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Rc 06

  1. 1. Institute of Power Engineering and Fluid Mechanics Division of Refrigeration and Air Conditioning Systems Refrigeration and Criogenics Heat pumps
  2. 2. What is a heat pump? A heat pump is a machine or device that moves heat from one location to another via work. Most often heat pump technology is applied to moving heat from a low temperature heat source to a higher temperature heat sink. Refrigeration and Criogenics 2
  3. 3. Historical overview The first person ever to came with the idea of heat pumping was William Thomson (Lord Kelvin). In 1852 he described an open air system with piston compressor, which he named as „heat multiplicator”. The air is the working fluid. It is sucked from the environment to the expansion cylinder where it is expanded and cooled. Then it flow through the heat exchanger where is absorbs heat, up to the temperature of environment. After that, it is compressed again up to the atmospheric pressure. Then, since its temperature is now above environent it it used to heat up the room. Rys. 1 – outside air 2 – inlet cylinder, 3 – heat exchanger, 4 – transmission, 5 – steam engine, 6 – outlet cylinder 7 – heated room Pompy ciepła 3
  4. 4. Historical overview Because of high demand and at the same time availability and high efficiency, refrigerators and cooling systems (especially vapor compression cooling systems) quickly become very popular among end users (domestic appliances). On the other hand, for many years, heat pums raised very limited interest, when compared to more traditional methods of house heating (which relied on low fuel prices. The popularity of heat pumps typically increase because of:   Energy and fuel crises;   Fuel prices increase;   Development of newer and safer technologies, refrigerants and materials ensuring safe and problemless work;   Decrease of equipment used in refrigeration technolgies;   Increased popularity of ecological movements encouraging limited energy use and development of environment free technologies. Pompy ciepła 4
  5. 5. Development of heat pumps The real development of the heat pump started in 1930s. In 1927 Thomas Graeme Nelson Haldane build the first heat pump capable of heating up the house. His device was an vapor compression ammonia system. In 1938 in Zurich, Switzerland 175kW heat pump was installed in order to heat up office builiding. This device was using nearby river as a low temperature source, providing temperature of the medium about 70oC. In 1940s a large heat pump unit was installed in Norwich, England. It was also usin river water and reached the COP about 3. In that decade, 2.4MW heat pump was installed in London, for year round air conditioning and heating of Royal Festival Holl. In following years, in the USA, England and Switzerland several heat pumps are installed using different heat sources, including waste heat of industrial processes. This is when the name „heat pump” was used for the first time: G. Flugel in Germany used the name: „die Warmepumpe” and independently F. Kraus in the USA introduced „heat pump”. Pompy ciepła 5
  6. 6. Development of heat pumps Further development of heat pumps was related to increased popularity of synthetic refrigerants (1950s). Lower prices, smaller size and higher reliability translated into increased demand. Heat pumps become popular heating equipment for domestic use. Thanks to convenient weather conditions, heat pumps become very popular in the USA. In 1970s, about 850k heat pumps were installed in this country. In 1980s almost 30% of all suburbian houses had installed some kind of heat pump. The demand is also visible in Europe, especially in Germany, France, Italy, Sweden and Norway. Many refrigeration system developers started mass production of the heat pumps. Since 1990s, heat pumps become more and more popular also in Poland. Nowadays, heat pumps can be observed in many places, in both domestic and industrial aplications. Pompy ciepła 6
  7. 7. The efficiency The heat pump is used to warm a closed space (i.e. house) with the rejected heat, while the refrigerator is used to maintain a low temperature in a closed space and the rejection of heat is just a part of the operation – not its purpose. For refrigerator QL is the desired output, while for the heat pump QH is the desired output. Refrigeration and Criogenics 7
  8. 8. The efficiency The efficiency of a heat pump fall significantly at low temperatures. Therefore, most of air-source heat pumps require a suplementary heating system such as electric resistance heaters or an oil or gas furnace. Since the operating temperatures of water-source or ground-source based systems are more stable such additions are not required. The heat pump is most competetive in areas that have a large cooling load during cooling season and small heating load during heating season. The heat pump is least competetive in areas where the heating load during heating season is very large and the cooling load during cooling season is small. Refrigeration and Criogenics 8
  9. 9. Different types of heat pumps   Vapor compression heat pump systems   one refrigerant:   electrical,   gas fired,   exhaust engine,   high temperature (multi stage);   with a mixture   zeotropic,   non-azeotropic; Pompy ciepła 9
  10. 10. Different types of heat pumps           Sorption heat pumps:   sorption;,   resorption; complex vapor compression and absorption systems; thermocompressor heat pumps; ejector heat pumps; others:   Thermoelectic, rotary, etc. Pompy ciepła 10
  11. 11. Bivalent heat pump     A heat pump to be described as economic needs COPHP at least 3 Bivalent (more than one heat source) heat pumps can be connected in series (left) or in parallel (right) CHC CHR parownik parownik T H 2O chłodziwo El woda gruntowa I woda głębinowa woda gruntowa woda głębinowa II I II Heat pump with sources connected in series Heat pump with sources connected in parallel Pompy ciepła 11
  12. 12. Heat sources         natural artificial Upper – energy is absorbed, the exergy is low Lower – determine application of the heat pump, high exergy In perferct case – isothermal heat source, losses are neglected. Pompy ciepła 12
  13. 13. Lower heat source Lower heat source – defines the pump type and determines its application. It should have clearly defined qualitative and quantitative properties: Qualitative Quantitative temperature and its changes in time availability exergy and its changes in time corrosion potential investment and operational cost Pompy ciepła 13
  14. 14. Heat source Typically small heat pumps are installed in houses with sources:   Air   Ground   Solar energy Abosrption of energy cannot influence other users of the source. Sometimes, but not often:   Underground water reservoirs   Wells If available:   Rivers   Lakes   Seas Pompy ciepła 14
  15. 15. Heat source Heat pumps are generally much more expensive than other heating systems, but in the long range they can save considerable amount of money, because they could significantly lower heating bills. The most common energy sources of heat pumps are:   Atmospheric air   Water   Soil (geothermal)   Waste heat The COP of heat pumps is between 1.5 to 4 depending on the particular system and its energy source. Refrigeration and Criogenics 15
  16. 16. Heat source The energy cannot be transfered from high temprature source due to the losses during transport. Lower heat source has to be present at the location of installation. This is important for large installations as well. Some special heat sources – require anti-corrosion materials   Salty underground water reservoirs   Sea water   Vapor in a drying room   Presence of SO2 i CO2 + condensation of humidity Sometimes it is a significant economic problem. Pompy ciepła 16
  17. 17. Heat source       The higher the temperature – the more efficient and reliable heat pump The changes during the year, month and evern during the day, has to be taken under consideration when evaluating heat pump capabilities. It is necessary to determine sources coherence, especially:   Possible significant temperature changes.   If the availability meets the demand. Pompy ciepła 17
  18. 18. Coherent and incoherent heat sources   Coherent heat source – gives more heat when this heat is really needed. Incoherent heat source – gives more heat when the demand for heat is lower, eg. The Sun is incoherent… in winter when demand is higher, the density of energy provided by the Sun is lower. 100 Ilość energii słonecznej %   90 80 70 60 50 40 30 20 10 0 Sty Lut Mar Kwi Maj Cze Lip Pompy ciepła Sie Wrz Paź Lis Gru 18
  19. 19. Heat sources Artificial – the heat is a result of some technological process (the temperature 290-350 K, sometimes higher, not depended on the year period) The most of natural heat sources is incoherent (air, water, earth) Cost – investment, operation, maintenance: For 20 kW:   Air 1250 EUR   Water from the well 2500 EUR   Ground 500 EUR   Solar energy 750 EUR   Typical cost of deep drilling 5000 EUR / 1 m It is very hard to determine costs related to the artificial heat sources. Pompy ciepła 19
  20. 20. Perfect heat source Properties of the perfect heat source:             Infinite heat capacity (renewable source) Possibly high and constant temperature Without contaminants and corrosion inductors Easily and cheaply acessed available at the location of installation coherent It doesn’t exist ! Pompy ciepła 20
  21. 21. Heat sources Secondary heat pumps Waste heat of industrial processes       •      Primary heat pumps Renewable energy sources Air Exhaust gases Exhaust fumes: from combustion of gases, from combustion of solid fuels. Condensate Vapor Water             Atmospheric air Groud Water: underground surface deep underground reservoirs urban Sun radiation Geotermal energy Wind energy Pompy ciepła 21
  22. 22. Air heat pump Refrigeration and Criogenics 22
  23. 23. Heat exchanger for ambient air Pompy ciepła 23
  24. 24. Atmospheric air Heating of the air at the inlet with solar energy. Pompy ciepła 24
  25. 25. Surface water reservoirs Surface water reservoirs can be used as a lower heat source of a large heat pump systems. Typically, we use energy resources of larger rivers and lakes. The energy stored in surface waters comes from the exchange between water and the air or ground. Even rivers with small flow can transport significant amounts of energy. We can use e.g. 1/5 of the flow with corresponding temperature drop of 5K> The energy can be absorbed at many locations along the river. Pompy ciepła 25
  26. 26. Surface water reservoirs Temperature distribution over the year: a) rivers 1 - Wisła (Kraków Bielany), 2 - Wisła (Warszawa Nadwilanówka), b) lakes: 1 - Mamry (Przystań), 2 - Myczkowice (Myczkowo) Pompy ciepła 26
  27. 27. Ground In the surface layer of the ground (about 10m deep), the heat of solar radiation and the heat exchanged with the atmosphere is accumulated. Deeper, more than 20m, both the energy from the Sun (radiation) and from the Earth is stored. At 10m depth, the temperature of the ground is constant, and typically 1K higher than the temperature of the air. The type of the ground determines its usefulness (sand, clay, gravel) and humidity (the higher, the better heat transfer ability). Typically, to abosrb the energy stored in the ground, ground heat exchanger are used (collectors). The shape and position of the collector, significantly influence heat transfer. Pompy ciepła 27
  28. 28. Ground An example of a ground heat exchanger for the heat pump.The pipes are installed 1-1,5 m below the surface. Pompy ciepła 28
  29. 29. Grunt Temperature difference between ground and year average. Pompy ciepła 29
  30. 30. Grunt Pompy ciepła 30
  31. 31. Grunt Pompy ciepła 31
  32. 32. Grunt Pompy ciepła 32
  33. 33. Grunt Pompy ciepła 33
  34. 34. Grunt Pompy ciepła 34
  35. 35. Grunt Pompy ciepła 35
  36. 36. Ground heat exchangers Refrigeration and Criogenics 36
  37. 37. Ground based heat pump installation Refrigeration and Criogenics 37
  38. 38. Heat pump - winter Refrigeration and Criogenics 38
  39. 39. Heat pump – summer Refrigeration and Criogenics 39