地源热泵在室内游泳池供暖空调中的应用研究

在分析了地源热泵系统的特点和概算了室内游泳池的冷热负荷的基础上，提出采用地源热泵系统可同时满足室内游泳池的供暖、空调及池水加热3项需求；分析了不同季节地源热泵在游泳池的运行工况。通过分析比较表明，地源热泵系统的运行费用比传统的冷水机组加燃油锅炉系统的运行费用节省约50％，比冷水机组加燃气锅炉系统的运行费用节省21％。     

Performance evaluation and modeling of a hybrid cooling system combining a screw water chiller with a ground source heat pump in a building

The performance of a hybrid cooling system that combines a screw water chiller with a ground source heat pump (GSHP) was measured and analyzed at various cooling loads. In addition, the hybrid cooling system in a building was modelled sophisticatedly using EnergyPlus and then validated with the measured data. The coefficient of performance of the GSHP was lower than that of a conventional chiller in the monitored building, but the hybrid cooling system helped to stably provide the required cooling capacity at high-load conditions. The mean bias error and the normalized root-mean squared error of the predicted cooling load of the building were −8% and 12.4%, respectively. The hybrid cooling system was simulated by varying four operating parameters: the operating schedule, chilled water temperature (T_CW), dry-bulb temperature (T_DB), and entering water temperature (T_EW). The T_CW is ascertained as being the most effective control parameter in the hybrid cooling system.     

地源热泵的优越性及前景展望

介绍了地源热泵的工作原理，并通过比较地源热泵与传统空调系统的运行费用，说明了地源热泵在运行费用方面具有较大优势。虽然地源热泵的应用受到一些制约因素的影响，但作为一项节能新技术，地源热泵必将拥有广阔的应用前景。     

A study on the performance of a geothermal heat exchanger under coupled heat conduction and groundwater advection

Being environmental friendly and with the potential of energy-efficiency, more and more ground-source heat pump (GSHP) systems are being widely used. However, the influence of groundwater advection on the performance of the geothermal heat exchanger (GHE) in a GSHP is not still clearly known. In this paper, the configuration of a vertical dual-function GHE used in an integrated soil cold storage and ground-source heat pump (ISCS&GSHP) system, which charged cold energy to soil at night and produced chilled water in daytime in summer, and hot water for heating in winter, is firstly presented. This is then followed by a report on a mathematical model for the GHE considering the impact of the coupled heat conduction and groundwater advection on the heat transfer between the GHE and its surrounding soil. The GHE model developed was then integrated into a previously developed simulation program for an ISCS&GSHP system, and the operating performances of the GHE in an ISCS&GSHP system having a vertical dual-function GHE have been studied by simulation and reported. These simulation results, firstly seen in open literature, are much helpful to the design of a GHE buried in soil and widely used in GSHP systems or ISCS&GSHP systems.     

Modelling of heat supply for natural gas pressure reduction station using geothermal energy

In this paper, a series of works are conducted to study the effect of replacing natural gas burning heaters by a ground source heat pumps (GSHPs) to prevent natural gas freezing in the pressure regulating stations. In fact, the pressure drop causes a great temperature drop that can block out the pipeline and it is very crucial to control the phenomenon. Firstly, a conventional heater in the gas pressure drop station of Damavand city is selected as a case study. Then, a shell and tube heat exchanger coupled with GSHP is modelled to replace the conventional heater for eliminating the natural gas consumption in heaters. Finally, consumed energy, costs, and greenhouse gasses emissions are compared with the conventional system. Some main findings from the model show that: (1). Based on the GS2000 software results, the GSHP pipe trench is 601?m which are 7% less than the calculated data. (2). considering different inflation rates (15%-30%), the payback time would change between 4.5 and 7.5 years. (3). Due to the reduction in fossil fuel consumption, the CO₂ emission would be reduced by 47%.     

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.     

Cooling performance of a vertical ground-coupled heat pump system installed in a school building

This paper presents the cooling performance of a water-to-refrigerant type ground heat source heat pump system (GSHP) installed in a school building in Korea. The evaluation of the cooling performance has been conducted under the actual operation of GSHP system in the summer of year 2007. Ten heat pump units with the capacity of 10 HP each were installed in the building. Also, a closed vertical typed-ground heat exchanger with 24 boreholes of 175 m in depth was constructed for the GSHP system. To analyze the cooling performance of the GSHP system, we monitored various operating conditions, including the outdoor temperature, the ground temperature, and the water temperature of inlet and outlet of the ground heat exchanger. Simultaneously, the cooling capacity and the input power were evaluated to determine the cooling performance of the GSHP system. The average cooling coefficient of performance (COP) and overall COP of the GSHP system were found to be ～8.3 and ～5.9 at 65% partial load condition, respectively. While the air source heat pump (ASHP) system, which has the same capacity with the GSHP system, was found to have the average COP of ～3.9 and overall COP of ～3.4, implying that the GSHP system is more efficient than the ASHP system due to its lower temperature of condenser.     

Verification study of a GSHP system Manufacturer data based modeling

GSHP (ground source heat pump) systems have become widely used as a result of the recent increasing demand for new and renewable energy polices in Korea. However, reliability issues have been key issues during installation and operation since they were initially designed. This paper introduces a systematic method for verification of the actual operating performance of a water-to-water GSHP system. The main idea is to compare the actual performance with the manufacturer's data, based on the ISO standard, and then to reduce the gap between the two. The manufacturer's performance data include the EWT (entering water temperature), LWT (leaving water temperature), capacity, flow rate, power, and COP (coefficient of performance). The verification technique was tested using a water-to-water GSHP system designed and installed at the KIER site. The verification study showed that actual performance was lower than that specified by the manufacturer's data. Accordingly, the refrigerant was recharged and the compressor and the expansion valve were replaced, resulting in an increase in the heating and cooling COP by 25.26% and 18.24%, respectively. The new verification method allowed the easy identification of the problems affecting the GSHP system and their subsequent correction.     

An integrated 3D approach to assess the geothermal heat-exchange potential: The case study of western Sicily (southern Italy)

This paper presents a multidisciplinary methodology to estimate the underground heat-exchange potential for Borehole Heat Exchangers (BHEs) coupled with Ground Source Heat Pumps (GSHPs) over wide areas. The proposed methodology was tested in four sites in western Sicily (southern Italy) where the shortage of subsurface geological data, in addition to the undefined authorization processes for this kind of system, is probably the main barrier to planning and exploiting geothermal heat for heating and cooling purposes. Reliable high-resolution 3D geological and petrophysical models were built based on the integration of airborne electromagnetic data and laboratory measurements of the thermal properties of rock samples. A GIS-based procedure was applied to assess the geothermal heat-exchange potential using 3D models of thermal conductivity as the main input. The results of the analyses are represented by thematic maps of the underground heat exchange potential for BHEs coupled with GSHPs. The study areas show a generally high suitability for the use of this technology and several municipalities in the area could take advantage of the resulting maps for energy planning.     

Theoretical study on the performance of an integrated ground-source heat pump system in a whole year

Being environmental friendly and with the potential of energy-efficiency, ground-source heat pump (GSHP) systems are widely used. However, in southern China, there exists large difference between cooling load in summer and heating load in winter. Thus the increase of soil temperature gradually year-by-year will decrease the COP of the GSHP system. In this paper, the configuration of a vertical dual-function geothermal heat exchanger (GHE) used in an integrated soil cold storage and ground-source heat pump (ISCS&GSHP) system, which charged cold energy to the soil at night and produced chilled water at daytime in summer, and supplied hot water for heating in winter, is presented. This is then followed by reporting the development of the mathematical model for the GHE considering the impact of the coupled heat conduction and groundwater advection on the heat transfer between the GHE and its surrounding soil. The GHE model developed was then integrated with a water-source heat pump and a building energy simulation program together for a whole ISCS&GSHP system. Then the operation performance of the ISCS&GSHP system used for a demonstration building is studied. These simulation results indicated the system transferred 71.505% of the original power consumption at daytime to that at nighttime for the demonstration building. And the net energy exchange in the soil after one-year operation was only 2.28% of the total cold energy charged. Thus we can see the feasibility of the ISCS&GSHP system technically.     

Investigation on the feasibility and performance of ground source heat pump (GSHP) in three cities in cold climate zone,China

As a renewable energy technology, ground source heat pump (GSHP) system is high efficient for heating and cooling in office buildings. However, this technology has strong dependence on the meteorological and building envelope thermal characteristic parameters. For the purpose of quantitative investigation on the feasibility and performance GSHP, three cities located in cold climate zone, Qiqihaer, Shenyang and Beijing, were sampled. Firstly, the office building dynamic loadings in these cities were calculated on basis of the different meteorological and envelope thermal characteristic parameters. The TRNSYS, one kind of energy simulation software, were employed to simulate the operation performances of GSHP on basis of these parameters. The simulation revealed the data on the outlet/inlet temperature of buried pipes, soil temperature, energy consumption distribution and the coefficient of performance (COP) for one year operation. Furthermore, ten years operation was also simulated to show the stability of the performance based on the outlet/inlet temperature of buried pipes and soil temperature. From these results, the GSHP had shown its most suitable performance in Beijing, second in Shenyang and worst in Qiqihaer. These results could be used as a reference on suitable utilization of GSHP systems in office buildings located in cold climate zone, China.     

Greenhouse gas emission savings of ground source heat pump systems in Europe: A review

An overview is presented on the last decade of geothermal heating by ground source heat pumps (GSHPs) in Europe. Significant growth rates can be observed and today's total number of GSHP systems is above 1 million, with an estimate of about 1.25 million mainly used for residential space heating in 2011. These systems are counted among renewable energy technologies, though heat pump operation typically consumes electricity and thus only a fraction of the energy produced is actually greenhouse gas (GHG) emission free. Consequently, only in the most mature markets of the Scandinavian countries and in Switzerland, calculated emission savings reach more than 1% compared to standard heatings. However, Sweden shows that more than 35% is possible, with about one third of these systems in Europe concentrated in this country. Our calculations demonstrate the crucial role of country-specific heating practices, substituted heat mix and primary electricity mix for country-specific emission savings. For the nineteen European countries studied in 2008, 3.7 Mio t CO₂ (eq.) are saved in comparison to conventional practice, which means about 0.74% on average. This reveals that many countries are at an early stage with great potential for the future, but even if the markets would be fully saturated, this average would barely climb to about 30%. These numbers, however, take the current conditions as reference, and when extrapolated to the future can be expected to improve by greener electricity production and increased heat pump performance.     

Evaluation of region-specific residential energy systems for GHG reductions: Case studies in Canadian cities

This study estimates energy use and greenhouse gas (GHG) emissions associated with operations of alternative residential energy systems. In case studies, the same detached four-bedroom house built in accordance with R2000 standards is studied in five Canadian cities with different climate and electricity mix. Conventional energy systems and alternatives using three technologies, namely ground source heat pumps (GSHPs), photovoltaics, and energy-efficient appliances; and their combinations are investigated. The results show that using a GSHP in Calgary may increase overall GHG emissions, as electricity to drive the pump is primarily produced in coal-fired power stations. Using photovoltaics to generate electricity from carbon-free sources or energy-efficient appliances to reduce electricity demands result in almost no GHG reductions in Montreal and Vancouver, where over 90% of electricity comes from hydro power. The results also show that the use of photovoltaics in combination with GSHPs in Ottawa and Toronto, or with energy-efficient appliances in Calgary, can lead to more GHG reductions, compared to the use of a single technology. As a result, while climate affects energy use to some degree, local sources of electricity may have a greater impact on overall GHG emissions, which is an important measure of environmental impacts.     

A study on utilization of ground source energy for space heating using a nanofluid as a heat carrier

Ground source heat pump (GSHP) systems are well established as an energy-efficient space conditioning device. However, for better utilization of the ground source, improvement in GSHP performance is desirable, which limits the small temperature difference between the ground and the circulating fluid. In this study, efforts have been made to investigate the performance of a ground heat exchanger (GHX) with a nanofluid as a heat carrier. Mathematical modeling is performed for the closed-loop vertical U-tube GHX with six different (Al₂O₃, CuO, graphite, multiwalled carbon nanotube, graphene, and Cu) water-based nanofluids. The effect of different operating parameters on GHX length, fluid temperature, and pressure drop with nanofluids is determined. On the basis of the analytical results, it is found that the graphite particle-based nanofluid plays a prominent role to enhance the performance of the GHX as compared with other nanoparticles. The maximum enhancement in the increase in outlet fluid temperature and reduction in pipe length with graphite particle-based nanofluid are 68.3% and 63.3%, respectively, for an increase in temperature difference from 7°C to 15°C between the atmosphere and the ground. Also, with the graphite particle-based nanofluid and the increase in pipe diameter from 20 to 50 mm, the fluid outlet temperature increases up to 11.2%, and the requirement in GHX length reduces up to 55%.     

Algebraic solution of capillary tube flows. Part II: Capillary tube suction line heat exchangers

Capillary tube suction line heat exchangers have been modeled using both numerical and analytical approaches. The former requires a reasonable understanding of the governing heat and fluid flow equations, thermodynamic relations, numerical methods, and computer programming, and therefore are not suitable for most refrigeration and air-conditioning practitioners. Alternatively, empirical algebraic formulations for diabatic capillary tube flows have been proposed in the literature, in spite of their lack of generality and accuracy. This paper introduces a physically consistent, unconditionally convergent, easy-to-implement semi-empirical algebraic model for capillary tube suction line heat exchangers, with the same level of accuracy as found with more sophisticated first-principles models. The methodology treats the refrigerant flow and the heat transfer as independent phenomena, thus allowing the derivation of explicit algebraic expressions for the refrigerant mass flow rate and the heat exchanger effectiveness. The thermal and hydraulic models are then conflated through the so-called Buckingham-π theorem using in-house experimental data collected for diabatic capillary tube flows of refrigerants HFC-134a and HC-600a. Comparisons between the model predictions and the experimental data revealed that more than 90% and nearly 100% of all data can be predicted within ±10% and ±15% error bands, respectively.     

Cooling characteristics of ground source heat pump with heat exchange methods

The objective of this study is to investigate the influence of the cooling performance for a water-to-water ground source heat pump (GSHP) by using the counter flow and parallel flow methods. The GSHP uses R-410A as a refrigerant, and its main components are a scroll compressor, plate heat exchangers as a condenser, an evaporator, a thermostatic expansion valve, a receiver, and an inverter. Based on our modeling results, the heat transfer rate of the counter flow evaporator is higher than that of the parallel flow evaporator for a heat exchanger length greater than 0.42 m. The evaporator length of the GSHP used in this study was set to over 0.5 m. The performance of the water-to-water GSHP was measured by varying the compressor speed and source-side entering water temperature (EWT). The cooling capacity of the GSHP increased with increased compressor RPMs and source side EWT. Also, using the counter flow method, compared to the parallel flow method, improves the COP by approximately 5.9% for an ISO 13256-2 rated condition.     

Direct numerical simulation of interphase heat and mass transfer in multicomponent vapour–liquid flows

A Volume-of-Fluid methodology for direct numerical simulation of interface dynamics and simultaneous interphase heat and mass transfer in systems with multiple chemical species is presented. This approach is broadly applicable to many industrially important applications, where coupled interphase heat and mass transfer occurs, including distillation. Volume-of-Fluid interface tracking allows investigation of systems with arbitrarily complex interface dynamics. Further, the present method incorporates the full interface species and energy jump conditions for vapour–liquid interphase heat and mass transfer, thus, making it applicable to systems with multiple phase changing species. The model was validated using the ethanol–water system for the cases of wetted-wall vapour–liquid contacting and vapour flow over a smooth, stationary liquid. Good agreement was observed between empirical correlations, experimental data and numerical predictions for vapour and liquid phase mass transfer coefficients. Direct numerical simulation of interphase heat and mass transfer offers the clear advantage of providing detailed information about local heat and mass transfer rates. This local information can be used to develop accurate heat and mass transfer models that may be integrated into large scale process simulation tools and used for equipment design and optimization.     

Is it only CO2 that matters? A life cycle perspective on shallow geothermal systems

Shallow geothermal systems such as open and closed geothermal heat pump (GHP) systems are considered to be an efficient and renewable energy technology for cooling and heating of buildings and other facilities. The numbers of installed ground source heat pump (GSHP) systems, for example, is continuously increasing worldwide. The objective of the current study is not only to discuss the net energy consumption and greenhouse gas (GHG) emissions or savings by GHP operation, but also to fully examine environmental burdens and benefits related to applications of such shallow geothermal systems by employing a state-of the-art life cycle assessment (LCA). The latter enables us to assess the entire energy flows and resources use for any product or service that is involved in the life cycle of such a technology. The applied life cycle impact assessment methodology (ReCiPe 2008) shows the relative contributions of resources depletion (34%), human health (43%) and ecosystem quality (23%) of such GSHP systems to the overall environmental damage. Climate change, as one impact category among 18 others, contributes 55.4% to the total environmental impacts. The life cycle impact assessment also demonstrates that the supplied electricity for the operation of the heat pump is the primary contributor to the environmental impact of GSHP systems, followed by the heat pump refrigerant, production of the heat pump, transport, heat carrier liquid, borehole and borehole heat exchanger (BHE). GHG emissions related to the use of such GSHP systems are carefully reviewed; an average of 63 t CO₂ equivalent emissions is calculated for a life cycle of 20 years using the Continental European electricity mix with 0.599 kg CO₂ eq/kWh. However, resulting CO₂ eq savings for Europe, which are between ?31% and 88% in comparison to conventional heating systems such as oil fired boilers and gas furnaces, largely depend on the primary resource of the supplied electricity for the heat pump, the climatic conditions and the inclusion of passive cooling capabilities. Factors such as degradation of coefficient of performance, as well as total leakage of the heat carrier fluid into the soil and aquifer are also carefully assessed, but show only minor environmental impacts.     

Catalytic upgrading of 4-methylaniosle as a representative of lignin-derived pyrolysis bio-oil: Process evaluation and optimization via coupled application of design of experiment and artificial neural networks

Catalytic upgrading of 4-methylanisole as a representative of lignin-derived pyrolysis bio-oil was investigated over Pt/γ-Al₂O₃ catalyst. The catalytic upgrading process was conducted at different operating condition to determine the detailed reactions network. Additionally, artificial neural network and design of experiment were applied by feeding the reaction temperature, operating pressure and space velocity to predict 4-methylanisole conversion, main products selectivity, reactions rate and reactions network. The main products of 4-methylanisole upgrading were toluene, phenol derivatives, cyclohexanone, 4-methylcyclohexanone, and 2-tert-butyl-4-methylphenol. The major classes of reactions during the upgrading process were hydrogenolysis, hydrodeoxygenation, alkylation, and hydrogenation. For optimization of experimental data obtained at suggested conditions by design of experiment, the response surface methodology was applied. Artificial neural network model was used to investigate the kinetics behavior of the system due to the complex nature of system. A combination of the response surface methodology, artificial neural network, and design of experiment has revealed its ability to solve a quadratic polynomial model. The coefficients of determination were close to 1, and the mean square error of the artificial neural network model was close to 0 which showed the high accuracy of model predictions. It was inferred that during the upgrading process of 4-methylanisole, increasing temperature and pressure and setting space velocity at the minimum value are the reasons to come close to the optimum reaction rate. The comparison of experimental results with simulated data from the artificial neural network and the response surface methodology models illustrated that the developed model can create an applicable situation for practical design of large-scale production of valuable fuels from renewable resources.