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Lecture Objectives: • Finish cooling / heat pump example • Review Psychrometrics • Swimming pool example

Lecture Objectives:

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Lecture Objectives:. Finish heat pump example Review Psychrometrics Swimming pool example. Heat pump example. A recreation center. Heat Pump. Ice Rink. Swimming pool. Condenser. Evaporator. 30 o F. 85-89 o F. Rejects heat energy. Consumes heat energy. Electric power - PowerPoint PPT Presentation

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Page 1: Lecture Objectives:

Lecture Objectives:

• Finish cooling / heat pump example

• Review Psychrometrics • Swimming pool example

Page 2: Lecture Objectives:

Heat pump example

Heat Pump

Consumes heat energy Rejects heat energy

A recreation center

Ice Rink Swimming pool

Electric power for a compressor

EvaporatorCondenser

85-89oF 30oF

Page 3: Lecture Objectives:

Ice Rinks Energy flow

Page 4: Lecture Objectives:

Challenges for this problem

• Circulating fluid

• Adjustment of evaporation and condensation temperatures

• Adjustment of capacity for design condition

• Control of capacity for non design conditions• Need to study load profiles • Design sophisticated control • Provide backup system

Page 5: Lecture Objectives:

Psychrometrics (Swimming pool example)

Page 6: Lecture Objectives:

High humidity

High humidity and low temperature

Page 7: Lecture Objectives:

Psychrometric Chart

• Need two quantities for a state point• Can get all other quantities from a state point

• Can do all calculations without a chart• Often require iteration• Many “digital” psychrometric charts available

• Can make your own

• Best source is ASHRAE fundamentals (Chapter 6)• Or electronic version at:

http://www.handsdownsoftware.com/

Page 8: Lecture Objectives:
Page 9: Lecture Objectives:

Connection between W and Pw(W humidity ratio – Pw water partial pressure)

• PV = mRT (Ideal Gas Law )

• P = Pw + Pa

w

a

a

w

TRVP

TRVP

a

w

R

R

P

P

m

mW

a

a

w

w

w

w

PP

PW

622.0

R = gas constantP = pressureV = volumeT = absolute temperatureW = humidity ratio

Subscripts: w is water vapor, a is dry air

Page 10: Lecture Objectives:

Calculation of psychometric quantities

• For an ideal gas,• hda = ∫cpadT, hw = ∫cpwdT

• So, hda = cp,dat which assumes a reference state of 0 °F or 0 °C – Tables A4• Note different reference

• hw = cpwt + hg0

• h = cp,dat + W(cpwt + hg0)Or you can use:• h = cpt + W∙hg0, cp = cp,da + Wcpw

cp = specific heath = enthalpyT = absolute temperaturet = temperature W = humidity ratio

Subscripts: w is water vapor, a is dry air, g is saturated water vapor

Page 11: Lecture Objectives:

Adiabatic mixing

• Governing equation hmQhmoutin

External heat

Page 12: Lecture Objectives:

Sensible heating

tcmQ p

Page 13: Lecture Objectives:

Dehumidification by Cooling

Page 14: Lecture Objectives:

Real Dehumidification Process

Page 15: Lecture Objectives:

Mold in a duct

Transport of saturated air

tsurface < tdp Condensation

Page 16: Lecture Objectives:

Humidification

hw Specific enthalpy of water added to system

hg Specific enthalpy of saturated water vapor

Page 17: Lecture Objectives:

Summary

• Describe psychrometric quantities

• Given any two psychrometric quantities, calculate any other quantity

• Use Tables A4 or psychrometric charts to look up psychrometric quantities

• Calculate psychrometric quantities at non-standard conditions

Page 18: Lecture Objectives:

Swimming pool energy and mass balance

Page 19: Lecture Objectives:

Evaporation

• Heat loss by evaporation:

pool W s W Tair

Tpool

hm pool WsTpool Wair

Further analysis can be conducted in the psychrometric chart

Depends on the air speed and even more on the condition of the water surface (people splashing in the water)

Page 20: Lecture Objectives:

Process in AHUs

• Example AHUs for swimming pools

MENERGAThermoCond 19

Page 21: Lecture Objectives:

Swimming pool heating

Page 22: Lecture Objectives:

Dehumidification using outside air in Winter and Summer

Page 23: Lecture Objectives:

More advance control

MENERGA ThermoCond 29

Page 24: Lecture Objectives:

Dehumidification using outside air in winter

Condenser in the swimming pool

Evaporator

Condenser in the air stream

Compressor of the heat pump

Page 25: Lecture Objectives:

Recirculation of air with dehumidification

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