Modeling and optimization of HVAC systems using artificial neural network and genetic algorithm

Intelligent energy management and control system (EMCS) in buildings offers an excellent means of reducing energy consumptions in HVAC systems while maintaining or improving indoor environmental conditions. This can be achieved through the use of computational intelligence and optimization. The paper thus proposes and evaluates a model-based optimization process for HVAC systems using evolutionary algorithm for optimization and artificial neural networks for modeling. The process can be integrated into the EMCS to perform several intelligent functions and achieve optimal whole-system performance. The proposed models and the optimization process are tested using data collected from an existing HVAC system. The testing results show that the models can capture very well the system performance, and the optimization process can reduce cooling energy consumption by about 11% when compared to the traditional operating strategies applied.     

集中空调控制参数的全局优化研究

大部分时间,建筑空调系统没有运行在设计工况下.为了使空调系统在非设计工况下高效地运行,提出遗传算法全局优化控制的策略,可以降低能耗,同时优化控制空调系统.选取空调送风温度、冷冻水供水温度以及冷却水供水温度作为独立控制参数建立VAV+VWV空调系统的能耗模型.通过对比分析传统控制策略和遗传算法全局优化控制策略的模拟结果,...     

公共建筑暖通空调系统提高能效的措施分析

根据重庆地区公共建筑的能耗调查,分析了目前国内公共建筑暖通空调系统在设计和运行管理方面存在的问题,结合公共建筑暖通空调系统的用能特点,分别从设计、运行管理和政策制度三方面讨论了公共建筑暖通空调系统提高能效的具体措施.     

Adaptive HVAC zone modeling for sustainable buildings

Control of energy flows within a building is critical to achieving optimal performance of heating, ventilation and air-conditioning (HVAC) systems. To design optimal HVAC control strategies, a dynamic model of the HVAC system - particularly the building zones that it services - is essential. As analysis of building energy consumption is facilitated by the accurate prediction of indoor environmental conditions, techniques that dynamically model HVAC zones are crucial, and as such, is an active area of research. This paper focuses on real-time HVAC zone model fitting and prediction techniques based on physical principles, as well as the use of genetic algorithms for optimization. The proposed approach is validated by comparing real-time HVAC zone model fitting and prediction against the corresponding experimental measurements. In addition, comparison with prediction results using an algorithm based on feedback-delayed Kalman filters has demonstrated the superiority of the proposed approach in terms of prediction accuracy.     

可持续建筑的低碳设计战略

在我国建筑能耗持续增长的严峻形势下,一种综合性的可持续建筑低碳设计战略呼之欲出,以实现“十二五规划”纲要中节能、减排的约束性目标.列出了建筑节能领域的现行法律法规与设计标准,根据可持续发展的原始定义,提出环保、生态、节能、绿色、生物和气侯适应性建筑,都是可持续建筑的实现途径.着重阐述了可持续建筑的低碳设计战略,包括5个...     

暖通空调系统优化控制与能量管理的现状及发展趋势

分析了暖通空调优化能量消耗的特点,介绍了暖通空调控制系统基础控制器参数整定、工作点优化和能量管理的现状。根据暖通空调系统的未来需求和相关技术的发展,提出了其控制技术的发展方向。     

HVAC system strategies for energy conservation in commercial buildings in Saudi Arabia

In recent years, there has been a dramatic increase in energy consumption in Saudi Arabia. The building sector being the largest consumer of electric energy represents a major potential contributor for reducing energy consumption. Due to their functional and operational characteristics, commercial buildings relatively consume more energy (per unit area) than other types of buildings. The heating, ventilating and air-conditioning system (HVAC) is one of the largest end-users of energy in these buildings, particularly in harsh climates. Energy efficient design and operation of HVAC systems in commercial buildings can offer major opportunities for reduced energy consumption and contribute to sustainable development. However, improper utilization of energy conservation measures can result in reduced environmental quality. This in turn exposes the occupants to thermal discomfort and health risks, and consequently diminishes the economic value of the facility. Therefore, a well assessed and balanced energy conservation strategy is required to achieve energy efficiency while maintaining desired level of thermal comfort. In this study, major design and operational parameters for different types of HVAC systems influencing energy consumption are investigated utilizing the Visual-DOE program. Results indicate that energy savings of up to 30% can be obtained while maintaining acceptable level of thermal comfort when HVAC systems are properly selected and operated.     

Predictive controllers for thermal comfort optimization and energy savings

The present work is focused on the study of indoor thermal comfort control problem in buildings equipped with HVAC (heating, ventilation and air conditioning) systems. The occupants’ thermal comfort sensation is addressed here by the well-known comfort index known as PMV (predicted mean vote) and by a comfort zone defined in a psychrometric chart. In this context, different strategies for the control algorithms are proposed by using an only-one-actuator system that can be associated to a cooling and/or heating system. The first set of strategies is related to the thermal comfort optimization and the second one includes energy consumption minimization, while maintaining the indoor thermal comfort criterion at an adequate level. The methods are based on the model predictive control scheme and simulation results are presented for two case studies. The results validate the proposed methodology in terms of both thermal comfort and energy savings.     

Application of an energy management and control system to assess the potential of different control strategies in HVAC systems

The significant and continuous increment in the global electricity consumption is asking for energy saving strategies. Efficient control for heating, ventilation and air-conditioning systems (HVAC) is the most cost-effective way to minimize the use of energy in buildings. In this framework, an energy management and control system (EMCS) has been developed to schedule electricity end-uses in the campus of the Universidad Politécnica de Valencia (UPV), Spain. This paper presents an evaluation performed by using the EMCS of different control strategies for HVAC split systems. It analyzed the effect of different schedules for a common air-conditioning device and demand response strategies are tested in several situations. The economic saving is calculated taking into account the electricity contract clauses. Finally, a test is made for the control of a group of similar devices in order to reduce the maximum peak power in consumption and to obtain a flexible load shape with the HVAC loads. The studies are then extrapolated to a larger system, the whole University campus, for which energy and economic savings are quantified.     

暖通空调的节能设计研究

建筑工程大规模的增加,其能源消耗的趋势也逐年增长,其中暖通空调在能源消耗上占据着巨大比例,因而暖通空调的节能问题在当今社会中也引发着公众巨大的关注。建筑节能的中暖通节能是关键也是基础,必须多加研究。文章针对当前暖通节能设计展开了探讨。     

A critical review of fault modeling of HVAC systems in buildings

Buildings consumed about 40% of primary energy and 70% of the electricity in the U.S. It is well known that most buildings lose a portion of their desired and designed energy efficiency in the years after they are commissioned or recommissioned. Majority of the Heating, Ventilation, and Air-Conditioning (HVAC) systems have multiple faults residing in the systems causing either energy, thermal comfort, or indoor air quality penalties. There are hundreds of fault detection and diagnostics (FDD) algorithms available, but there is lacking a common framework to assess and validate those FDD algorithms. Fault modeling is one of the key components of such a framework. In general, fault modeling has two purposes: testing and assessment of FDD algorithms, and fault impacts analysis in terms of building energy consumption and occupants’ thermal comfort. It is expected that fault ranking from the fault impact analysis can facilitate building facility managers to make decisions. This paper provides a detailed review of current state-of-the-art for the fault modeling of HVAC systems in buildings, including fault model, fault occurrence probability, and fault simulation platform. Fault simulations considering fault occurrence probability can generate realistic faulty data across a variety of faulty operating conditions, and facilitate testing and assessment of different FDD algorithms. They can also help the fault impact study. Three research gaps are identified through this critical literature review: (1) The number of available fault models of HVAC systems is still limited. A fault model library could be developed to cover all common HVAC faults for both traditional and non-traditional HVAC systems. (2) It is imperative to include the fault occurrence probability in fault simulations for a realistic fault impacts analysis such as fault ranking. (3) Fault simulation platforms need further improvements to better facilitate the fault impact analysis.     

空调系统控制的一种动态优化技术

为建筑空调系统控制提出一项动态的优化技术。在一个指定期间内，运用该算法，能得到使目标函数(例如运行成本或者峰值能耗)最小的房间温度曲线。该算法也能给出HVAC设备的最佳开、关时间。本文包括建筑热特性的模拟，优化技术和实例研究。     

绿色建筑对暖通空调专业的要求

20世纪90年代以来,绿色建筑逐步走向成熟.暖通空调能耗占建筑总能耗相当大的比重,对绿色建筑的实现至关重要.依据LEED NC和中国绿色建筑评价标准,探讨了暖通空调专业的设计、施工、验收、运行管理等建筑生命周期各环节有关绿色建筑的要求及可采取的措施.     

严寒地区公共机构既有建筑空调系统绿色改造情况调查与分析

公共机构建筑能耗是我国建筑能耗的重要组成部分。随着暖通空调系统的快速普及,其能耗作为建筑能耗大户的地位也日益突出。以严寒地区沈阳市为主要研究对象,主要调研了16栋典型公共机构建筑的暖通空调系统绿色改造情况,通过对调研数据分析研究,提出当前沈阳市公共机构既有建筑绿色改造过程中存在的问题,确定沈阳市公共机构既有建筑适宜的绿色改造技术措施。     

Cost effective energy and carbon emissions optimization in building renovation (Annex 56)

The construction sector has become an important target for reducing carbon emissions and energy consumption and for kerbing resource depletion, because of its relevance in all these important areas.Many of the current energy related policies have their focus on new buildings but, due to the low rates of replacement of the existing building stock, it is crucial that the low energy performances of these buildings are improved. Most of these buildings,due to design and construction constraints,may not be able to reach the new energy efficiency standards,which many times involve complex construction works. Nevertheless, the achievement of significant reductions in energy consumption and carbon emissions may not always require a highly efficient solution for the envelope. Other solutions, combining energy efficiency measures and the use of renewable energy, are also possible.In this context, the key research problem addressed in Annex 56 was to understand how far it is possible to go with energy conservation and efficiency measures and from which point the measures to foster renewable energy use become more economical taking into account the local context and the many restrictions the existing buildings face.Thus,a new methodology was developed to be used in the decision making process for energy related building renovation, allowing to find a cost-effective balance between energy consumption,carbon emissions and overall added value achieved in the renovation process.The methodology developed within IEA EBC Annex 56 project aims at defining,assessing and comparing energy renovation activities in a cost-effective way,o ptimizing the energy use and the carbon emissions reduction,mainly in residential buildings but also in non-residential buildings without complex HVAC technologies.The methodology explores the full range of cost-effective reduction of carbon emissions and energy use and takes into account also the additional benefits and the overall added value achieved by the building within the renovation process.     

A new methodology for the design of low energy buildings

The Kyoto protocol binded the developed countries to reduce the greenhouse gas emissions at least by 5% by 2008-2012 in order to tackle global warming and climate change. Some of the measures of the governments to achieve this goal are to promote new buildings construction and to retrofit existing buildings while satisfying low energy criteria. This means improving energy efficiency of buildings and energy systems, developing sustainable building concepts and promoting renewable energy sources.The design of a low energy building requires parametric studies via simulation tools in order to optimize the design of the building envelope and HVAC systems. These studies are often complex and time consuming due to a large number of parameters to consider. Hence, this paper aims to set up a methodology that simplifies parametrical studies during the design process of a low energy building. The methodology is based on the Design of Experiments (DOE) method which is a statistical method widely used in industry to perform parametric studies that reduces the required number of experiments.     

Analysis of local optima in predictive control for energy efficient buildings

We study the problem of heating, ventilation and air conditioning (HVAC) control in a typical commercial building. We propose a model predictive control (MPC) approach which minimizes energy cost while satisfying occupant comfort and control actuator constraints, using a simplified system model and incorporating predictions of future weather and occupancy inputs. In simplified physics-based models of HVAC systems, the product between air temperatures and flow rates arising from energy balance equations leads to a non-convex MPC problem. Fast computational techniques for solving non-convex optimization can only provide certificates of local optimality. Local optima can potentially cause MPC to have worse performance than existing control implementations, so deserve careful consideration. The objective of this article is to investigate the phenomenon of local optima in the MPC optimization problem for a simple HVAC system model. In the first part of the article, simplified physics-based models and MPC design for two common HVAC configurations are introduced. In the second part, simulation results exhibiting local optima for both configurations are presented. We perform a detailed analysis on the different types of local optima and their physical interpretation. We then use this analysis to derive physics-based rules to exclude classes of locally optimal control sequences under specific conditions.     

Evaluating performance indices of a shopping centre and implementing HVAC control principles to minimize energy usage

Heating, ventilating and air-conditioning (HVAC) systems in buildings must be integrated with an efficient control scheme to maintain comfort under any load conditions. Efficient HVAC control is often the most cost-effective option to improve the energy efficiency of a building. However, HVAC processes are non-linear, and characteristics change on a seasonal basis so the effect of changing the control strategy is usually difficult to predict. The present study aims to reduce energy consumption by defining new HVAC control strategies and tuning control loops in a shopping centre. First, an energy audit was performed to investigate the potential for energy savings and to redefine the control scenarios, while a methodology for the shopping centre was developed. Performance indices were then calculated and compared with the yardsticks. Next, normalised performance indices were computed to reach out a better understanding of the building’s efficiency. Finally, new strategies were implemented with the help of the existing building management system (BMS) and about 22% of energy saving was achieved.     

Applying a multi-objective optimization approach for Design of low-emission cost-effective dwellings

Modern buildings and their HVAC systems are required to be not only energy-efficient but also produce fewer economical and environmental impacts while adhering to an ever-increasing demand for better environment. Research shows that building regulations which depend mainly on building envelope requirements do not guarantee the best environmental and economical solutions. In the current study, a modified multi-objective optimization approach based on Genetic Algorithm is proposed and combined with IDA ICE (building performance simulation program). The combination is used to minimize the carbon dioxide equivalent (CO₂-eq) emissions and the investment cost for a two-storey house and its HVAC system. Heating/cooling energy source, heat recovery type, and six building envelope parameters are considered as design variables. The modified optimization approach performed efficiently with the three studied cases, which address different summer overheating levels, and a set of optimal combinations (Pareto front) was achieved for each case. It is concluded that: (1) compared with initial design, 32% less CO₂-eq emissions and 26% lower investment cost solution could be achieved, (2) the type of heating energy source has a marked influence on the optimal solutions, (3) the influence of the external wall, roof, and floor insulation thickness as well as the window U-value on the energy consumption and thermal comfort level can be reduced into an overall building U-value, (4) to avoid much of summer overheating, dwellings which have insufficient natural ventilation measures could require less insulation than the standard (inconsistent with energy saving requirements) and/or additional cost for shading option.