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ARCH-432 Dew Point Saturation and Psychometrics. Attendance Who is typically referred to as the “Father of Cool”? (hint: generally credited with developing.

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Presentation on theme: "ARCH-432 Dew Point Saturation and Psychometrics. Attendance Who is typically referred to as the “Father of Cool”? (hint: generally credited with developing."— Presentation transcript:

1 ARCH-432 Dew Point Saturation and Psychometrics

2 Attendance Who is typically referred to as the “Father of Cool”? (hint: generally credited with developing the science of psychometrics) A. Willis Carrier B. Karl Trane C. Bill Lennox D. Dr. Frederick Glock E. Prof. Max Kirk

3 What You Need to Know Understand the underlying principles of psychrometrics

4 What You Need To Be Able To Do Read a Psychrometric chart Be able to apply psychrometrics to predict and solve simple HVAC problems

5 Terms Dew point Wet bulb temperature Dry bulb temperature Enthalpy Relative humidity Sensible heat Latent heat Mixing line

6 Enthalpy To understand in a simple way, Enthalpy means change of heat. Enthalpy can be positive or negative. For water when heated to a very high temp changes its state into vapor. Here heat change takes place.

7 Enthalpy

8

9 Psychrometry Psychrometry is the science dealing with the physical laws of air – water mixtures. To obtain comfort, and select an appropriate HVAC system, the psychrometric conditions must be known.

10 Properties of Air on a Psychrometric Chart Dry-bulb temperature Wet-bulb temperature Dew-point temperature Relative humidity Humidity ratio

11 wet bulb dew point 30 Dry-Bulb Temperature (°F) Humidity Ratio (grains/lb of dry air) humidity ratio dry bulb relative humidity Air Conditions on the Psychrometric Chart

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

13 Saturation You get sheep? No you get Fog!  What happens when the DP, WB, and DB are the same?

14 Saturation When the dry-bulb, wet-bulb, and dew- point temperatures are the same, the air is saturated. It can hold no more moisture. When air is at a saturated condition, moisture entering the air displaces moisture within the air. The displaced moisture leaves the air in the form of fine droplets. When this condition occurs in nature, it is called fog.

15 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)

16 Relative Humidity The fourth property RH, is therefore a comparison of the amount of moisture that a given amount of air is holding, to the amount of moisture that the same amount of air can hold, at the same dry-bulb temperature.

17 Zones with ASHRAE Standard 55

18 Team Problem Solving Based upon your estimates of occupancy, met and clo value, what DB/RH condition point will create the most comfort in the first floor of Carpenter Hall in summer? A. 73 F/50% RH B. 75 F/45% RH C. 75 F/55% RH D. 78 F/40% RH Plot this point on your Psychrometric chart.

19 Team Problem Solving Assume that the gym is kept at 72° F and 35% RH in winter. At what temperature does the inside surface of the glass have to reach in order for water to condense? A.24° F B.35 ° F C.42 ° F D.56 ° F E.60 ° F


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