DDC Programming Logic Symbols 1 - DDC programming in HVAC Control can be rather complex especially to those who don’t understand software or programming. Some software and hardware manufacturers utilize symbols to build their logic programs for HVAC DDC control. Some of these logic blocks are rather complex but others are very simple. (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…)
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.
Duct Temperature Sensor - The duct static temperature sensor measures air temperature in the ductwork. The solid-state temperature sensing devices are commonly used in HVAC applications that are controlled by direct digital control or a modern building automation system. At the base of the box is a probe that sticks into the air stream of the ductwork. As the air passes over it, the probe changes resistance. (more…)
These Alerton controllers control a heat exchanger and air handler
Alerton Controllers DDC HVAC Control - HVAC DDC control has become an integral part of building automation systems. Modern DDC HVAC Control is a state-of-the-art computer-controlled system that adds efficiency to the system. These Alerton controllers are used to monitor and control an air handling unit for a large building. (more…)
York Variable Frequency Drives VFDs | HVAC Control - Variable Frequency Drives or VFDs have added a whole new dimension to energy efficiency and control. These drives, or VFDs, are hooked up to two different York VAV air handlers that have two three-phase motors a piece. (more…)
