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Humidity. Robert Fehr Professor Emeritus Department of Biosystems and Agricultural Engineering University of Kentucky. WATER VAPOR PROPERTIES. condensation. freezing. evaporation. W A T E R (liquid state ). melting. 144 btu / lb. 970 btu / lb. sublimation. 1223 btu / lb. I C E

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Humidity


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    1. Humidity Robert Fehr Professor Emeritus Department of Biosystems and Agricultural Engineering University of Kentucky

    2. WATER VAPOR PROPERTIES condensation freezing evaporation W A T E R (liquid state) melting 144 btu/lb 970 btu/lb sublimation 1223 btu/lb I C E (solid state) V A P O R (gas state)

    3. Definitions Humidity: The amount of water vapor in the air Relative humidity: The amount of water vapor actually in the air divided by the amount of water vapor the air can hold. Saturation of air: The condition under which the amount of water vapor in the air is the maximum possible at the existing temperature and pressure. 100% Relative Humidity

    4. Definitions Wet bulb temperature: The lowest temperature that can be obtained by evaporating water into the air at constant pressure.  Dew point: the temperature air would have to be cooled to in order for saturation to occur. 

    5. Psychometrics Basic Concepts

    6. Saturation Line

    7. Constant Dry Bulb Temperature

    8. Constant Relative Humidity

    9. Constant Humidity Ratio

    10. Constant Humidity Ratio Saturation Line Dew Point

    11. Constant Wet Bulb Temperature

    12. Dew Point Dew Point

    13. Humidity Ratio

    14. Psychometrics of Heating

    15. Psychometrics of Cooling Total Heat Latent Heat Sensible Heat

    16. Annual Hourly Outside Air Conditions – Lexington KY

    17. Annual Hourly Outside Air Conditions – Lexington KY

    18. Annual Hourly Outside Air Conditions – Lexington KY

    19. Annual Hourly Outside Air Conditions – Lexington KY

    20. Annual Hourly Outside Air Conditions – Lexington KY

    21. Annual Hourly Outside Air Conditions – Lexington KY

    22. App for Air Properties

    23. Moisture Balance Moisture Added People, Animals, Plants, Foundation Moisture Stored Fabric, Carpet, Wood Moisture Removed Dehumidifier Inside Air Leaving @ Inside Conditions Outside Air Entering @ Outside Conditions

    24. Winter Moisture Balance Moisture Added People, Animals, Plants, Foundation Moisture Stored Fabric, Carpet, Wood Moisture Removed Dehumidifier Inside Air Leaving @ Inside Conditions 70f 60% = 212 lbw/day Outside Air Entering @ Outside Conditions 32F 85% = 78 lbw/day 0.80 ACHn 134 lbw/day drying potential

    25. Winter Moisture Balance Moisture Added People, Animals, Plants, Foundation Moisture Stored Fabric, Carpet, Wood Moisture Removed Dehumidifier Inside Air Leaving @ Inside Conditions 70f 60% = 212 lbw/day Outside Air Entering @ Outside Conditions 53F 85% = 174 lbw/day 0.80 ACHn 38 lbw/day drying potential

    26. Winter Moisture Balance Moisture Added People, Animals, Plants, Foundation Moisture Stored Fabric, Carpet, Wood Moisture Removed Dehumidifier Inside Air Leaving @ Inside Conditions 70F 60% = 106 lbw/day Outside Air Entering @ Outside Conditions 53F 85% = 85 lbw/day 0.40 ACHn 21 lbw/day drying potential

    27. Summer Moisture Balance Moisture Added People, Animals, Plants, Foundation Moisture Stored Fabric, Carpet, Wood Moisture Removed Dehumidifier Inside Air Leaving @ Inside Conditions 76F 60% = 256 lbw/day Outside Air Entering @ Outside Conditions 85F 50% = 283 lbw/day 0,80 ACHn 27 lbw/day added

    28. Sources of Moisture • People • Respiration • Transpiration • Pets • Plants • Showers and Bathing • Dishwashing, and Cooking • 0.1 lb of water per ft3 of NG

    29. Sources of Moisture • Foundations • Difficult to quantify

    30. Effect of Humidity on Moisture Production

    31. Sources of Moisture - People Design Residential Moisture Generation Rates (TenWolde and Walker 2001) Number of Number of Moisture Generation Rate Bedrooms Occupants lb/h lb/day gallon/day 1 2 0.7 16.8 2.01 2 3 1.1 26.4 ` 3.17 3 4 1.3 31.2 3.74 4 5 1.4 33.6 4.03 Additional +1 +0.1 2.4 0.29 per bedroom

    32. Sources of Moisture - Plants • Potted flowers: 0.011–0.022 lb/h • Potted plants: 0.015–0.033 lb/h • Medium-size rubber plant: 0.022–0.044 lb/h

    33. Sources of Moisture - Pets It is a function of the weight of the animal. • A medium-size dog weighing 22 lb contributes about 0.015 lb/h, 0.36 lb/day, 0.043 gallons/day

    34. Sources of Moisture – Showers and Baths • 5.7 lb/h for showers • 5 minute shower = 0.475 lbs • 15 minute shower = 1.425 lbs • 1.5 lb/h for baths • 5 minute bath = 0.125 lbs • 15 minute bath = 0.375 lbs

    35. Suggested Dehumidifier Size Pints per day of Dehumidifier Capacity Source: Association of Home Appliance Manufacturers

    36. Humidity Level vs Ventilation Rate The Effect of Indoor Humidity on Water Vapor Release in Homes Anton TenWolde Crystal L. Pilon ASHREA 2007

    37. Older House 0.8 ACHn 0.4 ACHn

    38. New House 0.20 ACHn 0.35 ACHn

    39. Recommended Humidity Levels Soruce: American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE).

    40. Surface Condensation • Occurs when surface is cooler than the dew point of the surrounding air • Temperature of interior surfaces is dependent on: • Air temperatures on both inside and outside • Heat transmittance of assembly

    41. Surface Condensation • Raising the R value of a assembly • Increases the inside surface temperature • Reduces the condensation hazard

    42. Concealed Condensation • In cold temperatures, production of vapor inside an occupied building normally raised the vapor pressure • Difference for interior pressure to exterior pressure cause vapor diffusion into exterior walls and ceilings • Vapor has no where to escape • As the temperature drops, condensation begins.

    43. When is Condensation an Issue • Cooler climates in occupied, heated buildings • Humid, warm climates in air-conditioned buildings

    44. Why is Condensation an Issue Water is the DEATH of a building …after a FIRE

    45. Window Temperature Profile 70 60 50 40 30 20 10 0 66% 44% 14% Single Pane Double Pane Double Pane, low-E, Argon

    46. Uninsulated Wall Temperature Profile 70 60 50 40 30 20 10 0 30% Brick OSB Wall Cavity Air Space Gypsum Board

    47. Insulated Wall Temperature Profile 70 60 50 40 30 20 10 0 9% Brick OSB Cavity Insulation Air Space Gypsum Board

    48. Impedes the passage of water vapor into a building assembly before it can condense into a liquid • Prevents water vapor from penetrating into concealed space of exterior construction • Used on roofs, wall, and concrete slabs Vapor Retarders & Barriers

    49. Moisture Migration Into Walls Source: Building Science Corporation