Lecture Objectives:

• Finish heat pump example

• Review Psychrometrics • Swimming pool example

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

Ice Rinks Energy flow

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

Psychrometrics (Swimming pool example)

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/

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

Swimming pool energy and mass balance

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)

Process in AHUs

• Example AHUs for swimming pools

MENERGAThermoCond 19

Swimming pool heating

Dehumidification using outside air in Winter and Summer

More advance control

MENERGA ThermoCond 29

Dehumidification using outside air in winter

Condenser in the swimming pool

Evaporator

Condenser in the air stream

Compressor of the heat pump

Recirculation of air with dehumidification

catalog