<< Click to Display Table of Contents >> Navigation:  Wadiso 6 User Guide > Tank Cost Optimization to be included in future Wadiso version > When to use Tank Sizing Optimization

A few thoughts on when to use the optional tank sizing feature and when not may be appropriate. All systems which contain tanks, be they new or existing, should be optimized with tank sizing if an optimum in terms of total system cost is to be obtained. Of course, such systems can also be optimized without tank sizing but then the optimum is found only in terms of pipe and pumping cost, and there is no guarantee that the most inexpensive solution, or indeed a feasible solution in terms of tank volumes, had been obtained. Since tank sizing optimization runs slower than normal optimization a good starting point for a tank sizing optimization may be a solution found by optimizing without tank sizing. This will quickly give the user a "feel" for the solution, so that he may specify a much narrower range of candidate pipe sizes, resulting in fewer combinations that will be tested during the tank sizing optimization.

A tank sizing optimization cannot be executed on a system, which does not contain any storage tanks. When such a system is optimized with the tank sizing option on, the storage sizing function in Wadiso will automatically be bypassed, and the optimization will be done based on pipe cost and pumping cost only.

The tank sizing technique employed by Wadiso has not been tested extensively in the presence of CVs and/or PRVs and/or FCVs. Special care should in this case be taken to verify the obtained tank volumes by performing an additional time simulation on these type of systems.

The optimization module works exclusively with the Wadiso balancer, and not the EPANet balancer. For this reason, optimization cannot be performed on systems with PSVs, PBVs, TCVs, GPVs, emitters, pipes with minor losses, or pumps with multi-point curves, since these features are not supported by the Wadiso balancer.

Water distribution systems of the type shown in the Simple Pipe Network Layout are commonly found. In such systems, water is brought from a source via a feeder main to a tank upstream of the consumers. Downstream of the tank, the water is distributed with a system, which contains only pipes and no further storage tanks. Systems like these can either be optimized in one run with tank sizing, resulting in slower computer time, or separated into two problems, resulting in faster computer time. This can be done by optimizing the system downstream of the tank without tank sizing, and the system upstream of and including the tank with tank sizing.

The critical period tank sizing technique in Wadiso is based on a peak factor curve. This peak factor curve is based on the peak day factor and the 24-hour demand pattern for the system under consideration. Tank sizing with Wadiso can therefore not be done if the system consists of two or more distinctly different consumer areas, each with its own unique peak day factor and 24-hour demand pattern. Such systems should be optimized without tank sizing, and if the tanks in the system have to be sized, the time simulation routine of Wadiso can be used after optimization. Alternatively, a weighted peak day factor and weighted 24-hour demand pattern can be used, which should in most cases result in a reasonable optimum solution. The tank volumes for this solution can then be fine-tuned with the time simulation routine of Wadiso, which does take different peak factors and demand patterns within the same system into account.