Comprehensive Evaluation of Adaptability Zoning for Shallow Geothermal Energy Development and Utilization: Case of Nantong City, East Coast of China

The development of green energy sources, such as shallow geothermal energy, is one of the most important measures to reduce the environmental pollution caused by the use of traditional energy sources. At present, coastal cities in the east of the Yangtze River Delta, China, have favorable conditions for the development of shallow geothermal energy because of their abundant geothermal resources. However, the development and utilization of shallow geothermal energy are still in their infancy, and adaptability zoning is yet to be fully carried out. The study area is Nantong City, which is in the eastern coast of the Yangtze River Delta. A comprehensive analysis of the conditions of shallow geothermal energy is carried out based on the analysis of the regional geological, hydrogeological, and environmental geological conditions. The adaptability zoning index system of the groundwater source heat pump and buried pipe ground source heat pump system is then constructed, and the weight of evaluation factors is determined according to analytic hierarchy process. Finally, the adaptability zoning of shallow geothermal energy development and utilization mode is obtained by using the spatial analysis function of geographic information. The results showed that the areas with good suitability and better suitability account for 98.24% of the study area and those with good economy and better economy account for 99.67% of the study area. This method can provide reference suggestions for the orderly development and sustainable utilization of shallow geothermal energy in coastal cities in plain areas.

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.

Comparative economic analysis of air conditioning system with groundwater source heat pump in general-purpose buildings: A case study for Kayseri

In this study, which aims to reduce energy consumption and dependence on fossil fuels in buildings, the use of an alternative air conditioning system instead of conventional air conditioning systems (CACS), which are widely used in general-purpose public buildings (GPPBs) with high energy consumption, is investigated. A groundwater source heat pump system (GSHPS) was selected as the alternative air conditioning system that exploits an underground water source used in Kayseri province (Turkey). GSHPSs were used both for heating and cooling of a sample GPPB and all costs were determined in detail in the study. In order to compare whether the GSHPS is economical or not, a commonly used CACS, which consisted of a central heating system with natural gas and an air-cooled cooling system was selected. After system components was selected according to the thermal loads of the building, the system costs were determined considering the initial investment cost and the operating costs. Results showed that the proposed GSHPS was more economical than the CACS in terms of initial investment cost and equivalent uniform annual cost by 22.68% and 11.09%, respectively, despite being 3.87% more expensive in terms of total annual operating costs.

Geothermal dynamic constraints of groundwater source heat pump system in shallow aquifers

Due to the temperature of shallow aquifers being affected by atmospheric temperature, groundwater source heat pumps (GWSHPs) become unstable and the operation efficiency of GWSHP is constrained. In the study, the coupling numerical simulation model of the groundwater flow field and temperature field is established based on the continuous monitoring results in an actual experimental site, and the water and thermal migration of shallow aquifer is simulated under the influence of the atmospheric environment. The influence of the dynamic change in ground temperature is analyzed on a GWSHP. The results indicated that the temperature of the shallow aquifer is affected by the external temperature, and the recharge temperature in the summer cooling period was 33°C, and that in the winter heating period was 6°C in the actual site, to avoid the occurrence of thermal penetration when there is a gap between the actual situation and the design situation, the single cooler can balance the insufficient cooling capacity in summer under the most unfavorable situation. The research results can also provide a reference for the development and utilization of geothermal energy resources in shallow aquifers.

Estimation of the initial investment cost in systems equipped with heat pumps using regression analysis

"The present research aims to obtain a mathematical model for estimating the costs involved in the initial investment for heat pump systems using the regression analysis. In the current economic context towards a climate-neutral Europe by 2050, heat pumps are becoming increasingly used in the buildings sector. As innovative and sustainable heat energy systems, they require a higher capital investment than conventional heating and cooling systems. Therefore, this study addresses the current needs by carrying out a comprehensive analysis of the costs involved in the initial investing in a heat pump system. Three regression analyses will be carried out to estimate the costs for air source heat pumps, ground source heat pumps and water source heat pumps respectively."

Optimization of solar-assisted GWHP system based on the Trnsys model in cold regions

In this study, a Trnsys simulation prediction model for multistage utilization solar-assisted groundwater source heat pump system and a new year-round operation control strategy are proposed. A new dual-interface solar and groundwater heat storage module Type299 was created, which was imported into Trnsys transient simulation model for simulation. A one-year experiment was conducted to test the accuracy of the new model Type299 and Trnsys transient simulation prediction model, taking a case system in the Shenyang area as an example. When the proposed new system and control strategy was applied to the case system, the results showed that the maximum comprehensive performance coefficient of the new system is approximately 4.54, which is 23.8% higher than that of the original system. The annual solar energy utilization of the new system increased by approximately 4.68 × 105 MJ compared with the original system. After 10 years of simulation operation, it was found that the groundwater temperature under the action of the new system was approximately 3.1 °C higher than that of the original system. This effectively alleviates the underground water temperature decrease year by year caused by the operation of the original system.

Cyclic use of groundwater: An innovative way to improve performance of a groundwater source heat pump system during a cooling period

The building sector is a large user of energy and thus a large emitter of CO2. Replacing traditional energy with renewable energy in buildings can effectively reduce greenhouse gas emissions and global warming effects. This paper introduces a new groundwater source heat pump (GWSHP) system installed for air-conditioning of an official room. The main innovation of the new GWSHP system is the cyclic use of groundwater to save the electricity consumption of the lifting pump that pumps the groundwater from a well and also to reduce the amount of groundwater needed by the GWSHP system. The cyclic use of groundwater was realized by adding a circulating pump and a tank in the GWSHP system and intermittently running the lifting pump according to the water temperature in a groundwater heat exchanger. The performances of the new GWSHP system for four different operation modes of the lifting pump were evaluated and compared based on measurements of representative days in 2017 and 2019. The results show that the cyclic use of groundwater with an optimal operation mode can not only effectively improve the performance of the GWSHP system but also significantly reduce groundwater consumption. Specifically, the coefficient of performance of the GWSHP system was increased from 3.6 for conventional operation mode with no cyclic use of groundwater to 4.3 for the optimal operation mode, and the groundwater consumption per working day was significantly decreased from 9.2 m3 for conventional operation mode to 4.0 m3 for the optimal operation mode. Moreover, the long-term performance for three consecutive years from 2018 to 2020 was also evaluated based on measurements, and the results show that the long-term performance is almost the same as the performance of the representative day, which means that the representative day method used in this paper to evaluate the performance of the GWSHP system is feasible and reliable. The operating experience of this study can provide an important reference for the design and selection of GWSHP systems in areas with a different abundance of groundwater.

Analysis of the thermal performance reduction of a groundwater source heat pump (GWHP) system

This paper investigates the thermal performance reduction of a groundwater heat pump (GWHP) system installed in Hubei province, China by the monitoring of the system operation over a two-year period. Pipe corrosion and deposits were detected in the maintenance of heat pumps, which might contribute to the thermal performance reduction. In order to understand the physic-chemical dynamics inside heat pumps during the system operation, the groundwater pumped out from the aquifers and the deposits collected in a condenser of a heat pump were analyzed. The groundwater has electrical conductivity of 973 μS/cm, indicating low salinity. The X-ray fluorescence (XRF) analysis shows the deposits were composed mainly of 66.4% Fe2O3 and 17.8% CaCO3, indicating both effects of iron oxidation and groundwater fouling.The corrosion effects on the heat transfer efficiency of metal pipes were examined. The heat transfer coefficient (HTC) comparison of a raw pipe and three rusted pipes show that the HTC of the rusted pipes was reduced by 8.3–41.5%, meaning a significant decrease in heat transfer efficiency. It is verified that the thermal reduction of the GWHP system could be attributed to the pipe corrosion which desires to be carefully considered in system design and operation in future.

Performance evaluation of a hybrid heating system combined a groundwater source heat pump with an existing fuel oil heater for a horticultural greenhouse

ABSTRACT This paper reports a new hybrid heating system (HHS) installed in a horticultural greenhouse to lower the impact of high and unstable fuel prices on the greenhouse operation cost, to save the energy necessary to heat the greenhouse, and to reduce CO2 emissions. The HHS consisted of a groundwater source heat pump system for basic heating and an existing fuel oil heater for peak heating. The performance of the HHS, including the fuel oil and energy savings, and CO2 emissions reduction, was evaluated based on measurements during a heating period from November 2014 through May 2015. The results show that, comparing with only using the existing fuel oil heater to heat the greenhouse, the HHS can save 74.4% fuel oil and 22.8% energy, and reduce 35.5% CO2 emissions. In order to further increase the performance of the HHS, the operating control of the HHS, indoor hot air delivery system, and local thermal insulation of the greenhouse were improved. Performance evaluation based on measurements from November 2015 through May 2016 shows that the improved HHS can save 88.0% fuel oil and 35.9% energy, and reduce 48.7% CO2 emissions, which are significantly higher than those of the HHS before improved. Moreover, the comparison indicates that the performance of HHS was almost not changed with three different groundwater pumping rates tested herein. The proposed HHS is particularly suitable for transforming conventional fossil heating systems of horticultural greenhouses into a more energy-saving and thus sustainable heating system with a comparatively low initial cost.

Experimental Study on Automatic Switching of Solar Coupled Groundwater Source Heat Pump System

There have been few practical applications of solar coupled groundwater source heat pump (GWHP) systems in large public buildings, and data on this technology are scarce. A solar coupled GWHP system was investigated in this study. The system uses an underground water source heat pump system for heating in winter, cooling in summer, and providing part of the domestic hot water, and it also uses a solar energy system to prepare domestic hot water. These two types of energy are complementary. The system was tested throughout the cooling season. This experiment ran from May 10, 2021, to September 10, 2021. The results show that the system can guarantee the indoor design temperature and the supply of domestic hot water. The solar water heating system operated for 1233 min in the summer; hot water (2334 m3) was prepared. During the summer, the average energy efficiency ratio of the GWHP unit was approximately 4.88. The energy efficiency ratio of the entire system was approximately 3.34. Such projects can play a key role in demonstrating this type of system.

Four years monitoring of heat pump, solar thermal and PV system in two net-zero energy multi-family buildings

This work presents four-year monitoring results of two new multi-family houses in Innsbruck aiming to be net-zero energy buildings (NZEB). The project combines high-performance buildings designed in Passive House standard, highly-efficient HVAC systems i.e., low-temperature distribution and emission, a double-stage ground-water source heat pump including a desuperheater and mechanical ventilation with heat recovery, and maximum possible renewable sources i.e., roofs fully covered with photovoltaic panels (PV) and solar thermal collectors. The design goal of NZEB was to balance on an annual basis, the electricity consumption of the technical systems and the electricity production of the PVs, and later on the evaluation by means of a monitoring campaign. With a combination of high-performance technologies with respect to the building envelope, HVAC, and renewables, the measured annual onsite produced PV electricity is 6% (4-year average) higher than the one consumed by the heat pump. However, it was not sufficient to cover the consumption of all the technical systems (auxiliary and appliances). Concerning the building envelope, Passive House quality is recommended, concerning the HVAC, complex configuration seems not beneficial in practice and there was no clear indication of the benefit to implementing a desuperheater in this project. Solar thermal collectors produced 20% (4-year average) more heat per unit area than a PV-driven heat pump, however, the combination of both and the corresponding system complexity tends to show more negative aspects, and thus, a decision should be taken with care. Finally, it could be shown that reducing thermal losses and minimization of the auxiliary energies is of major importance to reach NZEB.

Research on simulation of energy consumption of ground water-source heat pump air conditioning system in plant factory

The study of low-cost energy supply methods for large plant factories in China is of great significance to promote the healthy and steady development of large greenhouses. Aiming at the problems of high cost, poor stability, chaotic production management, and no indicator of long-term operation energy consumption in the operation of large plant factories, this paper analyzes long-term operation data by studying the heating situation of Chongming plant factory to improve plant factory regulation methods for the purpose of energy saving and cost reduction. A plant factory model was constructed using TRNSYS to simulate typical annual energy supply throughout the year to obtain cooling and heating energy consumption. The simulation results show that the annual peak heat load of the plant factory is 1502.6 kW and the peak cooling load is 913.8 kW. The annual energy consumption of the whole plant factory is 3799.12 GJ for cooling and 4468.34 GJ for heating, and the annual energy consumption of the whole plant factory is 8267.46 GJ. A8 and its three surrounding greenhouses A6, A7, and A10 can be used as a single zone for energy supply. This zone takes advantage of the structural characteristics of the building to reduce energy consumption. The simulation shows that the ground source heat pump system is sufficient to supply the energy consumption of these four greenhouses and even to achieve the optimal temperature conditions for growing vegetables inside them.

Pore-Scale Simulations of Particles Migration and Deposition in Porous Media Using LBM-DEM Coupling Method

This paper studies the migration and deposition of suspended particles in porous media. This problem results from the fact that during the operation of a groundwater source heat pump, the recharging process will contribute to the impairment of soil permeability. A coupling lattice Boltzmann method, discrete element method and immersed moving boundary method were used to investigate the migration of particles in porous media. The DKT (Drifting, Kissing, Tumbling) phenomena were employed to validate our program. The coupled effects of concentration, flow rate and pH on the clogging mechanism of the porous media were analyzed. Results show that, due to the repulsive barrier between the particles and porous media, there is a critical velocity. At a low flow rate, the deposition ratio increases with the increase in velocity. Beyond the critical velocity, the deposition ratio decreases when the velocity increases due to higher shear force. Permeability impairment increases with the increase in concentration, especially in the low flow rate condition. Changes in pH mainly affect the repulsive barrier. For a low flow rate, the decrease in repulsive barrier greatly promotes the deposition of particles. Under the condition of favorable deposition, the increase in flow rate reduces the deposition phenomenon. Under the condition of unfavorable deposition, the lower flow rate condition has a lower deposition ratio. The process of particle deposition and the dynamic motion after deposition were observed such as particles gliding over the surface. Accumulated particles in the downstream form bridges and hinder fluid flow. At a high flow rate, strong shear force is more capable of destroying bridges and recovering permeability. Adsorbed particles glide on the surface of the grain and deposit in the downstream. This paper aims to help understanding of the micro-events of particle deposition and the clogging process.

Performance monitoring and verification of a groundwater source heat pump heating system in a greenhouse

The traditional heating of greenhouse is mainly by burning coal and fuel; this has some disadvantages such as low energy efficiency and high carbon dioxide emissions. As a renewable energy, groundwater source heat pump (GWSHP) has been widely concerned, and its heating application in greenhouse has a significant impact on energy saving and emission reduction. This paper introduces the GWSHP, and establishes a heating system combined with an existing fuel oil heater (FOH) in a horticultural greenhouse in Gunma Prefecture, Japan. The GWSHP bore most of the heat load, and the FOH was only used as an auxiliary heat source at low temperature. A heating cycle operation monitoring was carried out from November to May of the following year, and the fuel oil saving rate and energy saving rate of the system were calculated to be 74.4% and 22.3% respectively. The results show that the combined heating of GWSHP and FOH is energy-saving and environmentally friendly, and can be widely used in areas rich in groundwater.