SOLAR WATER HEATING SYSTEM INTEGRATED WITH

PCM AS THERMAL ENERGY STORAGESALEEM MOHAMMED HAMZA

250873614

OVERVIEW• INTRODUCTION• REVIEW TABLE• EXPERIMENTAL SETUPS• PERFORMANCE ENHANCEMENTS USING PCM• TEMPERATURE VS TIME • EFFECT OF FLOW RATE • EFFECT OF MASS OF PCM USED• DRAWBACKS• CONCLUSION

INTRODUCTION• Solar energy is the most abundant,

cleanest, renewable energy source available.

• Main Components:• Solar Collector• Storage Tank• Heat Exchanger• Heat Transfer Fluid• Expansion Tank

• Heat is stored by increasing the temperature of water in the form of sensible heat.

REVIEW TABLES.No

Name of Researcher

PCM Used Objectives

 1 Kamil Kaygusuz Calcium Chloride HexaHydrate (CaCl2.6H2O)

• The effect of latent heat storage in water based solar heating system.

• Effect of NTU on performance of SWHS with PCM 2 S. Canbazoglu

et alSodium Thiosulphate

Pentahydrate (Na2S2O3.5H2O)

• Thermal performance of an open loop passive SWHS (natural circulation) and compared its performance against the conventional system.

3 L.F Cabeza et al

Sodium Acetate Trihydrate PCM

graphite module(C2H3NaO2.3H2O)

• Compare performance of PCM SWHS with conventional.

• To study the performance with different amounts of PCM.

 4 Mettawee & Ghazy

Paraffin Wax • A parametric experimental study of a compact PCM solar collector to investigate the effects of water flow rates on performance.

 5 Prakash et al  Paraffin Wax • The effect of different flow rates and • Depth of PCM on the performance of the solar

water heating system and compared it with a system having no PCM storage.

EXPERIMENTAL SETUPS

(1) KAMIL KAYGUZUS [1] (2) CANBAZOGLU ET AL [2] (3) CABEZA ET AL [3]

EXPERIMENTAL SET UPS CONTD…

(4) METTAWEE & GHAZY [4] (5) PRAKASH ET AL [5]

PERFORMANCE ENHANCEMENTS USING PCM

• Disodium hydrogen phosphate-dodecahydrate is the best pcm for solar water heating applications followed by sodium sulfate decahydrate.

• Due to their higher latent heats & specific heat capacity. • Maximum of 3.45 times of the energy stored using conventional

can be achieved.

RESULTS OF CANBAZOGLU ET AL THEORETICAL ANALYSIS[2]

TEMPERATURE VS TIME• PCM CHARGING:

• Temperature of PCM rises gradually as it gains heat from the solar heated water.

• At melting point of PCM temperature remains constant.

• This is due to latent heat absorption at constant temperature (phase change).

• PCM DISCHARGING:• Temperature of PCM decreases

gradually as it loses heat to the stored water.

• During solidification of PCM temperature remains constant.

• This is due to latent heat release at constant temperature (phase change).

CONTD…• Canbazoglu et al :

• In conventional system, the storage water temperature decreases as solar radiation decreases until the sunrise of the next day.

• In system with PCM, the temperature of the water decreases indicating PCM charging.

• Off sunshine hours, the water in the tank gains temperature and remains constant due to latent heat release by PCM.

• Since no hot water was extracted, the temperature of water in the storage tank remained constant. Otherwise, a drop in the temperature of storage water would be expected.

EFFECT OF FLOWRATES• The efficiency of the system decreases with increase in the flow rates. Thus, Time for

which the energy is stored and supplied is less.• Due to:

• Low thermal conductivity of solid paraffin wax.• More water carries away more heat from the PCM, thereby generates hotter water but reduces

the time for which the energy is stored in the system.

*Average efficiency with varying flow rates from Prakash et at experiments[5] ** Mettawee & Ghazy results[4]

System Studied 20 l/hr 30 l/hrConventional Storage water

heater

38.04 33.29

Storage water heater with 2cm

PCM

50.44 47.46

Storage water heater with 4cm

PCM

61.36 59.86

EFFECT OF MASS OF PCM• Increase in the amount of PCM used in the system increases the time for which

the energy is stored.• More PCM extracts more heat from water. thus, low water temperature during

PCM charging.• There is an optimal value after which the efficiency would drop.

Effect of Mass of PCM on Storage energy time from Cabeza et al experiment[3]

 No. modules PCM mass (kg)

 Volume occupied (%) Storage Energy

Time (hrs)

2 2.1 2.05 2

4 4.2 4.1 2.30

6 6.3 6.16 2.45

CONTD..• Kaygusuz graph:

– As NTU increases, fluid outlet temperatures decreases during charging of PCM .– Increase in NTU increases the storage energy time.

• Prakash et al graph: – The peak temperature of the water in storage tank decreases as mass of PCM increases.– Hot water was generated for longer time as mass of PCM was increased.

Conclusion:– Lower fluid outlet temperatures, as PCM extracts more heat from water during charging process. – Higher energy storage time as mass of PCM increases and thus hot water generation for longer time during discharging.

DRAWBACKS• Kaygusuz considered the PCM to behave ideally, thus neglecting

problems such as phase segregations and super cooling.• Canbazoglu et al observed that the PCM lost its ability to change phase

after 25-30 cycles of solidifying and melting process.• Canbazoglu et al could have used a closed system with forced system

using a pump to enhance efficiency rather than using a open loop passive system.

• Salt hydrates absorb moisture, thereby requiring expensive encapsulation methods. Increases total cost of the system.

• Storage water temperature of systems with PCM is always less than 60C which leads to legionella growth in the tank. No control measures where discussed to prevent its growth.

• Thermal losses from the collector where not taken in consideration.

CONCLUSION• Integrating PCM in solar water heating systems is of great benefit. • The best salt hydrates among those studied for solar water heating application is

disodium hydrogen phosphate dodecahydrate. • As high as 3.45 times of mass of hot water was generated using PCM when

compared to the conventional system.• The PCM stores the energy from the solar heated water during sunshine hours.

During off sunshine hours the water gets heated by the PCM. This is a isothermal process due to large energy absorbed or released due to latent heat of PCM.

• Flow rates – decreased efficiency of the system but higher temperature of water at the outlet. Energy storage time decreased.

• Mass of PCM used – Increased the energy storage time of the system, but lower temperatures of storage water during charging process.

• The use of PCM reduces the storage tank volume required to store the same amount of energy with that in conventional system. This reduces the overall cost of the system.

REFERENCES• Kayugz k, et al. experimental and theoretical investigation of latent heat storage for

water based solar heating systems. energy convers manage 1995;36(5):315–23.• Canbazoglu S, S¸Ahinaslan A, Ekmekyapar A, Gokhan Aksoy Y, Akarsu F. enhancement

of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar water-heating system. energy build 2005;37:235–42.

• Cabeza LF, Ibanez M, Sole C, Roca J, Nogues M. experimentation with a water tank including a PCM module. solar energy mater solar cells 2006;90:1273–82.

• Mettawee E-BS, Assassa GMR. experimental study of a compact PCM solar collector. energy 2006;31:2958–68.

• Prakash J, Garg HP, Datta G. A solar water heater with a built-in latent heat storage. energy convers manage 1985;25(1):51–6.

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