Development of a radiant heating and cooling model for building energy simulation software

Efficient radiant heating and cooling systems are promising technologies in slashing energy bills and improving occupant thermal comfort in buildings with low-energy demands such as houses and residential buildings. However, the thermal performance of radiant systems in buildings has not been fully understood and accounted for in currently available building energy simulation software. The challenging tasks to improve the applicability of radiant systems are the development of an accurate prediction model and its integration in the energy simulation software. This paper addresses the development of a semi-analytical model for radiant heating and cooling systems for integration in energy simulation software that use the one-dimensional numerical modeling to calculate the heat transfer within the building construction assemblies. The model combines the one-dimensional numerical model of the energy simulation software with a two-dimensional analytical model. The advantage of this model over the one-dimensional one is that it accurately predict the contact surface temperature of the circuit-tubing and the adjacent medium, required to compute the boiler/chiller power, and the minimum and maximum ceiling/floor temperatures, required for moisture condensation (ceiling cooling systems), thermal comfort (heating floor systems) and controls. The model predictions for slab-on-grade heating systems compared very well with the results from a full two-dimensional numerical model.     

Effect of external shading on household energy requirement for heating and cooling in Canada

Shading by neighbouring buildings and trees impacts the energy requirement of a building by reducing the amount of radiant energy absorbed and stored by its thermal mass. This study intends to quantify the magnitude of the effect of site shading on the energy requirement of residential buildings in Canada using a representative two-storey detached house. Site shading effects of neighbouring buildings and trees on annual heating and cooling energy requirements are evaluated using a building energy simulation program. The effects of the orientation, distance and size of the neighbouring object on heating and cooling energy requirement are investigated for four major cities (Halifax, Toronto, Calgary, Vancouver) representing the major climatic regions in Canada (Atlantic, Central, Prairies, Pacific). It is found that the annual heating and cooling energy requirement of a house in Canada may be affected by as much as 10% and 90%, respectively, by the existence as well as the orientation, size and distance of a neighbouring obstruction. Therefore, it is recommended that in building energy simulation studies, external shading should be given due consideration.     

我国供热节能中的问题和解决途径

分析了我国集中供热系统热利用效率低,运行能耗高的主要原因,并讨论了目前分户计量、按热量收费改革的问题。认为根据目前居住特点,这种热改方式不适合在我国推广。应采取按楼计量、楼内按面积分摊的方式。这可以激励围护结构的保温改造,并在技术上和经济上都可行。为了解决由于系统设计不当和调节不当导致局部过热造成的热损失问题,提出在楼的热入口采用换热或混水,在楼内实行“大流量、小温差、低水温”的供热方式,使每栋楼可在不同的入口水温下运行,以有效减少由于散热器面积不匹配、建筑内局部热源、系统流量不均等原因造成的局部过热现象,提高集中供热系统的热利用效率。     

Dynamic simulation of space heating systems with radiators controlled by TRVs in buildings

The objective of this paper is to develop a model for simulating the thermal and hydraulic behavior of space heating systems with radiators controlled by thermostat valves (TRVs) in multi-family buildings. This is done by treating the building and the heating system as a complete entity. Sub-models for rooms, radiators, TRVs, and the hydraulic network are derived. Then the suggested sub-models are combined to form an integrated model by considering interactions between them. The proposed model takes into account the heat transfer between neighboring rooms, the transport delay in the radiator, the self-adjusting function of the TRV, and the consumer's regulation behavior, as well as the hydraulic interactions between consumers.     

An algorithm for calculating convection coefficients for internal building surfaces for the case of mixed flow in rooms

The treatment of convective heat transfer at internal building surfaces has a significant impact on the simulation of heat and air flow. Accurate approaches for the range of flow regimes experienced within buildings (buoyant flow adjacent to walls, buoyant plumes rising from radiators, fan-driven flows, etc.) are required, as is the ability to select an appropriate method for the case at hand and to adapt modelling to changes in the flow.A new approach — drawing upon previously published methods — has been developed for modelling mixed convection within mechanically ventilated rooms. It is applicable for rooms ventilated with ceiling mounted diffusers and is appropriate for both heating and cooling. ESP-r simulations performed with the mixed flow model indicate that the prediction of heating and cooling loads is highly sensitive to the treatment of surface convection and that significant errors can result if an inappropriate model is employed. The results also reveal that the choice of convection algorithm can influence design decisions drawn from a simulation-based analysis.     

DALEC – a novel web tool for integrated day- and artificial light and energy calculation

DALEC is a novel, combined lighting and thermal simulation web tool. This tool allows building designers to evaluate their individual façade concepts in terms of thermal and visual performance and ultimately their impact on overall building energy use. Although easy to use, the software accounts for the complex thermal and light processes in buildings, by way of sophisticated and time-saving pre-calculations. Based on climatic data a calculation of heating, cooling and electric lighting loads can be obtained within a simulation time shorter than one second. The model has been validated by comparison with experimental data and other state-of-the-art software and shows deviations less than 15%. Not only energy demand is considered, but also user behaviour (e.g. glare protection), as well as visual and thermal comfort. This innovative, holistic approach facilitates and accelerates the design of sustainable and energy-efficient building for new, as well as for refurbished buildings.     

外墙保温对不同地区大型公共建筑冷热负荷的影响分析

随着我国建筑总量的增加,建筑能耗急剧上升,已成为我国的能耗黑洞,随之建筑节能逐渐被广大公民重视.目前建筑节能有很多措施,外墙保温就是其中一项.采用建筑热环境模拟工具DeST对同一大型公共建筑的冷热负行模拟计算,分析了在不同建筑气候分区下外墙的保温层厚度对空调负荷的影响,分析其有无节能效果,可为不同气候分区的大型公共建筑外墙隔热保温提供参考依据.     

降低建筑空调能耗研究

在分析贵阳市气候特点及实例建筑空调负荷特性的基础上,采用建筑环境模拟软件DeST对实例建筑室内基础室温以及全年建筑冷热负荷进行模拟,在分析模拟结果的基础上,结合贵阳市气候特点,提出如下三条贵阳市降低建筑空调能耗建议：1)舒适性空调设计应首先满足冬季采暖,然后考虑夏季制冷;2)自然通风是夏季降温的优先考虑方式,过渡季节调节是降低建筑制冷能耗的重要手段;3)增加围护结构保温和控制窗墙比是降低建筑采暖能耗的首要手段。研究结果不但能对贵阳市的建筑节能提供参考,而且还对广大温和地区建筑节能有参考意义。     

A rapid calibration procedure and case study for simplified simulation models of commonly used HVAC systems

A rapid procedure for calibrating simplified building energy simulation models of commonly used HVAC systems has been developed. The procedure developed will allow building professionals to project annual cooling and heating energy consumption of buildings with multiple HVAC systems from short-term field measurement data. This paper describes the general calibration procedure developed, and demonstrates the use of the calibration procedure by applying it to an office building. The calibration methodology requires as little as two weeks of measured hourly heating and cooling consumption data. In the example presented, the simulation model was calibrated using only two weeks of measured heating and cooling data. After calibrating the simulation using this procedure, the RMSE is reduced significantly. The simulation calibrated to two weeks of measured data is then used to simulate the hourly consumption of the building for the year 2004. Comparison of the results of this simulation with the measured data gave monthly CV(RMSE) values of 10.3% and 3.7% for cooling and heating, respectively, which are both well below the 15% values considered acceptable in ASHRAE Guideline 14 [1]. It also shows monthly NMBE values of 2.2% and 1.4% for cooling and heating respectively.     

Uncertainty propagation of material properties in energy simulation of existing residential buildings: The role of buildings features

Although energy simulation can provide valuable information about building energy behavior, the inaccuracy of input data can undermine the reliability of the results. Despite the vast literature about uncertainty analysis, little is known about the influence of building characteristics on the propagation of uncertainty through the energy simulation models. This study investigates the extent to which uncertain thermal conductivity and specific heat of structural layers affect the annual heating and cooling needs for a set of 144 simplified reference building configurations in three European climates. The analysis is carried out by means of a Monte Carlo technique coupled with TRNSYS hourly simulations. This study points out that the uninsulated residential buildings with a high aspect ratio, a small transparent surface with south exposure and low SHGC are more sensitive in the cooling needs estimation to the propagation of uncertainty in material properties. Similarly, the heating needs precision is greatly reduced when the uncertainty affects the thermal conductivity in uninsulated buildings with a low aspect ratio, a high SHGC and small window size. On the contrary, the uncertainty in specific heat is emphasized in buildings with external insulation having large windows oriented to either east or south and with glazing characterized by high SHGC.     

Naturally ventilated and mixed-mode buildings—Part I: Thermal modeling

Mixed-mode cooling strategies rely on several different means of delivering cooling to the occupied spaces of buildings. These different means, or modes, of cooling include different forms of natural ventilation through operable windows, ventilation assisted by low-power fans, and mechanical air conditioning. Control of mixed-mode cooling systems requires a thermal model tuned to accurately predict the dynamics of a specific building. This paper presents a flexible system-identification framework for linear thermal models that is well suited to accommodate the unique features of mixed-mode buildings. The effectiveness of this framework was demonstrated on a multi-zone, mixed-mode building, with model-prediction accuracy shown to exceed that published for other naturally ventilated or mixed-mode buildings, none of which exhibited the complexity of this building. A companion paper employs the thermal model in an efficient algorithm to optimize control strategies over extended planning horizons.     

建筑环境设计模拟分析软件DeST第5讲 影响建筑热过程的各种外界因素的取值方法

除供暖和空调系统的作用外，影响建筑物内热状况的外界因素主要是室外的气象条件、建筑周围的环境热状况以及室内发热量。在建筑热环境的动态模拟过程中，这些外界因素的数量大小和随时间的变化将对模拟结果产生较大的影响，因此各项因素的取值方法必须准确反映其数量大小和随时间的变化。讨论了这些外界因素的取值方法，详细介绍了DeST中对室外气象参数的取值方法。     

住宅建筑采暖空调能耗模拟方法的研究

住宅建筑的采暖空调能耗受室内居住人员行为方式的影响,在调查研究基础上,确定了两种反映室内居住人员行为方式的计算模式。在两种不同计算模式下,利用建筑热环境模拟工具DeST对上海地区同一住宅建筑能耗进行模拟,并将模拟结果与调研结果进行比较,分析计算模式对上海地区住宅建筑采暖空调能耗大小的影响,从而获得能正确反映上海地区住宅建筑采暖空调能耗大小的模拟计算方法。此方法可用于上海地区住宅建筑采暖空调的能耗分析与评价,并正确指导住宅建筑的节能设计。     

Selection of micro turbines to meet electrical and thermal energy needs of residential buildings in Iran

Micro gas turbines are considered to meet the electrical, domestic hot water, heating and cooling energy needs of a residential building located in Tehran, Ahvaz and Hamedan. The building is 10 stories high and has a total of 8000 m² floor area with the peak demands of electricity of 32.96 kW, DHW of 0.926 kW, heating load of 1590 kW and the cooling load of 2028 kW, when the building is located in Tehran. With these demands, 30 micro turbines of 30 kW (nominal power) are needed to meet all the energy needs of the building. The excess electricity generated by the micro turbines is to be used in a heat pump, and the energy in the exhaust gases is to be used to meet other thermal energy needs of the building. With proper energy conservation measures and the use of ceiling fans in each room, the peak heating and cooling demands of the building were reduced to 225 kW and 760 kW, respectively. With these measures, two micro gas turbines of 30 kW nominal capacity, or one of 40 kW, could meet all the electrical, DHW, heating and a great portion of the cooling needs of the building. The remaining cooling needs of the building during the hot hours of summer could be met by an additional absorption refrigeration, utilizing natural gas as its energy source. It is recommended that with energy conservation measures, the heating and cooling loads of buildings be reduced as much as possible, and micro gas turbines be employed to meet the electrical demands and a portion of heating and cooling needs. The remaining thermal energy needs are to be met through the use of natural gas. Only with these measures, the on-site combined heat and power (OS-CHP) is a viable option for residential buildings in Iran.     

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。     

Transient analysis of an external building cladding

Energy performances and building quality can be achieved by high performance envelopes. In this paper the thermal and mechanical performances of external cladding, applied to a traditional wall, largely used in existing buildings, were investigated by a transient simulation. Result comparison with the thermal performances obtained by simulating the wall without the insulation system showed that external insulation is particularly effective in reducing cooling and heating loads and can also guarantee indoor thermal comfort. Fatigue stresses of the external cladding, investigated by ANSYS simulation, showed that continuous change of the loads over time with limited cyclic stress can cause deterioration of materials.     

Analysis of annual heating and cooling energy requirements for office buildings in different climates in Turkey

A great amount of world energy demand is connected to the built environment. Electricity use in the commercial buildings, accounts for about one-third of the total energy consumption in Turkey and fully air-conditioned office buildings are important commercial electricity end-users since the mid-1990s. In the presented paper, the interactions between different conditions, control strategies and heating/cooling loads in office buildings in the four major climatic zones in Turkey – hot summer and cold winter, mild, hot summer and warm winter, hot and humid summer and warm winter – through building energy simulation program has been evaluated. The simulation results are compared with the values obtained from site measurements done in an office building located in Istanbul. The site-recorded data and simulation results are compared and analyzed. This verified model was used as a means to examine some energy conservation opportunities on annual cooling, heating and total building load at four major cities which were selected as a representative of the four climatic regions in Turkey. The effect of the parameters like the climatic conditions (location), insulation and thermal mass, aspect ratio, color of external surfaces, shading, window systems including window area and glazing system, ventilation rates and different outdoor air control strategies on annual building energy requirements is examined and the results are presented for each city.     

Virtual Building Dataset for energy and indoor thermal comfort benchmarking of office buildings in Greece

The knowledge of building stock energy data of a country is a very significant tool for energy benchmarks establishment, energy rating procedures and building classification boundaries determination, according to the Directive 2002/91/EC and its implementation in EU Member States. The lack of building energy databases in many EU Countries, including Greece, and the difficulties of collecting them lead to the investigation of other potential solutions. The aim of this paper is to present a method of a Virtual Building Dataset (VBD) creation for office buildings in Greece. The philosophy of VBD is based on the creation and simulation of random office buildings that could be found or built in Greece, taking into account the Greek constructional and operational characteristics of office buildings and Greek legislation. The VBD consists of 30,000 buildings (10,000 in each climatic zone) with their detailed constructional and operational data and of their simulation outputs: the annual specific energy consumption for heating, cooling, artificial lighting, office equipment and an indoor thermal comfort indicator. Based on VBD results the energy and indoor thermal comfort benchmarks for office building sector in Greece are assessed and presented.     

Numerical simulation and performance assessment of an absorption solar air-conditioning system coupled with an office building

To minimize environmental impact and CO₂ production associated with air-conditioning, it is reasonable to evaluate the prospects of a clean energy source. Solar energy, via thermal collectors can provide a part of the heating needs. Moreover, it can drive absorption chiller in order to satisfy the cooling needs of buildings. The objective of the work is to evaluate accurately the energy consumption of an air-conditioning system including a solar driven absorption chiller. The complete simulation environment includes the absorption chiller itself, the cooling tower, the solar collectors field, heater, storage devices, pumps, heating-cooling distribution, emission system and building. A decrease of primary energy consumption of 22% for heating and cooling is reached when using a solar air-conditioning system instead of classical heating and cooling devices. The modelling of each subsystem is detailed. TRNSYS software modular approach provides the possibility to model and simulate this complete system.     

Identification of key factors for uncertainty in the prediction of the thermal performance of an office building under climate change

There is growing concern about the potential impact of climate change on the thermal performance of buildings. Building simulation is well-suited to predict the behaviour of buildings in the future, and to quantify the risks for prime building functions like occupant productivity, occupant health, or energy use. However, on the time scales that are involved with climate change, different factors introduce uncertainties into the predictions: apart from uncertainties in the climate conditions forecast, factors like change of use, trends in electronic equipment and lighting, as well as building refurbishment / renovation and HVAC (heating, ventilation, and air conditioning) system upgrades need to be taken into account. This article presents the application of two-dimensional Monte Carlo analysis to an EnergyPlus model of an office building to identify the key factors for uncertainty in the prediction of overheating and energy use for the time horizons of 2020, 2050 and 2080. The office has mixed-mode ventilation and indirect evaporative cooling, and is studied using the UKCIP02 climate change scenarios. The results show that regarding the uncertainty in predicted heating energy, the dominant input factors are infiltration, lighting gain and equipment gain. For cooling energy and overheating the dominant factors for 2020 and 2050 are lighting gain and equipment gain, but with climate prediction becoming the one dominant factor for 2080. These factors will be the subject of further research by means of expert panel sessions, which will be used to gain a higher resolution of critical building simulation input.