Design criteria Standard district heating systems Standard district heating systems are designed in accordance with the specifications in EN 13941.
The right product choice It is crucial to choose components that can withstand the large movements in the solar district heating system.
The system In the solar panel field, single pipes must always be used.
The system is designed for a minimum service life of 30 years with the following number of load cycles:
Pre-insulated components Fundamentally, branches and bends must be carried out with pre-insulated components. T-joint or bend joint solutions are not applicable. Casing joints Experience has taught that most shrink joint solutions or solutions with shrink wrap/collars cannot withstand the large number of temperature load cycles. They are simply dislocated from the position, where they are installed due to the friction between the casing joint and the surrounding material. Weld joint solutions should therefore always be used for solar district heating projects, so the PE casing and PE casing joint are welded together. Standpipes for solar panel connection Around the standpipes, there must always be room for free movement. This is ensured by inserting the pipe in an empty conductor pipe, which allows full movement in the temperature range, which the system operates in. See Fig. 7 as regards the conductor pipe solution.
Transmission pipelines Distribution pipelines House connections
A full temperature load cycle appears from Fig. 6, where 1 is the time and 2 the temperature cycle in relation to the mean temperature.
Fig. 6 - Full temperature cycle
Large-scale solar district heating systems In solar district heating projects, the extent of temperature load cycles is much larger, which is decisive for the system design.
For the hot pipeline it is not unusual to apply the following conditions:
• Design temperature: 10–110°C (cyclic load, 1 cycle/day) • Short-term temperature peak: 110-150°C max. 5 hours twice a year • Full load cycles during 30 years’ service life: 10950 cycles. • The cold pipeline will naturally have a considerably lower number of full-temperature load cycles, but still more than in a normal district heating system. • The solar district heating pipe system must be designed to cope with the vast number of full load cycles – both as regards handling the movement itself and the fatigue in the steel. • In general, directional changes in solar district heating systems should be made as 90° bends.
Fig. 7 - Principle for vertical introduction to the solar panel
Pipes with branches to the standpipes It is advantageous to make pipes with branches to the standpipes, designed for the specific project. Indoor manufacturing of such pipes ensures the optimum conditions for making special solutions of high quality.
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