狭长空间强扰动排热通风量的优化研究

针对存在强扰动气流的狭长空间内热量不容易排出的问题,本文采用全面通风的手段来消除空间内持续散发的大量热量,并依据相似理论,利用Revit软件辅助设计搭建了模型实验台,对不同热射流温度及对应不同排热通风量的排热效果进行了优化研究。文中以评价全面排热通风量效果的评价指标——排热效率为参考,得到热射流温度在小于591K的范围内,最优的全面排热通风量值约为144．7万m3／h,当热射流温度位于591～709K时,最优的全面排热通风量值约为159．7万m3／h。     

Optimal control strategies of eight parallel heat pumps using Gaussian process emulator

This study describes the development of the optimal control strategies of eight parallel heat pumps in an existing building. The building consists of seven floors above ground and two floors underground with a total floor area of 22,440?m². The chilled water generated by each of the eight parallel heat pumps runs through a common primary pipe to multiple air-handling units in the building. Because only one flowmeter and two thermometers (entering and exiting) are installed in the primary pipe, the heat removal rate and efficiency of each heat pump are unknown. The existing control of the heat pumps is as follows: if the chilled water return temperature in the primary pipe becomes greater than a predetermined temperature, the controller increases the number of operating heat pumps. The heat removal rate and efficiency of each heat pump were first identified using a Gaussian process (GP) machine-learning algorithm to develop the optimal control strategy of the eight heat pumps. Two GP models, one for estimating the heat removal rate and the other for estimating the coefficient of performance (COP), were developed based on the measured data for 27 days in July at the sampling time of 15?min. After developing the GP models, the authors applied a COP-based sequencing control strategy to the eight parallel heat pumps. The new optimal control strategy is to switch on the heat pumps in order from highest to lowest COP. Compared with the existing control logic, the new optimal control can reduce energy consumption by 20.9%.     

Multi-objective optimal control of an air-to-water heat pump for residential heating

The current study investigates the optimal operation of an air-to-water heat pump system. To this end, the control problem is formulated as a classic optimal control or dynamic optimization problem. As conflicting objectives arise, namely, minimizing energy cost while maximizing thermal comfort, the optimization problem is tackled from a multi-objective optimization perspective. The adopted system model incorporates the building dynamics and the heat pump characteristics. Because of the state-dependency of the coefficient of performance (COP), the optimal control problem (OCP) is nonlinear. If the COP is approximated by a constant value, the OCP becomes convex, which is easier to solve. The current study investigates how this approximation affects the control performance. The optimal control problems are solved using the freely available Automatic Control And Dynamic Optimization toolkit ACADO. It is found that the lower the weighting factor for thermal discomfort is, the higher the discrepancy is between the nonlinear and convex OCP formulations. For a weighting factor resulting in a quadratic mean difference of 0.5°C between the zone temperature and its reference temperature, the difference in electricity cost amounts to 4% for a first scenario with fixed electricity price, and up to 6% for a second scenario with a day and night variation in electricity price.     

热源循环泵流量对热电联供系统优化运行影响

建立利用热网蓄热以促进风电消纳的热电联合优化运行模型,分析热源循环泵流量对热电联供系统运行经济性的影响。案例分析结果表明,循环泵日电费随相对流量减小而降低。相对流量87%~100%范围内,目标函数(热电机组的日运行费用、日市电费、日弃风罚款之和最小)不变。当相对流量降至86%后,目标函数不降反升,且增大幅度大于循环泵日电费降低幅度。受供水温度及供回水温差的限制,随着相对流量减小,日间热电机组制热功率受到限制。为了满足热电联合优化运行模型热平衡条件(总供热量等于总耗热量),夜间热电机组制热功率无法降低,热电机组发电功率居高不下,导致风电消纳受限,弃风电量增大。日弃风罚款随之增加,最终导致目标函数升高。相对流量为87%时,热电联供系统的日运行费用最低。     

Thermal design tool for outdoor spaces based on heat balance simulation using a 3D-CAD system

This paper focuses on the development of a thermal design tool for use in planning outdoor spaces by combining a heat balance simulation for urban surfaces, including buildings, the ground and greenery, with a 3D-CAD system that can be run on a personal computer. The newly developed tool is constructed by improving the previous simulation model, which uses the geographic information system (GIS) for the input data. The simulation algorithm is constructed so as to predict the surface temperature distribution of urban blocks while taking into account the actual design of the outdoor space using the 3D-CAD system. A method of multi-tracing simulation to calculate the sky view factor and radiative heat transfer is established. The optimal mesh size is examined for the tool so as to provide detailed spatial geometry within a suitable calculation time. The simulation model is integrated with an all-purpose 3D-CAD software, and the pre-processing method are constructed for practical use. The results obtained by applying this simulation tool to an area of detached houses reveals that the tool is able to evaluate the effects of building shape, materials, and tree shade on the surface temperature distribution, as well as the MRT and HIP, which are evaluation indices of the outdoor thermal environment.     

相变材料蓄冷堆积床的优化设计

根据相变材料蓄冷堆积床的传热特性,提出了一种堆积床的优化设计方法。以一种新型相变材料为蓄冷媒介,以堆积床的总费用为优化目标,以蓄冷量、蓄冷时间及载冷流体温度作为约束条件建立优化模型,得出了给定蓄冷量条件下系统初投资和年运行费用总和最低时的蓄冷单元数量、定性尺寸和换热流体温差等优化参数。定量分析了谷峰电价比对系统运行电费的影响。     

含跨季节储热的多能互补分布式能源系统容量配置优化

为了满足我国对环保及能源的需求,多能互补分布式能源系统成为了分布式能源系统的发展的趋势.文章针对北京地区某办公建筑构建了含跨季节储热的多能互补分布式能源系统,以年总成本最低为目标函数,在满足全年负荷的情况下利用P SO算法(粒子群算法)对该系统中的跨季节储热系统关键设备(储热水箱和基岩储热设备)的容量进行优化,得出了其...     

Thermodynamic analysis and evolutionary algorithm based on multi-objective optimisation of the Rankine cycle heat engine

This study demonstrates the outcomes of a research implement for the power and efficiency optimisation of a Rankine cycle heat engine employing the non-dominated sorting genetic algorithm (NSGA-II) algorithm. Two objective functions comprising the efficiency and power were included concurrently maximised. To assess this idea, multi-objective optimisation approach founded on NSGA-II method has been utilised in which following variables have been considered as decision variables: (1) the inlet temperatures of a heat source, (2) the inlet temperatures of a heat sink, (3) temperature difference (x), (4) temperature difference (y), (5) heat conductance and (6) heat capacitance. By applying the addressed multi-objective optimisation approach, Pareto optimal frontier was determined and utilising different decision-making techniques that include the LINMAP, TOPSIS and fuzzy Bellman–Zadeh approaches help us to figure out the final optimal solution.     

Numerical simulation of ground heat and water transfer for groundwater heat pump system based on real-scale experiment

The groundwater heat pump (GWHP) system is an open-loop system that draws water from a well or surface water, passes it through a heat exchanger and discharges the water into an injection well or nearby river. By utilizing the relatively stable temperature of groundwater, GWHP system can achieve a higher coefficient of performance and can save more energy than conventional air-source heat pump (ASHP) system. The performance of the system depends on the condition of groundwater, especially temperature and depth, which affect performance of the heat pump and system. For the optimization of design and operation of GWHP systems, it is necessary to develop a simulation tool which can predict groundwater and heat flow and evaluate system performance comprehensively. In this research, 3D numerical heat-water transfer simulation and experiments utilizing real-scale equipment has been conducted in order to develop the optimization method for GWHP systems. Simulation results were compared with the experimental results, and the validity of the simulation model was confirmed. Furthermore, several case studies for the optimal operation method have been conducted by calculating the coefficient of performance on various groundwater and well conditions.     

A novel on-off TRV adjustment model and simulation of its thermal dynamic performance

Field test results show that about 15% to 40% of building heat loss in China is attributable to poor heating systems regulation. The current method for addressing this problem is to install thermostatic radiator valves (TRVs) to the ends of radiators, a method adapted from northern Europe. However, this method has resulted in poor performance from delayed controlling action due to thermal inertia as well as insufficient system control accuracy. This is further compounded by incorrect operation by system users and a lack of financial incentives to regulate the system if users are not billed for their heat consumption. We present a new method for simultaneously heat controlling and metering. The core challenge is to design a control strategy that will maintain the room’s temperature. Thus, we established dynamic heat transfer models for water flow, the radiator and the building so as to obtain the optimal heating strategy. We also simulated the indoor thermal dynamic performance of the heating system with different heating loads, supply water temperatures, and supply water flow rates using three methods: a continuously changing flow rate (Method 1), a step-change flow rate based on temperature deviation (Method 2) and an intelligent step-change flow rate (Method 3) which predicts the duty cycle of the valve in the proceeding period and controls the valve’s on-time. The simulation results indicate the performance of these three methods. For Method 1, as the room temperature is above the set point, the flow rate can be automatically reduced to a level which is proportional to the room temperature deviation. Further, the scale factor of the flow rate is designed according to the +2°C deviation, so it is accepted that the room temperature is higher than the set point by +2°C using this method. However, this low control precision is unsatisfactory. The mean temperature is higher than the set point and greatly affected by the heating load and supply water’s temperature and flow rate. For Method 2, the controlling action is delayed by thermal inertia, the room temperature fluctuates between the highest and lowest levels, and the temperature deviation can be greater than the set value. For Method 3, both the simulation and field test results showed that room temperature deviation was maintained within a ±0.5°C range under the various conditions. This method appears relatively robust and adaptable, and was the best control strategy of the three methods.     

Exergetic performance optimization of an endoreversible intercooled regenerated Brayton cogeneration plant. Part 2: Exergy output rate and exergy efficiency optimization

The exergy output rate and exergy efficiency performances of an endoreversible intercooled regenerative Brayton cogeneration plant are optimized based on the model which is established using finite time thermodynamic in Part 1 of this paper. It is found that the optimal heat conductance allocation of the regenerator is almost zero. When the total pressure ratio and the heat conductance allocation of the regenerator are fixed, it is shown that there exist two optimal intercooling pressure ratios, and two optimal groups of the heat conductance allocations among the hot-, cold- and consumer-side heat exchangers and the intercooler, which correspond to a maximum dimensionless exergy output rate and a maximum exergy efficiency. When the total pressure ratio is variable, there exist two optimal total pressure ratios which correspond to a double-maximum dimensionless exergy output rate and a double-maximum exergy efficiency, also the corresponding exergy efficiency and exergy output rate are obtained. The effects of the total heat exchanger conductance and the consumer-side temperature on the double-maximum dimensionless exergy output rate and the double-maximum exergy efficiency are discussed. It is found that there exists an optimal consumer-side temperature which correspond to a thrice- maximum dimensionless exergy output rate, and the intercooling process is not necessary by taking exergy efficiency as the objective when the consumer-side temperature is high.     

蓄冷系统新型节能优化运行控制方法

本文提出了基于排序思路的冰蓄冷系统节能优化运行控制方法—优先权法,有别于以往的优化控制算法。算例结果表明:该算法较好地实现了优化运行的目标,所得结果便于工程实施,具有较高的工程应用价值。     

Optimal control development for chilled water plants using a quadratic representation

Optimal supervisory control strategy for the set points of controlled variables in the cooling plants has been studied by computer simulation. A quadratic linear regression equation for predicting the total cooling system power in terms of the controlled and uncontrolled variables was developed using simulated data collected under different values of controlled and uncontrolled variables. The optimal set temperatures such as supply air temperature, chilled water temperature, and condenser water temperature, are determined such that energy consumption is minimized as uncontrolled variables, load, ambient wet bulb temperature, and sensible heat ratio are changed. The chilled water loop pump and cooling tower fan speeds are controlled by the PID controller such that the supply air and condenser water set temperatures reach the set points designated by the optimal supervisory controller.The influences of the controlled variables on the total system and component power consumption were determined. The predicted power obtained from the quadratic regression equation was found to be a good fit to the simulated one. Because the Hermitian matrix of the system quadratic cost function was positive, the optimal control variables for the minimum power consumption were able to be obtained. There are relatively high effects of the load and sensible heat ratio on the optimal supply air and chilled water set temperatures, while the effect of ambient wet bulb temperature is less. In contrast to that result, the ambient wet bulb temperature has a much larger effect on the optimal condenser water set temperature, while the load has less, and the sensible heat ratio has no influence on it. The trade-off among the components of power consumption results in that the total system power use in both simulated and predicted systems are minimized at lower supply, higher chilled water, and lower condenser water set temperature conditions.     

Application of model based predictive control for water-based floor heating in low energy residential buildings

A model based predictive control method is applied in order to determine the optimal supply fluid temperature in the case of concrete embedded water-based floor heating in low energy residential buildings. The aim of the control is to keep the indoor temperature within a defined comfort interval. The forthcoming supply fluid temperature is obtained through a numerical optimisation based on a prediction of the upcoming heat demand. The elementary response function, which is the basis for the method, is obtained from a numerical control volume model, and as an alternative, from a simplified 2-node lumped model. The accuracy of the results obtained from the simplified model is surprisingly good in comparison to the detailed numerical model. The control method is applied for a single room for which a perfect prognosis of the heat demand exists. The results show a fairly steady optimised supply fluid temperature.     

供热系统换热首站计算机监控系统

以某集中供热系统蒸汽换热首站为例,介绍了换热首站计算机监控系统的结构,对温度控制回路、温度控制算法、温度控制策略、换热机组一次侧蒸汽调节阀的动作方式、二级管网循环水泵控制、补水泵控制、凝水泵控制及监控系统的安全保障功能进行了研究.     

大过冷度逆流式过冷器换热特性研究

阐述了大过冷度制冷-高温水蓄冷空调系统原理，对该系统中的关键设备过冷器进行了选型和计算。在液-液换热型板式换热器传热特性无资料的情况下，根据板式蒸发器的传热特性和管式液-液热交换换热器与管式蒸发器式蒸发器的传热系数的比值来估算板式过冷器的传热系数或传热单元数，实验证明，这种设计方法是成功的。     

大过冷度逆流式过冷器换热特性研究

阐述了大过冷度制冷——高温水蓄冷空调系统原理,对该系统中的关键设备过冷器进行了选型和计算。在液——液换热型板式换热器传热特性无资料的情况下,根据板式蒸发器的传热特性和管式液——液热交换换热器与管式蒸发器的传热系数的比值来估算板式过冷器的传热系数或传热单元数。实验证明,这种设计方法是成功的。     

Predictions of energy savings in HVAC systems by lumped models

An approach to optimizing the energy efficiency of a Heating, Ventilating, and Air Conditioning (HVAC) system is presented that utilizes computational predictions of the effect of heat load distribution on moist air temperature, density, and humidity variation. Lumped-HVAC (L-HVAC) is a new lumped parameter code that couples fluid transport, energy transport, thermodynamics, and psychrometrics in an HVAC system. This code contains a nonlinear implicit solution algorithm for steady-state and transient calculations for flow resistance, water mass balance, and energy conservation. L-HVAC has been validated using a simplified analytical model, the commercial lumped parameter code SINDA/FLUINT, and experimental measurements. Steady-state calculations for a single-room system suggest an order of magnitude greater energy savings using a variable chiller power control approach compared to control damper and variable-drive fan approaches. L-HVAC was also applied to predict that the fraction of latent to total heat load influences the steady-state system temperature by up to 0.4 °C for the example system in this study.     

Dynamic performances of solar heat storage system with packed bed using myristic acid as phase change material

This paper is aimed at analyzing the thermal characteristics of packed bed containing spherical capsules, used in a latent heat thermal storage system with a solar heating collector. Myristic acid is selected as phase change material (PCM), and water is used as heat transfer fluid (HTF). The mathematical model based on the energy balance of HTF and PCM is developed to calculate the temperatures of PCM and HTF, solid fraction and heat release rate during the solidifying process. The latent efficiency, which is defined as the ratio between the instantaneous released latent heat and the maximum released heat, is introduced to indicate the thermal performances of the system. The inlet temperature of HTF (50 °C), flow rate of HTF (10 kg/min) and initial temperature of HTF (66 °C) were chosen for studying thermal performances in solar heat storage system. The influences of inlet temperature of HTF, flow rate of HTF and initial temperatures of HTF and PCM on the latent efficiency and heat release rate are also analyzed and discussed.     

Thermodynamic analysis and optimisation of an irreversible radiative-type heat engine by using non-dominated sorting genetic algorithm

Finite-time thermodynamics with an ecological principle is used for a heat engine with an irreversible radiative along with losses owing to internal irreversibilities and the heat transfer through finite-temperature differences. In this study, the ecological function is optimised regarding the cycle temperature ratio and the effects of the extreme temperature ratio and the internal irreversibilities are investigated on the optimum cycle performance. Paper presented here used a non-dominated sorting genetic algorithm called NSGA-II to optimise the thermal efficiency, the dimensionless ecological function and the dimensionless power simultaneously. Rather than a sole ultimate optimum outcome resulting in conventional single-objective optimisation, a set of optimum solutions were obtained called the Pareto optimal frontier. Hence, in order to select a final optimal answer, a progression of decision making was utilised. Two decision-making procedures were employed in the objectives’ space to obtain the optimum answers from the Pareto optimum outcomes.