# Psychrometry HVAC CNST 305 Environmental Systems 1 Dr. Berryman 5cIndoor Air Quality, Psychometrics; Dry and Wet Bulb; Enthalpy; Condensation; Dew Point.

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Psychrometry HVAC CNST 305 Environmental Systems 1 Dr. Berryman 5cIndoor 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

Psychrometric Chart

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

Thermometers Dry Bulb Wet Bulb Measured in degrees Fahrenheit ( o F)

Dew Point Condensation occurs at the Dew Point Temperature ( o F)

Saturation Fog

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

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

wet bulb dew point 30 Dry-Bulb Temperature (°F) Humidity Ratio (grains/lb of dry air) 2535404550556065707580859095100105110 20 40 60 80 10 0 12 0 14 0 16 0 18 0 20 0 22 0 humidity ratio dry bulb relative humidity Air Conditions on the Psychrometric Chart

Specific Volume 14.0 13.0 13.5 14.5 specific volume lines (cubic feet / pound of dry air) specific volume lines (cubic feet / pound of dry air) 30 Dry-Bulb Temperature (°F) Humidity Ratio (grains/lb of dry air) 2535404550556065707580859095100105110 20 40 60 80 10 0 12 0 14 0 16 0 18 0 20 0 22 0

Enthalpy Enthalpy (h) = Sensible Heat + Latent Heat

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

Answer 95°F 78°F 50% 40% 72°F

Condensation EXAMPLE Beach Conditions 92 o F 60% RH Beverage 45 o F

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

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

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

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

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

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

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

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

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

Next Time Calculating Heating Loads Section 2.5 Toa Heat Transmission

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