Practical Psychrometrics B Jerry Cohen President Jacco & - - PowerPoint PPT Presentation

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Practical Psychrometrics B Jerry Cohen President Jacco & - - PowerPoint PPT Presentation

Aug 10, 2023 261 likes •1.08k views

Practical Psychrometrics B Jerry Cohen President Jacco & Assoc. Psycho or Psychro What is the Purpose of your Job? How Hard is it to Fulfill Your Purpose? Psychrometrics from Greek Psychro To breathe, blow, or make cold. Metrics

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B

Jerry Cohen President Jacco & Assoc.

Practical Psychrometrics

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Psycho or Psychro

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What is the Purpose of your Job?

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How Hard is it to Fulfill Your Purpose?

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Psychrometrics

  • from Greek Psychro – To breathe, blow, or

make cold. Metrics – to measure.

  • the field of engineering concerned with the

determination of physical and thermodynamic properties of gas-vapor mixtures.

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The Psychrometric Chart

  • Graphical Representation of Properties of Air /

Water Mixtures.

  • Dry-Bulb (°F db)
  • Wet-Bulb (°F wb)
  • Dew-Point (°F dp)
  • Specific Volume (ft3/lb)
  • Humidity Ratio (Gr/lb)
  • Enthalpy (Btu/lb)
  • Two state points required to fix properties – i.e.

DB/WB, DB/%RH, DB/H, etc.

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Psychrometric Chart

The relationship between DB, WB, and RH is given

by the Mollier diagram (pressure-enthalpy) for water in air, developed by Richard Mollier. Willis Carrier rearranged the Mollier diagram for moist air to allow graphical solutions. Many variations and improvements to the Psychrometric charts have occurred since. ASHRAE now publishes what are considered the modern, standard Psychrometric charts, in both I-P and SI units, for a variety of elevations or air pressures.

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Clever that Carrier guy

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So really, what is Psychrometrics?

  • Study of Air / Water (Vapor) Mixture
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What is Air?

  • Mixture of Gases:
  • Nitrogen – 4 Parts
  • Oxygen – 1 Part
  • Other: Argon, Helium, Krypton, Xenon, Neon,

Carbon Dioxide. and

  • Water Vapor
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So Who Cares?

  • Reconsider the Components of Air:
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So Who Cares?

  • Reconsider the Components of Air:
  • Nitrogen
  • Oxygen
  • Noble Gases
  • Carbon Dioxide
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So Who Cares?

  • Reconsider the Components of Air:
  • Nitrogen
  • Oxygen
  • Noble Gases
  • Carbon Dioxide

Stable in Gas Phase.

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So Who Cares?

  • Reconsider the Components of Air:
  • Water Vapor
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So Who Cares?

  • Reconsider the Components of Air:
  • Nitrogen
  • Oxygen
  • Noble Gases
  • Carbon Dioxide

Stable in Gas Phase

  • Water Vapor

Phase Changes (liq./gas)

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If it’s Not the Heat, It’s the Humidity

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Psychrometric Chart

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Some Definitions

  • Sensible heat, or enthalpy of dry air, is heat

which manifests itself as a change in temperature.

  • Latent heat is the amount of energy in the

form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas), also called a phase transition

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Some Definitions

  • The total heat, or enthalpy, of the

atmosphere is the sum of the sensible heat, latent heat, and superheat of the vapor above the saturation or dew-point

  • temperature. Total heat is relatively

constant for a constant wet-bulb temperature, deviating only about 1.5–2% low at relative humidity's below 30%.

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Some Definitions

  • Dry Bulb Temperature
  • Temperature as read by regular (dry) thermometer.
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Dry Bulb

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Some Definitions

  • Wet Bulb Temperature
  • Temperature of air that has gone through an

adiabatic saturation process.

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Wet Bulb

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Some Definitions

  • Relative Humidity
  • The ratio of vapor pressure to saturation pressure.
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Relative Humidity

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Some Definitions

  • Specific Volume
  • cubic feet of air per lb. of air
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Specific Volume

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Some Definitions

  • Dew Point
  • Temperature at which moisture begins to condense

in a particular air / water vapor mixture.

  • This corresponds to the intersection of the wet-bulb

and the saturation curve.

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Dew Point

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Some Definitions

  • Humidity Ratio
  • The ratio of water vapor (mass) to total air (mass).
  • Can be expressed as lb (water) / lb (dry air), or

Gr (water) / lb (dry air).

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Humidity Ratio

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Relative Humidity vs. Humidity Ratio

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Some Definitions

  • Enthalpy
  • Total amount of energy contained in Air /

Water Mixture.

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Enthalpy

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Some Definitions

  • Sensible Heat Ratio
  • The ratio of sensible cooling to total cooling in

a space.

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Sensible Heat Ratio

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  • Adiabatic Saturation Process
  • Process follows lines of constant enthalpy/wet bulb.
  • Change occurs in: dry-bulb temperature, specific

volume, relative humidity, humidity ratio, dewpoint temperature, and vapor pressure of the moist air.

  • No change occurs in: wet-bulb temperature and

enthalpy

  • Representative of any process involving evaporation
  • Cooling Towers, Evaporative Cooling, Fog &

Ultrasonic Humidification, etc.

Some Definitions

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Adiabatic Saturation Process

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Useful Psychrometric Calculations - Air Mixing

  • Based on ratio of mass flows
  • Stream 1: 95 DB / 75 WB
  • Stream 2: 75 DB / 50% RH

V1=2,000 CFM, M1=137 LB/MIN V3=10,000 CFM, M3=704 LB/MIN V1=8,000 CFM, M1=567 LB/MIN

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Air Mixing - Mathematically

  • Plot both points on chart and connect with a line
  • Mixed air dry bulb =

(Stream 1 DB x Stream 1 CFM / Total CFM) + (Stream 2 DB x Stream 2 CFM / Total CFM)

  • Plot mixed air dry bulb on above referenced line

to calculate mixed air wet bulb

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Air Mixing - Measuring

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Sensible Heating / Cooling

  • Process line is horizontal on Psych. Chart.
  • Humidity Ratio does not change
  • Relative Humidity does change.
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Sensible Cooling

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Sensible Heating

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Total Cooling Cycle

  • Process line is horizontal & vertical on

Psychrometric Chart.

  • Humidity Ratio does change
  • Relative Humidity does change.
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Total Cooling Cycle

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Applications – Blow Through

  • Large VAV systems
  • High sensible loads
  • Higher efficiency requirements
  • Sound sensitive applications
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Blow Through

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Applications – Draw Through

  • Compact space requirements
  • High latent loads

– Pools – Underfloor or Displacement

  • Initial cost constraints
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Draw Through

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Applications – Heat Recovery

  • Anything above 30% OA
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Heat Wheel

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Heat Wheel – 33% OA

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Heat Pipe/Plate

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Heat Pipe/Plate – 33% OA

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Applications – Humidification

  • OR rooms
  • Laboratories
  • Wood / Printing
  • Adiabatic especially economical with

economizer systems

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Steam Humidification

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Adiabatic Humidification

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Steam Humidification @ Min OA

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Adiabatic Humidification @ Min OA

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Applications - Dehumidification

  • Desiccant best for < 40 DP
  • Mechanical best for > 40 DP
  • Ice Rinks
  • Swimming Pools
  • Surgery Suites
  • DOAS
  • VRF
  • Geothermal
  • Chilled Beam
  • Corridor Ventilation
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Mechanical Dehumidification

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Return Air Bypass

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Single Pipe/Plate HX

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Dual Wheel – Latent & Sensible

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Desiccant Dehumidification Pre-Cool

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Desiccant Dehumidification - Post-Cool

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Desiccant Dehumidification, Pre & Post-Cool

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Dual Wheel, Low Temp Regeneration Desiccant Dehumidification, Pre Cool

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Is this Dehumidified?

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Tight Temperature and Humidity Control

  • High SHR Equipment
  • Low SHR Equipment
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Reheat for SHR

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Conquer & Divide for SHR

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Conquer & Divide for SHR

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ASHRAE Data Sets

  • Nine Cooling Data Sets:
  • Presented as 0.4%, 1%, 2% Values.
  • DB/MCWB: Useful for Typical Mixed Air Cooling.
  • WB/MCDB: Useful for Adiabatic Saturation

Processes: Cooling Towers, Evaporative cooling

  • DP/MCDB: Highest moisture content of Outside
  • Air. Useful for De-humidification and 100%

Ventilation Systems.

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ASHRAE Data Sets

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Psychrometric Cheat Sheet

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Psychrometric Cheat Sheet

A – Humidify Only B – Heat & Humidify C – Sensible Heat Only D – Desiccant Dehumidify E – Dehumidify Only F – Cool & Dehumidify G – Sensible Cool Only H – Evaporative Cool

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Psychrometric Cheat Sheet

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How Can Jacco Help You?

  • Tight Temperature & Humidity Control
  • Low SHR Applications with Aaon, Munters,

Seasons 4 & Energy Labs

  • High SHR Applications with WaterFurnace,

Samsung, TROX, Beka & Whalen

  • Standard SHR Applications with Aaon
  • Humidification with MeeFog & Vapac
  • Dehumidification with Aaon, Munters,

Seasons 4 & Energy Labs

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Jerry Cohen President Jacco & Assoc.

Thank You