Ventilation and energy performance of partitioned indoor spaces under mixing and displacement ventilation

Large variation in indoor air quality (IAQ) and thermal comfort can occur in partitioned office spaces due to heterogeneous air mixing. However, few published studies examined IAQ, thermal comfort, and energy performance of partitioned occupied spaces, which are commonly found in today’s buildings. The objective of this study is to evaluate indoor environmental quality and air conditioning performance of a partitioned room under two typical ventilation modes: (1) mixing ventilation and (2) displacement ventilation. For a total of six representative air-conditioning scenarios, three-dimensional computational fluid dynamics (CFD) simulations are performed to examine temperature distribution, ventilation effectiveness, energy consumption, and local thermal comfort for two partitioned spaces. Simulation results indicate that temperature distribution in a partitioned room is a strong function of ventilation strategy (mixing vs. displacement), but marginally affected by diffuser arrangements. Local age-of-air (air freshness) significantly varies with both diffuser arrangement and ventilation strategy. Regarding energy consumption, displacement ventilation can achieve an indoor set-point temperature in the partitioned spaces about two times faster than mixing ventilation. Under mixing ventilation, the time to achieve a set-point temperature was notably reduced when each partitioned space is served by its own diffuser. For the same supply airflow rate, displacement ventilation can generate local draft risk at ankle level, while mixing ventilation may result in a draft sensation in wider areas around an occupant. Overall, the results suggest that mixing ventilation system can save energy if each partitioned zone is served by its own diffuser such as a multi-split air conditioning. However, when multiple partitioned zones are served by only one diffuser, displacement ventilation is more energy-efficient and can achieve higher ventilation effectiveness than mixing ventilation.     

Combating overheating: mixed-mode conditioning for workplace comfort

ABSTRACT

Using post-occupancy evaluations of seven mixed-mode buildings – three in Australia and four in India – this paper demonstrates that effective mixed-mode conditioning (instead of year-round air-conditioning) can deliver comfortable workspaces. Occupant feedback reinforces strong associations between overheating, thermal comfort, overall comfort and perceived productivity. However, differing levels of thermal acceptability within and between the Australian and Indian contexts are evident. Occupants in the Indian buildings were found to tolerate a wider range of temperatures when compared with Western contexts where lower temperature limits entrench an energy demand through a greater reliance on air-conditioning. The outcomes from the study suggest that the perception of overheating and consequent risk to building performance can be intensified when occupants perceive limited adaptive opportunity or problems are not rectified quickly, whereas perceived control is less important where building systems are user responsive. Occupants in three of the study buildings also perceived higher-than-anticipated comfort which could be attributable to well-liked attributes, such as break-out spaces, daylight and fresh air included in these buildings. The findings challenge designers and clients to develop user-responsive climate interactive workplaces that capitalize on spatial and mixed-mode environmental control to tackle the question of overheating.     

A holistic approach to energy efficient building forms

Minimizing energy consumption in buildings has become an important goal in architecture and urban planning in recent years. Guidelines were developed for each climatic zone aiming at increasing solar exposure for buildings in cold climates and at reducing solar exposure for buildings in hot climates. This approach usually plans for the season with the harshest weather; often forgetting that temperatures in cities at latitude 25° can drop below thermal comfort limits in winter and that temperatures in cities at latitude 48° often rise above thermal comfort limits in summer. This paper argues that a holistic approach to energy efficient building forms is needed. It demonstrates a generic energy efficient building form derived by cutting solar profiles in a conventional block. Results show that the proposed building form, the Residential Solar Block (RSB), can maximize solar energy falling on facades and minimize solar energy falling on roofs and on the ground surrounding buildings in an urban area in winter; thus maximizing the potential of passive utilization of solar energy. The RSB also supports strategies for mitigating the urban heat island through increased airflow between buildings, the promotion of marketable green roofs and the reduction of transportation energy.     

建筑热缓冲空间的设计理念和类型研究——以国际太阳能十项全能竞赛作品为例

对建筑热缓冲空间的设计理念和策略进行分析,将其功能归结为热缓冲空间的蓄热能力和对换热速率的调节两个因素;以历届太阳能十项全能竞赛的参赛作品为例,依据热缓冲空间的形式和在建筑中的位置,将其分为中庭式、包围式、外廊式和辅助空间式四个类型,并分别举例阐述其特点。分析结果表明,热缓冲空间是一种综合性的节能设计策略,它通过被动式节能措施的合理整合,建筑主次空间的合理组织,能有效的改善建筑的内部环境,其设计理念为绿色建筑设计提供了新思路。     

Thermal comfort evaluation with virtual manikin methods

Computational fluid dynamics has become an important tool in the prediction of thermal comfort in occupied spaces. Despite its ability to predict temperature and velocity fields, it is more difficult to evaluate the degree of thermal comfort experienced by an occupant. This article describes the construction of a new numerical thermal manikin, with new comfort evaluation methods based on data from thermal manikin measurements as well as subjective results from several hundred experiments. The level of thermal comfort is highly dependent on the local environment. Human beings respond differently to local heat transfer in different parts of their bodies. It is suggested for that reason that local results from manikins should be presented in new clothing independent comfort zone diagrams. The research presented in here is intended to be used to evaluate system solutions that provide improved thermal climate in many different everyday situations, e.g. all types of buildings and vehicles.     

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.     

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.     

厦门市大型公共建筑能耗统计分析

对厦门市大型公共建筑(单幢建筑面积大于1×104m2)的能耗进行了调查和统计,对不同年代不同类型公共建筑的能耗情况进行了分析。选取40幢典型公共建筑进行了能源审计,分析了不同类型公共建筑的能耗指标。对大型公共建筑的节能潜力进行了分析,估算了潜在的节能量。     

校园旧宿舍建筑节能改造分析——以重庆大学老宿舍楼为例

随着能源危机的情况日益加剧,低碳生活、环保节能等理念得到倡导.一些既有建筑或是老旧建筑的节能改造问题开始受到建筑设计师的关注.对既有建筑进行节能改造,避免能源的浪费,提高建筑热舒适度更是设计师的责任.在既有建筑改造研究的基础上,针对夏热冬冷地区的建筑节能改造问题提出综合性改造思想,以重庆大学B区1号学生公寓为实例进行节...     

某高校宿舍楼综合节能改造设计方案研究

当前能源危机的情况日益加剧,环保节能理念已成为全社会关注的焦点。高校既有建筑的节能改造问题开始受到建筑设计师的关注。对既有建筑进行节能改造,降低能源浪费,提高建筑热舒适度是一个具有重大实践意义的项目。在夏热冬冷地区,针对既有建筑物提出综合性节能改造技术方案,以某高校学生宿舍为实例进行节能改造分析,确定具体改造措施。     

Evolving opportunities for providing thermal comfort

The building industry needs a fundamental paradigm shift in its notion of comfort, to find low-energy ways of creating more thermally dynamic and non-uniform environments that bring inhabitants pleasure. Strategies for providing enriched thermal environments must be conjoined with reducing energy; these are inseparable for any building striving for high performance. The objective of current comfort standards is to have no more than 20% of occupants dissatisfied, yet buildings are not reaching even that scant goal. A significant energy cost is incurred by the current practice of controlling buildings within a narrow range of temperatures (often over-cooling in the summer). If building designers and operators can find efficient ways to allow building temperatures to float over a wider range, while affording occupants individual control of comfort, the potential for energy savings is enormous. Five new ways of thinking, or paradigm shifts, are presented for designing or operating buildings to provide enhanced thermal experiences. They are supported by examples of research conducted by the Center for the Built Environment, and include shifts from centralized to personal control, from still to breezy air movement, from thermal neutrality to delight, from active to passive design, and from system disengagement to improved feedback loops.     

严寒地区公共建筑光热环境贡献度研究

结合简单教学模型,利用Ecotect软件,针对建筑物理性能中的光、热性能进行仿真模拟分析。对于光环境分析,得出在进深较大的教学建筑中采取矩形天窗较有优势;通过设置不同窗墙比得到了与采光系数及达标面积之间关系。在窗墙比增加一定幅度基础上,通过达标面积率变化情况得到建筑采光得分变化。针对热环境,设置不同围护结构改造方案进行模拟,在以节能单方面考虑,改造外窗比改造外墙具有优势;但以节能为基础热舒适为目的,改造外墙比改造外窗具有优势。围护结构不仅影响节能,还会影响建筑室内环境,综合对比,得到相对最优围护结构方案。     

Passive designs and strategies for low-cost housing using simulation-based optimization and different thermal comfort criteria

An optimum design of low-cost housing offers low-income urban inhabitants great opportunities to obtain a shelter at an affordable price and acceptable indoor thermal conditions. In this paper, the design and operation of a low-cost dwelling were numerically optimized using a simulation-based approach. Three multi-objective cost functions including construction cost, thermal comfort performance and 50-year operating cost were applied for naturally ventilated and air-conditioned buildings. Thermal environment inside the house was controlled and assessed by two thermal comfort models. Optimization problems which consist of 18 design parameters and 6 ventilation strategies were examined by two population-based probabilistic optimization algorithms (particle swarm optimization and hybrid algorithm). Optimum designs corresponding to each objective function, differences in optimal solutions, energy saving by the adaptive comfort approach and optimization effectiveness were outlined. The optimization method used in this paper shows a considerable potential of comfort improvement, energy saving and operating cost reduction.     

基于关键技术集成的校园既有建筑节能改造研究

随着低碳循环经济和低能耗建筑设计理念的倡导,校园既有建筑的节能改造问题越来越受到建筑设计师的关注.在低能耗建筑及生态建筑的设计中,集成设计是一种重要的方法.对既有建筑进行节能改造,从实践角度对技术集成系统的既有建筑改造设计方法进行了探讨,来达到满足人们热舒适要求与降低建筑能耗之间的平衡,不仅为建筑师以及建筑节能的相关研究人员提供了设计参考和新的思路,同时也促进了绿色生态校园的发展.     

Comparison of thermal comfort algorithms in naturally ventilated office buildings

With the actual environmental issues of energy savings in buildings, there are more efforts to prevent any increase in energy use associated with installing air-conditioning systems. The actual standard of thermal comfort in buildings ISO 7730 is based on static model that is acceptable in air-conditioned buildings, but unreliable for the case of naturally ventilated buildings. The different field studies have shown that occupants of naturally ventilated buildings accept and prefer a significantly wider range of temperatures compared to occupants of air-conditioned buildings. The results of these field studies have contributed to develop the adaptive approach. Adaptive comfort algorithms have been integrated in EN15251 and ASHRAE standards to take into account the adaptive approach in naturally ventilated buildings. These adaptive algorithms seem to be more efficient for naturally ventilated buildings, but need to be assessed in field studies. This paper evaluates different algorithms from both static and adaptive approach in naturally ventilated buildings across a field survey that has been conducted in France in five naturally ventilated office buildings. The paper presents the methodology guidelines, and the thermal comfort algorithms considered. The results of application of different algorithms are provided with a comparative analysis to assess the applied algorithms.     

An experimental technique for thermal comfort comparison in a transient pull down

Various types of spaces are controlled for maintaining a desired comfort-condition level. Examples include buildings, automobiles, airplanes, and trains. The steady-state or longer-duration HVAC control is well established. However, situations are encountered where a rapid march towards a thermal space comfort level is required such as in the parked automobiles or in buildings where thermal mass is utilized for conserving energy. Many times design changes are proposed to improve the transient pull down in one zone but that could significantly affect the transient pull down in another zone. Further, in addition to the temperature, other parameters such as air velocity, mean radiant temperature, humidity need to be considered for assessing space comfort level. In our work we have developed an experimental technique for the multi-zone or comparative assessment of thermal comfort in a transient pull-down situations. First, the fan and system curves were developed for the competing designs. The predicted mean vote (PMV) methodology was employed for determining perceived comfort level. PMV is an ideal technique since it accounts for all of the above-mentioned parameters that are needed to assess space comfort level. Using an indoor climate analyzer, the transient PMV response at various locations was obtained. Conclusions are drawn to illustrate how this technique can be utilized for the simultaneous assessment of thermal comfort level in multiple zones, especially when transient pull downs are encountered.     

Adaptive temperature limits for air-conditioned museums in temperate climates

Indoor temperature (T) and relative humidity (RH) are important for collection preservation and thermal comfort in museums. In the 20th century, the notion evolved that T and RH need to be stringently controlled, often resulting in excessive energy consumption. However, recent studies have shown that controlled fluctuations are permissible, enabling improved energy efficiency. Consequently, the thermal comfort requirements are increasingly important to determine temperature limits, but knowledge is limited. Therefore, a thermal comfort survey study and indoor measurements were conducted at Hermitage Amsterdam museum in Amsterdam, the Netherlands for one year, including: (1) monitoring of existing conditions (T?=?21°C, RH?=?50%); and (2) an intervention in which T is controlled based on an adaptive comfort approach (T?=?19.5–24°C, RH?=?50%). The results show that the thermal comfort of the existing conditions is far from optimum; visitors feel too cool in summer and slightly too warm in winter. The adaptive temperature limits were developed to improve thermal comfort significantly without endangering the collection, thereby saving energy. Furthermore, facilitating visitors to adapt their clothing may contribute to enlarging the temperature bandwidth and improve (individual) thermal comfort.     

中国被动房外围护系统研究——以寒冷、严寒气候区被动房项目为例

德国的被动房是目前世界公认的具有超低能耗、超低碳排放量、超高室内舒适度等特点的建筑技术体系。德国的气候特征与中国华北地区的气候特征具有相似性,因此,研究并建造被动房对于我国建筑节能工作的发展具有重大的意义。外围护系统作为被动房设计的重点要素,对建筑的节能效率有重大的影响。以寒冷、严寒气候区的被动房项目为例,对被动房外围护系统进行分析与阐述,并以秦皇岛"在水一方"被动式住宅示范项目为例,进行能耗模拟与对比分析。提出适合我国寒冷、严寒气候区气候特点的被动式超低能耗建筑外围护系统的设计策略。     

The impact of zoning regulations on thermal comfort in non-conditioned housing in hot,humid climates: findings from Dhaka,Bangladesh

In parts of the developing world where densities are high but the availability of air conditioning is limited, building massing and height regulations can influence interior comfort levels. Dhaka, Bangladesh, is characterized by high population densities, a lack of open spaces, and high poverty levels, combining to produce living conditions which are not only uncomfortable, but may lead to the spread of disease. A recent change in zoning regulations provides an opportunity to assess the success of building heights and setbacks in improving indoor thermal comfort conditions. We assess the impact on thermal comfort within Dhaka’s non-conditioned apartment buildings of four zoning schemes which differ in their specifications for setbacks, maximum buildable area, and building heights; but that maintains the current density. Computer simulation techniques model the buildings to test solar, daylight, and ventilation inside the central building to calculate resultant indoor temperature, mean radiant temperature, relative humidity and air velocity. Comparison between these values helps to determine which zoning schemes produce the most favorable thermal conditions. Findings suggest that zoning schemes that provide better solar protection and better natural ventilation are able to reduce indoor temperature and increase indoor air velocity over that provided by current zoning regulations. Recommendations for revising current zoning regulations are given along with general recommendations for how buildings in hot, humid climates can maximize passive cooling, encouraging energy savings and environmental sustainability.     

计算机模拟在建筑节能设计中的应用

依据DBJ13—62—2004《福建省居住建筑节能设计标准实施细则》,从节能率、成本、建筑热舒适性、节能方案适宜性等方面对比分析了规定性指标节能设计法与动态权衡计算设计法的优劣。得出计算机仿真模拟技术在建筑节能设计中应用的重要性。