Adaptive and fuzzy control represents a range of techniques that can provide better control than conventional HVAC systems. Fuzzy control is based on establishing a set of "verbal" rules for system operation such as "If the temperature is cold increase the valve opening." These rules are consistent with the way people talk about controlling systems, but they require interface to their input and output variables. The interface to input variables is called "fuzzification" and the interface to output variables is called "defuzzification."