Svend Svendsen

Energy performance of glazings and windows

The purpose of the work is to make it possible to compare the energy performance of different glazings or windows in an easy way. The energy performance is expressed by the net energy gain, which is given as the solar gain minus the heat loss. The net energy gain from glazings and windows both depend on the thermal transmittance (the U-value) and the total solar energy transmittance (the g-value). This fact makes it difficult to choose the glazings or windows with respect to energy performance in a given case. To compare different glazings or windows in an easy way, diagrams have been produced which give the net energy gain based on the orientation, the tilt, the U-value and the g-value of the glazings or windows. In addition, a single diagram showing the net energy gain in a one-family house has been produced which takes into account the orientation of the windows in the building. This makes it possible to evaluate the energy performance of different glazings or windows for a one-family house using a single diagram. The diagrams give an easy way of comparing different glazings or windows so the best solution in a given case can be chosen. In addition, the diagram showing the net energy gain in a one-family house is used in the Danish Energy Labelling and Rating system for classification of glazings.

Solar collector with monolithic silica aerogel

A solar collector with monolithic silica aerogel insulation was designed. Prototypes with an area of 1.4 m2 were tested with satisfactory results. The collector contains aerogel tiles at the top, back and edge of the absorber. The collector box, which is reduced to a frame with glass on both sides, is airtight. The aerogel is evacuated to a pressure below 100 mbar. In order to optimize and evaluate the collector design, a model of the efficiency of the collector was used to perform a parametric study. The study indicated that the thickness of the aerogel should be 20 mm or less. In a solar heating system used for district heating with a constant load temperature of 80°C, the performance of the aerogel collector was twice as good as that of commercial high temperature flat plate collectors.

WinSim: A simple simulation program for evaluating the influence of windows on heating demand and risk of overheating

A two-node model of a room has been implemented in a computer program, WinSim, developed for evaluation of thermal performance of windows in new buildings and in case of retrofitting. The program calculates the annual heating demand and the number of hours with indoor temperatures higher than a user defined limit. WinSim is characterised by the limited amount of required input data. Guidelines for calculation of the effective thermal capacity of the room are given, and results obtained with WinSim have been compared to results from an advanced building simulation program. Good agreement has been found between the two programs with respect to calculated annual heating demand and energy savings due to window exchange, and also the calculated number of hours with overtemperature is similar. Based on the limited examples used for the comparison, it can be concluded that WinSim is well suited for a quick but realistic evaluation of thermal performance of windows.

Investigation of interior post-insulated masonry walls with wooden beam ends

The preponderant number of multistorey buildings constructed in Denmark in the period between 1850 and 1930 were built with masonry walls incorporating wooden floor beams. Given the nature of this construction, it is supposed that significant energy savings could be achieved by simply insulating the facades of such buildings. To maintain the exterior appearance of the facade, the only possible means of installing the required insulation is placing it on the interior of the wall. However, the installation of insulation on the interior of the wall assembly reduces the overall drying potential of the wall, and this in turn may lead to increased freeze–thaw damages and moisture problems at the beam ends embedded in the masonry, when the masonry facade is subjected to driving rain. This article presents a method to investigate retrofit measures of interior-insulated masonry walls having wooden floor beams based on a failure mode and effect analysis combined with hygrothermal simulations. The method was first used to determine the potential for failure in retrofitted walls and their effects and causes, and thereafter, the expected hygrothermal performance of the retrofit measures was further investigated using both thermal and hygrothermal simulation software. The results show that the risk to incurring moisture problems at the wooden beam ends can be resolved by not insulating that portion of the wall directly above and below the floor division. Additionally, this proposed retrofit measure would reduce the heat loss of the original wall structure by half.

ENERGY LABELLING OF GLAZINGS AND WINDOWS IN DENMARK: CALCULATED AND MEASURED VALUES

Abstract The influence of windows on the energy consumption in buildings is well known and in order to encourage the development and the appropriate use of high performance glazings and windows in Denmark, an Energy Labelling and Rating system is being developed. During this work a need for establishing a common and well-defined method to characterise the performance of glazings and windows on the Danish market has been recognised. This paper gives a short description of the Danish energy labelling and rating system for glazings and windows, which was put into operation during 2000. Furthermore, the results of a comparison between measured and calculated thermal transmittance for five different window types are given. The calculations on the glazing part have been performed in five different programmes (WIS, WINDOW, VISION, CALUMEN and GLAD99). The calculations on the frame part have been performed in three different programmes (FRAME, THERM and WinIso). The comparison indicates that all investigated programmes are qualified for calculating energy labelling data for glazings and windows.

Changes in heat load profile of typical Danish multi-storey buildings when energy-renovated and supplied with low-temperature district heating

Denmark has a long-term objective of being free of fossil fuels by 2050, with the energy supply mix for buildings being fossil-free by 2035. Energy consumption for existing buildings needs to be decreased concurrent with the conversion from fossil-fuel supply to renewable-energy (RE) supply. When end-use savings are implemented in buildings concurrent with the application of low-temperature district heating (LTDH), the heat profiles of the buildings will change. Reducing peak loads is important, since this is the dimensioning foundation for future district heating systems. To avoid oversized RE-based capacity, a long-term perspective needs to be taken. Applying LTDH in existing buildings without changing the heating system implies reduced radiator performance, so it is of great importance that acceptable comfort temperatures can still be provided. The results indicate that it is possible to apply LTDH most of the year without compromising on thermal comfort if energy renovation is also implemented.

Modeling Transient Heat Transfer in Small-Size Twin Pipes for End-User Connections to Low-Energy District Heating Networks

The low-energy district heating concept has the potential of increasing the energy and exergy efficiencies of heat supply systems and of exploiting renewable energy, provided that technical solutions for its wide application can be developed and implemented. This article investigates the dynamic behavior of district heating branch pipes in low-temperature operation (supply temperature 50–55°C and return temperature 20–25°C). We looked at state-of-the-art district heating branch pipes, suitable for the connection of a typical single-family house to a substation equipped with a heat exchanger for domestic hot water preparation. Experimental measurements of the supply temperature profiles at the outlet of the pipe, that is, at the inlet to the substation, were compared with detailed simulations based on the finite-volume (FV) method. A programming code was developed to model these profiles, and this was validated against experimental measurements and compared to the results of an analytical formula and the FV simulations. The model proved accurate, since it gives results that represent well the outlet temperature profiles measured in the experiments and calculated in the FV simulations, both where there was a step change of the inlet temperature and where there was a sinusoidal inlet temperature profile. The model could be used for the development of improved substation concepts and enhanced control strategies.

The effect of different weather data sets and their resolution on climate-based daylight modelling

Climate-based daylight modelling is based on the available weather data, which means that the weather data used as input to the daylight simulations are of great importance. In this paper, the effect on the outcome of the daylight simulations of using one weather data file rather than another for the same location was investigated. Furthermore, the effect of using weather data sets with an hourly resolution compared to a one-minute resolution was investigated. The results showed that the lighting dependencies varied by up to 2% depending on the chosen weather data file and indoor illuminance threshold. The energy consumption for artificial lighting was underestimated when simulating with time steps of hourly means compared to one-minute resolution. The findings from this comparison show that the dynamic, short-term effects of the weather have a surprisingly small impact on the simulation outcome.

Illuminance Level in the Urban Fabric and in the Room

The decisions made on the urban planning level could influence the building design at later stages. Many studies have shown that the utilisation of daylight in buildings would result in significant savings in electricity consumption for lighting, while creating a higher quality indoor environment. The surroundings of a building have a great influence on the indoor environment of that building. A major factor is the shading that the surrounding buildings could provide, blocking and diminishing the available amount of daylight in nearby buildings. This paper reports a study that combine the effect of the exterior illuminance levels on façades with the interior illuminance levels on the working plane. The paper also explains an easy to use tool (EvUrban-plan) developed by the authors, which was applied to their findings in the early stages of urban planning to ensure daylight optimisation in the buildings.

Alternative solutions for inhibiting Legionella in domestic hot water systems based on low-temperature district heating

District heating is a cost-effective way of providing heat to high heat density areas. Low-temperature district heating (LTDH) is a promising way to make district heating more energy-efficient and adaptable to well-insulated buildings with low heating demand in the future. However, one concern is the multiplication of Legionella due to insufficient temperature elevation with low-temperature supply. The aim of this study was to find optimal solutions to this dilemma for specific situations. The solutions were of two types: alternative system designs and various methods of sterilization. The alternative design approach can eliminate the risk factors of Legionella by local temperature boosting and restricting system volume. Decentralized substations, micro heat pumps, electric heating elements and electric heat tracing are all investigated as alternative designs. With regard to sterilization methods, thermal treatment, ionization, chlorine, chlorine dioxide, ultraviolet light, photocatalysis and filtration are discussed as the most frequently used methods in hot water systems. The characteristics, efficacy and operation methods of LTDH using the solutions investigated are documented and compared. Finally, recommendations are given for their use in practice. Practical application : The methods for inhibiting Legionella should fit into applicable situations according to their characteristics. This study aims to recommend optimum solutions for inhibiting Legionella in LTDH scenarios, and includes a comprehensive overview of their efficiency, installation, operation and costs, so as to give adequate information for selecting appropriate solutions. In addition to sterilization methods, alternative system design implemented with new technologies can also help prevent Legionella in hot water systems. They have the additional benefit of reducing the heat loss of the hot water system. The alternative design solutions both enrich our options for water sanitation and improve the energy efficiency of our energy systems.