NIST Multizone Modeling Website 
Controls
Controls allow the characteristics of one building element to be modified during transient simulations in response to a change in characteristics of another building element. You can also use controls to simply monitor building performance by polling building components for values and logging them to a control log file during a simulation.
Controls include sensors, links, modifiers and actuators. Sensors are control elements that are used to obtain a value, calculated during simulation, of a building component and then provide it to a control network. You can use sensors to obtain contaminant concentrations and temperatures of zones, duct junctions and duct terminals and to obtain pressure differences and airflow rates of airflow paths, duct segments and duct terminals. You can use actuators to control schedulable items including airflow paths, duct segments, junctions and terminals, simple air-handling systems, and contaminant source/sinks.
The connection between sensors and other nodes in a control network are made up of control links. Control modifiers are nodes within the control network that are used to change or modify their input signals. Control actuators are used to modify various characteristics of building components based on control signals obtained from sensors and even modified by signal modifiers. For example, a sensor can be used to obtain a contaminant concentration within a zone, and a proportional control actuator can be used to adjust supply airflow through a supply airflow path into the zone based on the sensed concentration.
Control Elements
A control network can consist of many different control nodes, each of which is defined by a control element. There are several different types of control elements provided, such as a report element, that can be used to convert dimensionless sensor values to engineering units; mathematical elements to perform simple mathematical and logical operations on input signals; and classical control elements such as proportional/integral, band and limit controls. There is a phantom control element that can be used to reference an existing control node, which is convenient for linking nodes that may be on different levels of a building or simply too far apart to conveniently draw a physical link. Each of these element types is described in detail in the Control Element Types section. While every node in the control network must refer to a single control element, multiple nodes can refer to the same control element using the phantom node/control element.
Collections of control elements can be grouped into Control Super Elements, which can be stored in CONTAM Library files and shared within and between projects. Super elements can reduce the amount of drawing of repetitive control logic and enable the creation of custom reusable sensors and control algorithms.
