The wireless sensor networks, which development has begun by military applications, is applied in all human activities; in medicine for patience monitoring, in huge scale environmental monitoring e.g. to reduce the effects of disasters, and even many industrial and everyday applications. Nowadays the area of wireless sensor networks, WSNs is one of the emerging and fast growing fields in the scientific world. This has brought about developing low cost, low-power and multi-function sensor nodes. However, the major fact that sensor nodes run out of energy quickly has been an issue and many energy efficient routing protocols have been proposed to solve this problem and preserve the longevity of the network. This is the reason why routing techniques in wireless sensor network focus mainly on the accomplishment of power conservation. Most of the recent publications have shown many protocols mainly designed to minimize energy consumption in sensor networks. Fast development of wireless sensor networks can also be challenging for a designer, not only due to solution and structure complexities, but first of all due to demanding requirements. Case studies of WSN design are presented in the paper. A hierarchical routing technique which shows energy efficiency has been validated. The technique selects cluster head with highest residual energy in each communication round of transmission but it also takes into account, the shortest distance to the base station from the cluster heads. Simulation results show that hierarchical routing technique with different level of hierarchy prolongs the lifetime of the network compared to other clustering schemes and the residual energy mean value, after some communication rounds of simulation, increases significantly. The presented case study shows the advantages of hierarchical WSN structure. The advantages are validated by comparative studies. The analysis shows that energy efficiency of WSNs can be further improved. For instance the clusters formed dynamically on base of shortest distance to initial cluster head affects the network lifetime of WSN.