ZEMCH 2019 International Conference Proceedings April.2020 | Page 138

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
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 � � 𝜌 𝑍𝑍 �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 ����� � 𝜌 ℎ � 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