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
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:
||Setpoint / Feedback
||VAV Box Cooling / Heating Coils|
||Fan Inlet Vanes / V.F.D.'s|
||Chiller Pumps / V.F.D.'s|
||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 45°F chilled water
supply temperature, 47°F or 50°F will suffice if the internal load or exterior
conditions are moderate enough. It is generally cheaper to produce 50°F water
than 45°F 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 45°F to 50°F when the outside temperature cools off from 100°F to 55°F 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.
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