BEWAG District Heating: On the Way to the Individual Customer

Right now there are seven combined heat and power stations in operation in Berlin capable of supplying a heating capacity of 2,800 Megawatts. Entire quarters of the city - such as the Hansaviertel and Gropiusstadt - are heated by District Heating only. How does this immense energy potential get to the individual consumer?

District Heating Piplines with Thermal Insulation in Concrete Duct.

The Three-pipe System

The first prerequisiste for the distribution of District Heating is a transport medium. Of two well-known energy carriers, steam and water, BEWAG had already decided at an early date to use circulating water pumped through an extensive pipeline network to the various areas of heat consumption.

Almost without exception, the usual system for District Heating networks makes do with a two pipe system. Not so at the BEWAG's pipeline system in Berlin. Here every customer is linked to a three-pipe system: two pipes transporting the flow from the heat and power station and one pipe for the return of the circulating waer. (And we may somewhat proudly add that this system has been utilized for more than sixty years.)

One of the flow pipes is used exclusively to supply the radiators in the individual households during the heating period in the cold months of the year. Every building is given an individual heating supply profile determined according to its specific needs - the necessary amount of circulating water from the District Heating System delivered to the building's supply station remains constant. The water temperature in this pipleline is variable, however, and always adapted to the weather conditions: from a minimum temperature of 55 degrees Celsius for mild spring days to the maximum temperature of 110 degrees Celsius for cold winters at -15 degrees Celsius.

The second flow pipe serves all appliances needing heat throughout the year such as warm water supplies, air conditioning and ventilating systems; the water in this pipeline circulates at a constant temperature level of 110 degrees Celsius. In the return pipe shared by the two flow pipes the cooled heating water is transported back to the heat and power stations.

Needless to say, BEWAG did not decide upon the three-pipe system without good reasons. This system offers decisive advantages as compared to systems with only one flow-pipe:

Convergence of heat connsumption peaks during the morning with the enormous increase of electric power demand during these hours is avoided since the heating waterflow cannot be changed by the individual consumer.
The additional fuel input for District Heat generation is kept low through the partition of the hot water flow into two separate pipes: Since all installations needing 110 degrees Celsius throughout the year are served via their own pipeline, Bewag can afford to supply all other households with just the temperature needed in the radiators as according to current weather conditions and outdoor tempatures. Hence the mean flow temperature in this pipeline is only about 75 degrees Celsius during all heating periods.
Reliability of the system is high since all three pipes pipes can be temporarily changed and linked in case any technical problems or irregularities should occur in pipeline network.

The System at a Glance: From the Combined Heat and Power Station to the Customers.

Transport Functions of the Network's Pumping Stations

Powered by the pumps of the heat and power station, the hot water in the two flow pipes can bridge distances within a radius of up to 10 kilometers. The common return pipe can barely bridge distances of more than 5 kilometers. The additional pressure required is currently suplied by 5 subterranean pumping stations. These pumps are installed at central locations of the BEWAG District Heating pipeline network and monitored by remote control from the heat and power stations.

Reliable Energy Supply Through Linked Networks

After the newly constructed Reuter West heat and power station has been connected to the system, there will be eight combined heat and power stations in the city of Berlin. Every single one of these utility plants guarantees a high level of reliability through its own additional stand-by capacity. And even if a failure should occur not only in the pipeline system but in the power station itself, there would be no shortages in the supply of heat: all the heat and power stations are linked into a pipeline network - in case of malfunctioning they can fill in any gaps in heating demand through their stand-by capacities.

The following figures show the efficiency of BEWAG's District Heating System: through a pipeline network with a length of about 370 kilometers, BEWAG furnishes about 15 percent of the total heating demand in Berlin (West). One out of every six inhabitants of the city of Berlin - a total of well over 300,000 people - already enjoys the advantages that District Heating offers. And the number of these persons is increasing day by day.

Right now our heat and power stations provide enough capacity to serve another 40,000 apartments with District Heating. The Reuter West heat and power station will furnish additional heating capacity for yet another 55,000 apartments, so that within the next few years fully one fourth of the total heating demand of the city of Berlin will be supplied by the District Heating System.

Construction Sites Cannot be Avoided

For these advantages the Berliners have to put up with temporary construction work in various parts of the city, however.

Wherever BEWAG is extending the District Heating pipeline network, the experts concerned with the planning and building of the extensions take into account all specific charateristics of the construction site location such as traffic and public or commercial infrastructure, parks, playgrounds and athletic grounds. Concretely speaking, this means that e.g. important traffic intresections are bypassed via pipe tunnels so as not to hinder smooth traffic flow.

The pipelines of the Bewag District Heating System are thermally insulated against heat losses. Until now these pipes were almost without exception constructed as steel pipes and laid in concrete ducts (see graphic above). Covered with prefabricated concrete slabs and insulated with bitumen these ducts are well protected against humidity and corrosion. This costly method of construction ensures the longevity of and reliability of the pipeline system.

In the course of the last few years advances in technology have made it possible to increasingly use plastic-sheathed pipes for smaller pipe dimensions. This noticably reduces construction time since the time-consuming tasks of the building of ducts and the application of insulating become unnecessary.

In a city like Berlin, the planning and construction of pipelines naturally enough is complicated business: amidst the undergound maze of service and supply lines - everything from electric wiring to sewer pipes - the finding and mapping of alignments for District Heating mains calls for the special expertise of our planners and engineers.

The "Hidden" Construction Sites of the Bewag District Heating System

Various structures that make regular construction work impossible result in great challenges: think of the railroad and S-bAhn tracks, the big waterways, great industrial zones and the subway tunnels, to list but a few.

Here the method of construction is pipejacking. Similar to tunneling in the mining industry concrete pipe segments are subterraneously pushed forward from one shaft to the next. The soil is broken up and processed in the cutting bit of the driving device according to various procedures - usually the soil is cut and crushed, under great pressure dissolved in water and pumped to the surface where the water is again separated from the soil. This technically quite complex procedure is known as wet conveying and is quite expensive.

Currently a pipe tunnel is under construction from the Reuter West heat and power station to the pumping station at Mierendorff-platz in Charlottenburg. This tunnel spanning a distance of 3.7 kilometers is built at a depth of between 17 and 22 meters and traverses among other buildings the River Spree, the park of Charlottenburg Palace, and both the railway tracks and the main expressway of the city, the Stadtautobahn.

Pipejacking at Hochmeisterplatz. Star-shaped Tunnel Driving for the District Heating Mains.