Charlotte Reidhav

Flexible district heating pipes made of a copper service pipe, semi-flexible polyurethane foam and a low density polyethylene (LDPE) casing are widely used today. The bendable quality of flexible district heating pipes allows them to be produced and used in long lengths – thereby resulting in fewer pipe joints and to overcome obstacles in the ground. As a result of the facilitated ground work, flexible pipes are often used when connecting detached houses to district heating systems. The distribution heat losses are considerable in these areas and there is at present no standard regulating the thermal properties of flexible pipes. The insulation capacity of polyurethane foam decreases over time due to diffusion of gases (air and blowing agents) into and out of the foam. The change in cell gas content over time was measured and thereby the decrease of insulation capacity could be calculated. The results show that the insulating performance of flexible pipes differs from that of straig...

The aim of this thesis is to describe sparse district heating conditions and explore how to improve them. Few sparse areas are heated by district heat, which reflects the economic competitiveness. A method that could be used by the district heating companies to identify the boundaries of profitable district heat is presented. Important key figures are identified when investigating the boundaries of competitive district heat. This method was identified using data gained from research on sparse areas in Goteborg, Sweden and demonstrates what to focus on in order to improve competitiveness. It is concluded that distribution heat losses must decrease in future connected sparse areas to be an efficient and competitive heating alternative. The insulation properties of flexible district heating pipes, widely used when connecting sparse areas, are an important issue when improving the energy efficiency. The long term insulation properties of flexible district heating pipes are experimentally investigated by studying the cell gas transport in semi-flexible polyurethane foams. The results show that the insulation properties are impaired more rapidly than for traditional straight pipes. The flexibility of the material is partly achieved at the cost of faster gas transport. An effective diffusion barrier hindering this gas transport is thus important. A new method to determine the temperature-dependent thermal conductivity of flexible district heating pipes is presented. The method is based on the fact that the temperature decline of hot water in a district heating pipe placed in cool water depends on the thermal conductivity of the polyurethane foam. The temperature decline of the water inside the service pipe is measured and modelled numerically. The difference between measured and calculated temperatures is used to determine the temperature-dependent thermal conductivity and the specific heat by fitting. The method is based on simple measurements of the temperature decline of the service pipe water, and it is applied on single and twin pipes. A single experiment gives the thermal conductivity for a large temperature span.

The thermal conductivity of the insulating polyurethane foam in district heating pipes is an important factor when improving the competitiveness of district heating, especially in areas of low heat density, where flexible district heating pipes are widely used. The standardised methods to measure the thermal conductivity of straight pipes are not applicable due to the small pipe dimensions and the fact that they are coiled. The paper presents a new transient method to determine the thermal conductivity, including the temperature dependence, for such district heating pipes. A coil of the flexible pipe is immersed into cold water (10°C). The temperature decline of hot water inside the service pipe (starting at 80ºC) is measured. The method is based on the fact that the temperature decline depends on the thermal conductivity of the insulation. The experimentally measured declining water temperatures give with rather simple theoretical expressions the thermal conductivity as function of...

The district heating sector is challenged in its traditional way of doing business by buildings increasingly more energy efficient (with low heat demand for space heating). This paper reports on work of mapping out such challenges connected to passive houses in Sweden. It should be noted that the conditions might be different in different geographical areas. To gain climate friendliness in the building sector a system perspective must be used both regarding energy and environmental issues. The levels of energy use in buildings in Sweden today and in the future are discussed together with marginal vs. average thinking regarding energy and heat production. From our findings we conclude that it is not necessarily so that electricity or natural gas should be the option of choice for hot water demand or peak loads that need to be externally covered also in energy efficient buildings. However, it will require active work by district heating companies to stay competitive. It will be increa...

Denna studie har tagit sitt avstamp i den for fjarrvarmebranschen nagot provocerande men anda viktiga fragestallningen: Har fjarrvarmen nagon roll i ett samhalle med energieffektiv bebyggelse? Studiens slutsats ar att fjarrvarme definitivt kan spela en fortsatt betydande roll i svensk energiforsorjning aven i framtiden, men att det kraver ett mer aktivt forhallningssatt hos branschen an vad som traditionellt varit fallet och en aktiv kunskapsuppbyggnad for utveckling av hallbara energisystem. Fjarrvarmebranschen star inte infor nagon omedelbar kris, men maste redan nu forbereda sig for nya marknadsforutsattningar i framtiden. Studien arbetar huvudsakligen med fyra omraden som beror fjarrvarme, som getts de vida benamningarna Fjarrvarmens roll, Energianvandningens niva, Energianvandningens fordelning och Nya varmeapplikationer. Rapporten utmynnar i ett antal fragestallningar och markanta kunskapsluckor som beror dessa fyra omradena. Fjarrvarme anvands huvudsakligen for att tacka varm...

District heating supplies heat and hot water to about 10% of the 1.6 million detached houses in Sweden. A future realistic market share of district heating is however 40% in such areas in Sweden according to previous studies. The expansion of district heating into another 600 thousand detached houses in Sweden would probably be accelerated if the profitability was increased for the district heating companies when supplying heat to such areas. Currently, the Swedish district heating industry focuses on reducing the investment costs for construction of distribution systems from the main pipes into the detached houses. This paper presents a model to be used for estimating the investment cost. Actual data was collected from 55 areas with 2500 detached houses district heated in Göteborg, Sweden. Multiple regression analysis was used to determine the model coefficients. The results explain some variations in the investment cost. The model shows that the pipe line layout is important since...

The standardized methods to measure the thermal conductivity of straight district heating pipes are not applicable on flexible district heating pipes. This paper presents a transient method determining the temperature dependent thermal conductivity of flexible twin pipes. A transient method to determine the temperaturedependent thermal conductivity of flexible single district heating pipes is presented in this paper. A flexible pipe coil is immersed into cold water. Hot water is distributed in the coil. The temperature decline of the coil water is measured and calculated. Minimizing the difference between the calculated and measured temperatures gives λ(T) of the flexible polyurethane foam. The method gives small errors.

The expansion of district heating into areas of low heat densities (heat sparse areas) constitutes a challenge due to the higher distribution costs. The profitability of sparse district heating has been analysed from actual investments in 74 areas with 3227 one-family houses connected to district heating between 2000 and 2004 in Göteborg, Sweden. The profitability was estimated from a probable