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ARCH-432

ARCH-432. Dew Point Saturation and Psychometrics. Attendance. Who is typically referred to as the “Father of Cool”? (hint: generally credited with developing the science of psychometrics) Willis Carrier Karl Trane Bill Lennox Dr. Frederick Glock Prof. Max Kirk. What You Need to Know.

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ARCH-432

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  1. ARCH-432 Dew Point Saturation and Psychometrics

  2. Attendance Who is typically referred to as the “Father of Cool”? (hint: generally credited with developing the science of psychometrics) • Willis Carrier • Karl Trane • Bill Lennox • Dr. Frederick Glock • Prof. Max Kirk

  3. What You Need to Know • Understand the underlying principles of psychrometrics

  4. What You Need To Be Able To Do • Read a Psychrometric chart • Be able to apply psychrometrics to predict and solve simple HVAC problems

  5. Dew point Wet bulb temperature Dry bulb temperature Enthalpy Relative humidity Sensible heat Latent heat Mixing line Terms

  6. Enthalpy To understand in a simple way, Enthalpy means change of heat. Enthalpy can be positive or negative. For water when heated to a very high temp changes its state into vapor. Here heat change takes place.

  7. Enthalpy

  8. Enthalpy

  9. Psychrometry • Psychrometry is the science dealing with the physical laws of air – watermixtures. • To obtain comfort, and select an appropriate HVAC system, the psychrometric conditions must be known.

  10. Properties of Air on a Psychrometric Chart • Dry-bulb temperature • Wet-bulb temperature • Dew-point temperature • Relative humidity • Humidity ratio

  11. 220 200 180 160 140 120 Humidity Ratio (grains/lb of dry air) dew point 100 humidity ratio 80 60 wet bulb 40 dry bulb relative humidity 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 Dry-Bulb Temperature (°F) Air Conditions on the Psychrometric Chart

  12. Dew Point (oF) • Condensation occurs at the Dew Point Temperature

  13. Saturation • You get sheep? • No you get Fog! • What happens when the DP, WB, and DB are the same?

  14. Saturation • When the dry-bulb, wet-bulb, and dew-point temperatures are the same, the air is saturated. It can hold no more moisture. When air is at a saturated condition, moisture entering the air displaces moisture within the air. The displaced moisture leaves the air in the form of fine droplets. When this condition occurs in nature, it is called fog.

  15. Amount of moisture that a given amount of air is holding = RelativeHumidity Amount of moisture that a given amount of air can hold Relative Humidity (percentage) 100% RH - Saturated 50% RH

  16. Relative Humidity • The fourth property RH, is therefore a comparison of the amount of moisture that a given amount of air is holding, to the amount of moisture that the same amount of air can hold, at the same dry-bulb temperature.

  17. Zones with ASHRAE Standard 55

  18. Team Problem Solving • Based upon your estimates of occupancy, met and clo value, what DB/RH condition point will create the most comfort in the first floor of Carpenter Hall in summer? • 73 F/50% RH • 75 F/45% RH • 75 F/55% RH • 78 F/40% RH Plot this point on your Psychrometric chart.

  19. Team Problem Solving • Assume that the gym is kept at 72° F and 35% RH in winter. At what temperature does the inside surface of the glass have to reach in order for water to condense? • 24° F • 35 ° F • 42 ° F • 56 ° F • 60 ° F

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