•  Control structure : It is ideally a 2x2 multivariable process whereby flow rates of hot and cold water are regulated in order to maintain the flow rate and temperature of warm water. It may be obvious that valve of hot water pipeline may be paired with the temperature of warm water while valve of cold water pipeline may be paired with its flow rate. For more complicated processes, such paring may not be obvious. In such cases, some quantitative analysis such as Relative Gain Array (RGA) can be used. This will be discussed in appropriate lecture module later. The process can be both feedback as well as feedforward in nature. Once the human body feels the loss of temperature in the warm water, one would increase the flow of hot water by regulating the valve. This is feedback control. On the other hand, when a person, while taking shower, hears someone else opening another tap of hot water and thereby anticipates loss of temperature of the warm water and re-tunes the valve of his own hot water supply, the operation can be termed as feedforward control.

•  Suppressing the influence of external disturbance as soon as possible : Whenever the loss of temperature or loss of supply of hot water is sensed , a quick control action in terms of regulating the valves is advocated so that the temperature and flow rate of warm water reaches the desired condition in minimum possible time.

•  Ensuring the stability of the process : It is obvious that following a disturbed condition, the warm water would not reach at the desired temperature/flow rate monotonically. Overshoot/undershoot of temperature/flow rate is an obvious fall out for such a control action. However, one should ensure that the stability condition (desired value) is reached in a reasonably less time.

•  Optimizing the performance : One should target to achieve a clean body by using minimum water, least heating and spending minimum time.