HVAC Control and Direct Digital Controls 2 - An HVAC technician who knows nothing about HVAC control systems would wonder how these HVAC control systems work. To understand HVAC controls, one must understand basic electricity and circuits.
Variable Frequency Drives VFDs | Energy Efficiency - In HVAC variable frequency drives add energy efficiency and precise control for fans and pumps. The VFDs offer demand control for airflow and water in chilled water systems, hot water systems, and air handling systems. Additionally, they are used to control airflow in a variable air volume system. More on how VAV boxes work.
VFDs require inverter duty motors and variable frequency drives can be purchased for three-phase and single-phase applications although the vast majority of variable frequency drives are used in commercial three-phase applications. (more…)
DDC Programming Logic 3 - DDC control logic blocks have practically an unlimited way of arranging the blocks for HVAC control. Below is an example of a line of logic blocks arranged for static pressure control of a VAV air handler supply fan using a variable frequency drive. This same arrangement could also be used for static pressure control using a bypass damper instead of a VFD. (more…)
Programming DDC Logic 2 - The analog network input is similar to an analog input except this input is not hardwired to the local controller but on a remote controller in the network. It is very important that the communication works effectively for this analog network input to work. An example of this is the outside air temperature which is hardwired to a DDC controller in the penthouse of a multistory building.
The building engineer only wants the boilers to fire if the outside air temperature is less than 55° F. Instead of having an outside air temperature device hardwired to the boiler controller an analog network input can be placed into the boiler controller program and linked to the outside air temperature reading which is in the penthouse controller where the outside air temperature thermistor is hardwired. This saves devices and wires necessary for optimum control.
