Air Conditioning

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Air-Conditioning Processes
Presented by: Nichole Whisman April 26, 2001

• Review – Basic air-conditioning processes • Refrigerant based air-conditioners • Evaporative cooling • Cooling with dehumidification – Example • Video – Importance and applications of humidification

TERMS YOU NEED TO KNOW

Specific Humidity –
The amount of water vapor in the air.

Relative Humidity –
The amount of water vapor in the air relative to the amount of water the air can hold.

Four Basic Air-Conditioning Processes

Simple Heating
Just raising the temperature!

Relative humidity
DECREASES with simple heating
( since the moisture capacity of air INCREASES with temperature)

Simple Cooling
Lowering the temperature!

Relative humidity
INCREASES with simple cooling
(since the moisture capacity of air DECREASES with temperature).

Humidifying
Simply adding moisture!

Dehumidifying
Removing moisture!

(Low relative humidities combined with high temperatures.)

Air-Conditioners
(simple cooling)

•Refrigerant •Compressor •Expansion Valve •Heat-exchanging coils

A. Compressor B. Fans C. Expansion valve D. Hot air to outside E. Cold air to inside

HOW CAN YOU SAVE 60%-90% ON YOUR COOLING BILL AND HELP THE ENVIRONMENT?

EVAPORATIVE COOLING!!

• Work well in dry climates. • Don’t use CFC’s or other ozone depleting compounds. • Operate on a basic principle: As water evaporates, the latent heat of vaporization is absorbed from the water and the surrounding air. Both the water and the air are cooled in the process.

Examples of Evaporative Cooling
• Waterfalls • Sprinklers on a hot day • Dogs - panting

Evaporative Coolers
• Large fan draws fresh outside air through wetted pads. • Some water evaporates – specific humidity is increases. • Air is cooled 10-30 degrees F.

TEMPERATURE DELIVERED BY EVAPORATIVE COOLER

COOLING WITH DEHUMIDIFICATION
•In humid climates is is desirable to cool the air and remove some of the moisture. •In order for condensation (and removal of moisture) to occur the air must be cooled below comfortable room temperature. •The air is then passed over heating coils to raise the temperature to a comfortable level. Cooling section Heating section

T1 φ1
1 w

T2
2 3

T3 φ3

Heat Pipe Technology Inc.
Gainsville, Fl

HEAT PIPES
A run-down on how they work

A. Heat is absorbed from hot, humid air in the evaporating section. B. Fluid boils to vapor form and rises. C. Heat is released from the upper part of cylinder to the over-cooled air. Vapor condenses back to liquid phase. D. Liquid returns by gravity to the lower part of cylinder (evaporating section).

HEAT PIPES
CUT POWER REQUIREMENT BY

20%-50%
• ELIMINATE the heating coils •LESSEN the load in the cooling section.

For more information:

www.heatpipe.com

EXAMPLE 13-68 (pg 756)
An air-conditioning system is to take in air at 1 atm, 34°C, and 70% relative humidity and deliver it at 22 °C and 50% relative humidity. The air flows first over the cooling coils, where it is cooled and dehumidified, and then over resistance heating wires, where it is heated to the desired temperature. Assuming that the condensate is removed from the cooling section at 10°C, determine (a) the temperature of the air before it enters the heating section, (b) the amount of heat removed in the cooling section, and © the amount of heat transferred in the heating section. [(b) and © in kJ/kg dry air] Cooling section T1 = 34°C φ 1 = 70% 1 w 10°C T2 = 10°C Heating section T3 = 22°C φ 3 = 50% 3

1 atm AIR

2

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