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Objectives
• Complete high-quality projects
• Understand expectations
• Control theory and design
• “Second Day of Bombing Fails to Bring Peace to Gorazde”
Seattle Post Intelligencer: April 11, 1996
Ground Rules
• 6 pages single-spaced, 12 pt 1 inch margins• Excludes references• Includes figures and tables• No appendices
• Bottom line – You have to be very concise
Key Words
• The goal of this project is for you to develop a comprehensive design guide for a specific HVAC component. The design guide should both serve as a reference for HVAC engineers specifying the component, as well as summarize current research on the component.
Objectives/Criteria
• Locate and use high quality references to solve HVAC design problems
• Concisely summarize technical material
• Present technical work in oral and written forms
Questions
• How do you select this component? • What are most important factors? • What are typical values of these parameters for residential
and commercial HVAC systems? • What should designers know about this component?• What are the current/recent research issues for this
component? • What are recent improvements and what benefits do they
yield?• What will this component look like in 30 years?
Some Cautionary Notes
• Don’t use others figures and tables• Your job is to identify and concisely
describe relevant work• Papers you are reading serve as good
sources for style• Consistency is really important
– Consistent reference and citation style– Consistency between sections
Grammar and Style
• Common grammatical and stylistic errors– Colloquial– Articles and prepositions– Overuse of parentheses– Unclear subjects– Long sentences– Not defining terms
Strategies for Avoiding Grammatical Errors
• Peer review/edit before submission
• Read paper out loud– Even better (more embarrassing) with an
audience
• Read each sentence, starting from end of paper
• Look at previous versions to try and catch recurring errors
Written Report Evaluation
• 10% Thoroughness and utility
• 15% Depth and justification
• 15% Answers requested questions
• 20% Quality of writing and analysis
• 10% Quality and completeness of references
Oral Presentation
• Very different than written communication
• Must be much more concise
• Must work harder to maintain interest and attention
Preparing an oral presentation
• Consider your audience• Tell a story• Mix visuals and text• Be selective about what you present
– Listeners can read paper if they want more• Keep presentation clear and simple• Be consistent• Don’t ever read from notes or from slides• PRACTICE PRACTICE PRACTICE• Aim for readability
Consistency
• Headaches are bad
• Impairs thought process.• Hard to get work done• I don’t like it when I have headaches because
my brain hurts a lot and I can’t get anything meaningful done.
• Relatively few fonts, consistent format between slides
Referencing in a presentation
• Don’t have to give full references
• Listeners want to know– Who– When– Where
• 25% headaches hurt Migraine Boy, 1997, J. Traumatic Stress
Random comments
• Be careful with humor• Be cautious about transitions• Plan for contingencies• Have extra material available• Back-up your presentation• Extraneous visual material on slides is distractingExtraneous visual material on slides is distracting• Misteaks are very obvious to audience
• Any questions about presentations?
Objectives
• Terminology
• Types of controllers – Differences
• Controls in the real world– Problems– Response time vs. stability
Motivation
• Maintain environmental quality– Indoor air quality– Occupant comfort– Material protection
• Conserve energy
• Protect equipment
History
• Process controls
• Self powered controls
• Pneumatic and electro-mechanical controls
• Electronic controls
• Direct Digital Control (DDC)
Terminology
• Sensor– Measures quantity of
interest
• Controller– Interprets sensor data
• Controlled device– Changes based on
controller outputFigure 2-13
DirectClosed Loop or Feedback
IndirectOpen Loop or Feedforward
• Set Point – Desired sensor value
• Control Point– Current sensor value
• Error or Offset– Difference between control point and set point
Two-Position Control Systems
• Used in small, relatively simple systems
• Controlled device is on or off– It is a switch, not a valve
• Good for devices that change slowly
Humble Honeywell T87
• ~50 years old
• Innards are deceptively complicated
• Elegant design
• Significant patent issues
• Anticipator can be used to shorten response time• Control differential is also called deadband
Not-So-Humble Chronotherm III
• DDC – measures temperature many times every second
• Incorrectly accounted for wall temperature
• Wide swings in air temperature
Modulating Control Systems
• Used in larger systems• Output can be anywhere in operating range• Three main types
– Proportional– PI– PID
Proportional Controllers
O is controller output
A is controller output with no error
KP is proportional gain constant
e is error (offset)
PO A e K
P
O Ae
K
• Very big gain leads to big changes in output and instability
• Goal is to pick biggest possible gain and still have have a stable system
PO A e K
Stable systemUnstable system
Proportional + Integral (PI)
P iO A e K K edt Ki is integral gain
If controller is tuned properly, offset is reduced to zero
Figure 2-18a
Proportional + Integral + Derivative (PID)
• Improvement over PI because of faster response and less deviation from offset– Increases rate of error correction as errors get larger
• But– HVAC controlled devices are too slow responding– Requires setting three different gains
P i d
deO A e K K edt K
dt
Ref: Kreider and Rabl.Figure 12.5
The Real World
• 50% of US buildings have control problems– 90% tuning and optimization– 10% faults
• 25% energy savings from correcting control problems
• Commissioning is critically important
Practical Details
• Measure what you want to control
• Verify that sensors are working
• Integrate control system components
• Tune systems
• Measure performance
Commission control systems