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.
This is an HVAC chilled water system cooling tower fan for a large chilled water system. Four large cooling towers for two chiller plants in a data center. Data center cooling systems generally are redundant not only for emergency situations but also for maintenance. The cooling tower fan typically has vibration switches installed in the fan assembly to shut the fan off in the event of too much vibration. (more…)
Magnehelic Duct Pressure Sensor - The Magnehelic measures duct pressure inside of ductwork. It is important, for many reasons, to know the pressure inside of ductwork. This Magnehelic measures the supply side pressure of the blower inside the air handler. (more…)
In HVAC a variable speed drive is a speed control system for electric motors. The variable speed drive (VSD) or variable frequency drive (VFD), among other names (adjustable-frequency drives (AFD), AC drives, micro-drives, or inverter drives). The application of variable speed drives has brought about a new way of engineering buildings and control systems HVAC.
The flow of water and air can now be regulated precisely using VSD’s and state-of-the-art control systems. By combining VSD’s with state-of-the-art control systems, large savings in energy usage can see realization because the exact quantity of flow of water or air can be delivered to satisfy demand.
Demand-based control is energy efficient. VSD’s can be stand-alone or controlled by a building automation system.
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…)
Air Handler Filter Pressure Sensor - This is a pressure sensor. It tells a maintenance technician if the air filters are dirty and clogged. The pressure control is a low static pressure switch to trip the unit if the mixing box drops below the setpoint pressure. The pressure the switch is calibrated to.
In addition, the low static pressure sensor protects the fan and the ductwork including dampers from damage. If the economizer damper and the return air damper would fail closed (or another possible scenario) that would cause the unit to pull negative pressure in the mixing box. (more…)
York VAV Air Handlers | HVAC Zoning - This York air handling unit serves several VAV boxes and runs on a static pressure control set point determined by a DDC program. This program has a static pressure control setpoint and sends a signal to the variable frequency drive to speed up or slow down the blower to maintain the proper static pressure control setpoint. When the VAV boxes need more air the drive speeds the air handler blower up.
When the VAV boxes need little the drive slows the blower down. The VAV boxes are controlled by a thermostat in their respective zones.
