Objectives Complete high-quality projects Understand expectations Control theory and design

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