Hygrothermal conditions in ventilated attics with different air change rates and ceiling constructions

A recently Danish study reported that no vapour barrier is needed in ceilings, if the attic is well ventilated and the ceiling towards the dwelling is airtight. Based on that study, new investigations were initiated with focus on the hygrothermal behaviour in ventilated attics with different air change rates. A test house with three sets of four different ceiling constructions – all airtight – was used in this study. The ventilation rate was reduced in two of the sets with approx. 35 % and 50 %, respectively. Air change rates were measured with tracer gas. Furthermore, temperature and relative humidity was measured every hour. Measurements in similar ceilings with mineral wool or cellulose-based insulation material show that hygroscopic properties of the insulation have very limited effect on relative humidity. Furthermore, only at low ventilation rate the effect of a vapour barrier could be measured with minor impact. Based on the short-measured period the calculations of the risk of mould growth showed no risk. The results indicate that even when the ventilation is reduced by 50 %, the ventilated attic still performs well if the ceiling is highly airtight. However, the importance of vapour barriers becomes more important at lower air change rates.

Download Full-text

Moisture behavior of external insulated precast concrete wall panels

Journal of Building Physics ◽

10.1177/1744259120925850 ◽

2020 ◽

pp. 174425912092585

Author(s):

Pauli Sekki ◽

Timo Karvinen ◽

Juha Vinha

Keyword(s):

Relative Humidity ◽

Precast Concrete ◽

Concrete Surface ◽

Mineral Wool ◽

Insulation Material ◽

Concrete Wall ◽

Building Stock ◽

Interior Surface ◽

Insulation Materials ◽

Wall Panels

Excess moisture in concrete structures is a major problem in building industry. It is claimed that degradation of the finishing materials of concrete slabs is the largest source of volatile organic compound in the building stock in the Nordic countries. Considering concrete wall panels, the choice of the insulation material influences concrete drying considerably and causes a risk for moisture accumulation on the interior surface, if vapor tight finishing materials are used or if finishing materials are installed prematurely. Mineral wool insulation, which has predominately been used in Finland, is a vapor open material. However, vapor tight plastic foam insulation materials are nowadays more commonplace. Here we show that the overall rate of drying of the concrete panel with a vapor open insulation material is higher in comparison to the concrete panel with vapor tight insulation materials. However, relative humidity distribution near the inner surface of the concrete panel at the end of the drying phase is almost identical irrespective of the insulation material and the water vapor resistance of the interior surface material has a greater impact on the relative humidity level on the inner concrete surface. Moisture behavior of concrete panel walls is studied under a certain building schedule in Finnish environment and building conditions by numerical simulation. The model for drying of concrete is calibrated based on laboratory measurements. According to our study, self-desiccation and changing diffusivity due to the hydration process of the concrete cannot be ignored when evaluating the moisture behavior of the concrete wall panel structure with a low water binder ratio ( w/ b < 0.5). Measurements indicate that the early age humidity drop is by up to 10 percentage points.

Download Full-text

Hygrothermal performance of cold ventilated attics above different horizontal ceiling constructions: Full-scale test building

Journal of Building Physics ◽

10.1177/1744259119894028 ◽

2019 ◽

Vol 44 (1) ◽

pp. 67-91

Author(s):

Thor Hansen ◽

Eva B Møller ◽

Torben Tvedebrink

Keyword(s):

Relative Humidity ◽

Full Scale ◽

Moisture Level ◽

Insulation Material ◽

Full Scale Test ◽

Indoor Climate ◽

Outdoor Climate ◽

Hygroscopic Properties ◽

Insulation Thickness ◽

Scale Test

It is often assumed that reduced heat flux to a ventilated attic reduces the temperature and thereby increases the relative humidity. Consequently, the importance of having a tight air and vapour barrier in the ceiling becomes more important with increased insulation. Therefore, in Denmark, the recommendation is to have a tight vapour barrier when re-insulating ceilings against cold ventilated attics to a total of 150-mm insulation material. The recommendation is independent of the insulation material’s hygroscopic properties or the indoor moisture level. The aim of this project was to test the relevance of the recommendation through testing in a full-scale test building (7 × 22 m) with a series of six different ceilings with or without a vapour barrier and variation in the insulation material comprising insulation thickness and its hygroscopic properties. The examination was performed with a controlled indoor climate after an European humidity classes 1–3 and a natural outdoor climate. The study showed very little differences in temperature and relative humidity in the cold ventilated attics, while the humidity class of the indoor climate significantly affects the absolute moisture content in the attic. However, the climate in the attic did not cause mould growth in the test sections, even for humidity class 3. Consequently, in the test building the thickness or hygroscopic properties of the insulation material did not have a significant effect on the moisture level in attics and did not determine whether a vapour barrier should be installed. In this study with the given climate, a vapour barrier is unnecessary in well-ventilated attics if the ceiling is airtight.

Download Full-text

23. Practical Methods for Measuring Ventilation Rate Using Carbon Dioxide as a Tracer Gas

10.3320/1.2762897 ◽

1999 ◽

Author(s):

M.D. Walters

Keyword(s):

Carbon Dioxide ◽

Ventilation Rate ◽

Tracer Gas

Download Full-text

110. Evaluation of the Measurement of Ventilation Rate Using Carbon Dioxide as a Tracer Gas

10.3320/1.2762492 ◽

1999 ◽

Author(s):

M.D. Walters ◽

F-T. Lin ◽

R.J. Sherwood

Keyword(s):

Carbon Dioxide ◽

Ventilation Rate ◽

Tracer Gas

Download Full-text

Figure 2: Dust concentration (mg/m3 ), ventilation rate (m3/ pig h), temperature (°C), and relative humidity dust p ig 1) he n 2) origi n o tin g without bedding battery bedding from •/. % •/. feed 8 0 -9 080 -9 0n.r. bedding --5 5 -6 8an im a ls 5 -1 1 2 -1 2 m an u re n.r. OOiao1i

Odour Prevention and Control of Organic Sludge and Livestock Farming ◽

10.1201/9781482286311-136 ◽

1986 ◽

pp. 342-342

Keyword(s):

Relative Humidity ◽

Ventilation Rate ◽

Dust Concentration

Download Full-text

Deliquescence, efflorescence, and phase miscibility of mixed particles of ammonium sulfate and isoprene-derived secondary organic material

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-9903-2012 ◽

2012 ◽

Vol 12 (4) ◽

pp. 9903-9943 ◽

Cited By ~ 4

Author(s):

M. L. Smith ◽

A. K. Bertram ◽

S. T. Martin

Keyword(s):

Liquid Phase ◽

Relative Humidity ◽

Ammonium Sulfate ◽

Organic Material ◽

Important Variable ◽

Oxidation Products ◽

Liquid Separation ◽

Inorganic Particles ◽

Photo Oxidation ◽

Hygroscopic Properties

Abstract. The hygroscopic phase transitions of ammonium sulfate mixed with isoprene-derived secondary organic material were investigated in aerosol experiments. The organic material was produced by isoprene photo-oxidation at 40% relative humidity. The low volatility fraction of the photo-oxidation products condensed onto ammonium sulfate particles. The particle-phase organic material had oxygen-to-carbon ratios of 0.67 to 0.74 for mass concentrations of 20 to 30 μg m−3. The deliquescence, efflorescence, and phase miscibility of the mixed particles were investigated using a dual arm tandem differential mobility analyzer. The isoprene photo-oxidation products induced deviations in behavior relative to pure ammonium sulfate. Compared to an efflorescence relative humidity (ERH) of 30 to 35% for pure ammonium sulfate, efflorescence was eliminated for mixed aqueous particles having organic volume fractions ε of approximately 0.6 and greater. Compared to a deliquescence relative humidity (DRH) of 80% for pure ammonium sulfate, the DRH steadily decreased for increasing ε, approaching a DRH of 40% for ε of 0.9. Parameterizations of the DRH(ε) and ERH(ε) curves were as follows: DRH(ε)= Σ i ci,d xi valid for 0 ≤ ε ≤ 0.86 and ERH(ε)= Σ i ci,e xi valid for 0 ≤ ε ≤ 0.55 for the coefficients c0,d= 80.67, c0,e = 28.35, c1,d= −11.45, c1,e = −13.66, c2,d = 0, c2,e = 0, c3,d = 57.99, c3,e = −83.80, c4,d = −106.80, and c4,d = 0. The molecular description that is thermodynamically implied by these strongly sloped DRH(ε) and ERH(ε) curves is that the organic isoprene photo-oxidation products, the inorganic ammonium sulfate, and water form a miscible liquid phase even at low relative humidity. This phase miscibility is in contrast to the liquid-liquid separation that occurs for some other types of secondary organic material. These differences in liquid-liquid separation are consistent with a prediction recently presented in the literature that the bifurcation between liquid-liquid phase separation versus mixing depends on the oxygen-to-carbon ratio of the organic material. The conclusions are that the influence of secondary organic material on the hygroscopic properties of ammonium sulfate varies with organic composition and that the degree of oxygenation of the organic material, which is a measurable characteristic of complex organic materials, is an important variable influencing the hygroscopic properties of mixed organic-inorganic particles.

Download Full-text

Innovative composite on the basis of an aerogel mat with an epoxy resin modified with PET waste and PCM

E3S Web of Conferences ◽

10.1051/e3sconf/20184400031 ◽

2018 ◽

Vol 44 ◽

pp. 00031 ◽

Cited By ~ 3

Author(s):

Bernardeta Dębska ◽

Lech Lichołai ◽

Jerzy Szyszka

Keyword(s):

Epoxy Resin ◽

Thermal Insulation ◽

Thermal Capacity ◽

Mineral Wool ◽

Insulation Material ◽

Composite Sandwich ◽

Poly Ethylene Terephthalate ◽

Large Heat ◽

Poly Ethylene ◽

Encapsulated Phase Change Material

The article presents a patent proposition of a composite – sandwich panel made of aerogel mat and a composition of encapsulated phase-change material PCM and epoxy resin modified by glycolysis based on poly(ethylene terephthalate) waste. A multifunctional thermal insulation material with a large heat capacity was obtained. This ability makes it possible to limit the temperature fluctuation in the space encased with the composite. In addition, thanks to the use of aerogel mat, which is characterized by much higher thermal insulation than commonly available materials, it is possible to achieve the assumed thermal resistance using more than two times lower thickness of insulation. The combination of aerogel and resin-PCM makes it possible to give the material virtually any shape. After the hardening process is completed, it has incomparably greater tensile, bending and compression strengths than Styrofoam and mineral wool. These features predispose it for use in situations where high thermal insulation is required while maintaining a low thickness of insulation material and a large thermal capacity of the housing material is indicated, e.g. thin divisions used in passive buildings, window joinery elements, engine compartments and cabin components in vehicles, household appliances etc.

Download Full-text

Unused Plant Waste and Thermal Insulation Composition Boards on their Basis

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.887.480 ◽

2021 ◽

Vol 887 ◽

pp. 480-486

Author(s):

T.N. Vachnina ◽

I.V. Susoeva ◽

A.A. Titunin ◽

S.V. Tsybakin

Keyword(s):

Thermal Conductivity ◽

Thermal Insulation ◽

Wood Fiber ◽

Mineral Wool ◽

Wood Waste ◽

Insulation Material ◽

Plant Fibers ◽

Coefficient Of Thermal Conductivity ◽

Plant Waste ◽

Technology Of Production

Many plant wastes are not currently used in production, they are disposed of in landfills or incinerated. The aim of this study is to develop a composite thermal insulation material from unused spinning waste of flax and cotton fibers and soft wood waste. Samples of thermal insulation materials from plant waste were made by drying using the technology of production of soft wood fiber boards. For composite board defined physico-mechanical characteristics and thermal conductivity. The experiment was carried out according to a second-order plan, regression models of the dependences of the material indicators on the proportion of the binder additive, drying temperature and the proportion of wood waste additives were developed. The study showed that composites from unused spinning waste of plant fibers and soft wood waste have the necessary strength under static bending, the swelling in thickness after staying in water is much lower in comparison with the performance of boards from other plant fillers. The coefficient of thermal conductivity of the boards is comparable with the indicator for mineral wool boards.

Download Full-text

Hydrodynamic Modeling of Mineral Wool Fiber Suspensions in a Two-Dimensional Flow

Volume 5: Fuel Cycle and High and Low Level Waste Management and Decommissioning; Computational Fluid Dynamics (CFD), Neutronics Methods and Coupled Codes; Instrumentation and Control ◽

10.1115/icone17-75308 ◽

2009 ◽

Author(s):

Gregory M. Cartland Glover ◽

Alexander Grahn ◽

Eckhard Krepper ◽

Frank-Peter Weiss ◽

So¨ren Alt ◽

...

Keyword(s):

Numerical Models ◽

Mineral Wool ◽

Wool Fiber ◽

Turbulent Dispersion ◽

Insulation Material ◽

Fiber Suspensions ◽

Loss Of Coolant Accident ◽

Wool Fibers ◽

Two Dimensional Flow ◽

Mineral Wool Fiber

A consequence of a loss of coolant accident is that the local insulation material is damaged and maybe transported to the containment sump where it can penetrate and/or block the sump strainers. An experimental and theoretical study, which examines the transport of mineral wool fibers via single and multi-effect experiments is being performed. This paper focuses on the experiments and simulations performed for validation of numerical models of sedimentation and resuspension of mineral wool fiber agglomerates in a racetrack type channel. Three velocity conditions are used to test the response of two dispersed phase fiber agglomerates to two drag correlations and to two turbulent dispersion coefficients. The Eulerian multiphase flow model is applied with either one or two dispersed phases.

Download Full-text