Thermal comfort in naturally ventilated dwellings in the central Mexican plateau

A third of Mexico's population (35 M people) lacks decent housing. Current efforts to improve housing focus on structural strength and security rather than thermal comfort. However, as 59% of the population earns less than the median income, the building itself must provide adequate internal temperatures, i.e., the range between the minimum temperature suggested by WHO of 18 °C, and the maximum temperatures suggested by the CIBSE TM59:2017 criteria. Despite the perception of being a “warm” country, 38% of the Mexican population lives in places where the external temperatures often drop to 0 °C in winter falling to −6 °C during seasonal cold fronts. This is worrying, as a lack of adequate protection from low indoor temperatures is associated with high excess winter mortality rates. Hence, we undertake one of the first Class-II thermal comfort studies in a cold climate in Mexican homes. For eleven months, hourly indoor environmental and occupancy data, complemented with language-localised bi-monthly thermal comfort surveys, were matched against the Adaptive and PMV thermal comfort models. We find that only 42% of the living room occupied hours were within acceptability ranges, dropping to 22% in winter. Finally, we find that current strategies for achieving homeostatic heat balance are garment based (i.e., extra blankets or clothing), in addition to electric heaters to a lesser extent. Hence, we find that Mexican houses are presently not capable of providing adequate internal thermal environments during cold periods, suggesting the need for an extensive insulation programme.