Direct Digital Control (DDC) is the control system that is aimed to control HVAC (Heating, Ventilating, and Air Conditioning) by the means of electronic schemes and logical elements. DDC receive analog and digital inputs from the sensors and devices installed in the HVAC system and, according to the control logic, provide analog or digital outputs to control the HVAC system devices.
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Types of Direct Digital Control
The DDC systems may be used for controlling any type of HVAC: from the in-car air conditioner, to the climate control system within the industrial object. The climate control systems include air conditioners, ventilation and heaters. Advanced control systems include not only the system of turning on and off the climate control systems, but these also follow the current temperature, humidity, oxygen concentration and make the conclusion on the matters, which system should be activated, and which deactivated.
The simplest just follow the speed of air ventilation, and are controlled manually, by the means of the controlling panel.
The security systems react, if the surrounding temperature corresponds the temperature of the open fire, or these systems get activated, if mention smoke in the room. In this case these systems activate the fire-extinguishing systems.
Pneumatics Control Devices
The pneumatic control devices often entail the mechanisms that are controlled electronically. These devices are used almost in every sphere of the everyday life, and taking into account the HVAC systems, which are mainly pneumatic by nature, the Direct Digital Control Systems are often aimed to control the pneumatic elements and blocks. Thus, the pneumatic and DDC systems are often joined, but some manufacturers give preferences to some particular system: either pneumatic, or DDC.
The advantages of the systems are the following: the pneumatic systems are more solid, and have larger safety factors. These systems are also featured by the subjection of the electricity misses. The Advantages of the DDC: These systems are more comfortable in operating and functioning, they are not subjected to leakages and often produce the minimum noise.
As for the disadvantages: the pneumatic systems are too noisy, thee may give leakages and they require constant technical examination. The Direct Digital Control systems are often not protected from the electricity misses (but currently the problem is partly solved by the application of the UPSs).
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The pneumatics will not be phased out by the DDCs, but the advantages of the latter are obvious and most users now select the DDCs. This is also featured by the simplicity of the installation of such systems, and the simplicity of further technical maintenance and examination. The reserve parts, if needed, are more available for the DDCs, as these systems are more standardized, in comparison with the pneumatics. Moreover, there is a strong tendency of uniting both systems, thus attributing the advantages of both variants in the only system.
In conclusion it is necessary to mention, that the HVAC systems, controlled either by the DDCs or pneumatic systems are also developing, and increasing the number of functions, electronically controlled, so, the matter of the choice is more and more obvious for the DDCs.
Coffin, M. J. Direct Digital Control for Building HVAC Systems Springer publishing, 2007