•  Control objectives : The overall objective of the process of taking hot water shower is to become clean and refreshed whereby the body dirt is removed and activity of a person increases. Hence the control objectives of the process should be maintaining the temperature and flow rate of the water from the shower head at an ideal level so that the overall objectives are met.

•  Operating characteristics : The process of taking shower is a 5-7 minutes job, hence it would ideally be termed as a batch process which may be run once or twice a day. However, the control objectives, i.e. ideal flow rate and temperature of warm water, cannot be reached instantaneously. One needs to carefully balance between opening of two shower knobs (hot and cold) so that sudden surge of hot/cold water flow is avoided which would otherwise risk scalding/cold bite. The similar balanced operation is needed while closing the valves too. Hence, the features of start-up and shutdown are observed in this process. Between the startup and shutdown, the process becomes a continuous one as one would ideally take shower continuously at an ideal flow rate and temperature of warm water.

•  Inputs and Outputs : Tuning of two valves in the hot/cold water pipeline may be termed as manipulated inputs of the process that can be set in order to achieve the ideal flow rate and temperature of warm water. The orientation of the shower head and the position of the human body are also tuned so that the body receives maximum flux of water flow. However, there are two potential disturbances for the process, viz ., drop of pressure of hot water and/or change of its temperature. It might so happen that a second tap of hot water is turned on by someone while one is already ON, resulting in loss of temperature and pressure of hot water supply. On the other hand, flow rate and temperature are the measured outputs. In this process, the human body is the measuring instrument for flow rate/temperature.

•  Constraints : The valves cannot be opened more than its “FULLY OPENED” condition even if the process requirement demands so. Hence valve position is the hard constraint for this process. On the other hand, temperature of warm water may be termed as soft constraints, because a maximum/minimum limit of the temperature should be maintained to avoid scalding/cold bite, however, slight overshoot/undershoot of that limit might be permissible.