Evaluation of a turbine driven CCHP system for large office buildings under different operating strategies

Combined cooling, heating, and power (CCHP) systems use waste heat from on-site electricity generation to meet the thermal demand of the facility. This paper models a CCHP system for a large office building and examines its primary energy consumption (PEC), operational costs, and carbon dioxide emissions (CDE) with respect to a reference building using conventional technologies. The prime mover used in this investigation is a load share turbine, and the CCHP system is evaluated under three different operation strategies: following the electric demand of the facility, following the thermal demand of the facility, and following a seasonal strategy. For the various strategies, the percentages of total carbon dioxide emissions by source are presented. This paper explores the use of carbon credits to show how the reduction in carbon dioxide emissions that is possible from the CCHP system could translate into economic benefits. In addition, the capital costs available for the CCHP system are determined using the simple payback period. Results indicate that for the evaluated office building located in Chicago the CCHP operation reduces the operational cost, PEC, and CDE from the reference building by an average of 2.6%, 12.1%, and 40.6%, respectively, for all the different operational strategies.     

典型办公楼负荷预测

对于冷热电三联供系统而言,为了使系统更好的发挥出优势,就要使系统和建筑的负荷较好的匹配,那么得到逐时的冷热电负荷数据就变得至关重要.参照日本三联供手册的方法,根据我国国情,以北京典型办公楼为例,采用模拟结合经验值的方法,得到适合中国办公楼的逐时负荷系数,以便为办公楼类建筑配置系统时提供参考依据.     

办公建筑中庭空调冷负荷简化计算

以北京地区某实际工程为例,在一定简化计算的前提下,基于工程中常用的冷负荷系数法,根据太阳能的入射能量分析热平衡,介绍了具有高大中庭的办公建筑的空调冷负荷计算简化方法。并与中庭实测温度梯度进行对比,得出可应用于工程中的高大中庭及周边办公环境的负荷计算方法。     

寒冷地区建筑负荷对围护结构热工参数的敏感性分析

为研究建筑围护结构属性对同一热工分区不同城市节能建筑负荷影响的敏感性,以同属于寒冷地区的兰州和郑州为研究目标所在城市,在节能65％的前提下将4种外墙、3种外窗和4种窗墙比进行组合得到了48个可能的办公建筑围护结构计算房间。分别计算了这些房间的冷负荷、热负荷和全年总负荷并分析了各热工参数对负荷的影响。通过与基准房间负荷对比,获得了具有不同热工性能的计算房间的节能率及最优的办公建筑围护结构。     

夏热冬冷地区办公建筑降低供暖空调能耗的技术路径

以上海地区某办公建筑为例,基于EnergyPlus能耗模拟,探讨了围护结构性能提升和暖通空调系统优化这2条节能技术路径对夏热冬冷地区办公建筑降低供暖空调全年能耗的有效性.结果 表明:围护结构性能提升的节能潜力较小,经济性较差;单纯提高围护结构保温隔热性能并不能保证降低建筑年耗冷量,应综合分析全年供热供冷能耗确定围护结构...     

Opportunities for reversible chillers in office buildings in Europe

Europe with more than 600 millions of square meters of air-conditioned office buildings offers an opportunity to save energy and reduce CO₂ emissions by reconverting chillers into reversible heat pumps in office buildings. One of the questions asked in the framework of the IEA ECBCS Annex 48 is how to assess the energy saving potential and how to identify the most interesting building cases. The methodology proposed here is based on the simulation of office buildings representative of the building stock. The energy consumption has been simulated for different office building types in five European climatic zones on the one hand with boilers for heating and chillers for cooling, and on the other hand with reversible chillers plus back-up boilers. The results of the simulations in terms of energy consumption allow us to assess the primary energy savings and CO₂ emission reduction in Europe by reconverting chillers into reversible heat pumps. The results show that the potential of annual primary energy savings and annual CO₂ emission reduction are about 8 TWh_PE and 3 millions of tons of CO₂ in Europe-15. Even if the temperature level in terminal units can be solved using the cooling coil instead of the heating coil, a back up boiler turns generally out to be required for the coldest days in the year or when simultaneous heating and cooling demands occur.     

不同类型玻璃在北京地区的节能研究

分别采用5种不同传热系数和遮阳系数的外窗玻璃,利用建筑能耗模拟软件eQUEST模拟北京地区某办公建筑的能耗,研究分析在北京地区玻璃的传热系数和遮阳系数对办公建筑逐月冷热负荷的影响;在全年能耗方面,6mm白玻+12mm空气+6mm白玻、6mm Low-E玻璃+12mm空气+6mm白玻、4mm超白玻+13.5mm气凝胶+4mm白玻、气凝胶玻璃(遮阳型)相对于12mm白玻的节能率分别为2％、11％、1％、13％,通过分析比较得出气凝胶玻璃这一新型建筑材料具有较好的节能效果.     

Internal convective heat transfer modeling: Critical review and discussion of experimentally derived correlations

Heat is transferred through building envelopes by conduction, radiation, and convection. Of these, convective heat transfer is often the weakest ‘link’ in the overall heat transfer model. While conduction and radiation heat transfer are supported by well-established analytical and numerical models, the treatment of convection is much less rigorous. Convection modeling involves solution of fluid dynamics problems in which the complexity of an enclosed space's geometry and the diversity of indoor airflow patterns require many fit-for-purpose convection correlations. These must take into account specifics of the space and of the heating ventilation and air-conditioning (HVAC) system. This paper provides an overview of the current knowledge on the modeling of convective heat transfer in load calculation and building energy simulation programs. The paper also discusses various issues related to the robustness of convection coefficient correlations, and reports on new experiments conducted to test the sensitivity of existing convection correlations. The discussed issues relate to: (1) the non-uniformity of the indoor temperature field; (2) the selection of a proper characteristic dimension; (3) the effect of adiabatic and non-adiabatic obstructions in the zone; and (4) the impact of airflow disturbance.     

广州地区办公建筑外围护结构的热工性能与节能分析

办公建筑的空调能耗是围护结构的温差传热、室内热扰、太阳辐射等因素动态综合作用的复杂结果。本文采用DeST软件对广州地区某办公建筑围护结构的各项节能措施的节能效果进行分析,结果表明:降低外窗的遮阳系数、外墙和屋顶的传热系数对减少建筑全年空调能耗和最大空调冷负荷是有利的,但降低窗的传热系数对减少建筑全年空调能耗和最大空调冷负荷不利。建议在办公建筑节能设计过程中,模拟计算全年能耗,确定能耗低且技术经济合理的方案,尤其要慎重考虑是否采用低传热系数的窗。     

Efficiently produced heat and cold is squandered by inappropriate control strategies: A case study

The large thermal time constant of thermally activated building systems (TABS) hampers communication between the system's production and emission. Therefore, conventional building control strategies, typically using room temperature feedback, are unadapted to control thermal comfort efficiently. In this paper, measurement data and simulation results reveal that unadapted TABS control has a dramatic impact on overall energy performance. Measurements in a TABS building with room temperature feedback show the HVAC system switching between heating and cooling in a very short time frame. A simplified, generic room model is used to simulate, understand and evaluate this behaviour. For room temperature feedback control, only 45% of the cold and 15% of the heat produced actually controls room temperature. The remainder is stored in the TABS and exchanged between the heating and cooling system. Enlarging the heating-to-cooling set point band improves this ratio, while maintaining thermal comfort. On the other hand, night time operation control of the circulation pump, adapted to the TABS thermal time constant, eliminates this ‘unused’ energy completely. In this case, however, even with perfect heat gain forecasts, it is difficult to avoid room temperatures dropping below thermal comfort limits during initial office hours. Hence, a supplementary air-conditioning system seems inevitable.     

基于逐时太阳辐射强度与动态逐时负荷分析的太阳能空调系统设计要点研究——以天津市某办公楼项目为例

建筑的地理气候特征影响太阳能在建筑中的收集与利用。以天津市某办公楼项目为例,基于日照遮挡模拟分析确定集热器布置区域,并根据逐时动态冷负荷与热负荷综合情况确定集热器面积,以动态逐时负荷与供热(冷)量匹配的方法辅助备用能源设计,降低了系统的造价,提高了太阳能的利用率和建筑供能系统的稳定性,为后续其他项目太阳能空调系统的设计提供了借鉴。     

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。     

Application range of thermally activated building systems tabs

This paper presents application range and functionality of thermally activated building systems (tabs). Tabs are increasingly used for energy efficient and economical cooling and heating of commercial buildings. Thereby, the building structure is used as thermal storage allowing the use of renewable energy sources. Based on a simulation study for a typical office building the aspects of thermal comfort, maximum permissible heat gains in the room and the re-cooling of the building mass are analysed. It is shown that depending on the maximum permissible daily room temperature amplitude with tabs typical heat gain profiles with peak loads up to around 50 W/m² floor area can be managed. However, the transitional (mid-season) periods with already high solar gains and still restricted comfort range, in most cases will be decisive for the dimensioning of tabs, thus limiting maximum loads to lower values. The results also show that processes on the room side are almost unaffected from the processes on the supply side. In the cooling case, this allows for the re-cooling period of the fabric being extended to 24 h a day with accordingly “high” supply temperatures and peak load reductions of up to 50%. The results given may serve as orientation guide whether a tabs may be applicable in a specific building, and provides relevant parameters for the dimensioning of tabs.     

Reducing peak requirements for cooling by using thermally activated building systems

This paper presents general guidelines for the required cooling capacity of an entire office building using thermally activated building systems (TABS). By activating the thermal mass of the building using pipes embedded in the floor, peak loads can be reduced. On-site measurements were performed to obtain the required cooling power of an entire building as well as individual zones. Beside this, the internal climate conditions of rooms and surface temperatures of the TABS were measured. The measured data were used to analyze the predictive performance of a simulation model. In order to acquire general guidelines for the required cooling capacity of a standard office building, simulations of an entire building were used to determine the impact of variable internal heat gains and different sized windows. The required cooling capacity was compared to the cooling capacity of a system without energy buffering (e.g. chilled ceiling panels). It was found that reductions up to 50% of the cooling capacity for a chiller can be achieved using TABS. The presented results within this paper can be used as design guidelines in the first stage of a design process. The results focus on temperate climates and were derived using Dutch climate conditions.     

冰蓄冷辐射供冷系统的综合评价

日本办公建筑的空调耗电占其总耗电的50％以上，尤其在夏季是加剧电力需求高峰的主要因素。为了平衡负荷，电力生产部门和政府都在致力提倡蓄热空调系统。介绍了东京一座典型办公楼的与冰蓄冷系统结合的辐射供冷系统，包括其均衡负荷的作用，节能的潜力，施工及运行费用的估算等。     

夏热冬冷地区窗墙比对办公建筑能耗的影响

本文根据南京地区典型年逐时气象参数,基于建筑墙体动态传热反应系数法,利用MATLAB编程分析了建筑围护结构动态热负荷变化,研究了在南北朝向和不同外窗类型的条件下,窗墙比为0.2～0.7对全年建筑供暖、空调能耗及全年总耗电量的影响规律.结果表明,北向窗墙比的增加会导致全年供暖、空调总能耗加大;对于PVC塑料中空窗,随南向窗墙比的增大,全年总耗电量的增加量较小,建议在夏热冬冷的南京地区使用.     

An investigation of design parameters that affect commercial high-rise office building energy consumption and demand

There are many factors that drive the energy consumption and demand in high-rise commercial office buildings. Understanding the effects of individual building parameters and two-factor interactions can be very useful for directing building audits and developing energy simulation models. A fractional factorial analysis was conducted to evaluate a large number of building parameters in an effort to quantify their effect on building energy consumption and demand. The analysis utilized building data collected from 22 building audits of high-rise commercial office buildings located in the downtown Chicago Loop area. Simulation results for three of the buildings show the effects of each factor and two-factor interactions on energy consumption and demand over a set of climate zones. The factors of primary importance include lighting and equipment power density, chiller efficiency, window U-value, the mass of interior furnishings and supply fan static pressure.     

商务办公建筑能耗调研及分析

对山东某地区商务办公建筑进行了调研。应用抽样调查的方法,对该地区37个样本量的能耗进行统计处理,得出了该地区单位面积建筑能耗为72.14 k W·h/(m~2·a),单位面积供暖能耗为14.74 kgce/(m~2·a)。研究结果表明,山东某地区的商务办公建筑在用能方面还存在一些问题,建筑节能潜力较大。这对于科学确定商务办公建筑的能耗指标,进而实施用能超定额加价政策具有一定的参考价值。     

办公建筑内部负荷扰量特性与计算方法

随着建筑围护结构保温性能的逐步提高,以室内人员为代表的内部因素已成为影响建筑负荷的重要不确定性因素,内部负荷扰量(简称内扰)在空调负荷设计中的重要性需要被强调。通过对两栋办公建筑的实地测试发现,办公建筑中人员在室率普遍只有设计人数的40%～60%,设备的实际功率也远低于20 W/m~2的概算指标,过大的经验值是造成机组选型偏大的重要原因。重新思考标准中的人员密度系数和设备使用密度系数,以人为核心将建筑内扰负荷结合起来,提出"代表人"的内扰负荷计算方法,并对案例建筑的负荷设计进行修正。相比最大实测冷负荷,修正后的设计冷负荷富余率均在10%以内。     

夏热冬暖气候区医院门诊楼能耗评价指标研究

医院建筑能耗逐年升高,其中空调能耗占总能耗比例较大。在医院建筑的节能改造或能耗状况分析中,多数以单位建筑面积、门诊人数、床位数的能耗来评价医院能耗的高低。以夏热冬暖气候区医院门诊楼为研究对象,通过理论分析建立建筑负荷分析模型,设计建筑负荷正交模拟实验,利用模拟软件De ST进行负荷模拟,研究建筑面积、床位数、门诊量/床位数、医院类型对建筑全年总负荷的影响,模拟结果表明:建筑面积(床位数)越大,门诊量/床位数越大,未开展预约门诊的医院的年总负荷越大,反之越小。建筑年总负荷影响因素的主次顺序为门诊量/床位数建筑面积(床位数)医院类型,其中门诊量/床位数、建筑面积(床位数)对年总负荷影响显著(P0.05);医院类型对年总负荷影响不显著(P0.05)。建议采用人均单位面积能耗占用床位数指标来评价门诊楼的能耗,更加科学。