| The water source heat pump system is widely used in hot summer and cold winter areas because of high efficiency and low pollution.In the simulation study of water source heat pump systems,there are a large number of uncertainties,including model uncertainty and parameter uncertainty.These uncertainties will affect the efficiency,economy evaluation and optimization design of water source heat pump system.Therefore,it is necessary to conduct a comprehensive study on the uncertainties in the simulation of water source heat pump systems and assess their impact on the performance evaluation.In this study,the source of uncertainties in water source heat pump system simulation is analyzed and classified.Then the model uncertainty and parameter uncertainty as well as their impacts on the performance of the water source heat pumps and decision making is evaluated.Sensitivity analysis is conducted to identify the uncertainties with high importance.The work and corresponding results are summarized as follows:(1)The influence of model uncertainty of heat pump unit on the performance of water source heat pump system is quantified.Thirteen water source heat pump unit models were selected and the water source heat pump system platform was built.By calculating the energy consumption of the water source heat pump system under different water source heat pump unit models,and comparing with the traditional chiller & boiler system,the influence of the uncertainty of the water source heat pump unit model is obtained.Results show that the uncertainty of the water source heat pump unit model has an important effect on the system performance,which can cause a variation of 7.73%～36.3% in the annual energy consumption of the water source heat pump system.The annual average COP of the system fluctuates between 2.87 and 4.24.Compared with the traditional air-conditioning system,the energy saving rate is between-21.62% and 17.65%,and the relative net present value varies from-89.41% to 19.05%.(2)The influence of parameter uncertainty on building load and performance of water source heat pump system is quantified.Considering the uncertainty of parameters such as outdoor weather,building envelope,indoor heat gain and indoor air state,the Monte Carlo method was used to quantify the influence of parameter uncertainty on the cooling/heating load and system energy consumption of the building.The results show that the uncertainty of parameters has a great impact on the cooling/heating load of the building and the energy performance of the water source heat pump system.Compared with the benchmark values of deterministic situation,the relative change rate of peak cooling/heating load is-38%～45.4% and 34.4%～36.2% respectively,the relative change of the energy consumption of the water source heat pump system ranges from-41.8% to 50.4%.When the load uncertainty is taken into account,the energy saving rate of the water source heat pump system is distributed between 7.2% and 12.4%(the base value is 10.75%)compared with the traditional airconditioning system,and the relative change of the net present value of the investment is from-41.9% to 55%(the base value is 3.616 million yuan).(3)Considering the heat pump model uncertainty and parameter uncertainty simultaneously,the influence of multi-source uncertainty on the performance evaluation of the water source heat pump system is quantified and analyzed.For parameter uncertainty,both the demand/load side uncertainty and the parameter uncertainty of the heat pump system are considered.Combined parameter uncertainty with the model uncertainty,the performance of the water source heat pump system under uncertainty is calculated.The results show that the relative change range of the water source heat pump energy consumption is-48%～118%,the energy saving rate is distributed between-78.5% and 32%,and the relative change of the net present value of the investment is-215%～83.4%.Which means that considering the multisource uncertainty,the performance of the water source heat pump system fluctuates in a large range,and the energy saving rate can be even negative compared with the traditional system.(4)Based on random forest,global sensitivity analysis was carried out on uncertainty influence factors of building load and energy consumption of water source heat pump system.The results show that the main factors affecting the cooling/heating load of office building are outdoor air dry bulb temperature,solar radiation,outdoor air relative humidity,personnel and fresh air volume.The main factors affecting system energy consumption are COP of heat pump unit,outdoor air dry bulb temperature,solar radiation,outdoor air relative humidity,heat pump model,personnel and fresh air volume.In the stage of performance evaluation or optimization for system,the above important parameters should be considered with emphasis to reduce their uncertainty,thereby reducing the uncertainty of load calculation or system performance prediction and improving the accuracy of performance evaluation and final decision.In conclusion,model uncertainty and parameter uncertainty have a great impact on the simulation performance of the water source heat pump system,which can cause the simulated energy consumption of the water source heat pump system to fluctuate in a large range.Compared with the traditional air-conditioning system,the energy saving potential may be negative,which will affect the final decision in the scheme selection stage.Among them,outdoor meteorological parameters,unit COP,fresh air and personnel have great influence,so it should be carefully selected when simulating the performance of water source heat pump system for design scheme selection and optimization design. |
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