Psychrometric Chart Basics. Basic Concepts Saturation Line.

PsychrometricChart

Basics

PsychrometricChart

Basics

Basic Concepts

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DRY BULB TEMPERATURE - °F

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PSYCHROMETRIC CHARTLexington, Kentucky USABAROMETRIC PRESSURE 28.874 inches of Mercury

Linric Company Psychrometric Chart, www.linric.com

Staturation Line

Saturation Line

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Constant Dry Bulb Temperature


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Constant Humidity Ratio

Constant Humidity Ratio

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10% RELATIVE HUMIDITY

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Constant Relative Humidity

Constant Relative Humidity

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Constant Specific Volume

Constant Specific Volume

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Constant Web Bulb Temperature

Constant Wet Bulb Temperature

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Constant Enthalpy

Constant Enthalpy

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Constant Enthalpyand

Constant Web Bulb

Constant Enthalpy and Web Bulb

Typical Chart With Enthalpy LinesTypical Chart With Enthalpy Lines

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Typical Chart Without Enthalpy LinesTypical Chart Without Enthalpy Lines

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State Point

State PointState Point

Reading a Psychrometric Chart Practice

Sea Level ChartDry-bulb temperature = 70 F

Relative humidity = 60%

State PointState Point

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70Dry Bulb

State Point 70 FState Point 70 F

State Point 60%State Point 60%



Wet-bulb temperature = ? F

Wet-bulbWet-bulb

Wet-bulbWet-bulb



Wet-bulb temperature = 61 F

Wet-bulbWet-bulb



Dew point = ?

Dew PointDew Point

Dew PointDew Point

Dew PointDew Point



Dew point = 55.5 F

Dew PointDew Point



Specific volume = ?

Specific VolumeSpecific Volume


Relative Humidity = 60%

Specific volume = 13.6 ft3 / lb dry air




Humidity ratio = ?

Humidity RatioHumidity Ratio



Humidity ratio = 0.0094 lb water / lb dry airor

7000 grains = 1 lb water7000 x 0.0094 = 65.8




Enthalpy = ?

EnthalpyEnthalpy

EnthalpyEnthalpy



Enthalpy = 27.0 Btu / lb dry air

EnthalpyEnthalpy

http://linricsoftw.web127.discountasp.net/webpsycalc.aspx

Calculating Air Property ValuesCalculating Air Property Values

Sensible HeatingSensible Heating

Raise Room Temperature 1 degree FConstant Humidity Ratio

27.31 Btu/lb27.06 Btu/lb00.25 Btu/lb

Length (ft) x Width (ft) x Height (ft) = Volume (ft3)

Volume (ft3) / Specific Volume (ft3/lb) = Mass of Air (lb)

Mass of Air (lb) x Enthalpy Change (Btu/lb) = Heat Input (Btu)

Bedroom

12 x 12 x 8 = 1152 ft3

1152 / 14.02 = 82.17 lb

82.17 x 0.25 = 20.54 Btu

Raise Room Temperature 1 degree FConstant Humidity Ratio

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FurnaceExpected

Result

Heating System Example

supply air from furnace

return air to furnace

1) Return Air 65 F and 60%2) Supply Air 95 F and 22%

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1) Return 65 F and 60%2) Supply 95 F and 18%

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Measured Values

How is this possible?

supply air from furnacereturn air to furnace


Mixing Air Streams

ma1

h1

w1

ma2

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ma3

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Energy Balance

ma1 h1 + ma2 h2 = ma3 h3

Mass Balance

ma1 w1 + ma2 w2 = ma3 w3

By Algebra

h2 – h3 = w2 – w3 = ma1

h3 – h1 w3 – w1 ma2

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Resulting mixture lies on the line between the two state points.

Mixing Two Equal Air Streams = the center of the line

Mixing Air Streams

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1) Return 65 F and 60%2) Supply 95 F and 18%

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Measured Values

How is this possible?

supply air from furnacereturn air to furnace


Cooling

Cooling Systems

Total Heat

q = (cfm) (4.5) (∆h)

q = Btuh

h = enthalpy, Btu per lb dry air

Sensible Heat

q = (cfm) (1.08) (∆t)

t = temperature F

Latent Heat

q = (cfm) (4840) (∆w)

w = humidity ratio, lb water per lb dry air

Solving the General Equations for Air Conditioning

Sensible Heat

q (Btuh) = (cfm) (1.08) (∆t)

(∆t) = q (Btuh) (cfm) (1.08)

cfm lower - (∆t) higher

cfm higher - (∆t) lower

q lower - (∆t) lower

q higher - (∆t) higher

Solving the General Equations for Air Conditioning - Sources of Error

12,000 Btuh / ton

400 cfm /ton

Sensible heat fraction = 0.70

Latent heat fraction = 0.30

Standard Operation of an Air Conditioner

Total Heat

q = (cfm) (4.5) (∆h)

12,000 = (400) (4.5) (∆h)

(∆h) = 27.3 Btu / lb dry air

Sensible Heat

q = (cfm) (1.08) (∆t)

12,000 (0.7) = (400) (1.08) (∆t)

(∆t) = 19 F

Latent Heat

q = (cfm) (4840) (∆w)

12,000 (.3) = (400) (4840) (∆w)

(∆w) = 0.002 lb water / lb dry air


What if humidity ratio of return air equals the humidity ratio of the

supply air?

Operation of an Air Conditioner

Air Conditioner ExampleAir Conditioner Example

0.002

0.002



0.002

19 F

Evaporative Cooling

Annual Hourly Outside Air Conditions – Lexington KY

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85 WET BULB TEMPERATURE - °F

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Human Comfort Zones

Annual Hourly Outside Air Conditions – Phoenix, AZ

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PSYCHROMETRIC CHARTSea LevelBAROMETRIC PRESSURE 29.921 inches of Mercury


Crawl Space Conditions Example

Annual Hourly Outside Air Conditions – Lexington KY

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Psychrometric Chart Basics. Basic Concepts Saturation Line.

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Transcript of Psychrometric Chart Basics. Basic Concepts Saturation Line.