Stig Geving

Mean and diurnal indoor air humidity loads in residential buildings

In this study, indoor air humidity and temperature levels have been measured in 117 houses in Trondheim, Norway. The houses were randomly selected for each of the following types: detached one-family houses, semidetached two-family houses, row houses, and apartment buildings. The temperature and relative humidity (RH) were measured at 15-min interval over a period of 1 week. The measurements were made in bedrooms, living rooms, bathrooms, and outdoors. The internal moisture excess, which is the difference between indoor and outdoor air water vapour content, was calculated. The dataset was analysed in regard to average values of internal moisture excess and its dependency of outdoor climate. The daily variations of indoor RH, temperature, and internal moisture excess for the various types of rooms were also analysed. The typical diurnal variations of RH, temperature, and internal moisture excess are presented together with the statistical variation. The effect of influencing factors such as occupancy (area per person), type of basic ventilation of the house, type of building, time of the year, and the level of average indoor air humidity was investigated. To get a deeper understanding of some of the factors influencing the diurnal variations of the indoor air humidity observed in the field measurements, computer simulations of the indoor air humidity were also performed. The simulations were made using the numerical software WUFI Plus.

The Drying Potential and Risk for Mold Growth in Compact Wood Frame Roofs with Built-in Moisture

Built-in moisture in the insulation layer of a compact roof will generally dry out very slowly, compared to the drying rate in a ventilated roof construction. Intended or unintended leakages of outdoor air through the insulation layer may, however, speed up the drying rate. In this investigation, the drying potential of various configurations of compact wood frame roofs with a high level of built-in moisture has been investigated, through test house measurements and hygrothermal simulations. Compact wood frame roof elements has been wetted, and mold spores has been added to the elements. The hygrothermal conditions of the elements has been monitored through a period of 2 years, and the microbial conditions has also been registered. The possible drying effect of outdoor air leaking through the insulation layer from one side of the roof to the other has been investigated.

Measurements and Two-Dimensional Computer Simulations of the Hygrothermal Performance of a Wood Frame Wall

Knowledge of the expected long-term performance of building envelopes subjected to simultaneous heat and moisture transport is critical during the design stage. In the past thirty years researchers have concentrated their efforts in extensive laboratory experiments. These experiments have been expensive as well as time consuming to conduct due to the slow moisture transport phenomena. This paper critically investigates a set of experimental results generated from laboratory controlled measurements on a wood frame wall construction, by employing a state of the art hygrothermal model. The analysis was carried out using the LATENITE model, a three-dimensional heat and moisture transport program tailored specifically for building envelope investigations. For the present simulations this model was adapted for two-dimensional conditions and hourly hygrothermal performances were predicted for a laboratory instrumented wood frame wall section. The investigation showed three main advantages of combining measurements and simulations. By carrying out simulations early in the design stage of laboratory experiments the experimental design will probably yield better quantification of data, placement and types of sensors, and assessment of workmanship influences, etc. Measurements can calibrate, adapt, or check calculated results. Finally, simulations can be performed to explain and interpret experimental results. Marrying experi ments and modeling allows researchers to generate effective hygrothermal perfor mance guidelines.

Moisture conditions in well-insulated wood-frame walls. Simulations, laboratory measurements and field measurements

Abstract Buildings for the future, that is, zero emission buildings and passive houses, will need well-insulated building envelopes, which include increased insulation thicknesses for roof, wall and floor constructions. Increased insulation thicknesses may cause an increase in humidity levels and thereby increased risk of mould growth. There is need for better knowledge about moisture levels in wood constructions of well-insulated buildings, to ensure robust and moisture-safe solutions. Various envelope constructions were simulated using HAM-tools (Heat, Air and Moisture). In addition, a laboratory experiment was performed to investigate the effect of a slower drying out of built-in moisture. Walls with varying insulation thicknesses and with a high degree of built-in moisture were instrumented with moisture sensors, and the drying speed was monitored. A field monitoring of wood moisture levels and temperatures was performed in wall and roof constructions of five passive houses in three different locations representing different climate conditions in Norway. The general conclusion is that the risk for mould growth increases somewhat in well-insulated envelopes compared to more traditional envelopes. However, in most cases this can be counteracted by making the right choices during design and construction.

Local loss coefficients inside air cavity of ventilated pitched roofs

Pitched roofs with a ventilated air cavity to avoid snow melt and ensure dry conditions beneath the roofing are a widely used construction in northern parts of Europe and America. The purpose of this study has been to determine pressure losses at the inlet (eaves) and inside the air cavity consisting of friction losses and passing of tile battens. These results are necessary to increase the accuracy of ventilation calculations of pitched roofs. Laboratory measurements, numerical analysis as well as calculations by use of empirical expressions have been used in the study. A large difference in the local loss coefficients depending on the edge design and height of the tile batten was found. The local loss coefficients of the round-edged tile battens were approximately 40% lower than the local loss coefficients of the sharp-edged tile battens. Furthermore, the local loss factor increased by increasing height of the tile batten. The numerical analysis was found to reliably reproduce the results from the measurements.