As regards the domed ice houses without ice-making plant, the simpler layout does not seem to have been an important issue. This type was sometimes located near village centers (e.g. Tarshanbeh, YC·10), in village outskirts (e.g. Sudaghlan, YC·60), and occasionally in the middle of an open field (e.g. Ghasemabad, YC·104). Ice had to be insulated and kept dry, and so ventilation was very important. The wind blowing across the dome would suck air out at the vent; however, no indication was found of how the domes were protected in case of bad weather (except one near Damghan where there was a wooden grill to support a cover). Presumably, before a rainstorm sacking would be wrapped around the top of the dome to keep the water out. At any rate, constant evaporation through the mud brick dome shell would reduce both humidity and temperature inside the dome.
Dome shapes Fig. 7.3 shows typical examples of the domes encountered during the survey. The shapes vary greatly in the spectrum between pure cones and paraboloids for the 94 domed ice houses surveyed. As could be seen from the descriptions in Chapter 5, the majority are termed paraboloids, some with tapered and others with smooth surfaces, but not one particular shape could be judged to prevail. There also seems to have been no significant difference between the shape of ice house domes standing alone (DVO and DCO) and the shape of domes having associated shading walls for ice-making ponds (DVP and DCP). The basic principles determining the shape are partly the need to use a form, which will be self-bearing during construction, as there would usually be no wood for support, and partly the need to arrive at an outside shape that minimizes the surface towards the sun and at the same time having a certain height. The higher the dome, the better the cooling effect at the bottom, due to what Hourcade calls “the thermal piston” (1994:93). In terms of stability and bearing capacity, a dome with a paraboloid cross section is the best and, the higher, the better, also as regards cooling effect. But the building process puts a limit on the height and that limit seems to be about 18 meters, as I could observe during the survey. However, to obtain stability against buckling, i.e. to ensure that no tension forces occur in the dome, the dome must
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Ice Houses of Iran