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KChatterjea, 2008 1
Psychrometrics&
Air Conditioning Design
Kalyan Chatterjea
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Chatterjea - Psychrometrics & Air Conditioning Design
Introduction to Comfort Introduction to Comfort Air-conditioningAir-conditioningIntroduction to Comfort Introduction to Comfort Air-conditioningAir-conditioning
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Chatterjea - Psychrometrics & Air Conditioning Design
Introduction - PsychrometryIntroduction - PsychrometryIntroduction - PsychrometryIntroduction - Psychrometry
The air conditioning processes are best understood by studying Psychrometry.
Psychrometry is the study of atmospheric air and its associated water vapour.
A psychrometric chart presents physical and thermal properties of moist air in a graphical form.
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Psychrometry – Dry Bulb TempPsychrometry – Dry Bulb TempPsychrometry – Dry Bulb TempPsychrometry – Dry Bulb Temp
Dry-bulb temperature (DBT) is the commonly measured temperature from a thermometer.
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Psychrometry – Wet Bulb TempPsychrometry – Wet Bulb TempPsychrometry – Wet Bulb TempPsychrometry – Wet Bulb Temp
Wet Bulb Temperature (WBT) is determined when air is circulated past a wetted sensor tip.
Intersection of DBT and WBT provides the status point.
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Psychrometry – Saturation LinePsychrometry – Saturation LinePsychrometry – Saturation LinePsychrometry – Saturation Line
Saturation line is a temperature condition at which water will begin to condense out of moist air.
It is also called the dew point temperature line.
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Psychrometry – Relative HumidityPsychrometry – Relative HumidityPsychrometry – Relative HumidityPsychrometry – Relative Humidity
Relative Humidity (RH) is a ratio between actual moisture content of the air compared with the moisture content of the air required for saturation at the same temperature.
RH is affects human comfort significantly.
Sensible heat removalwith increase in RH
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Psychrometry – Specific VolumePsychrometry – Specific VolumePsychrometry – Specific VolumePsychrometry – Specific Volume
Specific Volume indicates the space occupied by air.
This is useful in converting volumetric flow to mass-flow rate calculation.
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Chatterjea - Psychrometrics & Air Conditioning Design
Psychrometry - EnthalpyPsychrometry - EnthalpyPsychrometry - EnthalpyPsychrometry - Enthalpy
Enthalpy is the energy content of dry air & moisture expressed in kJ/kg of dry air.
The information is useful is sizing up heating & cooling coils.
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Psychrometry – Sensible Heat Psychrometry – Sensible Heat ProcessesProcessesPsychrometry – Sensible Heat Psychrometry – Sensible Heat ProcessesProcesses
Heating & Cooling process – addition or removal of sensible heat without change in absolute moisture content.
But RH changes as temperature changes.
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Psychrometry - DehumidificationPsychrometry - DehumidificationPsychrometry - DehumidificationPsychrometry - Dehumidification
Dehumidification by cooling – in cooling coils temp of air reduces and the saturation point (dew point) is reached.
Further cooling results in reduction of absolute humidity.
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Psychrometry – Comfort ZonePsychrometry – Comfort ZonePsychrometry – Comfort ZonePsychrometry – Comfort Zone
Comfort Zone – statistical studies have been performed on large numbers of subjects of all ages, sexes and nationalities to arrive at a quantitative description of human comfort.
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Comfort zone … comfort is a very subjective term!
Statistically, majority of human beings are comfortable when temp is between 18-220C and RH is 40-65%
Psychrometry – Comfort ZonePsychrometry – Comfort ZonePsychrometry – Comfort ZonePsychrometry – Comfort Zone
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Chatterjea - Psychrometrics & Air Conditioning Design
Psychrometry – Climate ClassificationPsychrometry – Climate ClassificationPsychrometry – Climate ClassificationPsychrometry – Climate Classification
Climate Classification shows the various approximate zones of temperature and humidity on the psychrometric chart.
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Chatterjea - Psychrometrics & Air Conditioning Design
Psychrometry – Heating at SeaPsychrometry – Heating at SeaPsychrometry – Heating at SeaPsychrometry – Heating at Sea
Heating without humidification at sea.
Sensible heat addition with decrease in RH…away from comfort zone
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Chatterjea - Psychrometrics & Air Conditioning Design
Psychrometry – Heating at SeaPsychrometry – Heating at SeaPsychrometry – Heating at SeaPsychrometry – Heating at Sea
Heating with humidification at sea.
Heat addition with humidification resulting in more comfortable RH
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Chatterjea - Psychrometrics & Air Conditioning Design
Heating Process in DetailHeating Process in DetailHeating Process in DetailHeating Process in Detail
Process showing sensible heat addition.
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Heating Process in DetailHeating Process in DetailHeating Process in DetailHeating Process in Detail
Applying the SFEE
hgzvmWQ Air2
2
1
hgzvmWQ Air2
2
1
12 hhmQ Air h-values can be directly
read from the psychrometricchart
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Process showing sensible heat cooling, followed by
Further cooling, which leads to precipitation.
Cooling & Dehumidification in DetailCooling & Dehumidification in DetailCooling & Dehumidification in DetailCooling & Dehumidification in Detail
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Chatterjea - Psychrometrics & Air Conditioning Design
Cooling & Dehumidification in DetailCooling & Dehumidification in DetailCooling & Dehumidification in DetailCooling & Dehumidification in Detail
Applying the SFEE
Mass flow balance equation forthe water & steam
WaterAirAir mmm
31
13 hhmQ AirIn practice, water mass flow is very small compared to air mass flow. So a simplerequation could be used without undue error.
2)( 13 fWaterAir hmhhmQ
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References
Psychrometric Chart Download–
http://www.ent.ohiou.edu/~thermo/me328/quiz.info/Nautica_SI.pdf
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References
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References
Overview of Psychrometrics: – http://www.handsdownsoftware.com/Overview_of_Psychrometrics.pdf
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References
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References
Coil Load Calculations: – http://courses.washington.edu/me425/425%20Psychrometric%20Review%202007.pd
f
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References
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References
Glossary: – http://air.1800anytyme.com/info/air_conditioning_glossary.php
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References
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References
Standard: British Standards Institution QC100.B862 BS EN ISO 2006– Ship and Marine Technology - Air-conditioning &
Ventilation of Accommodation Spaces - Design Conditions & Basis of Calculations
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References
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References
Thermodynamic Expert System– http://energy.sdsu.edu/testcenter/testhome/index.html
TEST - a visual platform to analyze thermo-fluids problems, verify hand calculations, pursue what-if scenarios, visualize thermal systems, and engage in a life-long journey to master thermodynamics.
Developed by Dr. S. Bhattacharjee, San Diego State University.
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References
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References
ABS Guide for Crew Habitability on Off-shore Installations, 2002
– "habitability" is defined as the acceptability of conditions of an offshore installation in terms of vibration, noise, indoor climate and lighting, as well as physical and spatial characteristics, according to prevailing research and standards for human efficiency and comfort
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References
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References
Simulation– Hui, S. C. M. and K. P. Cheung, 1998. Application of building energy
simulation to air-conditioning design, In Proc. of the Mainland-Hong Kong HVAC Seminar '98, 23-25 March 1998, Beijing, pp. 12-20.
http://www.arch.hku.hk/~cmhui/hvac98b.pdf
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References
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Thank You!