An approach to evaluate the energy performance of buildings based on incomplete monthly data

The energy performance of buildings has become increasingly important in the general strive to reduce the overall energy use, which is manifested in the Energy Performance of Buildings Directive launched by the European Union. An important first step is of course to identify and address buildings that have an energy saving potential. In order to achieve this, robust methods for evaluation as well as reliable energy key figures are needed.     

空气源热泵结霜除霜损失系数的计算

在总结和分析空气源热泵结霜特性及其对热泵性能影响的研究成果的基础上,提出了结霜量指标和相对结霜量概念。统计分析了我国空气源热泵适用地区的气候特点,得出了相应地区不同使用情况下的平均结霜除霜损失系数,推荐作为设计参考依据。     

西藏节能建筑围护结构传热系数朝向修正

针对现行供暖居住建筑节能设计标准应用于西藏地区存在有供暖能耗指标却没有完整的能耗计算基本参数,即没有围护结构传热系数的朝向修正系数的问题,以拉萨典型气象年气候参数为依据,采用反应系数法对围护结构各部分供暖负荷进行了动态模拟计算,得到了围护结构各朝向修正系数,对南窗传热系数提出了变系数修正方法。     

The application of heat pipe heat exchangers to improve the air quality and reduce the energy consumption of the air conditioning system in a hospital ward—A full year model simulation

Research was conducted to study the effect of heat pipe heat exchangers on the existing air conditioning system of a hospital ward located in Malaysia, a tropical region. The present research employs the transient system simulation software (TRNSYS) to study the hour-by-hour performance of the system in terms of supply duct air and indoor air conditions in the ward space. Fieldwork study showed that the existing air conditioning system operating in the Orthopaedic Ward, University of Malaya, Malaysia is not capable of providing the desired supply duct air and indoor air to the space. Therefore, the possibility of improving the air conditioning system by adding heat pipe heat exchangers was investigated. The impact on energy consumption, power savings, supply duct air and indoor air with heat pipe heat exchangers incorporated in the air conditioning system were simulated and the results were compared with the existing system.Based on the present research, the system with the added eight-row heat pipe heat exchangers is recommended to provide convenient and healthy air into the ward space according to the ASHRAE recommendations. Moreover, it was found that by applying the new design, a considerable amount of energy and power could be saved.     

Determination of the combined heat transfer coefficient to simulate the fire-induced damage of a concrete tunnel lining under a severe fire condition

To avoid underestimating the severity of damage to tunnel concrete lining under the high-temperature conditions of a fire using thermal analysis, it is important to consider the cross-sectional loss of a concrete lining during heating. This study simulates the structural loss by numerical analysis using an element elimination model and a combined heat transfer coefficient. A series of fire tests was performed with fire curves that differed in the initial temperature gradient and maximum temperature. Values of the optimized combined heat transfer coefficient were obtained from the coincidence of the results of the numerical analysis with experimental data. The results reveal that an increase in both the initial temperature gradient and maximum temperature causes greater damage to the concrete structures and also gives rise to an increase in the combined heat transfer coefficient. Values of the combined heat transfer coefficient can be inferred from values of initial temperature gradient and maximum temperature in the case of structural concrete loss. Two sets of regression equations were derived from the results depending on whether or not a structural loss occurs. The proposed method of thermal analysis outperforms the conventional method in terms of accurately simulating observed results.     

Experimental and numerical determination of the total solar energy transmittance of glazing with venetian blind shading

In response to the increased occurrence of overheating problems in glazed buildings in recent years, EMPA has focussed on the determination and modelling of the total solar energy transmittance (TSET) of multiple glazing combined with different shading systems. Measurements were performed in a calorimetric outdoor test facility near Zurich, Switzerland. In the first phase, average TSET-values related to the incident global solar radiation were identified for various Venetian blind configurations with a measurement period of a few days each. As expected the results strongly depend on the slat tilt angle as well as on the solar reflectance of the slat surface. The influence of the directional distribution of the incident radiation is demonstrated by comparison of results from different measuring periods with the identical shading–glazing configuration. An extended identification model accounting for the angle-selective transmittance is presented. The experimental results are also compared with weighted g-values from numerical modelling, which are based on a view factor method extended for curved slats in a louver type shading device. In general, the agreement between the measured and calculated results is satisfactory. Some deviation is explained by a significant non-diffuse albedo component in the hemispherical radiation field.     

Evaluation of the ground-coupled quasi-stationary heat transfer in buildings by means of an accurate and computationally efficient numerical approach and comparison with the ISO 13370 procedure

The purpose of this article is to present and validate a computationally efficient numerical approach for the calculation of the ground-coupled heat transfer in buildings with periodic boundary conditions. When the boundary conditions of the heat transfer problem are described by periodic functions, it is possible to consider the transient state problem as a quasi-stationary problem with considerable savings in terms of computational time. The method is presented in detail from a mathematical point of view, together with a validation for two simple cases of slab-on-grade thermal losses, four comparisons with the ISO 13370:2007 procedure, a case with a complex shape and an evaluation of the computational efficiency.     

Evaluating the effect of building construction periods on household dampness/mold and childhood diseases corresponding to different energy efficiency design requirements

Despite concerns about building dampness and children’ health, few studies have examined the effects of building energy efficiency standards. This study explored the connections between self-reported household dampness and children’ adverse health outcomes across buildings corresponding to construction periods (pre-2001, 2001-2010, post-2010). Significant differences of dampness-related indicators were found between buildings; the prevalence was remarkable in pre-2001 buildings. The prevalence of lifetime-ever doctor-diagnosed diseases for children was significantly associated with building dampness (adjust odd ratios > 1), but was not affected by construction periods. The hygrothermal performance for a typical residence was simulated, varying in U-values of envelopes and air change rates. The simulated performance improvement increased indoor temperatures in 2001-2010 and post-2010 buildings. The frequency with higher indoor relative humidity was higher in pre-2001 buildings, leading to the highest values for maximum mold index (M_max) on wall surface, especially in winter. Compared to buildings in 2001-2010, increased insulation and lower air change rate led to a relatively higher relative humidity in post-2010 buildings, adversely increasing the M_max values. The findings addressed the positive and negative role of building standard development, which help suggesting appropriate environmental and design solutions to trade-off energy savings and dampness/mold risk in residences.     

Measured effect of airflow and refrigerant charge on the seasonal performance of an air-source heat pump using R-410A

The objective of this study was to measure the effects of improper airflow and refrigerant charge on the seasonal performance of a typical 10.6 kW, R-410A residential heat pump with a thermostatic expansion valve.Heating and cooling tests were performed in combinations of three refrigerant charges of 75%, 100%, and 125% of nominal value and two airflows of 75% and 100% of rated airflow. In addition, cyclic tests were performed to estimate the heating and cooling seasonal coefficient of performance (COP) at six climate zones specified by Air-Conditioning, Heating, and Refrigeration Institute (AHRI) Standard 210/240-2008. Results showed that, in each climate zone, increases in refrigerant charge at the rated airflow could improve the unit's heating seasonal COP by as much as 5%. However, combined decreases in airflow and refrigerant charge could penalize the unit's heating seasonal COP by as much as 10%.