Analysis of the Temperature Limit of Dynamic Water Intake of Open loop Surface Water Source Heat Pump Systems

Energy consumption of water intake is one of the key factors for energy saving in the application of the open loop surface water heat pump system. An energy efficiency ratio coupling model for open loop surface water source heat pump systems was established on the basis of the energy consumption model for the water intake and the heat pump units. According to energy saving rate and regulation of energy consumption of water intake, dynamic temperature limits of water intake in different water supply temperature of cooling tower and different pump head were proposed so as to find a calculation method of temperature limits of water intake of open loop surface water heat pumps. Moreover, the energy saving rate of surface water source heat pump systems compared with traditional air conditioning systems under various condition was also calculated.     

The determination method of limit energy consumption of water supply in open-loop surface water source heatpump systems

For the open-loop surface water source heat pump systems, energy consumption of water supply is the key factor for energy saving of system. On the basis of energy consumption model of heat pump unit and energy consumption model of water supply etc., open-loop surface water source heat pump system energy efficiency ratio coupling model is established. Based on energy efficiency ratio,the coupling limit value of surface water source heat pump system in different temperature of water supply and different energy consumption of water supply is obtained.Through the actual case, energy saving rate of the system is calculated in different temperatures of water supply and different system modes. And the determination method of the limit energy consumption of water supply of open-loop surface water source heatpump systems is established.     

Energy Efficiency of Water Transportation System for Surface Water Source Heat Pump

The forms of water transportation, arrangement and operation of pumps contribute to the water transportation energy consumption, which influences the energy-saving effect of surface water source heat pump. The relation between the pumping height and energy consumption of pumps is found by analyzing the model of pump energy consumption. The concept and calculation of critical pumping height is presented considering the limited rate of system energy efficiency. Based on the principle that the pump power changes with water flow rate, the determination of pumps arrangement of one or two stage pumps is described with a concrete example. The influence of water flow rate on heat pumps and water pumps is analyzed, and the energy efficiency of constant and variable water volume are compared. The operation way of this example is concluded for the optimal system energy efficiency. It is found that there is a critical pumping height for the energy-saving effect of surface water source heat pump compared with the traditional system. Moreover, the operation strategies should be determined by the system optimal model since the energy consumptions proportions of heat pumps and water pumps are variable.     

The Key Parameters Method of Calculating Geothermal Heat Exchanger Length

The geothermal heat exchanger is the key component of ground coupled heat pump systems. We discuss the key parameters method of calculating geothermal heat exchanger length based on line source theory. Typical meteorological year data is used to determine the hottest month, the coldest month and annual average surface temperature. The building hourly load can be obtained by introducing the concept of equilibrium temperature. The cooling fraction and the heating fraction then can be calculated using building hourly load and performance parameters curve fit of a water source heat pump unit. The method for selecting the hottest and lowest entering fluid temperature and calculating the borehole and ground thermal resistance is given. A vertical U tube heat exchanger length calculation procedure is proposed.     

Influence of heat storage mode of domestic hot water on the performance of ground heat exchanger in ground-source heat pump system

The vertical U-tube ground-coupled heat pump system provides cold and heat for the controlling of indoor environment. Under the air-conditioning condition, the vertical U-tube ground-coupled heat pump system with heat recovery can provide domestic hot water. The influence of supplying domestic hot water on the heat transfer performance of ground heat exchangers is different under different operating modes in summer and winter. Through a project design of ground-source heat pump system, the influence of supplying domestic hot water under heat storage mode on the heat transfer performance of ground heat exchangers in summer and winter is respectively analyzed. The dynamic performance of heat exchangers under different working conditions is analyzed, and through numerical calculation, the heat transfer performance parameters of ground heat exchangers under different operating modes are obtained. From the calculation results, the adjusting methods based on the load characteristics of this project represent.     

Control strategy of variable flow between cooling water and chilled water in chilled plant

In order to reduce energy consumption of chilled plant, a new control strategy with variable flow and variable temperature for all variable chilled plant based on orthogonal experimental analysis is presented. The presentation and the implementation idea of that control strategy are firstly introduced. Secondly, a screw chiller model and a pump model are established, and these two models are then coded and embedded into the TRNSYS software to simulate and verify. Finally, a surface water chilled plant simulation platform composed of chillers and pump are developed based on TRNSYS. By using conducting quadratic orthogonal regression experiment on that platform, the empirical correlation formula between the total power of chilled plant and cooling load, supply cooling water temperature, cooling water flow, chilled water flow, and supply temperature of chilled water is obtained. By data processing, the optimized values of chilled water flow, cooling water flow, and supply temperature of chilled water which make the total power of chilled plant minimum under different cooling load and supply cooling water temperature are also gotten. Result shows that the new control strategy can decrease the power of chilled water plant by 4.94 kW and 14.023 kW respectively relative to the constant speed and the conventional variable speed, the saving power can increase by 54.6% relative to the corresponding conventional variable speed plant does.     

Influence of Distributed Drainage on Reservoir Water Temperature Field Under Reservoir Water Source Heat Pump System

By adopting fluid calculation software to establish three dimensional reservoir model and simulating reservoir's natural temperature on design day, the measured temperature was used to correct and treated as the initial condition. According to the annual hourly calculation load of villa cluster, dynamic water temperature and flow were used as boundary conditions. Inputted water surface heat transfer conditions were identified by user defined function based on the data of typical meteorological year. For the distributed drainage combining the discharge network and rainwater pipe network and traditional integrated drainage of reservoir water source heat pump system, dynamic numerical simulation of the water temperature field was conducted. The results show that water's temperature rises 0.33℃ weekly when integrated drainage is adopted and the temperature rises 0.16℃ when distributed drainage is adopted. There is obvious heat accumulation phenomenon when continuous drainage in narrow area works. The simulation of intake water temperature shows that below perennial water level 4.6m depth, the intake water temperature is between 27~23.5℃ from July to October, in which the heat pump system operates efficiently.     

Operating analysis on finite volume of lake water source heat pump in winter heating

The feasibility of the main teaching building of Chongqing University additional lake water source heat pump during the winter heating is analyzed and the water temperature and quality of the artificial lake are determined,that the water is more serious eutrophication,and it must be purified before the water enters heat exchangers. Heat carrying capacity of lake is analyzed and hourly temperature of the lake is simulated during the winter heating operating conditions. When the average temperature is 5~8 ℃in January in Chongqing,the lake as an evaporator cycle water provide energy to heat pump constantly,assumed initial temperature of water is 13.7 ℃,hourly water temperature is simulated in January. The water temperature has dropped to 4.04 ℃ at 24 d,the evaporator surface may be frozen and cause the phenomenon of ice clogging,which will endanger the safety of heat transfer equipment,therefore,auxiliary heater must be set to ensure the main building heating.     

River Water Quality Comprehensive Evaluation for Water Source Heat Pump

River water quality is one of the important conditions must be considered when river water source heat pump is used. It is also the key factor of efficiency of river water source heat pump. Based on analysis of the water quality factors which influence the river water source heat pump heat exchanger fouling, the main quality indicators and value are conformed. Using fuzzy comprehensive evaluation method and the actual monitoring data, quality classification of river water which is the source of water source heat pump is analyzed. For the difficulty of multiple indicators which need to detect and meet the related national standard in practical engineering application, the definition of scaling potential value is put forward. As the water quality comprehensive evaluation index of water source heat pump, the scaling potential value not only can consider the influence of the main water quality parameters on water source heat pump heat exchanger fouling, but also can conveniently and quickly provide direct basis for water quality judgment and system selection in the engineering application.     

Thermodynamic Analysis of River Water Fouling on Constant Wall Temperature Tube of Small Diameter

In order to improve utilization of cold and heat source from river, turbulence theory and entropy generation theory were adopted to analyze the effect of fouling on convective heat transfer performance in small diameter tube of constant wall temperature.It is found that the entropy generation caused by conduction of fouling plays a more important role in total entropy generation of heat transfer process through a duct than that in cveast rate of caused by temperature difference.The entropy generation caused by viscous flow is more than the entropy generation caused by temperature difference in flow with bigger Reynolds and small radius.The increase rate of entropy generation monotonically increase with Reynolds and the generation process of fouling resistance.Thereafter, the effect of fouling resistance on the heat transfer performance of water source heat pump heat exchanger should be paid more attention, when river water are used as the cold and heat source of heat pump.     

Optimization of Subway Indirect Evaporative Cooler Water Distribution Methods

In conventional indirect evaporative cooler, the lack of uniformity and integrity of water film surface results in low thermal efficiency. To solve the problem,an indirect evaporative cooler with rotating water on both sides is put forward. The experiment was carried out to explore the heat transfer performance of heat exchanger under three types of arrangement and the factors influence the performance were studied by orthogonal experiment. The study results show that when the hole is on the direction of air flow, the thermal performance of heat exchanger is optimal and the recommended rate of rotating water distribution installation 76 r/min. Heat exchange increases with the increase of water spray quantity, air velocity, cooling water flow rate, cooling water inlet temperature and decrease with increase of water temperature, air temperature cooling water inlet temperature has the most significant effect on the performance of heat transfer. And when the temperature increases form 35 ℃ to 39 ℃, the heat transfer improved 37.62%, Heat transfer in per unit area is about 1.14 kW. The heat exchanger can be installed in exhaust tunnel of underground stations, which can effectively solve the subway station cooling tower installation location problem.     

Experimental Analysis on Optimal Tail Water Discharge Method of River Water Source Heat Pump

In order to study the influence on water temperature raise of river water source heat pump tail water discharged in different methods, the real sensor network is established by using digital temperature sensors. The simulation experiments of different discharging methods of river water source heat pump are carried out, including submerged-type discharge, surface-type discharge and jet-type discharge with 12 effluent ways. By using weighted average method, the preferred values of such factors as the average temperature raise,the temperature raise variance, the biggest temperature raise value, and the number of temperature measure points above the temperature raise average value are calculated. Moreover, the experiment results are analyzed by the three-dimensional figures of water temperature raise, which shows that jet-type discharge is better than submerged-type discharge and surface-type discharge,and the double-port way is better than single-port way. In addition, the double-port way along with the current in surface-type discharge method is the one that exerts least influence on river water temperature raise.     

STUDY ON HEAT TRANSFER MATHEMATICAL MODEL BETWEEN BILLETS AND ROLLERS FOR THE SECONDARY COOLING ZONE IN BILLET CONTINUOUS CASTING

A mathematcal model of heat transfer between the billet and the roller for the seeondary cooling zone in billet continuous casting is established. By means of the simulated test,a regres sion relation between the heat flow from the billet into the roller and the surface temperature and cast ing speed and spray water density obtained. The calculated theoretical values for change of surface temperature are in agreement with the measured data, these studies may contribut to the quantitative analysis and the calculation of the heat transfer of the secondary cooling zone.     

Gray Multi-level Comprehensive Evaluation of Household Central Air Conditioning Systems

There are many schemes of residential central air conditioning systems for selection, the selection is affected by many factors, the reasonable selection of evaluation indexes is the key factor for the proper option. In this paper, in order to evaluate the performance of the whole system synthetically, the gray comprehensive evaluation method is introduced and used, the mathematical model for optimization and selection of air conditioning schemes is established, and with an example of residential building in Beijing the index values of chosen six air conditioning systems are calculated and optimized. The schemes are the air-source heat pump system, household gas-fired air conditioning system, air-cooled chiller unit/gas-fired boiler system, water loop heat pump system, ground-source heat pump system and solar heat pump system. In the process of optimization calculation, the aspects of economics benefits, energy saving, environment protection and system reliability are taken into account. According to the calculation results, the water loop heat pump system is proposed to be optimal option under the given conditions.     

Low frequency oscillation restraint in power systems that include asynchronized turbogenerators

Yangtze River is abundant of water and can provide enough water as cooling and heating source for water source heat pumps (WSHP). A pair of contrast experiments with open loop system and close loop system of WSHP were finished in order to get the heat pump's COP, the system's COP and the distribution of water temperature in the heat exchanger etc. This paper compared the characteristic and the COP of these two kinds of system. The heat pump's COP of the open loop system and close loop System are 3.08 and 3.77 respectively, and the system's COP are 2.83 and 2.80 respectively. At last, applications of open loop system and close loop System of WSHP at Yangtze River were analyzed and the key problem for attention was pointed out in the paper.      

Calculation Method of Water Temperature in the Condition of Heat Rrejection for Lake Water Source Heat Pump Systems

The temperature of water used for surface water source heat pump（WSHP） could make dynamic changes in the condition of heat or cold rejection. When the water temperature is over the amount of heat or cold rejection that water can take, WSHP system will run irregularly even paralyze. Based on two dimensional model of the initial water temperature, dynamic model of water used for WSHP was proposed with mass equation and energy equation. And with flow equation coupled with temperature equation, the equation of water temperature changes in load was obtained.     

Experimental Study of Ground-source Heat Pump Systems with Horizontal Heat Exchanger

This paper describes the double layer horizontal ground source heat pump systems constructed in 1998 with the buried depth of 0.9 m and 1.8 m. The program of study includes experimental equipments, heat exchanger size, testing meter and methods for data analysis. In addition, the heating and cooling performance at typical days are also illustrated. Among the influencing factors on the performance of the ground source heat pump systems, the parameter of heat exchanger and operation patterns of heat pump systems are analyzed.A heat transfer model has been set up for horizontal heat exchanger.     

Analysis on tail-water temperature of river water-source heat pump and its optimization

The temperature field diffusion issue of a water source heat pump drainage system in a certain river is studied,and dynamic tests to the water temperature of the drainage canal sector and the outfall area are carried out. The temperature drop trends of th     

Analysis of the Ground Adjustment Ability of the Ground Source Heat Pump Systems in Winter

Based on an actual ground source heat pump system in hot summer and cold winter area, the system operation parameters were tested for 6 years under the state of using cooling tower for cooling in summer but the ground heat exchanger and fire pool for heating in winter. A three dimensional (3D) tube group model was established, and the thermal balance analysis and calculation of the ground temperature distribution around the ground heat exchanger were conducted by the numerical calculation. According to the comparison between the test data and the theoretical results, the influencing factors of the ground adjustment ability were obtained.     

Energy efficiency analysis on intermittent operation based on life cycle cost in the vertical ground source heat pump system

Intermittent operation can affect the heat exchange performance of the vertical ground source heat pump system, thereby affecting life cycle cost (LCC) of the ground source heat pump system. The simulation analysis on the hourly load of an office building is implemented by using the DeST software.The heat exchange model of vertical ground heat exchanger pipe-group and energy consumption model of per part of heat pump system are established. Through the comparison between calculation results of continuous operation for 15 years and calculation results of intermittent operation 15 years of the heat pump system, it can be concluded that the LCC value of intermittent operation decreased by 13.45%,relative to the LCC value of continuous operation, and the average energy saving rate of intermittent operation mode is 17.20% in the entire life cycle. Intermittent operation mode can effectively improve energy efficiency of the ground source heat pump system and reduce the LCC value.