Doug Jefferson, Business Development Engineer 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 (ft3/lb) Volume per pound of dry air. Also referred to as inverse density: (ft3/lb)-1 = lb/ft3
Psychrometrics Problems
Psychrometric Quiz 1. Given the two conditions, find the remaining. 70 °F DB 50 %RH °F WB °F DP Gr/Lb ″Hg Btu/Lb Ft3/lb volume 65 °F DB %RH °F WB 20 °F DP Gr/Lb ″Hg Btu/Lb Ft3/lb volume 16.3 58.5 50.7 45.7 54.7 0.37 14.9 0.10 25.3 13.5 17.9 13.3 122.3 °F DB %RH 75 °F WB °F DP 55 Gr/Lb ″Hg Btu/Lb Ft3/lb volume 10.1 75 °F DB %RH 40 °F WB °F DP Gr/Lb ″Hg Btu/Lb Ft3/lb volume 50.6 0.37 38.1 14.9 2. What is the difference in Temperature, Gr/Lb and Energy between: 74°F DB, 69.3°F WB and 50°F DB, 100% RH 1 2 Delta Temperature (°F ) 74 50 Humidity Ratio (gr/lb) Energy / Enthalpy (Btu/lb) Wet Bulb (°F) 69.3 Relative Humidity (%) 100 24 100 53.5 46.5 33.5 20.3 13.2 50 19.3 79.4 - 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) N2 = 14x2 =28 H2O = 2 x (1) + 16 = 18 18 < 28 therefore clouds float