Strategies to Manage Heat Losses - Technique and Economy
Description of the project
The main share of operational costs in heat distribution are the inevitable heat losses in networks. As total costs of heat losses depend on a broad spectrum of parameters it is a complex task in district heating engineering to optimise economy in relation to these influences.
Two extreme examples may illustrate the situation:
- In DH areas with scattered small houses and with low heat demand a reliable supply of the DH system needs well insulated pipelines.
- In big systems with main lines of big diameters and operated at moderate temperatures at least the return lines should be constructed without any insulation due to pure economic optimisation.
Engineering practice has to find an optimal balance between these extremes according to boundary conditions. - A technically independent demand is the protection of environment. In today's practice conceptions on heat losses are influenced by a good portion of experience, custom and intuition. A better knowledge of the technical and economic interdependencies would help to make network design on a more reliable basis.
The main target of the project will be to make cost relations transparent and to number standard cost situations.
Costs of measures for lowering heat losses will be calculated for real situations. Results will be given in handy values [$/MWh and €/MWh]. Costs will be calculated for defined parameters and will be presented in form of tables and diagrams.
Summary of the final report of the project
Heating utilities should review their concepts for insulating their district-heating lines at regular intervals. Not only should the volume of investment costs be taken into consideration, but also the expected operating expenditures need to be included when conducting required cost-efficiency analyses. After all, heat losses and thus the selected insulation concept substantially influence accruing operating costs. When calculating operating expenditures, heating utilities should regularly review whether the general technical and/or economic setting has/have changed compared to the last computation process. Redetermining them on a five-year basis should be deemed sufficient.
Detailed cost-efficiency calculations should be made in consideration of the deteriorating insulation quality of the pipelines as a result of the ageing PUR foam. If such ageing process is not taken into account, the actual heat losses may be underestimated by up to 20%. Excellent insulation qualities stand for the distinguishing feature of twin pipes being a special range of preinsulated plastic jacket pipelines. By contrast, the method of laying preinsulated plastic jacket pipelines on top of one another does not have a substantial impact on the occurrence of heat losses.
Most heat losses occur on pipes of small nominal diameters. Even though Insulation Series 1 is today still considered the standard series - in particular in Germany -, there are very well application cases in which insulation of a higher quality proves to be more cost-efficient. Higher-quality insulation is recommended for projects marked by low-cost pipeline construction, in case of high heating costs, and a high temperature difference between the medium and its surroundings.
The related marginal costs were calculated for typical application cases to determine when a higher or lower insulation series will lead to cost benefits. As a minor deviation from the calculated optimal insulation costs only results in relatively low additional costs, it is recommended to change over to the next higher insulation series prior to reaching the relevant level of marginal costs, since it is expected that heating costs will rise in the future due to an ever-increasing shortage of resources. For instance, changing over to the next higher insulation series may be implemented when the relevant marginal costs are underrun by approx. 10% to 20%.
Apart from upgrading the insulation series, the application of enhanced insulation materials marked by lower heat conductivity may help improve insulation efficiency. However, when opting for this approach, it is indispensable that the saved heat loss costs exceed the higher material expenditures.
The closing discussion focuses on how heat suppliers normally deal with heat losses. For the purpose of assessing the state of their own grids, heating utilities are recommended to regularly compare themselves with other district-heating networks on the basis of benchmarks. To provide for - to the extent possible - realistic comparisons of district-heating grids on the basis of statistical data or benchmarks from other enterprises, further ratios, i.e. not just the usual loss factor should be taken into account, as well. The last part revolves around outlining and evaluating measures aiming at reducing heat losses occurring within installed district-heating networks.
MVV Energie AG
F. Schmitt, Dr.-Ing.
H.-W. Hoffmann, Dipl.-Ing.
T. Göhler, Dipl.-Ing.
MVV Energie AG, Germany
Chalmers University of Technology, Göteborg, Sweden