**3.3 Effect of the ACH and Win on the heat-transfer coefficients**

To analyse the effect of the number of air changes per hour on the heat-transfer coefficients for each of the typologies, we employ the correlation obtained for cases where the walls are at the same temperature. Within the application range of the

**Figure 11.** *Effect of the size of the inlet opening and typology on the heat-transfer coefficients at every wall.*

variables, **Figure 10** shows the maximum values of the heat-transfer coefficients for each wall and typology compared with the number of air changes per hour. The maximum values are reached at wall two and its symmetric pair wall four; however, wall one shows the least sensitivity to variations in the number of changes. In cases where the enclosure is used for storing energy during the day and releasing it at night through ventilation, **Figure 10** shows that typology 1 provides the highest heat transfer rates through cross ventilation. More specifically, the floor and roof (in the symmetric case) are the recommended enclosures for energy storage because they have higher heat-transfer coefficients and larger solid-to-fluid heat transfers compared with the rest of the enclosures. This is a good example that can be used as a design tool.

To analyse the influence of the variable Win on the heat-transfer coefficients as a function of the typology, **Figure 11** shows the maximum values of the heat-transfer coefficients reached for each wall. The maximum values are obtained for typology 1, and in general, the coefficient decreases as the opening size increases because increases in opening size lead to decreases in the speed of the air that interacts with the walls and thus reduces the heat exchange between the wall and air.
