| At present, there are many researches based on life cycle cost (LCC) calculationmethod for the open-loop surface water source heat pump system. In these researchmethods, almost all assumed the water temperature constant, while, neglected intaketemperature would change with season or in cooling seasons and heating seasons whenthe system was continue running; the majority didn’t consider the system dynamic load,ignored the actual system energy efficiency in operation condition; some onlyconsidered the efficiency change of heat pump unit, but didn’t consider the change ofwater intake quantity when analysis plan through changing the temperature differencebetween water intake and drainage. The above research methods were directed toflowing water of surface water at most, while, less for remaining water.This paper in view of remaining water, aiming at source water side of open-looplake water source heat pump system, establish simplified life cycle cost (LCC)calculation method model applied in engineering evaluation. The following factors wereconsidered simultaneously in this model:①all-year hourly dynamic load;②dynamicintake temperature in cooling seasons and heating seasons when the system wascontinue running;③the change of water intake quantity and the efficiency of heatpump unit with the temperature difference between water intake and drainage. A casestudy of villa-cluster open-loop lake water source heat pump system in Qingqing, usedDest-h simulate all-year hourly dynamic load. Analyzed load demand characteristicsaccording to the load simulation results, combining performance curve of heat pumpunit and intake pump, calculated LCC accurately. Compared the LCC of villa-clusteropen-loop lake water source heat pump system and villa-cluster air-cooled heat pumpsystem, the result shows that the former is the better scheme, it can get lower LCC.Analyzed the expenses composed of LCC of that open-loop lake water source heatpump system, obtained the remarkable influence factors of LCC: intake watertemperature, design temperature difference between water intake and drainage,construction cost. Optimized the scheme from three directions based on the LCCevaluation method and two significant factors which were intake water temperature anddesign temperature difference between water intake and drainage. Respectively: ①improve the heat dissipation of thermal discharge, optimize drainage schemePut forward an intake and outfall project that concentrated intake water anddistributed drainage combined outdoor rainwater pipe network, which is unlike thetraditional concentrated drainage in remained water source heat pump system. Thedistributed drainage scheme can reduce outdoor pipe network, save investment andreduce the difficulty of construction.Through numerical simulation, on natural condition in summer, the one-weektemperature rise of water model is1.29℃. For summer cooling condition, the one-weektemperature rise is respectively0.33℃and0.16℃for concentrated drainage systemand distributed drainage system. The distributed drainage scheme can realize the heatdissipation of thermal discharge better. After system operating one week in summer, thetemperature intake of concentrated drainage scheme is only0.04℃higher than that ofdistributed drainage scheme. It shows that when the lake volume is large, the reasonablesetting of the distance between water intake and drainage outlet can make the intaketemperature less affected by heat rejection.②reduce system energy consumption, optimize the temperature differencebetween water intake and drainageIn open-loop lake water source heat pump system, the annual water level change oflake is small, geographic location and source water level decided water intake lift, theinitial design water intake temperature decided by source water temperature, so thedesign of the temperature difference between water intake and drainage is reasonable ornot would directly affect the energy consumption of filling and emptying system.In summer cooling condition, regard LCC as judgment basis, get LCC curvecorresponding the temperature difference between water intake and drainage, the curveshows that the best temperature difference between water intake and drainage is5.4℃.Regard system energy efficiency as judgment basis, get system energy efficiency curvecorresponding the temperature difference between water intake and drainage under theworst condition in summer, the curve shows that the best temperature differencebetween water intake and drainage is5℃.The difference between the two results issmall, and the two curves both show that: when the temperature difference betweenwater intake and drainage is between4℃~6℃, it can achieve smaller LCC and higherenergy efficiency ratio. Considering if the temperature difference between water intake and drainage is too small, it would cause the water intake quantity and construction costincreases, therefore the best temperature difference range between water intake anddrainage is5℃~6℃. When choice the heat pump unit with high energy efficiency, thebest temperature difference between water intake and drainage would become larger, theoptimal temperature difference range between water intake and drainage would changedaccordingly.③varying duty operation, optimize the equipment configurationAccording to all-year hourly dynamic load calculation results, the time that theload rate of system under50%is more than90%in cooling season.The selection of intake pump is in accordance with the water intake quantity underload rate of50%and the maximum pressure drop. It can through increasing thetemperature difference between water intake and drainage to meet the load requirementswhen the load rate is between50%~100%. When the load rate is at between0%~50%,keep the temperature difference between water intake and drainage5℃constant.Enable the heat pump unit to maintain high energy efficiency ratio except a small part ofthe time near full load rate, reducing the intake pump energy consumption greatly at thesame time. It gets a lower LCC shows that the varying duty operation is with energysaving potential.In order to ensure the operation safety and reliability of unit, the temperature ofsource side circulating water should not be lower than4℃in winter. By the numericalsimulation results, the intake temperature in heating season is between19℃~10.2℃, thelowest intake temperature is10.2℃when the temperature difference between waterintake and drainage is5℃, the design temperature difference should not be increased.Therefore, the analysis of varying duty operation and optimal temperature differencebetween water intake and drainage is only for cooling condition in summer.Finally, analyzed the sensitive factor of the open-loop lake water source heat pumpsystem by the single factor sensitivity analysis method, the result shows the influencedegree of LCC by the price and discount rate. Also it introduced the application ofgradient in the multifactor sensibility analysis.The above conclusions got through the analysis of actual engineering have certainreference significance for the same type water source heat pump project.The LCC model is clear and easy to understand. Many interacting dynamic factors are considered in the calculation model. The calculation model is with high accuracy, byreasonable simplification, it can be conveniently applied to the evaluation andoptimization by practical engineering project. |
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