ZEMCH 2019 International Conference Proceedings April.2020 | Page 141
The cooling capacity of the system without and with integrating PCM‐based pre‐cooling system
have been calculated and the reduction of the cooling capacity applying PCM‐based pre‐cooling unit is
presented in Fig. 6. Applying PCM cooling system reduced the capacity of the system by almost 6%
providing the prolonged efficiency.
4.2. Numerical Analysis
The average summer temperature of the UAE (45 °C) is applied as an input for the duct system
with velocity levels of v=4 m/s. Fig. 5 shows the evaluation of air outlet temperature over the time
period of 24 hours employing the PCM containers as heat storage units.
The cooling effect of employing PCM enclosures in the duct system on the passing air is clearly
seen in Fig7. Applying high velocity of 4 m/s as input (green‐ dashed line), passing by PCM enclosures,
diminish the outlet air temperature below the input temperature attaining a temperature drop of
approximately 4°C compared to the reference (system without the PCM enclosures) due to heat
absorbed by the PCM during the phase transition. As the PCM melted the outlet air temperature rise
up reaching the steady state with the input after 10hours.
The melting friction of the PCM inside the enclosures was monitored to predict the required time
for the material to completely melt and optimize the amount of the PCM that can completely melted
within the daytime and the PCM cooling performance was tested at different level of velocity rate. A
similar PCM temperature trend was achieved applying different air velocities of 3,2 and 1 m/s.
However, with lower magnitude & higher temperature drop as presented in Fig. 8. The temperature
drop in case of the 1 m/s was 4.5°C as a maximum for single column of PCMs (design 1) while
employing series of PCM enclosures (design #2) dropped the inlet air temperature of 46°C to 35°C
yielding a temperature difference of 11°C.
Fig.9 shows the reduction in the released heat by percentage at different velocity levels. It is clearly
observed from Fig.9, integrating PCM‐based pre‐cooling system cooled the inlet air temperature
offering a daily heat reduction of 16.6%, 19.4% , 22.2%, and 25% for design #1 & 33.3% , 33.8%, 47.2%
and 56.6% for design#2 at velocity 4, 3,2 and 1m/s respectively.
The reduction of the cooling capacity applying PCM‐based pre‐cooling unit is presented in Fig.
10. Applying PCM cooling system reduced the capacity of the system by almost 8% for design 1 and
22.5% for design 2 at velocity 1 m/s.
4.3. Economical Analysis
Although inclusion of the PCM incurred additional cost at the rate of 1 dollar/kg for paraffin wax
[17]. However, integrating the proposed pre‐cooling unit over time, the amount of reduced electricity
can reduce the payback period. The PCM cost is expected to drop with increased interest in PCM
systems thus creating an optimal economic scenario [18].
5. Conclusions
Latent cooling technique of air conditioning duct system have been studied using phase change
material as a thermal heat storage. Two types of PCMs have been characterized namely paraffin waxes
and salt hydrate. A commercial grade of paraffin wax with optimum melting point of (31°C) have been
selected for its favorable characteristic of availability, high thermal conductivity, volumetric latent heat
storage capacity and heat of fusion. A single column of PCM containers have been placed in the duct
system and experimentally evaluated in the hot weather of in Falaj Hazza Campus, UAE University Al
Ain – UAE. Inclusion of PCM in the air conditioning duct system offers a pre‐cooling for the air
supplied through the duct system due to latent heat absorption resulting in reduced peak air‐
conditioning demand. A drop in the peak temperature by almost 4°C at air velocity of 4m/s have been
achieved.
New Perspective of Phase Change Material Application for Energy Efficient Building
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