Carl-Eric Hagentoft

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).

Heat loss to the ground from a building—I. General theory

Abstract The heat flow to the ground from a building depends on the complicated thermal process in the ground. An extensive analysis of the processes involved is presented in this series of papers. A main goal is to obtain sufficiently accurate, and as simple as possible, formulae for the heat flow to be used for design purposes. This first papers presents the general theory that is used. The main difficulties in obtaining manageable formulae concern the three-dimensionality of the thermal problem, the strong temporal variability of the outdoor temperature, and the large number of parameters involved in describing foundation geometry, thermal insulation and so on. Superposition and dimensional analysis are used to meet these difficulties. Basic components of the thermal process are the steady-state solution, the solutions for a periodic outdoor temperature and a unit step of the outdoor temperature. The dimensional analysis leads to a steady-state heat loss factor, corresponding factors for the periodic solution and the temperature step. The penetration range of the two transient processes is studied in detail. It is shown that these normally involve only a region around the periphery. So-called edge solutions, which are two-dimensional and depend on the parameters near the periphery only, may be used.

HEAT LOSSES AND TEMPERATURE IN THE GROUND UNDER A BUILDING WITH AND WITHOUT GROUND WATER FLOW-II. FINITE GROUND WATER FLOW RATE

Abstract Analytical formulae are presented for the temperature and the heat loss for the case of a finite ground water flow rate. Both uninsulated and insulated ground slabs are studied. The formulae account for different thermal conductivities above and below the ground water table.

Temperature under a house with variable insulation

Abstract A calculation method of high accuracy is presented for the two-dimensional steady-state ground temperature under a long house. The thermal insulation thickness is arbitrarily variable along the ground surface. Explicit, iterative formulas with rapid convergency are given. The heat loss from the house and the ground surface temperature are given for three types of insulations. The method is available as a PC-program.

Moisture Conditions in a North Facing Wall with Cellulose Loose Fill Insulation: Constructions with and without Vapor Retarder and Air Leakage

This paper presents calculated moisture conditions of a wall exposed to a climate equivalent to the North of Sweden. A north facing timber wall with a brick facade and cellulose loose fill thermal insulation is studied both with and without vapor retarder and air leakage. If the vapor retarder is eliminated from the construction, the moisture levels will increase to unacceptable high values. The con struction becomes sensitive to the choice of facing materials and the indoor moisture supply. Air leakage carrying moist air into the construction leads to unacceptably high values even for moderate indoor moisture supplies.

Heat loss to the ground from a building—II. Slab on the ground

Abstract The heat flow to the ground from a rectangular slab with an even thermal insulation is analysed. The steady-state heat loss factor is given in complete diagrams for any ratio between length and width of the slab and for any constant insulation of slab and ground surface. A two-dimensional edge approximation for time-dependent heat loss at the perimeter of the slab is introduced. New analytical solutions for the edge heat loss due to periodically variable outdoor temperature or a step change in the outdoor temperature are presented. The effect on the heat loss due to different variations of the outdoor temperature is easily analyzed with these solutions. For example, daily periodic variations can certainly be neglected. Based on this, simple design rules for the heat loss during a heating season and the peak effect are given.

Steady-state heat loss for an edge-insulated slab: Part I

Analytical solutions for the steady-state ground heat loss for buildings with only perimeter insulations are derived. Interior and exterior edge insulations are treated in detail. A number of asymptotic solutions are presented. The two-dimensional case considered, accounts for adiabatic edge insulations with varying tilting angle and width. As a special case the non-insulated ground floor, with the wall area as the only protecting zone, can be handled. The optimal combination of tilting angle and insulation width is presented.

An Example of Application of Limit State Approach for Reliability Analysis of Moisture Performance of a Building Component

Application of limit state approach for the reliability analysis of building performance in the context of building physics characteristics is presented. Analysis of the probability of surface condensation on windows carried out on the basis of statistical description of the climatic parameters and the moisture production is shown as an example of application of this technique for reliability analysis of moisture performance of a building component. The first-order reliability method (FORM) is employed to estimate the probability of performance failure. The results of probabilistic approximations are verified with the help of statistical analysis of the results obtained from deterministic simulations.

Periodic heat loss for an edge insulated slab: Part II: A mixed boundary value problem

This paper presents an analytical method of determining the periodic heat loss for an uninsulated slab on the ground. General integral equations are derived for the mixed boundary value problem of a half-plane, with prescribed periodic temperature on both sides of a totally insulated segment.

A Numerical Study of Effect of Natural Convection on Thermal Properties of Horizontal Oriented Porous Insulation

This paper deals with numerical computations carried out to predict the effect of natural convection on the thermal performance of porous material. The effect of natural convection in a horizontal porous layer on heat transfer will be discussed. The study of this configuration is essential to understanding the performance of insulation of the type commonly used in roofs and attics. The influence of natural convection on the global heat transfer rate for mineral wool, loose-fill and insulation made of small and large polystyrene balls was studied. The results are presented in terms of dimensionless Nusselt and Rayleigh numbers as a function of temperature difference across the insulation. The temperature distribution across the insulation are also plotted.