Measurement and analysis of airtightness safeguard measures for typical ultra-low energy buildings

Zero-energy buildings constitute an effective means of reducing urban carbon emissions.High airtightness,a typical characteristic of zero-energy building,is closely related to the building’s air infiltration and has a signifi-cant impact on the performance of the building envelope,indoor air quality,building energy consumption,and efficient operation of air-conditioning systems.However,thus far,systematic developments in high-airtightness assurance technologies remain scarce.Most existing studies have tested the airtightness of buildings and typical building components;however,in-depth analyses into the formation of infiltration have not been reported.There-fore,for realizing zero-energy buildings,ensuring airtightness is an urgent problem that needs to be addressed.Accordingly,in this study,based on several building airtightness measurement studies,the typical air leakage paths in buildings were summarized,and the causes of typical air leakage components in buildings were further analysed by tracing construction processes.Moreover,targeted measures for airtightness in buildings were estab-lished and applied to practical cases.Lastly,the resulting improved building airtightness was measured and the results show that the airtightness of the measured ultra-low energy consumption buildings ranges from 0.13 h^(−1)to 0.57 h^(−1),with a mean value of 0.32 h^(−1).The effectiveness of the airtightness safeguard measures was verified.This study serves as a basis for the assumption of the air leakage path distribution when simulating building air infiltration and also provides a design reference for improving the construction technologies and airtightness of buildings.

Prediction model of air infiltration in single-zone buildings with high airtightness

Air infiltration through building envelopes has a considerable impact on the comprehensive performance of build-ings,especially in terms of their energy demand and indoor air quality.Therefore,it is important to accurately predict building air infiltration rates under various scenarios.High airtightness is one of the typical character-istics of passive ultra-low energy buildings.With the rapid application of passive technology in building energy efficiency,the airtightness of new urban buildings has been significantly improved.The centralized air leakage path distribution assumption of current prediction model for building air infiltration rate is inconsistent with the actual situation of high airtightness buildings,which reduces its prediction accuracy and application range.Therefore,it is of great practical significance and academic value to carry out the research on the prediction model of air infiltration rate of buildings with high airtightness.This paper presents an air infiltration prediction model for single-zone buildings with adventitious openings.The building envelope was broken down into permeable parts and impermeable parts,and the air leakage path-ways were assumed to be uniformly and continuously distributed in the permeable envelope.A linear pressure distribution over the building facade was assumed,and the airflow rate was integrated in the vertical and hori-zontal planes to theoretically predict the air infiltration rate.The feasibility of the proposed model was tested by comparing the air infiltration rates simulated by this model with those determined using the tracer gas attenua-tion method of an airtight building.The initial test results suggest that this model is mathematically robust and is capable of modeling the air infiltration of a building in a wide variety of scenarios.Reasonable agreement was found between the tested and simulated results.This study can provide basic theoretical support for the coupling performance analysis of high airtightness buildings.

Performance Assessment of the Overall Building Envelope Thermal Performance-Building Envelope Performance(BEP)Metric

Today,to describe the thermal performance of the building envelope and its components we use a variation of metrics;such as,R-value,ACH(air exchange rate per hour),SHGC(solar heat gain coefficient)of windows,U-factor etc.None of these performance indicators is meant to represent the overall thermal performance.In this paper,such a metric is introduced,the BEP(building envelope performance)value.Unlike the thermal resistance,typically expressed as an R-value,the BEP-value considers additional elements of heat transfer that affect the energy demand of the building because of exterior and interior(solar)thermal loads:conductive and radiant heat transfer,and air infiltration.To demonstrate BEP’s utility,validation studies were carried out by comparing the BEP-value to theoretical results using whole building energy simulation tools such as EnergyPlus and WUFI Plus.Results show that BEP calculations are comparable to calculations made using these simulation tools and that unlike other similar metrics,the BEP-value accounts for all heat transfer mechanisms that are relevant for the overall energy performance of the building envelope.The BEP-value thus allows comparing envelopes of buildings with different use types in a fair and realistic manner.

Effectiveness of Hermetic Storage Using PICS Bags and Plastic Jars for Post-Harvest Preservation of <i>Acacia macrostachya</i>Seeds

In Burkina Faso, the availability of Acacia macrostachya “Zamnè” seeds throughout the year is threatened by the attacks of pests. So, the effectiveness of airtight (hermetic) storage for the preservation of these seeds was evaluated using 20-litre plastic jars and 50 kg PICS bags as hermetic containers with 50 kg polypropylene bags as controls. Seeds of Acacia macrostachya (17.5 kg) were stored in each of these storage devices for six months under ambient conditions in the laboratory. The number of storage pest Bruchidius silaceus increased significantly in polypropylene bags from 235 to 715 individuals on average/500 g of seeds. But in PICS bags and plastic drums, the number of this pest did not vary significantly (191 and 239 individuals on average/500 g of seeds for plastic jars and PICS bags respectively). In both hermetic devices, we found few individuals of another major storage pest Caryedon furcatus. However, polypropylene bags, haboured more pests’ in addition high numbers of C. furcatus and Oryzaephilus mercator which were not found in the hermetic devices. Seeds damage and weight loss increased significantly in polypropylene bags from 7.40% to 20.23% and 0.50% to 3% respectively compared to PICS bags and plastic jars. The germination rate of A. macrostachya seeds decreased significantly in PICS bags, plastic jars and polypropylene bags with average percentages of 14%;11% and 15% respectively compared to the initial average of 27%. PICS bags and plastic jars are therefore effective in preserving the quality of A. macrostachya seeds, but the effects of these hermetic devices on seed viability need to be explored further.

Study on the conversion coefficient between ACH_(50)and ACH in typical zones of public buildings

The air infiltration of buildings is closely related to its indoor and outdoor environment and energy consumption.However,measuring air infiltration of a building under natural conditions is time-consuming,easily affected and expensive,so it’s often inferred based on building airtightness in practical engineering.Empirical models can nevertheless make a rapid prediction without building parameters,which are widely applied in practical engineering.At present,most of the existing empirical models take residential buildings as objects,therefore they are difficult to be applied to public buildings.Hence,it is imperative to build an empirical model applicable to public buildings.In this study,the conversion coefficients between the airtightness(air change rate under the pressure difference of 50Pa)and the air infiltration rates under natural conditions of four typical zones of public buildings were analyzed.Firstly,the airtightness of four zones of public buildings in the cold region of China was measured.Secondly,their air infiltration rates under 1800 combined conditions of wind pressure and stack effect pressure were simulated based on the airtightness measured results.Finally,calculation and statistical analysis of the conversion coefficient were carried out based on the measured and simulated results,and the recommended value of conversion coefficient was proposed.Analysis results show that the CC of each zone is significantly affected by outdoor meteorological conditions and varies in a wide range(1#zone:3.21 to 188.44).It is advised to ignore the extreme data and take the mean value of the CC corresponding to 95%of the data volume as the recommended value(22.2).This study can provide theoretical basis for the formulation of standards for the performance evaluation of building airtightness.

Impact of weather conditions and building design on contaminant infiltration from crawl spaces in Swedish schools-Numerical modeling using Monte Carlo method

Some Swedish school buildings built in the 1960s and 1970s experience indoor air quality problems,where the contaminants are suspected to come from the crawl space underneath the building.The poor indoor air quality causes discomfort among pupils and teachers.Installing an exhaust fan to maintain a negative pressure difference in the crawl space relative to indoors or increasing the ventilation in the classroom are two examples of common measures taken to improve the indoor air quality.However,these measures are not always effective,and sometimes the school building has to be demolished.The relation between pressure distribution,contaminant concentration in the classroom,outdoor temperature,wind,mechanical ventilation,and air leakage distribution is complex.A better understanding of these relations is crucial for making decisions on the most efficient measure to improve the indoor air quality.In this paper,a model for contaminant infiltration from the crawl space is used together with the Monte Carlo method to study these relations.Simulations are performed for several cases where different building shapes,building orientations,shielding conditions,and geographical locations are simulated.Results show,for example,that for a building with an imbalanced ventilation system,air is leaking from the crawl space to the classroom for the majority of cases and that concentration levels in the classroom are usually the highest during mild and calm days.

Research and development of airtight biosafety containment facility for stainless steel structures

Objective:Airtightness of containment structures of a high-level biosafety laboratory is a critical parameter for preventing leakage of harmful bioaerosols.The aim of this study is to investigate the sealing technology of stainless steel structural airtight biosafety containment facilities.Methods:An experimental study was conducted on a domestic high-level pathogenic microorganism model laboratory,considering the sealing process of the containment structure,including airtight doors,pass boxes,dunk tanks,through-wall pipeline sealing devices,and sealed floor drains.Results:The results indicate that the airtightness of the model laboratory containment structure meets the tightness requirements of a biosafety level-4(BSL-4)laboratory.They also indicate that the construction technology of stainless steel enclosure structures used by the laboratory and the tightness performance and installation process of the developed airtight protective equipment meet the technical requirements of a BSL-4 laboratory.Conclusions:This successful model laboratory indicates that China has the research and development capacity for stainless steel airtight containment structure manufacturing processes,airtight protective equipment,and technical capacity for independent construction of the highest-level pathogenic microorganism laboratories.