Water vapor transport to a semi-infinite material with simultaneous varying surface relative humidity and temperature

The water vapor transfer between the indoor air and hygroscopic finishing materials is of importance for the moisture balance of the room. Most protocols for determining the effect are based on isothermal conditions and cycling relative humidity in the form of square wave or sinusoidal functions. A new analytical solution for a material exposed to a both time varying surface relative humidity and temperature is presented in the paper. The time varying temperature inside the material is assumed to follow the surface temperature throughout the material layer since the reaction time for temperature changes in a reasonable thin surface material is rather short compared with the one for moisture changes. The semi-infinite approach is justified by the fact that the penetration depth for moisture variations are very limited for diurnal variations. The analytical approach and solution are presented in the paper

Stochastic simulation of rain intrusion through small defects due to water rivulet overpressure. Introducing a driving rain leakage potential

There is a need of upgrading the old building stock with respect to the thermal insulation of the building envelope and specifically the fa\ue7ades. There are several systems on the market, and some are quite new and innovative. To bring down the cost some of the systems many are based on prefabricated moisture tight insulated units. This means that in case there is moisture tight barrier on the interior side, two moisture tight barriers surround the wall structure. The leakage of driving rain into the structure then represents a major threat to the durability of these systems. This paper investigates the pressure build up in water rivulets running down a fa\ue7ade acting together with the wind pressure. A driving rain leakage potential is introduced. Using real weather data years and Monte Carlo Simulations, the mean and standard deviation of the annual leakage through small hole is estimated. The examples show that the leakage can reach a level 0-0.5 liter/year for a hole with a diameter of 1-2 mm, and 0.5-3 liter/year for a diameter of 3-4 mm

New algorithm for water leakages flow through rain screen deficiencies

There is a need of more knowledge about the mechanisms of water leakage through façades exposed to driving rain to make reliable risk analyses. Therefore, we have studied it in more detail and the outcome include inter alia a new algorithm. The algorithm is developed for calculation of water leakages through rain screen deficiencies. The algorithm is based on empirical values from many measurements according to standardized test method and validation. Even though the leakage process is very complicated, simple correlations have been shown. The leakages flow rate through deficiencies are mainly limited by the runoff rate and the catch area above the hole and around the hole with dam. Apart from wind pressure as a driving force, the inlet of the holes is often on a higher level than the outlet at the rear of the façade, which creates significant hydrostatic pressure, which can be elevated by impoundment at the obstacle. This is the main reasons to comprehensive water leakages through façades without any wind pressure (pressure equalized façades). If precise information about defects data is not available, there are extensive measurements supporting the following assumption – a realistic leakage flow for a small or invisible spot leakage at a façade detail is presumed to be 0.5 to 2% of the runoff rate per meter of façade width. If there are multiple penetrations or obvious defects in the façade design in combination with the dams, a significantly higher proportion of the runoff flow can leak in

A conceptual model for how to design for building envelope characteristics. Impact of thermal comfort intervals and thermal mass on commercial buildings in U.S. climates

The paper presents a simplified conceptual model for energy demand calculations based on building envelope characteristics, thermal mass and local climate. It is based on a network model and lumped analysis of the dynamic process. Characteristic parameters for the buildings are suggested; Driving temperature (DT), Driving temperature difference, (DTD), External Load Temperature (ELT), and Thermal Load Resistance (TLR). The Building Envelope Performance (BEP0), based on a controlled constant indoor temperature is introduced. Solution techniques using stable explicit forward differences based on analytical solutions are derived. The conceptual model has been used for mapping the Driving temperature difference and introduced two performance factors α and β. The first factor represents the effect of thermal comfort interval and thermal mass on the energy demand. The latter represents the ratio between cooling and heating energy demand. These three parameters and factors have been visualized on U.S. maps and enable a possibility to communicate the demand of energy, and cooling and the coupling to building characteristics, in a concise way

The Future Climate Moisture Susceptibility of Wall Assemblies: Analysis Based on Monte Carlo Simulation Using a Simplified Deterministic Hygrothermal Simulation Model

A newly developed generic algorithm to assess moisture susceptibility of simplified wall assemblies has been developed within the CIB-W080 WG 2. This group is focusing on guidelines for design for durability of building envelopes. The algorithm is implemented in a publicly available Matlab code. A simplified wall assembly consisting of up to four material elements is considered. Optional vapor retarder and thermal resistances are located between the elements. In this paper modelling of a ventilated cladding is implemented. Using the simplified numerical model, a probability‐based risk analysis using the Monte Carlo method is demonstrated. The risk assessment of the wall assembly considers the interior and exterior climatic load. The moisture transport mechanism accounted for in the analysis is diffusion. The rain load is assumed to be transferred directly to a chosen outer susceptible material element in the construction. An insulated wooden wall structure is analyzed and the probability distribution of the time of wetness is presented for cases using sequence of 31 consecutive climatic years, randomly varying indoor moisture excess, indoor temperature and driving rain leakages

Implementing a framework for qualitative assessment of new technical solutions: A case study on CLT

New technical solutions are introduced at a fast pace in the Swedish construction industry, mainly driven by issues concerning costs and productivity. These new technical solutions can comprise new materials, new goods, new designs but also new processes. The record of accomplishment when introducing new technical solutions in the industry is not unproblematic and serial failures of different new technical solution have occurred. In an earlier interview study exploring introduction of new technical solutions in the Swedish construction industry, a common lack of thorough methods for evaluation of new solutions was identified. To address this issue, a case study was performed, exploring a method of evaluation with respect to building physics while implementing a cross laminated timber frame in a multifamily building. The case study uses a framework of assessment with focus on building physics. This paper presents the findings from the case study focusing on how evaluation of a new technical solution with respect to building physics is performed, together with an evaluation of the method, using the experiences of the participants in the case study

Risk assessment framework to avoid serial failure for new technical solutions applied to the construction of a clt structure resilient to climate

Design-build contractors are challenged with the task of minimizing failure risks when introducing new technical solutions or adapting technical solutions to new conditions, e.g., climate change. They seem to have a disproportional trust in suppliers and their reference cases and might not have adequate resources or methodologies for sufficient evaluation. This creates the potential for serial failures to spread in the construction industry. To mitigate this, it was suggested that a predefined risk assessment framework should be introduced with the aim of providing a prequalification and requirements for the use of the technical solution. The objectives of this paper are to develop a comprehensive risk assessment framework and to explore the framework’s potential to adequately support the design-build contractor’s decisions. The framework uses qualitative assessment, relying on expert workshops and quantitative assessments, with a focus on simulation and probabilities. Tollgates are used to communicate risk assessments to the contractor. The framework is applied to a real-life case study of construction with a CLT-structure for a Swedish design-build contractor, where exposure to precipitation during construction is a key issue. In conclusion, the chosen framework was successful in a design-build contractor context, structuring the process and identifying difficulties in achieving the functional requirements concerning moisture. Three success factors were: documentation and communication, expert involvement, and the use of tollgates. Recommendations to the design-build contractor on construction of CLT structure are to keep construction period short and to use full weather protection on site

Method for Detecting Contaminant Transport through Leakages in a Condemned School

Many schools in Sweden, have problems with the indoor air, affecting the wellbeing and health of both pupil and teachers. Contaminants in the air, such as mold spores, radon, odors, and VOC, cause problems and it can be difficult to find the contaminant source, in particular if it is within the building construction. The aim of this project is to investigate air leakage paths and pressure differences in a school building with IAQ problems and to analyze how these parameters are related to contaminant transport. An increased knowledge of how contaminants are transported will then form the base for an improved strategy for dealing with renovations of schools with IAQ issues. The main method of investigation in this initial part of the project is blower door measurements and leakage paths detection. A method to use CO2 from dry ice as tracer gas for leakage detection is under development and tested in a condemned school building. Results presented in this paper show that it is possible to use this method to determine whether air leakages are coming from the crawlspace or from elsewhere

Relying on reference cases when evaluating new technical solutions? Evaluation of technical documentation in a case study

Serial failures have occurred when introducing new technical solutions in the Swedish construction industry. In an earlier interview study exploring introduction of new technical solutions, documentation and reference cases provided by the supplier are given as the main sources for evaluation. This paper aims at addressing the questions: 1. What kind of documentation concerning building physics are provided by suppliers? 2. How well does the suppliers\u27 documentation meet the need for verification? In order to address these questions, the case of hygrothermal performance of cross laminated timber structures in multifamily dwellings was chosen. An inquiry of data was sent out to four suppliers at the Swedish market, asking for documentation and reference cases provided. Based on the documentation given, an assessment was made of to which extend the documentation can support verification of appliance to the relevant requirements of the Swedish building regulations. The case study shows reference cases are scarce and existing documentation is not comprehensive, thus indicating the building industry might have a disproportional high confidence in reference cases. The results will be used to suggest requirements for reference cases to be used for verification

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