The input heat flux boundary subjected to the exterior ambient conditions are applied . The differential Eq . ( 1 ) governs the transient heat transfer in two dimensions imposing heat losses yields .
ρρρρρ �� � �� �� �kk
�� �� �� �� � ZZ
� �� � �ρZZ �ρρ �� ( 1 ) �
where , ρρρ is density , cccis heat capacity , kk is thermal conductivity , TT is temperature , tt is time and xx � , aaaaaaaaa � are unit vectors . Where ZZ � and ZZ �ρρ account for heat convection and radiation losses as given in Eq . ( 2 ) and ( 3 ):
ZZ � �h � ρAAρ�TT � TT ��� � ( 2 )
ZZ �ρρ � σσ�AA�TT � �TT � � � ( 3 )
where , h � is convective heat loss coefficient , AAA is wall surface area , σσσis Stefan‐Boltzman constant , TT ��� is ambient temperature and TT � is the sky temperature .
The problem is modeled and solved in ANSYS platform ( Version 18 , Computer software company , Cecil Township , PA , USA , 2019 ). The numerical model is subjected to average UAE weather temperature at summer in July ( Tamb , avg = 45 ° C ), while the paraffin wax with melting point of 31 ° C was used as a PCM material and initially set to the temperature of 24oC to assure the solidus phase of the material . The solution is updated every 5‐minuts time step with 20 iterations per time step for a total flow time of 24 hour .
2.4 . Building Implementation
A typical one‐story building size ( 20 × 20 × 3 m3 ) located in Al Ain ( UAE ) was used in the calculation of the heat load and the effectiveness of the system
Table 2 . Building Characteristics and type of systems .
Characteristics Floor Area Window Area Window Solar Absorbance Occupancy Density Lighting Power Density Equip . Power Density
Description 300 m2 10 % of the gross wall area , uniformly distributed 6 mm Single Green Tinted Glazing 0.50 for external walls and roof 6 People 4.5 W / m2 7 W / m2
The heat losses , for three days were calculated by comparing the resulting indoor temperatures with and without PCM‐base using the expression below :
QQ ����� �ρh � ρ� ρAAρ �ρ�TT � �TT � � ( 4 )
where hc is the convective heat‐transfer coefficient , Ts is the inner surface temperature , and Ti is the indoor air temperature . The hc value at the inner surface facing indoors was calculated at 6.5 W / m2 ° C using Eq . ( 5 ), assuming free cooling and applying the wind speed ( vv � ) for UAE [ 16 ].
h � ρ � ρ���ρvv � ρ� ρ��� ( 5 )
127 ZEMCH 2019 International Conference l Seoul , Korea