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A Trane Air Conditioning Clinic Psychrometry Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Psychrometry period one The Psychrometric Chart Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Psychrometric Chart Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Properties Of Air s Dry-bulb temperature s Wet-bulb temperature s Dew-point temperature s Relative humidity s Humidity ratio
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Dry-Bulb Thermometer
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Wet-Bulb Thermometer
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Condensation Occurs At Dew Point Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Fog Occurs When Air Is Saturated Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Relative Humidity …describes the degree of saturation Relative Humidity Amount of moisture that a given amount of air is holding = Amount of moisture that a given amount of air can hold
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 50%100% (saturated) Relative Humidity …compares moisture content to saturation
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Humidity Ratio …compares water vapor to dry air, by weight
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Knowing Two Properties …lets you determine the remaining three s Dry-bulb temperature s Wet-bulb temperature s Dew-point temperature s Relative humidity s Humidity ratio
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 EXAMPLE Summer Design Conditions s 95°F DB (dry bulb) s 78°F WB (wet bulb)
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 “X Marks The Spot”… 95°F 78°F 50% 40% 72°F
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 25°F 30°F 35°F 40°F 45°F 50°F 55°F 19.14 24.19 29.94 36.51 44.34 53.63 64.63 60°F 65°F 70°F 75°F 80°F 85°F 90°F 77.61 92.89 110.82 131.83 156.38 185.03 218.42 DB Temp. Humidity Ratio DB Temp. Humidity Ratio Saturated Air …grains of moisture per pound of dry air
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 Plotting Saturation Points 218.42 185.03 156.38 131.83 110.82 92.89 77.61 64.63 53.63 44.34 36.51 29.94 24.19 19.14 Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 Saturation Curve 100% Relative Humidity Curve Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 relationship between… Dry Bulb, Wet Bulb And Dew Point 60°F Dew Point 60°F Wet Bulb A B C D Dry Bulb60°F62°F75°F90°F Wet Bulb60°F60.8°F65.2°F70°F Dew Point60°F60°F60°F60°F Rel Humidity100%92%60%37% D D C C B B A A Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 moisture content doesn’t change by… Adding Sensible Heat 100% Saturation 60°F Dew Point 60°F Wet Bulb Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 Relative Humidity Curves Relative Humidity 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 intersection represents… Three Air Properties Humidity Ratio Dry Bulb Relative Humidity Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 Determining Wet-Bulb Lines A A BIBI BIBI CICI CICI DIDI DIDI B B C C D D AIAI AIAI Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 intersection of two known air properties… Determines The Remaining Three Humidity Ratio Dry Bulb Relative Humidity Wet Bulb Dew Point Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 A Final Property…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) Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Adding Sensible Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Removing Sensible Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Adding Moisture Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Removing Moisture Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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effect of changing… Sensible Heat And Moisture Content Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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effect of changing… Sensible Heat And Moisture Content Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Psychrometry period two Air Mixtures Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioner Supply Fan Mixture Outdoor Air (OA) Recirculated Air (RA) A A C C B B Cooling Coil Determining Entering Air Conditions Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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80°F 95°F Determining Entering Air Conditions B B A A Outdoor Air Recirculated Air Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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1,000 cfm 4,000 cfm = 0.25 OA RA Mixture ====== 25% 75% 100% A A C C B B 4,000 cfm Mixed Air 1,000 cfm OA 3,000 cfm RA Determining Entering Air Conditions Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 95°F × 0.25 = 23.75°F 80°F × 0.75 = 60.00°F Mixture = 83.75°F Mixed Air Temperature Determining Entering Air Conditions
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83.75°F 70°F Determining Entering Air Conditions B B 80°F 95°F C C A A Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Psychrometry period three Sensible Heat Ratio Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Removing Sensible Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Removing Latent Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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effect of… Removing Sensible And Latent Heat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Supply Air Sensible Heat Sensible Heat Latent Heat Latent Heat Return Air supply air conditions determine… Heat And Moisture Transfer Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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sensible and latent heat… Effects Of Improper Removal Cooler & Damper Cooler & Damper Warmer & Drier Warmer & Drier Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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A Look At “Heat Gain”... Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 SHR Sensible Heat Gain Sensible Heat Gain + Latent Heat Gain = determining the… Sensible Heat Ratio (SHR)
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78°F DB 65°F WB 78°F DB 65°F WB Index Point Sensible Heat Ratio Scale Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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0.80 SHR Line Drawing An SHR Line A A Index Point Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Sensible Heat Ratio Line Room SHR dictates… Supply Air Conditions A A Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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C C D D B B 80°F drawing an SHR line for… Other Room Conditions 0.60 SHR Line Index Point Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Psychrometry period four Air Quantity Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Coil Curves Coil Curves …show changes in air properties through a cooling coil Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 80,000 Btu/hr sensible heat gain 20,000 Btu/hr latent heat gain = 0.80 STEP 1: Calculate the sensible heat ratio (SHR) 80,000 Btu/hr 100,000 Btu/hr SHR = Determining Supply Airflow
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Room — 78°F DB, 50% RH OA — 95°F DB, 78°F WB Ventilation — 25% OA Determining Supply Airflow Design Conditions:
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95°F × 0.25 = 23.75°F 78°F × 0.75 = 58.50°F Mixture = 82.25°F Determining Supply Airflow STEP 2: Plot room, outdoor, and entering conditions 0.80 SHR A A C C B B Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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56.5°F 78°F STEP 3: Identify supply air conditions 0.80 SHR A A C C B B D D Determining Supply Airflow Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Sensible Heat Gain 1.085 × (Room DB – Supply DB) Supply Airflow = STEP 4: Solve the supply airflow equation Determining Supply Airflow
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 80,000 Btu/hr 1.085 × (78°F – 56.5°F) 3,430 cfm = STEP 4: Solve the supply airflow equation Determining Supply Airflow
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D A C B 3,430 cfm 56.5°F DB 55.2°F WB RA OA 82.2°F DB 68.6°F WB Mixture Determining Supply Airflow SA 56.5°F D D A A C C B B Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 effect of… Arbitrarily Using 55°F Supply Air 47,000 Btu/hr sensible heat gain 20,000 Btu/hr latent heat gain = 0.70 47,000 Btu/hr 67,000 Btu/hr SHR =
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A A C C B B D D 55°F DIDI DIDI AIAI AIAI effect of… Arbitrarily Using 55°F Supply Air 0.70 SHR 51°F Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Psychrometry period five Tons Of Refrigeration Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 What is Enthalpy? Enthalpy (h) = Sensible Heat + Latent Heat The total heat energy in one pound of air (Btu/lb) at its present condition:
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Determining Tons Of Refrigeration STEP 1: Find enthalpies entering and leaving coil A A B B C C D D 32.7 23.5 Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Determining Tons Of Refrigeration STEP 2: Solve the total refrigeration load equation 4.5 × Supply Airflow × (h 1 – h 2 ) Refrigeration Load (Btu/hr) = where: h 1 = enthalpy of air entering coil (Btu/lb) h 2 = enthalpy of air leaving coil (Btu/lb)
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 = 11.8 tons of refrigeration Determining Tons Of Refrigeration STEP 2: Solve the total refrigeration load equation 4.5 × 3,430 cfm × (32.7 – 23.5) = 142,000 Btu/hr 142,000 Btu/hr 12,000 Btu/hr/ton
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determining cooling coil… Sensible And Latent Loads 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
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Sensible Coil Load: 4.5 × 3,430 cfm × (29.6 – 23.5) = 94,150 Btu/hr 7.8 tons of refrigeration (sensible) determining cooling coil… Sensible And Latent Loads Latent Coil Load: 4.5 × 3,430 cfm × (32.7 – 29.6) = 47,850 Btu/hr 4.0 tons of refrigeration (latent)
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Psychrometry period six Psychrometric Analyses Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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SHR Changes Throughout The Day Full-load conditions 56.5°F 78°F D D A A B B C C Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Full Load: 80,000 Btu/hr 80,000 Btu/hr + 20,000 Btu/hr SHR = Part Load: = 0.80 47,000 Btu/hr 47,000 Btu/hr + 20,000 Btu/hr SHR == 0.70 SHR Changes With Room Load
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D D A A B B C C New SHR Requires New SA Condition 0.80 SHR 0.70 SHR Part-load conditions Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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D D A A B B C C at part-load, with constant supply airflow … Raising SA Temp. Increases Room RH 0.80 SHR 0.70 SHR AIAI AIAI DIDI DIDI 50%50% 60%60% 47,000 Btu/hr 1.085 × (78°F – Supply DB) = 3,430 cfm Supply DB = 65.4°F 65.4°F Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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constant quantity of variable-temperature air OA RA SA Constant-Volume System B D C A Modulating Cooling Coil Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Reheat Coil Cooling Coil Room Thermostat adding reheat improves humidity control B E D C A Constant-Volume With Reheat Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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D D A A C B B 47,000 Btu/hr 1.085 × (78°F – Supply DB) = 3,430 cfm Supply DB = 65.4°F Effect Of Adding Reheat… E E 0.80 SHR 65.4°F 56.5°F Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Adding Reheat… D D A A C C B B E E 0.80 SHR 65.4°F 56.5°F 0.70 SHR Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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mixed air bypass improves humidity control Mixed Air Bypass OA RA SA B D C A Face-and- Bypass Dampers Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Mixed Air Bypass… D D A A C C B B E E 82.25°F × 0.455 = 37.4°F 51.40°F × 0.545 = 28.0°F Mixture = 65.4°F 65.4°F 51.4°F Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Effect Of Mixed Air Bypass… 0.70 SHR A A C C B B AIAI AIAI 65.4°F 51.4°F D D E E Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 Variable-Air-Volume (VAV) System OA RA SA B D A C variable quantity of constant-temperature air VSD
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D D A A C C B B Calculating Part-Load Airflow 47,000 Btu/hr 1.085 × (78°F – 56.5°F) = 2,015 cfm 0.80 SHR 0.70 SHR AIAI AIAI 55.5°F Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999 PC-based software tools… Simplify Psychrometric Analysis
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Psychrometry period seven Review Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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30 Dry-Bulb Temperature (°F) Grains Of Moisture Per Pound Of Dry Air When Saturated (grains/lb of dry air) 2535404550556065707580859095100105110 20 0 40 60 80 100 120 140 160 180 200 220 review… Five Properties Of Air Humidity Ratio Dry Bulb Relative Humidity Wet Bulb Dew Point Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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80°F 95°F 83.75°F 70°F C C B B A A review… Determining Mixed Air Conditions 95°F × 0.25 = 23.75°F 80°F × 0.75 = 60.00°F Mixture = 83.75°F Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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A A Sensible Heat Ratio Line review… Determining Sensible Heat Ratio SHR = Sensible Heat Gain Sensible Heat Gain + Latent Heat Gain Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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A A C C B B D D Coil Curve Sensible Heat Gain 1.085 × (Room DB – Supply DB) Supply Airflow review… Determining Coil Leaving Conditions SHR Line = Supply DB Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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A A C C B B D D review… Determining Tons Of Refrigeration 4.5 × Supply Airflow × (h 1 – h 2 ) = Refrigeration Load Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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C C OA RA B B A A D D SA review… Psychrometric Analysis SHR Line A B C D Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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Air Conditioning Clinic TRG-TRC001-EN © American Standard Inc. 1999
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