District heating is facing challenges which will require decisions involving changes both in the internal organisation of companies and extension of the range of activities related to a change in heat generation and transmission technologies. In the area of generation these are: developing cogeneration and trigeneration, using renewable energy and also using waste as fuel. Changes regarding transmission and distribution of heat apply to both the network and “downstream” – that is, in the consumers' installations – in particular where heat will be used for cooling purposes.
Combined generation of electricity and heat, and recently also cooling, is one of the preferred solutions for economical and at the same time sustainable generation of energy. This trend is reflected in European legislation in Directive 2004/8/EC of the European Parliament and Council promoting cogeneration – the so-called CHP Directive.
The main benefit of combined generation is the economy of fuel compared to plants in which electricity and heat are generated separately. In addition to obvious economic benefits, it has at the same time an ecological effect, reducing emissions of pollutants, and in particular, CO2. The reduction of losses in power engineering systems is also significant since due to a more distributed but denser network of generating plants power is sent smaller distances.
Poland is a country in which the share of production of heat in combined cycles compared to total production in centralized sources is relatively high. In 2012 heat produced in cogeneration corresponded to 62.5 % of its global production. However, in businesses deriving their income mainly from heat production only half of heat is produced in cogeneration.
Evidently there is still a large potential to increase fuel savings if the capability of district heating is utilized and the existing heating stations are replaced by combined cycle plants.
Boiler plants and heating stations supplying heat to municipal consumers in small and medium-size areas in Poland on an annual basis produce more than 100,000 TJ of heat. This is a potential in the form of the existing stable selling market which could be used in converting heat sources into cogenerating sources. It is estimated that, skipping sources with power lower than 15 MW and peak-load boilers, 70 % of the above-mentioned heat could be produced by cogeneration.
Conversion of the existing boiler plants and heating stations into combined heat and power plants (of course where such conversion would be effective) would have a huge economic and environmental effect.
Combined trigeneration systems are a technological development of cogeneration since heat can be used for heating – like in a classic district heating system – or in chillers. This technology, using a single source of primary energy, aims to reduce the amount of primary Energy required to produce any form of energy separately. In district heating systems where the heat requirement in summer is limited at most to heating hot service water, the possibilty of producing chill improves the effectiveness of combined generation of electricity and heat.
Until recently there were two economic barriers to chill being sourced from district heating network in summer. The first was a low requirement for cooling and high temperature of service water which in summer exceeded “normal” temperature of water in the network by 15÷20 °C. Such problems were due to technology using absorption chillers. Both of them caused excessive losses of heat and made such solutions unprofitable. Only adsorption chillers, using water with a temperature of 65÷90 °C as the heating medium, enabled the use of service water with a temperature required in summer to heat hot service water (70÷75 °C) for producing chill.
Thanks to this such systems can be implemented in various types of facilities. They use effective management of produced heat energy all year round (also on a 24h basis), and thus generate measurable savings.
The chances of development for entities dealing with transmission and distribution of heat must be sought in the growth of the heat selling market by connecting new consumers, including buildings built using obsolete technologies, which is connected with eliminating low emission. Heat losses must be further reduced by replacing the pipelines with new ones – pre-insulated. Currently, 46.4 % of transmission networks and 30.4 % of low-parameter networks have been built using this technology. The plans also include installing hot service water systems in places where they have been missing, and building local generating sources in areas where access to district heating is difficult. They also include services downstream.