A Numerical and Analytic Study of the Humidity Impact of Kharkhona on Vernacular Sistan Housing

A look at today’s construction models in rural architectures shows that rural houses are being built based on urban housing models and many aspects including climatic issues and natural ventilation are being ignored. Implementation of urban standards for rural housing is not considered suitable and housing models in villages must be revised according to the the current needs of each region. Designers need to learn and derive from the experiences of traditional housing and select design models which are appropriate for the local climatic conditions of the concerned regions. The vernacular architecture of Sistan Region provides a number of valuable methods for improving quality of life in the area. The harsh climatic conditions of this region have motivated the local architects to search and devise the best and the most suitable ways of adaptation with the climate and use climatic conditions in favor of the residents by means of innovative principles and models. Through proper integration with advanced technologies, these principles and models can be used in modern architecture as well. Kharkhona (a pad made by interlacing desert bushes and moistened with water) is one of the elements of the vernacular architecture of Sistan Region which has proven effective for ventilation and cooling of the living spaces in the area. The vernacular architects of this region have installed Kharkhona in houses and buildings to create cooling facilities and reduce the indoor temperature by means of evaporation of the water drops entangled in the desert bushes. The aim of this research was to identify and study the function of Kharkhona, analyze the relative humidity of indoor air in the vernacular abodes of Sistan Region and specify appropriate Kharkhona for applying in contemporary rural houses. For achieving this end, field measurements were performed in two structurally identical rooms, one equipped with Kharkhona as the experimental group (or rather room) and one without this architectural element as the control room. The humidity figures in the experimental room, the control room and an outdoor point were measured and the results were compared. Descriptive statistics, Microsoft Excel and Minitab software were used for integrated understanding and interpretation of the collected data. The results of data analysis indicated that, overall and based on the mean daily relative humidity in the three measurement stations, the relative humidity of the room without Kharkhona was almost the same as that of the outdoor open space while the relative humidity of the indoor air of the room equipped with Kharkhona was significantly different from that of the other two measurement stations, namely the room without Kharkhona and the outdoor point. While the relative humidity of the space without Kharkhona was only 12%, the figure exceeded 30% in the Kharkhona-equipped room, a number that easily falls in the range of thermal comfort according to the studies carried out by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and Victor Olgyay (the range is 20-80% according to ASHRAE and 30-65% according to Olgyay). The reason of this difference was the humidity created by evaporation of the water sprinkled over the desert bushes which reduced the indoor temperature, moderated the microclimate and improved the overall climatic conditions. This study indicated that Kharkhona has a very favorable impact on the hot and dry climate of Sistan Region and the effect would be favorable in dry areas with low relative humidity. Therefore, use of this Iranian architectural element is strongly recommended as a passive technique for achieving thermal comfort in environments with high sensible heat.