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Psychrometry

5c. Indoor Air Quality, Psychometrics; Dry and Wet Bulb; Enthalpy; Condensation; Dew Point Temp. Chapter 2.1 – 2.3 (Toa). 2.11 Mathematics and Science - Physics (1hr); 4.11 Analysis and Design of Construction Systems - Mechanical (2 hrs). Psychrometry. HVAC CNST 305 Environmental Systems 1

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Psychrometry

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  1. 5c Indoor Air Quality, Psychometrics; Dry and Wet Bulb; Enthalpy; Condensation; Dew Point Temp. Chapter 2.1 – 2.3 (Toa) 2.11 Mathematics and Science - Physics (1hr); 4.11 Analysis and Design of Construction Systems - Mechanical (2 hrs) Psychrometry HVAC CNST 305 Environmental Systems 1 Dr. Berryman

  2. Psychrometry

  3. Psychrometric Chart

  4. Properties of Air • Dry-bulb temperature • Wet-bulb temperature • Dew-point temperature • Relative humidity • Humidity ratio

  5. Thermometers Dry Bulb Measured in degrees Fahrenheit (oF) Wet Bulb

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

  7. Saturation • Fog

  8. 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

  9. Humidity Ratio at sea level one pound of 70°F air occupies approximately 13.5 cubic feet, and one grain of water in that air weighs about two-thousandths (0.002) of an ounce

  10. 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

  11. 220 200 180 specific volume lines (cubic feet / pound of dry air) 160 14.5 140 120 Humidity Ratio (grains/lb of dry air) 100 80 60 14.0 13.5 40 13.0 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 Dry-Bulb Temperature (°F) Specific Volume

  12. Enthalpy Enthalpy (h) = Sensible Heat + Latent Heat

  13. Using the Chart • Summer Design Conditions • 95°F DB (dry bulb) • 78°F WB (wet bulb) EXAMPLE Find: Relative Humidity Humidity Ratio Dew Point

  14. 78°F 50% 40% 72°F 95°F Answer

  15. Condensation Beverage 45oF EXAMPLE Beach Conditions 92oF 60% RH

  16. Condensation (cont.) Winter: Glass surface temperature = 40oF EXAMPLE Inside Design: 77oF 30% RH

  17. Comfort Zone wet-bulb temperature 60 % RH humidity ratio A 30 % RH 70°F [21.2°C] 80°F [26.7°C] dry-bulb temperature

  18. Effect of Adding Sensible Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  19. Effect of Removing Sensible Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  20. Effect of Adding Moisture Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  21. Effect of Removing Moisture Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  22. Removing Sensible Heat and Moisture Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  23. Removing Sensible Heat and Moisture A Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  24. Sensible and Latent Coil Loads latent load B sensible load C A 32.7 D 29.6 23.5 Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999

  25. Next Time • Calculating Heating Loads • Section 2.5 Toa • Heat Transmission

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