Refrigeration (Kylteknik) - Åbo Akademiusers.abo.fi/rzevenho/REF17-OH8.pdf · Heat pumps /1 Using a refrigeration cycle for ... low-temperature (waste) heat, replacing sources of

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. 2017

ÅA 424519 Refrigeration / Kylteknik

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8.1 Heat pumps

22.2.2017 Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku

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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-freeheating, and air conditioning P

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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


outputheatingseasonaltotalHSPF


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


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

COPHP ~ TH / (TH-TL) → COPHP decreases if TH-TL increases

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


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 concentratingprocesses;

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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Heat pumps in Finland(2015 - 2016)

Source / picture: http://www.sulpu.fi (accessed: 13.1.2017)

Heat pumps: to be continued

Total capacity (2015): ~730 000 HPs using~ 5 TWh yeararound buildings


Heat pump system @ ÅA VST (T&FE)

22.2.2017Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 12

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



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


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


Heat pipe applications /1 Spacecraft thermal control Electronics cooling

Sources: http://mscweb.gsfc.nasa.gov/msctech/attd.htmand RK06

CAPL-3 on space shuttle


Heat pipe applications /2 Computer

CPU cooling

Pictures: RonZ ↑http://www.gamersnexus.net/guides/981-how-cpu-coolers-work ↑


Heat pipe applications /3 Prevention of permafrost

thaw (Alaska)

Snow melting, de-icing (Japan, also Russia, USA)

using ground source heat!

Pictures: RK06



8.3 Cold thermal energy storage(cold TES)


Cold thermal energy storage Night-time off-peak (cheaper) energy

can be stored (batteries) for day-timepeak use for air conditioning

Cooling capacity can be stored as coldor frozen water, or other materials such as glycol and eutectic salt + water systems

Also special phase transitionmaterials (PCMs) were developed

Note also that with loweroutside (night-time) temperatures, cooling and freezing processes are more efficient!

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PCMs: see http://www.teappcm.com/ (Accessed Feb. 2017)

Chilled water vs. ice banks


Source: S?

Dependson ΔT


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Ice bank with plastic-filled balls

↑ An ice CTES system has 18x more capacity per kg than a water CTES system

Example of an ice TES system →atmosperic ice ball (single tank) system

Pictures: DR02

Other ice banks


A brine solution (glycol-water mixture) flows through the heat exchanger tubes.

Source: S?Pic: http://www.theadmat.com/gatrane/equipment/calmac/offpeak-tank.jpg

Partial storage vs. full storage


refrigerationdemand

Pictures: S?

LiBr chiller with cold storage


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-

Heinemann (2006) S??: Refrigeration technology, Siemens Building technologies (year?) section 7

https://www.downloads.siemens.com/download-center/Download.aspx?pos=download&fct=getasset&id1=8359

SKL: Suomen Kylmäliikkeiden Liitto http://www.skll.fi/

SN01: Shankara Narayanan K.R. “ What is a Heat Pipe?” http://www.cheresources.com/htpipes.shtml

Ö96: G. Öhman ”Kylteknik”, Åbo Akademi University (1996) http://users.abo.fi/rzevenho/Kylteknik%20_Ohman%2019962000.pdf

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Refrigeration (Kylteknik) - Åbo Akademiusers.abo.fi/rzevenho/REF17-OH8.pdf · Heat pumps /1 Using a refrigeration cycle for ... low-temperature (waste) heat, replacing sources of