P12
INVESTMENT IN PRE-INSULATED MATERIALS There are more aspects to take into consideration when choosing pre-insulated pipe systems. Which pre-insulated pipe system you choose has a large influence on other elements in the Total Cost of Ownership analysis, such as the contractor costs of establishing a district heating system (welding, handling pipes, casing joint work, excavation/backfilling, asphalt etc.), as well as the heat loss costs. • Is it a TwinPipe or a single pipe system you want to establish? • Are flexible pipes used for minor dimensions? • Are mastic-sealed shrink joints or weld joints used? • Which surveillance system is chosen to ensure that damages, if any, are detected in due time? • Which insulation series is chosen? • How is the static design of the system made and how are the movements absorbed in the system? When choosing products for a district heating network, you must demand that the materials and product properties ensure that you get the system service life you expect. The European standards EN13941, EN253, EN448, EN488, EN489, EN14419, EN15632, EN15698 define the minimum requirements to components, system and design to be complied with, in order to obtain a minimum service life for the district heating system of 30 years, provided the continuous operating temperature is 120°C, and the peak load temperature for individual periods are up to 140°C. On average, the sum of these peak load temperatures must not exceed 300 h per year. Most energy companies have a considerably lower load on the district heating system as regards temperature, load cycles, pressure etc. than prescribed in the European standards, and the service life is therefore expected to be higher than 30 years – up to 50 years.. TWINPIPE VERSUS SINGLE PIPE This is an essential choice, as it influences the contractor costs (investment) and the heat loss costs. Today TwinPipe systems up to DN250 are available.
In addition, the costs of casing joint work will typically be lower, because the number of casing joints is halved, but the dimension of the casing joints is bigger. When using TwinPipe systems, the heat loss will be considerably lower than that of a single pipe in similar dimension, what appears from below figure, in which the heat loss in kW is stated for 1,000 trench meters DN50 in different systems.
RIGID STEEL PIPE SYSTEM OR FLEXIBLE SYSTEMS It must be assessed whether it is advantageous to establish the minor dimensions with flexible systems in coils or not. There are flexible systems with different service pipes like Alupex, steel, copper, and PEX, which can be used dependent on temperature, pressure, and dimension.
The contractor costs of excavation/backfilling, and handling, and joining pipes are typically lower for flexible pipe systems.
The exercise is to compare this to the difference in investment in the pre-insulated pipe materials and the difference in heat loss costs.
CASING JOINT SYSTEM TO CHOOSE
Historically, statistics show that damages in a system typically occur at casing joints, and that the majority is due to faulty installation.
By using TwinPipes the contractor costs for excavation/ backfilling can be reduced, compared to single pipes due to a smaller trench profile.'
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