Investigation of the performance of individual sorption components of a novel thermally driven heat pump for solar applications

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Master’s of Science Thesis

KTH School of Industrial Engineering and Management Energy Technology EGI-2014-074MSC

Division of Applied Thermodynamics and Refrigeration SE-100 44 STOCKHOLM

Investigation of the performance of individual sorption components of a novel thermally driven heat pump for solar

applications

Corey Blackman

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Master of Science Thesis EGI-2014-074MSC

Investigation of the performance of individual sorption components of a novel thermally driven cooling system for solar applications

Corey Blackman

Approved

30 July 2014

Examiner

Björn Palm

Supervisor

Björn Palm

Commissioner Contact person

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Abstract

An enhanced-modularity thermally driven chemical heat pump was conceptualised as a second generation product for various heating and cooling applications with special emphasis on solar applications. The typical characteristics of the absorption heat pump were studied and the key performance parameters were selected for further investigation. An experimental test rig was constructed to allow for the testing of each component’s performance characteristics with special attention being paid to the ability to interchange components to test various configurations as well as to the facilitation of standardised relatively rapid testing. The heat transfer coefficient of the condenser/evaporator was found to be between 260 and 300 W/m²-°C during evaporation and between 130 and 170 W/m²-°C during condensation. Salt type has major impact on the system’s cooling power and cooling energy with the LiBr and water sorption pair having a 62% higher cooling/heating power than LiCl with the same matrix type and thickness. Matrix types and sorption pairs were compared with regards to the principal parameters of power and energy density with results ranging from 60 to 163 Wh/litre. The final section of the study tackled the theoretical foundation behind the system processes with modelling and simulation of the processes and comparison with the experimental data. The model makes the foundation of the continuous development of a more detailed and accurate physical model to enhance the design and optimisation process of the system.

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Acknowledgements

To my friends and family, mother and father for their eternal support.

Thanks to professor Björn Palm for his guidance and patience in this thesis project.

To Olof Hallström for his immense support, availability and untethered knowledge.

To Dmitri Glebov and Göran Bolin for their support and assistance.

Special thanks to all employees of ClimateWell AB.

A mis profesores y colegas de la Universidad de Oriente, Santiago de Cuba quienes hicieron más fácil esta segunda tesis con todo el aprendizaje que me aportaron.

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Preface

The shift to a more sustainable society is a daunting task, with continual debates over environmental degradation, global warming and depletion of natural resources pushing the sustainability challenge to the forefront. Despite much news and public exposure, moving towards sustainable technologies and practices is still on a relatively slow rise in spite of its agreed upon importance by many.

In the built environment a large percentage of energy is utilised to keep us comfortable all year round within our wooden, steel or concrete cocoons protecting us from the ever more impressive harshness and temperature extremes of nature. A positive shift has been seen to improve building facades, insulation and general building planning. However the systems used to create comfortable indoor conditions need an overhaul and energy and exergy efficiency upgrades. Over the years, heating in cold and temperate zones has become more and more efficient due to improved insulation used to trap internally generated heat for increased comfort in low outdoor temperature conditions. This increased winter efficiency on the other hand has brought with it increased summer discomfort, as internally generated heat is unwantedly trapped indoors under high outdoor temperature conditions.

Reducing indoor comfort energy requirements for the entire year incorporating both heating and cooling requirements is of paramount importance. Employing technology and systems that are both energetically and exergetically efficient, that use environmentally benign substances and materials, that are easily maintained, have good technical longevity and are economically viable is key to sustainability.

Solar driven heating and air conditioning systems have the possibility of either totally or partially meeting indoor comfort heating or cooling requirements while reducing non-renewable energy use and its associated environmental impacts.

The heat driven cooling system components studied in this research thesis are based on prototypic iterations from a currently commercially available system. The state-of-art prototypes are designed in order to exploit the modular potential of the technology and mitigate limitations in a cost effective manner.

Systems can be driven by solar, waste process and/or district heat, or any form of low grade heat with temperature levels between 70°C and 200°C.

The research focuses on studying the performance characteristics of the system components with various configurations as well as increasing the knowledge base in testing procedures and system optimisation. By designing highly modular components the possibility of giving birth to a wealth of well designed, robust, quickly manufacturable and easily adapted-to-purpose heat driven cooling systems becomes tangible.

Fabricating systems that have a range of capacities that are as low or as high as applications require i.e. a few kW for individual homes and small offices to ≥100 kW for commercial, industrial and municipal applications increases significantly the scope and impact of the systems.

Even though the heat driven cooling system can be driven by any low grade heat source, driving it with solar energy is one of the more attractive applications, given the system’s intrinsic capability of being able to store energy chemically for an indefinite period of time without losses. This is a feature that is very important when utilising an intermittent energy source like solar energy. Cost effectiveness is also increased by reducing backup system needs. The systems adaptability to utilise solar energy is therefore a principal consideration in all design aspects and performance studies.

Given the system’s potential and possibilities, especially in my homeland of Barbados, continuous research is needed to ensure full implementation potential is reached. There are many variations, performance tests, design optimisation and process characterisation elements that need to be studied. Much of this work can be carried on well into the realm of PhD studies especially in terms of modelling operational sub- processes to advance possibilities of predicting and optimising system performance for any application under any given conditions.

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A vision of an efficient and cost effective alternative for heating and air conditioning systems that can be employed not only in large but also in small applications is what intrigues me most about this thesis research. Bestowing both developed and developing nations with a tool to combat environmental abuse along with promoting energy independence in the built environment is, with a bit of work, quite possible in the near future.

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Nomenclature

(ρCp)eq – equivalent volumetric heat capacity (J/kg-K)

̇ – mass flow rate of water in vessel heat exchanger (kg/s)

̇ - mass flow rate of water vapour to or from matrix material (kg/s) - temperature of water at inlet of the vessel heat exchanger (K)

- temperature of water at outlet of the vessel heat exchanger (K) Amx – area of matrix material in contact with vessel wall (m²)

Aw – Area of vessel wall in contact with heat exchanger (m²) c - concentration of water vapour in the matrix (-)

c – vapour concentration/density (kg/m³)

cb – bulk concentration (i.e. concentration of water vapour in the vapour channel) (-) Cp – heat capacity of material (J/kg-K)

Cp,L – heat capacity of salt/salt hydrate (J/kg-K) Cp,mx – heat capacity of matrix material (J/kg-K)

CpL – fluid specific heat capacity at constant pressure (J/kg-K) cpcev – specific heat capacity of condenser/evaporator vessel (J/kg-K) cpmx – specific heat capacity of matrix material (kJ/kgK)

cprv – specific heat capacity of reactor vessel (J/kg-K) cpw - specific heat capacity of water (kJ/kgK)

D – diffusion coefficient (m²/s) din – inner diameter of vessel (m) dout – outer diameter of vessel (m)

Echarge – energy required for the charging process (Wh)

Ecool – cooling energy originating from the discharge process (Wh)

Eheat – thermal energy rejected (to the heat sink) in the discharge process (Wh) Hf – specific enthalpy of liquid water in matrix (kJ/kg)

Hg – specific enthalpy of water vapour (kJ/kg)

hhx – heat transfer coefficient for thermal transfer from vessel wall to the heat exchanger (W/m²K) hmx – heat transfer coefficient for thermal transfer from matrix to vessel wall (W/m²K)

K – gas diffusivity (m²/s)

k – thermal conductivity of matrix material (W/m-K) Ka – kinetic coefficient (1/m²-s)

kc – mass transfer coefficient

keq – equivalent thermal conductivity (W/m-K) kl – thermal conductivity of salt/salt hydrate (W/m-K)

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L – length of vessel (m) Ma – kinetic coefficient (-)

Mcev – mass of condenser evaporator vessel (kg) Mmx – mass of matrix material (kg)

Mrv – mass of reactor vessel (kg)

Mw - mass of water contained in matrix material (kg)

N0 – is the flux expression (kg/m²-s) that may represent a flux into a much large surrounding, a phase change or a flux due to chemical reaction.

Pc – constraint (vapour) pressure (Pa) Pea – absorption equilibrium pressure (Pa)

Pi – pressure at the interface between product and reactant grain (Pa) q – heat flux (W/m²)

Q – heat source – which corresponds as the heat of dissolution plus latent heat of condensation (J) Q – heat source or heat sink (W/m³)

Q0 – Total heat rejected (W)

QA – Heat rejected due to absorption/adsorption (W) QC – Heat rejected due to condensation (W)

qccool - thermal energy rejection rate from fixed condenser/evaporator vessel via its heat exchanger (W) Qcharge - average heating input during the charge process (W)

qcloss – thermal losses of fixed condenser/evaporator (W)

qctotal – total thermal energy rejection rate from fixed condenser/evaporator vessel (W) QE – Cooling power due to evaporation (W)

QG – Driving heat added to the generator (W)

qinput – thermal load on fixed condenser/evaporator (W) qinput = power input to electrical heater (W)

qvcool - cooling effect of cooling fluid passing through the heat exchanger of the test vessel (W) qvloss – thermal losses of test vessel (W)

qvtotal – total cooling effect of test vessel (W)

R – reaction rate expression for water vapour with salt/salt complex (kg/(m³-s)) rc – interface radius (m)

rg – grain radius (m)

T – temperature of material (K)

T – temperature of the discrete matrix element (K) Tamb – Ambient temperature (°C)

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Tavec – average temperature of exterior wall of fixed condenser/evaporator (°C) Tavev – average temperature of exterior wall of the test vessel (°C)

Tc – Condensation temperature (K)

Tc – constraint (matrix/salt) temperature (K)

Tce – temperature of on the condenser/evaporator vessel surface (K) Tcev – average temperature of condenser/evaporator vessel (K) Te – Evaporation temperature (K)

Tg – Generation temperature (K)

Tmx – average temperature of matrix (K)

Tr – temperature of on the reactor vessel surface (K) Trv – average temperature of reactor vessel (K)

Tsat – saturation temperature of vapour in the system (°C) Tvin – water temperature into test vessel heat exchanger (°C) Tvout – water temperature out of test vessel heat exchanger (°C) u - velocity vector (m/s)

UAcloss – thermal loss coefficient of fixed condenser/evaporator determined by heat loss calibration (see Appendix) (W/°C)

UAloss – heat transfer coefficient describing losses (or gains) from the vessel (W/K)

UAvloss – thermal loss coefficient of test vessel determined by heat loss calibration (see Appendix) (W/°C) Uv – overall heat transfer coefficient from inside the test vessel to its exterior wall (W/m²°C).

ϴL – volume fraction of salt/salt hydrate (-) ϴmx – volume fraction of matrix material (-) ρ – density of material (kg/m³)

ρL – density of salt/salt hydrate (kg/m³) ρL – fluid density (kg/m³)

ρmx – density of matrix material (kg/m³)

- specific enthalpy change of absorption (kJ/kg) - specific enthalpy change of desorption (kJ/kg)

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Abbreviations

CHPC – Combined Heat, Power and Cooling COP – Coefficient of Performance

PID – Proportional Integral Derivative TCA – Thermochemical Accumulator SOC – State of Charge

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List of Tables

Table 1-1-LiBr + Water absorption chiller component descriptions [26], ...20

Table 1-2 -Typical operational parameters and general characteristics of heat driving cooling systems [26]. ...24

Table 1-3 - Main performance characteristics of ClimateWell SolarChiller ...31

Table 1-4 -General Characteristics of ClimateWell SolarChiller ...32

Table 2-1 - Properties of hygroscopic salts used in this study [22][24][24][25] ...35

Table 3-1 - Components used for experimental testing (not to scale) ...43

Table 4-1 – Results summary for tests done with 9mm thick CF matrix material ...53

Table 4-2 - Results summary for tests done with 1 mm thick CF matrix material ...53

Table 4-3 - Testing parameter for GE450-16 reactor performance tests...55

Table 4-4 - Testing parameter for GE450-16 reactor performance tests...58

Table 4-5 - Testing parameters for matrix materials performance tests ...62

Table 4-6 - Cycle data for tests with NCS + LiBr + H2O ...62

Table 4-7 - Cycle data for tests with CF9mm + LiBr + H2O ...62

Table 4-8 - Testing parameter for NCS and CaBr2 performance tests ...64

Table 4-9 - Cycle data for tests with NCS + CaBr2 + H2O ...64

Table 5-1 – Summary of experimental and simulation results ...76

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List of Figures

Figure 1-1 - Schematic of a LiBr and water absorption chiller ...20

Figure 1-2 - Schematic of a silica gel and water adsorption chiller [28]...23

Figure 1-3 - COP of typical Absorption and Adsorption chillers versus driving temperature [26] ...25

Figure 1-4 – ClimateWell SolarChiller (Left). Main components of SolarChiller (Right). ...26

Figure 1-5 - Pictorial diagram and schematic of the discharging process of the solar cooling unit. ...27

Figure 1-6 – Pictorial diagram and schematic of the charging process of the solar cooling unit ...28

Figure 1-7 - Schematic of SolarChiller system when used for cooling. ...28

Figure 1-8 - Schematic of SolarChiller system when used for space heating...29

Figure 1-9 - Schematic of SolarChiller system when used for domestic water heating. ...30

Figure 1-10 - Schematic of SolarChiller system when used for domestic water preheating and cooling...31

Figure 1-11 - Modular core component for increased system flexibility ...32

Figure 2-1 - Water vapour pressure at the surface of pure LiCl and LiBr salts versus temperature [24]. ...36

Figure 2-2 - Energy flows in the absorption system ...37

Figure 2-3 - Ideal intermittent absorption cycle schematic ...38

Figure 3-1 – Schematic of experimental setup for component performance tests. ...42

Figure 3-2 - Test setup. [1] Condenser/Evaporator [2] Pressure Sensor [3] Reactor with Heat Pads and Insulation [4] PID Power Controller [5] Adjustable Temperature Water Bath (Heat Sink) [6] Peristaltic Pump ...43

Figure 3-3 - Screen shot of experiment monitoring and recording set up. ...48

Figure 4-1 - Diagrams of CE220-50 with interior cladding with CF9mm ...50

Figure 4-2 – Characteristic diagram evaporation cycle with CF9mm matrix material ...51

Figure 4-3 - Figure 3 3 – Characteristic diagram condensation cycle with CF9mm matrix material ...51

Figure 4-5 – Characteristic diagram of parameters and performance profile of system during the condensation process. ...52

Figure 4-4 - Figure 3 3 – Characteristic diagram evaporation cycle with CF1mm matrix material ...52

Figure 4-6 - Overall heat transfer coefficient versus evaporator and reactor temperature difference for CF9mm matrix material during discharge ...54

Figure 4-7 - Overall heat transfer coefficient versus evaporator temperature for CF9mm matrix material during discharge ...55

Figure 4-8 - Overall heat transfer coefficient versus evaporator temperature for CF1mm matrix material during discharge ...56

Figure 4-9 - Overall heat transfer coefficient versus condenser temperature for CF9mm matrix material during charge. ...56

Figure 4-10 - Overall heat transfer coefficient versus condenser temperature for CF1mm matrix material during charge. ...57

Figure 4-11 - Average cooling power versus evaporator temperature for 1 hour discharge cycle with GE450-16 Reactor with LiBr and LiCl. Heat sink temperature to the inlet of the reactor 44°C. ...58

Figure 4-12 - Average heating power versus evaporator temperature for 1 hour discharge cycle with GE450-16 Reactor with LiBr and LiCl. Heat sink temperature to the inlet of the reactor 44°C. ...59

Figure 4-13 - Characteristic diagram of 1 hour discharge cycle of GE450-16 with LiCl and water ...60

Figure 4-14 - Characteristic diagram of 1 hour discharge cycle of GE450-16 with LiBr and water...60

Figure 4-15 - Average cooling power heat sink temperature for discharge cycle with GE450-16 Reactor with LiCl. ...61

Figure 4-16 - Average heating power heat sink temperature for 1 hour discharge cycle with GE450-16 Reactor with LiCl. ...61

Figure 4-17 - Cooling power density comparison of NCS and CF9mm matrix material with sorption pair LiBr and Water...63

Figure 4-18 - Cycle coefficient of performance comparison of NCS and CF9mm matrix material with sorption pair LiBr and Water ...63

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Figure 4-19 - Cooling power density for matrix material NCS and sorption pair CaBr2 and water ...65

Figure 4-20 - Cycle COP for matrix material NCS and sorption pair CaBr2 and water ...65

Figure 5-1 - Diagram of various system parameters and corresponding dependencies. ...68

Figure 5-2 - One dimensional model of vessel wall, matrix and vapour channel in COMSOL ...72

Figure 5-3 - Three dimensional curve generated in COMSOL from temperature, salt concentration and vapour pressure of LiCl salt and salt hydrates data inputs. ...73

Figure 5-4 – Diagram of experimental result of 1 hour discharge cycle of GE450-16 with LiCl and water with reactor heat exchanger inlet temperature at 44°C. ...74

Figure 5-5 - Diagram of simulation of 1 hour discharge cycle of GE450-16 with LiCl and water with reactor heat exchanger inlet temperature at 44°C. ...74

Figure 5-6 - Diagram of experimental result of 1 hour discharge cycle of GE450-16 with LiCl and water with reactor heat exchanger inlet temperature at 30°C. ...75

Figure 5-7 - Diagram of simulation of 1 hour discharge cycle of GE450-16 with LiCl and water with reactor heat exchanger inlet temperature at 30°C. ...75

Figure 5-8 - Cooling effect that would be generated in an attached evaporator ...77

Figure 5-9 - Diagram showing temperature distribution in the matrix at an instant during simulation ...77

Figure 7-1 - Exerpt of table input to COMSOL. ...83

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Chapter 1- Introduction

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ClimateWell is a Swedish company that develops sorption heat pumps based on the so-called ‘triple state absorption process’ or ‘three-phase sorption cycle’. The cycle functions as a batch absorption process where there are two main phases; charge and discharge. The system comprises two main components the first of which is known as the reactor while the second is called the condenser/evaporator. The reactor component contains a matrix infused with hygroscopic salt, while the condenser/evaporator contains pure water. The latter component may act as either condenser or evaporator depending on the flow direction of the water vapour within the system.

During the process of charging, the difference in vapour pressure between the salt and the pure water causes water to evaporate from the end of the module (acting as an evaporator in this case) and form a salt hydrate and/or salt solution in the reactor. This process creates a temperature difference between evaporator and reactor where the evaporator can absorb heat at below ambient temperatures, creating a cooling effect, while heat is rejected at above ambient temperature from the reactor. This process continues until all water has been transferred from the condenser/evaporator and absorbed into the reactor matrix. The module can then be regenerated by heating the reactor to force water desorption from the reactor matrix where it condenses in the second component (now acting as a condenser) with condensation heat being removed at above ambient temperature. The regeneration phase is aptly called charging.

Objectives

The main objectives of the thesis work are to:

 Define and refine laboratory-scale experimental procedures for measurement of component performance parameters.

 Investigate the influence on system performance of individual sorption components.

 Investigate the performance of different matrix materials and salts.

 Improve and validate the current system’s theoretical model or formulate a new one.

Problem Formulation and Methodology

In the testing of the two main components of the sorption cooling device; the reactor and the integrated (dual purpose) condenser/evaporator there’s a tendency for these components to influence each other as they function. At present there is no method, given the pressure and temperature variations throughout the absorption cycles, to assess how each given parameter (namely temperature, heat transfer fluid flow rate, sorption power and time) affects each individual component. This fact makes it difficult to fully understand the limiting factors created by each component on the overall process and to optimise each component for maximum system performance. Additionally, optimal design for different applications utilising different matrix materials, system configurations and sorption pairs is also challenging given the current dearth of knowledge in the performance characteristics of various component configurations.

The typical characteristics of the absorption heat pump were studied and the prime performance parameters were selected for further investigation. An experimental rig was constructed to allow for the testing of each component’s performance properties with special attention being paid to the ability to interchange components to test various configurations as well as to the facilitation of rapid testing. The final section of the study then tackles the theoretical foundation behind the system processes with modelling and simulation of the processes and comparison with the experimental data. The model is to be the foundation of the continuous development of a more detailed and accurate physical model to enhance the design and optimisation process of the system.

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1 Space Cooling and Air Conditioning

Air conditioning systems have become a necessity in modern times, as in the case of homes, offices, commercial establishments, industry, laboratories etc. To this effect, the habitants of homes have seen the benefits of air conditioning as a comfort convenience; office managers have seen its benefits in improving the efficiency and productivity of their employees. Commercial business owners have seen the benefits of air conditioning for the well-being of their clients, and in the industrial sector, not only for comfort for workers but also in some cases to improve the manufacturing process. The use of air conditioning systems has also permeated into the transport sector with both public and private vehicles such as cars, buses, trucks, trains & planes all requiring systems that provide comfortable interior conditions [1].

Air conditioning may be defined as the process by which air is treated to regulate temperature, humidity, quality, velocity, sound and pressure levels [1]. Where air cooling deals primarily with the control of air temperature to maintain it within required levels.

Over the last half century, there has been an increasing trend towards more dense building plans and increased thermal insulation of building envelopes. This along with a significant boost in the use of information technology systems, higher illumination levels and more rigid comfort and air quality standards has brought about the overheating of buildings even in cooler, temperate climates. This signifies that even in colder climates cooling is required for a large portion of the year. As the heating demand is reduced in these improved building practices a proportional increase in cooling demand comes about.

This signifies that even in colder climates cooling is required for a large portion of the year [2].

Given the importance of air conditioning in modern society and the growing demands in all echelons of the world, the onus falls on the technologists and policy makers to reduce the environmental impact of air conditioning, while maintaining the same level of comfort and convenience for consumers. With growing environmental concern, increased fuel prices, modernisation of developing economies and a thrust towards energy independence, there has been growing emphasis placed on solar driven cooling cycles.

These types of systems have the potential to revolutionise air conditioning in the built environment by providing significant reduction in the use of fossil fuels bringing with it considerable emissions reductions.

Given the fact that space heating and cooling tend to be a large percentage of total energy consumption in the built environment, any impact on this consumption will have major impact on overall emissions.

Running systems with solar energy has the intrinsic advantage that generally the more solar energy available the more cooling is needed reducing the need for storage and compensatory system over-sizing.

Added benefits of being able to provide heating when required and cooling when desired make solar driven heat pumping a very attractive incorporation into the built environment.

1.1 Solar Cooling and Air Conditioning

Using electricity to produce low grade heating is not the most exergetically efficient method. It can be argued that using a high quality energy source such as electricity to produce low quality energy services such as heating is not the most sustainable way to deliver indoor climate services [4]. On the basis of efficiency, comparing vapour compression systems with heat driven systems may be somewhat of a dispute. Where system efficiency measured in terms of useful cooling energy output versus total electrical energy input for a vapour compression system yields typical efficiencies between 2.0 and 4.0. While for a heat driven system the performance determined via the quotient of total useful cooling energy and of total heat energy supplied is between 0.5 and 1.4 [6]. However, if the electricity used to power the vapour compression chiller comes from a typical fossil fuel powered plant, the overall efficiency of the vapour compression air conditioning plant will be around 1.05 to 1.22 considering electrical generation efficiency and electricity transmission and distribution losses [21]. This tends to place both technologies at a similar level of efficiency where the less mature heat driven technologies still have significant potential for improved efficiency with further and more intense research and development. Not to mention significant added environmental benefits especially since heat sources may include waste heat and/or solar energy.

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Heat driven cooling and air conditioning is also very promising in combination with electrical power generation. Since most electricity generation processes include burning fossil fuels where work is extracted from a fluid which has a heat rejection temperature higher than surrounding ambient temperatures.

Utilising this rejected energy is very important in augmenting total system efficiency.

Heat driven cooling can be carried out by a variety of methods, where three principal techniques have reached commercial availability, these are:

 Absorption Cooling - The most popular method of producing cooling from heat is by use of an absorption cooling system. This type of system employs a chemical heat pumping mechanism where refrigerant vapour produced in the evaporator is absorbed by chemical affinity in a solution in liquid form. This solution is then easily pressurised to condenser pressure by means of a pump, where heat is used to drive off the previously absorbed refrigerant vapour from the solution.

Though this type of system requires some electricity to run pumps and control systems, the amount of electrical energy is significantly less than that required for vapour compression systems.

 Adsorption Cooling ^–Adsorption cooling is a chemical heat pumping mechanism similar to that of absorption. The main difference is in the sorption pair used to produce the cooling effect. A solid adsorbent such as silica gel is used in conjunction with water as the refrigerant. The vapour produced in the evaporator is adsorbed on to the surface of the solid silica gel. After the adsorption process is complete the silica gel is heated up to liberate the attached water molecules as water vapour, this vapour is then condensed in the condenser. As in the case of absorption cooling, electricity is needed to run pumps and controls however, the quantity of electrical power required is significantly less per kW of cooling power generated, than in a vapour compression system of similar capacity.

 Desiccant Cooling – Desiccant cooling systems, also known as open adsorption cooling systems, work with a very similar principle as adsorption system where silica gel is employed as the adsorbent. However, in this type of system a stream of air is cooled directly, rather than chilling water for use in fan coils or radiant cooling distribution systems. Moisture is removed directly from the air by passing it over the silica gel, and then this air is sensibly and/or evaporatively cooled to provide the required indoor climate.

1.1.1 Absorption Cooling

Absorption chillers have been effectively used for large capacity cooling systems of several hundred kW for many years, employing waste heat from industrial applications, natural gas, and combined heat and power installations. One of the most used sorption pairs¹ is lithium bromide (LiBr) (absorbent) and the absorbate is water. A typical absorption chiller comprises four (4) main components; generator, absorber, evaporator and condenser as shown in Figure 1-1. Water which acts as the refrigerant in the LiBr + Water chiller leaves the condenser as pure liquid refrigerant (8) and passes through an expansion valve (9) (where its pressure is reduced) to that of the evaporator where it evaporates. This change of phase from liquid to vapour absorbs thermal energy (QE) which produces the required cooling effect. The vapour generated in the evaporator is absorbed by the strong salt solution in the absorber. This absorption process generates heat due to the chemical reaction between the water vapour and the salt solution. In the absorber this heat is rejected to an appropriate heat sink which could be cooled water from a cooling tower, ground source heat exchange or swimming pool. In the generator weak solution is regenerated by the addition of heat which causes the desorption of water. The heat added in the generator (QG) is the system driving heat required to carry out the cooling process. Desorbed water vapour is cooled down to liquid water in the condenser by rejecting thermal energy (QC). The process is a cyclic one which can be likened to that of a vapour compression system where the compressor is replaced by the absorber and generator.

1 Refers to hygroscopic salt absorbent and refrigerant that work together in a heat driven cooling system [26].

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Figure 1-1 - Schematic of a LiBr and water absorption chiller

Table 1-1-LiBr + Water absorption chiller component descriptions [26],

Component Brief Description

Condenser Water vapour (refrigerant) is condensed to liquid water in this component by the removal of heat (QC).

Evaporator

In this element, liquid refrigerant evaporates changing to vapour phase. This phase change absorbs heat from the evaporator vessel which in turn creates the desired cooling effect (QE). The water vapour must be extracted from the evaporator or the internal pressure increases reducing and eventually halting the evaporation process.

Absorber

Concentrated (strong) salt solution flows into the absorber component which absorbs water vapour from the evaporator forming a diluted salt solution.

During the absorption process heat is generated when water vapour changes from vapour to liquid phase (i.e. heat of condensation) and additionally the heat of dilution which is the chemical energy released when a particular solvent is added to a solution. As the temperature of the solution rises its ability to absorb water vapour rapidly diminishes, therefore the generated heat (QA) must be removed by a cooling medium which traverses the absorber to improve the absorption process and thus system performance.

Generator The generator is in charge of ‘re-strengthening’ the diluted salt solution that

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leaves the absorber by facilitating the desorption of water from the salt solution.

To carry out this operation heat must be supplied to the generator (QG).

Generated vapour passes to the condenser while the strong solution makes its way back to the absorber.

Pump The pump moves the salt solution from the low pressure absorber to the higher pressure generator.

Heat Exchanger

The heat exchanger recuperates and transfers thermal energy from the hot solution leaving the generator to the cooler solution entering it. This in turn reduces the heating load on the generator and also reduces the cooling load on the absorber which improves overall system efficiency.

Expansion Valve Produces strangulation as the liquid water pressure is reduced from the higher pressure in the condenser to the lower pressure of the evaporator.

Regulation Valve The solution pressure in the generator is reduced to the lower pressure in the absorber in the quantity necessary to meet the cooling load of the system.

1.1.1.1 Benefits of Absorption Cooling

Compared with other heat driven cooling technologies absorption cooling is the most mature of these techniques and also exhibits the highest coefficient of performance (COP). Some of the most important benefits of using absorption cooling technology are:

 Quiet and vibration free operation – since there are very few moving parts the system is very quiet and generates no vibrations.

 No harmful refrigerants used – with lithium bromide and water as the absorption pair these substances are safe and environmentally benign.

 Low operating costs – if waste or solar heat is employed as the main energy source of the chiller then the only energy cost would be that for the relatively small amount of electricity required to run the system.

 Frees up electricity for other applications – if the absorption cooling system replaces a vapour compression system of similar capacity the electricity avoided for the cooling process could be used in another process or system without incurring significantly increased overall energy costs.

 Low maintenance – the limited amount of moving parts of the system directly translates to reduced maintenance requirements compared to vapour compression systems.

1.1.1.2 Issues with Absorption Cooling

Air leakage – absorption systems which utilise lithium bromide (LiBr) and water as the sorption pair are very susceptible to air leakage. LiBr solution is highly corrosive and a continuous leak can lead to severe corrosion. Additionally, system performance will deteriorate significantly with air infiltration since very low pressures are required for water to evaporate in the evaporator, air in the evaporator increases pressure and therefore limits the lowest temperature at which water evaporates in the system [21].

Materials – with most employed construction materials such as mild steel and copper it is difficult to prevent corrosion under the aggressive conditions which originate from utilising LiBr solution. More costly materials may need to be employed such as stainless steel or titanium which is generally less economically viable as plant size decreases.

Design – condenser sizing has a particularly significant impact on plant performance, therefore much attention needs to be given in the design of the condenser taking special consideration in available heat

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sink temperatures. In many cases condensers need to be oversized to ensure good performance under unfavourable conditions. This has a tendency to drive up system costs.

Control – excellent system control is necessary to ensure good performance and additionally to ensure no damage occurs to system components. In LiBr + water systems the formation of crystals in the solution should be avoided at all costs to avoid damage to pumps and blockage of spray mechanisms (if employed).

Freezing in the evaporator could also cause significant damage to heat exchanger tubing.

Efficiency – overall system efficiency is highly susceptible to generator, heat sink and evaporator temperatures. In this case the thermal COP is determined by: . While the electrical COP is determined by:

Where QElec is the electrical power consumption of the system, including pumps and control apparatus.

1.1.2 Adsorption Cooling

Like absorption cooling systems, adsorption cooling systems work with a sorption pair such as silica gel (adsorbent) and water (refrigerant). The process is referred to as adsorption due to the fact that the refrigerant vapour becomes attached to the surface of the solid sorbent as opposed to absorption in which the vapour becomes dissolved in a solution. In a typical adsorption cooling system there are two chambers packed with solid silica gel adsorbent (see Figure 1-2). Each chamber is attached to a common evaporator and a common condenser via a flap valve. The evaporator is opened to one chamber where water vapour evaporates and is adsorbed by the silica gel in the chamber. The adsorption process liberates heat which is removed via the heat exchangers. The adjacent chamber is heated via its heat exchanger while being open to the condenser. In this case desorption takes place where water vapour moves from the adsorber to the condenser where it is condensed to liquid water as it is cooled by the heat exchangers of the condenser.

Having two silica gel adsorption chambers allows for quasi-stationary operation where one chamber undergoes adsorption while the other undergoes desorption and then the processes swap. This way an almost constant cooling capacity can be attained by the cyclic operation.

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Figure 1-2 - Schematic of a silica gel and water adsorption chiller [28]

1.1.2.1 Benefits of Adsorption Cooling

In addition to the cited benefits of absorption cooling systems adsorption systems are good for use with solar energy installations since the driving temperature of the machine tends to be relatively low which makes for more efficient use of solar thermal energy. Adsorption chillers also have a somewhat simple construction without the corrosion problems exhibited by LiBr + Water absorption machines.

1.1.2.2 Issues with Adsorption Cooling

Air leakage – like absorption chillers, air leakage can significantly deteriorate system performance since the system depends on very low internal pressures (vacuum) to operate.

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Large size – silica gel tends to have a low volumetric sorption capacity which signifies that to provide large cooling capacities a large volume of substance is required making the overall machine size relatively large.

Control – the cyclic nature of the system operation complicates control and the various heat and mass recovery strategies that improve system performance.

Design – as with the case of absorption chillers, the performance of the adsorption chiller depends on the design parameters in terms of condenser sizing as well as heat sink and chilled water temperature levels.

Efficiency – overall system efficiency is highly susceptible to generator, heat sink and chilled water temperatures. In this case the thermal and electrical COP is determined by same means as absorption chillers.

1.1.3 Comparison of Absorption and Adsorption Cooling

Absorption and adsorption chillers have various similar attributes, as the heat driven systems both possess the primary benefits of having a working principle that is thermally rather than electrically driven.

However, each system type has its benefits and disadvantages when compared to the other. The table below explores the typical technical attributes of the two system types.

Table 1-2 -Typical operational parameters and general characteristics of heat driving cooling systems [26].

Attribute

Absorption Cooling with

Lithium Bromide -

Water

Closed Cycle Adsorption Silica

Gel - Water

Refrigerant Water Water

Sorbent LiBr Silica Gel

Chilling Carrier Water Water

Chilling Temperature 6 - 20°C 6 - 20°C Driving Temperature 80 - 110°C 55 - 100°C Heat Sink Temperature 30 - 50°C ≤35°C

Cooling Power Range 35 – 7 000kW 10 – 10 000kW

COP 0.6 – 0.75 0.3 – 0.7

Approximate Investment Cost 550 – 1000€/kW 500 – 1000€/kW

Maintenance Low Low

Control Medium

Complexity

Medium Complexity

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In adsorption systems, in contrast to absorption, there is technically no lower limit to the heat sink temperature since there is no chance of crystallisation of the sorbent. Absorption systems require higher driving temperatures than adsorption systems; however they have higher coefficients of performance for a given cooling water (i.e. heat sink) temperature [26].

1.2 The ClimateWell SolarChiller

ClimateWell has developed a thermally driven chiller which is specialised for utilisation with solar energy.

It incorporates the benefits of both adsorption and absorption systems while integrating a large thermochemical storage capacity. This allows the machine to work quite effectively with intermittent heat sources, with high efficiency under part load conditions, as well as provide cooling for extended periods in the absence of a heat source. Nevertheless, it also suffers from similar drawbacks in terms of air leakage and system component design and operating parameters sensitivity.

The ClimateWell SolarChiller product may be classified as a chemical heat pump with integrated thermochemical storage (dubbed thermochemical accumulator (TCA)), which is driven by heat. The main functioning principle is based on a chemical absorbent (hygroscopic salt) and absorbate (water) pair. The system works similarly to an adsorption refrigeration system where there is a batch process of sorption and desorption. However, in the case of the SolarChiller system, a hygroscopic salt is employed making it, technically speaking, an absorption process driven system. The SolarChiller is characterised by a patented tri-state system where water vapour, solid salt as well as salt solution all interact in various phases of the system’s operation. The two main components can be represented as two vessels connected to each other via a pipe (communication channel). Both vessels are evacuated with the vessel known as the absorber or reactor clad with a special matrix material containing the chemical absorbent salt lithium chloride. The second vessel – the condenser/evaporator contain the absorbate (refrigerant) which is pure water.

Figure 1-3 - COP of typical Absorption and Adsorption chillers versus driving temperature [26]

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1.2.1 System Operational Modes Discharge

When cooling and/or heating is required the communication channel between the two vessels is opened and the water vapour travels towards the absorbent (hygroscopic salt) due to the difference in surface

Figure 1-4 – ClimateWell SolarChiller (Left). Main components of SolarChiller (Right).

Reactor

• Acts as generator and absorber (see absorption chiller description).

• Contains lithium chloride (LiCl) salt suspended in a matrix.

Condenser/Evaporator

• As the name suggests this component acts as condenser or evaporator depending on operational mode.

• Contains water suspended in a matrix.

Heat Sink

• System required to reject excess heat from the SolarChiller. This may be a cooling tower, an air cooled heat exchanger, swimming pool, or borehole . It may also used to extract heat from a given medium depending on operational mode.

• Provides a sink for thermal energy where thermal energy can be rejected at an adequate temperature level.

Solar Thermal Energy Collection System

• Interconnected group of solar collectors (flat plate, evacuated tube or compound parabolic panels).

• Provides thermal energy at the required temperature level for system operation.

Barrel

• A connected reactor and condenser/evaporator pair.

• Each solar chiller comprises 2 barrels which allow for continous (quasi-stationary) operation.

/Evaporator

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vapour pressure, where the vapour pressure of the absorbent is lower in the reactor than in the evaporator. The phase change which occurs when the liquid water evaporates and becomes vapour creates a cooling effect in the evaporator which can be harnessed for air conditioning purposes via heat exchange with a secondary refrigerant fluid. In the reactor absorption of the water vapour occurs releasing heat which needs to be carried away by heat exchange with an external cooling medium (heat sink) (see Figure 1-5). The absorption process continues with gradually diminishing cooling/heating capacity until the absorbent becomes saturated at which time the process halts and no more cooling/heating power can be harnessed. This operational process is also known as the discharge, where the stored thermochemical energy is released as cooling which is harnessed from the evaporator and heating which is discarded (or harnessed) via the reactor [12].

Charge

After discharge, the system must be ‘charged’ again which is done via heating the reactor. This heat can be derived from solar thermal energy or waste heat. By increasing the temperature in the reactor the opposite process, that is, desorption occurs. The absorbate is desorbed from the absorbent which in turn condenses in the condenser which is cooled by a cooling fluid from the heat rejection system (see Figure 1-6). This process continues until all the absorbate is desorbed from the absorber leaving dry absorbent crystals, thus completing the cycle. Depending on the length of time the charge is carried out, the heat source and heat sink temperatures a state of charge (SOC) can be determined, where 0% SOC is a system that is fully discharged and can provide no more heating or cooling while 100% SOC refers to a system that is fully charged and can provide maximum heating and/or cooling effect when swapped to discharge.

Figure 1-5 - Pictorial diagram and schematic of the discharging process of the solar cooling unit.

To cooling

distribution system

(between 7 & 15°C)

From cooling distribution system Cooling fluid

(between 30 & 50 °C)

Reactor ^Condenser/

Evaporator

Return to heat sink

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Cooling energy can be extracted from a charged system via discharging, that is, allowing water to evaporate from the condenser/evaporator while be absorbed in the reactor. The heat sink is connected to the absorber to remove absorption heat and the condenser/evaporator connected to the cooling distribution system which leads to a fan coil or chilled ceiling system to provide the required space cooling. The chilled water returns from the distribution system at a higher temperature where it is again cooled by heat exchange with the evaporator. The lower the heat sink temperature and the higher the chilled medium temperature the better the system performance. Therefore good design of heat sink and distribution systems play an important role in minimising overall system costs.

Space Heating Cooling Tower

Figure 1-6 – Pictorial diagram and schematic of the charging process of the solar cooling unit

Space Cooling Solar Collectors

SolarChiller Heating fluid from solar

collectors (70 to 110 °C)

Cooling fluid (20 to 50°C)

Reactor ^Condenser/

Evaporator

Return to solar collectors

Return to Heat Sink

Figure 1-7 - Schematic of SolarChiller system when used for cooling.

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Charged energy may be extracted for heating purposes by discharging the system connecting the condenser/evaporator to an appropriate heat source and the reactor to the heating distribution system which leads to fan coils, radiators or a radiant floor heating system. The condenser/evaporator removes heat from the heat source fluid flowing through its heat exchanger while the evaporated vapour from the condenser/evaporator is absorbed in the reactor which in turn heats up. The heat is then exchanged with the heat transfer fluid of the heat distribution system. Higher heat source temperatures and lower distribution circuit temperatures enhance system performance. Therefore connecting the heat source to a heat recovery circuit from exhaust air or any other low temperature waste heat (e.g. sewage water) can significantly augment system performance in terms of COP and power. It is of course possible to connect the solar heating system directly to the heating distribution system to meet heating demand during the daytime, where thermal energy surplus can be stored in the SolarChiller system. This way it can be utilised at night or during cloudy periods. Since energy is stored as chemical energy when the system is charged there are essentially no thermal losses of energy in storage state. This type of storage is therefore superior to thermal storage systems such as accumulator tanks that store hot water which have inherent losses especially when storing water at relatively high temperatures (>60°) [5].

Space Heating

SolarChiller Solar Collectors

Ventilation Heat Recovery

Figure 1-8 - Schematic of SolarChiller system when used for space heating.

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Water heating is also a possibility where the system may be used to heat domestic water (55 to 60°C) or preheat (30 to 35°C). Full heating is possible from direct coupling of the water accumulator to the solar heating system or by connecting the tank to the SolarChiller while it is being discharged in heating mode.

Preheating is possible during cooling mode where space cooling and water preheating can occur simultaneously and also in charging mode via heat rejected from the condenser thus improving overall energy utilisation of the system.

SolarChiller

Domestic Water Heating Solar Collectors

Ventilation Heat Recovery

Figure 1-9 - Schematic of SolarChiller system when used for domestic water heating.

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1.2.2 SolarChiller Performance Characteristics

The main performance indicators of the absorption cooling system include cooling power, cooling energy, heating power, heating energy and coefficient of performance (COP).These indicators depend on driving heat and heat sink temperatures as well as evaporator temperatures. Due the cyclic nature of the system’s charge and discharge processes, available cooling power is also highly time dependent so averages over a given time period are most relevant. Additionally, utilising solar energy for charging also gives rise to fluctuations in the charging cycle temperature and/or power, though these can be somewhat mitigated by system design. Fluctuations in charging temperature and power causes fluctuations in charging time and maximum state of charge (SOC). It should be noted that these time dependent effects can have a strong impact on cycle COP. The SolarChiller system contains a connected reactor and condenser/evaporator is called a barrel and each system contains two barrels with a maximum output of 10 kW each. To provide a constant maximum output of 10kW barrel A is discharged while barrel B is charged. When the discharging power goes below the required level for Barrel A discharging is stopped and barrel B is discharged while barrel A is charged. Analogous to the adsorption cycle each barrel is charged and discharged cyclically.

However, in the case of the SolarChiller due to the storage capacity simultaneous charging and discharging can be carried out during the daytime allowing for full charge and the possibility of night time operation without the need for backup heating.

Table 1-3 - Main performance characteristics of ClimateWell SolarChiller

Mode Storage Capacity Maximum

Output Capacity Thermal COP Electrical COP

Cooling 56 kWh 10 kW 0.68² 15 – 303

Heating 64 kWh 18 kW 0.94³ 15 - 545

2Charging Temperature: 80°C, Heat Sink Temperature: 30°C, Cooling Temperature: 18°C

3Charging Temperature: 80°C, Heat Source Temperature: 15°C, Heating Temperature: 35°C

Space Cooling Solar Collectors

SolarChiller

Domestic Pre-Heating

Figure 1-10 - Schematic of SolarChiller system when used for domestic water preheating and cooling.

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Due to the SolarChiller’s sizable storage capacity, a fully charged system can operate at full cooling capacity for approximately 5.6 hours or at half capacity for 11.6 hours. This signifies that for overnight operation or operation during cloudy periods there is little need to rely on auxiliary heating systems to ‘re- charge’ the device.

Table 1-4 -General Characteristics of ClimateWell SolarChiller

Average Charging Energy per Cycle 114 kWh

Maximum Heat Source Temperature 120°C

Average Electrical Power Consumption 22W Average Electrical Energy Consumption 200 kWh/year

Useful Lifetime 15 years

Heat Exchange Fluids Tyfocor or Water

Sorption Pair LiCl + H2O

1.3 System Research Motivation

In efforts to increase system reliability and reduce certain design drawbacks the core technology employed in the SolarChiller can be further enhanced in future system version developments to create a more modular and flexible system. Such a system could potentially improve the performance and reduce maintenance requirements of the solar heat driven cooling technology and also extend its application and integration into:

 Combined heat, power and cooling systems (CHPC)

 Dedicated water heating and/or water cooling systems

 Direct air cooling or heating apparatus

 Solar refrigeration (especially for rural areas/off-grid applications)

 Mobile air conditioning systems

The enhanced modular components would involve a diminutive reactor and condenser/evaporator connected in similar way as the larger system. However each core component could be connected in such a way as to provide a wide range of cooling and/or heating power outputs while providing for different heat exchanger arrangements, reduced moving parts and diverse sorption pairs to facilitate highly efficient adaptation to the aforementioned applications.

Figure 1-11 - Modular core component for increased system flexibility

Communication Channel

Condenser/Evaporator

Reactor

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Chapter 2 – Absorption Systems

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2 Absorption System Fundamentals 2.1 Matrix Concepts

The matrix is not much more than a porous material that is employed to house the hydroscopic salt in such a way as to enhance heat transfer between salt particles and the heat transfer fluid and also to enhance mass transfer allowing water vapour to easily come into contact with salt/salt solutions during system operation. The current matrix material employed in the novel absorption chemical heat pump developed by ClimateWell has specific properties which are important to the system’s overall performance. Low thermal conductivity and the carcinogenic nature of the matrix can be listed as the principal issues with the material. Various studies are being carried out to enhance the properties of the currently employed matrix material along with various alternatives.

The most desirable properties for a matrix material include [10]:

o High suction ability (large capillary force) o High ability to retain liquid

o Corrosion and degradation resistance with the various absorbate-salt pairs used (i.e.

chemically inert)

o High temperature resistance (up to 300°C) o High thermal conductivity

o Low thermal mass

o Expected technical lifetime of at least 20 years

In the evaluation of the sorption components of the system the characterisation of the processes which occur in the matrix are fundamental. All process mechanisms have strong time dependence and heat transfer surface, matrix porosity and thickness are important parameters that must be taken into consideration [10]. There are various processes which occur at the matrix level during the operation cycle of the thermal heat pump system. These include (but are not limited to):

Preheating – This phase occurs at the beginning of the charging cycle the matrix material is initially heated where heat is delivered to the matrix. The desorption rate at this stage is considered to be quite small [10].

Charging – Surface desportion of the absorbate rate increases with heat being transferred into the matrix via the reactor heat exchanger. Charging continues until all of the absorbate is removed leaving crystallised salt (provided that charging power is high enough) [10].

Discharging – This may be considered the reverse of the charging process. Due to the differences of vapour pressure at the surface of the salt infused matrix and the absorbate housed in the evaporator, the absorption of the absorbate into the salt occurs. Initially absorption occurs at the vapour to solid level, with absorbate vapour interacting directly with salt crystals. Subsequently the process occurs at the vapour-solution level when the absorbate vapour then reacts with the salt solution. Cooling power originate in the discharge cycle from the absorption of water (or other refrigerant) from the evaporator into the salt infused matrix. As more absorbate is absorbed the vapour pressure at the matrix surface increases and therefore occasions a decrease in cooling power until the process halts [10].

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2.2 Sorption Pairs

For heat driven cooling purposes, sorption (absorbent-refrigerant) pairs are highly important with regards to system application and system performance. Various sorption pairs have different chemical and physical properties which are assessed in relation to the necessities of the system.

Preferable properties of the refrigerant include [10].

 A large latent heat of vaporisation - to produce a large cooling effect for a given mass of refrigerant that is absorbed.

 A low heat of desorption – to reduce energy/temperature requirements to desorb a given mass of refrigerant.

 Low thermal capacity – to reduce the energy required to raise the absorbent to the required desorption temperature and also to provide for high heating and cooling powers of the absorbent.

 Low toxicity and environmental impact –spills, leakage or human contact should pose minimal risk.

 Low cost

In this research work three different sorption pairs are employed:

 Lithium Chloride (LiCl) + Water

 Lithium Bromide (LiBr) + Water

 Calcium Bromide (CaBr2) + Water

Many different sorption pair combinations are possible including mixtures; however these are beyond the scope of this study.

Table 2-1 - Properties of hygroscopic salts used in this study [22][24][25]

Property LiCl LiBr CaBr2

Molecular Weight (g/mol)

42.4 86.9 199.9

Melting

Point (°C) 614 547 730

Solubility in Water (g/100g- H2O)

63.7 (0°C) 130 (95°C)

145 (4°C) 254 (90°C)

125 (0°C) 312 (100°C) Physical

Properties

White deliquescent crystals

White cubic

deliquescent crystals or pinkish white granular powder, odourless, sharp bitter taste.

White powder or crystals, odourless, sharp saline taste.

Typical

Uses Air conditioning, welding, batteries, heat

Drying agent, batteries, medicine, air

Photography, medicine, drying agent, food

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desiccant, soft drink additive.

conditioning, pharmaceuticals, humectants.

preservative, fire retardant, wood preservative.

Potential Health

Hazards Eye and skin irritation

Extremely hazardous in case of ingestion, severe eye irritation, skin irritation.

Severe eye irritation, skin irritation, respiratory tract irritation if ingested.

Figure 2-1 - Water vapour pressure at the surface of pure LiCl and LiBr salts versus temperature [24].

The total vapour pressure of a solution is the sum of partial vapour pressures of solute and solvent. In the case of solutions like LiCl and water and LiBr and water the vapour pressure of the LiBr or LiCl is very low, therefore the vapour pressure at the surface of the solution is attributed to that of water vapour.

2.3 System Performance

The thermally driven heat pump system though it functions in a batch/cyclic process similar to that of an adsorption chiller as described in Chapter 1, the fundamental operation process is that of an absorption system. In order to adequately characterise the system’s core components on an energetic basis an adaptation of characteristic absorption and adsorption models is used. Expressions are defined for the

Investigation of the performance of individual sorption components of a novel thermally driven heat pump for solar applications

Investigation of the performance of individual sorption components of a novel thermally driven heat pump for solar

applications

Corey Blackman

Abstract

Acknowledgements

Preface

Table of Contents

Nomenclature

Abbreviations

List of Tables

List of Figures

Chapter 1- Introduction

Objectives

Problem Formulation and Methodology

1 Space Cooling and Air Conditioning

1.1 Solar Cooling and Air Conditioning

1.2 The ClimateWell SolarChiller

1.3 System Research Motivation

Chapter 2 – Absorption Systems

2 Absorption System Fundamentals 2.1 Matrix Concepts

2.2 Sorption Pairs

2.3 System Performance