Controllers are used in ApacheHVAC to govern the operation of the system. Their function is to control airflows and the behavior of devices such as coils, mixing dampers, flow splitters, energy-recovery heat exchangers, spray chambers, and steam humidifiers.
Figure 6 - 1 : The example of a VAV system with “mixed-mode” controls above illustrates some of the broad range of controller applications and configurations possible in ApacheHVAC (this is system 07c
Mixed-mode VAVr - Nat Vent in the HVAC systems library). Controllers can include various combinations of sensors, a control point (if independent), as well as logical AND connections and OR connections to other controllers. The green boxes represent independent controllers; the blue boxes are dependent controllers. The green control leads with arrowheads point to controlled nodes for airflows and equipment; those with a round bulb at the end are sensors. Dashed green lines are logical AND connections. Dashed blue lines are logical OR connections. Controllers can be variously placed within or outside of the multiplexed region of a system (see section 6.1.1 Rules for Multiplexes and controllers within them), which determines whether just one or multiple control signals will be “voting” on the controlled variable at a particular node (see section 3.4.1 Multiple controllers at a single network node).
In this example, four controls have been added to a standard VAV system to create an advanced mixed-mode system: The primary mixed-mode control senses the difference between the room or zone temperature and outdoor temperature. This is coupled by an AND connection to prevent the VAV damper opening for mechanical cooling air supply when conditions are appropriate for natural ventilation. A dependent time switch controller coupled by an OR connection (thin dashed blue line) is used to enable or disable mixed-mode controls during autosizing of the mechanical system. There are two additional mixed-mode controls coupled via OR connections to turn the mechanical air supply back on again when natural ventilation is insufficient to address either thermal or ventilation demands, as determined by room temperature and CO2 concentration.
