Minggu, 25 Oktober 2009

Introduction to Direct Digital Control Systems

Purpose of this Guide
The purpose of this guide is to describe, in generic terms, the various architectures, hardware components and software associated with Direct Digital Control (DDC) systems. To accomplish this goal, a generic framework of the various components and configurations used in current DDC systems has been defined. This framework is used as a yardstick for several DDC manufacturers so readers may compare the relative features and benefits.

Intended Audience


Due to the complexity and proprietary nature of DDC systems, it has become difficult to stay current with the designs, installations, operation and maintenance of DDC systems. This guide was developed specifically to help building owners and consulting/specifying engineers with these issues.

What is an Energy Management System?
For the purposes of this guide, an energy management system (EMS) is defined as a fully functional control system. This includes controllers, various communications devices and the full complement of operational software necessary to have a fully functioning control system. This guide addresses approximately twenty of the DDC vendors who serve the institutional and commercial marketplace in the United States. Vendors who supply a complete line of all the necessary hardware and software are included. This guide does not cover specialty markets (retail grocery, hotels), nor does it cover industrial or process controls.

What is Control?
The process of controlling an HVAC system involves three steps. These steps include first measuring data, then processing the data with other information and finally causing a control action. These three functions make up what is known as a control loop. An example of this process is depicted in Figure 1.
 





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