Experimental investigation of heat recovery from R744 based

refrigeration system

ZAHID ANWAR

Master of Science Thesis

KTH School of Industrial Engineering and Management

Energy Technology EGI-2011-02MSC

Division of Applied thermodynamics & Refrigeration

SE-100 44 STOCKHOLM

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Experimental investigation of heat recovery

from R744 based refrigeration system

Zahid Anwar

Master of Science Thesis Energy Technology 2011:02MSC

KTH School of Industrial Engineering and Management

Division of Applied Thermodynamic and Refrigeration

SE-100 44 STOCKHOLM

iv

v

Master of Science Thesis EGI 2011/ETT:02MSC

Experimental investigation of heat recovery from

R744 based refrigeration system

Zahid Anwar

Approved

Date

Examiner

Professor Per Lundqvist

Supervisor

Yang Chen

Commissioner

Contact person

Abstract

With increasing energy price and concern on environmental impacts, more attention has been

paid to refrigeration and heat pump systems. Several regulations have already been applied

on the choice of refrigerants and the search for more energy efficient system solutions has

been intensified. Due to these reasons, CO2 as an environmental benign natural refrigerant

has attracted great interest since 1990s.

Due to its low critical temperature (31.1 oC) and high critical pressure(73.8 bar), CO2

refrigeration cycle works as a transcritical cycle, which means part of the cycle is located in

supercritical region, where the temperature is independent of the pressure. Depending on the

heat sink fluid temperature profile the temperature glide of CO2 in the supercritical region

makes it possible for the CO2 refrigeration cycle to have less irreversibility in a heat recovery

process than traditional refrigeration cycles.

A new CO2 refrigeration/heat pump test rig is built at the division of Applied

Thermodynamics and Refrigeration to investigate CO2 refrigeration/heat pump systems. With

the newly built test rig following main tasks were performed in this thesis work,

Overall system performance on various imposed operating conditions.

Second law analysis of the system by exergy and entropy balance methods

Basic components testing, namely the heat exchangers and the compressor.

Uncertainty analysis.

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Table of Contents

Table of Contents ..................................................................................................................... vii

List of Figures ........................................................................................................................... ix

Nomenclature ............................................................................................................................ xi

Chapter 1 .................................................................................................................................... 1

1.1 Heat pump basics ................................................................................................................. 1

1.1.1 Heat Pump ..................................................................................................................... 1

1.1.2 Heat pump classification ............................................................................................... 1

1.1.3 Why heat pump ............................................................................................................. 2

1.2 Heat pump water heater (HPWH) ........................................................................................ 3

Chapter 2 .................................................................................................................................... 5

CO2 and the transcritical cycle ................................................................................................... 5

2.1 Refrigerant progression history........................................................................................ 5

2.1.1 Ozone Layer Depletion ............................................................................................. 5

2.1.2 Global warming ........................................................................................................ 5

2.2 CO2 as refrigerant ............................................................................................................ 6

2.2.1 History of CO2 .......................................................................................................... 8

2.3 CO2 Transcritical cycle .................................................................................................... 9

2.4 CO2 heat pump water heater case studies ...................................................................... 11

Chapter No 3 ............................................................................................................................ 15

3.1 System performance Evaluation ........................................................................................ 15

3.1.1 Coefficient of Performance (COP) ............................................................................. 15

3.2 References for Transcritical cycle ................................................................................. 16

3.2.1 The modified Lorenz cycle ..................................................................................... 16

3.2.2 Ideal Lorentzen cycle .............................................................................................. 17

3.2.3 Real Lorentzen cycle ............................................................................................... 17

Chapter No 4 ............................................................................................................................ 19

Heat Pump testing at KTH ....................................................................................................... 19

4.1 CO2 heat pump at KTH (system layout) ........................................................................ 19

4.1.1 System modifications .............................................................................................. 20

4.2 Working principle .......................................................................................................... 20

4.2.1 Methodology ........................................................................................................... 21

4.2.2 Direct and Indirect mass flow measurement ........................................................... 21

4.3 Results ............................................................................................................................ 23

4.3.1 Overall system performance from meter reading ................................................... 23

Case A .......................................................................................................................... 23

Case B .......................................................................................................................... 26

Case C Part 1 ................................................................................................................ 28

Case C Part 2 ................................................................................................................ 30

Case D .......................................................................................................................... 32

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4.3.2 Results based on the compressor data ..................................................................... 34

Case A .......................................................................................................................... 34

Case B .......................................................................................................................... 35

Case C Part 1 ................................................................................................................ 36

Case C Part 2 ................................................................................................................ 36

Case D .......................................................................................................................... 37

4.3.3 Results for the components testing ......................................................................... 39

4.3.3.1 Heat exchanger effectiveness ........................................................................... 39

4.3.3.1.1 For the 1ST

heat exchanger ........................................................................ 39

4.3.3.1.2For the 3RD

heat exchanger ........................................................................ 41

4.4.4 Second law analysis of the transcritical cycle ......................................................... 44

Chapter 5 .................................................................................................................................. 49

Uncertainty Analysis ................................................................................................................ 49

5.1 Uncertainty in the measurement of heating capacity ..................................................... 49

5.1.1 Uncertainty in temperature measurement ...............................................................