This paper has indicated the law that reliability indexes R (t ) of a branch network and a looped network change with scale of the network . In the planning design we suggest to adopt branch network for a heating system, whose scale is smaller. If the network's scale is bigger, We suggest to adopt looped network. It easily reaches or surpasses provided reliability level.
This paper also studies the relation of structure condition of a network, distribution of heat loads and Its level of reliability. From the point of view of reliability, in the district with high density load heat source arrangement is suitable to a branch network. In the network near the heat source to decrease distance between two sectional valves is favorable. In the looped network we may in tall heat source in any place. When load distribution of a network is non-uniform, we must adopt "oppositely directed method" to arrange the pipes and sectional valves to opposite the density distribution of heat loads.