Gudni Jóhannesson

Accuracy of Energy Analysis of Buildings: A Comparison of a Monthly Energy Balance Method and Simulation Methods in Calculating the Energy Consumption and the Effect of Thermal Mass

The purpose of this article is to analyze the effects of thermal mass on heating and cooling energy in Nordic climate and for modern, well-insulated Nordic buildings. The effect of thermal mass is analyzed by calculations made by seven researchers and by seven different calculation programs. Six of these programs are simulation programs (Consolis Energy, IDA-ICE, SciaQPro, TASE, VIP, VTT House model) and one monthly energy balance method (maxit energy) based on the standard EN 832, which is the predecessor of ISO DIS 13790. It is purpose to evaluate the reliability of the monthly energy calculation method and especially its gain utilization factor compared with the simulation programs. In addition some sensitivity analysis concerning e.g., the effects of the size and the orientation of windows and the weather data on the energy consumption are made.The results show that the simplified standard methods of EN 832 and of ISO DIS 13790 generally give accurate results in calculating the annual heating energy, e.g., in the context of energy design and energy certification. However, the gain utilization factor of these standards is too low for very light buildings having no massive surfaces resulting in a too high energy consumption. The study shows, that the differences in input data cause often greater differences in calculation results than the differences between various calculation and simulation methods.

Dynamic calculation of thermal bridges

Abstract Thermal bridges play a relatively large role in heat loss with increasing thermal insulation level of building envelope. In this paper, multi-dimensional dynamic models are set up to predict the thermal performances of thermal bridges using a frequency response method. The thermal bridge is divided into finite meshes where the nodal temperatures are expressed in the form of complex quantities that are related to amplitude and phase lag of the variations of the temperature. By considering the heat balance for the nodes, the real and imaginary parts of the nodal temperatures can be solved simultaneously. A PC computer program has been developed to calculate the dynamic responses of temperatures and heat flows within thermal bridges, and has been utilized for thermal bridges such as a light weight metal stud wall, a heavy weight wall—intermediate floor junction and a wall foundation with ground coupling.

Air gaps in building construction avoiding dampness and mould

Purpose - Water damage is a severe problem in modern construction, causing economic loss and health implications. The patented Air Gap Method, which is a slight modification of the common infill wa ...

Sampling and Analysis of Natural Isotopes in Moisture Transport from Porous Materials: Applications to Capillary Suction:

Apart from the most common 1H and 16O we have the sister isotopes: deuterium D and 18O in water. Isotope fractionation (the change in its concentration) occurs in any thermodynamic reaction. The isotopic composition serves as a distinct mark for each water sample. To carry out the isotope analysis of pore water, which may be used to reveal the source of excessive water in building elements, firstly one has to extrude water from voids. For this we tested three different methods of retrieving water from the porous material: squeezing and evaporation - the direct methods, dilution - the indirect method. The influence of capillary suction on the hydrogen and oxygen isotopes abundance ratio was also analysed. Materials whose substantial part of voids are gel pores (cementitious materials) act as a membrane during isotope transport separating lighter from heavier isotopes and therefore cause the fractionation of isotopes. The results of performed experiments indicate that moisture transport (capillary suction) has an influence on the isotopic composition of water. Therefore the isotope analysis can be useful in the investigation of moisture behaviour of porous building materials.

Discussion on surface condensation in free convection cooling baffles

Abstract Cooling with free convection cooling baffles has attracted increasing interest in Sweden in recent years. Risk of surface condensation is a practical restriction. Consequently, it is required that the inlet water temperature of a cooling baffle must be higher that a room air dew-point temperature, and this is at the expense of lessening the cooling capacity. In this paper, we discuss the surface condensation problem in the free convection cooling baffle system, simulate its operation under different conditions and introduce a new method to prevent dripping of condensate water using a highly absorptive paint.