Assessment of natural and hybrid ventilation models in whole-building energy simulations

Natural ventilation is a traditional cost-effective technique to cool and ventilate buildings. Proper simulation tools are highly desired to ensure acceptable thermal performance of naturally ventilated buildings and to assist the design and optimization of such buildings. This study is to advance the use of natural and hybrid ventilation concepts in building design by assessing the accuracy and usability of current thermal-ventilation models. Because of the similarity noted among various models and tools, a prevalent airflow-thermal modeling program, EnergyPlus, was evaluated by simulating three selected real buildings that were supplied with most detailed building and measurement information. The study of these cases reveals that the current model has (1) significant functional limitations for venting and exhaust fan control schemes; (2) need for additional relationships to describe horizontal openings and fully-open connections between zones; and (3) possible over-prediction of buoyancy-driven flows in the case of multi-story buildings. The study further indicates the building and measurement data that are critical for a more accurate validation of thermal-ventilation models, including, on-site measured temperature, wind, and solar conditions; measured volume flow rate data, at critical points throughout the building; and effective area and discharge coefficients for specific vents used in building.     

中美节能标准中办公基准建筑的能耗比较

对比了中美两国节能标准,以上海地区某办公楼为例,分别建立了在中美公共建筑节能标准下的基准建筑模型,按照ASHRAE 90.1对能耗模拟的要求进行计算,得到该办公楼的空调系统能耗和总能耗.结果表明,我国标准在围护结构、机组效率方面的要求均低于ASHRAE 90.1标准,但是由于美国的空调系统因控制湿度而导致再热量增加,所以根据我国标准和ASHRAE 90.1计算出来的办公建筑的平均能耗强度基本一致.建议我国标准适当减小围护结构的传热系数,提高机组的性能,以利于节能；并且,应详细规定能耗模拟原则,以减少能耗模拟结果的人为因素.     

Investigation on energy performance and energy payback period of application of balcony for residential apartment in Hong Kong

The provision of balcony to the living room of a residential flat offers a number of merits including improved view enjoyment, enhanced ventilation and increased planting space. In addition, a balcony can act as an overhang and provide solar shading as well as electricity saving of the air-conditioning system. This paper reports the findings on the energy and environmental impact due to the provision of a balcony. In this study, a typical residential flat with balcony constructed at the living room was modeled and the energy performance was investigated with the use of the typical weather data set of a subtropical city, Hong Kong. The effects of balcony's orientation and glazing material of window were also evaluated. It was found that the residential flats facing various orientations (N, E, S, W, NE, SE, SW and NW) can offer substantial energy saving in air-conditioning system due to the shading effect of balcony. The building case with southwest facing balcony and clear glass glazed window gave the highest saving percentage of 12.3% in annual air-conditioning consumption. In terms of cost payback period, the values were estimated as 25.9 years (based on extra construction cost of a balcony) and over 100 years (based on extra purchasing cost), respectively. On the other hand, the energy payback period was 22.4 years for this building case. The provision of balcony to the living room of residential flat was found environmentally feasible in Hong Kong.     

广州市某高校图书馆能耗模拟与节能性研究

以广州市某高校图书馆为研究对象,根据建筑空间、功能布局、空调系统分布,建立图书馆的SU模型,利用能耗模拟软件Energy Plus,并针对模型进行全年能耗模拟仿真,并对模拟结果进行分析。采用改善建筑外墙、外窗隔热性能及添加遮阳设施3种不同的节能方案,分别对其进行理论节能性分析,并计算得到理论节能效率。     

Estimation of heat rejection based on the air conditioner use time and its mitigation from buildings in Taipei City

The main work in the research focuses on the analysis and mitigation of the anthropogenic heat discharged from buildings, which is one of the main reasons leading to the heat island effect. The residential and commercial buildings, divided into 10 categories, with HVAC systems were analyzed by the building energy program, EnergyPlus. With the help of GIS, the heat rejection of all the residential and commercial buildings in DaAn Ward of Taipei City were evaluated, in which the spatial data and diurnal variation of the heat rejection were described by 3-h time periods. Furthermore, the effect of mitigation strategies was discussed. The first strategy was to change the wall/roof material of building envelope. The second and third strategies, from the viewpoint of energy saving, were to change the temperature setting of air conditioners and to turn off the lighting and equipment when not in use. The fourth strategy was to use a better efficiency of the cooling systems. Finally, the evaluation of installing the water-cooled cooling system, which discharges heat in the form of sensible and latent heat, was also included.     

Urban and building multiscale co-simulation: case study implementations on two university campuses

The co-simulation of both urban and building-level models leverages the advantages of both platforms. It better accounts for the localized effects of surrounding buildings, geography and climate conditions while maintaining high-fidelity building systems representation. This paper describes the co-simulation process of the building and urban-scale models of two university campuses in Switzerland using EnergyPlus and CitySim. In the first case study, on-site measured performance data is compared to the co-simulation results. The second case study examines the results of the two engines. The results show that coupling of EnergyPlus with CitySim resulted in a ?15.5% and ?7.5% impact on cooling consumption and a +6.5% and +4.8% impact on heating use as compared to solo simulations.The co-simulation process was able to better model realistic conditions for heating, but not cooling in one case study. It was able to substantially reduce the discrepancies in prediction between the engines in the other study.     

Comparing computer run time of building simulation programs

This paper presents an approach for comparing the computer run time of building simulation programs. The computing run time of a simulation program depends on several key factors, including the calculation algorithm and modeling capabilities of the program, the run period, the simulation time step, the complexity of the energy models, the run control settings, and the software and hardware configurations of the computer used to run the simulation. To demonstrate this approach, we ran simulations for several representative DOE-2.1E and EnergyPlus energy models. We then compared and analyzed the computer run times of these energy models.     

基于EnergyPlus的地板辐射与置换通风空调系统模拟分析

辐射供冷与置换通风复合系统不仅能提供较高的热舒适性,并且具有很大的节能潜力,本文建立了复合系统的能耗分析模型,并采用EnergyPlus能耗分析软件对该复合系统进行能耗模拟,模拟得到的室内温度和辐射地板所承担冷量与实验结果的误差小于±7%,在此基础上,改变置换通风的送风温度,得到辐射地板提供冷量随置换通风送风温度提高而增加的变化规律,置换通风送风每增加1℃,辐射地板提供的冷量增加1.9%左右。     

Development and performance evaluation of a methodology,based on distributed computing,for speeding EnergyPlus simulation

This article presents an approach for speeding EnergyPlus simulations. The computing run time of an energy simulation depends on several variables and is directly proportional to the simulation RunPeriod. In the proposed approach, data parallelization is achieved by breaking an annual simulation into several segments of smaller RunPeriod, each handled by a separate computer/processor. The speed gain achieved by running 12 one-month RunPeriod segments in parallel as compared to single simulation of 12 months is between three and six times. Segmentation of simulation has resulted in minor deviations between the results obtained through segmented simulations and annual simulations. Methods for reducing these deviations on annual and monthly basis are presented in this article using 12 benchmark models each simulated for five cities. On annual basis, a maximum deviation of 0.06% was observed in cooling, heating, and lighting consumption. In a month-to-month comparison between the segments and annual simulation, the maximum deviation was 1.7% for heating and 0.8% for cooling.     

Implementation of a building foundation heat transfer model in EnergyPlus

In this article, a two-dimensional transient ground-coupled numerical model for slab-on-grade foundation is developed and integrated into EnergyPlus. A verification analysis is first presented to ensure that the developed building foundation heat transfer module is properly implemented within EnergyPlus. Then, predictions from the developed model are compared with those obtained from a simplified building foundation model currently used in EnergyPlus. Finally, the impact of several foundation insulation configurations on the annual variation of both heating and cooling loads is investigated for a one-storey single-family ranch house. The results show that the developed foundation heat transfer module accounts more accurately for the effects of the ground thermal mass than the foundation model currently used in EnergyPlus. In particular, it was found that annual heating and cooling loads can be overestimated by over 20% for a typical residential building if ground-coupled heat transfer calculations are not fully integrated in EnergyPlus.