Energy optimization of the Ab-Anbar domes; Case study: Domes of Qazvin city

Traditionally, the public has used Ab-Anbars (water reservoirs) in hot and dry areas and also in cold regions of Iran. One of the main elements of Ab-Anbar is the reservoir coverage (reservoir lining), which is made of various brick vaults such as barrel and colombo vaults with different rises and forms. Due to the dry weather in most parts of Iran and insufficient rainfall in more than six months of the year in most places, which has resulted in the seasonality of rivers and the lack of access to water, various arrangements have been established for freshwater supply in dry seasons. The construction of the Ab-Anbar (water reservoir and cistern) is one of the innovative ways to supply drinking water. In this regard, the Ab-Anbar, as its name implies, is used to store water in rainy seasons to be used for the rest of the year. The main structure of the Ab-Anbar consists of an underground storage tank and a dome to cover it. In some areas in Iran, a wind catcher is added to this structure to keep the water cool in summer. The construction material used for Ab-Anbars was a special mortar called Sarooj, which was made of sand, clay, lime, goat hair, egg whites, and ash in specific proportions, depending on the location and climate of the place. Some Ab-Anbars had rectangular storage tanks, and some tanks had a cylindrical shape. This study aims to determine the amount of solar radiation received on the surfaces and heat flow inside the Ab-Anbar domes of Qazvin, which leads to recognizing the most optimal form of reservoir coverage for Ab-Anbars among the studied samples. 

The data, including dry and humid temperature, air, radiation, and current radiation situation of Qazvin city weather station, were prepared over a ten-year period (1996-2006). The library documents also provided the map of the Ab-Anbar domes. In order to conduct the research, four samples of Ab-Anbars with different dome structures in Qazvin city were selected. After that, the domes were modeled in Revit 2016, and the amount of solar radiation received by the domes on the hottest day of the year, at 14, 16, and 18 o’clock, were determined using honeybee & ladybug plugins with Energy plus Engine. COMSOL software, and the CFD airflow analysis, were performed for validation in high-rise and low-rise domes. 

The results of the analyses showed that low-rise domes with large surface contact receive more heat than high-rise domes with a small surface contact, and the area of the domes is effective in receiving the sun radiation. Sardar Kouchak (Little Commander) dome, a low-rise dome, is approximately exposed to its total surfaces and solar heat by 84.3% at 14 o’clock. In comparison, the high-rise dome next to the Grand Mosque is exposed by 52.5% at 14 o’clock. The low-rise dome is exposed by 74.7%, while the high-rise dome is exposed by 53.5% at 16 o’clock. Finally, the low-rise dome is exposed by 62.4%, and the high-rise dome is exposed by 43.2% at 18 o’clock. Therefore, low-rise domes in the cold climate are more efficient in receiving solar radiation than high-rise ones.

The airflow inside the domes was graphically performed for validation using CFD analysis on a hot day. The results are consistent with the outputs from honeybee & ladybug plugins. Low-rise domes can retain more heat than high-rise domes, and the vortex of hot air created in low-rise domes is less than in high-rise domes, which leads to more heat gain inside the dome. Therefore, the most suitable dome for Ab-Anbar in the cold climate of Qazvin are low-rise domes.