1. Institute of Power Engineering and Fluid Mechanics
Division of Refrigeration and Air Conditioning Systems
Refrigeration and Criogenics
Heat pumps
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.
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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
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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.
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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”.
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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.
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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.
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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.
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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;
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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.
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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
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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.
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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
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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
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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.
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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.
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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.
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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
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Lis
Gru
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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.
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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 !
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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
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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.
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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)
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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.
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28. Ground
An example of a ground heat exchanger
for the heat pump.The pipes are
installed 1-1,5 m below the surface.
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