1

ww

w.n

tb.c

h/ie

s

1

IESInstitute for Energy Systems

Cordin ARPAGAUS1, Fréderic BLESS1, Jürg SCHIFFMANN2, Stefan S. BERTSCH1

1NTB University of Applied Sciences of Technology Buchs, Switzerland2Ecole Polytechnique Fédérale de Lausanne, Switzerland

2016 Purdue ConferencesMulti-Temperature Heat Pumps –A Literature Review

2

ww

w.n

tb.c

h/ie

s

Outline

1. Motivation2. Objectives3. Heat pump cycles for multi-temperature applications4. Advantages and challenges5. Simulation study (COP, 2nd Law efficiency) – comparison of cycles6. Conclusions

3

ww

w.n

tb.c

h/ie

s

• Requirements of heating & cooling at different temperature levels at the same time

• Upgrading low quality heat• Research question:

Which multi-temperature heat pump cycles are reported in the literature?

Motivation

adapted from IEA (2014)International Energy Agency

> 35°C> 70°C

120 – 150°C

> 15°C-10 – 25°C

> 30°C 50 – 100°C

more advanced cycles are needed

Potential heat sources and heat sinks

Single-stageheat pump

cycle

4

ww

w.n

tb.c

h/ie

s

Objectives

1. Screening of research activity based on publications with focus on cycles with heating/cooling at two temperature levels

2. Identification of design strategies to reach multi-temperature levels

3. Classification of identified cycles4. Identification of trends and research areas5. Comparison of cycles

1. COP (1st Law) and exergetic efficiency (2nd

Law efficiency)2. Thermodynamic simulation based on EES

software (Klein, 2015)

Extended version of this study:Cordin Arpagaus, Frédéric Bless, Jürg Schiffmann, Stefan S. Bertsch,Multi-temperature heat pumps: A literature review, International Journal of Refrigeration (2016), http://dx.doi.org/10.1016/j.ijrefrig.2016.05.014

5

ww

w.n

tb.c

h/ie

s

SUPERMARKET REFRIGERATION

freshfood+2°C

ambient air+25°C

frozen food-23°C

Multi-stage compressorsCascades

(Multi)-ejectors

5

ww

w.n

tb.c

h/ie

s

6

ww

w.n

tb.c

h/ie

s

SUPERMARKET REFRIGERATIONMulti-stage compressors

HT: 21 to 32°C MT: -10 to -5°C LT: -35 to -30°C

Transcritical CO2 booster system

(Advansor, 2015; Bitzer, 2014; Sharma et al., 2014) 6

ww

w.n

tb.c

h/ie

s

7

ww

w.n

tb.c

h/ie

s

SUPERMARKET REFRIGERATION

Multi-stage compressorsCascades

(Multi)-Ejectors

CascadesCascade cycle with secondary loop

HT: ambient airMT: -7°CLT: -29°C

(Bitzer, 2014; Hill Phoenix, 2011; Sharma et al., 2014)7

ww

w.n

tb.c

h/ie

s

8

ww

w.n

tb.c

h/ie

s

SUPERMARKET REFRIGERATION

Multi-stage compressorsCascades

(Multi)-Ejectors

HT: 36°CMT: -3°CLT: -33°C

(Hafner et al., 2014; Schönenberger, 2014, 2013)

(Multi)-Ejectors

8

ww

w.n

tb.c

h/ie

s

Multiple ejector cycle with CO2

9

ww

w.n

tb.c

h/ie

s

HOUSEHOLD REFRIGERATION

freshfood+5°C

ambient air+25°C

frozen food-18°C

Expansion valvesEjector

9

ww

w.n

tb.c

h/ie

s

10

ww

w.n

tb.c

h/ie

s

HOUSEHOLD REFRIGERATION

Parallel expansion valve cycle with two evaporators

(Visek et al., 2014; Yoon et al., 2011, 2010)

Expansion valves

HT: 20°C MT: 5°C LT: -18°C

10

ww

w.n

tb.c

h/ie

s

11

ww

w.n

tb.c

h/ie

s

HOUSEHOLD REFRIGERATION

Expansion valvesEjector

(Elakhdar et al., 2007)

Ejector

HT: 28 to 44°CMT: -5 to 10°CLT: -40 to -20°C

Subcritical ejector cycle

11

ww

w.n

tb.c

h/ie

s

12

ww

w.n

tb.c

h/ie

s

AUTOMOTIVE AIR CONDITIONING

batterycooling+20°C

cooler+40°C

cool air+5°C

Image Source: http://calopera.com/41596/2016-tesla-model-x-open-door-side-view.html

Expansion valve cyclesEjector cycles

12

ww

w.n

tb.c

h/ie

s

13

ww

w.n

tb.c

h/ie

s

HOUSEHOLD WATERHEATING

solar+40°C

hot water+60°C

ground source+5°C

Image Source: www.yorkshireenergysolutions.co.uk

Multi-stage compressorsCascades

Separated Gas Coolers

13

ww

w.n

tb.c

h/ie

s

14

ww

w.n

tb.c

h/ie

s

HOUSEHOLD WATERHEATING Separated Gas Cooler

(Blanco et al. 2012, 2013a, 2013b)

Separated gas cooler and desuperheater for combined space and hot water heating

HT: 65°CMT: 30 to 45°CLT: -5 to 5°C

14

ww

w.n

tb.c

h/ie

s

15

ww

w.n

tb.c

h/ie

s

INDUSTRIAL WASTE HEAT RECOVERY

dryingprocess+70°C

process heat+120°C

waste heat+40°C

Image Source: https://commons.wikimedia.org/w/index.php?curid=7500704

Multi-stage compressorsCascades

15

ww

w.n

tb.c

h/ie

s

16

ww

w.n

tb.c

h/ie

s

application areas

heat pump technologies

17

ww

w.n

tb.c

h/ie

s

Design strategies – classification of cycles

TRL: Technology Readiness Level (status 2016)

18

ww

w.n

tb.c

h/ie

s

Comparison of cycles – efficiency analysis Ref

Reference cycle with two parallel

heat pumps

MC 1Multi-stage

compressor cycle with subcooler

(Stoecker, 1998)

MC 2 with open

economizer(Granwehr and Bertsch, 2012;

Uhlmann et al., 2014)

MC 3 with closed economizer(Granwehr and Bertsch, 2012)

CAS Cascade(Dincer &

Kanoglu, 2010; Kanoǧlu, 2002)

EXV Expansion

valve (Visek et al.,

2014; Yoon et al., 2010, 2011)

MC 4with booster

system(Advansor, 2015;

Bitzer, 2014; Sharma et al.,

2014)

EJ Ejector

(Elakhdar et al., 2007)

19

ww

w.n

tb.c

h/ie

s

Thermodynamic models - Assumptions

1. no pressure drops, no heat losses2. no superheating, no subcooling3. ideal heat exchangers and separators 4. cascade heat exchanger (∆𝑇𝑇𝐶𝐶𝐶𝐶𝐶𝐶= 5°𝐶𝐶)5. isenthalpic expansion6. isentropic compressor efficiency

(η𝑐𝑐 = 0.7)7. ejector model approach according to

Kornhauser (1990)• 80% efficiencies for motive

nozzle, suction nozzle and diffuser

Example: Ejector (EJ) cycle

20

ww

w.n

tb.c

h/ie

s

Operating conditions for the simulation

ratio of the two heat sources𝛽𝛽 =

�̇�𝑄𝑀𝑀𝑀𝑀�̇�𝑄𝑀𝑀𝑀𝑀 + �̇�𝑄𝐿𝐿𝑀𝑀 0 < 𝛽𝛽 < 1

𝐶𝐶𝐶𝐶𝐶𝐶𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 =�̇�𝑄𝐻𝐻𝑀𝑀

𝑊𝑊𝑐𝑐𝑐𝑐,1 + 𝑊𝑊𝑐𝑐𝑐𝑐,2

η2𝑛𝑛𝑛𝑛 =𝐶𝐶𝐶𝐶𝐶𝐶𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑛𝑛𝐶𝐶𝐶𝐶

Heating Application

𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑛𝑛𝐶𝐶𝐶𝐶 = 𝑓𝑓 𝛽𝛽,𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑛𝑛𝐶𝐶𝐶𝐶,𝐿𝐿𝑀𝑀 ,𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑛𝑛𝐶𝐶𝐶𝐶,𝑀𝑀𝑀𝑀

21

ww

w.n

tb.c

h/ie

s

Simulation Results - First and Second Law Efficiencies

heat supply ratio across the LT and MT

evaporators𝛽𝛽 =

�̇�𝑄𝑀𝑀𝑀𝑀�̇�𝑄𝑀𝑀𝑀𝑀 + �̇�𝑄𝐿𝐿𝑀𝑀

Ref Reference cycle (two parallel heat pumps)MC 1 Multi-stage compressor cycle with subcoolerMC 2 with open economizerMC 3 with closed economizerMC 4 with booster systemCAS Cascade cycleEXV Expansion valve cycleEJ Ejector cycle

COP vs. β Second Law efficiency vs. β

𝐶𝐶𝐶𝐶𝐶𝐶 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐

𝛽𝛽 𝛽𝛽η 2

𝑛𝑛𝑛𝑛

Heating Application

22

ww

w.n

tb.c

h/ie

s

Conclusions

1. Design strategies for multi-temperature heat pumps:• Multi-stage compressors, cascades (with secondary loops), expansion

valves, (multiple) ejectors, and separated gas coolers• Most heat pump designs use two heat sources and one heat sinks

2. Multi-temperature applications• Major part in refrigeration (supermarket, households)• Domestic space heating and hot water production

3. Simulation of COP and 2nd Law efficiency - cycle comparison • Multi-stage compressor > cascade > ref > ejector > expansion valve cycles

4. Outlook – current R&D efforts• Multiple ejectors in transcritical CO2 cycles (efficiency improvement)• Multi-stage compressors with better capacity control and intercooling• Oil-free compressors• Natural refrigerants with low ODP and GWP

23

ww

w.n

tb.c

h/ie

s

23

IESInstitute for Energy Systems

Thank you for your attention!

NTB University of Applied Sciences of Technology Buchs, SwitzerlandCampus Buchs Campus St. Gallen HTW Chur (Cooperation Partner) 9471 Buchs 9013 St. Gallen 7004 Churoffice@ntb.ch www.ntb.ch www.htwchur.ch

Contact details: cordin.arpagaus@ntb.ch+41 81 755 34 94

http://www.ntb.ch/fue/institute/institut-fuer-energiesysteme-ies/projekte/

WEBLINK