Cooling and dehumidification

Moisture is removed as saturated liquid.

O

Where iw — water enthalpy riia(W — W2)iw is normally small Sensible heat:

H senate =C lXl’2-‘l)

Latent heat

‘hate,« = (W2 ~ )ifg

Example

Air at 60% RH, Tdry =30°C, Cooled to 18°C. Determine fa ew? ^sensible? ^latent

Solution:

O

4>new=100%, from the psychrometric chart, we can find

By using the formula

Sensible Heat Factor (SHF) is

Q

Defines process slope on the chart. Use protractor (semicircular scale) in the upper left hand corner to read the sensible heat factor.

Chapter2

AE 310 Fundamentals of Heating. Ventilating, and Air-Conditioning 2.3.3 Heating and humidification

Enthalpy

— —————— -> Look at the semicircular scale in the psychrometric chart.

Humidity ratio

Defines the process slope.

For adiabatic humidification, then

0=0 ij — ij = AW 7W

W2 — Wi = AW Since 7W of the water is rather small, i2 ~ /,

Example

In Phoenix, it is possible to use evaporative cooling in summer. In a room of 50 m3, the air temperature is 45°C and relative humidity is 20%. Comfort standard allows the relative humidity to be increased to 60% by evaporative cooling. Determine the dry bulb temperature and water needed if there is no internal heat source and no air infiltration. Assume local pressure is 101325 Pa.

Solution:

O

This is an adiabatic humidification process. The air process in a psychrometric chart is iso­enthalpy. For the psychrometric chart, we can determine the starting humidity ratio and ending humidity ratio as O

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