Energy Saving and Conversion (MSJ0200)

1. Energy Saving and Conversion(MSJ0200) 2011. Autumn semester 5.and 6. lectures Energy conversion. Buildings. Different heating systems

2. Energy Conversion. Buildings. Thermal energy conversion in buildings, low energy and passive houses. Different heating systems, district heating and local heating.

3. Buildings • Thermal energy conversion in buildings, low energy and passive houses, eco materials • Different heating systems, appliance of heating and ventilations systems, district heating and local heating • Electrical management of buildings. • Heating and ventilation control systems

4. District heating • The European Union is extremely dependent on its external energy supplies, with imports currently accounting for 50% of requirements. This figure is projected to rise to 70% by 2030 if current trends persist. • At present green house gas emissions in the European Union are on the rise making it difficult to respond to the challenge of climate change and to meet the commitments under the Kyoto Protocol. • The European Union has relatively limited scope to influence energy supply conditions. Efforts will have to focus on orienting the demand for energy in a way that respects the EU’s Kyoto commitments and is mindful of security of supply.

5. What is District Heating? • District heating is a convenient way to heating space and tap water. • In many processes, for example when electricity is generated or waste is burned, large parts of the energy are set free in the form of surplus heat. • The fundamental idea behind modern district heating is to recycle this surplus heat which otherwise would be wasted- from electricity production, from fuel and biofuel-refining, and from different industrial processes. Furthermore, district heating can make use of the many kinds of renewables (biomass, geothermal, solar thermal).

6. The recycled heat is used to heat water which is transported to the customer via a well-insulated network of pipes. District heating can serve residential. public and commercial buildings as well as meeting industrial demands for low-temperature heat. • A heat exchanger serves as an interface between the district heating network and the building's own radiator and hot water system. There's no boiler, no burning flame needed in the house and maintenance is taken care of by professionals.

7. Why should the European Union care about a local business like district heating? The EU has set targets to reduce energy consumption by 20% and to reduce C02 emissions by at least 20% (possibly 30%) by 2020.

8. Though a local business, district heating can greatly contribute to achieving global policy objectives. Doubling sales of district heating by 2020 will reduce Europe's: • Primary energy supply by 2.6% or 50.7 Mtoe/year • Import dependency by 105.4 Mtoe/year • Carbon dioxide emissions by 9.3% or 404 Mtoe/year

9. How can we compare DH with other heating options? Heating systems can be compared in terms of their contribution to reducing the use of fossil energy. Only an assessment encompassing the whole energy cycle -from conversion to delivery (thus including transportation losses) - will give a realistic picture. An approach based on primary resource factors (PRF) makes it possible to compare heating systems. Primary resource factors measure the combined effect of efficiency and the use of renewables and surplus heat resources. The lower the PRF of a technology, the greater its contribution to reducing the use of fossil fuel.

10. How much does it cost? An international study has shown that district heating prices are, on average, lower than natural gas prices. However, prices vary from one system to another, due to local circumstances and in respect of locally available resources.

11. The CHP/DH offers an almost complete flexibility of fuel selection covering all kinds of fossil, renewable and bio fuels as well as waste heat from various sources, whereas small scale heating systems in individual buildings are restricted to few and sophisticated fuels like gas, light clean fuel oil or pelletised wood and peat.

12. The importance of CHP is increasing, because the electricity consumption is increasing everywhere in Europe but the available production methods are restricted: • Some new nuclear capacity may be expected but a lot of existing to be retired during the years to come; • Most economic hydro power resources are developed already and most of the remaining will stay undeveloped for environmental reasons;

13. Use of renewable energy sources, windmills, bio fuel and solar power, are expanding strongly in many countries, but are not sufficient to cover the increasing need. Using renewable fuels, however, CHP/DH offers the most efficient way to proceed. In addition, solar heating and waste heat can preferentially be integrated in such systems; and,DH opens for efficient integration of combined generation of heating and cooling services in a CHP system.

14. Basically, the CHP and DH represent well-known technology and every day practice. In several countries of the Northern Europe, • DH covers of the residential and public heating market 85% in Iceland, 70% in Russia and Lithuania, 68% in Latvia, 53% in Poland, 52% in Estonia, 50% in Denmark and Finland, 42% in Sweden, and 12% in Germany; • The bulk of DH is produced by CHP, for instance, in Germany 79% and 75% in both Finland and Denmark;

15. Moreover, electricity generated by CHP covers a substantial portion in the electricity production balance of a number of countries: In Finland 36%, in Denmark 62%, in Germany 11% and in Sweden 6%.

17. CHP = Cogeneration of Heat and Power

18. LOW-EX CONCEPT In a technical CHP process electricity is generated and the unavoidable waste heat is used to heat up residential, public and commercial buildings as well as industrial facilities.

19. Example CHP analogous to hydropower. In order to have a hydro power plant, there must be a waterfall first. Similarly, to have a CHP plant, there must be the demand of heating or cooling of the local municipal or industrial facilities available. Therefore, from the physical and economic point of view, the waterfall and the heat demand are both considered as necessary assets for generation of electric power at high efficiency.

21. Economic Boundaries of CHP The CHP technology is very capital intensive. In order to pay back the high investments, • the annual operation time shall be as long as possible, typically more than 4 000 hours; • the produced heat energy usually covers the major part, 50-80%, of the industrial and/or the municipal heat demand; • the price of fuel and waste heat should be relatively low, and, • The price of the electricity sold to the grid shall be sufficiently high to gain sales revenues.

22. The size and type of the CHP plant should be optimised case-by-case depending on the local availability and price of fuels, waste heat and electricity sold to the grid. Despite the complexity of the issue, however, some practical examples may be given to CHP capac-ity optimisation depending on whether there is a single CHP unit or a couple of them in the particular case, as follows:

23. 1) The optimal capacity of a single solid fuel fired CHP plant, either with bio or fossil fuel, may range from 10 to 20% of the peak heat load of the DH system. Usually the relatively high investment costs require a very long peak load duration time to pay back the investment. Therefore, it is assumed that the CHP plant should be operated on the summer time, too, when the heat load consists of DHW load only.

24. 2)The optimal capacity of a single gas and oil fired CHP plant with gas turbines or en-gines ranges from 15 to 40% of the peak heat load of the DH system. Operation of such a plant in practice is possible in the range of 20% (gas engines) or 40% (gas tur-bines) up to 100% of the nominal capacity. In order to be able to operate on the low summer load, the minimum summer load should not be lower than 20% (gas engines) or 40% (gas turbines) of the DH capacity of the CHP plant. The optimised level, however, depends on the case and the type of the plant.

25. 3) The total capacity of a number of various CHP plants in a united DH system is opti-mal on the range of 45 to 60% of the peak heat load of the DH system. The individual CHP units can be located at and connected to various nodes of the network, which is densely looped. Operation of those plants will be optimised, because different fuels, power to heat ratios, efficiencies and maintenance needs may have impact on their merit order type operation during the year. Normally, among the various plants, there is at least one that is able to supply the minimum (e.g. summer time) heat load.

26. The above three conditions are typical only and may be different in a special case. The case may be special if, for instance, there is a lot of low price electricity in the grid avail-able in the summer time and the CHP plant is not needed for power production. The summer time heat load can be supplied by HoBs, or by possibly existing electricity driven heat pumps, if the electricity prices are extremely low.

28. Economic Boundaries of DH As comparative advantages the DH offers: • The ability to use a variety of fuels, which provides flexibility in using the fuel of the lowest price, redundancy in heat supply and stability in heat price development; • The only way to use various waste heat sources to heat up the residential buildings; • The centralised flue gas cleaning benefiting from economy of scale;

29. Safety to customers: there is no possibility for fire or explosion caused by handling of fuels in houses and buildings; • Benefits from economy of scale while producing heat at the central plant; • Reliability of heat supply due to professional operation and continuous monitoring of heat production and distribution; • Improvement of the urban air quality;

30. The only way to generate electricity from solid fuels at high efficiency by means of the cogeneration process; and finally, • The most efficient cogeneration of electricity from natural gas. A modernised DH allows the heat customer to regulate heat consumption according to the actual and individual need and be invoiced according to the heat meter readings.

31. On the other hand, the comparable advantages of the individual gas heating are as follows: • No heat transmission losses; • Lower investments in underground pipes; and, • Economy not sensitive to city planning.

32. Economic Links between CHP and DH Despite the obvious physical link between the CHP plant and the DH system, there are a number of economic links, which have to be taken into account when optimising the CHP/DH system as follows: • The heat source sets the supply temperature, but the customer defines the water flow and the return temperature; • The supply and return temperature have a linear impact on the heat losses of the heat transmission and distribution network;

33. The supply and return water temperatures usually have a direct impact on the power to heat ratio at the CHP plant. At low water temperatures relatively more electricity can be generated with CHP or the total plant efficiency is improved, the impact depending on the type of the CHP plant; • The cooling defined by the customers, as the difference of supply and return temperature, has a linear impact on the water flow needed for heat supply at the heat source;

34. The water flow has a direct impact on the pumping need at the heat source and the size of the pipelines in the network; and, • The pressure difference required by the consumer substations has a direct impact on the electricity consumption of the DH circulation pumps at the heat source.

35. Traditional CHP Plants

36. Solid Fuel Fired CHP Plant The steam boiler using coal, peat or renewable fuels produces steam at high pressure and temperature to be used in a steam turbine either of backpressure or extraction- condensing type. The turbine runs the generator to produce electricity. The plant is relatively expensive but is able to use low-grade fuels at low operational costs.

37. Gas Turbine Plant The flue gases of the gas turbine, run by natural gas or light fuel oil, will be directed to a heat boiler, where the heat is recovered to heating purposes and simultaneously the flue gas temperature is cooled down close to the ambient temperature. The turbine will run the generator to produce electricity. The plant is usually small and economic but with poor power to heat ratio on partial heat load

38. CHP Engine Plant Fuel oil or natural gas depending on the engine design runs the piston engine of the CHP engine plant. The heat energy of both the flue gases of the gas engine and the engine cooling system will be recovered for useful needs. The power to heat ratio is high but the engine needs a little more maintenance than the gas turbine.

39. Combined Cycle CHP Plant • Interconnection of the gas and steam cycles will yield more electric energy and at higher efficiency than the cycles separately would do. • In a genuine combined cycle CHP plant the flue gases of the gas turbine (gas cycle) are used to produce steam at high pressure and temperature of about 500 oC (steam cycle). The steam will flow to an ordinary steam turbine to generate additional electric energy.

40. The electric power is the more valuable product of the CHP, because alternatively it is usually generated by other thermal (nuclear or coal driven) power plants in a condensing process at low efficiency. Therefore, the gas engine and the combined cycle CHP plants are superior to most other traditional plant types in electricity gain (e.g. power to heat ra-tio).

42. New CHP Technologies under Development

43. Stirling Engines The Stirling engine is an external combustion device and therefore differs substantially from a conventional combustion plant, where the fuel burns inside the machine. In this case an external device supplies the heat and the Stirling engine uses helium as a working fluid. The Stirling engine is quieter than the traditional engines and requires little maintenance. The emissions of particulate, nitrogen oxides, and unburned hydrocarbons are low. The efficiency of these machines is potentially greater than that of small internal combustion or gas turbine devices.

44. There are more than 60 years of experience with this technology, but its application for micro-cogeneration boilers is the new idea. For this type of boilers, there is a need for small engines with a capacity between 0,2 and 4 kWe, for which a Stirling engine offers a good opportunity. • There are some low capacity Stirling engines in development or already in the market. The electrical efficiency is still not very high and is in the range of 10% (350 We engine); 12,5% (800 We engine) up to 25% (3 kWe engine), but it should be possible to develop a design with at least 25% electrical efficiency and total efficiency of 90%.

45. Micro-turbines The systems smaller than 1 MWe have so far been uneconomic, but this is starting to change. Manufacturers are developing smaller and smaller systems and nowadays there are micro turbines as small as 25 kWe. In general, micro turbines can generate anywhere from 25 kWe to 200 kWe of electricity. They are primarily fuelled with natural gas, but they can also operate with diesel, gasoline or other similar high-energy fossil fuels. Research is ongoing on using biogas.

46. The micro-turbines are smaller than conventional reciprocating engines with lower capital and maintenance costs. The NOx emissions are low. • In the future, the micro-turbines could be used as a distributed generation resource for power producers and consumers including industrial, commercial and even residential users of electricity.

47. Fuel Cells Fuel cells convert the chemical energy of hydrogen and oxygen directly into electricity without combustion and mechanical work such as in turbines or engines. The hydrogen used as fuel can be derived from a variety of sources, including natural gas, propane, coal and renewables such as biomass, or, through electrolysis, wind and solar energy.

48. Even if fuelled with natural gas as a source of hydrogen, the emissions are negligible. • A number of different types of fuel cells are being developed. The characteristics of each type are very different, and they are also in very different stage of development: some of them have not emerged from the laboratory so far, whereas some others seem to approach a commercial breakthrough.

49. Centralised versus Decentralised CHP In a small municipality there are not many options for optimal structuring of the CHP capacity. In large municipalities, however, there are two main policies for consideration: the centralised and the decentralised CHP.

50. The centralised CHP, the typical solution, consist of one or a few large plants, which are connected to the DH system. The comparative advantages are as follows: • Low investment unit costs due to economy of scale; • Centralised flue gas cleaning benefits from economy of scale; and, • Less staff needed due to economy of scale.