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Psychrometrics: Understanding and Calculating Psychrometric Quantities for HVAC Systems - , Study Guides, Projects, Research of Architecture

The University of Texas at AustinArchitecture
Prof. Jeffrey A. Siegel

The objectives of a project on psychrometrics for hvac systems. Students are required to investigate a hvac component, conduct research, prepare an annotated bibliography, deliver an oral presentation, and write a report. Details on the project deliverables, evaluation criteria, and the importance of psychrometric quantities such as humidity ratio, wet-bulb temperature, and dew-point temperature. It also explains how to use psychrometric charts and tables to calculate psychrometric quantities.

Typology: Study Guides, Projects, Research

Pre 2010

Uploaded on 08/26/2009

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koofers-user-5f1 🇺🇸

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Objectives
• Describe project
• Describe psychrometric quantities (Ch. 7)
• Given any two psychrometric quantities, calculate
any other quantity
• Use Tables A4 or psychrometric charts to look up
psychrometric quantities
• Calculate psychrometric quantities at non-standard
conditions
• Next: Evaluate psychrometric processes (8.1-8.4)
Project
• Goal is for you to conduct an in-depth
investigation of a HVAC component
• Select your component and e-mail your 3 top
preferences (ranked) by Wednesday (2/11) at 5
pm
• I will maximize happiness
• 30% of your grade
pf3
pf4
pf5
pf8
pf9
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Download Psychrometrics: Understanding and Calculating Psychrometric Quantities for HVAC Systems - and more Study Guides, Projects, Research Architecture in PDF only on Docsity!

Objectives

  • Describe project
  • Describe psychrometric quantities (Ch. 7)
  • Given any two psychrometric quantities, calculate any other quantity
  • Use Tables A4 or psychrometric charts to look up psychrometric quantities
  • Calculate psychrometric quantities at non-standard conditions
  • Next: Evaluate psychrometric processes (8.1-8.4)

Project

  • Goal is for you to conduct an in-depth investigation of a HVAC component
  • Select your component and e-mail your 3 top preferences (ranked) by Wednesday (2/11) at 5 pm - I will maximize happiness
  • 30% of your grade

Deliverables

  • Annotated bibliography (March 5th)
  • At least 6 references
    • And, no more than 3 non-peer-reviewed references
    • Two sentences about each reference
      1. Relevance of work to your topic
      2. Specific results that you used
  • Primary grading criteria are specificity and quality of references
  • Submit copies (electronic or analog) with your bibliography

Deliverables

  • Oral Presentation April 16th-23rd
    • 10 minute oral presentation
    • +3 minutes questions
  • Evaluation criteria:
    • Clear visuals
    • Engaging speaker
    • Depth of investigation
    • Creativity/innovation
    • Response to questions
  • Portion of evaluation will come from peers

Psychrometric Chart

  • Need two quantities for a state point
    • Can get all other quantities from a state point
  • Can do all calculations without a chart
    • Often require iteration
    • Many “digital” psychrometric charts available
      • Can make your own
    • Best source is ASHRAE fundamentals (Chapter 6)
      • Also in your text (back cover fold-out)

Ref: Tao and Janis (2001) Ref: Tao and Janis (2001)

Examples

  • What is enthalpy of air in the classroom right now?
  • Condensation on windows when taking a shower - How cold does it have to be outside for condensation to form on windows? - Assumption is that windows are the same temperature as outside air - 80 °F, RH = 80%

Humidity Ratio, W

  • W = mw/ma
  • Degree of saturation,^ μ^ = W/Ws
  • Humidity ratio is hard to measure, but very useful in calculations
  • What are units?
  • Is W a function of temperature? What about Ws? Ws = humidity ratio at saturation ma = mass of dry air mw = mass of water vapor

Alternate calculation for W

  • PV = mRT (IGL)
  • What do we know about R ratio?
  • P^ =^ Pw +^ Pa R = P = pressure^ gas constant V = volume T = absolute temperature W = humidity ratio Subscripts: w is water vapor, a is dry air

Tables for Moist Air (P = 1 atm)

  • Tables A.4 in your text
  • Ability to get Ws for calculations
  • Subscripts:
    • a = dry air, s = saturated air v = va+μvas h = ha+μhas s = sa+μsas

Wet-bulb temperature, t*

  • Temperature at which water, by evaporating into the air, will bring air to saturation adiabatically
    • superscript is designation that variable is evaluated at the wet-bulb temperature
  • Note, distinct from that measured by a sling psychrometer - Section 9.

A diversion…

  • For an ideal gas,
    • ha =^ ∫cpadT, hw =^ ∫cpwdT
  • So,^ ha =^ cpat^ which assumes a reference state of 0 °F or 0 °C – Tables A - Note different reference
  • hw =^ cpwt + hg
  • h = cpat + W(cpwt + hg0)
  • h = cpt + W·hg0, cp = cpa + Wcpw cp = specific heat h = enthalpy T = absolute temperature t = temperature W = humidity ratio Subscripts: w is water vapor, a is dry air, g is saturated water vapor

Summary

  • Describe psychrometric quantities
  • Given any two psychrometric quantities, calculate any other quantity
  • Use Tables A4 or psychrometric charts to look up psychrometric quantities
  • Calculate psychrometric quantities at non- standard conditions