浅层地能热泵采集系统关键科技问题与对策

本文阐述了浅层地能的概念、利用原理及其研究目的和意义,重点分析了地能热泵采集系统现存的关键科技问题,包括地能热泵采集系统回灌问题、埋地管与机组耦合作用机制、主要参数对热泵换热效果的影响等。针对地能热泵采集系统的特点和关键问题提出了一些有价值的解决对策与合理建议,对提高浅层地能热泵行业的科技水平、促进浅层地能热泵行业健康发展具有一定意义。

天津地区采用浅层地能热泵空调系统的技术分析

地源热泵和水源热泵系统均是环保、节能的冷/暖空调系统,对该系统的大力推广势必会对减少污染、降低能耗起到积极的作用。但该系统对不同的项目和地域具有不同的适应性,只有针对地域和项目特征提出最适合的方案才能真正发挥其优势。本文主要针对天津的地质特征,从技术方面分析了水源热泵和地源热泵的适应性,指出了在系统设计和施工中应重点注意的问题。

“浅层地能”热泵的利用方式

随着可再生能源法的实施，国家有关部委的深入调研和北京市九委局支持政策的发布，“浅层地能”越来越经常的出现在科技文献和政府文件中。这就说明人们越来越重视“浅层地能”的开发与利用。

Alternate operation characteristics of a solar-ground source heat pump system

In order to investigate the alternate operation characteristics of a solar-ground source heat pump system（SGSHPS）,various alternate operation modes are put forward and defined.A two-dimensional mathematical model with freezing/melting phase changes is developed for the heat transfer analysis of the soil.Based on the numerical solution of the model,the variation trends of underground soil temperature of the SGSHPS operated in various alternate operation modes are discussed.The results indicate that,for the day-night and short-time interval alternate operation modes without solar energy,the operation time fraction of a solar heat source should be confined to from 50% to 58% when operated in an alternate period of 24 h.Meanwhile,the disadvantages of a natural resumption of soil temperature can be overcome effectively by solar energy filling,and an optimal operation effect can be achieved by integrating the mode of solar energy filling with other alternate modes.In addition,the accuracy of the presented model is verified by the experimental data of borehole wall temperatures.The conclusions can provide a reference for the optimization operation of the SGSHPS.

Performance analysis of U-vertical direct-expansion ground-source heat pump

The performance of a direct-expansion ground-source heat pump（DX GSHP）system is theoretically analyzed.Compared with the conventional ground-source heat pump（GSHP）,the DX GSHP has a lower condensing temperature in the cooling mode and a higher evaporating temperature in the heating mode,and the ground heat exchanger（GHE）in the DX GSHP has a low thermal resistance.Therefore,the coefficient of performance（COP）of the DX GSHP is higher than that of the GSHP.In addition,the system performance of the DX GSHP system is higher than that of the conventional GSHP system because there are no secondary solution loops and water circulating pumps in the DX GSHP system.The experimental energy performance of the DX GSHP system is also investigated based on the actual operational data.The tested DX GSHP system is installed in Xiangtan,China.The U-vertical GHE of the DX GSHP is buried in a water well.The length and the outside nominal diameter of the GHE are 42 m and 12.7 mm,respectively.The experimental results show that the maximum（COP）and the average COP of the DX GSHP system in the heating mode are 5.95 and 4.72,respectively.

Energy saving analysis of a hybrid ground-coupled heat pump project

A hybrid ground-coupled heat pump（HGCHP）project in Nanjing,China is chosen to analyze the building energy-consumption properties in terms of different control strategies,building envelope and the terminal air-conditioning system.The HGCHP uses a supplemental heat rejecter to dissipate extra thermal energy to guarantee underground soil heat balance.The software EnergyPlus is employed to simulate the project and design the heat flow of the cooling tower and the borehole heat exchanger（BHE）.Then two feasible control strategies for the cooling tower and the borehole heat exchanger are proposed.The energy-saving potential of the building envelope is analyzed in terms of the surface color of the wall/roof.With the same terminal system,it is found that in the cooling season the heat flow of the insulated building with black wall/roof is 1.2 times more than that with white wall/roof.With the same insulated building and gray wall/roof,it is concluded that the heat pump units for a primary air fan-coil system show an annual energy consumption increase of 44.7 GJ compared with a radiant floor system.

Fabrication and thermal performance of grooved-sintered wick heat pipe

Some novel grooved-sintered composite wick heat pipes(GSHP) were developed for the electronic device cooling.The grooved-sintered wicks of GSHP were fabricated by the processes of oil-filled high-speed spin forming and solid state sintering.The wick could be divided into two parts for liquid capillary pumping flow:groove sintered zone and uniform sintered zone.Both of the thermal resistance network model and the maximum heat transfer capability model of GSHP were built.Compared with the theoretical values,the heat transfer limit and thermal resistance of GSHP were measured from three aspects:copper powder size,wick thickness and number of micro grooves.The results show that the wick thickness has the greatest effect on the thermal resistance of GSHP while the copper powder size has the most important influence on the heat transfer limit.Given certain copper powder size and wick thickness,the thermal resistance of GSHP can be the lowest when micro-groove number is about 55.

Field evaluation of a ground-coupled heat pump in hot-summer and cold-winter regions

The experimental performance of small-sized ground-coupled heat pump (GCHP) is researched intensively. However, there are little data documenting the operation performance of existing large-sized GCHP system. We presented the actual performance measurement of a GCHP installed for apartment buildings in Wuhan, Hubei province, P. R. China. The system was constructed with a closed vertical typed ground heat exchanger with a total pipe length of 32 000 m. During one year, various operating parameters were monitored, including the outdoor temperature, the flow rate, the electrical consumption, and the water temperature. The seasonal coefficients of performances of the heat pumps and the system based on the measured data were found to be 4.01 and 2.96 in the cooling season, and 3.54 and 2.86 in the heating season, respectively. The GCHP system was more economical than the air-source room air conditioner in the energy efficiency which was increased by 29% in cooling mode and 50% in heating mode. There was an obvious heat imbalance of soil between the injection rate and the extraction rate in the residential GCHP system operation.

Optimization of Serial Combined System of Ground-Coupled Heat Pump and Solar Collector

A mathematical optimization model was set up for a ground-solar combined system based on in-situ experimental results, in which the solar collector was combined serially with a ground-coupled heat pump (GCHP). The universal optimal equations were solved by the constrained variable metric method considering both the per-formance and economics. Then the model was applied to a specific case concerning an actual solar assisted GCHP system for space heating. The results indicated a system coefficient of performance (COP) of 3.9 for the optimal method under the serial heating mode, and 3.2 for the conventional one. In addition, the optimum solution also showed advantages in energy and cost saving, leading to a 16.7% improvement in the heat pump performance at 17.2% less energy consumption and 11.8% lower annual cost, respectively.

Case study of underground pipe ground coupled heat pump system

Aiming to give some advices on the ground coupled heat pump system design in Siehuan Province, China, a typical ground source heat pump （GSHP） system in Sichuan Province was tested in a whole operational year, and the parameters of temperature and flow rate in different parts of system were measured during this period. The seasonal energy efficiency ratio was calculated and the performance of heat pump system in summer was compared with that in winter. The result shows that the coefficient of performance of the system reaches 3.63 in summer and 3.49 in winter, respectively. The heat balance in underground rock mass is acquired basically throughout the year, and the heat accumulation in the earth tends to be zero.

Comparison between Conventional and Improved Gas Engine-Driven VRF under Same Climate Conditions

This paper reports the on-site performance evaluation of conventional and improved gas engine-driven VRF （variable refrigerant flow） units and （abbreviated as GHP） units. The study aims to elucidate two actual GHP units by using the probe insertion method. There is a tendency to decrease energy efficiency compared to a high loading factor. GHP operation was almost all part load operation. This on-site evaluation indicates a clear difference between conventional and improved GHP.

Energy savings and CO_2 emission reduction by using geothermal heat pumps

The renewable energy will play significant role in the world primary energy consumption in the future. Geothermal energy is immense with 5 000 EJ/a of technical potential, and geothermal heat pumps (GHPs) are one of the fastest growing applications of renewable energy in the world with annual increases of 10 % and much faster in China. With high coefficient of performance (COP) up to 6, GHPs make efficiency of primary energy more than 240 % with assumed a 40 % of electricity generation efficiency, which means energy savings and CO2 emission reduction. In this paper,the geothermal resources and its utilization are talked about, and GHPs technology was introduced. Due to its high efficiency, there will be energy savings by using GHPs. There is also CO2 emission reduction because of using geothermal heat pumps, which is analyzed in the end.

Utilisation of Geothermal Heat Pumps within Permeable Pavements for Sustainable Energy and Water Practices

Geothermal heat pumps （GHPs） are an attractive proposition for renewable energy worldwide as it uses energy naturally stored in the earth. The Earth is a very resourceful form of energy, using the natural solar energy collection and heat storage capabilities as an infinite heat source/heat sink at the base of permeable pavements, which can provide excellent temperature gradients for GHP＇s. Experimental rigs were setup up at The University of Edinbttrgh for a combined permeable pavement and GHP system. At the base of a pavement structure （approximately 1 meter） below the ground＇s surface, temperatures are constant of 10℃ in the U.K all year round. The GHP performance efficiency was analysed by the coefficient of performance （COP） in a heating cycle and the energy efficiency ratio （EER） in a cooling cycle. The mean COP and EER for both systems averaged between 2-4.5 and 3-5 respectively. The combined GHP and pavement structure operated at an optimum efficiency for both heating and cooling cycles and has shown to be unaffected by higher summer or lower winter temperatures. This hybrid system is an attractive renewable energy technology and has additional environmental benefits such as urban runoff reuse and recycling.

Optimizing GSHP Performance with ICT and RETScreen Plus

Under the RHO （renewable heat obligation）, public buildings in the Republic of Korea must achieve an 11% overall reduction to thermal energy consumption in buildings more than 10,0O0 m^2. RETScreen Plus is a freely available software tool developed by the Canadian Government which can be used to develop energy baselines of clean energy technologies. Using curve-fitting and statistical methods like CUSUM, the software can combine actual energy performance with near real time weather information from NASA. We developed a method to simulate the performance of a GSHP （ground source heat pump）. The three distinct energy zones involve heating, no-energy, and cooling. RETScreen Plus methodology is used to develop curve fits for each distinct zone as it builds a correlation with NASA satellite data. The model then factors the impact of ICT （information and control technologies） as a means to improve and lower the building＇s energy consumption. Two values of COP （coefficient of performance） are used--the first is a standard ICT COP, while the second is an improved ICT COP with a smart controller. This methodology can then be expanded to incorporate current and future smart meter technologies, time of use rates, energy price signals, demand response and electricity storage options. In summary, this methodology enables a building owner or energy conservation official to quickly and accurately determine the baseline energy for a building and the potential impacts of smart ICT technologies, especially for buildings equipped with GSHP technologies.