1. A controller of a heating, ventilation, and air conditioning (HVAC) system, comprising: a user interface configured to receive: an approximate relationship between each of a number of controlled variables of an HVAC system and each of a number of manipulated variables of the HVAC system; a designation of one of the number of controlled variables as a primary controlled variable and the other controlled variables as secondary controlled variables; and a confidence level from a user for the approximate relationship between the primary controlled variable and each respective manipulated variable, wherein the confidence level is an indication of the accuracy and/or reliability of the relationship; a memory; and a processor configured to execute executable instructions stored in the memory to: determine operating parameters for each of the number of manipulated variables that maintain the primary controlled variable at a particular set point or within a particular range based, at least in part, on the approximate relationship between the primary controlled variable and each respective manipulated variable and the confidence level from the user for the approximate relationship between the primary controlled variable and each respective manipulated variable; and determine operating parameters for each of the number of manipulated variables that maintain each of the secondary controlled variables at a particular set point or within a particular range based, at least in part, on: the approximate relationship between each respective secondary controlled variable and each respective manipulated variable; and the determined operating parameters for each of the number of manipulated variables that maintain the primary controlled variable; and maintaining the environment of a building at a particular set point or particular range based on the determined operating parameters.