Psychrometrics Doug Jefferson Business Development Engineer Psychrometrics Dry

• Psychrometrics Doug Jefferson, Business Development Engineer

Psychrometrics

Dry Bulb Temperature (DB, ºF) Air temperature as measured by a thermometer with a dry sensing bulb

Relative Humidity (RH, %) The moisture content of air expressed as a percent of the maximum moisture at the specified dry bulb temperature

Humidity Ratio (HR, gr/lb) The ratio of the weight of the water to the weight of the dry air. ‘Grains’ of water vapor per pound of dry air.

Wet Bulb Temperature (WB, ºF) Air temperature as measured by a thermometer with a wet sensing bulb

Dew Point Temperature (DP, ºF) The temperature at which existing moisture will condense from the air (forming dew)

Enthalpy (h, Btu/lb) The total energy of the air, equal to the sensible energy (temperature) plus the latent energy (originally used to evaporate the water in the air)

Vapor Pressure (VP, ″Hg) The pressure exerted by the water vapor molecules on the surrounding environment

Specific Volume (ft 3/lb) Volume per pound of dry air. Also referred to as inverse density: (ft 3/lb)-1 = lb/ft 3

Psychrometrics Problems

Psychrometric Quiz 1. Given the two conditions, find the remaining. 70 °F DB 50 58. 5 °F WB 54. 7 16. 3 %RH 65 °F DB 50. 7 °F DP 45. 7 °F WB Gr/Lb 0. 37 ″Hg 14. 9 Gr/Lb 0. 10 ″Hg 25. 3 Btu/Lb 13. 5 Ft 3/lb volume 17. 9 Btu/Lb 13. 3 Ft 3/lb volume 122. 3 °F DB 10. 1 %RH 75 °F DB %RH 75 °F WB 50. 6 °F DP 40 °F WB °F DP 55 Gr/Lb 0. 37 ″Hg Gr/Lb ″Hg 38. 1 Btu/Lb 14. 9 Ft 3/lb volume Btu/Lb Ft 3/lb volume 20 %RH °F DP 2. What is the difference in Temperature, Gr/Lb and Energy between: 74°F DB, 69. 3°F WB Temperature (°F ) and 1 2 50°F DB, 100% RH Delta 74 50 Humidity Ratio (gr/lb) 100 53. 5 46. 5 Energy / Enthalpy (Btu/lb) 33. 5 20. 3 13. 2 Wet Bulb (°F) 69. 3 50 19. 3 Relative Humidity (%) 79. 4 100 24 - 20. 6

Psychrometric Quiz 3. What method of “Conditioning of air” to move between these points? Cooling 4. Why do clouds float? Psychrometric: recall psychrometric chart analysis Re: density Chemical: (70% of air is Nitrogen) N 2 = 14 x 2 =28 H 2 O = 2 x (1) + 16 = 18 18 < 28 therefore clouds float