District heating in Poland started to develop intensively after World War II. However, at the beginning, the operation of state-owned enterprises related to reconstruction and construction of heating facilities generally did not employ any different methods than before the war. With regard to the huge variety in conditions and needs, it is difficult to talk about a uniform model of district heating common throughout Poland.
Every city where district heating systems were introduced had to work out its own, unique operating scheme. Therefore, an attempt at describing the main trends in the history of Polish district heating must be limited to a presentation of general issues. Detailed histories of companies operating in this industry are published in the monographs of respective district heating companies, heating stations and combined heat and power plants.
From 1948 the Workers' Housing Development Administration (ZOR) – a state-owned institution acting as an investor – was in operation. ZOR built complete city units, thanks to which the flats were built along with accompanying infrastructure such as schools, shops, streets and boiler plants and district heating networks. By 1955 the capacity of boiler plants built by ZOR was ca. 800 kcal/h, and the average capacity of plants with water with the temperature of 90/70 °C was ca. 8 kcal/h, and with a high temperature medium (130/80 °C) – 12 15 kcal/h. The length of district heating networks was only 310 km in the housing sector, but in the industrial sector it was 880 km.
At the first stage of the post-war reconstruction of cities the priority was to ensure basic living conditions to their inhabitants as soon as possible. City infrastructure was reconstructed vigorously and all measures were determined by current needs. In this situation planned development of district heating was still out of the question. Boiler plants were restored to their original pre-war locations; however, in most premises where heating stoves prevailed changes were not implemented and the existing systems remained in place. In new housing estates and districts the situation was different – local low-parameter boiler plants were built there to heat a number of buildings. Their designs were mostly subordinated to the criteria of saving time and materials, which regrettably had an adverse impact on the use of such plants in the following years. These facilities mainly used coal or fine coal as fuel. They were devoid of dust removal systems, so flue gas was discharged into the atmosphere without any previous treatment. Water in the systems was not subject to any treatment either, so limescale was deposited in the pipes and the boilers were often out of order. The plants were mostly operated by hand. A boiler plant was normally operated by several people – stokers and helpers, who, using two-wheeled barrows, charged the boiler with fuel. Afterwards slag had to be disposed of – also by hand. The work was very hard. It was performed in very hot and considerably dusty conditions. A large number of local boiler plants and individual tiled stoves had a significant influence on the city landscape in the 1960s and 1970s. It was mostly due to smoke – hundreds of chimneys shooting completely untreated flue gas into the sky were without any doubt a sign that the heating season had begun.
At that time the heating season started on the date appointed by city and regional authorities. A decision to turn on heating was often taken when the family of a voivode or another dignitary complained about the cold. Fuel was transported to boiler plants by all available means of transport: horse-drawn wagons, tractors, and with time also by trucks. District heating companies found it a considerable logistical challenge.
At the next stage of development of centralized heat sources the so-called central boiler plants, that is, municipal heating stations with a range covering a few housing estates, whole districts or even the whole town were put into operation. These plants were usually equipped with stoker-fired water boilers (WR-25, WR-10) with natural draught.
The scheme of expansion of remote district heating in Poland also covered facilities where heat was most often deemed a waste product. Nearly all cities after the war had condensing power plants built in the 1920s and 1930s or earlier. In 1945-1955 they were modernized and some of them were expanded by adding new boilers and turbines or auxiliary units.
At that time these plants, although fitted with turbine sets of relatively low power at low steam parameters, were the fundamental sources of electrical energy. With time, as high-pressure condensing power plants were put into service, power plants in cities were in decline as sources of electrical energy, even during the peak requirement. Thus, works commenced to convert them into combined heat and power plants.
This was justified by the following arguments:
• a power plant located within city limits was very convenient to supply heat energy to city buildings due to the proximity of consumers; therefore, keeping investment expenditure at a low level it was possible to build district heating networks very fast and give up heating boiler plants to provide heat to new buildings;
• the requirement of heat energy in the area of the power plants normally exceeded the heat production capacity of such power plants, so their load was achieved in a relatively short time with full economic effect;
• the specific consumption of heat by condensing turbine sets working in a combined cycle was 1,200-1,400 kcal/(kWh), or even less; that is, it was smaller than in condensing power plants built these days [ca. 2,000 kcal/(kWh)];
• the conversion of uneconomical municipal condensing power plants into combined heat and power plants enabled maintaining in operation boilers and turbines which in a condensing cycle should be decommissioned or their use limited;
• the costs of reconstruction of a power plant calculated per unit of generated heat energy were lower than the costs of construction of heating boiler plants;
• the use of existing power plants as sources of heat Energy improved sanitary and hygienic conditions in cities due to the reduced amount of dust and sulphur in atmospheric air; in addition, it decreased the scale at which fuels were transported within city limits.
Referring to Warsaw as an example, the design and construction of combined heat and power plants could be divided into three stages of development:
• construction of the Warsaw-Żerań Combined Heat and Power Plant; it was designed and built in compliance with the then typical USSR standards, e.g. steam inlet parameters of 90 atm, 500 °C with 25-30 MW condensing and extraction turbines and boilers with an output capacity of 230 t/h;
• construction of the Warsaw-Siekierki Combined Heat and Power Plant; steam temperature was increased to 535 °C; the main units in the Warsaw-Siekierki CHP Plant were not considerably changed but all of them were made in Poland;
• combined heat and power plants built in 1960-1970 and expansion of the Warsaw-Żerań and Warsaw-Siekierki CHP Plants; a characteristic feature of these plants was an increase in steam inlet parameters up to 130 atm, 535 °C, i.e. parameters that are presently used by condensing power plants; another innovation was the use of backpressure turbines and covering peak loads using water boilers with a capacity of up to 120 Gcal/h.
At the initial stage of introducing district heating in Poland heating networks were built as ducted systems with suspended insulation. In subsequent years, for reasons of economy, they were replaced by ductless systems (for pipes Ř<350 mm) and prefabricated ducts with foamed concrete (for 250-600 mm pipes). The ducts were built as a continuous footing on which painted and insulated pipes were laid and covered with concreto shells. Later, the joints between the elements were coated with cement, glue and pitch. The pipe insulation layer was made of mineral wool attached by means of wire or metal mesh and covered with building paper. Ductless piping was covered by fill insulation – a special material which was a mixture of petroleum asphalt and other fillers. Inaccurate workmanship and low quality materials later caused severe failures and heat losses.
At the early stage of district heating development heat exchanger substations we are familiar with these days were not in use. Hydroelevator substations or substations with mixing pumps were standard equipment. As a result, household radiators were supplied with water from boiler plants – often very hot and at variable pressure. These solutions had serious drawbacks for district heating networks (uncontrolled losses of service water), but they were also burdensome for heat users who had very limited possibility to adjust their radiators.