The project develops a design complex for a district heating system, which, by using new technologies, materials and operating modes, will be able to lower total costs by so much that tomorrow’s low-energy buildings can be supplied on profitable terms. The project develops prototypes of new main components, and the product will be demonstrated in practice.
Project description
The objective of the project is to develop a design concept for future district heating systems using new technology, materials and operation strategies to reduce total costs and to create a platform for district heating in low energy buildings in Denmark as well as internationally. The project basis is very low district heating temperatures and reduction of supply pipe peak power by equalization of the heat load during the day. To bring the design concept into operation prototypes of supply pipes and consumer substations are developed. The whole concept is demonstrated in a specific development area
Results
The project describes a design concept for district heating supply of low energy houses based on 24 hour equalizing of load and very low district heating flow temperatures. District heatingis a very flexible system in terms of utilizing waste heat from CHP-plants, refuse incineration and industrial processes as well ad renewable enregy sources in an energy efficient manner. However, in relation to district heating for low energy houses there are some challenges according to investment costs and costs related to heat loss from distribution network. The objective of the project is to develop a design concept that will reduce these costs and be a 'de-facto' standard of district heating to low energy houses. The design concept is based on a new type of comsumer station with a domestic hot water plate heat exchanger connected to a tank on the district heating primary side. To specify design and operating parameters a simulation model of the consumer station was developed in TRNSYS. Different parameters were investigated e.g. tank size (60-200 liter) and charge flow (120-14 kg/h). An area of 92 single family houses classified as 'class 1' (42.6 kWh/m2) according th the Danish Building Regulation was chosen as reference area. Hydraulic and thermal analysis in the calculation tool TERMIS were used to lay out the distribution network based on pre-insulated twin-pipes (supply and return in same casing pipe) with low-lambda PUR insulation and diffusion barrier. The design concept is compared with 3 other types of district heating systems. For a traditional system with single pipes and high district heating temperatures, the heat loss of the distribution network is calculated to 36%. In comparison, the distribution loss of the design concept can be as low as 12%. the total investment costs are almost equal for the 4 systems. In the new design concept, the cost of distribution network is reduced due to the use of smaller dimensions and twin-pipes. Though, the consumer station is more expensive. A socio-economic calculation of the design concept and an alternative solution with individual heat pumps shows that district heating is a competitive solution. A prototype of the consumer station is built and relevant operating characteristics have been tested. Furthermore a prototype of a flexible twin pipe in very small dimensions 14/14/110 mm (other diameter of flow pipe/return pipe/casing pipe) was produced and the heat conductivity was assessed by measurements to 0.022-0.024 W/(mK) which is in correspondence with the expectations and the values used in the analysis. Finally 2 demonstraiton areas have been appointed for the next phase of the project.
