Energy efficient PCM-based variable air volume air conditioning system for modern buildings

This work aims at achieving enhanced energy conservation for space conditioning with the application of a new combined variable air volume (VAV)-based chilled water air conditioning (A/C) system and thermal energy storage (TES) system. The phase change material (PCM) used in this system exhibited good charging and discharging characteristics that directly helped in conserving the overall energy spent on cooling and ventilation. The present system was experimentally investigated for summer and winter climatic conditions under demand controlled ventilation (DCV) and DCV combined with the economizer cycle ventilation (ECV) to substantiate its energy savings capability. Based on the results, in the DCV and combined DCV-ECV modes, this system achieved 28% and 47% of per day average energy conservative potential, respectively, while compared to the conventional chilled water-based A/C system. Similarly, the VAV-TES system yielded an on-peak total energy savings of 38% and 42%, respectively, for the same operating conditions.     

The impact of indoor thermal conditions,system controls and building types on the building energy demand

It is possible to evaluate the energy demand as well as the parameters related to indoor thermal comfort through building energy simulation tools. Since energy demand for heating and cooling is directly affected by the required level of thermal comfort, the investigation of the mutual relationship between thermal comfort and energy demand (and therefore operating costs) is of the foremost importance both to define the benchmarks for energy service contracts and to calibrate the energy labelling according to European Directive 2002/92/CE. The connection between indoor thermal comfort conditions and energy demand for both heating and cooling has been analyzed in this work with reference to a set of validation tests (office buildings) derived from a European draft standard. Once a range of required acceptable indoor operative temperatures had been fixed in accordance with Fanger's theory (e.g. −0.5 < PMV < −0.5), the effective hourly comfort conditions and the energy consumptions were estimated through dynamic simulations. The same approach was then used to quantify the energy demand when the range of acceptable indoor operative temperatures was fixed in accordance with de Dear's adaptive comfort theory.     

Improving energy performance of school buildings while ensuring indoor air quality ventilation

Energy conscious design of school buildings, as well as deemed-to-satisfy provisions in a Performance Based Energy Code, should address the problem known as the energy efficiency—thermal comfort—indoor air quality dilemma (EE-TC-IAQ Dilemma). In warm and moderate climates, the large internal heat sources usually found in school buildings prevent achieving thermal comfort without active cooling in summer, but are not sufficient to eliminate the need for heating in winter. Commonly used air-conditioners do not improve air quality, while natural ventilation induces uncontrolled energy losses. In this study, a step by step process was used for the development of deemed-to-satisfy design solutions, which cope with the EE-TC-IAQ Dilemma, for a performance based code. A distinction is made between improving building design variables and improving ventilation schemes. Results indicate that implementation of improved ventilation schemes in an otherwise well designed energy-conscious building result in savings of 28–30% and 17–18% for northern and southern classroom orientations, respectively.     

Energy optimized-ventilation constrained variable air volume system control

The analytical energy performance of an advanced energy optimized-ventilation constrained control approach to variable air volume systems was compared to four other controls. The other controls are either currently used or have been proposed in the literature. The advanced control demonstrated its potential to meet the ventilation requirements of ASHRAE Standard 62–1989 for every zone of the building with minimal energy consumption.

The analytical work was carried out in a single story prototypical commercial building. The building was analyzed in five US cities to provide insight into the impact of climate on the performance of the advanced control. The advanced control consumed less total energy, considerably less in some cities, than the other four controls. The advanced control provides an excellent opportunity to apply to buildings new automation equipment and software never attempted before.     

Energy saving and improved comfort by increased air movement

In this study, the potential saving of cooling energy by elevated air speed which can offset the impact of increased room air temperature on occupants’ comfort, as recommended in the present standards (ASHRAE 55 2004, ISO 7730 2005 and EN 15251 2007), was quantified by means of simulations with EnergyPlus software. Fifty-four cases covering six cities (Helsinki, Berlin, Bordeaux, Rome, Jerusalem and Athens), three indoor environment categories I, II and III (according to standard EN 15251 2007) and three air velocities (<0.2, 0.5 and 0.8 m/s) were simulated. The required cooling/heating energy was calculated assuming a perfectly efficient HVAC system. A cooling energy saving between 17 and 48% and a reduction of the maximum cooling power in the range 10–28% has been obtained. The results reveal that the required power input of the fan is a critical factor for achieving energy saving at elevated room temperature. Under the assumptions of this study, the energy saving may not be achieved with the methods for air speed increase, such as ceiling, standing, tower and desk fans widely used today when the power consumption of the fan is higher than 20 W.     

Modeling and energy simulation of the variable refrigerant flow air conditioning system with water-cooled condenser under cooling conditions

As a new system, variable refrigerant flow system with water-cooled condenser (water-cooled VRF) can offer several interesting characteristics for potential users. However, at present, its dynamic simulation simultaneously in association with building and other equipments is not yet included in the energy simulation programs. Based on the EnergyPlus's codes, and using manufacturer's performance parameters and data, the special simulation module for water-cooled VRF is developed and embedded in the software of EnergyPlus. After modeling and testing the new module, on the basis of a typical office building in Shanghai with water-cooled VRF system, the monthly and seasonal cooling energy consumption and the breakdown of the total power consumption are analyzed. The simulation results show that, during the whole cooling period, the fan-coil plus fresh air (FPFA) system consumes about 20% more power than the water-cooled VRF system does. The power comparison between the water-cooled VRF system and the air-cooled VRF system is performed too. All of these can provide designers some ideas to analyze the energy features of this new system and then to determine a better scheme of the air conditioning system.     

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.     

Energy, comfort and indoor air quality in nursery and elementary school buildings in the cold climatic zone of Greece

Schools are the most suitable type of building for the application of energy efficiency and good indoor air quality measures. This is justified by the fact that such measures can promote sustainability to the future citizens, and even more, ensure a comfortable and healthy environment for educational purposes. Unfortunately, in practice school buildings face the same, or even more intense, energy performance and indoor air quality problems as any other building. The purpose of this study is to investigate the energy efficiency, thermal environment and indoor air quality in public nursery and elementary school buildings in the city of Kozani, located at the cold climatic zone of Greece. The survey, conducted both by in-field measurements and by questionnaires, reveals the main parameters affecting the overall performance of the investigated buildings. The problematic building envelope, the improper control of heating and lighting systems, the absence of proper legislative measures and, above all, the lack of interest concerning the efficiency of such buildings are the main factors in the reported efficiency.     

Analysis of thermal comfort and indoor air quality in a mechanically ventilated theatre

Theatres are the most complex of all auditorium structures environmentally. They usually have high heat loads, which are of a transient nature as audiences come and go, and from lighting which changes from scene to scene, and they generally have full or nearly full occupancy. Theatres also need to perform well acoustically, both for the spoken word and for music, and as sound amplification is less used than in other auditoria, background noise control is critically important. All these factors place constraints on the ventilation design, and if this is poor, it can lead to the deterioration of indoor air quality and thermal comfort. To analyse the level of indoor air quality and thermal comfort in a typical medium-sized mechanically ventilated theatre, and to identify where improvements could typically be made, a comprehensive post-occupancy evaluation study was carried out on a theatre in Belgrade. The evaluation, based on the results of monitoring (temperature, relative humidity, CO₂, air speed and heat flux) and modelling (CFD), as well as the assessment of comfort and health as perceived by occupants, has shown that for most of the monitored period the environmental parameters were within the standard limits of thermal comfort and IAQ. However, two important issues were identified, which should be borne in mind by theatre designers in the future. First, the calculated ventilation rates showed that the theatre was over-ventilated, which will have serious consequences for its energy consumption, and secondly, the displacement ventilation arrangement employed led to higher than expected complaints of cold discomfort, probably due to cold draughts around the occupants’ feet.     

变风量空调系统的建模与控制

介绍了变风量空调系统的基本原理。结合变风量空调系统的特点,在基于被控房间数学模型的基础上,将模糊控制和常规PID控制相结合,提出了一种模糊PID控制方法并将其应用于变风量空调室温控制中。     

某办公楼空调系统故障分析及调试

针对某办公楼出现的室内相对湿度过高、新风量不足、空气有异味等问题,分析了设计资料进行现场调研,采取降低冷水机组供回水温度、调节风机盘管风速、适当关闭风机盘管台数、清洗在等措施,基本解决了室内空气品质问题。探讨了该工程空调系统设计中不足之处和运行管理中应注意的问题。     

Winter indoor air quality,thermal comfort and acoustic performance of newly built secondary schools in England

Previous studies have found that classrooms are often inadequately ventilated, with the resultant increased risk of negative impacts on the pupils. This paper describes a series of field measurements that investigated the indoor air quality, thermal comfort and acoustic performance of nine recently built secondary schools in England. The most significant conclusion is that the complex interaction between ventilation, thermal comfort and acoustics presents considerable challenges for designers. The study showed that while the acoustic standards are demanding it was possible to achieve natural ventilation designs that met the criteria for indoor ambient noise levels when external noise levels were not excessive. Most classrooms in the sample met the requirement of limiting the daily average CO₂ concentration to below 1500 ppm but just a few met the need to readily provide 8 l/s per person of fresh air under the easy control of the occupants. It would seem that the basic requirement of 1500 ppm of CO₂ is achieved as a consequence of the window areas being just sufficient to provide the minimum of 3 l/s per person at low and intermittent occupancy. Thermal comfort in the monitored classrooms was mostly acceptable but temperatures tended to be much higher in practice than the design assumed.     

Correlation between minimum airflow and discharge air temperature

Airflow and discharge air temperature can be varied to maintain room temperature setpoint according to heating load. Increasing discharge air temperature and the decreasing airflow can save energy, but it causes reduced air circulation as supply air temperature rises above the space temperature. On the other hand, increasing airflow can improve air circulation; however, it may waste energy. The objective of this study is to identify the correlation between the minimum airflow and discharge air temperature that will maintain room thermal comfort. Near-optimal room airflow and discharge air temperature were analyzed, and the impact of room airflow and discharge air temperature on thermal stratification was evaluated and potential energy savings was estimated. Its performance was conducted through field experiment.     

室内空调条件下围护结构(墙体、屋盖)的隔热控制 ——建筑热环境与节能研究(之一)

该文在自然通风条件下的室内热环境控制条件的基础上,提出空调条件下的室内热环境控制条件,并根据文中所提出的简化公式计算出了围护结构（屋顶、墙）的隔热控制指标,由此拓展了《民用建筑热工设计规范》（GB50176－93）．进而为窗的隔热控制和屋顶、墙的节能控制提供了重要理论基础与简便计算方法。     

低温送风空调系统节能分析和舒适度的研究

阐述了低温送风空调方式的特点及节能方式，并将其与常规空调方式做了比较，探讨了低温送风方式的热舒适性及评价指标，分析结果表明，低温送风空调方式与冰蓄技术相结合具有推广使用的实用价值。     

浅谈VRV空调系统原理及应用

简要介绍了VRV空调系统的起源、概念、热力学原理及构成,阐述了VRV空调系统常见的几种控制方式,指出了VRV空调系统的优缺点和在施工过程中应该注意的一些问题,从而推广VRV空调系统的应用。     

Dynamic evaluation of airflow rates for a variable air volume system serving an open-plan office

In a typical air-conditioned office, the thermal comfort and indoor air quality are sustained by delivering the amount of supply air with the correct proportion of outdoor air to the breathing zone. However, in a real office, it is not easy to measure these airflow rates supplied to space, especially when the space is served by a variable air volume (VAV) system. The most accurate method depends on what is being measured, the details of the building and types of ventilation system. The constant concentration tracer gas method as a means to determine ventilation system performance, however, this method becomes more complicated when the air, including the tracer gas is allowed to recirculate. An accurate measurement requires significant resource support in terms of instrumentation set up and also professional interpretation. This method deters regular monitoring of the performance of an airside systems by building managers, and hence the indoor environmental quality, in terms of thermal comfort and indoor air quality, may never be satisfactory. This paper proposes a space zone model for the calculation of all the airflow parameters based on tracer gas measurements, including flow rates of outdoor air, VAV supply, return space, return and exfiltration. Sulphur hexafluoride (SF6) and carbon dioxide (CO2) are used as tracer gases. After using both SF6 and CO2, the corresponding results provide a reference to justify the acceptability of using CO2 as the tracer gas. The validity of using CO2 has the significance that metabolic carbon dioxide can be used as a means to evaluate real time airflow rates. This approach provides a practical protocol for building managers to evaluate the performance of airside systems.     

Vertical Temperature Profiles in Rooms Ventilated by Displacement: Full-Scale Measurement and Nodal Modelling

The vertical temperature profiles have been measured in a full-scale office room ventilated by displacement. Different wall radiative emissivities have been employed to study the effect of thermal radiation. The change of the vertical locations of the heat source does not affect the stationary front, but modifies the temperature profile. Two new nodal models, i.e. a four-node model and a multi-node model, are developed for predicting the temperature profile based on the flow and thermal characterization in the room. Agreement between the models and the experiments are very good. The calculated results are applied to show that the temperature profile is influenced considerably by the heat conduction through the walls and the thermal radiation between the wall surfaces. The models developed can be used for design purposes, as well as to supply the thermal boundary conditions in a CFD code.     

某办公建筑多联机空调系统能耗调查与分析

根据对某办公楼全年电耗的调查结果及当地当年的气象资料,得到了该办公楼多联机空调系统全年能耗数据,分析了该空调系统低能耗的主要原因——机组部分负荷性能系数IPLV值较高,空调自控效果好。以该办公楼为例,计算了多联机空调系统与集中空调系统的能耗,结果表明,多联机空调系统能耗的计算值接近实测值,且略低于集中空调系统能耗;建议在评估空调系统的能耗时应采取理论计算与类似建筑实测值验证结合的做法。