John Grunewald

Assessment method of numerical prediction models for combined heat, air and moisture transfer in building components: benchmarks for one-dimensional cases

The standardised Glaser method for calculation, prediction and evaluation of moisture performance is considered as rarely applicable. The present state of knowledge, analytical as well as experimental, concerning heat, air and moisture demands updating of standards. This paper presents five numerical benchmark cases for the quality assessment of simulation models for one-dimensional heat, air and moisture (HAM) transfer. In one case, the analytical solution is known and excellent agreement between several solutions from different universities and institutes is obtained. In the remaining four cases, consensus solutions have been found, with good agreement between different HAM models. The work presented here is an outcome of the EU-initiated project for standardisation of HAM calculation methods (HAMSTAD WP2).

Coupled heat air and moisture transfer in building structures

Abstract Based on the energy, mass and linear momentum conservation laws as well as the entropy law, a coupled, partial, non-linear, differential equation system for the heat, air and moisture transfer in porous materials follows, and for the more-dimensional solution of it, a suitable algorithm including the simulation software has been developed. Its efficiency is demonstrated by a recent building structure—chuted concrete between fibre board with polystyrol-foam outside insulation-under the boundary conditions of the TRY Essen: hourly values of outdoor climate. As a result of the high built-in moisture, moisture damages (mould growing) in the base level (exterior wall/concrete plate over the basement garage) and inadmissible high heat losses caused by the moisture depending thermal conductivity and the additional enthalpy flows coupled to the moisture movement and phase changing are observed in the first years.

Towards an Engineering Model of Material Characteristics for Input to Ham Transport Simulations - Part 1: An Approach

Heat, Air and Moisture (HAM) modelling of building performance is a quite young research subject but the experimental determination of material properties is often based on classical methods. One should review the manner in which we define characteristic material parameters and there is a need to develop an approximation used to generate the required material functions for input to HAM-transport simulations. The paper presents such an approach, called an engineering model for hygrothermal material characterisation. The paper poses the question, how to arrive at input data that can be used for a model based on thermodynamically defined potentials (Only such a model allows introduction of new potential components (freezing depression, osmotic pressure, air pressure, overburden envelope pressure)) (e.g., Grunewald, J. (1997) and Grunewald, J. (1999)) and yet the respective functions used to describe changes in the material response as a function of the variables of state. Such functions should have a reasonable precision and goodness of fit while the number of measured points must be reduced to a minimum. Those measurements should be relatively easy to perform (i.e., they would not require determination of temporal and spatial profiles of moisture). This discussion paper highlights steps already taken (Part 1), and lists issues that need to be resolved before reaching this goal (Part 2).

Stochastic study of hygrothermal performance of a wall assembly—The influence of material properties and boundary coefficients

An accurate description of material properties and boundary conditions is the prerequisite to achieve reliable results of a hygrothermal performance simulation. However, the uncertainties widely exist in those input variables, e.g., due to the inhomogeneous nature of materials and discrepancies in material manufacturing and measurement processes, the material properties are subjected to considerable variation. Therefore, the simulation result may not be only a single value, but in a range of possibilities. In this article, a stochastic approach is developed and implemented by using uncertainty analysis which assesses the uncertainties of a models input variables on that of the output variables, and sensitivity analysis, which identifies the most influential input variables. The hygrothermal performance of one typical wall assembly in North America is studied by applying this approach, considering the uncertainties of material properties of each individual layer and the uncertainties of the interior and exterior boundary coefficients. The influence of wall orientation is also presented. The results show that the effect of a single input variable on an output variable is not constant but varies with time. The key variables that affect the results are also different over time.

On the Hysteresis in Moisture Storage and Conductivity Measured by the Instantaneous Profile Method

The relative humidity (or the capillary pressure) and volumetric water content can be determined at specific locations inside a porous medium by means of the proposed instantaneous profile method (IPM). The measurements are carried out with temperature and relative humidity (RH) sensors as well as with time domain reflectometry probes during the whole duration of the experiment. Thus, the IPM allows a transient measurement of the moisture retention characteristic. In addition, from the spatial and temporal distributions of moisture content and RH one may calculate the moisture conductivity as a function of moisture content and RH as well. The adsorption and successive desorption experiments presented in this article have been performed on calcium silicate (a capillary active material). The results show a hysteretic behavior that appears to depend on the nature of the process. The moisture conductivity as function of RH shows a significant hystereses; however, the moisture conductivity in relation to the moisture content appears to be non-hysteretic.

Application of clustering technique for definition of generic objects in a material database

In this article, generic objects are introduced into material databases of building simulation tools. A generic object has the common characteristics of one type of specific object and can represent specific ones in the simulation. The application of generic objects only requires some general design information; thus, it is convenient for the simulation users who do not have a detailed knowledge of building specification in the early design stage. First, the method to uncover the underlying cluster structure in the dataset is illustrated. Clustering of the objects depends on the adopted clustering variables and clustering procedure. Therefore, different clustering techniques are applied to agglomerate specific materials into different clusters, and the clustering solutions are compared for validation. Generic synthesis is then conducted to derive the generic material from each identified cluster. The approach on how to apply generic materials to fill in missing values of the incomplete material data is also described.

CHAMPS-Multizone—A combined heat, air, moisture and pollutant simulation environment for whole-building performance analysis

A computer simulation tool, named “CHAMPS-Multizone,” is introduced in this article for analyzing both energy and indoor air quality (IAQ) performance of buildings. The simulation model accounts for the dynamic effects of outdoor climate conditions (solar radiation, wind speed and direction, and contaminant concentrations), building materials and envelope system design, multi-zone air and contaminant flows in buildings, internal heat and pollutant sources, and operation of the building HVAC systems on the building performance. It enables combined analysis of building energy efficiency and indoor air quality. The model also has the ability to input building geometry data and HVAC system operation related information from software, such as SketchUp and DesignBuilder via IDF file format. A “bridge” to access static and dynamic building data stored in a “Virtual Building” database is also developed, allowing convenient input of initial and boundary conditions for the simulation and for comparisons between the predicted and measured results. This article summarizes the mathematical models, adopted assumptions, methods of implementation, and verification and validation results. The needs and challenges for further development are also discussed.

Evaluation of Discretized Transport Properties for Numerical Modelling of Heat and Moisture Transfer in Building Structures

Over the past decade, a large number of numerical models have been developed to predict heat and moisture transfer within building envelopes. In these models, the moisture transfer mechanism has been described and correlated by reference to the various transport phenomena and corresponding theories, viz. heat transfer and fluid flow. However, predicting the coupled heat and moisture performance of a building construction has never been a straightforward task, since a steady state situation hardly ever occurs and the transport properties (heat and moisture) of a material vary with moisture content and temperature. This paper discusses the transport phenomenon and the various numerical algorithms used in the discretization equations and how different algorithms affect the modelled results. Computer simulations have been conducted for different building materials and material combinations and comparisons have been made to evaluate the selection of discretized transport properties. Discrepancies in results are demonstrated between different mathematical interpolations, namely the Resistance(R) type formula and Linear(L)interpolation. Recommen-dations are given as guidance towards applying the most appropriate formulations for a given modelling scenario.

An integral building simulation method for evaluation of indoor climate applied to mold risk inside a library building

This article introduces recent advances in the development of a new multi-zone simulation model prototype for coupled heat, air, moisture, and pollutants transport in buildings. The enhanced capabilities of the model will be demonstrated by application to a reference test case that deals with mold risk inside a library building. Selected rooms of the library have been monitored by measurements and visual observations. Mold was found even on historical books. With the aid of numerical simulation, the complex phenomena that have led to this critical situation were investigated and can be better understood.

The Thermohygric Performance of Insulated Building Structures Under Conditions of Use

Based on the energy, mass and momentum conservation laws, a system of coupled non-linear transport equations including a suitable computer code has been developed to determine the temperature, moisture, ice, vapour pressure, air pressure fields and the heat, enthalpy, vapour, water and air flows in porous building materials and in building structures under conditions of use. The contribution demonstrates the thermohygric behaviour of a typical heavy concrete flat roof with a mineral wool insulation layer, the drying out process of an insulated light-weight wooden roof caused by a capillary-active vapour barrier, the moisture and temperature field in an air permeable building component, and the impact of a capillary-active inside insulation of a framework-house (exposed timber) being thermally renovated right now.