District Heating

District Heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements, such as big space heating and ACS generation. The heat is often obtained from a cogeneration plant burning fossil fuels, but increasingly biomass, geothermal heating and central solar heating are also used, as well as nuclear power. District heating plants can provide higher efficiencies and better pollution control than individual boilers.

Heat Generation.

The principal element of a district system is usually a cogeneration plant (also called combined heat) or a heat production boiler station. Both have in common that they are based on combustion of primary energy carriers. The difference between the two systems is that, in a cogeneration plant, heat and electricity are generated simultaneously, whereas in heat production boiler stations- as the name suggests- only heat is generated.
The combination of cogeneration and district heating is very energy efficient. A thermal power station which generates only electricity can convert less than approximately 50% of the fuel input into electricity. The major part of the energy is wasted in form of heat and dissipated to the environment. A cogeneration plant recovers that heat and can reach total energy efficiency beyond 90%.
Other heat sources for district heating systems can be geothermal heat, solar heat, surplus heat from industrial processes, and nuclear power.

Heat distribution

After generation, the heat is distributed to the customer through insulated pipes. District heating systems consists of feed and return lines. Usually the pipes are installed underground but there are also systems with overground pipes. Within the system heat storages may be installed to even out peak load demands.

The common medium used for heat distribution is water, but also steam is used. The advantage of steam is that in addition to heating purposes it can be used in industrial porcesses due to its higher temperature. The disadvantage of steam is a higher heat loss due to the high temperature. Also, the thermal efficiency of cogeneration plants is significantly lower if the cooling medium is high temperature steam, causing smaller electric power generation. Heat transfer oils are generally not used for district heating, although they have higher heat capacities than water, as they are expensive, and have environmental issues.

Typical annual loss of thermal energy through distribution is around 10%, as seen in Norway’s district heating network.

Pros y contras

District heating has various advantages compared to induvidual heating systems, Usually district heating is more energy efficient, due to simultaneous production of heat and electricity in combined heat and power generation plants. The larger combustion units also have a more advanced flue gas cleaning that single boiler systems. In the case of surplus heat from industries, district heating systems do not use additional fuel because they use heat (heat recovery) which would evacuate to the enviroment.

District heating is a long-term commitment that fits poorly with a focus on short-term returns on investment. Benefits to the community include avoided costs of energy, through the use of surplus and wasted heat energy, and reduced investment in induvidual household or building heating equipment. District heating networks, heat-only boiler stations, and cogeneration plants require high initial capital expenditure and financing. Only if considered as long-term investments will these translate into profitable operations for the owners of district heating systems, or combined heat and power plant operators. District heating is less attractive for areas with low population densities, as the investment per household is considerably higher.Also it is less attractive in areas of many small buildings; e.g. detached houses than in areas with a few much larger buildings; e.g. blocks of flats, because each connection to a single-family house is quite expensive.

District Heating solar power

The success of the solar district heating , goes through the right alignment of the heat demand, to maximize the profitability of the heating facilities and it also goes through the right dimensions of the solar field.

Facts to consider:

0. The highest heating demand takes place in winter months, when there is fewer solar hours and the light is more diffuse than other year season, and therefore less heat production.
0. If a solar field is measured for the winter months, in summer there will take place an important surplus of heat.

Due to this facts, the solutions that SRB Energy proposes and are in an advanced project phase, integrate the following points:

0. The use of the UHV Collectors from SRB Energy which pick up at least 40% of the diffuse light available, due to its flat design and the specific design of the concentrating ones.
0. In case the solar field is measured to supply the clients for the winter months, a heat excess will take place in summer that will be used by nearby industries in their processes changing the length of  ties.
0. On the other hand the heat excess in summer can be in use generating water on cooled with absorbency equipment in every family unit or with bigger machines, for buildings or small areas.

The key to obtain a suitable return in the district heating plants for a concept which is the alignment of the generation with the demand, can be achieved with the following actions:

0. Solar field measurement suitable to the annual energy consumption
0. The use of both heating systems and air conditioning through absorbency systems.
0. Location of the plant near the heat consuming centers, like industries or industrial parks.
0. The use of accumulation systems suitable to the consumption standard.

Projects in phase of offers

Nowadays we are involved in the district heating projects in locations of superior latitude to those of the spanish geography.