Risk Of Condensation Research Articles

Thermal bridges in buildings as a result of urban transformation

The paper analyzes the deterioration of energy performance in buildings and construction defects caused by thermal bridges resulting from changes taking place in urban planning, for example in Vojvode Stepe street in Belgrade. The transformation of the urban matrix done over the last 50 years coupled with a time lag in implementation, resulting in partial sequences to completed buildings, has left a number of free side walls (gable ends), which are exposed to temperature influences. In some cases, these walls are adequately heat-treated, but in many others (especially in existing buildings) they are not, causing increased heat loss mould growth, leading to construction damage, and health risks to users. This paper presents a methodology for testing the risk of condensation in a specific example, using the computational support of T Studio software, intended for 2D calculations of thermal bridges, with an emphasis on contact temperature in the interior, relative humidity, and a term that is new to us: Temperature factor.

A passive–active dynamic insulation system for all climates

Common features of Passive House design are thick walls and air tight construction, to minimise heat loss and infiltration respectively. This is due to the use of thick conventional insulation to achieve the very low U-values required for the Passive House Standard, which adds to the overall cost of construction and also potentially contributes to problems such as interstitial condensation. High performance, exotic insulation materials such as silica aerogels and vacuum insulation products could help to reduce thickness but at a cost that is at present prohibitive. In this paper the author introduces the basic concept and some illustrative simulated performance results of a new Void Space Dynamic Insulation (VSDI) technology that couples low cost conventional insulation materials with efficient ventilation to deliver low loss building envelopes and high indoor air quality in thin wall construction. The advantages of VSDI are that it eliminates the risk of interstitial condensation and the risk of over-heating during extreme summer months. Importantly, VSDI can be used as a 100% passive component, without a fan to drive the air flow.

Equivalent wall method for dynamic characterisation of thermal bridges

Although there are specific rules in the standard ISO 10211 for the characterization of thermal bridges, they are mainly focused on steady state calculations to obtain the linear thermal transmittance (Ψ) or the temperature factor at the internal surface (fRsi). These parameters are respectively indicators of the additional heat flow and the risk of internal surface condensation of thermal bridges.However, in the calculations of building energy demand the dynamic thermal aspects of the envelope take a very important role. Moreover, a high percentage of the envelope is influenced by thermal bridges. Therefore it is necessary to take into account the implicit inertia of thermal bridges for accurate calculations.This paper presents a methodology based on thermoelectric analogy to calculate an equivalent wall of three homogeneous layers, which have the same dynamic thermal behaviour as the thermal bridge. Furthermore, each thermal bridge is associated with an influence area within the envelope, so that they can be easily implemented in building energy simulation programs where the heat flow is usually considered one-dimensional.

Experimental study on hygrothermal behaviour of retrofit solutions applied to old building walls

Rural houses are usually built with traditional materials, stone and wood, and have a poor thermal and hygrometric behaviour. On the other hand, this kind of residences are generally degraded, and it is necessary to study adequate solutions to rehabilitate roofing (wood structures), walls (stone masonry) and floors (wood), particularly to improve house envelop resistance to water penetration and thermal comfort. Is it also urgent, as well, to study and develop adequate methodologies for the rehabilitation of such typical construction having this specific characteristics. Thus, under this scope, an experimental study on hygrothermal behaviour of retrofit solutions applied to old building stone masonry walls is presented. This analysis has been carried out in order to evaluate the influence of some wall retrofit solutions that can increase its thermal resistance. The study took place in laboratory, using a climate chamber, in which variations of temperature and humidity that occur in a stone masonry wall have been measured. The results obtained in laboratory were compared with analytical results obtained using specific software for the assessment of probability of occurrence of walls internal condensation. The experimental results obtained in this work contribute to a better understanding of the thermal-hygrometric behaviour of stone masonry walls, when thermal rehabilitation solutions are applied to its inside surface. The study also points out the importance of using repair-building solutions that can minimize the risk of superficial and internal condensation.

Performance analysis on a residential radiant chilled ceiling system and evaluation on indoor thermal environment in summer: an application

The performance of a residential radiant chilled ceiling system combined with an outdoor air handling unit under steady operating conditions in summer was tested, and the stable operating characteristics of this system were analyzed. Indoor thermal environment parameters of room which employed this system were measured and analyzed and the thermal comfort evaluation of occupants was given. The results show that the composite system works well in summer, which can provide low- and high-temperature chilled water for the air supply terminal and the radiant terminal devices. Good thermal comfort can be achieved in room which employed this system, and no condensation risk occurs when it is applied in hot summer and cold winter zone of China. All the analysis provides a technical support for the popularization of the residential radiant chilled ceiling system combined with an outdoor air handling unit in China, and provides a reference for the further optimization of this system.

Characterization of a Hygro-Regulated Wall Base Ventilation System for Treatment of Rising Damp

The treatment of rising damp in the walls of historical buildings is very complex, due to the thickness and heterogeneity of the walls. The techniques traditionally used for dealing with this problem (such as watertight barriers, injection of hydrofuge products, etc.) have sometimes proved ineffective, and that is why it is necessary to find a new approach. In recent years, the Building Physics Laboratory at the Faculty of Engineering, University of Porto has been conducting experimental research on the effectiveness of the wall base ventilation system, using natural or mechanical higro-regulate systems to reduce the level of the damp area. This experimental research and the simulations that were performed, clearly show that wall base ventilation is a system with potential. This paper presents the characterization of the hygro-regulated systems operation based on experimental studies developed in laboratory, which allowed the influence of the velocity of the air, condensation risk and the possibility of salt crystallization.

Neural network based prediction method for preventing condensation in chilled ceiling systems

Condensation is prone to occur at the startup moment in chilled ceiling systems, due to the infiltration and accumulation of moisture during system-off. To prevent condensation, an effective method is to operate the dedicated outdoor air system (DOAS) to dehumidify indoor air before operating chilled ceiling system. The pre-dehumidification time is critical. However, there is little experience in determining the pre-dehumidification time in both research and practice. In this study, neural network (NN) is used to predict condensation risk and the optimal pre-dehumidification time in chilled ceiling systems. Two NN models are developed to predict the temperature on the surface of chilled ceiling and indoor air dew-point temperature at the startup moment so as to evaluate the risk of condensation. The third NN model is developed to predict the optimal pre-humidification time for condensation prevention. Both training data and validation data are obtained from simulation tests in TRNSYS. The results show that 30 min pre-dehumidification is sufficient for the simulated building in Hong Kong. The influence of infiltration rate on the pre-dehumidification time is also investigated. This study also shows that NN-based method can be used for predictive control for condensation prevention in chilled ceiling systems.

Condensation risk assessment on box windows: the effect of the window–wall interface

Windows generally have the lowest temperature index in current building types, and will consequently be the primary location for interior surface condensation. Surface temperatures can easily be calculated using thermal finite-element models, but these generally omit the effect of convection in the windows and the window–wall interface. Hence, there is a need to determine if specific interface details provide potential for condensation on the window components in which air leakage paths may be prominent. The article reports on a laboratory evaluation of condensation risk assessment in a hotbox with varying pressure differences and the introduction of deficiencies. It was concluded that the effect of the type of insulation in the window–wall interface was very low for isobaric boundary conditions, whereas it has a significant effect when pressure differences are applied.

Laboratory Tests of Window-Wall Interface Details to Evaluate the Risk of Condensation on Windows

Abstract The development of alternative details to manage water intrusion at the window-wall interface has produced a number of novel approaches to detailing the interface between the window and the adjacent wall assembly. Many of these approaches advocate the need to provide drainage at the rough opening of the window subsill, given that the window components themselves are susceptible to water entry over their expected life. Depending on the types of windows used and the cladding into which the windows are installed, there arise different methods to provide drainage that may also affect air leakage through the assembly. This in turn may give rise to the formation of condensation along the window, at the sill, or along the window sash and glazing panels. Hence, there is a need to determine if, under cold weather conditions, specific interface details that incorporate sill pans provide a potential for condensation on the window components in which air leakage paths may be prominent at the sill or elsewhere on the window assembly. The paper reports on a laboratory evaluation of conditions suitable for the formation of condensation at the window frame perimeter of the interface assembly as a function of both temperature deferential and air leakage rate across the test assembly. A summary of the laboratory test protocol is provided, which includes a description of the test setup and apparatus, fabrication details of the specimen, information on instrumentation and calibration, and experimental results for one type of window (flange window). In parallel, preliminary simulation results were presented and compared to those obtained from the experiment using the commercially available thermal software BISCO.

Air permeability measurements of dwellings and building components in Portugal

Ventilation represents a significant part of heat loss in winter, leading to the need to minimize airflow. However, it is absolutely necessary to ensure indoor air quality and the safety of the users and to control the risk of condensation. Ventilation is responsible on average for 30%–40% of energy consumption in air conditioning in Western European buildings. There is great variability in air change rates ( ACH [h −1]) from country to country and the minimum value takes into account comfort, sensory and hygrothermal criteria. In Portugal improvements have been made in the air permeability of window frames, but despite the improvements also made in installing mechanical extraction ventilation devices in kitchens and toilets, these often do not guarantee the minimum number of air change rates required. Air permeability tests were recently carried out in five flats with identical construction characteristics, in the same building, with the aim of characterizing the air permeability of buildings and components, in Portugal. These data are particularly useful for improving the design of building components (e.g., windows and roller shutter boxes) and to perform simulations with reliable data.

Moisture Damage in Vented Air Space of Exterior Walls of Wooden Houses

Abstract Most of the exterior walls of wooden houses in Japan have a vented air layer between the exterior cladding and the insulation. This vented air layer is designed to dehumidify the exterior walls by discharging humidity to the outside and allowing outdoor air to enter, thereby decreasing the risk of condensation on the exterior wall during winter. It is assumed that the source of this moisture is the indoor air, and that the outdoor air is drier. However, the outdoor air is often highly humid during the rainy season and may become a source of moisture. The vented air layer also allows rain water to drain away. Any rain water penetrating through the exterior cladding is drained away through the vented air layer. However, rain can also enter the vented air space through the air inlets. Since it takes a certain amount of time for all the rain water to drain away, water may accumulate in the vented air layer and produce high humidity in the exterior wall. In order to evaluate the effectiveness of an exterior wall with a vented air layer, its hygrothermal characteristics should be investigated, taking the effect of rain water into consideration. This paper describes a case of moisture damage where stain appeared on the outer surface of the plywood wall in a wooden residential building. Experiments were carried out in climate chambers to clarify the conditions that are causing stain. Hygrothermal conditions in the vented air layer were simulated using heat, air, and moisture model, and the causes of staining were investigated.

Preliminary investigation of a vapor-open envelope tailored for subtropical climate

Concerning global warming and resource depletion, the impact of buildings in subtropical regions is becoming even greater due to a high growth rate of urbanized areas. From the viewpoint of building physics, the main problem concerning subtropical climate is the high level of humidity in combination with high temperature. In this study, a flexible building envelope consisting of wood and clay components was developed so that the materials and the assemblies can be easily tailored to comply with local climatic conditions. The movement and accumulation of moisture in the wall was of prime concern. This has been investigated by means of testing full scale walls in a climate chamber and the corresponding one dimensional transient heat and transfer simulation. In order to achieve a consistency between calculation and measurement, the individual materials were tested for their hygric and thermal properties. Based on these findings attempts were made to calculate the behavior of an optimized wall assembly under real climatic conditions of central Japan. As a result, it was shown that the hygrothermal behavior of the envelope is predictable by means of the models and the simulation program used, and that no risk of interstitial condensation and mold growth was predicted under the real climatic conditions of Kyoto.

Durability of light steel framing in residential applications

This paper presents a summary and analysis of research findings on the durability of galvanised cold-formed steel sections used in housing in order to deduce their design life. These cold-formed sections are produced from pre-galvanised strip steel. It reviews reports and publications from research projects carried out by Corus and the Steel Construction Institute on zinc-coated, cold-formed steel products. New data have also been gathered from measurements on houses and similar buildings that have used galvanised steel components. The data also extend to over-cladding applications in building renovation. The performance of galvanised (zinc-coated) steel components within warm-frame applications is very good. The research leading to this paper shows that the predicted design life of the standard G275 coating, based on the measured loss of zinc from the strip steel, is over 200 years, provided that the building envelope is well insulated and properly maintained. The evidence for this conclusion is based on measurement of zinc loss on light steel frames in various applications and locations. A formula for the loss of zinc over time in areas subject to low condensation risk is presented.

Corrosion in Electronics at Device Level

This work presents device level testing of a lead free soldered electronic device tested with bias on under cyclic humidity conditions in a climatic chamber. Besides severe temperature and humidity during testing some devices were deliberately contaminated before testing. Contaminants investigated are ionic or airborne contaminants likely to be introduced by production or service conditions. The effect of changes in processing parameters as a result of production shift to lead free solder (e.g. higher soldering temperature) has also been investigated. Analysis have shown that one printed circuit board assembly (PCBA) in the device is more prone to corrosion reliability and this was further analysed using thermography to detect areas that have high risk of condensation due to lower temperature under working condition. Tested PCBAs are subjected to detailed investigation before and after testing using high resolution photography, detailed optical microscopy and SEM/EDS.

Hygrothermal properties applied in numerical simulation: Interstitial condensation analysis

The problem of moisture damage in buildings has attracted interest from the early days of the last century, but it was only with the development of hygrothermal modelling that the general topic of moisture transport in buildings became the subject of more systematic study. Today, the evaluation of the risk of interstitial condensation in building envelope components can benefit from models of different complexity levels. This article starts with the analysis of the main material properties applied in the models that can tackle interstitial condensation, regarding standardization and experimental evaluation. Additionally, two commercial programmes that support two different levels of complexity of interstitial condensation analysis are compared: the more complex WUFI 4.2 and the simpler Condensa 13788. The comparison of both programmes uses a brick wall with interior insulation. The results of this exercise allow for conclusions on the applicability of the models in view of material properties availability.

Towards Development of a Performance Standard for Assessing the Effectiveness of Wall-Window Interface Details to Manage Rainwater Intrusion

Abstract Laboratory water spray testing identifies the performance of a component or assembly under a specified set of simulated wind-driven rain conditions. Well-developed water spray test protocols can also help identify where an assembly is vulnerable to water entry, the test loads at which water entry occurs, and whether the water entry is managed by the installation details in such a way that it does not result in within-wall damage. This paper presents a proposed laboratory test protocol for assessing the effectiveness of wall-window interface details with regard to management of rainwater and provides a rationale for a performance-based approach to the evaluation method. An overview of the test approach is provided, and details of the test apparatus and test specimen are given, including information on implementation of the test method. Examples of testing performed according to the proposed protocol are provided. Finally additional tests for evaluating the performance of installation details are suggested. The additional tests are for field evaluation of installation details and for laboratory evaluation of installation details with regard to the risk of condensation along window frames.

Analysis and Optimization of Drying of Green Bricks in a Tunnel Dryer

One way to avoid the risk of condensation in a tunnel dryer for drying of green bricks is to use higher air flow rates. However, higher air flow rates accelerate the drying rate and thus cause damages. It is necessary to determine the optimal values of the hot and outdoor air mass flow rates and optimum stack temperature to avoid the condensation. Four different temperatures, (−5, 10, 20, and 30°C) and three different relative humidities (40, 60, and 80%) for the outdoor air were selected. Optimal operation parameters and the required stack temperature to avoid condensation for different cases were computed.

Condensation and moisture transport in cold roofs: effects of roof underlay

Cold pitched roofs, with their form of construction situating insulation on a horizontal ceiling, are intrinsically vulnerable to condensation. This study reports the results derived from using a simulation package (Heat, Air and Moisture modelling tool, or HAM-Tools) to investigate the risk of condensation in cold pitched roofs in housing fitted with a vapour-permeable underlay (VPU) of known characteristics. In order to visualize the effect of the VPUs on moisture transfer, several scenarios were modelled, and compared with the results from a conventional bituminous felt with high resistance (200 MNs/g, Sd = 40 m). The results indicate that ventilation is essential in the roof to reduce condensation. However, a sensitivity analysis proved that reducing the overall tightness of the ceiling and using lower-resistance VPUs would help in controlling condensation formation in the roof. To a large extent, the proposed characteristic performance of the VPU as predicted by manufacturers and some researchers may only be realistic if gaps in the ceiling are sealed completely during construction, which may be practically difficult given current construction practice. Les toitures froides inclinées, caractérisées par l'isolation sur un plafond horizontal sont intrinsèquement exposées à la condensation. Cette étude rend compte des résultats obtenus de l'utilisation d'un programme de simulation (outil de modélisation de la chaleur, de la ventilation et de l'humidité ou outils HAM) pour analyser le risque de condensation dans les toitures froides inclinées dans les maisons équipées d'un pare-vapeur (VPU) aux caractéristiques connues. Afin de visualiser les effets du VPU sur le transfert d'humidité, plusieurs scénarios ont été modélisés et comparés aux résultats obtenus avec un feutre bitumineux classique à haute résistance (200 MNs/g, Sd = 40 m). Les résultats indiquent que les toitures doivent être ventilées pour réduire la condensation. Toutefois, une analyse de sensibilité a prouvé qu'en réduisant l'imperméabilité globale du plafond et en utilisant des VPU de moindre résistance cela devrait aider à maîtriser la formation de la condensation dans les toitures. Dans une grande mesure, les performances caractéristiques proposées des VPU telles qu'elles sont prévues par les fabricants et par un certain nombre de chercheurs ne peuvent être réalistes que si les interstices dans le plafond sont totalement obturés hermétiquement pendant la construction, ce qui risque d'être difficile sur le plan pratique compte tenu des méthodes utilisées actuellement dans la construction. Mots clés: fuites d'air, imperméabilité à l'air, toitures froides inclinées, condensation, outils HAM, perméabilité, conception de toitures, pare-vapeur

Condensation Risk in a Room with a High Latent Load and Chilled Ceiling Panels and with Air Supplied from a Liquid Desiccant System

Radiant cooling has shown great advantages when it comes to improving thermal comfort and can also reduce energy demand. But the system may have a high condensation risk if used with a high latent load. This study proposes a new type of ventilation system that uses a radiant cooling panel and air supplied from a liquid desiccant dehumidification system, which provides very dry supply air and chilled water for radiant cooling. This study uses an office with a high latent load to demonstrate the application of such a system in a hot and humid climate. By using a validated computational fluid dynamics (CFD) program to calculate the distributions of air temperature, humidity, and velocity, as well as the predicted mean vote in the office, the results show that the new system could reduce the risk of condensation on the cooling panels and offer a comfortable indoor environment. The new system has great potential when it comes to use in hot and humid climate regions.

The effect of traditional wind vents called zarceras on the hygrothermal behaviour of underground wine cellars in Spain

This paper studies the hygrothermal behaviour of traditional underground wine cellars in one of the most important wine growing areas of Spain, the Ribera del Duero, paying special attention to the effects of traditional wind vents called zarceras. The purpose is to highlight energy-saving practices that aid the design and renovation of similar constructions. This was carried out by monitoring the temperature and relative humidity inside two wine cellars of similar properties throughout 2007, one with a zarcera and the other without. The results of the analysis show that the existence of the wind vent does not increase the ventilation from May to August. On the other hand, from September to March, the zarcera favours ventilation, affecting both temperature and relative humidity. The interior temperature is more greatly affected by the exterior temperature, giving rise to greater variations, although this difference is of little importance for maturing wine (annual variation 2.5 °C more than the cellar without a zarcera). The interior relative humidity is reduced, reducing the risk of condensation and problems of mould (the cellar without a zarcera reached excessively high values, 97% as an annual average, compared to 91% in the cellar with a zarcera). Thus the existence of zarceras in underground cellars improves the overall hygrothermal behaviour, providing suitable conditions for maturing wine without air conditioning systems, an advisable element in the building of new underground wine cellars.