Study on phase change material thermal characteristics during air charging/discharging for energy saving of air-conditioner

Abstract

In this study, RT-18 HC phase change material (PCM) having a melting point at 18 °C in a form of packed bed was used to reduce the power consumption of a 1 TR inverter air conditioner. A set of spherical balls was packed and integrated with the air conditioner for reducing the air temperature before entering the evaporator coil. The enthalpy method was developed for calculating the PCM temperatures and verified by testing results. The operating parameters such as bed thickness, air mass flow rate, inlet air temperature, operating time and properties of air and PCM during charging and discharging modes were also correlated in dimensionless forms. With the correlations, the charging and the discharging modes for three PCM bed thicknesses: 0.08 m, 0.16 m, and 0.24 m were evaluated, and it could be found that the results from the correlations agreed well with those from the experimental data within ±6% deviation. In addition, the electrical power consumptions of the air conditioner with these integrated PCM beds were 4.96 kWh/d, 4.7 kWh/d and 4.34 kWh/d compared with 5.04 kWh/d of the normal unit or 1.58, 6.80 and 13.84% of electrical energy could be saved, respectively.

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Abbreviations

L :

packed bed length (m)

X :

packed bed thickness (m)

A :

cross-sectional area (m2)

M :

mass of PCM (kg)

D :

diameter (m)

e :

void fraction

T :

temperatures (°C)

\( \dot{m} \) :

mass flow rate (kg/s)

Cp :

specific heat capacity (kJ/kg K)

h v :

volumetric heat transfer coefficient (W/m3 K)

G :

mass flow rate per area (kg/s m2)

V :

volume (m3)

h :

specific enthalpy of the PCM (kJ/kg)

t :

time (s)

l :

PCM latent heat (kJ/kg)

x :

the position at any section

Y :

dimensionless of thickness and mass flow rate

PCM :

phase change material

Sim:

simulation

Exp:

experiment

P :

power (kW)

Q :

cooling load (kW)

i and i + 1:

the entering and the exit of the ith section

a :

(air)

s :

(solid)

l :

(liquid)

m :

(melting)

b :

(bed)

ref :

reference at initial condition

AC :

air conditioner

amb :

(ambient)

r :

(room)

Eva :

(evaporator)

normal:

normal condition

inlet:

inlet

outlet:

outlet

ρ :

density (kg/m3)

τ :

dimensionless of time

θ :

dimensionless of temperature

∆:

increment

References

  1. 1.

    Tao YB, He Y-L (2018) A review of phase change material and performance enhancement method for latent heat storage system. Renew Sust Energ Rev 93:245–259. https://doi.org/10.1016/J.RSER.2018.05.028

    Article  Google Scholar 

  2. 2.

    Madad A, Mouhib T, Mouhsen A, Madad A, Mouhib T, Mouhsen A (2018) Phase change materials for building applications: a thorough review and new perspectives. Buildings 8:63. https://doi.org/10.3390/buildings8050063

    Article  Google Scholar 

  3. 3.

    Song M, Niu F, Mao N, Hu Y, Deng S (2018) Review on building energy performance improvement using phase change materials. Energy Build 158:776–793. https://doi.org/10.1016/J.ENBUILD.2017.10.066

    Article  Google Scholar 

  4. 4.

    Sattari H, Mohebbi A, Afsahi MM, Azimi YA (2017) CFD simulation of melting process of phase change materials (PCMs) in a spherical capsule. Int J Refrig 73:209–218. https://doi.org/10.1016/J.IJREFRIG.2016.09.007

    Article  Google Scholar 

  5. 5.

    Li W, Li S-G, Guan S, Wang Y, Zhang X, Liu X (2017) Numerical study on melt fraction during melting of phase change material inside a sphere. Int J Hydrog Energy 42:18232–18239. https://doi.org/10.1016/j.ijhydene.2017.04.136

    Article  Google Scholar 

  6. 6.

    Li W, Wang Y-H, Kong C-C (2015) Experimental study on melting/solidification and thermal conductivity enhancement of phase change material inside a sphere. Int Commun Heat Mass Transf 68:276–282. https://doi.org/10.1016/J.ICHEATMASSTRANSFER.2015.09.004

    Article  Google Scholar 

  7. 7.

    Zarajabad OG, Ahmadi R (2018) Numerical investigation of different PCM volume on cold thermal energy storage system. J Energy Storage 17:515–524. https://doi.org/10.1016/J.EST.2018.04.013

    Article  Google Scholar 

  8. 8.

    Iten M, Liu S, Shukla A (2016) Experimental study on the thermal performance of air-PCM unit. Build Environ 105:128–139. https://doi.org/10.1016/J.BUILDENV.2016.05.035

    Article  Google Scholar 

  9. 9.

    Iten M, Liu S, Shukla A (2018) Experimental validation of an air-PCM storage unit comparing the effective heat capacity and enthalpy methods through CFD simulations. Energy 155:495–503. https://doi.org/10.1016/j.energy.2018.04.128

    Article  Google Scholar 

  10. 10.

    Said MA, Hassan H (2018) Effect of using nanoparticles on the performance of thermal energy storage of phase change material coupled with air-conditioning unit. Energy Convers Manag 171:903–916. https://doi.org/10.1016/j.enconman.2018.06.051

    Article  Google Scholar 

  11. 11.

    Said MA, Hassan H (2018) An experimental work on the effect of using new technique of thermal energy storage of phase change material on the performance of air conditioning unit. Energy Build 173:353–364. https://doi.org/10.1016/j.enbuild.2018.05.041

    Article  Google Scholar 

  12. 12.

    Madyira DM (2017) Experimental study of the performance of phase change material air cooling rig. Procedia Manuf 7:420–426. https://doi.org/10.1016/J.PROMFG.2016.12.023

    Article  Google Scholar 

  13. 13.

    Mosaffa AH, Farshi LG (2016) Exergoeconomic and environmental analyses of an air conditioning system using thermal energy storage. Appl Energy 162:515–526. https://doi.org/10.1016/J.APENERGY.2015.10.122

    Article  Google Scholar 

  14. 14.

    Zhao D, Tan G (2015) Numerical analysis of a shell-and-tube latent heat storage unit with fins for air-conditioning application. Appl Energy 138:381–392. https://doi.org/10.1016/j.apenergy.2014.10.051

    Article  Google Scholar 

  15. 15.

    Arkar C, Medved S (2007) Free cooling of a building using PCM heat storage integrated into the ventilation system. Sol Energy 81:1078–1087. https://doi.org/10.1016/J.SOLENER.2007.01.010

    Article  Google Scholar 

  16. 16.

    Medved S, Arkar C (2008) Correlation between the local climate and the free-cooling potential of latent heat storage. Energy Build 40:429–437. https://doi.org/10.1016/J.ENBUILD.2007.03.011

    Article  Google Scholar 

  17. 17.

    Arkar C, Vidrih B, Medved S (2007) Efficiency of free cooling using latent heat storage integrated into the ventilation system of a low energy building. Int J Refrig 30:134–143. https://doi.org/10.1016/J.IJREFRIG.2006.03.009

    Article  Google Scholar 

  18. 18.

    Yamaha M, Misaki S (2006) The evaluation of peak shaving by a thermal storage system using phase-change materials in air distribution systems. HVAC&R Res 12:861–869. https://doi.org/10.1080/10789669.2006.10391213

    Article  Google Scholar 

  19. 19.

    Chaiyat N, Kiatsiriroat T (2014) Energy reduction of building air-conditioner with phase change material in Thailand. Case Stud Therm Eng 4:175–186. https://doi.org/10.1016/J.CSITE.2014.09.006

    Article  Google Scholar 

  20. 20.

    Löf GOG, Hawley RW (1948) Unsteady-state heat transfer between air and loose solids. Ind Eng Chem 40:1061–1070. https://doi.org/10.1021/ie50462a017

    Article  Google Scholar 

  21. 21.

    Rubitherm GmbH 2015. https://www.rubitherm.eu/en/index.php/productcategory/organische-pcm-rt (accessed September 2, 2018)

  22. 22.

    Chen J, Chen C (2017) Uncertainty analysis in humidity measurements by the psychrometer method. Sensors 17:1–19. https://doi.org/10.3390/s17020368

  23. 23.

    Enthalpy of Moist Air n.d. https://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.html (accessed December 27, 2019)

Download references

Acknowledgments

This research project is supported by Faculty of Engineering (Research Assistant Program); Center of Excellence for Renewable Energy, Chiang Mai University and National Research Council of Thailand through the project on “Development of Alternative Energy Prototypes for Green Communities”.

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Correspondence to Thoranis Deethayat.

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Annex 1

Annex 1

Uncertainties of some important parameters

$$ {\displaystyle \begin{array}{c}\kern1em G=m/A\\ {}\kern0.66em {h}_v=650{\left(\frac{G}{D_b}\right)}^{0.7}\\ {}\;\theta =\frac{T_{a, inlet}-{T}_{a, outlet}}{T_{a, inlet}-{T}_m}\\ {}\kern1em Y=\frac{h_vA}{{\overset{\cdot }{m}}_aC{p}_a}x\\ {}\tau =\frac{h_vV\left|{T}_{a, inlet}-{T}_m\right|}{M_bl}t\end{array}} $$
Equation Differential Uncertainty
\( G=\frac{m}{A} \) \( \frac{\partial G}{\partial {\dot{m}}_a}=\frac{1}{A} \) \( \delta G=\left|\frac{1}{A}\delta {\dot{m}}_a\right| \)
\( {h}_v=650{\left(\frac{G}{D_b}\right)}^{0.7} \) \( \frac{\partial {h}_v}{\partial G}=650\left(\frac{0.7}{D_b}\right){\left(\frac{G}{D_b}\right)}^{0.3} \) \( \delta {h}_v=\left|650\left(\frac{0.7}{D_b}\right){\left(\frac{G}{D_b}\right)}^{0.3}\delta G\right| \)
\( \theta =\frac{T_{a, inlet}-{T}_{a, outlet}}{T_{a, inlet}-{T}_m} \) \( \frac{\partial \theta }{\partial {T}_{a, inlet}}=\frac{T_{a, outlet}-{T}_m}{{\left({T}_{a, inlet}-{T}_m\right)}^2} \)
\( \frac{\partial \theta }{\partial {T}_{a, outlet}}=\frac{-1}{T_{a, inlet}-{T}_m} \)
\( \delta \theta =\sqrt{{\left(\frac{\partial \theta }{\partial {T}_{a, inlet}}\delta {T}_{a, inlet}\right)}^2+{\left(\frac{\partial \theta }{\partial {T}_{a, outlet}}\delta {T}_{a, outlet}\right)}^2} \)
\( Y=\frac{h_vA}{{\dot{m}}_aC{p}_a}x \) \( \frac{\partial Y}{\partial {h}_v}=\frac{Ax}{{\dot{m}}_aC{p}_a} \)
\( \frac{\partial Y}{\partial {\dot{m}}_a}=\left(\frac{h_v Ax}{C{p}_a}\right)\left(-\frac{1}{{\dot{m}}_a^2}\right) \)
\( \delta Y=\sqrt{{\left(\frac{\partial Y}{\partial {h}_v}\delta {h}_v\right)}^2+{\left(\frac{\partial Y}{\partial {\dot{m}}_a}\delta {\dot{m}}_a\right)}^2} \)
\( \tau =\frac{h_vV\left|{T}_{a, inlet}-{T}_m\right|}{M_bl}t \) \( \frac{\partial \tau }{\partial {h}_v}=\frac{V\left({T}_{a, inlet}-{T}_m\right)}{M_bL}t \) \( \delta \tau =\left|\frac{V\left({T}_{a, inlet}-{T}_m\right)}{M_bL}t\bullet \delta {h}_v\right| \)
$$ {\displaystyle \begin{array}{l}\kern0.33em {T}_{a, outlet}={T}_b+\left({T}_{a, inlet}-{T}_b\right){e}^{\frac{h_vA}{{\overset{.}{m}}_aC{p}_a}L}\\ {}{T}_b^{t+\Delta t}={T}_b^t+\frac{\overset{.}{m}C{p}_a\left({T}_{a, inlet}-{T}_{a, outlet}\right)}{\rho_b AL\left(1-e\right)C{p}_b}\Delta t\end{array}} $$
Equation Differential
\( {T}_{a, outlet}={T}_b+\left({T}_{a, inlet}-{T}_b\right){e}^{-\frac{h_vA}{{\dot{m}}_aC{p}_a}L} \) \( \frac{\partial {T}_{a, outlet}}{\partial {T}_b}=1-{e}^{-\frac{h_vA}{{\dot{m}}_aC{p}_a}L} \)
\( \frac{\partial {T}_{a, outlet}}{\partial {T}_{a, inlet}}={e}^{-\frac{h_vA}{{\dot{m}}_aC{p}_a}L} \)
\( \frac{\partial {T}_{a, outlet}}{\partial {h}_v}=\left({T}_{a, inlet}-{T}_b\right)\left(-\frac{A}{{\dot{m}}_aC{p}_a}L\right){e}^{-\frac{h_vA}{{\dot{m}}_aC{p}_a}L} \)
\( \frac{\partial {T}_{a, outlet}}{\partial {\dot{m}}_a}=\left({T}_{a, inlet}-{T}_b\right)\left(\frac{h_vA}{{\dot{m}}_a^2C{p}_a}L\right){e}^{-\frac{h_vA}{{\dot{m}}_aC{p}_a}L} \)
\( {T}_b^{t+\Delta t}={T}_b^t+\frac{\dot{m}C{p}_a\left({T}_{a, inlet}-{T}_{a, outlet}\right)}{\rho_b AL\left(1-e\right){Cp}_b} \) \( \frac{\partial {T}_b^{t+\Delta t}}{\partial {T}_b^t}=1 \)
\( \frac{\partial {T}_b^{t+\Delta t}}{\partial {T}_{a, inlet}}=\frac{\dot{m}C{p}_a}{\rho_b AL\left(1-e\right){Cp}_b}\Delta t \)
\( \frac{\partial {T}_b^{t+\Delta t}}{\partial {T}_{a, otlet}}=\frac{-\dot{m}C{p}_a}{\rho_b AL\left(1-e\right){Cp}_b}\Delta t \)
\( \frac{\partial {T}_b^{t+\Delta t}}{\partial {\dot{m}}_a}=\frac{C{p}_a\left({T}_{a, inlet}-{T}_{a, outlet}\right)}{\rho_b AL\left(1-e\right){Cp}_b}\Delta t \)

Uncertainty

$$ {\displaystyle \begin{array}{c}\delta {T}_{a, outlet}=\sqrt{{\left(\frac{\partial {T}_{a, outlet}}{\partial {T}_b}\delta {T}_b\right)}^2+{\left(\frac{\partial {T}_{a, outlet}}{\partial {T}_{a, inlet}}\delta {T}_{a, inlet}\right)}^2+{\left(\frac{\partial {T}_{a, outlet}}{\partial {T}_{a, otlet}}\delta {T}_{a, otlet}\right)}^2+{\left(\frac{\partial {T}_{a, outlet}}{\partial {\overset{.}{m}}_a}\delta {\overset{.}{m}}_a\right)}^2}\\ {}\kern2em \delta {T}_b^{t+\Delta t}=\sqrt{{\left(\frac{\partial {T}_b^{t+\Delta t}}{\partial {T}_b^t}\delta {T}_b^t\right)}^2+{\left(\frac{\partial {T}_b^{t+\Delta t}}{\partial {T}_{a, inlet}}\delta {T}_{a, inlet}\right)}^2+{\left(\frac{\partial {T}_b^{t+\Delta t}}{\partial {h}_v}\delta {h}_v\right)}^2{\left(\frac{\partial {T}_b^{t+\Delta t}}{\partial {\overset{.}{m}}_a}\delta {\overset{.}{m}}_a\right)}^2}\end{array}} $$
Table 6 Uncertainty of important parameters

Uncertainty of the evaporator heat rate (\( {\dot{Q}}_{eva} \))

$$ {\dot{Q}}_{eva}={\dot{m}}_a\left({h}_{in}-{h}_{out}\right)-{\dot{m}}_a\left({\omega}_{in}-{\omega}_{out}\right){h}_f $$

By measuring Tdb and Twb the following parameters could be calculated as [22, 23]:

$$ {\displaystyle \begin{array}{l}h=1.006{T}_{db}+\omega \left(1.84{T}_{db}+2501\right)\\ {}\kern1em \omega =0.62069\times \frac{p_v}{103-{p}_v}\\ {}\kern0.33em {p}_v={p}_{sat}-0.067193\left({T}_{db}-{T}_{wb}\right)\\ {}{p}_{sat}=0.61078\times \exp \left(\frac{17.2694{T}_{wb}}{238.3+{T}_{wb}}\right)\end{array}} $$
EquationDifferential
\( {p}_{sat}=0.61078\times \exp \left(\frac{17.2694{T}_{wb}}{238.3+{T}_{wb}}\right) \)\( \frac{\partial {p}_{sat}}{\partial {T}_{wb}}=\frac{2510.38}{238.3+{T}_{wb}}\exp \left(\frac{17.2694{T}_{wb}}{238.3+{T}_{wb}}\right) \)
pv = psat − 0.067193(Tdb − Twb)\( \frac{\partial {p}_v}{\partial {p}_{sat}}=1 \)
\( \frac{\partial {p}_v}{\partial {T}_{db}}=-0.067193 \)
\( \frac{\partial {p}_v}{\partial {T}_{wb}}=0.067193 \)
\( \omega =0.62069\times \frac{p_v}{103-{p}_v} \)\( \frac{\partial \omega }{\partial {p}_v}=\frac{103}{{\left(103-{p}_v\right)}^2} \)
h = 1.006Tdb + ω (1.84Tdb + 2501)\( \frac{\partial h}{\partial {T}_{db}}=1.006+1.84\omega \)
\( \frac{\partial h}{\partial \omega }=1.84{T}_{db}+2501 \)
\( {\dot{Q}}_{eva}={\dot{m}}_a\left({h}_{in}-{h}_{out}\right)-{\dot{m}}_a\left({\omega}_{in}-{\omega}_{out}\right){h}_f \)\( \frac{\partial {\dot{Q}}_{eva}}{\partial {\dot{m}}_a}=\left({h}_{in}-{h}_{out}\right)-\left({\omega}_{in}-{\omega}_{out}\right){h}_f \)
\( \frac{\partial {\dot{Q}}_{eva}}{\partial {h}_{in}}={\dot{m}}_a \)
\( \frac{\partial {\dot{Q}}_{eva}}{\partial {h}_{out}}=-{\dot{m}}_a \)
\( \frac{\partial {\dot{Q}}_{eva}}{\partial {\omega}_{in}}=-{\dot{m}}_a{h}_f \)
\( \frac{\partial {\dot{Q}}_{eva}}{\partial {\omega}_{out}}={\dot{m}}_a{h}_f \)
\( \frac{\partial {\dot{Q}}_{eva}}{\partial {h}_f}={\dot{m}}_a\left({\omega}_{in}-{\omega}_{out}\right) \)
$$ {\displaystyle \begin{array}{c}\kern8em \delta {p}_{sat}=\left|\frac{\partial {p}_{sat}}{\partial {T}_{wb}}\delta {T}_{wb}\right|\\ {}\delta {p}_v=\sqrt{{\left(\frac{\partial {p}_v}{\partial {p}_{sat}}\delta {p}_{sat}\right)}^2+{\left(\frac{\partial {p}_v}{\partial {T}_{db}}\delta {T}_{db}\right)}^2+{\left(\frac{\partial {p}_v}{\partial {T}_{wb}}\delta {T}_{wb}\right)}^2}\\ {}\kern9em \delta \omega =\left|\frac{\partial \omega }{\partial {p}_v}\delta {p}_v\right|\\ {}\delta {\overset{.}{Q}}_{eva}=\sqrt{{\left(\frac{\partial {\overset{.}{Q}}_{eva}}{\partial {\overset{.}{m}}_a}\delta {\overset{.}{m}}_a\right)}^2+{\left(\frac{\partial {\overset{.}{Q}}_{eva}}{\partial {h}_{in}}\delta {h}_{in}\right)}^2{\left(\frac{\partial {\overset{.}{Q}}_{eva}}{\partial {h}_{out}}\delta {h}_{out}\right)}^2+{\left(\frac{\partial {\overset{.}{Q}}_{eva}}{\partial {\omega}_{in}}\delta {\omega}_{in}\right)}^2+{\left(\frac{\partial {\overset{.}{Q}}_{eva}}{\partial {\omega}_{out}}\delta {\omega}_{out}\right)}^2+{\left(\frac{\partial {\overset{.}{Q}}_{eva}}{\partial {h}_f}\delta {h}_f\right)}^2}\\ {}\delta h=\sqrt{{\left(\frac{\partial h}{\partial {T}_{db}}\delta {T}_{db}\right)}^2+{\left(\frac{\partial h}{\partial \omega}\delta \omega \right)}^2}\end{array}} $$
δT wb 0.5 °C
δT db 0.5 °C
\( \delta {\dot{m}}_a \) 5%
δh f 5.02%
δp sat, in 3.08%
δp v, in 3.80%
δω in 3.87%
δh in 2.92%
δp sat, out 3.34%
δp v, out 3.33%
δω out 3.37%
δh out 3.98%
\( \delta {\dot{Q}}_{eva} \) 1.81%

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Loem, S., Deethayat, T., Asanakham, A. et al. Study on phase change material thermal characteristics during air charging/discharging for energy saving of air-conditioner. Heat Mass Transfer 56, 2121–2133 (2020). https://doi.org/10.1007/s00231-020-02839-4

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Keywords

  • Charging/discharging
  • Packed bed cool storage
  • Phase change material
  • Correlation
  • Inverter air-conditioner