A model-based optimal ventilation control strategy of multi-zone VAV air-conditioning systems

This paper presents a model-based optimal ventilation control strategy for multi-zone VAV air-conditioning systems aiming at optimizing the total fresh air flow rate by compromising the thermal comfort, indoor air quality and total energy consumption. In this strategy, one scheme is used to correct the total fresh air flow rate dynamically by utilizing the unvitiated fresh air from the over-ventilation zones based on the detected occupancy of each zone and the related measurements. At the meantime, another scheme is developed to optimize the temperature set point for the temperature control of critical zones with the aim at reducing the variation of the required fresh air fractions among all the zones and further reducing the total fresh air intake from outdoors for energy saving when the first scheme is implemented. This scheme is based on a constructed cost function relating thermal comfort, indoor air quality and total energy consumption together while the cost function is calculated based on the prediction of system responses using dynamic simplified models. Genetic algorithm is used for optimizing the temperature set point of critical zones in the optimization process. This strategy was evaluated in a simulated building and air-conditioning environment under various weather conditions.     

Model-based optimal control of a dedicated outdoor air-chilled ceiling system using liquid desiccant and membrane-based total heat recovery

This study presents a model-based control strategy for a novel dedicated outdoor air-chilled ceiling (DOAS-CC) system with the aim of optimizing the overall system performance. The DOAS-CC system incorporates liquid desiccant dehumidification and membrane-based total heat recovery technologies. Simplified but reliable models of major components in the DOAS-CC system are firstly developed to predict the system performance. A cost function is then constructed to minimize total energy consumption while properly maintaining thermal comfort reflected by indoor air temperature and relative humidity. Genetic algorithm is used to search for optimal set-points of the supply air temperature and humidity ratio of the dedicated outdoor air subsystem as well as the supply water temperature. The performance of this strategy is tested and evaluated with different control settings in a simulated multi-zone space served by the DOAS-CC system under various weather conditions. The results show that optimized control variables produced by the optimal strategy can improve the system energy performance and maintain indoor thermal comfort.     

A cost‐effective operating strategy to reduce energy consumption in a HVAC system

The operation of the building heating, ventilating, and air conditioning (HVAC) system is a critical activity in terms of optimizing the building's energy consumption, ensuring the occupants' comfort, and preserving air quality. The performance of HVAC systems can be improved through optimized supervisory control strategies. Set points can be adjusted by the optimized supervisor to improve the operating efficiency. This paper presents a cost‐effective building operating strategy to reduce energy costs associated with the operation of the HVAC system. The strategy determines the set points of local‐loop controllers used in a multi‐zone HVAC system. The controller set points include the supply air temperature, the supply duct static pressure, and the chilled water supply temperature. The variation of zone air temperatures around the set point is also considered. The strategy provides proper set points to controllers for minimum energy use while maintaining the required thermal comfort. The proposed technology is computationally simple and suitable for online implementation; it requires access to some data that are already measured and therefore available in most existing building energy management and control systems. The strategy is evaluated for a case study in an existing variable air volume system. The results show that the proposed strategy may be an excellent means of reducing utility costs associated with maintaining or improving indoor environmental conditions. It may reduce energy consumption by about 11% when compared with the actual strategy applied on the investigated existing system. Copyright © 2007 John Wiley & Sons, Ltd.     

Application of terminal box optimization of single‐duct air‐handling units

Terminal boxes maintain room temperature by modulating supply air temperature and airflow in building heating, ventilation and air‐conditioning (HVAC) systems. Terminal boxes with conventional control sequences often supply inadequate airflow to a conditioned space, resulting in occupant discomfort, or provide excessive airflow that wastes significant reheat energy. In this study, the procedure for the optimal minimum airflow setpoint was developed to improve thermal comfort and reduce energy consumption. The determined minimum airflow setpoint was applied in an office building air‐conditioning system. Improvements in indoor thermal comfort and energy reduction were verified through measurement. The results show that the minimum airflow reset can stably maintain room temperature, satisfy comfort standards and reduce energy consumption compared with the conventional control. Copyright © 2009 John Wiley & Sons, Ltd.     

变风量空调系统中的实时优化节能控制

在对变风量空调系统局部控制的分析基础上,利用其变风量末端风门的开度作为各区域相对负荷的指示信号,提出送风静压的实时优化控制方案;同时,针对新的ＡＳＨＲＡＥ通风标准,还提出了基于室内人数检测和焓控制的新风实时优化控制方案。试验结果证明,同常规的控制方案相比,在保证室内热舒适性和空气质量的前提下,这两个方案分别有较好的节能作用。综合采用两种优化方案,系统不仅能够达到节能的目的,而且在较小负荷情况下能够提高室内空气的品质。     

Effectiveness of the earth tube heat exchanger system coupled to a space model in achieving thermal comfort in rural areas

The aim of this work is to investigate by modelling the possibility of reducing the operational energy of a typical house without negatively affecting its embodied energy. This is done through consideration of different building materials coupled with the use of an earth to air heat exchanger (EAHE) for fresh air supply and cooling. For known indoor and outdoor conditions and for given building materials (thermal capacity and conductance), a ventilation controller determines the amount of flow rate needed to temperate the indoor air temperature to achieve thermal comfort. Different wall configurations are assumed for each of the living zone and the bedroom zone of the apartment. It is found that the use of an optimal wall configuration in each zone coupled with the EAHE results in 76.7% energy savings compared with the reference case with conventional cooling.     

Multi-objective optimization of HVAC system with an evolutionary computation algorithm

A data-mining approach for the optimization of a HVAC (heating, ventilation, and air conditioning) system is presented. A predictive model of the HVAC system is derived by data-mining algorithms, using a dataset collected from an experiment conducted at a research facility. To minimize the energy while maintaining the corresponding IAQ (indoor air quality) within a user-defined range, a multi-objective optimization model is developed. The solutions of this model are set points of the control system derived with an evolutionary computation algorithm. The controllable input variables — supply air temperature and supply air duct static pressure set points — are generated to reduce the energy use. The results produced by the evolutionary computation algorithm show that the control strategy saves energy by optimizing operations of an HVAC system.     

Indoor thermal comfort characteristics under the control of a direct expansion air conditioning unit having a variable-speed compressor and a supply air fan

Indoor thermal environment is important as it affects the health and productivity of building occupants. Direct expansion (DX) air conditioning (A/C) units are commonly used for environmental control in small- to medium-scaled buildings. This paper reports on an experimental study to investigate the indoor thermal comfort characteristics under the control of a DX A/C unit having variable-speed compressor and supply fan at a fixed space cooling load but having three different ratios between its sensible part and latent part. The experimental results suggested that under a fixed indoor total cooling load with three different space sensible heat ratios (SHRs) of 0.92, 0.72 and 0.62, varying both speeds of compressor and supply fan in the DX A/C unit would influence indoor thermal comfort. Furthermore, when a DX A/C unit having variable-speed compressor and supply fan is used for indoor thermal comfort control under abnormal indoor load conditions, its ability of indoor thermal comfort control through varying compressor speed and supply fan speed may be duly restricted.     

An experimental tool for research and educational applications on HVAC systems

This paper describes an experimental tool elaborated at the building sciences laboratory (LASH/DGCB). The objective of this tool is to develop control strategies for heating, cooling and ventilation, and test them on heating, ventilating and air conditioning equipment. The tests are conducted in a large room of the laboratory equipped with a double-flow ventilation system and a global control/data acquisition system. The tool is used for research and some experiments are led by engineering students. It enables the identification of optimal parameters for each developed control strategy, in order to reach good thermal comfort, acceptable indoor air quality and good stability of actuators at the least energy cost. In this paper we present an example of global control strategy for heating and cooling periods based on interior temperature control (fuzzy regulator). This strategy includes an indoor air quality controller (proportional integral or fuzzy regulator) based on indoor CO₂ level control. A measurements campaign during an occupied period is shown with an overview of the actuators’ behaviour. This tool also highlights the key role of advanced control techniques to manage heating, cooling and ventilation systems.     

Chilled ceiling and displacement ventilation system for energy savings: A case study

This paper studies the design and performance of cooled ceiling and displacement ventilation (CC/DV) systems application for buildings in Beirut for the purpose of saving energy. The transient thermal response of spaces cooled by the combined CC/DV system is needed for performance assessment. For that reason, the plume‐multi‐layer model of CC/DV cooled spaces is extended to transient applications. A design procedure for the combined CC/DV system in Beirut humid climate and buildings is developed to insure that both indoor air quality and comfort are satisfied within the conditioned zone. The contribution of the proposed procedure is that it guarantees that the stratification height (occupied zone) is at 1.1 m taking into consideration the plumes from internal sources and non‐isothermal walls. The design procedure is applied to a case study in Beirut to design a system for a typical office space at 85 W m^?2 sensible cooling load. The CC/DV system size is compared with the size of a conventional mixed convection system. It is found that the size of the CC/DV system is 10.2 kW compared to conventional system size of 7.9 and 13.4 kW at the 30 and 100% fresh air supply, respectively. For the same indoor air quality and thermal comfort level, the CC/DV system consumed 21% less cooling energy than the conventional 100% fresh air system over the cooling season. The initial cost of the CC/DV system is higher, but the pay back period based on transient operation is less than 5 yr. Copyright © 2006 John Wiley & Sons, Ltd.     

哈尔滨冬季高校教室IAQ及热舒适现场研究

为了研究适于寒地教室建筑室内空气品质(IAQ)和室内人员热舒适指标及探讨改善措施,本文对哈尔滨市6所高校23个教室的IAQ和热环境进行了现场调查研究,得到有效问卷623份。在此基础上利用线性回归方法建立了冬季教室环境下的热感觉方程,得到了该环境下学生的热中性温度,发现低于哈尔滨居民的热中性温度;且受试者在较低或较高CO2浓度下都不能对IAQ做出合理的主观判断。同时,分析结果表明,哈尔滨教室冬季IAQ普遍较差,热量浪费严重,亟需有效的改善措施,并加强相关知识的宣传教育。     

地板下送风式相变蓄热电采暖系统

提出了一种利用定形相变材料蓄存夜间廉价电热，并能控制放热速率的地板下送风式相变蓄热电采暖系统。可有效利用夜间廉价电并提高室内环境热舒适性，搭建了应用此采暖系统的实验房间，测量了系统和室内空气的温度变化，分析了此采暖方式的使用效果。结果表明，该系统蓄放热性能较好。白天的电热负荷全部转移到夜间低谷电价时段，白天供热量可借送风量调节，冬季采用该系统供暖可满足热舒适的要求。     

采用室内热舒适性控制的变风量空调系统节能控制研究

在对变风量空调系统及控制系统分析的基础上,利用ＤＤＣ控制器可采集多点和多种信号的优点,提出采用室内热舒适性控制取代室内温度控制的控制方案。仿真试验结果证明,同常规的室内温度控制方案相比,室内热舒适性控制方案可以较好地改善室内的热舒适性,同时,在保证室内热舒适性前提下,采用室内热舒适性控制方案不仅能够保证控制的稳定性,而且有较好的节能作用。     

空调新风防冻节能调控机组在工业厂房应用浅谈

现代厂房设计都对室内工业生产生成烟尘和机械加工有害挥发物的送新风置换和通风排烟给予充分的考虑,通常的基本设计目标是在厂房实现送新风保证室内基本空气洁净度要求的同时,还将提供良好厂房室内的温度舒适及节能优化效果。     

隔断式工位空调系统气流组织与人体热舒适评价

采用K-ε湍流模型对采用隔断式工位空调的典型办公室工作微环境进行数值模拟,分析工位空调在人体周围所形成的非均一环境参数场,并进一步研究非均匀环境对人体热舒适的影响.在不同工位送风参数下对房间和人体周围环境参数的分布状况及吹风感和热舒适性进行研究.模拟结果发现:工位空调送风可以使室内温度呈现分区分布,工位送风效率高,可以...     

某城市商业综合体公共空间热环境数值模拟

用数值模拟方法,对北京某城市商业综合体内部公共空间空调工况热环境进行了研究,分析了各层不同送风比例下,综合体内部公共空间纵截面温度分布情况和人员活动区域内的温度分布情况。通过比较,确定了满足综合体内部公共空间各层热舒适要求的空调送风方案。数值模拟结果表明,对于城市商业综合体内部公共空间采用各层均匀送风,顶层与公共空间相连的走廊区域温度在夏季不能满足热舒适要求,适当减少内部公共空间下层的送回风量,增加至顶层,在冬夏工况下均可有效改善内部公共空间热环境,增加舒适度,有效解决顶层走廊温度偏高及温度不均等问题。     

Optimization of an HVAC system with a strength multi-objective particle-swarm algorithm

A data-driven approach for the optimization of a heating, ventilation, and air conditioning (HVAC) system in an office building is presented. A neural network (NN) algorithm is used to build a predictive model since it outperformed five other algorithms investigated in this paper. The NN-derived predictive model is then optimized with a strength multi-objective particle-swarm optimization (S-MOPSO) algorithm. The relationship between energy consumption and thermal comfort measured with temperature and humidity is discussed. The control settings derived from optimization of the model minimize energy consumption while maintaining thermal comfort at an acceptable level. The solutions derived by the S-MOPSO algorithm point to a large number of control alternatives for an HVAC system, representing a range of trade-offs between thermal comfort and energy consumption.     

Inherent correlation between the total output cooling capacity and equipment sensible heat ratio of a direct expansion air conditioning system under variable-speed operation (XXG SMD SHR DX AC unit)

Appropriately controlling indoor air humidity at a suitable level in buildings is important. To simultaneously control both indoor air dry-bulb temperature and relative humidity requires the match between the total output cooling capacity of an A/C system and the total cooling load in a space served by the A/C system, as well as the Equipment sensible heat ratio (SHR) of the A/C system and the Application SHR of the conditioned space. This paper reports on an experimental study on the inherent correlations between the total output cooling capacity and Equipment SHR of a DX A/C system. Experiments were carried out under different combinations of compressor speed and supply fan speed, and also under different inlet air conditions to the DX evaporator. The results obtained would lead to a better understanding of the operating characteristics of a DX A/C system under variable-speed operation, as well as the constraint of using these characteristics in developing appropriate control strategies, so as to better design, operate and control DX A/C systems for improved indoor thermal environmental control.     

Effect of ventilation strategies on air contaminant concentrations and energy consumption in buildings

Considering the diversity of indoor contaminant characteristics and generation patterns, finding an appropriate ventilation strategy that can secure acceptable indoor air quality with minimum energy consumption is a challenging task for HVAC system designers and operators. This study theoretically models and investigates the impact of various ventilation strategies on contaminant concentration behaviour and corresponding ventilation cooling energy requirements for a single‐zone enclosure. Two types of contaminants are considered; carbon dioxide as an occupancy dependent and formaldehyde, which is independent of occupancy. An airflow model is used to predict space pressure and air leakage rates across the enclosure envelope, and an air quality model is used to predict time‐varying contaminant concentrations. In addition, a building energy simulation model is utilized to predict the corresponding ventilation cooling energy requirements under hot climatic conditions. Results from this study show that acceptable contaminant concentrations during occupied periods can be achieved by different ventilation strategies but at substantially different ventilation energy requirements. More than 50 per cent reduction in ventilation energy requirements can be obtained while maintaining acceptable IAQ if proper ventilation strategy is employed. Copyright © 2001 John Wiley & Sons, Ltd.     

Comparing different control strategies for indoor thermal comfort aimed at the evaluation of the energy cost of quality of building

The rapid improvement in the standard of living requires more detailed and sophisticated methods of evaluating comfort conditions. But, maintaining thermal comfort conditions in confined environments may require complex regulation procedures and the proper management of heating, ventilating and air conditioning (HVAC) systems. In turn, the requirements for indoor thermal comfort do not necessarily coincide with those of energy saving purposes, which in the last years are becoming a crucial issue owing to the enactment of the European Energy Performance of Buildings Directive (EPBD).The aim of this work is to compare different indoor control thermal comfort strategies in view of the evaluation of the energy cost of quality in buildings.In particular, a new PID-fuzzy controller is presented and compared with a classic ON–OFF controller. The performances of the two controllers are quantified and compared by means of two cost functions that are based on the quadratic forms of the overall energy required by the thermal fluid and of the deviation from the preferred set point of the predicted mean vote (PMV). It is found that the application of the PID-fuzzy controller results in lower costs of energy input and lower deviation from set point of PMV.