Optimal location and thickness of insulation layers for minimizing building energy consumption

This work aims to optimize the position and thickness of insulation layers in building external wall for climates in the coastal Mediterranean zone and in the inland plateau of Lebanon. A space and an air-conditioning system performance models are developed to predict the space and system loads and associated thermal comfort of occupants. A genetic algorithm is used for the optimization of the life cycle cost of the insulation based on energy load while including the productivity loss associated with thermal discomfort during transient periods. For continuous operation of building HVAC system, adding insulation reduces life cycle cost by 20% over current thermal code requirements. During intermittent operation, locating the insulation at the inner side of the walls results in 15% reduction in energy load compared to locating it on the outer wall. The optimum thickness varied between 3 cm and 5 cm depending on wall orientation climate season.     

Regression analysis of high-rise fully air-conditioned office buildings

The building energy simulation computer program DOE-2 was used to carry out a parametric study of a generic high-rise air-conditioned office building in Hong Kong. A total of 28 design parameters related to the building load, the heating, ventilating and air-conditioning (HVAC) system and the HVAC refrigeration plant were found to correlate well with the predicted annual electricity consumption. Both linear and non-linear multiple regression techniques were used to develop regression models and energy equations for the prediction of annual electricity use. Twelve input design parameters (six from building load, four from HVAC system and two from HVAC refrigeration plant) were considered to be the most significant design variables and were used in the energy prediction equations. It is hoped that the resulting models and energy equations can be used as a simplified design tool for comparing the relative thermal and energy performance of different design schemes during the early design stage. This paper presents the methodology and the development work, and discusses the findings.     

高层建筑暖通空调设计特点探讨

本文基于高层建筑暖通空调设计特点,论述了暖通空调系统的特点类型和高层建筑暖通空调系统设计中特点,在特点分析中主要探讨了空调循环水泵的选型、供暖、空调通风等方面设计特点问题。这一研究对于提高高层建筑的节能目的具有一定的借鉴意义。     

Indoor cooling/heating load analysis based on coupled simulation of convection,radiation and HVAC control

A computational fluid dynamics (CFD) simulation for analyzing indoor cooling/heating load is presented in this study. It is coupled with a radiative heat transfer simulation and heating, ventilating, and air-conditioning (HVAC) controlling system in a room. This new method feeds back the outputs of the HVAC system control to the input boundary conditions of the CFD, and this method includes a human model to evaluate the thermal environment. It would be used to analyze the heating/cooling loads of different HVAC systems under the condition of the same human thermal sensation (e.g. PMV, operative temperature, etc.) even though the temperature and air-velocity distribution in the room are different from each other.To examine the performance of the new method, a cooling load and a thermal environment within a semi-enclosed space, which opens into an atrium space, is analyzed under the steady-state conditions during the summer season. This method is able to analyze the indoor cooling load with changes of target thermal environments of a room and/or changing clothing conditions of occupants considering the temperature and air-velocity distribution in the room. In this paper, two types of HVAC system are compared; i.e. radiation-panel system and all-air cooling system. The radiation-panel cooling system is found to be more energy efficient for cooling the semi-enclosed space. Changes of the level of thermal environment reduce cooling load effectively in case of the all-air cooling system while the radiation-panel system does not reduce cooling load even though the targeted thermal condition is relaxed. Energy saving effect is expected by easing the clothing conditions of occupants. In this study, the reducing effect of cooling load is quantitatively evaluated with clothing conditions also.     

Cooling load calculations in subtropical climate

Heating, ventilation and air-conditioning (HVAC) system is the major electricity consumer in an air-conditioned building; therefore, an accurate cooling load calculation method is indispensable. ASHRAE has developed a Radiant Time Series (RTS) method to improve the accuracy of cooling load calculation. However, outdoor design conditions and occupant load patterns vary with the buildings and cities. This study discusses the development of a new example weather year and a mathematical model to generate design occupant load profiles using Monte Carlo simulation for a subtropical climate. The results would be useful for determining the HVAC energy consumption in buildings in order to obtain more representative data for the prediction of annual energy consumption.     

Energy simulation in the variable refrigerant flow air-conditioning system under cooling conditions

As a high-efficiency air-conditioning scheme, the variable refrigerant flow (VRF) air-conditioning system is finding its way in office buildings. However, there is no well-known energy simulation software available so far which can be used for the energy analysis of VRF. Based on the generic dynamic building energy simulation environment, EnergyPlus, a new VRF module is developed and the energy usage of the VRF system is investigated. This paper compares the energy consumption of the VRF system with that of two conventional air-conditioning systems, namely, variable air volume (VAV) system as well as fan-coil plus fresh air (FPFA) system. A generic office building is used to accommodate the different types of heating, ventilating, and air-conditioning (HVAC) systems. The work focuses on the energy consumption of the VRF system in the office buildings and helps the designer's evaluation and decision-making on the HVAC systems in the early stages of building design. Simulation results show that the energy-saving potentials of the VRF system are expected to achieve 22.2% and 11.7%, compared with the VAV system and the FPFA system, respectively. Energy-usage breakdown for the end-users in various systems is also presented.     

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.     

Coupled simulation of convicton,radiation, and HVAC control for attaining a given PMV value

A new computational fluid dynamics (CFD) simulation for designing indoor climates is presented in this study. It is coupled with a radiative heat transfer simulation and heating, ventilating, and air-conditioning (HVAC) control system in a room. This new method can feed back the outputs of the CFD to the input conditions for controlling the HVAC system, and includes a human model to evaluate the thermal environment. It can be used to analyze the conditions of the HVAC system (e.g. temperature of supply air, surface temperature of radiation panel, etc.) and the heating/cooling loads of different HVAC systems under the condition of the same human thermal sensation (e.g. PMV, operative temperature, etc.) To examine the performance of the new method, a thermal environment within a semi-enclosed space which opens into an atrium space is analyzed under steady-state conditions in the summer season. Using this method, the most energy efficient HVAC system can be chosen under the same PMV value. In this paper, two types of HVAC system are compared: one is a radiation-panel system and the other is an all-air cooling system. The radiation-panel cooling is found to be more energy efficient for cooling the semi-enclosed space in this study.     

A combined system of chilled ceiling,displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.     

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.     

Optimal supply air temperature with respect to energy use in a variable air volume system

In a variable air volume (VAV) system with 100% outdoor air, the cooling need in the building is satisfied with a certain air flow at a certain supply air temperature. To minimize the system energy use, an optimal supply air temperature can be set dependent on the load, specific fan power (SFP), chiller coefficient of performance, outdoor temperature and the outdoor relative humidity. The theory for an optimal supply air temperature is presented and the heating, ventilation and air-conditioning (HVAC) energy use is calculated depending on supply air temperature control strategy, average U-value of the building envelope and two outdoor climates. The analyses show that controlling the supply air temperature optimally results in a significantly lower HVAC energy use than with a constant supply air temperature. The optimal average U-value of the building envelope is in practise mostly zero.     

Needs and trends in integrated building and HVAC thermal design tools

Buildings are responsible for approximately 40% of the total energy consumption in developed countries. More than half of this is used to condition the indoor environment. Studies have shown that savings of between 30 and 70% may be realized through improved design and retrofit procedures for buildings and air conditioning equipment.

Designing for energy efficiency requires a system approach that includes the building, the HVAC system and the controller. Traditional design philosophy based on load calculations is inadequate. New user-friendly design tools allowing an integrated simulation of the complete system are needed.

The main features of a suitable design tool are identified. It should allow dynamic analysis of the passive performance of the building combined with pseudo-steady HVAC system simulation. HVAC component models should be based on simplified fundamental principle analysis to ensure flexibility. The tool should allow for a fully integrated simulation of the building, its HVAC system and controller.

A flexible icon-based graphical interface must be complemented be expandable databases for all components to ensure user-friendly operation. The software must run on a personal computer and should also allow standard system design calculations, life-cycle cost analysis, automatic optimization features and data exchange with CAD software. No tool could be found that provided all of these needs.

The use of such a tool will result in more energy-efficient solutions when designing, managing and retrofitting buildings. This will help to reduce the burden on the environment. The tool will make commissioning of new systems more precise and less laborious. The ability of the designer to guarantee desired comfort conditions will also be enhanced.     

Double cooling coil model for non-linear HVAC system using RLF method

The purpose of heating, ventilating and air conditioning (HVAC) system is to provide and maintain a comfortable indoor temperature and humidity. The objective of this work is to model building structure, including equipments of HVAC system. The hybrid HVAC model is built with physical and empirical functions of thermal inertia quantity. Physical laws are used to build the sub-model for subsystems that have low thermal inertia while the empirical method is used to build the sub-model for subsystems with high thermal inertia. The residential load factor (RLF) is modeled by residential heat balance (RHB). RLF is required to calculate a cooling/heating load depending upon the indoor/outdoor temperature. The transparency, functionality of indoor/outdoor temperatures and simplicity of RLF makes it suitable for modeling. Furthermore, the parameters of the model can be calculated differently from room to room and are appropriate for variable air volume (VAV) factor. Nowadays, a VAV system is universally accepted as means of achieving both energy efficiency and comfortable building environment. In this research work, a pre-cooling coil is added to humidify the incoming air, which controls the humidity more efficiently inside conditioned space. The model presented here is verified with both theoretical and numerical methods.     

夏季空调热舒适响应空间及节能潜力研究

在满足人体热舒适要求的前提下,通过对空调热舒适方程的仿真分析,建立了空调系统环境参数的舒适空间,确立各参数对舒适性指标的影响程度;通过对空调建筑房间冷负荷计算分析,验证了空调系统在热舒适环境参数空间内存在一定节能潜力。     

暖通空调系统的环境影响价值工程

本文将暖通空调系统所营造的建筑室内舒适环境与暖通空调系统耗能引起的温室气体排放相结合，提出了一个新的评价概念——暖通空调系统的环境影响价值工程。本文在对此概念给予理论定义的同时，讨论了其量化计算方法。并在此基础上，以重庆市一酒店建筑为例，进行了实例计算分析。暖通空调系统的环境影响价值工程作为一个性能化评价方法，将暖通空调系统的价值、环境功能和环境成本作为一个整体同时来考虑，充分体现了建筑节能与室内环境改善的统一，旨在对暖通空调系统给予科学合理的评判。     

Simulation of a building and its HVAC system with an equation solver: Application to benchmarking

The today-availability of powerful engineering equation solvers is opening very new possibilities in technical component modelling and in system simulation. The simulation models, the “user guide” and the “reference guide” are all included in a same file. Reliable “reference” and “simplified” models are currently available for the building zone and for most (heating, ventilation and air-conditioning) HVAC components. Focus is given here on “simplified” models and on a simulation tool, called “Benchmark”. This tool should help an auditor to make the best use of the limited information usually available about actual fuel and electricity consumptions and to get a very first evaluation of the actual performances of a given HVAC system. An example of such use is presented. Another simulation tools and more information about the modelling of HVAC components will be presented in a further paper.     

某住宅小区地源热泵系统设计分析

本文阐述了某住宅小区地源热泵系统的设计方案,空调冷热负荷的计算,即针对代表建筑用DeST软件模拟全年动态负荷,结合建筑物的特点及工程经验取得同时使用系数并确定最终空调负荷值,分析了居住类建筑集中供能系统装机容量与最终空调负荷之间的关系,总结了地源热泵系统设计过程中的思考体会。     

HVAC system optimization for energy management by evolutionary programming

Energy management of heating, ventilating and air-conditioning (HVAC) systems is a primary concern in building projects, since the energy consumption in electricity has the highest percentage in HVAC among all building services installations and electric appliances. Without sacrifice of thermal comfort, to reset the suitable operating parameters, such as the chilled water temperature and supply air temperature, would have energy saving with immediate effect. For the typical commercial building projects, it is not difficult to acquire the reference settings for efficient operation. However, for some special projects, due to the specific design and control of the HVAC system, conventional settings may not be necessarily energy-efficient in daily operation.In this paper, the simulation-optimization approach was proposed for the effective energy management of HVAC system. Due to the complicated interrelationship of the entire HVAC system, which commonly includes the water side and air side systems, it is necessary to suggest optimum settings for different operations in response to the dynamic cooling loads and changing weather conditions throughout a year. A metaheuristic simulation–EP (evolutionary programming) coupling approach was developed using evolutionary programming, which can effectively handle the discrete, non-linear and highly constrained optimization problems, such as those related to HVAC systems. The effectiveness of this simulation–EP coupling suite was demonstrated through the establishment of a monthly optimum reset scheme for both the chilled water and supply air temperatures of the HVAC installations of a local project. This reset scheme would have a saving potential of about 7% as compared to the existing operational settings, without any extra cost.     

Co-simulation of innovative integrated HVAC systems in buildings

Integrated performance simulation of buildings' heating, ventilation and air-conditioning (HVAC) systems can help in reducing energy consumption and increasing occupant comfort. However, no single building performance simulation (BPS) tool offers sufficient capabilities and flexibilities to analyse integrated building systems and to enable rapid prototyping of innovative building and system technologies. One way to alleviate this problem is to use co-simulation, as an integrated approach to simulation.

This article elaborates on issues important for co-simulation realization and discusses multiple possibilities to justify the particular approach implemented in the here described co-simulation prototype. The prototype is validated with the results obtained from the traditional simulation approach. It is further used in a proof-of-concept case study to demonstrate the applicability of the method and to highlight its benefits. Stability and accuracy of different coupling strategies are analysed to give a guideline for the required coupling time step.     

天津地区某高层办公楼能耗模拟与节能潜力分析

建筑能耗中供暖空调能耗所占比例约为55%,是实现建筑节能的关键。采用DeST-c模拟了天津地区某新建高层(20层)办公楼能耗,将模拟结果与传统负荷计算结果进行了对比,同时分析了空调系统的风系统和水系统分别采用排风热回收和变流量技术后的节能潜力。对比分析表明与传统负荷计算方法相比,能耗模拟软件计算的全年累计冷热负荷值分别减少43.0%和31.0%,全年累计冷热负荷指标仅为传统负荷计算值的21.0%和26.0%。风系统采用排风热回收技术后,冷水机组总容量从1 800 kW降到为1 500 kW,全年制冷能耗节省5.3万kW·h;水系统采用变流量水系统技术后,理论上每年节省2.5万kW·h能耗。采用排风热回收和变流量两项节能措施后,空调系统总能耗降低约8%,节能效果明显。