Article - January 2003
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I believe the possibilities of this type of technology for the future is unlimited. From the space shuttle to the refrigerator in our homes, almost every mechanical device we can think of requires some type of control, and in most all cases it will be Direct Digital Control. 

Roger  J. Des Rosiers
Occupational Studies, 3881 Section 002
May 1, 2001

Course Paper

The objective of this paper is to introduce a fairly new technology that has been developing and improving over the past forty years in environmental quality controls; the control of air conditioning systems with Direct Digital Controls. The control of air-conditioning systems today are critical due to the high cost of energy, and the requirements made by science and industry. 

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Air quality control systems have come a long way in the past forty years. Beginning with electric controls, then pneumatic controls, electronic controls, and today we have "Direct Digital Controls." 

This paper will present a better understanding of Direct Digital Controls, and the improvements made over all prior systems of air quality control. This understanding is very important because as people gain knowledge of what these controls are capable of doing, the more energy we will save, which turns into the elimination of large amounts of air pollution. This report will show the history, background and the description of "DDC" technology, the planned and actual effects of this technology, and the future effects of this technology as well as an example of an inappropriate setting for this type of technology. I will also demonstrate the operational definition of this technology and finally my conclusion on the technology of Direct Digital Controls.

Willis H. Carrier, born in 1876 in Angola, New York, developed an apparatus for treating air with a low pressure, centrifugal refrigeration machine using a non toxic, non flammable refrigerant. According to Refrigeration and Air Conditioning Technology, (1999); by controlling humidity as well as temperature, Willis H. Carrier invented modern air conditioning. 

Direct Digital Controls for the control of air conditioning and refrigeration systems, is the direct result of technological advances in air conditioning electronics. 

With the invention of the air conditioning systems, other components had to be integrated in order to control this technology. Ductwork to carry and distribute the conditioned air to various areas throughout a building was required. In addition, the system needed something to move this conditioned air, such as a supply fan with a motor. "The controls are a major component and the heart of the system", as, noted in the research presented in Direct Digital Control, A Guide to Distributed Building Automation, (1995). These controls are responsible for the sequence of the operation for the air conditioning units and all of the sub systems required making a complete system work. 

Originally, controls were electric, and by today's standards, were quite primitive. Then came the advent of pneumatic controls. This was a large improvement over electric controls, because of the simplicity and ease of maintenance, and ability to control equipment from long distances. With the introduction of electronic controls, the control systems were smaller, and more functional. However, the controls could not communicate with each other. Today, by using Direct Digital Controls, the systems are integrated, allowing each control to communicate with any other control within a system structure. 

The Iowa Energy Center, (1999), tells us that a Direct Digital Control System, (DDC), consists of a microprocessor-based controller with the control logic performed by software. Analog to Digital (A/D) converters transform analog values into digital signals that a microprocessor can use. Analog sensors can be resistive, voltage, or current generators. 

Most systems distribute the software to the remote controllers to eliminate the need for continuous communication capability (stand-alone). The computer is primarily used to monitor the status of the energy management system, store back-up copies of the programs and record alarming and trending functions. 

contemporary Complex strategies and energy management functions are readily available at the lowest level of the system architecture. If pneumatic actuation is required, it is accomplished with electronic to pneumatic transducers. Calibration of sensors is mathematical; consequently the total man-hours for calibration are greatly reduced. Software and programming are constantly improving, becoming increasingly user-friendly with each update. The three major components for the Direct Digital Control system are the sensor, controller and a controlled device. These three components or, functions, interact to control a medium. For example, air temperature is a controlled medium. The sensor measures the data, the controller processes the data, and the controlled devise causes an action. The sensor measures the controlled medium or other control input, in an accurate and repeatable manner. Common heating, ventilating, and air conditioning (HVAC Sensors), are used to measure temperature, pressure, relative humidity, cubic feet per minute, and carbon dioxide. Other variables may also be measured that impact the controller logic. Examples include other temperatures, time-of-day, or the electrical current demand condition. Additional input information, (sensed data), that influences the control logic may include the status of other parameters. 

The controller processes according to Direct Digital Control: A Guide to Distributed Building Automation. (1995); states in part, that the controller processes data that is input from the sensor, applies the logic control and causes an output action to be generated. This signal may be sent directly to the controlled device or to other logical control functions and ultimately to the controlled device. 

The control device is a device that responds to the signal from the controller, or the control logic, and changes the condition of the controlled medium or the state of the end device. These devices include, valve operators, damper operators, electric relays, fans, pumps, compressors, and variable speed drives for fan and pump applications. 

The Survey of Electrical Energy Strategies, Association of Energy Engineers Journal, (1991), tells us the planned effects of this technology, was originally designed to improve the control of air conditioning comfort. However, through technological developments, other benefits were realized and implemented such as 1) Fire, life safety, and smoke evacuation; 2) Security and access control; 3) Lighting; 4) Energy management; 5) Vertical movement (elevators). 

As Direct Digital Control systems improve, they are replacing older systems, which are obsolete. These obsolete systems consume large amounts of energy. 

The benefits of Direct Digital Control over past control technologies is that it improves the control effectiveness and increases the control efficiency. 

The three main direct benefits of Direct Digital Controls are 1) Improved effectiveness; 2) Improved operation efficiency; and 3) Increased energy efficiency. 

After the DDC technology was implemented in the Heating, Ventilating, and Air Conditioning (HVAC) field, many of the older employees working needed to be retrained in order to keep up with the constant changes. In addition, many mechanics were laid off or retired because, the efficiency of DDC, required less manpower to function. 

The positive side of having DDC diffused in our large building management control systems is improved energy management, cost control and the ability to control the entire campus from one central control system. With the adaptation of this system we now have precise control, technical capabilities and remote communication. 

Precise control lends itself directly to occupant comfort. Technical capabilities refer to such features as being able to reduce building and equipment down time. Remote communication allows for a local system to dial out to a location and conduct troubleshooting prior to a trip to that site by service personnel. 

Another very important consideration of this technology, discussed in Direct Digital Control: A Guide to Distributed Building Automation. (1995), is the matter of fire, life safety, and smoke evacuation. Fire and life safety enable sophisticated sequences in a building to help extinguish fires and protect occupants from exposure from fire and smoke. These systems also serve as communications links for use by fire fighting personnel. 

Direct Digital Control systems have undergone a number of changes over the years. They have been called energy management and building automation systems, to name just two. Yet more important than the name is the fact, according to American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) (2000), that DDC remains one of the most universally applied and successful technologies installed in buildings today. 

The major reason that people began installing computerized controls in their buildings was to save energy costs. This impetus started the trend, but the many benefits that these systems have offered users over the years have spurred growth of this business, according to the American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) (2000), to nearly one billion dollars per year. 

An industry of this magnitude creates a sufficient number of jobs and further involves significant capital investment on the part of a wide variety of users. 

The future of Direct Digital Control systems looks better with each passing year. As these types of controls get more popular they will be used world wide because of their great energy management efficiencies. As energy problems become acute around the world, the need for DDC technology becomes greater. A good example is the modern automobile, which was a gas-guzzler in the beginning of its use, but thanks to advanced microprocessors that have helped to control such things as fuel, speed, consumption, breaking systems, and satellite tracking systems, the automobile is one of the many modern advanced technologies we all share. Today, according to Time for an Upgrade? (1999), many of the newer smaller, air conditioning units are now being manufactured with DDC controls right at the factory. 

Direct Digital Control can only be effective with communications between devices. This can be characterized as peer-to-peer, or polling. On a peer-to-peer Local Area Network, (LAN), each device can share information with any other device on the LAN without going through a communications manager. 

Some of the possibilities of the future trends are that communications between sensors and multiplex boxes and the head systems will be by a combination of technologies; traditional means such as; twisted wire, co-axial, infrared, and radio wave. By the year 2005, the following scenario will most likely be in actual use: 

An operator wants to add a sensor to a previously unmonitored room; the operator goes to the store room and picks up a $10.00 sensor; when the operator peels off the self adhesive backing and sticks it on the wall; several things simultaneously occur: a) power is supplied to the unit by a built in solar cell with battery back-up; b) the sensor starts broadcasting that it is now active; c) the computer recognizes the sensor, assigns a point number internally to the computer and within the sensor; d) the system will know the location by triangulation of the signal and its internal map of the building; e) the system will start a self-optimization routine to discover the appropriate control strategies to utilize this new sensor; f) by the time the operator returns, the data for this sensor will be fully integrated with the man/machine interface. The information will be presented to the operator in the format that the operator prefers without ever once issuing a manual request. 

The history of controls indicates that the performance has increased more than ten fold each decade. According to Direct Digital Control: Guide to Distributed Building Automation (1995), by the year 2005 wireless communications, self-optimizing software and improved operator interfaces will far surpass any of our current expectations. The systems will be easier to use, provide comfort, reduce energy costs and be less expensive to install. 

The term "Energy Management" will no longer exist. All of this will be conducted as "business as usual". Finally, I believe the possibilities of this type of technology for the future is unlimited. From the space shuttle to the refrigerator in our homes, almost every mechanical device we can think of requires some type of control, and in most all cases it will be Direct Digital Control. 

An inappropriate place for the Direct Digital Control technology to exist would have been among the Shoshone Band of Indians. In a paper by Thomas J. Elpel, titled "The Art of Nothing", we find the following: 

Westerners who first met the Shoshone Bands of Indians in the Great Basin Desert typically described them as being "wretched and lazy". Many observers remarked that they lived in a total wasteland and yet seemed to do nothing to improve their situation. They built no houses or villages; they had few tools or possessions, almost no art, and they stored little food. It seemed that all they did was sit around and did nothing. The Shoshone were true hunter-gathers. They spent their lives walking from one food source to another. The reason they did not build houses was because houses were useless to them in their nomadic lifestyle. Everything they owned they carried on their backs from place to place. They did not manufacture a lot of tools or possessions or art, because it would have been a burden to carry. We often expect that such primitive cultures as the Shoshone to work all the time just to stay alive, but in fact these were very leisured people. Anthropological studies in different parts of the world have indicated that nomadic hunter-gathers type societies typically worked only two to three hours per day for their subsistence. Like the deer and other creatures of the wild, hunter-gatherer peoples have nothing more to do than wander and eat. 

The Shoshone had a lot of time on their hands only because they produced almost no material culture. They were not being lazy they were just being economical. Sitting around and doing nothing for hours on end helped them to conserve precious calories of energy so they would not have to harvest so many calories each day to feed themselves. 

By understanding the lifestyle and needs of the Shoshone Indians at that time in history, one is likely to see that they worked and lived with the elements of nature in the universe, and did not require improvements with the air they were breathing. Only in a confined environment, in a society that remained fixed in one place, would you consider working to improve the quality of that environment. Nature was the technology of that time. The Shoshone had to adapt to nature and all the gifts and at times, the hardships that it offered the Shoshone people. Any introduction of our modern technology could not be adopted. The need was not in place, and therefore could never be adapted. The basic requirements for diffusion into a society were missing from the Shoshone people at that time in history. 

Direct Digital Control is basically a black box microprocessor, with tentacles of twisted wires that can reach out to every other black box that contains software for operational instructions in order to compare variable outputs to set points through a process of measurements of algorithms. A set point is a programmed measurement target. The set point can be established for any type of control, for temperature, pressure, humidity, smoke, heat, water flow, lighting, energy management, and many other types of measurements. 

The basic premise is to measure something in the real world (analog), change it to digital in a series of zeros (0's), and ones (1's), measure this, and convert it back to real world (analog) form. 

This process is then able to take the analog output to drive a final controlled device, which in turn would drive the original measured value to the required set point value. This process is constantly taking place as long as the set point is not achieved. 

These measurements are taken constantly in microseconds. The whole process takes place with constant feed back to the microprocessor. 

This technology is used everyday all around the country in office buildings to control the building environment. With buildings ranging from one floor to many floors, with various companies occupying different floors. Direct Digital Control Systems are installed to maintain perfectly controlled temperature and humidity for any floor, in any area at any time of day or night. The control system would monitor all energy usage; reduce energy loads if necessary in order not to exceed electric demand, which is preprogrammed into the control system. 

As a safety measure the DDC will alert the building occupants if smoke is detected on any floor of the building, and people would be evacuated to safety. All the elevators would stop at a floor and people would be required to exit the elevator and use the stairs. In addition, special fans would start to evacuate any smoke sensed on the floors. All supply and return air fans would shut down in order to contain the smoke or fire. DDC would also activate the control systems to activate the fire sprinkler systems. 

With the development of Direct Digital Controls, we have the best technology at the present time. This type of control technology can be found in many applications besides air conditioning; in science, health and engineering applications to name only a few. The future looks very promising with the advancement of Direct Digital Technology. There can be no doubt that with future advances in electronic technology, the Direct Digital Control system will improve to the point that they will be self checking and in many cases will be able to repair or modify themselves to meet any ongoing or new problems as they may arise.


Elpel, T.J., (1995). The Art of Nothing. [online]. Available from:  
Golden, P. , (1991). Electrical Energy Strategies, The Survey. Association of Energy Engineers Journal, 88 (5), 73-79. 
Iowa Energy Center. (1999). Direct Digital Control. [online]. Available from:
Jarnigan, R., Mc Bride,M., Skalko, S.V.,Schwedler, M.,Howley,Jr.,J.G.(2000). The new standard 90.1 [online]. Available from: http:// 
Mc Gowan, J.J., (1995). Direct Digital Control: A Guide to Distributed Building Automation. Liburn, GA. The Fairmont Press. 
Piper, J.,(1999).Time for an upgrade? [online]. Available from: 
Whitman, W.C., (1999). Refrigeration and Air Conditioning Technology. Delmar.

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