two adjacent collectors which are 47 feet apart whereas only 47 feet are required for the return liquid water flow if it is at ambient temperature. Calcium silicate, an organic, fibrous insulation material in common industrial usage by the power industry for applications up to 815°C, was adopted for the present system; costs including installation were taken from Reference 1. For the study the possibility of using a multifoil insulation with vacuum jacket and an effective thermal conductivity much lower than calcium silicate was also considered. It was concluded that this type of insulation is not cost effective and does not appear to be reliable for large pipe networks. Certain segments of the nuclear power industry use a multifoil insulation without vacuum jacket because it can be removed for pipe inspection purposes and replaced inexpensively compared to fibrous materials. However, the first cost is higher and thermal conductivity in air is not lower than for calcium silicate. For each fluid system at a particular size, the temperature rise in the collector field was assigned, and the required flowrate was calculated based on insolation assumptions and collector performance. The pipe internal diameter for the smallest pipe size was chosen, and the relative size of all other pipes was calculated based on a criterion which minimizes installed pipe cost. The pipe wall thicknesses were calculated based on the ANSI pipe code using the internal pressure and pipe design properties. A cost minimization criterion was developed for the installed insulation thicknesses for all the pipe sizes in the entire network. The insulation thickness for the smallest pipe size was assigned, and the cost minimized thickness was calculated for all the other pipes in the network. Thus, for given values of solar insolation, collector performance and ground cover ratio, the temperature rise in the field, the pipe size and insulation thickness were assigned. Parametric calculations varied the insulation thickness, then the pipe size and finally the temperature rise in the field. The combination was chosen that minimizes the system cost of the energy transport subsystem. The
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