• Energy Research

The International Building Physics Toolbox (IBPT) is a software library developed originally for heat, air and moisture system analysis in building physics. The toolbox is constructed as a modular structure of standard building elements, using the graphical programming language Simulink. To enable development of the toolbox, a common modelling platform is defined: a set of unique communication signals, material database and documentation protocol. The IBPT is an open source and available on the Internet. Any user can utilize, expand and develop the contents of the toolbox. This paper presents structure and essence of the library. Potential applications of the toolbox are illustrated through examples.

Many old listed buildings have an unsatisfactory thermal performance compared to the standards of today. The listing often limits the position and necessary thickness of an added insulation layer in the building envelope. Vacuum insulation panels (VIP) present unprecedented possibilities to reduce the required thickness of the insulation layer. The aim of this study is to explore the performance of VIP in the retrofitting of listed buildings. The goal is to improve the thermal transmittance and moisture performance of the wall and the thermal comfort for the occupants. Hygrothermal sensors were installed in the wall of a listed building insulated with VIP on the exterior. Sensors were also installed in a neighboring (non-retrofitted) wall as reference. Through a comparative analysis of the measured data it was concluded that the hygrothermal performance of the retrofitted wall was substantially better than of the reference wall. The measurement results were also compared to hygrothermal simulations to quantify the improvements in the thermal transmittance and moisture performance. A deviation was found between the measured and simulated relative humidity in the wall which was explained by vertical air leakage paths in the wall.

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.

AbstractA variable U-value would be beneficial for a buildings thermal performance. One way to switch the U-value of a wall, insulated with nano-porous material, is to change the internal pressure of the insulation This paper present thermal conductivity measurements showing a possible variation around of 3 times for a fumed silica and less than 2 times for an aerogel blanket when the pressure was varied between 1 and 100kPa. The variation factor of 3 was used in building energy simulation of a Swedish office showing that a U-value which can be varied within that range can give a significant reduction energy demand. Especially when energy used for cooling is weighted as worse than energy used for heating.

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.

Old listed buildings need to be retrofitted to reduce the energy use for heating. The possible thickness of the insulation layer is limited by the existing construction. Vacuum insulation panels (VIPs) require less thickness than conventional insulation materials to reach the same thermal resistance. Therefore, it could be more appropriate to use VIPs than conventional insulation materials when retrofitting the building envelope of listed buildings. The aim of this study is to investigate the hygrothermal performance of a brick wall with wooden beam ends after it was insulated on the interior with VIPs. One- and two-dimensional hygrothermal numerical simulations were used to design a laboratory study in a large-scale building envelope climate simulator. The wall was exposed to driving rain on the exterior surface and a temperature gradient. The relative humidity in the wall increased substantially when exposed to driving rain. The moisture content in the wooden beams also increased. There was no significant difference between the relative humidity in the wooden beam ends for the cases with and without VIPs. However, it was found that the reduced temperature in the brick after the VIPs were added led to a higher relative humidity in the wooden beams. It was also clear that when VIPs were added to the interior, the drying capacity to that side of the wall was substantially reduced. Finally, calculations of the U-value showed a large potential to reduce the energy use using VIPs on the interior of brick walls.

© 2015 Elsevier Ltd. In Swedish district heating networks, around 10% of the supplied thermal energy is lost in the distribution system. One solution to decrease the losses is to use hybrid insulation district heating pipes, a concept where the innermost part of the thermal insulation consists of vacuum insulation panels, held in place by polyurethane foam. One problem with vacuum insulation panels are their sensitivity to high temperatures. This paper presents field measurements on a hybrid insulation district heating pipe where the temperatures have been measured continuously at various positions of a pipe section. The measurements show consistency and a large difference between hybrid insulation parts and reference parts without vacuum insulation panels. A superposition model has been used to calculate the temperature in a point and compare it to the measurement. The results are compared to the same calculation on the results from finite element simulations. The results show clearly that the vacuum panels in the pipes have not collapsed. A slow deterioration of the panels is harder to find with this model. Changes in the system, such as a return temperature which decreases over time, can give a larger impact, concealing the change in the panel performance.

Abstract General formulae are presented by which the heat loss and the temperature in the ground can be determined for the case of infinite ground water flow rate. Both uninsulated and insulated ground slabs are studied. Explicit analytical formulae for the temperature and the heat loss are given for several cases. It is shown that the relative increase due to ground water flow is smaller for insulated slabs than for uninsulated slabs.

A model based predictive control method is applied in order to determine the optimal supply fluid temperature in the case of concrete embedded water-based floor heating in low energy residential buildings The aim of the control is to keep the indoor temperature within a defined comfort interval The forthcoming supply fluid temperature is obtained through a numerical optimisation based on a prediction of the upcoming heat demand The elementary response function which is the basis for the method is obtained from a numerical control volume model and as an alternative from a simplified 2-node lumped model The accuracy of the results obtained from the simplified model is surprisingly good in comparison to the detailed numerical model The control method is applied for a single room for which a perfect prognosis of the heat demand exists The results show a fairly steady optimised supply fluid temperature.