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.     

The map of energy flow in HVAC systems

Heating, ventilation and air conditioning (HVAC) systems are the most energy consuming building services representing approximately half of the final energy use in the building sector and between one tenth and one fifth of the energy consumption in developed countries. Despite their significant energy use, there is a lack of a consistent and homogeneous framework to efficiently guide research and energy policies, mainly due to the complexity and variety of HVAC systems but also to insufficient rigour in their energy analysis. This paper reviews energy related aspects of HVAC systems with the aim of establishing a common ground for the analysis of their energy efficiency. The paper focuses on the map of energy flow to deliver thermal comfort: the HVAC energy chain. Our approach deals first with thermal comfort as the final service delivered to building occupants. Secondly, conditioned spaces are examined as the systems where useful heat (or coolth) is degraded to provide comfort. This is followed by the analysis of HVAC systems as complex energy conversion devices where energy carriers are transformed into useful heat and coolth, and finally, the impact of HVAC energy consumption on energy resources is discussed.     

室温传感器偏差故障对武汉地区暖通空调系统的影响研究

暖通空调系统的高效节能运行高度依赖于传感器测量的准确性。在传感器全寿命运行周期中,不可避免发生各种故障,影响其准确性。为探究传感器故障对不同暖通空调系统的影响,文章以室温传感器偏差故障为例,针对武汉地区某办公建筑,同时开展地源热泵和"冷水机组+锅炉"两种暖通空调系统形式的能耗建模,对比分析-5℃~+5℃偏差故障对两种系统运行能耗、工作性能及室内热舒适性的影响差异。结果表明:室温传感器故障的偏差幅值方向对两种系统运行能耗、工作性能及室内热舒适性的影响规律不同。其中,地源热泵系统能耗受室温传感器偏差故障影响相对更小。     

Hourly indoor thermal comfort and air quality acceptance with passive climate control methods

Nowadays, the effect of permeable coverings on conditioning of indoor air in real buildings, has become of special interest in the process of achieving a sustainable built environment. In these studies, the first hour of occupation is usually selected, because it is then that the strong effect of coverings is felt, due to the low ventilation rate that prevails during the unoccupied period. In this context, an hourly study enables us to understand the behaviour during working periods and the effect of coverings on indoor thermal comfort conditions, air quality acceptance and peaks of energy consumption.Results showed that permeable coverings reduce energy consumption and peak loads and this effect is controlled by air renewal. Consequently, during the summer season, indoor thermal comfort and acceptance of indoor air conditions were found to be better with permeable coverings. In winter, in offices with impermeable coverings inadequate operative conditions of heating, ventilation, and air-conditioning (HVAC) induced a slight improvement on indoor air conditions, during the period of occupation. Further studies are required to assess the real effect of building materials and their use, and substitution of the current HVAC systems with this type of passive method. In particular, a suitable method to determine the adequacy of coverings and their active thickness needs to be developed.     

An approach to optimised control of HVAC systems in indoor swimming pools

Indoor swimming pools are recognised as having a high level of energy consumption and present a great potential for energy saving. The energy is spent in several ways such as evaporation heat loss from the pool, high rates of ventilation required to guarantee the indoor air quality, and ambient temperatures with expressive values (typically 28?30°C) required to maintain conditions of comfort. This paper presents an approach to optimising control of heat ventilation and air conditioning systems that could be implemented in a building energy management system. It is easily adapted to any kind of pool and results in significant energy consumption reduction. The development and validation of the control model were carried out with a building thermal simulation software. The use of this control model in the case study building could reduce the energy efficiency index by 7.14 points (7.4% of total) which adds up to an energy cost saving of 15,609€ (7.5% of total).     

A new thermal comfort approach comparing adaptive and PMV models

In buildings with heating, ventilation, and air-conditioning (HVAC), the Predicted Mean Vote index (PMV) was successful at predicting comfort conditions, whereas in naturally ventilated buildings, only adaptive models provide accurate predictions. On the other hand, permeable coverings can be considered as a passive control method of indoor conditions and, consequently, have implications in the perception of indoor air quality, local thermal comfort, and energy savings. These energy savings were measured in terms of the set point temperature established in accordance with adaptive methods. Problems appear when the adaptive model suggests the same neutral temperature for ambiences with the same indoor temperature but different relative humidities. In this paper, a new design of the PMV model is described to compare the neutral temperature to real indoor conditions. Results showed that this new PMV model tends to overestimate thermal neutralities but with a lower value than Fanger’s PMV index. On the other hand, this new PMV model considers indoor relative humidity, showing a clear differentiation of indoor ambiences in terms of it, unlike adaptive models. Finally, spaces with permeable coverings present indoor conditions closer to thermal neutrality, with corresponding energy savings.     

Application of energy storage enclosure with phase change materials in building energy saving

相变材料具有高效的能量储存功能。相变材料与建材基体结合,制成一种具有储热功能的围护结构。该围护结构可发挥相变储热功能,降低建筑室内温度波动,增强建筑热舒适度,能够更加有效地减少建筑物运行能耗,从而实现建筑节能。本文对当前现有相变材料的优缺点、相变材料在不同围护结构中的应用、相变储能围护结构对室内热环境的影响及对建筑运行能耗的影响、相变储能围护结构应用的经济性等方面进行了分析,提出相变储能围护结构在工程应用中所存在的不足及其发展前景。     

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.     

Energy saving strategies in air-conditioning for museums

In the museum environment a strict thermal-hygrometric control is necessary primarily for the correct artwork conservation and then for the visitor thermal comfort. Considering that the air-conditioning system has to operate constantly, suitable techniques permit to obtain useful energy savings, allowing, however, a good dynamic microclimatic control.In this paper a case study is presented about various strategies used to reduce energy requirements for HVAC systems in an exhibition room of a modern museum. Using the dynamic simulation code DOE 2.2 and typical climatic hourly data sets, the annual energy use for an all-air system has been calculated, as well as the savings obtainable using different techniques, such as dehumidification by adsorption (desiccant wheel – saving equal to 15% with respect to a base configuration), total energy recovery from the relief air (passive desiccant – 15%), outdoor airflow rate variation (demand control ventilation – 45%). Moreover, the correspondence has been analyzed between the energy request and the admitted variation of indoor temperature and relative humidity: changing the admitted indoor RH range from 50 ± 2% to 50 ± 10%, energy savings around 40% have been obtained. As regards the thermal-hygrometric performance, an optimal control of temperature has been guaranteed with all the configurations, while the best performance in RH control has been obtained with the desiccant system.Considering a simple payback analysis, if the artworks preserved in a museum are particularly sensitive to indoor humidity variation, a desiccant system should be properly used; on the contrary, when the indoor humidity control is not strongly needed, the use of a HVAC system with demand control ventilation is advisable, because of the lowest payback value. The system with total energy recovery presents intermediate features.     

Numerical study of a hybrid ventilation system for single family houses

The main objective of this study is to develop and test hybrid ventilation systems and control strategies that are suitable for residential buildings. Two ventilation systems were modelled: a mechanical extract ventilation system (called the reference system) and a hybrid low pressure ventilation system that can support two different types of demand control strategies (occupancy detection and CO₂ concentration). The newly developed models were assembled with the existing thermal models of the SIMBAD Building and HVAC Toolbox developed by the CSTB.A single family house located in Athens (Greece), Nice (France), Trappes (France) and finally Stockholm (Sweden) was considered as the case study. Yearly simulations were performed to assess the performance of the hybrid ventilation control strategies. The assessment criteria used are related to indoor air quality, thermal comfort, energy consumption and stability of control strategies. The results show that the low pressure ventilation system can improve the indoor air quality and reduce the fan energy consumption compared to the reference system while maintaining the same building energy consumption for heating.     

基于毛细管型辐射供暖与供冷系统影响因素的研究

随着建筑节能的推广和人们对室内生活舒适性要求的提高,采用一种更先进、更节能的室内空气调节系统就显得日趋重要。毛细管型辐射供暖与供冷系统因具有舒适度高、节能效果显著、节省建筑空间等的优点逐渐被广泛采用。对以毛细管为末端的毛细管型辐射供暖与供冷系统布置形式作了介绍,分析了该系统的组成及优点。以辐射供冷为例,探讨了辐射冷系统的末端一毛细管席供冷量的影响因素。     

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。     

Thermal energy storage in building integrated thermal systems: A review. Part 1. active storage systems

Energy consumed by heating, ventilation and air conditioning systems (HVAC) in buildings represents an important part of the global energy consumed in Europe. Thermal energy storage is considered as a promising technology to improve the energy efficiency of these systems, and if incorporated in the building envelope the energy demand can be reduced. Many studies are on applications of thermal energy storage in buildings, but few consider their integration in the building. The inclusion of thermal storage in a functional and constructive way could promote these systems in the commercial and residential building sector, as well as providing user-friendly tools to architects and engineers to help implementation at the design stage. The aim of this paper is to review and identify thermal storage building integrated systems and to classify them depending on the location of the thermal storage system.     

被动式太阳房的降温研究

通风的目的是保证室内良好的空气品质,采用自然通风方式是生态建筑设计的重要内容,自然通风形成的室内热环境有利于人体舒适性.太阳能烟囱管能强化房间的自然通风,可以有效地改善室内的空气品质和室内热环境,但尚未达到舒适的温度.     

Nonlinear coupling between thermal mass and natural ventilation in buildings

An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h.     

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.     

顶板冷辐射加置换通风空调系统评价分析

介绍了顶板冷辐射与置换通风相结合的空调系统特点,分析了该系统在改善室内空气品质和满足人体的热舒适性方面的特点,评价了该系统的节能效果和经济性。     

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.     

Comparative study of room temperature control in buildings with and without the use of PCM in walls

The concept of thermal energy storage in building gains a specific importance in the present energy scenario related to energy consumption and indoor thermal comfort. The material used to store the thermal energy which undergoes a phase change referred as PCM and it is considered as a possible solution for reducing energy consumption in the building by storing and releasing heat within a certain temperature range; it raises the building inertia and also stabilizes indoor air temperature fluctuations. The room temperature is controlled by imposing PCM inside the walls. An attempt has been made to compare room air temperature with and without the use of PCM inside the walls of constructed modular building unit. The PCM imposed modular building shows the reduced temperature fluctuations in room, the PCM absorbs and liberates excess heat which is gained from the outer side of the room and maintains constant inner room temperature. The PCM imposed walls of modular building unit have an ability to reduce 10–30% of heat load in comparison with the plain wall. The results showed that reduction in room temperature is about 2–4°C and it has been concluded that the PCM imposed modular building unit has more energy saving opportunities than normal modular building unit.     

Optimising energy use in an existing commercial building: a case study of Australia’s Reef HQ Aquarium

Reef HQ Aquarium is a major tourism attraction in tropical North Queensland, Australia. In 8 years, a 50% reduction in grid electricity was achieved through targeted infrastructure investment, whilst growing the business. Initially, grid energy consumption was 2438 MWh per annum, with 490-kW peak demand and energy intensity of 1625 MJ m^?2 year^?1 used on typical equipment such as HVAC (heating, ventilation and air conditioning), machinery, lighting and catering equipment. Savings of 13% were achieved in the first year by increasing indoor air temperature set-points by 1.5 °C with no significant costs or impacts on occupant thermal comfort or worker productivity. Peak demand was decreased by 46% by upgrading the computerised building management system (BMS), HVAC, machinery and lighting; and by installing a 206-kW photovoltaic (PV) solar power system. This case study illustrates that (a) significant energy use reductions are possible at low cost; (b) capital investment in energy-efficient infrastructure can have short payback times and high direct and indirect benefits, particularly where equipment is ending its life. This study is unique as it examines how a commercial building with integrated chilled water thermal energy storage (TES) and a 3.2-ML chilled seawater aquarium system can be controlled by a BMS to optimise solar power to manage peak energy demand and also increase the utilisation of generated PV power in the absence of electrical battery storage. An interesting building is used to demonstrate efficiency methods with elements such as HVAC and lighting which usually consume over half commercial buildings’ energy use.