8. Heat pumps, heat pipes, cold thermal energy storage Ron Zevenhoven Åbo Akademi University Thermal and Flow Engineering Laboratory / Värme- och strömningsteknik tel. 3223 ; [email protected]Refrigeration (Kylteknik) course # 424519.0 v. 2018 ÅA 424519 Refrigeration / Kylteknik 27.11.2018 Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 2/28 8.1 Heat pumps
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8. Heat pumps, heat pipes, cold thermal energy storage
Ron ZevenhovenÅbo Akademi University
Thermal and Flow Engineering Laboratory / Värme- och strömningstekniktel. 3223 ; [email protected]
Refrigeration (Kylteknik) course # 424519.0 v. 2018
ÅA 424519 Refrigeration / Kylteknik
27.11.2018Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 2/28
8.1 Heat pumps
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Heat pumps /1 Using a refrigeration cycle for
heating is referred to as a heat pump (mostly based on a vapour-compression cycle)
Heat pumps make use of low-temperature (waste) heat, replacing sources of (unnecessarily) high temperature heat (and electricity!) for heating and air conditioning purposes
Heat pumps became popular in the 1970s, for combustion-free heating, and air conditioning
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Heat pumps /2 Energy balance:
QHigh temp = Win + QLow temp
COPHP > 1, typically 3 ~ 6, for a typical building20 ~ 40 kWh electricitygives 100 kWh heat; large units can achieve that with ~ 15 kWh power input
Primary energy ratio PER ηpower→work = 0.25 … 0.75
EER should be > 10 HSPF should be 5 ... 7,
equals ~ 3.4 · COPHP
SEER should be 8 ... 10, depends on location ! http://www.engineeringtoolbox.com/heat-pump-
efficiency-ratings-d_1117.html (Feb. 2017)
11 Rin
L
in
HHP COP
W
Q
W
QCOP
inputenergyelectrical
outputcoolingseasonaltotalSEER
inputenergyelectrical
outputheatingseasonaltotalHSPF
inputenergyelectrical
capacitycoolingEER
COPPER HPworkpower
ratio efficiency energy Seasonal
factor eperformanc season Heating
ratio efficiency Energy
ratio energy Primary
Unit:
W/W
U.S.A:
(BTU/h)/W
”
”
1 kW = 1000 W = 3413 Btu/h
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Heat pumps /3
The cheapest option of usingoutside air heat can becomelimiting in winter; in thosecases using ground- or water-source heat has a wider rangeof operation, at somewhathigher costs
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With the evaporator outsidethe space to be heated, the options are to use1) outside air heat, 2) outside ground heat, 3) outside water heat and 4) heat from another indoorspace, or 5) waste heat from a process or device
Low TL for a given TH, → COPHPmay become too low (partlybecause of lower compressorefficiencies !)
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Heat pumps /4
Typical heat pump output heat capacities range from a few kW for single family homes, via 100’s of kW for shops and offices up to 30 MW or more for industry
Heat delivery temperatures range from 5 -10°C for chilledwater and cool air to 50 - 200°C for hot water and steam
A great benefit is that the cycle can be used as a cooling system (air conditioning) by switching a reversing valve
see next slide
Energy input
Table: after D03
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Heat pumps using v-c cycle
A heat pump vapour-compression system with reversing valve for summer / cooling (a) or winter / heating operation (b)
Pictures: KJ05
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Heat pumps – heat sources
Top: vertical and horizontal closed loop ground heatBottom: surface water closed loop, well water open loop
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Table ↑: Input heat sourcesfor heat pumps and their temperature range
Table: D03
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Industrial heat pumps /1 Important applications of heat
pumps in industrial processesare
– Space heating– Water heating & cooling– Steam production– Drying and dehumidi-
fication processes– Evaporation, distillation and
concentrating processes;using cooling water, condensate and other liquideffluents, or condenser heat from refrigerator plants as input heat source
Diluted solution
Concentrated solution
Condensate
Compressor
Heat exchangers
Concentrating solutions by evaporationusing a heat pump system
Picture: Ö96
See also chemical heat pumps, metal hydride heat pumps, thermo-electric heat pumps, absorption heat pumps, ....
(→ for example: D03 chapter 4)
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Industrial heat pumps /2
A mechanical vapour recompression system (MVR) can be seenas an open cycle vapour recompression evaporator
The solvent that is removed acts as the operating fluid, the heat of vaporisation is recovered while the vapour is condensed after the compression
Picture: D03
A very important application: sea water desalination
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15 l/min 15 l/min
air
water
7 l/min7 l/min
Cold side Hot sideRefrigerant: R407c23% of R32, 25% of R125, 52% of R134aODP = 0, GWP =1610
ÅA 424519 Refrigeration / Kylteknik
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8.2 Heat pipes
note: vacuum tubes for solar thermal energyrecovery , like Double Glass Vacuum Heat Pipes (DGVHPs) are not considered here
“The DGVHP represents a special case of heat pipe: typically, no wick structure is used, and theinner surface where the primary loop working fluid is contained is non-porous glass. The circulationof the working fluid (usually, ethanol) is only controlled by gravity and by the surface tensioneffects taking place on a flat glass/ liquid interface.” (Text and pics: Fiaschi and Manfrida, ECOS2012, paper 312)
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Heat pipes /1
“A heat pipe is a simple device that can quickly transfer heat from one point to another. They are often referred to as the "superconductors" of heat as they possess an extra ordinary heat transfer capacity and rate with almost no heat loss.” (source: SN01)
Heat taken up at one end vaporises a liquid, which after moving to the other end, condenses and releases heat. As a result of gravity or capillary forces (using a porous material referred to as ”wick”) the liquid returns to the evaporator.
Picture: D03
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Heat pipes /2 Heat pipe main components:
– The container– The working fluid– The ”wick”
A cylindrical heat pipe
Pictures: D03
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Suitable heat pipe fluids can cover the range from very low to very high temperatures
The pressure inside the heat pipe is the saturation pressure of the fluid at the fluid’s temperature; freezing temperatures are not much affected by pressure
Most used are water (50 – 200°C) and methanol (20 – 120°C)
Picture: D03
Heat pipes /3
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Heat pipes: Loop heat pipe (LHP)
Very important: the compensation chamber, which is a two-phase reservoir that– Helps to
establish LHP pressure and temperature,
– Maintain the working fluid inventory
Picture: RK06
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Heat pipe applications /1 Spacecraft thermal control Electronics cooling
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refrigerationdemand
Pictures: S?
LiBr chiller with cold storage
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Source: Gerstler et al., General Electric Co. 2011; download: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA566206
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Sources #8 A11: R. C. Arora ”Refrigeration and air conditioning”, 2nd. Ed. PHI
Learning Private Limited , New Delhi (2011) CB98: Y.A. Çengel, M.A. Boles “Thermodynamics. An Engineering Approach”,
McGraw-Hill (1998) D03: İ. Dinçer “Refrigeration systems and applications” Wiley (2003) DR02: İ. Dinçer, M. Rosen “Thermal energy storage” Wiley (2002) KJ05: D. Kaminski, M. Jensen ”Introduction to Thermal and Fluids Engineering”,
Wiley (2005) RK06: D. Reay, P. Kew ”Heat pipes. Theory, design and applications” Butterworth-