Полагането на тръби в земята по лесен начин
Local heat networks are more and more frequently implemented in new construction projects and existing structures. Although the materials and technologies are known, this is still an unusual job for many heating and sanitary installers. With the right manufacturer support, however, you can get the job done without any problems. For implementation, it is very important to proceed carefully, as installation deficiencies may be discovered late and require substantial efforts to remedy.
Authors: Norbert Gosekuhl, Manager, Product Marketing, Application LHD and Michael Herlfterkamp, Application Engineering/Supply Planning, Uponor GmbH, Haßfurt
In the context of changing energy policy and the associated focus on heat supply that is as efficient and environmentally friendly as possible, a noticeable trend towards small and medium-sized local heat networks has been developing more recently. These systems feature comparatively low system temperatures, so that highly insulated plastic piping has become the material of choice for implementation. Compared to steel piping, which is generally used only for medium temperatures of 100°C and above, they are cheaper and the implementation of the local heat network is simpler and more flexible.
Available on reels, plastic piping is easier to lay underground and, most of all, requires significantly less connection points. At the same time, the extent of planning required for routing is reduced because it is possible to flexibly respond on-site to obstacles such as trees or crossing lines. In addition, due to a typical temperature level of 80°C or less, local heat networks (generally) dissipate significantly less heat thanks to the smaller difference in temperature between the ground and the medium and require less safety installations in system technology.
AN ALTERNATIVE FOR NEW AND EXISTING STRUCTURES
Local heat networks have become an independent alternative to district heating and building-specific heating supply. Typically, they are used for new developments of almost any size, with an investor or a utility company assuming the role of heat supplier. One important reason for this is that, as a consequence of significantly reduced energy consumption, it is often not economical anymore to connect each house to the municipal gas network individually. In addition, house owners do not have to pay any investment and maintenance costs for their own heat generator and do not need to construct an additional boiler room. But also when renovating entire existing estates, residential companies now often construct central heating systems, as they make a simple, efficient and environmentally friendly energy supply from a single source possible. For similar reasons, local heat networks are also increasingly implemented in office parks and industrial estates.
In all cited cases, the network structure should be radial and, in medium-sized to larger estates, should feature several lines if possible, with the heating station ideally located in the centre. Local geography and urban structures have a major impact on line routing, however. The objective is to keep the length and the connected load of the main routes for the individual building groups as short and low as possible. This keeps piping dimensions small right from the start, thus contributing to a highly efficient local heat network.
BALANCING THERMAL LOSSES AND NETWORK COSTS
When planning and dimensioning a local heat network, it is important to ensure that all buildings are optimally supplied in the most economical way possible. Thermal losses as well as investment and operational costs are significant factors here. This requires careful optimisation. For instance, small piping dimensions and short line lengths will ensure low thermal and pressure losses. Accordingly, investment and operational costs – e.g. for pumps – will be minimised. Flow rates of 0.6 to 1.2 m/s are common in practice.
Generally, local heat networks should be implemented using so-called twin pipes (Figure 2) as far as possible. They combine feed and return lines inside one PE jacket pipe. As opposed to two individual pipes, thermal losses are reduced due to the smaller surface. Construction costs are also significantly lower, as narrower trenches need to be dug, the twin pipes can be installed quicker and house connections are easier to implement.
However, twin pipes are only available with an outer diameter of up to 75 mm for the individual medium pipes, which means that two individual pipes have to be used if a certain heating capacity is exceeded. For instance, a twin pipe with maximum dimensions can supply a heating capacity of 240 kW per line at a temperature difference of 20 K and a flow rate of 1 m/s. It is therefore advantageous specifically for larger building projects if the entire estate can be supplied radially with several twin-pipe lines from a central location. Some suppliers of local heat networks, such as Uponor, offer comprehensive support for professionals by experienced engineers for planning, dimensioning and project design.
HIGH THERMAL INSULATION VS FLEXIBLE INSTALLATION
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