Design of a Sequential Logic Control System for Water Recycling in Car Wash Operations for Minimising Utility Costs

The car wash sector in Tanzania is expected to expand in the next few years, since the trend of imported cars is increasing. However, the traditional method of washing cars is subjected to water overuse and environmental pollution. This study presents a design of water recycling sequential logic control system to come up with a cost-effective car wash operation aimed at effectively utilising water and electricity resources. Data were collected at 78 car wash stations in Dar es Salaam region to determine water and electricity costs. Data were analysed using MS Excel and Minitab to establish the trend of utility cost against the number of washed cars. Logic functions were derived and used to develop the sequential control system in Matlab®. Minitab regression analysis found that water cost changes proportionally with number of washed cars showing that the basic water cost is TZS 227,311 and rises by TZS 3,927 for every car. Similarly, the electricity cost linearly changed with number of washed cars indicating that electricity cost is TZS 103,934 and increases by TZS 9,242 for each car. The simulated water recycling system shows decrease in water cost and increase in electricity cost. Despite the increase in electricity cost, the overall utility cost was positive justifying the implementation of water recycling system. In totality, the implementation of the control system will reduce the utility cost ranging from 48% to 33%. The study demonstrates how water recycling in car wash sector can improve cost effectiveness and enhance environmental preservation.