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George Owens is a past president of "Association of Energy Engineers", an "Energy Manager of the Year" and an "Energy Managers Hall of Fame" inductee.


 

Self-Optimizing Control
Energy Management Systems At Their Best
by George R. Owens, PE, CEM

In the paper, "Energy Management 2001", I stated that the software of Energy Management Systems has lagged far behind the significant technological developments in hardware. I am sure that many of you will exclaim, "George, where have you been, hiding your head in the sand? What about the advancements in graphics, menu driven systems and improved human interfaces?" I grant you that the systems are indeed easier to use and the graphics certainly aid the operator. However, I am referring to the guts of the system, namely, the logic for controlling space conditions, equipment operations and energy costs. I say a major breakthrough is required if we are ever to get the most out of these "expensive time clocks". Let me explain:


Owens' 9th Law of Energy Management

"At any instant, there is one and only one set of operating conditions that will meet comfort conditions AND cause the lowest amount of energy cost."

It is the goals (or should be) of the Energy Manager, Facilities Engineer, Building Operator, Building Owner, Tenants and the Automatic Control System to achieve comfort and the lowest energy cost. Unfortunately, the human operator cannot observe enough data, compute as fast as required nor be there 31,536,000 seconds a year. Also unfortunately, the Energy Management Systems of today are not smart enough to pick that "one and only one" operating condition that results in comfort and least cost. As a way of explanation, let me take you through the evolution of Control Systems.


Contol System Evolution #1 - Simple Control Loop

The simplest Control Systems (still widely used) have four basic elements consisting of a setpoint, feedback, control logic and the controlled equipment. The controller's logic compares the desired setpoint to the feedback signal. If there is a difference, the controller then generates an output signal which subsequently adjusts the controlled equipment until the controlled variable (feedback) matches the setpoint. The most common application is a thermostat in a room adjusting a VAV box to maintain space temperature.

In column format, typical Systems found in today's buildings include:

Controlled Variable Setpoint / Feedback Controlled Equipment
Space Conditions Space Temperature VAV Box Cooling / Heating Coils
Supply Air Temperature Static Fan Inlet Vanes / V.F.D.'s
Chilled Water Temperature Flow Chiller Pumps / V.F.D.'s
Hot Water Temperature Flow Boiler Pumps / V.F.D.'s

The advantage of this control logic is that it produces good stable control. However, this simple system does not optimize energy cost. For example, it is widely accepted that if a System is designed to operate on a 45F chilled water supply temperature, 47F or 50F will suffice if the internal load or exterior conditions are moderate enough. It is generally cheaper to produce 50F water than 45F water. Therefore,...


Control System Evolution #2 - Reset Systems

The current level of sophistication in software is to reset the setpoint (i.e., chilled water temperature) to compensate for interior and exterior conditions. As an example, the system would reset the chilled water temperature from 45F to 50F when the outside temperature cools off from 100F to 55F and thereby reduce chiller operating costs. Further sophistication can be produced by including interior conditions, humidity, sunlight and time of day to modify the shape or limits of the reset curve.

However, this Control System still does not produce the least cost. What about interactions from other systems? For example, what is the "one and only one" combination of all the variations of condenser water temperature/flow, chilled water temperature/flow, supply air temperature/static and VAV box position to obtain the least cost? What may be the optimum least cost for the chiller may so penalize the supply fan horsepower that total cost may actually increase instead of decrease. Therefore,...


Control System Evolution #3 - Optimizer

What is needed is an overriding program that looks at the entire system and system components to choose the "one and only one" solution.

The optimizer program would try to select the appropriate amount of reset to apply to each piece of equipment in the entire heating/cooling system.

Only two problems remain: 1) What is the cost for the engineer and programmer to develop the optimizer logic for each building? and 2) What happens if there is a change in the building such as degraded efficiency due to poor maintenance, new equipment or changes in occupancy? One must go back to the drawing board to write a new optimizer. Therefore,...


Control System Evolution #4 - Self-Optimizer - Future

The Self-Optimizer would have the goals of comfort and least cost and continually fine tune the algorithms to continually find the "one and only one" solution. To my knowledge, no Self-Optimizer Program (at least in the scope envisioned) exists. And furthermore, I contend that only infrequent or crude attempts have been attempted to optimize a complete system over all operative conditions. It is understandable that these attempts are lacking due to the extensive amount of programming time, expense and expertise required to drag that last drop of least energy cost out of a system. This can only be achieved by having the engineer or programmer 'baby-sit" a building over at least a one year period and fine tune the system extensively. A Self-Optimizer Program would automatically do just that.

In my discussions with the research arms and principals of leading Energy Management System suppliers, this concept of Self-Optimization is in the embryo stage. The areas currently being tinkered with include: expert systems, fuzzy logic, model-based reasoning and virtual reality. As this research is turned into working software, the Energy Management Systems of tomorrow will be able to find the "One and Only One" solution for comfort and least cost. This will be accomplished both in the initial system start-up stage as well as in response to continually changing conditions without the prohibitive cost of custom programming for each project.

My goal in writing this is to change the culture that surrounds both the users and the suppliers of Energy Management Systems while also promoting research and development into self-learning software to match the wonderful breakthroughs that have occurred in hardware. I welcome your challenges, comments and discussions.


To send comments to George R. Owens, click here: gowens@EESIenergy.com.

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