Seawater Source Heat Pump System Research Articles

Techno-economic evaluation of a seawater source heat pump system with auxiliary heat source in cold region of China

The utilizing of renewable seawater energy through seawater source heat pumps (SWHPs) in coastal areas is considered as a sustainable technology with minimal environment impact. Promotion of this technology needs clear understanding of its techno-economic performance but there are limited relevant studies. An empirical study was conducted in Qingdao, China, based on a practical installation comprising SWHPs supplemented by electric boilers. On-site measurements revealed considerable COP of 3.81 for SWHP and COPs of 2.87 for the whole system, implying SWHP as a viable and efficient solution for space heating in mild winter in this region. Results from TRNSYS simulations showed SWHP with auxiliary gas boilers (SWHP-GB) achieved the lowest annual primary energy demand and best economic and environmental benefits compared with other three schemes, namely SWHP with electric boilers (SWHP-EB), chillers with gas boilers (Chiller-GB) and air source heat pumps with gas boilers (ASHP-GB). SWHP played important roles in energy efficiency of the whole system with a considerable seasonal COP of 3.72 and 3.22 respectively for heating and cooling. Annual primary energy demand of SWHP-GB accounted for 55 %, 78 % and 56 % of SWHP-EB, Chiller-GB and ASHP-GB, respectively. SWHP-GB achieved the lowest life cycle costs and a rapid payback period of 10.9 years. Moreover, using direct or indirect heat exchange with seawater was found with limited impact on techno-economic performance of the system. To conclude, SWHP-GB could be used as an efficient solution for building heating and cooling in northern coastal cities in China.

Power consumption prediction model based on artificial neural networks for seawater source heat pump system in recirculating aquaculture system fish farm

Power consumption prediction model based on artificial neural networks for seawater source heat pump system in recirculating aquaculture system fish farm

Numerical investigation on operational performance of seawater-source heat pump system coupled with capillary-box heat exchangers

In view of the energy-saving potential of the seawater-source heat pump system (SWHPs) coupled with capillary-box heat exchangers (CBHEs), the operational performances of this system were investigated on various temporal scales, including annually, monthly, and daily. An overall system numerical model was developed by integrating the CBHEs, heat pump and dynamic building loads model. The results indicated that the annual COPh was 3.4. In the coldest month, the monthly COPh was 3.3, and the daily COPh was mainly determined by the daily heating demand. The corresponding annual COPc was 4.8. In the hottest month, the monthly COPc was up to 5.0, and the daily COPc was more sensitive to seawater temperature fluctuations. On a typical summer day, the operating time of the heat pump with an hourly capacity ratio above 50 % was about 2.7 times that of a typical winter day. Due to the effective removal of the heat discharged from the CBHEs in the seabed, the impact of heat accumulation on the performance of this system can be neglected in the long-term operation. This study provided practical implications for the design and application of the CBHEs-coupled SWHPs.

Performance of capillary box heat exchangers buried in seabed for seawater-source heat pumps

An innovative seawater-source heat pump system (SWHPs) was developed by employing capillary box heat exchangers (CBHEs) buried in the seabed as the front-end heat exchanger. Field experiments were firstly presented to test the efficiency of the SWHPs in a practical project. The experimental results show that even under extreme cold/hot climate conditions, the 24-hour COP/EER of the heat pump unit can reach respectively 2.96 and 5.39, which is superior to an alternative air source heat pump (ASHP). Furthermore, an unsteady state three-dimensional seepage and heat transfer model was established to study the thermal performance of CBHEs buried in the seabed using ANSYS FLUENT software. Based on the model, the influences of seawater seepage velocity, thermophysical characteristics of backfilled sand, and flow velocity in the capillary tube on the thermal characteristics of CBHEs were investigated. Moreover, considering the per area heat transfer rate of CBHEs as the evaluation target, the sensitivities of five representative factors including the flow velocity in capillary tubes, seawater seepage velocity, specific heat capacity, density and thermal conductivity of the backfilled sand were discussed using the single factor sensitivity analysis to detect the significant influence parameters.

Heat transfer performance analysis of seawater heat exchange pipelines in deep seawater closed cooling air conditioning system

The efficiency improvement of traditional seawater source heat pump system is limited and pipelines of the open seawater cooling air conditioning system experience scaling and corrosion. To overcome these problems, this paper proposes a deep seawater closed cooling air conditioning system. The system directly uses the closed heat exchange pipeline to exchange heat with the deep seawater and extracts the seawater cooling capacity for cooling. Numerical simulation is used to study the effects of different pipe diameters, flow rates, and inlet water temperatures on the heat transfer performance of vertical inlet sections, submarine heat exchange coils and vertical outlet sections. Since seawater has temperature and flow rate gradients in the vertical direction, the use of a hydraulic calculation table of the vertical pipe section and the calculation diagram of design and selection line of submarine heat exchange coil is proposed. Insulating subsections of the outlet section by dividing the section into 3 °C based on the seawater temperature is proposed. And the subsection insulation layer thickness corresponding to different pipe diameters are given. This study proposes a calculation method for the selection of key design parameters of deep seawater closed cooling air conditioning systems, providing a new method for making full use of seawater resources.

Performance study on the seepage and heat transfer in a bench-scale multi-well infiltration intake system for seawater source heat pump

The Beach Well Infiltration Intake (BWII) system is one of the various methods for pumping seawater for Seawater Source Heat Pump (SWHP) systems that improve the stability, reliability, and energy efficiency of the SWHP systems in cold climate areas. Because of the limitations of the site conditions, it is difficult to perform experimental studies on the BWII system under different experimental conditions, especially for multi-well systems. Therefore, a BWII experimental system that incorporated nine beach wells was established in a laboratory in this paper. The goal was to study the seepage and heat transfer performance of the multi-well infiltration intake system and calculate the influencing range for pumping groundwater on sands in a sandbox. Then, an established seepage and heat transfer model of the BWII system was validated by the experiment. Based on the validated model, the method for designing an experimental sandbox was studied. The research results showed that the effective width increased with an increase in the distance between the pumping well and the long water tank. However, the effective width in the back part of the pumping well decreased with an increase in this distance. The result that the effective length decreased with an increase in this distance was contrary to our subjective expectations. When the distance between the pumping well and the long water tank was 0.5 m, the effective length and effective width were 1.5 ∼ 2.1 m and 0.9 m respectively. The formulas of the effective width and the effective length were derived. The experimental study provided a method to study the seepage and heat transfer performance of the BWII system and was complementary to the theoretical research and the practical engineering field research. The research results provided in this study will contribute to the establishment of a set of seepage heat transfer similarity test methods.

Heating performance and spatial analysis of seawater-source heat pump with staggered tube-bundle heat exchanger

Seawater-source heat pump (SWHP) system exhibits merits of building energy conservation and reducing carbon emissions, while enhancing the heat transfer of seawater heat exchangers is the key to improve the system performance. Here, a model of SWHP system with staggered tube-bundle heat exchanger is established and its performance in winter is numerically studied and verified by experiments. The wave theory is introduced into the mathematical model to describe the flow field of actual ocean and improve the accuracy. The heat transfer performance of staggered tube-bundle exchanger is investigated under icing conditions, and the results indicate that the ice layer thermal resistance outside the tube accounts for more than 28% of the total thermal resistance. The impacts of seawater temperature on the SWHP system performance are discussed and the average increment of heating capacity and COP is 0.12 kW and 0.046 respectively with the increase of seawater temperature by 1 °C. Furthermore, a spatial analysis of SWHP system in 29 coastal cities of China are analyzed and compared with air-source heat pump (ASHP) system. The results show that SWHP system has greater advantages than ASHP system, especially in the southern cities. This research comprehensively analyzes the technology, economy and geography of SWHP system from a more macro perspective, and it can promote the application of ocean thermal energy.

Suitability Evaluation of Seawater Source Heat Pump in a Seashore Refrigeration Station

In this paper, the suitability of using seawater source heat pump in a seaside refrigeration station in Qingdao was evaluated. A systematic evaluation was made on the conventional chiller with cooling tower system, the conventional chiller with titanium plate heat exchanger system and the seawater source heat pump system, including energy saving evaluation, economic evaluation (initial investment cost and operating cost) and environmental evaluation. The evaluation results showed that the initial investment cost was slightly increased, the operating cost was low, the cop value was high and the impact on the marine environment was small when the seawater source heat pump system was directly used.

A comparative experimental study on the performance of staggered tube-bundle heat exchanger with unequally-pitch and equally-pitch arrangement in oscillating flow

A novel staggered tube-bundle seawater heat exchanger with unequally-pitch arrangement, which the transversal and longitudinal tube pitches are inhomogeneous, is firstly proposed and applied in the closed-loop seawater source heat pump system. An experimental system that can induce the regular wave to simulate the seawater flow is established to investigate the thermal resistance ratio, overall heat transfer coefficient, thermal efficiency of heat exchanger under various wave parameters. The thermal performance, hydraulic performance, and comprehensive thermal-hydraulic performance of heat exchangers with unequally-pitch arrangement and equally-pitch arrangement are compared. The results indicate that the unequally-pitch arrangement of tube-bundle heat exchanger can significantly enhance the overall heat transfer coefficient and thermal efficiency, meanwhile decrease the pressure drop, and consequently improve the comprehensive performance. The present study is conducive to improve the performance potential of staggered tube-bundle seawater heat exchanger and promote the exploitation of ocean thermal energy.

Mathematical Modeling and Performance Analysis of Seawater Heat Exchanger in Closed-Loop Seawater-Source Heat Pump System

AbstractThe seawater source heat pump (SWHP) utilizes low-grade energy from seawater to satisfy heating/cooling requirements of coastal buildings. Compared with the open-loop SWHP system, the close...

A practical research on capillaries used as a front-end heat exchanger of seawater-source heat pump

Traditional seawater-source heat pump (SWHP) needs to set water intake and titanium plate heat exchanger which result in high initial investment and large work quantity. A new type of SWHP was recommended, which use capillaries made by PPR (polypropylene random) submerged in seawater as the front-end heat exchanger. Glycol antifreeze solution was injected into the capillaries used as circulating medium. Capillaries were used as heat exchanger between seawater outside and glycol antifreeze solution inside. This method can greatly reduce the initial investment and improve COP of the SWHP system. This paper discusses the feasibility of capillaries used as the front-end heat exchanger of SWHP. An experimental platform was designed and constructed to measure the heat transfer coefficient of capillaries, and collect the operating data to calculate COP of SWHP in winter and summer. The experiment results show that, the average COP of the SWHP system is 3.17 in winter and 3.3 in summer. When the velocity of glycol in capillary tube is 0.15 m/s, the measured value of capillary heat transfer coefficient k is 161.01 W/(m2·°C). The efficiency of capillary heat exchanger was greater than 96.4%, which shows that it is feasible to use capillaries as the front-end heat exchanger of SWHP.

Large-area seepage and heat transfer model of beach well infiltration intake system for seawater source heat pump

The seawater source heat pump (SWHP) has attracted significant attention as a renewable energy utilization system. The beach well infiltration intake system (BWIS) effectively improves the stability, reliability, and energy-efficiency of SWHP systems in cold climate areas. A seepage and heat transfer model is established for scientific BWIS applications. MATLAB is used to analyze solutions for the seepage model, as well as to obtain a numerical solution for the heat transfer model. The analytical solution for the seepage model is a fast-solving method compared with the numerical solution. The method explicitly analyzes the qualitative and quantitative relationships among influencing factors of the system. In the heat transfer model, the advection term dominates the heat transfer, while the conduction term can be ignored. A BWIS for SWHP systems is tested and the simulation results agree with the measured data. The simulation model is used to analyze BWIS performance. All system influencing factors are identified and classed according the model. The results demonstrate the usefulness of the simulation model, thereby validating the method as a potential engineering tool for BWIS design.

Multifactor analysis on beach well infiltration intake system for seawater source heat pump

The seawater source heat pump (SWHP) is a renewable energy utilization system. The beach well infiltration intake system (BWIS) effectively improves the stability, reliability, and energy efficiency of SWHP systems in cold climate areas. BWIS research requires a multidisciplinary approach that involves both hydrogeology and heat transfer theory. There are many factors influencing the energy consumption and life-cycle costs of the systems, with each factor having many possible values. This paper aims to determine the degree of influence of ten representative factors of BWIS: specific heat capacity of rock-soil, rock-soil density, thermal conductivity of rock-soil, void fraction of rock-soil, rock-soil permeability, beach well radius, site length, site width, row number of beach wells, and column number of beach wells. In this paper, a BWIS seepage and heat transfer model is established. Based on the model, an orthogonal design optimization method is presented and analyses are conducted for heat pump unit energy consumption, seawater pump energy consumption, and economic cost for various conditions using MATLAB code. The results indicate that a greater number of beach wells is not always better and the number and placement of beach wells should be scientifically and objectively optimized by the orthogonal design method. The optimization method can scientifically guide engineering design for BWIS and offset the design deficiency that results from the current practice of only using a hydrogeological report of randomly selected test wells.

Effect of seawater intake methods on the performance of seawater source heat pump systems in cold climate areas

The Seawater Source Heat Pump (SWHP) system is an energy-saving and environmentally-friendly technology for the cooling and heating of buildings. The SWHP system is based on obtaining “free” heat from the sea by using heat pumps. In this study, field test and analysis were conducted to compare the performances of beach well infiltration intake system and direct intake system for SWHP systems at the Liaodong Peninsula, China. The average unit COP was 2.99 for the direct intake system and 4.66 for the beach well infiltration intake system, with the average seawater temperature being 5.83°C and 12.85°C, respectively. The test results indicate that the beach well infiltration intake method effectively improves the stability, reliability and energy efficiency of the SWHP systems in cold climate areas, and the intake seawater temperature is a critical factor influencing the performance of SWHP system. A simulation study was conducted for further illustration that how the intake seawater temperature of the beach well infiltration intake system was increased. The simulation result shows that the intake seawater temperature of beach well infiltration intake system is higher than the direct intake system, and the main reason is that the underground seawater with higher temperature is extracted. The intake seawater temperature is very sensitive to the seepage velocity in a range, and the flow quantity of pump seawater should not be too large under limited engineering conditions. The simulation results are foundations for further successful SWHP system engineering.

Heat transfer performance of a seawater-source heat pump with radiant floor heating system in cold areas of China

The thermal performance of seawater-source heat pump with radiant floor heating system during the whole heating season in cold regions of China is studied. High-density polyethylene helical coil heat exchanger and a new type radiant floor heating system with aluminium layer is adopted to improve the thermal performance of the system. The heat transfer characteristics of the heat exchanger in flowing seawater and the thermal resistance of each component is experimentally studied, which will be much helpful in the optimizing of heat exchangers used for the seawater-source heat pump system. The temperature distribution of the radiant floor heating system with aluminium layer is tested and the system thermal efficiency is studied during the whole heating days. The results indicate that the heating system has a large popularizing and utilizing value.

Numerical and experimental investigation of a helical coil heat exchanger for seawater-source heat pump in cold region

The heat transfer performance of a high-density polyethylene helical coil heat exchanger (HCHE) which is adopted by a seawater-source heat pump system (SWHP) is experimentally and numerically studied. The effects of seawater flow rate on heat transfer performance of the HCHE are investigated and the correlation between Nusselt and Reynolds number is fitted by the experimental results of cooling condition. The fitted results are compared with other similar studies of helical heat exchangers. Mathematical models in cooling condition, non-icy condition and icy condition are developed with the calculated external convective heat transfer coefficient. The simulation results are verified by the experimental data of icy condition and they show good agreement with each other. The effects of different key parameters on the heat transfer performance of the HCHE are investigated, such as inlet temperature, velocity of intermediate medium, pipe length and diameter, temperature of seawater and icing outside the pipes. The results indicates that the consideration of seawater flow rate in the study of subsea heat exchangers is much closer to the reality and the development of the mathematical models is very helpful in the designing and optimizing of the subsea heat exchangers used for the SWHP system.

The Thermal Characteristics of a Helical Coil Heat Exchanger for Seawater-source Heat Pump in Cold Winter

A high-density polyethylene helical coil heat exchanger (HCHE) is firstly adopted by a seawater-source heat pump system (SWHP) and experiments are conducted to study the thermal performance of the heat exchanger in icy condition. The external convective heat transfer coefficient is calculated by the experimental results and used in the development of the mathematical models. To predict the heat transfer process of the HCHE in icy condition in frigid periods of winter, a mathematical model is developed. Simulations with different parameters are conducted to investigate the effects of variable parameters on the thermal performance, such as inlet temperature, intermediate medium's flow rate, heat exchanger's length and diameter, temperature of seawater. The study indicates that the developments of the mathematical model are very helpful in the designing of heat exchangers used for the SWHP system.

Water pumping analysis and experimental validation of beach well infiltration intake system in a seawater source heat pump system

Based on energy conservation equation and Darcy’s law, a model of beach well infiltration intake system applied in a seawater source heat pump system was established. The model consists of the seawater seepage and the heat transfer process. A porous medium model in a software named FLUENT was applied to simulate the seepage and the heat transfer process. This model was also validated by field experiment conducted on the seashore in Tianjin, China. The maximum relative error between simulation results and experimental results was 2.1% (less than 5%), which was acceptable in engineering application. The porosity and coefficient of thermal conductivity of the aquifer soil were determined to be 0.49 W/(m·K) and 1.46 W/(m·K), respectively in the simulation. In addition, the influencing factors of pumping water of beach well were also analyzed. The pumping water was found to increase when the distance between the beach well and the impervious boundary becomes longer, when the distance between the beach well and the supplying water source shortens, when the diameter of the beach well enlarges, and the drawdown enlarges.

Experimental Investigation of the Heat Transfer Characteristics of a Helical Coil Heat Exchanger for a Seawater-Source Heat Pump

AbstractIn this study, a high-density polyethylene helical coil heat exchanger (HCHE) is firstly adopted by a seawater-source heat pump system (SWHP) and experiments are conducted to determine the ...

The thermal performance of seawater-source heat pump systems in areas of severe cold during winter

The research concerning ocean energy exploitation in North China is undoubtedly of significant importance to the development of the national ocean energy. The use of seawater heat pump (SWHP) systems is a better choice than air-source heat pump (ASHP) systems. The latter systems have a lower efficiency because of the formation of frost on the surface of its airside heat exchanger when the ambient air temperature is low. This paper reports research investigating the system efficiency of SWHP systems in areas of severe cold during winter. Experiments are conducted to compare the thermal performance of the beach well infiltration intake systems (BWIS) and the helical coil heat exchanger (HCHE) for SWHP systems in the Bohai Sea, Tianjin, North China. Heat transfer rate, COP (coefficient of performance) values, exergy efficiencies and exergy destruction rates of the SWHP systems with BWIS and HCHE are presented and compared with the ASHP systems. The study results indicate that the BWIS for SWHP systems has the highest thermal performance during the whole heating season in areas of severe cold during winter. That performance is observed because icing on the outer surfaces of the tubes of the HCHE and frost formation on the surface of the heat exchanger of the ASHP have great effects on the heat transfer performance. The Heating seasonal performance factor (HSPF) is used to express the performance of heat pump systems over the entire heating season. Economic analyses of the BWIS and HCHE are performed according to local economics to compare the application of the HCHE and BWIS, and the results indicate that the HCHE has a better economic value.